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Volcanic red-bed copper mineralisation related to submarine basalt alteration, Mont Alexandre, Quebec Appalachians, Canada
Abstract
Two types of native copper occur in Upper Silurian basaltic rocks in the Mont Alexandre area, Quebec Appalachians: (1) type
1 forms micrometric inclusions in plagioclase and is possibly magmatic in origin, whereas (2) type 2 occurs as coarse-grained
patches rimmed by cuprite in altered porphyritic basalt. Type 1 has higher contents of sulphur (2,000–20,263ppm) and arsenic
(146–6,017ppm), and a broader range of silver abundances (<65–2,186ppm Ag) than type 2 (149–1,288ppm S, <90–146 As, <65–928ppm
Ag). No mineral inclusions of sulphide or arsenide in native copper were observed at the electron-microprobe scale. Primary
igneous fabrics are preserved, but the basaltic flows are pervasively oxidised and plagioclase is albitised. Chlorite replaces
plagioclase and forms interstitial aggregates in the groundmass and has Fe/(Fe+Mg) ratios ranging from 0.29 to 0.36 with calculated
temperatures between 155°C and 182°C. Copper sulphides in vacuoles and veinlets are associated with malachite, fibro-radiating
albite and yarrowite (Cu9S8 with up to 0.3wt% Ag). Bulk-rock concentrations of thallium and lithium range from 70 to 310ppb and 10 to 22ppm, respectively,
and thallium is positively correlated with Fe2O3. Such concentrations of thallium and lithium are typical of spilitisation during heated seawater–basalt interaction. Spilitisation
is consistent with the regional geological setting of deepwater-facies sedimentation, but is different from current models
for volcanic red-bed copper, which indicate subaerial oxidation of volcanic flows. The volcanic red-bed copper model should
be re-examined to account for native copper mineralisation in basalts altered by warm seawater.
... Manto-type copper deposits occur in back-arc basins, island-arc or continental-arc tectonic settings (Cabral & Beaudoin, 2007;Espinnoza et al., 1996;Rosúa et al., 2014;Tristá-Aguilera et al., 2006; N. S. F. Wilson & Zentilli, 2006). Albite, chlorite, epidote, zeolite, quartz, been reported by some researchers (Ghelichkhani & Malakzadeh Shafaroudi, 2018;Jabbari et al., 2017;Mahvashi & Malekzadeh Shafaroudi, 2016;Soltani & Fardust, 2017). ...
... S. F. Wilson, Zentilli, & Spiro, 2003). Layered pyroclastics, lack of pillow structures and presence of volcanic clasts in pyroclastic rocks, and formation of limestones intercalations can best explain their formation in a subaerial or shallow marine sedimentary basin (Cabral & Beaudoin, 2007;Ramírez et al., 2006). Zangalou deposit formed in a subduction-related volcanic arc along a continental margin. ...
... S. F. Wilson, Zentilli, Reynolds, & Boric, 2003; N. S. F. Wilson, Zentilli, & Spiro, 2003;N. S. F. Wilson & Zentilli, 2006;Kojima et al., 2009, Tristá-Aguilera et al., 2006, Tosdal & Munizaga, 2003Oliveros et al., 2008, Espinnoza et al., 1996Ramírez et al., 2006, Rosúa et al., 2014Cabral & Beaudoin, 2007;Cisternas & Hermosilla, 2006, Cas & Zagorevski, 2009, Sato, 1984 (Haggan et al., 2003;Kojima et al., 2009). Cu content in these deposits is relatively high (1.5%-2%), ...
The Zangalou Cu deposit lies in the Sabzevar volcanic‐plutonic zone, northeastern Iran. The deposit is hosted by the middle Eocene volcanic‐sedimentary sequences and it has been affected by propylitic, carbonate, sericitic, and minor argillic alterations. The volcanics have features typical of calc‐alkaline and metaluminous magmas and are plotted in the continental volcanic arc region. Zircon U–Pb dating of the andesite porphyry yield ages of 41.2 and 38.4 Ma (Bartonian). Ore mineralization occurs as stratabound with open‐space filling, dissemination, veinlet, and replacement textures in mineralized conglomerate, andesite porphyry, and trachyandesite host rocks. Cu content in Zangalou deposit vary from 1,234 g/t to 6.24% which mostly occurred as chalcocite mineral. Fluid inclusion data of mineralization‐related calcites indicate medium salinities (12.8–16.6 wt.% NaCl equivalents) and a wide range of temperatures (154–295°C) and show evidence of fluid cooling trend during the ore formation. The δ13C (between 19.3 and −2.8‰) and δ18OSMOW (between 24.8 and 25.34‰) values of ore‐related calcites suggests a contribution of sedimentary organic matter and marine carbonates as the source of carbon in the ore‐forming fluid. High positive δ34S values (27.8–33.47‰) suggest that the source of sulphur is related to sedimentary country rocks. Mineralization is lithologically and structurally controlled and it is epigenetic. According to geological, petrological, alteration, mineralization textures and geometry of deposit, fluid inclusion, and isotopic studies, the Zangalou deposit is similar to manto‐type deposits. Properties of Zangalou deposit is very similar to manto‐type deposits. There are two reasons why assuming volcanic host rocks as the Cu source for manto‐type deposits is questionable: (1) High Fe content of volcanic host rocks (2) lack of vast argillic alteration and acidic (pH < 4) conditions of ore‐forming fluids.
... Campus (1980) has separated the Mesozoic Manto-type Cu deposits into the sedimentary-hosted deposits class (e.g., Cerro Negro), and the volcanic-hosted deposits class (e.g., Mantos Blancos and Buena Esperanza) (Wilson and Zentilli, 1999). Similar Proterozoic to Triassic deposits in North America (Kojima et al., 2009) are named "volcanic redbed" (Kirkham, 1996;Lefebure and Church, 1996;Cabral and Beaudoin, 2007), and are mainly distributed in the northwestern part of Canada and in the North Michigan district (e.g. White, 1968;Wilton and Sinclair, 1988). ...
... The volcanic rocks of Karaj formation form a thick, columnar jointed flow. The lack of pillow structures and the occurrence of layering and volcanic clasts in these pyroclastics provides good evidence of their formation by explosive eruptions in a subaerially or shallow marine sedimentary basin (Ramírez et al., 2006;Cabral and Beaudoin, 2007). The association of the Mari mineralization with subaerial volcano-sedimentary rocks suggested closer affinities to the Manto-type or volcanic redbed deposit type (Kirkham, 1984(Kirkham, , 1995Cas and Zagorevski, 2009). ...
... The association of the Mari mineralization with subaerial volcano-sedimentary rocks suggested closer affinities to the Manto-type or volcanic redbed deposit type (Kirkham, 1984(Kirkham, , 1995Cas and Zagorevski, 2009). Chilean Manto-type deposits are widely distributed in volcano-sedimentary sequences (Fig. 11) but also commonly occur in differentiated continental and island-arc volcano-sedimentary sequences (Wilson, 2000;Rosúa et al., 2014;Cabral and Beaudoin, 2007;Wilson and Zentilli, 2006). Similar to Manto-type deposits, the Mari mineralization is hosted by a volcano-sedimentary sequence (Fig. 11), deposited in a volcanic arc formed along a continental margin. ...
The Eocene volcano-sedimentary sequence, northern Zanjan, consist of 1.5 km of shallow-marine sediments. These include sandstone, lapilli tuff, andesite, basalt and felsic volcanic rocks. The Mari deposit is strata-bound that hosted by the Eocene andesite rocks. The major copper sulfides are bornite, chalcocite, and chalcopyrite associated mainly with pyrite that show open-space filling, disseminated, vein-veinlet, and replacement textures. The abundances of Cu and Ag in the ore-bearing andesite are up to 40,000 and 70 ppm respectively. Wall rock alterations include carbonatization, chloritization, epidotization, and sericitization. Sulfur isotope compositions have a negative range from δ34S = − 2.7 to − 3.4‰, suggesting the presence of a reducing environment resulting from activation of sulfate reducing bacteria. Mineralization formed two stages: stage one include volcanic activity and eruption of andesitic lava, in this stage syngenetic disseminated pyrites formed. In the second stage, increasing of the thickness of sediments, basin subsidence, and burial diagenesis accompanied with the entry of metal-rich fluids into the reduced host rock, caused the replacement of the first stage pyrites by copper sulfides. The geology, ore mineralogy, alteration characteristics and sulfur isotopic compositions suggest the Mari deposit may be classified as a Manto-type deposit.
... Mixed volcano-sedimentary formations have been recognized in the Picachos Project Coastal Range of north and north-central Chile (Merinero et al., 2019). Similar Proterozoic to Triassic deposits in North America (Kojima et al., 2009) are named "volcanic red-bed" (Kirkham, 1996;Lefebure and Church, 1996;Cabral and Beaudoin, 2007) (Fig. 1), and are mainly distributed in the northwestern part of Canada and the North Michigan district (e.g., White, 1968;Wilton and Sinclair, 1988). Most of the Manto-type Cu deposits occur in andesitic to basaltic rock-dominated stratigraphic sequences of Mesozoic (Chile and Iran), Proterozoic to Triassic (North America), Late Silurian-Early Devonian (China), and Cenozoic (Iran) (Fig. 1). ...
... Zeolite, prehnite-pumpellyite, and minor chalcedony are also found filling vesicles and in the breccia matrix (Nezafati and Stöllner, 2018). Based on studies by Nezafati and Stöllner (2018), the Veshnaveh Cu-(Ag) deposit shares several similarities with a broad range of volcanic-hosted copper deposits, including the so-called "Manto-type" deposits (Sato, 1984;Kojima et al., 2009) or "volcanic red-bed deposits" (Kirkham, 1996;Cabral and Beaudoin, 2007) respectively reported from Chile (Cretaceous Chilean Manto-Type Cu deposits). ...
Stratabound or “Manto-type/volcanic red-bed” Cu-(Ag) deposits occur along the Urumieh-Dokhtar magmatic arc
(UDMA), Sanandaj-Sirjan Zone (SSZ), Alborz Magmatic Assemblage (AMA), Sabzevar Zone, and Lut Block
structural zones of Iran, and are hosted by Cretaceous and Eocene volcanic and volcano-sedimentary rocks. The
most important deposits of this type are East Narbaghi, Khankishi, Kahak, Veshnaveh, and Koshkouieh in the
UDMA; Keshtmahaki in the SSZ; Mari, Qeblebolagh, and Yamaghan in the AMA; Abbasabad, Dochileh, Gol-
Cheshmeh, Zangaloo, Abri, Rahbari, and Cheshmeh-Marzieh in the Sabzevar Zone; and Vorezg in the Lut
Block. Back-arc extensional basins are the principal tectonic setting for the Manto-type deposits of Iran, that
developed during the subduction of the NeoTethyan crust beneath the Iranian micro-continental plates. The
stratigraphic sequences of these deposits are commonly formed from volcanics, volcaniclastics, and sedimentary
rocks, which are similar to other volcanic-hosted stratabound copper districts around the world. Iranian Mantotype
deposits are stratigraphically controlled in which Cu-(Ag) mineralization occurs as vein-veinlets, disseminated
grains, and filling vesicles. Copper mineralization is commonly closely related to framboidal pyrite and
pyrobitumen. The mineralogy of the Cu-(Ag) mineralization in all Manto-type deposits of Iran is simple and
consists of chalcocite, bornite, native copper, chalcopyrite, acanthite, and minor secondary digenite, covellite,
cuprite, tenorite, chrysocolla, anilite, malachite, azurite, and Ag-bearing clausthalite as the main economic
minerals, accompanied by pyrite, chlorite, calcite, quartz, and zeolite. Copper sulfides occur mainly as a
replacement of diagenetic pyrite, which in turn, replaced pyrobitumen. Iranian Manto-type deposits are interpreted
to be the result of mineralizing hydrothermal fluids derived from footwall volcanic rocks that migrated
upwards, driven by the late diagenetic processes. The UDMA and Sabzevar Zone are the most favorable metallogenic
provinces in Iran for Manto-type Cu-(Ag) exploration since these two zones host the largest copper
deposits of this type, including Abbasabad, Koshkouieh, East Narbaghi, and Abri deposits. Consequently,
reconstruction of orebearing basins, such as presented, is not only critical to understanding the genesis of ancient
deposits and their tectonic setting, but also for guiding exploration in deposit-proximal areas.
... Various fluid evolution trends adopted by Wilkinson (2001). Lefebure and Church, 1996;Cabral and Beaudoin, 2007 ) . ...
... This study Lefebure and Church (1996), Cabral and Beaudoin (2007) Brown (1971), Larson et al. (2003), Rosemeyer Kirkham (1984), Wilson (2000) Wilson and Zentilli (2006), Kojima et al. (2008) ...
The Saveh-Kashan-Qom copper belt, in the northern part of the Urumieh-Dokhtar Magmatic Arc (UDMA) consists of two of the oldest (gold and copper) zones in Iran, where Upper Eocene-Oligocene Mard Abad-Bouin Zahra volcanic suite is situated. This volcanic suite hosts several copper deposits including Jarou, Gomosh Dasht, Ghezel Cheshme, Bidestan and Afshar Abad that are known as the "Kuh-e-Jarou Mining District". The Kuh-e-Jarou Mining District has a total potential ore reserve of 2 Mt Cu with an average grade of 3%. Upper Eocene volcanic and pyroclastic rocks of rhyodacite, trachyandesite, andesite, and trachytic tuff with high-K calc-alkaline to shoshonitic affinity consist of the main host rocks for Cu mineralization. These units are primarily intruded by post Eocene intrusive bodies. The geochemistry and genesis of ore bodies have not been fully understood since most previous studies in this area have been focused on petrology of volcanic and intrusive rocks. Moreover, the main purpose of this study is to investigate mineralization style, geometry, and textural-structural features of orebodies, alterations, and fluid inclusions with implication for genesis of Jarou, Gomosh Dasht, Ghezel Cheshme, Bidestan and Afshar Abad copper deposits. In addition, this research provides more insight into understanding geology and mineralization conditions in the study area with an implication for future exploration.
... (1) Cabral and Beaudoin (2007) documented feldsparhosted inclusions of native copper,~50 μm in length, which were interpreted as magmatic in origin, in the Quebec Appalachians (Canada). Careful search for native copper inclusions in magmatic minerals of the host basalts of the PVP by backscattered-electron imaging did not yield inclusions. ...
... (2) Cabral and Beaudoin (2007) compared the hightemperature native copper from Québec, Canada, and the low-temperature native copper deposits from the Keweenaw volcanic province, MI, in a S versus As diagram. High concentrations of sulfur (~10,000 ppm) and arsenic (~1000 ppm) characterize the high-temperature native copper from Québec, whereas only~100 ppm S and 150 ppm As are detected in native copper from MI. ...
Different hypotheses exist on the origin of native copper mineralization in the Paraná volcanic province that invoke magmatic, late magmatic, or hydrothermal events. The average copper content in the host basalts is ~200 ppm. Native copper occurs as dendrites in cooling joints, fractures, and cavities within amygdaloidal crusts. Cuprite, tenorite, chrysocolla, malachite, and azurite occur in breccias at the top of the lava flows. Chemical analyses, X-ray diffraction, Raman spectrometry, electron microprobe analyses, LA-ICP-MS, and Cu isotope analyses were used to evaluate the origin of native copper in the volcanic province. Copper contents in magnetite of the host basalt are close to 1 wt.%, whereas clinopyroxene contains up to 0.04 wt.% Cu. Cretaceous hydrothermal alteration of magnetite and clinopyroxene released copper to generate hydrothermal copper mineralization. The isotopic composition of the native copper in the Paraná volcanic province varies from −0.9‰ in the southeastern portion (Rio Grande do Sul state) to 1.9‰ in the central portion (Paraná state) of the province. This study supports a hydrothermal origin followed by supergene enrichment for native copper in the Paraná volcanic province.
... On the basis of this study, we suggest that the Kahak Cu mineralization is a Volcanic Red Bed type deposit that formed and concentrated contemporaneously with volcanism through deep burial digenesis processes. Espinoza et al., 1996;Cabral and Beaudoin, 2006;Ramirez et al., 2006 ...
... . 1999; Wilson et al., 2003 Espinoza et al., 1996;Cabral and Beaudoin, 2006;Ramirez et al., 2006 ) . ...
Kahak copper mineralization in south Qom occurred in volcanic-pyroclastic rocks which based on the Kahak 1:100,000 geological map are attributed to Eocene. Volcanic rocks of the study area are found in two forms of lava and pyroclastics. Based on geochemical studies, these rocks show alkaline to calc-alkaline characteristics in an arc extensional setting. According to the mineralographical studies, the main copper minerals are chalcopyrite, pyrite, chalcocite, bornite, native Cu, covellite, digenite and malachite. The predominant textures of ore minerals include replacement, vein-veinlet, disseminated and open space filling. The lithological, mineralogical and microscopic investigations revealed that copper initially formed contemporaneously with volcanism in the volcanic-pyroclastic sequences. Then, in burial diagenesis, due to hydration of pyroclastics and detritals, copper was transported by oxide fluids, and in reduced conditions resulted from abundance of volcanic stage pyrites, replaced them as copper sulfide minerals in the permeable rocks. On the basis of this study, we suggest that the Kahak Cu mineralization is a Volcanic Red Bed type deposit that formed and concentrated contemporaneously with volcanism through deep burial digenesis processes.
... Based on theoretical considerations and experimental studies, it has already been suggested that native Cu in basalt may have a primary magmatic origin (Hofmeister and Rossman, 1985;Cabral and Beaudoin, 2007). The magmatic origin of Cu 0 supposes it has crystallized in equilibrium with the basaltic magma. ...
... Investigations of the Cu-isotope composition of primary Cu 0 grains in ultramafic rocks (Ikehata and Hirata, 2012) showed homogeneous δ 65 Cu values between −0.03 and 0.14‰, implying that there is no significant Cu-isotope fractionation during high-temperature magmatic processes. Studies on magmatic Cu 0 (Cabral and Beaudoin, 2007) revealed that it occurs as micrometric (~50 µm) inclusions in rock-forming minerals and contains high concentrations of volatile elements (0.2-2.0% S, up to 0.6% As). However, the native Cu from Site 597C occurs mainly as vein fillings and does not have EMP detectable (≥0.1 wt.%) content of S and As. ...
Ocean drilling has revealed that, although a minor mineral phase, native Cu ubiquitously occurs in the oceanic crust. Cu isotope systematics for native Cu from a set of occurrences from volcanic basement and sediment cover of the oceanic crust drilled at several sites in the Pacific, Atlantic and Indian oceans constrains the sources of Cu and processes that produced Cu-0. We propose that both hydrothermally-released Cu and seawater were the sources of Cu at these sites. Phase stability diagrams suggest that Cu-0 precipitation is favored only under strictly anoxic, but not sulfidic conditions at circum-neutral pH even at low temperature. In the basaltic basement, dissolution of primary igneous and potentially hydrothermal Cu-sulfides leads to Cu-0 precipitation along veins. The restricted Cu-isotope variations (delta Cu-65 = 0.02-0.19 parts per thousand) similar to host volcanic rocks suggest that Cu-0 precipitation occurred under conditions where Cu+-species were dominant, precluding Cu redox fractionation. In contrast, the Cu-isotope variations observed in the Cu-0 from sedimentary layers yield larger Cu-isotope fractionation (delta Cu-65 = 0.41-0.95 parts per thousand) suggesting that Cu-0 precipitation involved redox processes during the diagenesis, with potentially seawater as the primary Cu source. We interpret that native Cu precipitation in the basaltic basement is a result of low temperature (20 degrees-65 degrees C) hydrothermal processes under anoxic, but not H2S-rich conditions. Consistent with positive delta Cu-65 signatures, the sediment cover receives major Cu contribution from hydrogenous (i.e., seawater) sources, although hydrothermal contribution from plume fallout cannot be entirely discarded. In this case, disseminated hydrogenous and/or hydrothermal Cu might be diagenetically remobilized and reprecipitated as Cu-0 in reducing microenvironment.
... Manto deposits are stratiband and usually have a vein-veinlet texture (Kojima et al., 2009). Alterations in these deposits involve silicification, calcite, chlorite, epidote, and oxidation (Wilson et al., 2003;Cabral and Beaudoin, 2007). Carbonate, chlorite, quartz, hematite, and alkali feldspar constitute gangue minerals in Manto deposits (Wilson and Zentilli, 2006). ...
This study has aimed to introduce a novel strategy for exploring the Manto-Michigan copper deposits, considered a principal copper resource after the porphyry type. Faults and crushed zones have a prominent role in this deposit type, and so we hope to detect unique patterns in magnetic responses that provide a helpful indicator to determine the mineralized zone. Accordingly, we want to test the magnetometry in Manto-type exploration. We performed a magnetometry survey in the Dochileh copper deposit that other researchers have claimed to be a Manto-Michigan type with a distance of 10 meters between survey lines and a spacing of 5 meters among stations on each profile. After processing the required maps, the residual magnetic map does not show any typical dipole magnetic anomaly, but some linear trends exist. One of those linear trends belongs to a faulted and crushed zone with a length of almost 2.5 km and different widths between 50 and 250 meters. The previous mineralized zones indicated by other prospectors who relied more on geological evidence in the Dochileh area have mostly stayed inside this negative value on the residual map. Four new boreholes were made in the negative anomaly to evaluate our hypothesis, and the derived cores confirmed the native copper, malachite, and cuprite mineralization.
... and websterite from the Totalp ultramafic massif, Swiss Alps(Van Acken et al., 2007). Three hypotheses have been put forward to explain the genesis of native copper in peridotites and basalts: ((i) crystallization in equilibrium with a mafic magma (e.g.Cabral and Beaudoin, 2007;Ikehata and Hirata, 2012); (ii) lowtemperature in situ alteration of magmatic or hydrothermal Cu-sulfides at highly reducing conditions (e.g.Lorand and Grégoire, 2006;Schwarzenbach et al., 2014); (iii) precipitation from low-temperature hydrothermal fluids (e.g.Dekov et al., 2013;Ikehata et al., 2016). ...
The main objective of this Ph.D. dissertation is to better understand mass transfer of Fe, Cr and Cu, three elements of economical interest, during serpentinization of ultramafic rocks. During the last decade, processes of formation of serpentinite-hosted metal deposits with mineable sizes has attracted attention as curiosities. One of the characteristics of the serpentinisation process is to generate highly reducing conditions in its early stages. Indeed, serpentinization of peridotite triggers the generation of substantial amounts of dihydrogen (H2,aq) which favors the stability of native metals in serpentinites. The study of the effect of these extreme RedOx conditions achieved during serpentinization, on the mobility of metals is at the heart of this PhD work.To advance in this overall research goal, this Ph.D. thesis presents the results of two natural case studies of key processes of mass transfer and RedOx evolution during fluid-rock interaction: (i) serpentinite-hosted podiform magnetite ores in the Sabzevar ophiolite (NE Iran) and (ii) Cu-rich hydrothermally altered pyroxenites in the Cheshmeh-Bid ophiolitic massif (Southern Iran). These two occurrences have been selected since they provide a remarkable case study to better constrain Fe, Cr and Cu mobility during the hydrothermal evolution of peridotite-hosted hydrothermal systems. The systematic field observations together with textural observation at both µm- and nm-scales, geochemical signatures from whole-rock analyses and microanalysis and thermodynamic modelling were used to figure out the processes that promoted magnetite and copper formation in ophiolitic peridotites during serpentinization.To conclude, the strongly reducing conditions associated with serpentinization of oceanic peridotites is considered to be a prerequisite for the formation of native copper and magnetite deposits in serpentinites. Under these low-T/high H2 activity conditions, Cr is almost immobile whereas Fe and Cu are elements to be transferred to mineralization sites during reaction. The source of copper may be either desulfurization of primary Cu-sulfides or S-poor fluids during hydrothermal alteration for native copper formation. The source of iron necessary for magnetite ore formation is olivine breakdown and/or dissolution of nanoscale magnetite grains initially formed in the host serpentinite. Cumulative factors controlling the formation of ore deposits in serpentinites are fluid/rock ratio, silicate/spinel ratio, oxygen fugacity, permeable zone and initial composition of peridotites. Therefore, serpentinites in Tethyan ophiolites must be considered as a target for understanding the formation of the ores which helps for a future exploration.
... In these conditions' sericite, kaolinite, dickite, quartz and pyrite can precipitate. Formation of sericite occurs according to the following equation (Shahabpour, 2001): (Kojima et al., 2003) Mont Alexandre (Cabral and Beaudoin, 2007); Hinds lake area (Case and Zagorevski, 2009) White Pine (Brown, 1971;Swenson and Person, 2000); Copper Falls Mine (Larsen et al., 2003); Houghton County (Rosemeyer, 2011) THE BARZAVAND AND NEYSIAN COPPER DEPOSITS, NW NAEIN, CENTRAL IRAN … . ...
Field observations in the northwest of Naein (Central Iran zone) indicate various types of alteration products have extended into pyroclastic and volcanic units with Oligo-miocene age. It seems the Zefreh (with NW-SE trend) and Kachumesqal (with E-W trend) faults are effective factors in the formation of Neysian and Barzavand copper deposits respectively. Alteration in Barzavand copper deposit (with stratabound form) includes pyritization, propylitization, zeolitization, saussuritization, uralitization and silicification, while in Neysian (with oval form) include phyllic, advanced argillic, argillic and propylitic. Geochemical studies in Barzavand show the positive correlation between (La/Lu)N, (La/Yb)N and (La/Sm)N and CaO (r= 0.70 to 0.96) related to propylitization of host rock basalt and increase in pH of fluids responsible for mineralization that play important role in differentiation of lanthanides in study area. The Barzavand copper deposit has submarine volcanism, diagenesis, burial metamorphism and weathering stages during its evolution. Remarkable geochemical features in Neysian include high (La/Lu)N, Ba and Sr values than La, Ce and Y. It seems that extensive alteration occurred along with hypogene and supergene processes in Neysian. According to alteration properties, mineralogy and the whole-rock geochemistry, the Barzavand and Neysian copper deposits are most similar to Manto-type and porphyry copper deposits respectively. ARTICLE INFO
... Alteration of this type of copper ore deposits is propylitization, silicification, chloritization, epidotization, carbonatization, and albitization related to the activity of magmatic, diagenetic, and mineralized fluid (Boveiri Konari et al. 2013) which are associated with ore mineralization. Propylitization, silicification, and carbonatization are the most important alteration in manto-type ore deposit (Sato 1984;Wilson et al. 2003aWilson et al. , 2003bKojima et al. 2007;Cabral and Beaudoin 2007), similar to Mari (Maghfouri et al. 2017) and Gheshlagh ore despite. ...
The Gheshlagh Cu deposit is located in the Tarom-Hashtjin metallogenic belt (THMB) of northwest Iran. The mineralization is hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation at the subduction-related magmatic arc position. Wall rock alterations include propilitization, silicification, and carbonatization. The major copper sulfides are pyrite, chalcopyrite, chalcocite, idaite, bornite, covellite, and digenite associated mainly with hydroxide carbonate (malachite), oxide (hematite, magnetite, and goethite), and native copper that show open space filling, disseminated, vein-veinlet, and replacement textures. Commonly mineralization and alteration are structurally controlled by favorable structures (faults and fracture). Based on crosscutting, the relationship of vein, textural relationship, mineral assemblage, and fluid inclusion microthermometry, it was found that alteration and mineralization in the Gheshlagh ore deposit occurred in the fourth main stage. The first stage (stage I) is accompanied by the formation of pyrite (discontinuous) under reducing conditions in the seafloor and very shallow burial. During the increase of the burial depth (stage II), sediments have hardened, and also tectonic and lithostatic stress, dykes, and floods cause intraformational and magmatic fluid circulation by compaction and heat recharging. These high-temperature fluids are enriched in copper during circulation among volcanic units. Copper-rich fluids migrate upward and are reduced by entering the pyrite-rich andesitic-basaltic unit, and copper is deposited in sulfide forms such as chalcopyrite and chalcocite in favorable site. In deep burial (stage III), the copper mineral formed in the previous stage would be replaced by. At the supergene condition (stage IV), due to oxidizing conditions, weathering, and leaching, copper sulfides mostly appear as malachite in the joints and voids.
... M o b a s e r e t a l . (Kojima et al., 2003) Mont Alexandre (Cabral and Beaudoin, 2007); Hinds lake area (Case and Zagorevski, 2009) White Pine (Brown, 1971;Swenson and Person, 2000); Copper Falls Mine (Larsen et al., 2003); Houghton County (Rosemeyer, 2011) THE BARZAVAND AND NEYSIAN COPPER DEPOSITS, NW NAEIN, CENTRAL IRAN … . ...
Field observations in the northwest of Naein (Central Iran zone) indicate various types of alteration products have extended into pyroclastic and volcanic units with Oligo- miocene age. It seems the Zefreh (with NW- SE trend) and Kachumesqal (with E-W trend) faults are effective factors in the formation of Neysian and Barzavand copper deposits respectively. Alteration in Barzavand copper deposit (with stratabound form) includes pyritization, propylitization, zeolitization, saussuritization, uralitization and silicification, while in Neysian (with oval form) include phyllic, advanced argillic, argillic and propylitic. Geochemical studies in Barzavand show the positive correlation between (La/Lu)N, (La/Yb)N and (La/Sm)N and CaO (r= 0.70 to 0.96) related to propylitization of host rock basalt and increase in pH of fluids responsible for mineralization that play important role in differentiation of lanthanides in study area. The Barzavand copper deposit has submarine volcanism, diagenesis, burial metamorphism and weathering stages during its evolution. Remarkable geochemical features in Neysian include high (La/Lu)N, Ba and Sr values than La, Ce and Y. It seems that extensive alteration occurred along with hypogene and supergene processes in Neysian. According to alteration properties, mineralogy and the whole-rock geochemistry, the Barzavand and Neysian copper deposits are most similar to Manto- type and porphyry copper deposits respectively.
... The host rocks of Manto-type deposits are also composed of amygdaloidal andesitic lava in calc-alkaline sequences of andesite-basaltic to andesiticdacite (Oyarzun et al. 1998, Guzmán et al. 2000, Lane & George 2000, Tosdal & Monizaga 2003, Wilson et al. 2003, Tristá-Aguilera et al. 2006. Chilean Manto-type deposits formed in back-arc basins and continental-arc volcano-sedimentary sequences (Wilson & Zentilli 2006, Cabral & Beaudoin 2007, Carrillo-Rosúa et al. 2014, Maghfouri et al. 2017. The Davaran deposit is related to a subduction-related continental arc. ...
... Three hypotheses have been put forward to explain the genesis of native copper in peridotites and basalts: ((i) crystallization in equilibrium with a mafic magma (e.g. Cabral and Beaudoin, 2007;Ikehata and Hirata, 2012); (ii) low-temperature in situ alteration of magmatic or hydrothermal Cu-sulfides at highly reducing conditions (e.g. Lorand and Grégoire, 2006;Schwarzenbach et al., 2014); (iii) precipitation from low-temperature hydrothermal fluids (e.g. ...
In the Cheshmeh-Bid district of the Khajeh-Jamali ophiolitic massifs (Southern Iran), mantle peridotites are intruded by abundant pyroxenite dykes. A few of these dykes are remarkable for the occurrence of native copper associated with the development of a metasomatic reaction zone. The dykes are progressively reacted, from their margins towards the center, with an amphibole + antigorite selvage, followed by a centimeter-thick clinopyroxene + antigorite assemblage and, finally, by the native copper-bearing zone consisting of clinopyroxene + chlorite + antigorite. Native Cu occurs along cleavages and partially healed fractures in clinopyroxene, and as massive grains intergrown with antigorite. Copper isotope signatures and thermodynamic calculations show that the main driver for reaction zone formation is Ca-metasomatism. Native copper forms at the expense of chalcocite in the reaction zone. Such a reaction can only occur in reducing conditions, in agreement with the analysis of fluid inclusions composition displaying H2 and CH4. Such fluids presumably originated from the hydration of mantle rocks. The observed reaction zone and native copper mineralization are thus interpreted as the result of Ca-metasomatism during hydrothermal alteration of the oceanic lithosphere. This is consistent with U/Pb dating of titanite, suggesting formation during the Albian when the dykes were exposed on the seafloor in a supra-subduction setting. The source for copper mineralization, as revealed by Cu isotopes, is probably mantle-like.
... The veining is important as it links a hydrothermal component to the copper mineralisation. While spilitic alteration can produce native copper (255), there is no known 114 Celadonite, a phyllosilicate of potassium, iron, aluminium, and hydroxide, K(Mg,Fe 2+ )(Fe 3+ ,Al)Si4O10(OH)2 (254). 115 Thomsonite is a series of tecto-silicate minerals in the zeolite group. ...
This report presents a holistic view of north eastern Greenland’s geology. The empirical evidence of mineralisation and geological record are tied in with mineral system components from global through to prospect scales. The source rocks, geodynamic triggers, pathways, and deposition sites are all identified within a preserved terrane. This work defines the Kiffaanngissuseq metallogenic province, a previously undescribed mineral system.
For the first time, we identify a c. 1,250 Ma orogenic event in the basement as the geodynamic trigger related to the basalt-hosted native copper within the Arctic Rift Copper project. A c. 385 Ma fluid migration is identified as the trigger for a second copper-sulphide mineralising event expressed within the project, that also emplaced a distal zinc deposit within Kiffaanngissuseq. This multi-episodal mineral system is supported by a regional geochemical and hydrodynamic framework that is not articulated elsewhere. The large scale of the mineral system, widespread copper anomalism, combined with dual mineralising events are analogous to Earth’s great copper systems. The Company considers that Kiffaanngissuseq has the potential to be a world-class mineral province.
A coincident magnetic-gravity-conductivty and high-grade geochemical copper anomaly occurs within the project. The anomalism is located at an oxidation boundary and is proposed to be the expression of a hydrothermal outlet. This site of focussed fluid flow forms the basis of a high-priority, near-term target, known as the ‘Minik Singularity’.
... In regard to As, due to widespread volcanism and geothermal activity characteristic of the Precambrian, considerably more arsenic was accumulated on the Earth's surface than today (Cabral and Beaudoin 2007;Witt-Eickschen et al. 2009). Hence, as modern counterpart of Precambrian system, a living microbial mat from Laguna Brava has been investigated, using an array of conventional geochemical techniques (Farias et al. 2017;Sancho-Tomás et al. 2018). ...
High-altitude Andean lakes (HAALs) represent unique environments on the Earth where one can study the biological chemistry of life in one of its most extreme versions. The Atacama Desert, Argentine Puna, and Bolivian Altiplano harbor hypersaline lakes where polyextremophilic Andean Microbial Ecosystems (AMEs) inhabit microbial mats, evaporitic mats, biofilms (BF), evaporites (EV), and microbialites (Mi). These AMEs have two remarkable characteristics: (i) they are the only ones in the world that inhabit areas ranging from 3100 to 4200 masl; and (ii) they are excellent modern analogues of those which populated the primitive Earth ~3 billion years ago. In this chapter, we will delve into the different kinds of AMEs present in the HAAL, their formation, structure, and their adaptation to conditions largely influenced by volcanic activity, UV radiation, arsenic content, high salinity, low dissolved oxygen content, extreme daily temperature fluctuation, and oligotrophic conditions. All of these physicochemical parameters recreate the early Earth and even extraterrestrial conditions. The relevance of studying these ecosystems does not lie only in scientific-descriptive and/or economic interest. The scientific research community has a great responsibility to address climate change. In this scenario, the AMEs could have played a key role, influencing changes that allowed the origin of aerobic life and those who have faced the great climatic events of the Earth.
... In regard to As, due to widespread volcanism and geothermal activity characteristic of the Precambrian, considerably more arsenic was accumulated on the Earth's surface than today (Cabral and Beaudoin 2007;Witt-Eickschen et al. 2009). Hence, as modern counterpart of Precambrian system, a living microbial mat from Laguna Brava has been investigated, using an array of conventional geochemical techniques (Farias et al. 2017;Sancho-Tomás et al. 2018). ...
Extant stromatolites have been considered ecological similes to their ancient counterparts. We now know that these microbial assemblages are composed of a great diversity of microbes, which couple and intertwine their metabolic capabilities to create self-sustained microbial ecosystems. Presently, stromatolites thrive in a vast diversity of aquatic environments including freshwater, hypersaline, coastal lagoons, alkaline lakes, oligotrophic pools, abandoned pits, few marine systems, and brackish waters. In this chapter, we will summarize the research that has been done in two stromatolite-harboring sites in Mexico: the alkaline crater-lake Alchichica and the oligotrophic karstic coastal lagoon of Bacalar. Alchichica is located in the Transvolcanic belt in Central Mexico. It is a maar-alkaline crater lake (salinity 8.5 gl−1, pH 9.5) with water chemistry determined by high contents of carbonates, sodium, a high Mg/Ca ratio, and particularly low Ca2+ concentrations (~0.3 mM). Two main stromatolite-types, as defined by mineralogy, texture, and microbial composition, develop along its periphery from surface to over 30 m in depth. Alchichica is a modern environment that resembles Precambrian oceanic conditions. Stromatolites from Alchichica have been dated radiometrically in ~1.1–2.8 ka BP. Bacalar is a coastal lagoon located in the Yucatan Peninsula, which is a carbonate platform that emerged above sea level during the Oligocene. The Bacalar lagoon has high carbonate concentrations as a result of the influx of groundwater (salinity 1.2 gl−1, pH 7.6–8.3). It holds the largest freshwater stromatolite structures known, which have been radiometrically dated in ~6.8–9.2 ka BP. Their mineralogy, shape, and texture are similar along the lagoon’s coast, but microbial composition changes, possibly due to anthropogenic impact.
... In regard to As, due to widespread volcanism and geothermal activity characteristic of the Precambrian, considerably more arsenic was accumulated on the Earth's surface than today (Cabral and Beaudoin 2007;Witt-Eickschen et al. 2009). Hence, as modern counterpart of Precambrian system, a living microbial mat from Laguna Brava has been investigated, using an array of conventional geochemical techniques (Farias et al. 2017;Sancho-Tomás et al. 2018). ...
Deep hydrothermal systems result from the magmatic and tectonic activity of the ocean floor. This deep extreme biosphere represents a unique oasis of life driven by sulfur-based chemosynthesis instead of photosynthesis. The organisms inhabiting these systems are adapted to cope with harsh environmental conditions such as the absence of sunlight, high temperatures and hydrostatic pressures, and elevated concentrations of hydrogen sulfide, as well as high concentrations of heavy metals. Therefore, this biome is different from any other environment on modern Earth. As expected from such conditions, chemoautotrophic prokaryotes are the leading primary producers at the base of the food web considered as an analog to the oldest signs of life on Earth. Herein, we discuss prokaryotic diversity and community structure from the newly discovered hydrothermal systems in the Alarcón Rise (AR), the Pescadero Basin (PB), and the Pescadero Transform Fault (PTF) at the mouth of the Gulf of California, Mexico, using 16S rRNA gene amplicon Illumina sequencing. Despite the spatial proximity of the studied vent systems (<100 km), they differ considerably in their physical, chemical, geological settings, and biotic characteristics. Our results indicated that beta prokaryotic diversity is associated to the sampling source, suggesting a strong effect of environmental conditions in shaping microbial distribution. The most abundant phyla were Proteobacteria, Bacteroidetes, Actinobacteria, Chloroflexi, and Epsilonbacteraeota. Also, we found evidence on the oxidation of methane as a prevalent process in PB and PTF, since methylotrophic bacteria and Atribacteria were abundant, in contrast to AR basalt-hosted system. Bacteria associated with the sulfur cycle, in particular sulfur compounds reducing and sulfur compounds oxidizing bacteria predominated in all samples, confirming the importance of sulfur supporting vent communities. It is possible that vent systems played a significant role in the origins of life on Earth. Hence, they represent useful models when searching for life elsewhere in the universe.
... In regard to As, due to widespread volcanism and geothermal activity characteristic of the Precambrian, considerably more arsenic was accumulated on the Earth's surface than today (Cabral and Beaudoin 2007;Witt-Eickschen et al. 2009). Hence, as modern counterpart of Precambrian system, a living microbial mat from Laguna Brava has been investigated, using an array of conventional geochemical techniques (Farias et al. 2017;Sancho-Tomás et al. 2018). ...
A small community of scientists in Mexico has been contributing to the study of planetary bodies in our Solar System and around other stars, including their potential for habitability. Here, we present particular aspects of this research told as a journey: from the first attempts to reproduce cells and the laboratories where the first Mexican astrobiologists were educated to the sites in Mexico where scientists are studying the extremes of life and likely environments of other planets. We jump to space rocks that narrate the history of the Solar System. Then, we move to Mars and the debate of organics and the Viking experiment to continue with the hidden water oceans of the icy satellites and Titan, an exotic orange satellite with methane lakes, hydrocarbon dunes, and water ice rocks. Our journey continues toward other stars where we search for planets beyond our Solar System, known as exoplanets, that have shown a surprising diversity more familiar to science fiction with hot Jupiters, lava worlds, mini-Neptunes, super-Earths, and potentially habitable worlds.
... Anaerobic processes could include fermentation, methanogenesis, sulfate reduction, and likely arsenate reduction. The widespread volcanism and geothermal activity characteristic of the Precambrian environment would present considerably more arsenic accumulation on the Earth's surface than there is today (Cabral and Beaudoin 2007;Witt-Eickschen et al. 2009). However, very few biogeochemical data supporting this claim have been put forward so far. ...
Puna wetlands and salars are a unique extreme environment all over the world, since their locations are in high-altitude saline deserts, largely influenced by volcanic activity. Ultraviolet radiation, arsenic content, high salinity, and low dissolved oxygen content, together with extreme daily temperature fluctuations and oligotrophic conditions, shape an environment that recreates the early Earth and, even more so, extraterrestrial conditions. Microbes inhabiting extreme environments face these conditions with different strategies, including formation of intricate microbial communities with an increasing degree of complexity. In that way, biofilms, mats, endoevaporitic mats, domes, and microbialites have been found to exist in association with salars, lagoons, and even volcanic fumaroles in Central Andean extreme environments. They form microbial ecosystems, where light and O2 availability decrease with depth stratification, promoting functional group diversity. This microbial diversity, together with the geochemistry, may favor the precipitation of minerals. This chapter summarizes general concepts in the environmental microbiology of extreme Andean ecosystems, which are explored throughout this book.
... For instance, after the early accretionary phase of the Earth, after it had cooled and differentiated, sulfur and chalcophilic elements (e.g., As) were significantly enriched within the mantle and the core relative to the crust due to the sinking of the denser metal(loid)-sulfides. Due to widespread volcanism and geothermal activity characteristic of Archean Earth, As would have been brought back to the Earth's surface (e.g. Cabral & Beaudoin, 2007;Witt-Eickschen et al., 2009). In addition, like many modern hot springs, abundant hydrothermally-influenced systems on the Precambrian Earth presumably contained high concentrations of reduced As(III). ...
Arsenic is best known as an environmental toxin, but this element could also serve as a metabolic energy source to certain microorganisms. Moreover, As cycling may have driven microbial life on early Earth prior to oxygenation of the atmosphere. Still, little is known about the arsenic cycling processes occurring in the presence of microorganisms and the possible traces that could be preserved in the rock record. To advance our understanding of this we studied the geochemical proxies of microbial As metabolism in living microbialites from Laguna Diamante, a likely Precambrian ecosystem analogue (Catamarca, Argentina). In this study, we show that the coexistence of As(III) and As(V) strongly supports the presence of active microbially arsenic cycling in these microbialites. In addition, we propose a model by which arsenic metabolic processes can be preserved and interpreted as biosignatures in modern systems as well as in the rock record.
... These deposits are the consequence of the long-lived flow of copper-enriched fluids through red beds that may be continuing to the present day (hitzman et al. 2005, ingham et al. 2014). The location of Cu mineralization is controlled by sediment permeability, the direction of fluid flow, and the proportion of reducing components, such as organic matter and sulfides, in the host rock (suBias et al. 2003, gaBlina et al. 2006, CaBral & BeauDoin 2007, Brems et al. 2009, solimana & goresy 2012, greenwooD et al. 2013, PingKanga et al. 2013. ...
The Dozkand-Moshampa area is located in the northwest of Central Iran. The several-hundred-m-thick Miocene Upper Red Formation (URF) in northwestern Iran hosts stratiform copper mineralization. The main lithological units in the Dozkand-Moshampa area are Cenozoic sedimentary rocks. The stratigraphic sequence includes evaporites, continental red beds and limestone, similar to other sediment-hosted Cu belts around the world. Copper mineralization in Dozkand-Moshampa area appears as disseminated, laminated and replaced copper sulfides along a redox boundary between (a) gray sandstone, siltstone and mi-croconglomerate, and (b) hematitic sandstones, siltstones and shaly marl. Mineralization is closely related to plant fossils (wood fragments) and the main ore minerals include chalcocite, galena, sphalerite, chalcopyrite, pyrite, covellite and malachite. Copper sulfides occur mainly as replacement of diagenetic pyrite, which, in turn, replaced organic matter (wood fragments). Replacement, dissemination, banding and veinlet, are the most common mode of occurrence of ores, which suggest an origin related to diagen-esis. Investigations by electron microprobe analyses of chalcocite, sphalerite and galena revealed high Ag contents (up to 0.16, 0.11 and 0.01 wt%, respectively), whereas chalcopyrite and pyrite have only trace amounts of silver. The abundances of Cu and Ag in the chalcocite are up to 76.93 and 0.22 wt% respectively. Negative values of 834S (0.2 to -32.7 %o) show that sulfur was introduced by bacterial reduction of sulfate. Copper mineralization is mainly controlled by organic matter content and paleopermeability (from intragranular pore space and fractures), enhanced by calcite dissolution. Geology, ore paragenesis, mineral chemistry and sulfur isotopes suggest that the Dozkand-Moshampa Cu-Pb (Zn-Ag) deposits may be ascribed to the Red bed. © 2018 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
... Veshnaveh is a copper deposit, hosted by a Middle-Upper Eocene basalt andesite volcanic sequence in central Iran. It shares several similarities with a broad range of volcanic-hosted copper deposits, including the so called "Manto-type" deposits (Sato 1984, Kojima, et al., 2003Kojima, Trista-Aguilera and Hayashi, 2009) or "Basalt-andesite copper deposits" (Guilbert and Park, 2007), and or "volcanic red-bed deposits" (Kirkham 1995;Cabral and Beaudoin 2007) respectively reported from Chile (Cretaceous Chilean Manto Type Cu deposits), north Michigan and the west coast of North America (Keweenawan Michigan copper deposits and Canada), and China. Nevertheless, the host rock of the Veshnaveh mineralization is the youngest among the above mentioned deposits. ...
The Veshnaveh ancient copper mine is located in the middle of the Orumieh-Dokhtar volcanic belt in north central Iran and is hosted by middle-upper Eocene volcanic and sedimentary rocks. The focus of this paper is the investigation of ore and rock samples from Veshnaveh using diverse geochemical and mineralogical methods including ore microscopy, scanning electron microscopy, inductively coupled plasma mass spectrometry and lead isotope analysis in order to better understand the nature of mineralization. The results were then compared with the results from the ancient metallurgical relics from some key sites in central Iran including Tappeh Sialk, Arismān, Tappeh Sarm and Jamkarān. The results show the Veshnaveh deposit is a Manto type mineralization whose ore has been possibly used from the Middle Bronze Age until the early Iron Age by surrounding communities.
... کانه چینه واحد یک در نیز یمقان مس زایی به محدوده و خاص ای تراکی واحد .است داده رخ مگاپورفیر آندزیت ً عمدتا مانتو تیپ کانسارهای دگرسانی دارای کلریت ،کلسیتی ،سیلیسی های ی اپیادوت ، ی زئاولیت ، ی اکسایدی و ( Wilson et al., 2003;Cabral and Beaudoin, 2007 می ) دگرسانی .باشند های یمقان مس کانسار در عمده نیز ا نیاز و کلسایتی ،سیلیسای ،سریسایتی نوع ز اپیدوت ی کلریت ، ی زئولیت و ی می .باشند ...
Yamaghan copper deposit occurs in the Eocene volcanic-pyroclastic sequence of NE-SW orientation, 55 km southeast Zanjan in the Tarom volcano-plutonic subzone of the western Alborz structural zone. Lithologic units at the deposit consist of pyroclastic rocks and lava. The host rock to the deposit is a trachy-andesite unit with megaporphyritic and amygdaloidal textures in which copper ore formed as strarabound. Chalcocite together with bornite, native copper, chalcopyrite and pyrite are the major ore minerals, accompanied by secondary minerals including covellite, digenite, malachite, azurite, goethite and hematite. Replacement, vein-veinlet, disseminated and open space filling are the predominant textures. The main alteration types related to mineralization are carbonatization, silicification, chloritization, epidotization and zeolitic. Based on the conducted studies and various lines of evidence such as tectonic setting, host rock, ore texture and structure, mineralization and alteration, it is suggested that Yamaghan could be comparable to the Manto-type deposits.
... (Cabral & Beaudoin, 2007); Hinds Lake area (Case & Zagorevski, 2009) White Pine (Brown, 1971;Swenson & person, 2000); Copper Falls mine (Larson et al., 2003); Houghton County (Rosemeyer, 2011) ...
... These deposits are the products of the long lived flow of copper-enriched fluids through red beds that may be continuing to the present day ) Hitzman et al., 2005;Ingham et al., 2014). The location of Cu mineralization is controlled by the interplay between sediment permeability, the direction of fluid flow, and the proportion of reducing components, such as organic matter and sulfides, in the host rock (Subı'as et al., 2003;Gablina et al., 2006;Raphael Cabral and Beaudoin, 2007;Brems et al., 2009;Solimana and Goresy, 2012;Greenwood et al., 2013;Pingkanga et al., 2013). ...
... Brittle deformation dominates in the Cretaceous magmatic rocks of Eastern Tunisia as shown by fracturing of plagioclase and clinopyroxene grains, producing a progressive grain size reduction and allowing fluids to penetrate the rock, which enhances formation of hydrated minerals (Fitz Gerald and Stunitz 1993). A similar example has been described in the Jebilet Massif in Morocco (Essaifi et al. 2004) and in the Mont Alexandre area in Canada (Cabral and Beaudoin 2007). No evidence of plagioclase or clinopyroxene recrystallization has been identified in the Eastern Tunisian margin magmatic rocks. ...
Abstract
This study documents the Cretaceous intraplate magmatic-hydrothermal activity in the Eastern margin of Tunisia. The magmatic occurrences are believed to be directly linked to deeply rooted faults, trending E–W, N–S and NW–SE, and which enabled basaltic magmas ascension. The settling of this magmatism was accompanied by circulation of hydrothermal fluids, generating a local abnormal geothermal gradient. Magmatic rocks suffered effects of hydrothermal alteration during magma cooling. Slightly deformed zones are characterised by superimposed static paragenesis which began in green schist facies (T = 450–350 °C) and ended by analcime crystallization at relatively low temperatures (T = 180–130 °C). Temperature increase and hydrothermal conditions led to the generation of a new mineral paragenesis around the enclosing sedimentary deposits. CO2, H2S, CH4 and N2 occurrences are also thought to be driven by this magmatic repartition. In addition, it is most likely that the gases, produced at deeper depth, migrated upwards along the highly permeable fault zones. The carbon isotopic signatures of selected gas samples suggest a thermogenic origin for methane and a crustal origin for CO2. The latter could have been generated through thermal breakdown of carbonate rocks via contact metamorphism or through increasing burial depth and high heat flow induced by the hydrothermal event in the studied area.
... ʈɷ > @ ɳ ɷ> ɷ ɳ >ɷ ɳ> ʈ . (Cabral et al., 2007;Kojima et al., 2009) ɳ ɶ ɷ ɷ> < ɳɷʈʺ ʈ ʀ . (Kirkham, 1996;Kojima et al., 2009) Kojima et al., 2009 . ...
... with hematite leached Cu from the Kv unit and transported it away. Where the fluids infiltrated lithic tuffs with good permeability, Cu sulfide minerals were precipitated as suggested by CabraL & beaudoin (2007) for the Mount Alexandre volcanic redbed-type deposit. A schematic genetic model for the Keshtmahaki Cu deposit is shown in Fig. 10. ...
The Keshtmahaki Cu (Ag) deposit, hosted in the Lower Cretaceous lithic tuffs, is located in the southern part of the Sanandaj–Sirjan zone (SSZ), 180 km NE of Shiraz. The deposit consists of stratabound and lenticular orebodies that are distributed with a NW-SE trend for ∼35
km from NW to SW of Safashahr in the Fars province. The ore textures are dominated by open space filling, vein-veinlet and replacement with minor disseminated and laminated-like mineralization. The ore consists predominantly of primary chalcocite, bornite, native copper, and chalcopyrite and
to some extent secondary chalcocite, digenite, covelite, malachite, azurite, and minor Ag-bearing clausthalite, Ag-bearing selenide and black copper (copper wad). There are two types of alteration including regional propylitic alteration in lavas characterized by epidote, chlorite, calcite,
sericite and quartz and ore-related hydrothermal alteration in the lithic tuff resulting from fluids which generated due to deep burial diagenesis characterized by the assemblage of quartz, calcite, epidote, chlorite, albite, hematite and zeolite. Microthermometric data of the liquid-vapor
fluid inclusions in quartz show average homogenization temperatures varying between 129 and 145 °C and salinities between 19.1 and 22.9 wt.% NaCl equivalent, respectively. The mineralization is divided into pre-mineralization, mineralization and post-mineralization stages. The mineralization
is accompanied by hydrothermal alterations. Sulfur isotope compositions have a wide range from δ34S = −13.7 to −4.9 ‰, suggesting the presence of a reducing environment resulting from activation of sulfate reducing bacteria. The field observations, ore mineralogy,
alteration characteristics, sulfur isotopic compositions and fluid inclusion data suggest the Keshtmahaki deposit may be classified as a volcanic redbed-type copper (Manto-type) deposit.
... This kind of zonation also reported from Sustut deposit in British Colombia in which observed specific zonation from native copper and chalcocite in centre and bornite and chalcopyrite in border (Kirkham, 1996). Blades of chalcopyrite with exsolution form observed in bornite that could indicate either rapid cooling of this minerals in high temperatures (Cabral, 2007) or replacement of bornite in low temperature (Frence et al,2001). ...
... After the early accretionary phase of the Earth as it cooled and geologically differentiated, sulfur and chalcophilic elements like As were significantly enriched within its interior (core and mantle), relative to its crust because of the sinking of these denser metal(loid)-sulfides. Arsenic is brought back to the Earth's surface from the interior by volcanism, a phenomenon that "distills" upwards the ore bodies of precious metals as well (Cabral et al. 2007;Witt-Eickschen et al. 2009). Hence, at the beginning of the Archean (∼3.8 Ga), it is likely that considerably more arsenic occurred on the surface of our home orb than does today, thereby posing a biochemical challenge (and opportunity) for the early emergent life. ...
Arsenic, although known for millenia to be a potent poison, can also constitute the basis for energy metabolism by a number of Bacteria and Archaea. Hence, the oxyanion arsenate [As(V)] can serve as a respiratory electron acceptor for the growth of anaerobes, resulting in the accumulation of arsenite [As(III)]. Conversely, As(III) can serve as an electron donor for the growth of aerobic and anaerobic (e.g., nitrate-respiring) chemoautotrophs, as well as photoautotrophs that grow via anoxygenic photosynthesis. Collectively, these microbes carry out these redox reactions between the +3 and +5 oxidation states that have profound importance for the mobility of As in the environment, and perhaps for the pattern of microbial evolution on Earth. I will focus upon the occurrence of these microbes in extreme environments that are rich in naturally-occurring arsenic.
... Microprobe analysis (sample No. AN-5/01 and AN-7/01) shows that the plagioclase microphenocrysts have a composition close to albite-to-andesine (An 9-38 ), while the microlites are albite to oligoclase (An 5-18 ) ( Table 1). The sodic nature of the plagioclase may be due to hydrothermal alteration (Humphris and Thompson, 1978;Arvin et al., 2001;Cabral and Beaudoin, 2007). It is also suggested that during alteration, the plagioclasepyroxene aggregates are replaced by epidote and chlorite (Humphris and Thompson, 1978). ...
... After the early accretionary phase of the Earth as it cooled and geologically differentiated, sulfur and chalcophilic elements like As were significantly enriched within its interior (core and mantle), relative to its crust because of the sinking of these denser metal(loid)-sulfides. Arsenic is brought back to the Earth's surface from the interior by volcanism, a phenomenon that "distills" upwards the ore bodies of precious metals as well (Cabral et al. 2007;Witt-Eickschen et al. 2009). Hence, at the beginning of the Archean (∼3.8 Ga), it is likely that considerably more arsenic occurred on the surface of our home orb than does today, thereby posing a biochemical challenge (and opportunity) for the early emergent life. ...
If you were asked to speculate about the form extra-terrestrial life on Mars might take, which geomicrobial phenomenon might you select as a model system, assuming that life on Mars would be ‘primitive’? Give your reasons.At the end of my senior year at Rensselaer Polytechnic Institute in 1968, I took Professor Ehrlich's final for his Geomicrobiology course. The above question beckoned to me like the Sirens to Odysseus, for if I answered, it would take so much time and thought that I would never get around to the exam's other essay questions and consequently, would be “shipwrecked” by flunking the course. So, I passed it up. With this 41-year perspective in mind, this manuscript is now submitted to Professor Ehrlich for (belated) “extra-credit.” R.S. Oremland
... This is an introduction of metals by exhalations of hydrothermal events and heated seawater-basaltic interaction. A similar observation is known in tholeittic flows of the North Atlantic (LeHuray, 1989), in the California (Canet et al., 2005) and in Canada (Cabral and Beaudoin, 2007). The use of basin modelling to calculate palaeo-heat flows following the emplacement of the magmatism allowed us to build up a picture of the thermal events that affected this region. ...
The integrated use of geological, geophysical, and geochemical data from Eastern Tunisia onshore and offshore samples indicate a crustal thinning induced from the Tethyan rifting. This is responsible for the subsequent evolution of the North African passive margin during the Late Cretaceous, and the creation of the fold–thrust belt and associated foreland deformations. This thinned crust was an area of mantle upwelling that favoured the increase of isotherms, the uprise of basalt magma, and the circulation of hydrothermal fluids. The Cretaceous magmatism generated a major hydrothermal event characterised by the circulation of hot fluids along faults and a relatively high heat flow in the basin. Temperature elevation and hydrothermal conditions led to alteration of basalts and generated a new mineral equilibrium around the enclosing sedimentary deposits.
In Nasim deposit, mineralization has been done in conglomerate unit as a particular horizon. This unit is composed of volcanic fragments with carbonate and volcanic cements. Chalcocite is the most important and main sulphide mineral in the study area. Alteration can be divided into pre-mineralization and syn-mineralization stages. Pre-mineralization includes Celadonite, Carbonate, Silicified, and Propylitic alteration. Syn-mineralization consists of small amounts of Chlorite, Zeolite, and Calcite. In this system, the chemistry of solution is different from those of other systems such as IOCG, massive sulfide, porphyry etc., due to completely reduced and iron and silica-deficient solution
There are several massive deposits around the world with different geological characteristics. Thus, different mining methods and strategies are applied based on the particularity of each method and mine experience. Particularly, in this work, we review and summarize the underground exploitation of some world-class base metal deposits based on Poland and Chilean experiences. Here, the main geological and mining parameters of Poland and Chilean mines applied in massive deposits are reported and analyzed. In Poland, mainly room and pillar methods (and variants) have been applied in massive deposits. Here, back-filling is required to maintain the mine's stability due to the large deposit size and open areas. In Chile, the block caving method is commonly used in massive underground deposits where less development is required. Here, the cave is naturally filled with broken material and a large subsidence zone is generated. In this review, it has been observed that different underground methods and strategies can be effectively used in massive deposits. Some parameters that influenced the method selection are mainly related to rock mechanics, ore recovery and dilution, subsidence zone, extraction rate, and mining experience. Here, key mining variables and parameters such as productivity, support, and equipment, as well as various issues related to the world-class deposit are studied. Additionally, a comparison between both experiences is presented, highlighting the main geological and mining parameters. This study can be used as a reference to evaluate the different option of underground mining methods to be applied in future massive mine projects with similar geological characteristics.
Abri and Rahbari deposits are located 23 km NW Darooneh and are located in the part of the Khaf-Darooneh volcanic-plutonic belt and the Sabzevar Sub- Zone. The studied area rock units consisted of three categories with the age of Middle Eocene include: 1- submarine lava (andesite, basalt, porphyry andesite-basalt, trachy andesite), 2- pyroclastic (tuff and agglomerate) and 3- sedimentary (limestone, limestone marl, Siltstone and shale). The volcanic rocks belong to medium to high K calc-alkaline magmatic series and have been formed during a volcanic arc tectonic regime of active continental margin. Mineralization in Abri and Rahbari areas has occurred, on the border of limestone units with pyroclastic rocks and lava as strata bound and the mineral is formed as veins and vein- veinlet, cavities and open space filling and disseminated. the main minerals formed the deposits are classified in three groups of sulfide minerals (chalcocite, covellitis, bornite, chalcopyrite and pyrite), carbonate minerals (malachite, azurite) and oxide minerals (cuprite, magnetite, hematite and limonite). Based on the micro thermometry studies the average of fluid inclusions homogenization temperature in Abri and Rahbari area is 198 ˚C and The average of salinity is 8.9 wt% NaCl. Based on the geochemical studies copper in the base metals has the highest production coefficient (The equivalent of 4 to 5 weight percent). According to the studies, it can be said that mineralization in the Abri and Rahbari area is epigenetic, strata bound that is similar to the manto type copper deposits.
The Salar de Atacama depression is a unique geomorphologic structure in northern Chile and is the oldest and largest evaporitic basin in that country. In the lowest region of the Atacama basin, groundwater surfaces forms a series of lakes that are exposed to the extreme conditions of the salar, including high ultraviolet radiation, low humidity, high water-column conductivity, and arsenic concentrations. Among these lakes, Laguna La Brava harbors a variety of living microbialites and microbial mats. Several studies have determined the microbial diversity and the genomic basis of the main metabolic pathways that allow these microbial ecosystems to thrive in such extreme conditions, which resemble Precambrian/Paleoproterozoic conditions. This chapter reviews the results published since these unusual ecosystems were first described 4 years ago.
The Dochileh stratiform copper deposit in the Sabzevar Zone of northeastern Iran is hosted in the basaltic sequence of the Upper Eocene age. The host rock displays two hydrothermal events: zeolite–carbonate alteration that is a stratigraphic–lithologic feature and chlorite and chlorite/ferruginous alterations in the local mineralized structures. Ore formation is related to both hydrothermal events and occurs in both stratiform and vein mineralization types. Mineralization consists of main chalcocite with variable amounts of bornite, chalcopyrite, native copper, malachite, and cuprite minerals, which occur as hydrothermal breccias, and disseminated, vein, and veinlet forms. Geophysical field studies using resistivity and induction polarization (IP) methods were conducted along nine survey lines in the area. As a result of modeling and interpretation of the acquired geophysical data, high values of IP and resistivity corresponding to mineralization were observed at two depth levels: 0–20 m and more than 40 m. Based on these geological and geophysical investigations, six locations for drilling exploration boreholes were proposed. Drilling data confirmed the mineralization containing high copper values in the two depth levels: the vein‐type mineralization in the surface and shallow depth level, and the stratiform mineralization at the deeper level. Fluid inclusion studies in calcite and quartz from stratiform‐ and vein‐type mineralization show the evidence of mixing, and a linear dilution trend during the ore formation occurred at a wide range of temperatures: 121–308°C and 80–284°C, respectively, and varying salinities of between 3.2–16.8 and 0.8–22 wt% NaCl equivalents. The stable isotope composition of δ34S that falls in a range of −2.4 to +25.0‰ could be considered biogenetic sulfur from bacterial sulfate reduction and leaching of sulfur from hosting basalt. The δ13C values of calcite vary between −0.6 and −7.6‰, suggesting a major contribution of marine carbonates associated with igneous carbonates, and the δ18OSMOW values of calcite are between +15.2 and +19.9‰, suggesting a contribution of δ18O‐rich sedimentary rocks and δ18O‐poor meteoric water. Copper and sulfide‐rich hydrothermal fluid have flowed upward through the local faults and permeable interbeds within the Eocene volcanic sequence and have formed the mineralized veins and horizons. The geophysical results have detected the local faults as the channel ways for mineralization. The Dochileh stratiform copper deposit in the Sabzevar Zone of northeastern Iran is hosted in the basaltic sequence of the Upper Eocene age. The host rocks, alteration, ore mineralogy, ore structure and texture, fluid inclusions, and stable isotope characteristics in the Dochileh district are similar to those of the copper manto types of the northern area deposits in Chile.
Abstract
The Gercus Basalt is a recently discovered body within the Gercus Formation, which is exposed on both limbs of the large, double-plunging, NW/SE-trending Bekhair Anticline to the north of Duhok city, northern Iraq. The basalt is mostly basanitic and alkaline in nature, greenish to grayish black in color, and very fine-grained, vesicular, amygdaloidal and microscopically porphyritic in texture. It consists of anorthoclase, diopside, forsterite and accessory titaniferous magnetite, ilmenite and apatite as well as their alteration products. The primary minerals are pervasively altered by calcitization, zeolitization, serpentinization, chloritization, silicification, iddingsitization, martitization, and possibly anorthoclasization. Copper mineralization has taken place as veins and fracture/joint-filling which is mostly observed near the northwestern plunge of the anticline where the basalt attains its maximum thickness of about 16 meters. Twelve copper minerals were found within veins and fractures, including primary minerals (bornite, chalcopyrite and an unidentified sulfide - Cu2.3FeS3) and their secondary alteration and replacement products represented by sulfides (covellite, digenite, and chalcocite), native copper, cuprite, carbonates (malachite and azurite), silicate (chrysocolla) and possibly sulfates. The copper minerals are in many cases zonally arranged as spherules where the primary minerals acted as cores, surrounded outward by secondary minerals. Primary copper mineralization is of late magmatic hydrothermal origin, postdating the emplacement, consolidation, deuteric alterations, and fracturing/jointing of the Gercus Basalt; followed by the formation of secondary supergene copper minerals as a result of alteration and replacement of the primary copper sulfides along mineralized veins and fractures/joints due to chemical weathering by meteoric and/or groundwater during Eocene time.
چكیده
کانسار مس چاهمورا درجنوب باختری شاهرود و در بخش مرکزی کمان ماگمايی ترود- چاه شیرين قرار دارد. کانیسازی در منطقه چاهمورا درون واحد آتشفشانی به سن
ائوسن رخ داده است. سنگهاي آتشفشاني ياد شده بر پايه مطالعات صحرايي و آزمايشگاهي قابل تفکیک به آندزيت، آندزيت- بازالت، تراکیآندزيت، تراکیآندزيتبازالت
و رخنمونهاي کوچکي از آذرآواريها بهصورت آگلومرا هستند. تودههای نیمهآتشفشانی با ترکیب حدواسط توالیهای آتشفشانی آذرآواری را قطع کردهاند. ماهیت اين
سنگها، کالکآلکالن غنی از پتاسیم تا شوشونیتی است که از ديد جايگاه زمینساختی، در موقعیت کمان ماگمايی مرتبط با پهنه فرورانش قرار میگیرند. دگرسانی سیلیسی،
کربناتی، سريسیتی وکلريتی در سنگ های میزبان قابل تشخیص است. ساخت و بافت ماده معدنی بهصورت رگه- رگچهای، جانشینی، دانه پراکنده و پرکننده فضای خالی است.
بر پايه مطالعات کانهنگاری کانيهاي اصلي مس شامل کالکوسیت، کالکوپیريت، کوولیت، ديژنیت، کوپريت، مالاکیت و کمتر مس طبیعي است که با هماتیت همراهی میشوند.
از میان اين کانيها، کالکوسیت و مالاکیت بیشترين فراواني را دارند. مطالعات ژئوشیمی نشان از آن دارد که عنصر مس بیشترين همبستگی را با عناصر نقره )894.0 = R( و
آرسنیک )520.0 = R( دارد. اين در حالی است که با اين عناصر کانی مستقلی تشکیل نداده است و احتمال دارد که اين عناصر در شبکه کانیهای مسدار، جايگزين مس شده
باشند. مطالعه میانبارهای سیال روي سیالهاي به دام افتاده در کانيهای کوارتز و کلسیت انجام شده است. دماي همگنشدگي در میانبارهاي سیال، بهطور میانگین 200 تا 220
درجه سانتيگراد است. درجه شوري به دست آمده در اين سیالها، در محدودههاي 97/ 0-37/ 1 و 67/3- 07/4 درصد وزنی نمکطعام است. اين کانسار همانندیهای فراوانی
از ديد کانیشناسی، سنگ میزبان، ساخت و بافت و ژئومتری با کانسارهای نوع مانتو و مس در طبقات سرخ آتشفشانی دارد.
کلیدواژهها: چاهمورا، تودههای نیمهآتشفشانی، مس نوع مانتو، ترود- چاه شیرين
The Kahak copper deposit occurs in the Eocene volcano-sedimentary sequence of Qom region, Urumieh-Dokhtar magmatic arc. The oldest rock unit in this sequence is a crystal tuff, overlying by tuff, andesite, sandstone, conglomerate and limestone. Host rocks to the Kahak deposit include andesite and tuff and the geometry of mineralization is stratabound. According to the mineralographical studies, the ore minerals are pyrite, chalcopyrite, chalcocite, native copper, bornite, galena, covellite, digenite, and malachite accompanied by magnetite and hematite. Based on mineralogical studies, two types of alteration are recognized in the volcanic rocks of the area, general alteration and ore mineral alteration. The propylitic alteration is an indication of general alteration. The main alteration types in the mineralized zone of the deposit are carbonatization, silicification, chloritization, epidotization and zeolitic. The texture and structure of ore minerals are disseminated, open space filling, vein-veinlet, pseudo-laminated and replacement. Two major stages are distinguished for mineralization at the Kahak deposit. The first stage is volcanism and pyrite formation in the host rocks (andesite and tuff) and producing reduction state. The second stage involves diagenesis and entering Cu-rich oxidant fluids replacing Cu for Fe in the pyrite and forming Cu-sulfides and hematite and mineralization. The Kahak copper deposit shows high similarities in geometry, host rock, mineralogy, texture and structure and genetic model with Manto-type copper deposits worldwide.
Both spilitic and non-spilitic metabasaltic sills are hosted by greenschist-facies metasediments in the SW Scottish Highlands. Spilitization is mainly characterized by enrichment in Na(2)O, elevated modal plagioclase and epidote segregations. Mapping of the spatial distribution of spilitic metabasalts reveals an ancient sub-sea-floor fluid cell centred on the extrusive Tayvallich Volcanics. Fluid circulation was most extensive at shallow levels where most sills were spilitized. We attribute this to pervasive flow of saline fluid, which was thermally driven by the cooling suite of lava flows and sills. Spilitization below this lithostratigraphic depth was restricted to only a few sills. Their spilitization is largely unrelated to specific properties of these sills (e. g. width, chemistry or host lithology). We conclude that fluid channelling was an intrinsic property of sub-sea-floor fluid flow either at deeper levels or earlier during fluid circulation. By profiling of the size distributions of relic phenocrysts in a partly spilitized sill, we conclude that spilitization proceeds with the symmetric propagation of a spilitization front from the sill margins towards the sill interior. Based on chemical profiling across the margin of an epidote segregation, we conclude that spilitization is associated with chemical transport on scales ranging from 0.1 to 10 m.
We have carried out a complete study of the Upper-Triassic alkaline magmatism on the northwestern margin of the Iberian Chain. This magmatism is composed of mafic sills, which intrude the Keuper facies in two geographic sectors: the Cameros Massif (NW) and the Moncayo Massif (SE). In both of these sectors, the rocks are characterised by an intense alteration (spilitisation).
The field relationships point to an Upper Triassic age for the studied sills, given that: 1) interactions are recognised between the magma and wet, unconsolidated host sediments, suggesting that the magma was emplaced during or shortly after the deposition of the Keuper facies; 2) in the Moncayo sector a conglomerate bed that includes igneous clasts overlaies the sills and passes upwards to the Norian-Rhaetian Imón Fm.
According to the petrological and geochemical features of the sills, an internal differentiation can be recognised inwards, with the developments of three zones: chilled margins, central facies and pegmatoid facies. The rocks are porphyritic and are mainly composed of phenocrysts of pseudomorphed olivine and microcrysts of plagioclase, opaque minerals and minor clinopyroxene. Vesicles and xenoliths of the host sedimentary rocks are also recognised, especially at the chilled margins. The mineral assemblage
is constant across the sills but the mineral proportions vary among the different zones.
The sills are basic to intermediate rocks. They are classified as basalts to dacites with an alkaline geochemical affinity. According to the trace element contents, this magmatism is related to an enriched sub-lithospheric mantle source affected by crustal contamination.
Considering the Upper Triassic magmatisms from southwestern Europe, two types can be distinguished. On the one hand, the magmatisms in the Catalonian Coastal Ranges and SE France are paleogeographically located in the inner platform and are related to deep, astenospheric mantle sources with no evidence of crustal contamination. On the other hand, the magmatisms in the NW Iberian Chain –this study-, the External Betics and the Brescian Prealps are situated in a more litoral position and are related to a shallower, lithospheric mantle with evidence of crustal contamination. These differences could be related to the thickness of the continental crust, which might be thinner in the inner areas of the platform.
Recent studies on mineralogy, geochronology, fluid inclusion and stable isotope (Pb, Os, S, C, O, Sr) characteristics were reviewed to determine constraints for genetic models of the Chilean manto-type copper deposits. The Chilean manto-type deposits are divided into the two geologic categories of the northern areas (Arica–Iquique, Tocopilla–Taltal) and the central areas (Copiapó, La Serena, Santiago). The former is distributed in the coastal range composed of Jurassic andesite-dominated volcano-sedimentary piles and younger plutonic intrusions, and yields chalcocite (-digenite) and bornite as the principal hypogene copper sulfides. The latter is hosted mostly in Lower Cretaceous volcano-sedimentary sequences, and has chalcopyrite-rich mineral associations. The fluid inclusion data indicate that the primary copper mineralization was commonly generated in the temperature range 150–360°C under low-pressure conditions near the boiling curve, mediated with relatively saline brines. Generally, homogeneous Pb and S isotope compositions for primary copper minerals imply direct magma source or leaching of igneous rocks. Pb and Os isotope data published for some deposits, however, suggest that ore-forming metals were derived mainly from the volcano-sedimentary host rocks. The noticeably negative isotope ratios of primary sulfide sulfur and hydrothermal calcite carbon of some central area deposits indicate influx of sedimentary rock components, and the high 87Sr/86Sr initial ratios of hydrothermal calcite from the Tocopilla–Taltal area deposits imply contribution of the contemporaneous seawater or marine carbonates. These isotopic constraints imply a formation mechanism in which the Chilean manto-type copper deposits formed epigenetically in the process of hydrothermal interaction of non-magmatic surface-derived brine with the volcano-sedimentary host rocks, which is inferred to have been induced by a deep-seated plutonic complex as the possible heat source.
Base metal–Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed
during two episodes. Subeconomic Cu–Pb–Zn–Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520Ma ago)
in a set of E–W- and NE–SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic
composition (206Pb/204Pb = 18.07–18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides
were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE–SW-oriented faults into a
chalcocite-dominated Cu–Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of
lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the 207Pb/204Pb vs. 206Pb/204Pb diagram (206Pb/204Pb = 18.66–23.65; 207Pb/204Pb = 15.72–16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead
and uranium during a young fluid event possibly c. 100Ma ago. The Pb isotope systematics of local host rocks to mineralisation
also indicate some comparable young disturbance of their U–Th–Pb systems, related to the same event. They could have provided
Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu–Pb–Zn–Fe polysulphides,
whereas the U most likely originated from external sources. Local metal sources are also suggested by the 208Pb/204Pb–206Pb/204Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate
host rocks on the chalcocite-dominated Cu–Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu
Plateau clearly record a diachronous evolution.
KeywordsDikulushi Cu–Ag deposit-Lead isotopes-Polysulphide vein-type mineralisation-Lufilian Arc
Native Cu occurs in amygdules, fractures and groundmass of tholeiites from Site 642 on the Voring Plateau. Similar occurrences have been reported in other tholeiites of the early Tertiary North Atlantic Volcanic Province drilled at Deep Sea Drilling Project Sites 342 on the Voring Plateau and 553 on the Rockall Plateau. The flows containing the native Cu have distinctive alteration patterns characterized by the combination of reddened flow tops, distinctive pastel coloration of the upper parts of the flows, relative abundance of celadonite, and the presence of native Cu. These associations suggest that subaerial weathering and subsequent seawater-basalt interaction are related to the occurrence of native Cu. An additional factor may be the increase in compatibility of Cu in silicates and Fe- Ti oxides that may accompany sub-solidus oxidation of basaltic flows. Native Cu occurrences in Site 642 tholeiites have some striking similarities to the large native Cu deposits in the Pre-cambrian basalts of the Keweenaw Peninsula, Michigan, that are suggestive of similar mineralization processes. -Author
Elements of demonstrated immobility in hydrothermal alteration and metamorphism provide useful lithogeochemical parameters for mineral exploration in greenstone terranes. They yield precise identifications of precursor volcanic rock type and magmatic affinity, and quantitative estimates of mass, volume and mineralogical changes. Immobile incompatible elements (Zr, Y, Nb, REE) establish affinities, and monitor fractionation of compatible elements in tholeiitic and transitional volcanic suites. Mass changes in mobile components can be determined for a homogeneous rock unit or a continuous volcanic series. Mass change results also bear directly on the interpretation of REE profiles in altered rocks. Normative calculations allow chemical analyses to be portrayed as alteration minerals, which are also useful in interpreting oxygen isotope data. Immobile element techniques produce a large number of parameters that can be illustrated on maps and diagrams, and otherwise used in exploration. Usage of these techniques brings deeper insight to the evolution of volcanic stratigraphy and the hydrothermal processes that formed the alteration zones and ore deposits.
The Upper Silurian-Lower Devonian volcanic rocks in the southern Gaspe Peninsula of the Quebec Appalachians crop out at the northeast end of the Connecticut Valley-Gaspe Synclinorium. These shallow marine and subaearial sequences reach a thickness of up to at least 2000 m and comprise two groups: 1) the Late Silurian volcanic rocks; 2) the Early Devonian volcanic rocks. Although the basalts of both sequences were derived from lithospheric mantle, the Silurian basalts were generated from garnet peridotite at ~80 km depth while the Devonian basalts appear to have resulted from a larger degree of melting of spinel peridotite at a shallower depth (~60 km). The basalts are interpreted to have formed in a northwest-trending rift zone located in the Quebec Reentrant during dextral transpression along the Appalachian Orogen. -from Authors
Hydrothermal alteration processes occurring in oceanic crust impact the
physical, chemical, and biological processes of the Earth system. These
hydrothermal systems are manifested in vents ranging from 350 °C
black smokers, found exclusively in the axial zone of some ridge
segments, to 20 °C low-temperature vents at the ridge axis or
flanks. Collectively, these systems are responsible for ˜20% of
Earth's total heat loss (11 TW; C. A. Stein and S. Stein (1994a, b)) and
have major impact on ocean and solid earth chemistry. Elderfield and
Schultz (1996) estimate black-smoker water fluxes to be
˜3.5×1012 kg yr-1 and low-temperature fluxes to be
˜6.4×1014 kg yr-1 (at 20 °C). These hydrothermal fluxes
also carry substantial elemental flux between seawater and the oceanic
crust. Combined with ocean-crust generation and recycling, these
processes produce a two-way geochemical pathway between the oceans and
the mantle. Recycling of altered oceanic crust into the mantle is likely
to produce some of the mantle's chemical heterogeneity (e.g., Hofmann,
1988; see Chapter 2.04) and the delivery of mantle-derived materials to
seawater through hydrothermal systems has profound effects on seawater
chemistry (e.g., Wheat and Mottl, 2000; Chapters 3.15 and 6.07).
Hydrothermal vents in mid-ocean ridges offer a unique habitat for very
diverse biological communities that derive much of their energy needs
from chemical energy in vent fluids (Jannasch and Mottl, 1985; Jannasch,
1995). The interior of the oceanic crust is likely to host a deep-ocean
biosphere that reaches to at least 500 m depth ( Furnes and Staudigel,
1999).It is important to quantify hydrothermal chemical fluxes because
they bear on the chemical and biological evolution of the Earth, the
chemical composition of seawater, geochemical mass balance at arcs, and
the heterogeneity of the mantle. Hydrothermal fluxes can be
independently determined by analyzing the composition of hydrothermal
fluids or by analyzing the alteration-related chemical changes in the
oceanic crust. Ideally these two methods should yield the same results,
but a comparison of data shows that there are major discrepancies
between these types of estimates (e.g., Hart and Staudigel, 1982;
Chapter 3.15). Reconciling these discrepancies is important for
improving our understanding of this central theme in Earth system
sciences.This review focuses on chemical flux estimates derived from
studies of the oceanic crust, exploring in detail how such estimates are
made, and the underlying assumptions and uncertainties. Three main
themes will be covered. The first focuses the role of the original
igneous characteristics of the crust in determining the nature of
hydrothermal alteration processes. This includes how primary lithology
and composition influence alteration, and difficulties encountered in
determining an unaltered "fresh-rock" baseline composition for any
particular ocean-crust section. The second theme focuses on the methods
by which the bulk-altered oceanic composition is determined, and the
attendant uncertainties. These include the difficulty of determining an
average composition of a very heterogeneous medium by the analyses of
rather small samples, and the limitations imposed by an incomplete
sampling process on the ocean floor. Finally, hydrothermal fluxes
inferred from ocean-crust data are compared to fluxes from hydrothermal
vent studies and the reasons behind their differences are explored.
Sulfide ore samples recovered by corers from and beyond Orebody 1 in the Logatchev-1 hydrothermal field (Mid-Atlantic Ridge,
14°45′ N) are studied by optical, electron microscopic, X-ray microspectral, and X-ray diffraction methods. The major and
ore minerals are identified. Sulfides of the Cu-S system, the major ore-forming minerals in sediments, are investigated in
detail. Specific features of their composition, structure, secondary alterations, and distribution in sediments of the Logatchev-1
field are considered. It has been established that sulfide concretions in modern sediments primarily consist of nonstoichiometric
minerals of the chalcocite-digenite series, i.e., djurleite (Cu1.96S) and roxbyite (Cu1.75–1.86S). It is assumed that copper sulfides primarily precipitated from hydrothermal solutions as high-temperature hexagonal chalcocite
that was replaced after the hydrothermal activity by djurleite, roxbyite, and other nonstoichiometric minerals of the Cu-S
system. Based on the comparison of their paragenetic associations with those of copper sulfides in hydrothermal chimneys,
the paper discusses constraints of the diagenetic transformation of sulfides in ore-bearing sediments and the halmyrolysis
of modern hydrothermal edifices located in contact with seawater. Roxbyite recently discovered in oceanic sediments plays
a specific role in these processes.
Ocean island basalts are generally thought to be the surface expression of mantle plumes, but the nature of the components in the source regions of such mantle plumes is a subject of long-standing debate. The lavas erupted at Hawaii have attracted particular attention, as it has been proposed that coupled 186Os and 187Os anomalies reflect interaction with the Earth's metallic core. It has recently been suggested, however, that such variations could also result from addition of oceanic ferromanganese sediments to the mantle source of these lavas. Here we show that Hawaiian picrites with osmium isotope anomalies also exhibit pronounced thallium isotope variations, which are coupled with caesium/thallium ratios that extend to values much lower than commonly observed for mantle-derived rocks. This correlation cannot be created by admixing of core material, and is best explained by the addition of ferromanganese sediments into the Hawaii mantle source region. However, the lack of correlation between thallium and osmium isotopes and the high thallium/osmium ratios of ferromanganese sediments preclude a sedimentary origin for the osmium isotope anomalies, and leaves core-mantle interaction as a viable explanation for the osmium isotope variations of the Hawaiian picrites.
Aventurine labradorite from a basaltic lava flow of the Ponderosa mine, Oregon, USA, has been analyzed using microprobe techniques. Equivalent to sunstone is the sample of Ab28An69Ot3 composition (Ot = other endmembers) which has minute inclusions of copper. Thousands of micron-sized native copper platelets scatter throughout (001) and (010) planes of the labradorite, which has the incompletely Al/Si disordered distribution indicative of an intermediate-temperature structure. Features common to these Ca-plagioclases are fracturing and the presence of Cl, excess SiO2, hydrocarbons, MgAl2Si2O8 and FeAl2Si2O8 endmembers in their solid solutions. Purity of the native copper and their oriented distribution require the model of exsolution for yielding the present aventurine texture, image analysis of which fathoms an implication for both dissolution and growth of copper metal within a crystalline solid according to the theory of Ostwald ripening. The 87Sr/86Sr ratio of the Ponderosa labradorite, 0.7032, stands between those of MORB (0.7028) and of red-clouded anorthite megacrysts (0.7036) containing metallic copper in the basaltic lavas of the Japanese island arc. Crystallization from the magma involving little crust composition (the subducted oceanic crust) is implicit in the Ponderosa megacrysts. Moreover the fresh surface of these fractured megacrysts points to explosive ascending of the magma and the rapid cooling. Fracturation of the Ponderosa labradorite megacrysts is common to the plagioclase megacrysts in several basaltic rocks in the western continental margin of North America, in contrast to euhedral anorthite megacrysts in the eastern one and from island arc basalts. This contrast has an implication for the difference in continental-margin magmatism between the western- and eastern- continental margin regions as well as for that in the eruption power ascending the magma to the surface between the western and the Japanese island arc, based upon the storaged volatiles of hydrocarbons, CO2, Cl and H2O. Detection of both chlorine and hydrocarbons common to these aventurine plagioclases provides the continental-margin and island-arc basalts with constraints on the possible origin of mixing the slab-sediments with the magmas originated from the depleted mantle.
Products of late Silurian and early Devonian volcanism in the N Appalachians are well exposed in the Chaleurs Bay area of the peninsula. The volcanic association is dominated by plagioclase basalts and andesites, and includes dacitic and rhyolitic pyroclastic flows. Major- and trace-element chemical analyses of 174 rocks show that the association derives from alkaline and high-alumina basalt magmas. The basalts are usually ol-normative and high in Al2O3, TiO2, P2O5, and in incompatible elements Y and Zr. They follow a calc-alkaline differentiation trend. This volcanism is interpreted to be genetically related to a compressional regime controlled by fault zones. Quaternary volcanism associated with the major transcurrent fault zones of N Anatolia and Iran within the Alpine orogen provides a modern analogue to this Silurian-Devonian volcanism. (Authors' abstract)-C.N.
Many recent studies (ag., Potter 1977, Goble 1980, 1985) deal with the stability of blue-remzining covelline. This study shows that leaching and dissolution of synthetic digenite or anilite, in acidic ferric sulfate solution, produce metastable polymorphs of geerite, yarrowite, spionkopite, covelline and CuS2; the structures contain the sulfur atoms in cubic close-packing. Using X-ray-diffraction patterns, eight stages of transformation have been identified in the leaching of digenite to forms containing less copper. The phases produced do not have the typical optical properties of blue-remaining covelline, nor its hexagonal structure. These transformations were produced at leachate concen-trations greater than l0-3 M. In weaker leachates, digenite and anilite structures alternate in a constant time-cycle, in which digenite grains first leach to anilite and then quickly return to the digenite structure. Using synthetic chalcocite, at least two leach paths are observed: l) in weak solutions (= l0-t M, chalcocite leaches to tetragonal-phase chal-cocite and then to digenite, following the digenite leach-ing paths from that time onward; 2) in stronger concen-trations, synthetic chalcocite leaches directly to djurleite. With continued leaching, the rculting phases have the opti-cal properties and X-ray-diffraction patterns of spionkop-ite and yarrowite. Under special conditions covelline is formed. Compositions of leached grains, determined by microprobe analysis, show a tendency for copper to be leached at an accelerated rate as leachate concentration is increased. Goble's (1985) composition-structure relation-ships are confirmed by the addition of new data-points.
The giant stratiform Zn–Pb–Ag HYC deposit displays a broad Zn, Pb and Tl halo which extends laterally along the favourable pyritic black shale facies of the Barney Creek Formation for at least 15 km west of the deposit. A ferroan dolomite/ankerite halo overlaps with the Zn–Pb–Tl halo extending up to 250 m into the immediate stratigraphic hangingwall, and 50 to 100 m into the footwall sediments close to the deposit. A manganese carbonate halo is offset from the ferroan dolomite/ankerite halo, being concentrated in the immediate footwall of the deposit and extending laterally along the W-Fold Shale Member. Manganiferous carbonate forms the most pronounced and laterally extensive halo at HYC extending well beyond the Zn–Pb–Tl and ankerite halos. The geometry and extent of the halos described above are based on sampling and analyses from two drill holes reported in this study and a further six drill holes reported previously by I.B. Lambert and K.M. Scott [J. Geochem. Explor. 2, 307–330, 1973]. The SEDEX alteration index previously proposed as a vector for the Lady Loretta deposit [R.R. Large and P.J. McGoldrick, 1998, J. Geochem. Explor. 63, 37–56] has been shown to have applications in the McArthur Basin for defining the favourable stratigraphic unit hosting stratiform Zn–Pb–Ag mineralisation. A modified alteration index (AI Mark 3) has also been developed which eliminates the effect of the shale/dolomite ratio on the index and thus highlights the control of carbonate chemistry and its relationship to stratiform mineralisation. The application of a group of indices including Zn, Pb, Tl, SEDEX alteration index, AI Mark 3 and manganese content of dolomite (MnOd) is proposed for defining the most favourable stratigraphic units for stratiform Zn–Pb–Ag mineralisation within carbonate-bearing sedimentary basins.
Tl, Ga and Ge contents of Kuroko and other types of ore deposits were analysed semiquantitatively and quantitatively. The results show that Tl content is extremely high in Kuroko-type deposits compared to other types of mineralization. The T1 content is especially high in yellow ore and pyrite crystals; thus this element is considered to be incorporated in pyrite.
Trace element analyses have been carried out on hydrothermally altered pillow basalts of greenschist facies dredged from the median valley of the Mid-Atlantic Ridge. Sr is leached from the rock, and its behavior is apparently controlled by the same reactions as Ca. Cu is also leached from the basalt, but often shows local precipitation in veins as sulfides. Fe, B, Li, Ba, Mn, Ni and Co show sufficient variations in concentration and location within the altered basalts to indicate that some mobilisation occurs, but there may be subsequent uptake or precipitation into the secondary mineral assemblages. V, Y, Zr and Cr do not appear to be affected by hydrothermal alteration.The production of a metal-enriched solution by hydrothermal alteration and subsequent precipitation of metal salts to form metalliferous sediments is indicated, as is precipitation of metal sulfides in the basaltic basement.
Some gem-quality labradorite phenocrysts in Miocene basaltic lava from Lake County, Oregon, have a pink schiller due to metallic copper; some have a transparent red or green color. The copper content of the crystals varies systematically with color: pale-yellow labradorite sections have 0 40 ppm CuO; greens have about 100 ppm CuO; reds have 150 to 200 ppm CuO; schiller-bearing laths have 80 to 300 ppm CuO. The variation of Cu content among different crystals is primary and reflects a variation in magma chemistry during plagioclase fractionation. Similarity of absorption spectra of the red zones to that of copper-ruby color in glass shows that the red arises from the intrinsic absorption of colloidal Cu0 particles that are too small to scatter light (
Sea-level changes and synsedimentary tectonics affected the development of three potential hydrocarbon reservoir intervals in the Silurian-lowermost Devonian part of the Gaspé Belt on the margin of Laurentia. A relative sea-level curve is based on sequence analysis of facies and distribution of benthic faunas. The succession recorded two major, low-order sedimentary cycles, each composed of a regressive-transgressive couplet and represented by shallowing- and deepening-upward sequences. The first shallowing episode (S1) covered the Rhuddanian-Sheinwoodian (Llandovery-early Wenlock) interval, whereas a rapid deepening episode (D1) followed during the Homerian (late Wenlock). A second shallowing episode (S2) started during the late Homerian, and ended in the late Ludfordian (late Ludlow) or earliest Pridolian, and was then followed by a latest Silurian-Early Devonian deepening episode (D2). Potential reservoir rock units developed mostly during sea-level lowstands or early transgressions in the Gaspé Belt. Comparison of the Gaspé relative sea-level curve with eustatic curves, proposed for the same time interval, indicates that the Gaspé curve was significantly influenced by local synsedimentary tectonics. Salinic extensional tectonics, a predominantly Late Silurian-Early Devonian (Ludlovian-Pragian) event, resulted in block faulting and tilting along normal listric faults. Interaction between block faulting and eustatic sea-level fall at the end of the Ludlovian-early Pridolian exposed the highest parts of the blocks to subaerial erosion and diagenesis, and allowed reefs and reef complexes to settle at the margins of the blocks, or on erosional remnants. Salinic extensional tectonics may also have provided suitable pathways for hydrocarbon migration and charge at various times during the mid-Silurian to Early Devonian, particularly for hydrocarbons that may have been generated in the underlying Cambro-Ordovician shales. In the northeastern part of the Gaspé Belt, which is the most promising area for hydrocarbon reservoirs in the Gaspé Peninsula, block faulting and tilting have changed the fluid migration pattern from an updip-northeastward flow from the basin centre to basin margin during the Late Ordovician to early Late Silurian, to a potential updip-southwestward flow in each faulted block during the early Late Silurian. Basin tectonics may have played a significant role in driving hydrocarbon-rich fluids toward potential reservoirs, such as the Llandoverian Val-Brillant sandstone bodies, the Sayabec carbonate sands and knob reefs, or the West Point reefs.
There are two phases of post-Taconic, pre-Acadian magmatism: the Middle to Upper Ordovician Pabos suite and the Silurian-Devonian volcanic rocks and hypabyssal intrusions. The Pabos suite forms two large intrusions composed of LREE-depleted, normal MORB-like tholeiitic rocks. Evolution within this suite was controlled by fractional crystallization. Their occurrence suggests a tensional event between the Taconic and Acadian orogenies. The Silurian-Devonian rocks are widespread and chemically variable and do not belong to a single fractionation series. However, they appear to have evolved in a broadly similar way and are probably the product of the same petrogenetic processes acting on different batches of mantle-derived alkali and tholeiitic basalt magmas. Those carrying quartz xenocrysts are enriched in Si, K, Zr, and the LREE's. The observed enrichment/depletion patterns imply that felsic contamination/hybridization play an important role in their chemical diversity. Association of these rocks with local tensional environment in an orogenic foreland is preferred to a subduction model.-L.C.H.
The giant stratiform Zn–Pb–Ag HYC deposit displays a broad Zn, Pb and Tl halo which extends laterally along the favourable pyritic black shale facies of the Barney Creek Formation for at least 15 km west of the deposit. A ferroan dolomite/ankerite halo overlaps with the Zn–Pb–Tl halo extending up to 250 m into the immediate stratigraphic hangingwall, and 50 to 100 m into the footwall sediments close to the deposit. A manganese carbonate halo is offset from the ferroan dolomite/ankerite halo, being concentrated in the immediate footwall of the deposit and extending laterally along the W-Fold Shale Member. Manganiferous carbonate forms the most pronounced and laterally extensive halo at HYC extending well beyond the Zn–Pb–Tl and ankerite halos. The geometry and extent of the halos described above are based on sampling and analyses from two drill holes reported in this study and a further six drill holes reported previously by I.B. Lambert and K.M. Scott [J. Geochem. Explor. 2, 307–330, 1973]. The SEDEX alteration index previously proposed as a vector for the Lady Loretta deposit [R.R. Large and P.J. McGoldrick, 1998, J. Geochem. Explor. 63, 37–56] has been shown to have applications in the McArthur Basin for defining the favourable stratigraphic unit hosting stratiform Zn–Pb–Ag mineralisation. A modified alteration index (AI Mark 3) has also been developed which eliminates the effect of the shale/dolomite ratio on the index and thus highlights the control of carbonate chemistry and its relationship to stratiform mineralisation. The application of a group of indices including Zn, Pb, Tl, SEDEX alteration index, AI Mark 3 and manganese content of dolomite (MnOd) is proposed for defining the most favourable stratigraphic units for stratiform Zn–Pb–Ag mineralisation within carbonate-bearing sedimentary basins.
Warm (25°C) hydrothermal springs have been sampled on Baby Bare, a basaltic outcrop on 3.5-Ma-old crust ∼100-km east of the Endeavor Segment of the Juan de Fuca Ridge. The source for these springs is a 62 to 64°C formation water that has cooled conductively as it ascends to feed the springs. This water originated as bottom seawater that probably descended into basement ∼52 km to the southwest at another, much larger outcrop called Grizzly Bare. As this seawater flows towards Baby Bare, it is heated and altered by reactions within basaltic basement and by diffusive fluxes to and from the overlying sediment. Concentrations of Mn, Co, Ni, Zn, Cd, and Mo in the spring waters are greater than in bottom seawater, indicating that the oceanic crust is a source for these elements to the oceans. At least a portion of this increase probably results from the redox cycling of Mn in sedimentary sources near the basement interface that produces a diffusive flux to basement formation waters. Additional removal of Mo and inputs of the other five elements to two of the three springs are observed locally near sites of venting, where density gradients can form shallow circulation cells within the sediment and diffusive exchange occurs. Concentrations of Cu, U, V, Y, and the rare earth elements (REEs, excluding Ce) in these samples are less than in bottom seawater, indicating that the oceanic crust is a net sink for these elements in this environment. Copper is probably removed into newly formed carbonate and/or sulfide phases. Removal of the oxyanions U and V is consistent with a net removal of phosphate demonstrated previously for ridge-flank hydrothermal systems. Similarly, removal of Y and the REEs is associated with carbonate, phosphate-rich, and oxide phases. Calculated maximum global chemical fluxes from “warm” ridge-flank hydrothermal systems such as Baby Bare are insignificant relative to riverine fluxes for these elements, except possibly for Mn and Mo. The impact on global geochemical budgets for these elements from lower temperature (
The Keweenaw Peninsula of northern Michigan is well known for early diagenetic sulfide-dominant sediment-hosted stratiform copper mineralization hosted mainly by basal siltstone-shale units of the Nonesuch Formation in the White Pine district, and later native copper lodes hosted mainly by flow-top breccias and amygdaloidal portions of flood basalts and interbedded conglomerates of the stratigraphically lower Portage Lake Volcanics. The native copper mineralization is generally attributed to downdip burial metamorphism of the host strata. An alternative model is proposed here, involving a complementary influx of evolved meteoric water (elevated in salinity and progressively equilibrating with its aquifers), similar to the fluid which formed the White Pine mineralization. This model has several advantages over the metamorphogenic model alone. It would provide the salinity (by dissolution of evaporites) and moderately oxidizing conditions (as a result of hematitization, i.e., reddening, of coarse continental rift sediments) necessary for copper transport, and the evolved meteoric water would have been an important cupriferous brine owing to the leaching of trace amounts of copper from the voluminous aquifers. Further reduction of the evolved fluid would also explain the updip deposition of native copper in association with dehematitized pumpellyite- and chlorite-dominant (i.e., reduced) hydrothermal mineral assemblages. At the same time, this influx of meteoric water from highlands adjacent to the Keweenaw rift basin would have provided a mechanism to move the deep-seated hot, dense ore brine upward along the aquifers of the Portage Lake Volcanics. On its ascent from deep portions of the rift basin, the gravity-driven evolved meteoric brine would have mixed with the fluid generated by burial metamorphism to form a hybrid evolved meteoric-metamorphogenic ore-forming hydrothermal brine.
The emplacement of copper in sediment-hosted stratiform copper deposits requires the circulation of a low-temperature chloride-rich brine in rift-filling footwall red beds, probably driven by meteoric recharge in adjacent highlands. The descending oxygen-rich meteoric water may become saline (probably by leaching of footwall evaporites or possibly by mixing with brines draining down from contemporaneous evaporite pans) and evolve toward a moderately oxidized brine as oxygen is consumed during the diagenetic reddening of the initially nonred coarse-grained clastic rift sediments. Under these conditions, the pore solution attains its maximum ability to leach and transport trace amounts of copper from the red beds. Sediment-hosted stratiform copper deposits may form where the brine crosses a redox boundary into reduced sulfide-rich gray beds. With further consumption of oxygen during reddening, the brine may become highly reduced and able to take iron into solution, possibly explaining synsediment-hosted stratiform copper iron-oxide alterations and deposits. The timing of copper deposition is clearly linked to the diagenetic reddening of immature footwall sediments in rift basins, a process considered to extend over millions of years.
Native copper occurs in a wide variety of environments that includes mafic lavas, hypabyssal diabasic intrusives, ultramafic intrusives, clastic sedimentary rocks, and the oxidized zone of sulfide deposits. Native copper is the predominant copper mineral in mafic lava flows, best exemplified in the Lake Superior region, and in some sedimentary rocks, but is typically subordinate to sulfide copper in other types of deposits. Possible natural origins of native copper include: precipitation from sulfide-bearing hydrothermal solutions in rocks containing ferric oxide; deposition from sulfur-deficient magmatic or hydrothermal solutions; deposition from meteoric or hydrothermal chloride solutions in the presence calcite, prehnite, or zeolites; precipitation from hydrothermal solutions ferrous salts; organic precipitation from meteoric waters; reduction of copper sulftdes by meteoric waters in the zone of oxidation; reduction of primary copper sulfides by later hydrothermal solutions.
Native copper occurs in hematitic and zeolitic pillow basalts (spilites) of Cretaceous age or older from La Désirade, Lesser Antilles. No similar occurrence has been described from the Greater or Lesser Antilles. The copper bearing basalts are anomalously old in a region of active subduction and are remnants of oceanic crust or island arc tholeiites
The Gaspe Belt is the largest middle Paleozoic belt in the Canadian Appalachians. The most complete stratigraphic record of Upper Ordovician to Middle Devonian rocks of this belt occurs in the Gaspe Peninsula, in the northeastern part of the Quebec re-entrant. Rocks of the Gaspe Belt rest unconformably on Cambrian to Ordovician rocks of the Humber and Dunnage zones, and are unconformably overlain by Carboniferous rocks. The regional metamorphic grade of the Gaspe Belt rocks is very low, and some units are still in the oil window. The deformation history of the Gaspe Belt rocks comprises multi-stage deformation events represented by two phases. A Late Silurian to Early Devonian phase, the Salinic disturbance, manifested by an unconformity, NW-trending folding, synsedimentary faulting, and intra-plate volcanism. The late Early to Middle Devonian Acadian phase is recorded by NE-trending folding, cleavage development and both reverse and strike-slip faulting within a transpressive setting during the oblique continental collision between Laurentia and Avalon (a peri-Gondwanan terrane), which took place farther southeast. The tectonic setting during the Salinic disturbance is consistent with continuous plate convergence (without subduction) after the Taconian Orogeny and before the Acadian continental collision. The paleogeographic maps of the Gaspe Belt during Pridolian, Pragian and Emsian times reflect the tectonic activity south of the Gaspe Peninsula. The switch from sinistral to dextral relative motion between Laurentia and Avalon terranes on the St. Lawrence promontory (Newfoundland) created a transtensional rift in the Quebec re-entrant (Gaspe Peninsula). During the Pridolian, normal block-faulting occurred particularly along the NW-trending eastern margin of the basin where reefs developed on the footwall of the faults. Intra-plate volcanism also occurred from Wenlockian to Emsian along the crustal weakness developed parallel to the NW-trending eastern margin of the basin. Pragian paleogeography shows a deep shelf, carbonate-rich, distal foreland basin in the north, and a siliciclastic turbidite proximal foreland basin developed in front of, and adjacent to, a southern land area. This paleogeographic distribution is compatible with the development of a peripheral foreland basin in front of the Acadian orogenic wedge caused by loading of the Laurentian margin during the convergence of the Avalon terrane within the Quebec re-entrant. During the Emsian, the northern deep-shelf carbonates were replaced by littoral and continental sands and gravels reflecting the growing Acadian orogenic wedge to the south and its deep erosion.
Both copper and zinc were mobilized during prehnite-pumpellyite facies metamorphism in the Keweenawan basalts of northern Michigan. Cu, averaging 70 ppm in basalts, was leached from epidotized or more highly metamorphosed rocks in the zone of dehydration; it was introduced into hydrated rocks where pumpellyite, prehnite, laumon-tite, and chlorite are the principal hydrous secondary phases. Native copper is a common associate of the metamorphic assemblage in such rocks. The chemical data suggest that fluids evolved by dehydration at depth may well have contained from 1,500 to 2,000 ppm Cu. These fluids percolated upward toward lower temperature levels where hydration was dominant and where the residual concentration of Cu-ions in the fluids could have reached high levels if precipitation had not occurred. The model supplies nearly five orders of magnitude more copper than has been produced by a century of mining in the Keweenaw Peninsula. The data suggest that enrichment or depletion of native copper should be spatially related to the distribution of certain hydrous minerals in the Keweenawan lava pile. Zn, which averages 100 ppm in unaltered olivine tholeiites, was leached from all highly altered rocks in permeable zones and removed by metamorphic fluids. Abundance of Ni was not appreciably affected by the metamorphic process except where there was dilution by void-filling secondary minerals.
A unified stratigraphic nomenclature is proposed for Silurian and basal Devonian rocks in the eastern half of Gaspé Peninsula. The Gascons, West Point and Indian Point Formations of the Chaleurs Bay Synclinorium are extended into the northern part of Gaspé Peninsula. The term St. Léon is restricted to a sequence of mainly fine-grained sediments in which neither the West Point nor the Bouleaux is recognized. The term Lefrançois is abandoned. New lithostratigraphic units here proposed are the Anse à Pierre-Loiselle Formation in the Chaleurs Bay Synclinorium, the Ruisseau Bleau Formation and the Lac McKay Member of the St. Léon Formation in the Mount Alexandre Syncline, and the Ruisseau Louis Member of the St. Léon Formation in the Saint-Jean River Anticline and Mount Alexandre Syncline.
THE source of the hydrothermal fluids vented in active volcanic areas on the sea floor1–3 has been a matter of some debate4–7; they may arise purely from the interaction of circulating sea water with the hot rocks through which it passes1,3,8, or there may be an admixture of a fluid escaping from magma at depth, as is seen in subaerial geothermal systems9. The answer to this question also bears on the origin of the sulphide ores deposited by sea-floor hydrothermal systems, and their ancient analogues8,10,11 preserved on land. Here we present direct evidence for the presence of magmatic fluid in the lavas that host an actively forming massive sulphide deposit in the eastern Manus back-arc basin. We find high concentrations of chlorides and sulphides of ore-forming metals such as copper, zinc and iron in CO2-rich gaseous bubbles found both in melt inclusions trapped in the phenocrysts of the volcanic rocks, and in the matrix glass. We conclude that a metal-rich fluid was present in the magma before eruption, and probably exsolved as the pressure decreased. This finding suggests the possibility for the contribution of large quantities of ore-forming metals to a sea-floor hydrothermal system.
Ocean Drilling Program (ODP) Hole 504B near the Costa Rica Rift is the deepest hole drilled in the ocean crust, penetrating a volcanic section, a transition zone and a sheeted dike complex. The distribution of Li and its isotopes through this 1.8-km section of oceanic crust reflects the varying conditions of seawater alteration with depth. The upper volcanic rocks, altered at low temperatures, are enriched in Li (5.6–27.3 ppm) and have heavier isotopic compositions (δ7Li=6.6–20.8‰) relative to fresh mid-ocean ridge basalt (MORB) due to uptake of seawater Li into alteration clays. The Li content and isotopic compositions of the deeper volcanic rocks are similar to MORB, reflecting restricted seawater circulation in this section. The transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization. Li enrichment in this zone is accompanied by relatively light isotopic compositions (−0.8–2.1‰) which signify influence of basalt-derived Li during mineralization and alteration. Li decreases with depth to 0.6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high-temperature reaction zone. Rocks in the dike complex have variable isotopic values that range from −1.7 to 7.9‰, depending on the extent of hydrothermal recrystallization and off-axis low-temperature alteration. Hydrothermally altered rocks are isotopically light because 6Li is preferentially retained in greenschist and amphibolite facies minerals. The δ7Li values of the highly altered rocks of the dike complex are complementary to those of high-temperature mid-ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage. The inventory of Li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of Li in the ocean. On balance, the upper 1.8 km of oceanic crusts remains a sink for oceanic Li. The observations at 504B and an estimated flux from the underlying 0.5 km of gabbro suggest that the global hydrothermal flux is at most 8×109 mol/yr, compatible with geophysical thermal models. This work defines the distribution of Li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle.
The abundance and distribution of selected minor and trace elements (Ti, Zr, Y, Nb, Ce, Ga and Sc) in fresh volcanic rocks can be used to classify the differentiation products of subalkaline and alkaline magma series in a similar manner to methods using normative or major-element indices. A number of variation diagrams may be used to distinguish common volcanic rock types in terms of the above elements.As these elements are immobile during post-consolidation alteration and metamorphic processes, this method of rock-type classification may, when applied to metavolcanic rocks, prove more reliable than the commonly used methods that utilize major elements, some of which are known to be mobile.
Chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites, in the active geothermal system of Los Azufres (Mexico). Electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition. Correlation coefficients among chemical constituents were calculated. It is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content, and there is almost no correlation with the octahedral aluminium and magnesium content. A procedure is proposed to select end-members and substitution vectors, and to give a general formula for these chlorites.
Their formation temperatures are estimated with great accuracy, combining results of microthermometric data on fluid inclusions from gangue minerals of chlorites (quartz, calcite), direct measurements in wells (Kuster equipment), and chemical geothermometers. Correlations between chlorite compositions, range and nature of site occupancy, and temperature are good. Formation temperatures of chlorites range from 130° C to 300° C. As no other thermodynamic parameter varies significantly in the studied field (composition of the host rocks, nature of the geothermal fluids, pressure, ...), these variations of site occupancy (mainly Al(IV) and the octahedral occupancy (6-Al(VI)-(Mg+Fe(2+)) = VAC) are considered mainly as temperature dependent.
Molar fractions of each end-member show very different variations with increasing temperature: X-kaolinite decreases, and X-chamosite increases, while X-talc-3 brucite does not show significant change. From these data, activity coefficients and standard state chemical potential of major components, and molar free energy formation of chlorite have been calculated for each temperature of crystallisation.
Low grade hydrothermally metamorphosed mafic rocks from the Iberian Pyrite Belt are enriched in 18O relative to the oxygen isotopic ratio of fresh basalt (+6.51). The observed
18O whole rock values range from +0.87 to +15.71 corresponding to positive isotopic shifts of +5 to +10, thus requiring isotopic exchange with fluids under conditions of high water:rock ratios at low temperatures. The lowest
18O observed corresponds to an albitized dolerite still and is compatible with independent geochemical data suggesting lower water: rock ratios for the alteration of these rocks.The isotope data are consistent with the hypothesis that the spilites from the Pyrite Belt were produced by interaction of basaltic material with sea water.Significant leaching of transition metals from the mafic rocks during alteration coupled with available sulphur isotopic data for the sulphide ores also suggest that sea water may have played an important role in the formation of ore deposits in the Iberian Pyrite Belt.
The ophiolitic rocks of E. Liguria, Italy contain a spilitic metamorphic assemblage sequence, cross-cut by hydrothermal veins, which developed in the oceanic environment. Metamorphic parageneses indicate that temperatures as high as 400C were realised at depths as shallow as 300 m below the original rock/water interface. The inferred temperature interval was equivalent to a geothermal gradient of 1300C/km.It is suggested that metamorphism took place in a sub-sea-floor geothermal system, and that such systems are an integral part of the sea-floor spreading process. Modern evidence is provided to support this hypothesis, and to suggest that heavy metal rich solutions discharged from such systems are responsible for the formation of a metal enriched sedimentary component. A unified model of sub-sea-floor metamorphism and mass transfer is proposed, and possible differences between sub-sea-floor and terrestial geothermal systems are discussed. In the light of the model, the origins of certain aspects of bedded cherts found associated with ophiolitic rocks, of ophiolitic massive sulphide deposits and of certain trace element patterns are considered.
Basalts from DSDP Site 417 (109 Ma) exhibit the effects of several stages of alteration reflecting the evolution of seawater-derived
solution compositions and control by the structure and permeability of the crust. Characteristic secondary mineral assemblages
occur in often superimposed alteration zones within individual basalt fragments. By combining bulk rock and single phase chemical
analyses with detailed mineralogic and petrographic studies, chemical changes have been determined for most of the alteration
stages identified in the basalts.
1)
Minor amounts of saponite, chlorite, and pyrite formed locally in coarse grained portions of massive units, possibly at high
temperatures during initial cooling of the basalts. No chemical changes could be determined for this stage.
2)
Possible mixing of cooled hydrothermal fluids with seawater resulted in the formation of celadonite-nontronite and Fe-hydroxide-rich
black halos around cracks and pillow rims. Gains of K, Rb, H2O, increase of Fe3+/FeT, and possibly some losses of Ca and Mg occurred during this stage.
3a)
Extensive circulation of oxygenated seawater resulted in the formation of various smectites, K-feldspar, and Fe-hydroxides
in brown and light grey alteration zones around formerly exposed surfaces. K, Rb, H2O, and occasionally P were added to the rocks, Fe3+/FeT increased, and Ca, Mg, Si and occasionally Al and Na were lost.
3b)
Anoxic alteration occurred during reaction of basalt with seawater at low water-rock ratios, or with seawater that had previously
reacted with basalt. Saponite-rich dark grey alteration zones formed which exhibit very little chemical change: generally
only slight increases in Fe3+/FeT and H2O occurred.
4)
Zeolites and calcite formed from seawater-derived fluids modified by previous reactions with basalt. Chemical changes involved
increases of Ca, Na, H2O, and CO2 in the rocks.
5)
A late stage of anoxic conditions resulted in the formation of minor amounts of Mn-calcites and secondary sulfides in previously
oxidized rocks. No chemical changes were determined for this stage.
Recognition of such alteration sequences is important in understanding the evolution of submarine hydrothermal systems and
in interpreting chemical exchange due to seawater-basalt reactions.
Fresh tholeiitic basalt glass has been reacted with seawater at 150°C, (water/rock mass ratio of 10), and fresh diabase has been reacted with a Na-K-Ca-Cl fluid at 375°C (water/rock mass ratios of 1, 2, and 5) to understand better the role of temperature, basalt composition, and water/rock mass ratio on the direction and magnitude of B and Li exchange during basalt alteration. At 150°C, slight but nevertheless significant amounts of B and Li were removed from seawater and incorporated into a dominantly smectite alteration phase. At 375°C, however, B and Li were leached from basalt. B behaved as a “soluble” element and attained concentrations in solution limited only by the B concentration in basalt and the water/rock mass ratio. Li, however, was less mobile. For example, at water/rock mass ratios of 1, 2, and 5, the percent of Li leached from basalt was 58, 70, and 92% respectively. This suggests some mineralogic control on Li mobility during hydrothermal alteration of basalt, especially at low-water/rock mass ratios. In general, these results, as well as those for B, are consistent with the temperature-dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids.
Radiochemical neutron activation analysis for Tl in a number of young pillow basalts, hydrothermally altered basalts and associated hydrothermal and hydrogenous Mn crusts from the Mid-Atlantic Ridge and adjacent regions of the North Atlantic indicate that Tl is a sensitive indicator of both S saturation of silicate melts and of rock/seawater interactions. Rb-Cs-K-Tl trend lines for fresh MAR basalts (whose melts remained saturated with S during silicate fractionation) are distinctly different to Hawaiian basalts whose melts lost S during or prior to eruption, but were saturated with S at an earlier stage. Varying degrees of Tl enrichment are found in the hydrogenous Mn nodules (91,000 ppb), hydrothermal Mn crusts (2300–32,000 ppb), palagonitized glass (300–2700 ppb), hydrothermally altered basalts (1140–4560 ppb), and even slightly altered pillow interiors (11–45 ppb) relative to the fresh glasses (6–12 ppb). This enrichment has taken place due to incorporation of Tl into secondary silicate phases along with the alkalis and also due to co-precipitation of Tl with ferromanganese oxides and hydroxides. Thallium enrichment in the hydrothermal products is interpreted as being due to cooling and oxidation of hydrothermal fluids as these approached the sea floor. Haloes of Tl-enriched country rock may occur around sulfide deposits in which seawater has acted as the ore fluid.
Stratiform sediment hosted Zn–Pb–Ag deposits, often referred to as SEDEX deposits, represent an economically important class of ore, that have received relatively little attention in terms of defining lithochemical halos and geochemical vectors useful to exploration. This study concentrates on the Lady Loretta deposit which is a typical example of the class of Proterozoic SEDEX deposits in northern Australia. We examined the major and trace element chemistry of carbonate-bearing sediments surrounding the deposit and defined a series of halos which extend for several hundred metres across strike and up to 1.5 km along strike. The stratiform ore lens is surrounded by an inner sideritic halo [Carr, G.R., 1984. Primary geochemical and mineralogical dispersion in the vicinity of the Lady Loretta Zn–Pb–Ag deposit, North Queensland. J. Geochem. Expl. 22, 217–238], followed by an outer ankerite/ferroan dolomite halo which merges with low iron dolomitic sediments representative of the regional background compositions. Carbonate within the inner siderite halo varies in composition from siderite to pistomesite (Fe0.6Mg0.4CO3), whereas carbonate in the outer ankerite halo varies from ferroan dolomite to ankerite (Ca0.5Mg0.3Fe0.2CO3). Element dispersion around the stratiform ore lens is variable with Pb, Cu, Ba and Sr showing very little dispersion (<50 m across strike), Zn and Fe showing moderate dispersion (<100 m) and Mn and Tl showing broad dispersion (<200 m). Within the siderite halo Cu, Mg and Na show marked depletion compared to the surrounding sediments. The magnitude of element dispersion and change in carbonate chemistry around the Lady Loretta orebody has enabled the development of three geochemical vectors applicable to exploration. Whole rock analyses are used to calculate the three vector quantities as follows: (1) SEDEX metal index = Zn + 100Pb + 100Tl; (2) SEDEX alteration index = (FeO + 10MnO)100/(FeO + 10MnO + MgO); (3) manganese content of dolomite: MnOd = (MnO × 30.41)/CaO. All three vectors increase to ore both across strike and along strike. The manganese content of dolomite (MnOd) exhibits the most systematic pattern increasing from background values of about 0.2 wt% to a maximum of around 0.6 wt% at the boundary between the ankerite and siderite halos. Siderite within the inner halo contains considerably more Mn with MnO values of 0.4 to 4.0 wt%. It is suggested here that the basket of indices defined at Lady Loretta (Zn, Tl, metal index, alteration index, MnOd and MnOs) is applicable in the exploration for stratiform Zn–Pb–Ag deposits in dolomite-rich sedimentary basins generally. The indices defined can firstly assist in the identification of sedimentary units favourable for SEDEX mineralisation, and secondly provide vectors along these units to ore. The alteration index and MnOd, however, should only be used for exploration dolomitic sequences; they are not recommended for exploration in clastic sequences devoid of carbonates.
Hydrothermally altered pillow basalts dredged from the Mid-Atlantic Ridge, and belonging to the greenschist facies, have been studied in order to determine the mineralogical and corresponding chemical changes, that result from basalt-seawater interaction at elevated temperatures.The mineralogical transformations are predominantly to albite-actinolite-chlorite-epidote assemblages. Quartz and pyrite are common accessory minerals. On the basis of their mineralogy, the samples may be divided into chlorite-rich and epidote-rich assemblages. The chlorite-rich assemblages, which are the predominant variety, show the greatest chemical changes, while the epidote-rich samples show very little change in composition compared with their basaltic precursors.Mass balances across individual pillows in which the central portions are relatively unaltered allow the directions and ranges of elemental fluxes to be calculated. In general, SiO2 and CaO are leached from the basalt, while MgO and H2O are taken up. No consistent trends are observed for Na2O and K2O although they do show some variations in the core-and-rim analyses.Consideration of the elemental fluxes in terms of steady-state geochemical mass balances for oceanic inputs and outputs indicates that hydrothermal alteration provides a sink for Mg, which may be extremely important in solving the problem of apparent excess Mg input to the oceans. The amount of Ca that is leached from the rock may be of significance in the geochemical budget of that element. The amount of SiO2 in the circulating fluid is controlled by the solubility of quartz or amorphous silica, depending on temperature, and considerable redistribution of silica takes place within the basaltic pile. The changes in redox conditions during hydrothermal alteration do not affect the present day oxidation state of the atmosphere and hydrosphere.
The recently proposed [1] ThHfTa diagram is shown in the light of considerable additional data to be a sensitive indicator of the tectonic environment in which an unknown lava (basic of silicic) was erupted. With the presently available data it is now possible to distinguish calc-alkaline lavas from island arc tholeiites. Some of the fields of the different tectonic environments have been enlarged and the boundaries between the fields modified slightly, but the conclusions drawn by Wood et al. [1] are still supported by the data. It is not possible to discriminate between E-type MORB andtholeiitic within-plate basalts using this diagram, but when used in conjunction with the ZrTiY triangular diagram [23] (as originally suggested [1]) these magma types can be distinguished.The effects of different types of bulk lower and upper crustal contamination of a within-plate alkali basalt on the Th, Hf, Ta and radiogenic isotope concentrations of the residual liquids are calculated in detail. The ratios of ThHfTa are shown to be extremely sensitive to crustal contamination processes. Data published by Thompson and co-workers [2,5] for the Tertiary lavas of Skye, Scotland, are used to illustrate the complexity of crustal contamination and develop a petrogenic model for these lavas. These calculations suggest that the use of isotopic data alone to estimate the extent of crustal contamination a particular lava has suffered is fraught with errors and should be interpreted with care.
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