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Geologic map of the Precambrian core of the Black Hills, South Dakota (after DeWitt et al., 1986), with sample locations. Dark solid lines are faults. Heavy dashed lines are isograds. Metamorphic zones are: bt = biotite, grt = garnet, st = staurolite, sil = sillimanite, 2nd sil = second sillimanite. Position of isograds is after Nabelek et al. (2006). Second sillimanite isograd within the Harney Peak Granite refers to grade of schist inliers. Inset in the upper right shows the state of South Dakota (shaded) within United States. The Black Hills are on the western edge of the state.
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Fluid inclusions in quartz veins within Proterozoic metamorphic rocks in the Black Hills, South Dakota, were examined by microthermometry and Raman spectroscopy to assess the evolution of fluid compositions during regional metamorphism of organic-rich shales and late-orogenic magmatism, both of which were related to the collision of the Wyoming and...
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... Black Hills uplift is a domal structure with an approximately 40 · 80 km exposure of mostly Proterozoic igneous and metasedimentary rocks in its core ( Fig. 1). Ar- chean basement is exposed only into two isolated occur- rences along margins of this metamorphic core. Most of the metamorphic rocks were deposited as sediments in an ocean basin along a margin of a continental crustal block during the late Archean and early Proterozoic (Redden et al., 1990;Dahl et al., 1999). The original ...
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... planar foliation (S 2 ). The compression began $1776 Ma and lasted at least until $1740 Ma ( Dahl et al., 2005). The associated regional metamorphism (here called M 1 ) involved biotite and garnet grades, with the former confined to the east of the Silver City fault, one of the major faults in the Black Hills that follow the foliation trend ( Fig. 1; Nabelek et al., ...
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... waning stages of regional deformation were marked by intrusion of the Harney Peak leucogranite (HPG) and its satellite plutons and pegmatites, most of which are not shown in Fig. 1. Most pegmatites occur to the northeast (along the Keystone fault) and to the southwest of the main body HPG. Emplacement of the HPG reoriented the F 2 folds into recumbent positions and flattened the steeply- dipping regional S 2 foliation in its close proximity Hill et al., 2004). The intrusion-related defor- mation is referred to in ...
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... HPG and pegmatite emplacement (M 2 ) produced a several kilometers wide ther- mal and metasomatic aureole. At its outermost extent, M 2 is characterized by chlorite overgrowths over S 2 foliation in the upper garnet-biotite zone. Increasing grade of M 2 meta- morphism is then indexed by staurolite, sillimanite, and sec- ond-sillimanite isograds (Fig. 1). Partial melting occurred above the second-sillimanite isograd (Shearer et al., 1987;Nabelek, 1999). Mineral compositions suggest maximum pressure of 4-4.5 kbar in the highest-grade rocks of the aureole, but retrograde andalusite indicates decompression of the high grade aureole while the rocks were still hot ( Nabelek et al., 2006). A ...
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... small CO 2 -bearing primary inclusions occur in par- tially recrystallized quartz in Bt-2 ( Fig. 4b; GSI-1). Except for one inclusion, they have no evident aqueous compo- nent, but have $10% N 2 . Isochores of the CO 2 -rich inclu- sions pass near the estimated regional P-T conditions at the location of Bt-2 ($300 °C/3 kbar; Nabelek et al., 2006), plausibly indicating conditions at which recrystalli- zation of the host quartz and the final ...
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Citations
... (d) Organic carbon isotope compositions of the CM or graphites in the NCC and other regions. Data sources: graphites of the Liaohe Group (Zhu et al., 2021), the NCC (Chen et al., 2000;Yang et al., 2014), Borrowdala (UK) Luque et al., 2009;Ortega et al., 2010), Huelma (Spain) (Barrenechea et al., 1997), New Hampshire (USA) , and Black Hills (USA) (Huff and Nabelek, 2007;Nabelek et al., 2003Nabelek et al., ). 2014Grew, 1974;Pitcairn et al., 2005). ...
The Qingchengzi gold ore-concentration district, in the Liaodong Peninsula, northeastern North China Craton, is dominated by altered rock-type gold deposits and hosted within metamorphic rocks of the Paleoproterozoic Liaohe Group. The deposits are mainly controlled by a low-angle, north-dipping thrust structural system, containing numerous carbonaceous materials (CMs) and syn-deformational ore-bearing quartz veins and adjacent clastic rocks. Raman spectroscopy and CO isotope analysis were performed on CM samples from the fault zone to decipher their possible origins and potential genetic links with gold mineralization. Raman spectra analysis distinguishes three types of CM with low (CML), medium (CMM) and high (CMH) crystallinity and maturity. The estimated Raman-derived temperatures of CML range from 308 °C to 401 °C corresponding to greenschist- to blueschist-facies metamorphism. Large temperature variations of 363–678 °C for CMM and 442–664 °C for CMH suggest higher metamorphic grades from low blueschist to amphibolite-facies. The organic carbon isotopic valuess (δ¹³Corg = -20.9 ‰ – –23.1 ‰) suggest an organic carbon source, mixing with carbonate wall rocks characterized by the δ¹³Ccarb of −1.92 ‰ to −6.22 ‰. Combined with the Raman spectrum, the CMs are formed by the demethanation of the organic matter during the greenschist- to amphibolite-facies metamorphism. The disseminated CML coexists with Au-bearing quartz veins and is inferred to have facilitated the migration of Au in the fault zone as a solid lubricant and the precipitation of Au from hydrothermal fluids as a reductant. CMM and CMH are recognized in medium- to high-grade metamorphism with higher temperatures and occur with fewer Au-bearing pyrite or quartz veins, and thus they are unrelated to gold mineralization. In summary, the disseminated CML with low crystallinity contributes to the formation of the Triassic gold deposits and serves as a potential indicator for further prospecting.
... The N 2 -CH 4 -CO 2 ± H 2 O fluids that circulated throughout the Central Jebilet were probably sourced from the devolatilization of Sarhlef series rocks during HT-LP metamorphism (>500 • C, about 200 MPa [35,73]). Indeed, water-graphite equilibrium under reducing conditions produces H 2 O-CO 2 -CH 4 -rich fluids [78], while N 2 is released from micas and alkali feldspars during metamorphism [73,79]. The host rocks of Koudiat Aïcha ores, being mainly metamorphosed graphitic argillites, are thus a likely source of N 2 -CH 4 -CO 2 ± H 2 O metamorphic fluids. ...
The Koudiat Aïcha Zn-Cu-Pb deposit (3–Mt ore @ 3 wt.% Zn, 1 wt.% Pb, 0.6 wt.% Cu) in the
Jebilet massif (Morocco) comprises stratabound lenticular orebodies and crosscutting sulfide-bearing
quartz ± carbonate veins in the lower Carboniferous Sarhlef volcano sedimentary succession. The
veins are characterized by abundant pyrrhotite, sphalerite, subordinate chalcopyrite and galena
and rare Ag and Au minerals. The stratabound massive sulfide ores are attributed to a “VMS”
type, whereas the origin of the sulfide–quartz ± carbonate veins remains poorly understood. New
mineralogical and microanalytical data (SEM, EPMA and LA-ICP-MS) combined with fluid inclusion
results point to two-stage vein formation. The early stage involved C–H–O–N Variscan metamorphic
fluids which percolated through fractures and shear zones and deposited pyrite at >400 ◦C, followed
by the formation of pyrrhotite and sphalerite (300 ± 20 ◦C) in quartz veins and in banded and
breccia ores. The pyrrhotite–sphalerite mineralization was overprinted by aqueous brines (34 to
38 wt% eq. NaCl + CaCl2
) that precipitated carbonate and Cu-Pb sulfides (±Ag-Au) at ~180–210 ◦C
through mixing with low-salinity fluids during tectonic reworking of early-formed structures and
in late extension fractures. The latter ore fluids were similar to widspread post-Variscan evaporitic
brines that circulated in the Central Jebilet. Overlapping or successive pulses of different ore fluids,
i.e., metamorphic fluids and basinal brines, led to metal enrichment in the quartz–carbonate veins
compared to the massive sulfide ores. These results underscore that even a single deposit may record
several distinct mineralizing styles, such that the ultimate metal endowment may be cumulative over
multiple stages.
... CO 2 -N 2 -CH 4 -NaCl-(CaCl 2 -MgCl 2 ) would provide an attractive mechanism to explain the presence in both beryl and quartz of the two populations of CO 2 -N 2 -and H 2 O-dominated FIs. Similar bimodal distributions of CO 2 -N 2 and aqueous FIs attributed to fluid immiscibility are known, for example, from biotite and garnet-zone metapelites (Huff & Nabelek 2007). ...
Fluid inclusions trapped in quartz, beryl, and cassiterite from a granitic pegmatite of the Austroalpine basement of the Eastern Alps in Northern Italy were analyzed using a cooling/heating stage and micro-Raman spectroscopy with the following aims: (1) to characterize the range in fluid compositions and fluid densities, (2) to calculate minimum pressures of fluid entrapment from density data and temperature estimates for pegmatite crystallization based on pegmatite mineral assemblages, and (3) to assess possible relations between the compositions of the fluids, in particular their N contents, and potential sources of pegmatite parent melts. The pegmatite intruded into Al-rich metapelitic gneisses during the Permian tectonometamorphic event (∼290 Ma) and was overprinted at amphibolite-eclogite-facies P-T conditions during Eoalpine (∼80–90 Ma) metamorphism. It is characterized by a major phase assemblage quartz + muscovite + paragonite + albite with minor garnet + beryl and accessory columbite-group phases + cassiterite + ixiolite/wodginite + chrysoberyl + cordierite + staurolite + apatite + wyllieite-group phases + zircon. Two types of fluids are preserved in the phases investigated: (1) complex CO2±N2±CH4-H2O-NaCl±MgCl2±CaCl2 fluids with highly variable proportions of the constituent species trapped in all three host phases. The compositions of these fluids range from CO2-rich (∼72–92 mol.%) to N2-rich (∼25–66 mol.%) with additional minor (∼3–8 mol.%) CH4 contents; and (2) H2O-rich fluids with variable salinity (∼3–23 mass%) trapped in beryl and quartz. Trapping of CO2-N2-CH4 fluids in cassiterite along interfaces between the cassiterite host and columbite-group phase inclusions indicates that these fluids were present during joint cassiterite-columbite-group phase crystallization when the pegmatite solidified. In the absence of clear textural evidence for a successive trapping of the two types of fluids, a possible explanation for their simultaneous presence is fluid immiscibility. Isochores for fluid inclusions with the highest densities observed in cassiterite and beryl yield trapping pressures of ∼9–10 kbar for 650–700 °C. By comparison, temperatures estimated for pegmatite crystallization based on the assemblage beryl + chrysoberyl + gahnite and the stability of albite + muscovite + quartz lie in the range ∼650–700 °C. As a potential source of N for the N2-rich fluids, biotite and muscovite from the metapelites of the pegmatite host rocks were identified. Infrared analysis yields NH4 contents of 1430–1772 μg/g in biotite and of 297–489 μg/g in muscovite from two representative gneiss samples. This finding provides further evidence for an anatectic origin of most, if not all, Permian pegmatites found throughout the Austroalpine basement of the Eastern Alps.
... The results of carbon isotope analysis of graphite in different rocks from the WLG and MG are summarized in Table 2 and Fig. 7. The carbon isotopic compositions of graphite deposits from the three graphite metallogenic belts (WGB, WGB, and SGB) around the NCC (Chen et al., 2000;Yang et al., 2014), KeralaKhondalite Belt, Southern India (Radhika et al., 1995;Radhika and Santosh, 1996;Santosh and Wada, 1992;Santosh and Wada, 1993a;Santosh and Wada, 1993b), Borrowdala (UK) Luque et al., 2009;Ortega et al., 2010), Huelma (Spain) (Barrenechea et al., 1997;Luque et al., 2009), New Hampshire (USA) and Black Hills (USA) (Huff and Nabelek, 2007;Nabelek et al., 2003) are shown for comparison. The carbon isotopic values (δ 13 C) of graphites in the ore samples from the WLG exhibit wide variation, which range from − 13.69 to − 17.82‰. ...
... Fig. 7. Carbon isotope composition of graphites from WLG and MG in this study. The carbon isotopic characteristics of graphites from Jiamusi Block, Jiaodong Peninsula, Inner Mongolia (Chen et al., 2000), Khondalite belt (Yang et al., 2014), KeralaKhondalite Belt, Southern India (Santosh andWada, 1992;Santosh and Wada, 1993a;Santosh and Wada, 1993b;Radhika et al., 1995;Radhika and Santosh, 1996), Borrowdala (UK) Luque et al., 2009;Ortega et al., 2010), Huelma (Spain) (Barrenechea et al., 1997;Luque et al., 2009), New Hampshire (USA) and Black Hills (USA) (Nabelek et al., 2003;Huff and Nabelek, 2007) are shown for comparison. ...
... Because the carbon-bearing fluids also can deposit graphite with a light carbon isotope. For example, the fluid deposited graphite from Borrowdala (UK) Luque et al., 2009;Ortega et al., 2010) Huelma (Spain) (Barrenechea et al., 1997;Luque et al., 2009), New Hampshire (USA) and Black Hills (USA) (Huff and Nabelek, 2007;Nabelek et al., 2003) all have biogenic carbon isotopes (Fig. 7). Thus, additional evidence is needed to reveal the carbon source of the graphite in WLG and MG. ...
As the northern segment of the Jiao-Liao-Ji Paleoproterozoic graphite metallogenic belt, the Liaohe Group contains a significant amount of phaneritic graphite deposits, which are of great significance to the exploration of graphite resources in China. However, few studies have investigated the metallogeny of these deposits. To unravel the carbon source and metallogenic process of the graphite deposits in the Liaohe Group, we performed detailed petrological, zircon U-Pb dating, Raman spectroscopy, and carbon isotope studies for the graphite deposits in the North (MG-Magou graphite deposit) and South (WLG-Wuligou graphite deposit) Liaohe Groups. The results show that the graphite-bearing rocks of the two groups are located in the sandstone, shale, wacke, and arkose regions in the log (Fe2O3/K2O) – log (SiO2/Al2O3) sediment classification diagram. They have similar trace element characteristics and exhibit similar rare earth element features with post-Archean Australian average shales (PAAS). Geochemical data show that these samples are compositionally immature and underwent a relatively low degree of weathering, which are the products of rapid accumulation of sediments. The carbon isotopic values of graphites from the WLG and MG both show a wide range of variation (δ¹³CWLG = −13.69 to −17.82‰, δ¹³CMG = -16.49 to −25.72‰), which are caused by the demethanation of organic matter during metamorphism. Raman spectroscopy indicates that the peak metamorphic temperature of the graphite from WLG is higher than 650 ℃, which is higher than that of MG graphite deposits (T = 551–627 ℃) from the North Liaohe Group. Combined with previous geochronology data, we suggest that a large amount of organic matter was deposited in an active continental margin environment at 2130–2175 Ma. During the collisional orogeny between the Longgang and LiaonanNangrim blocks (1950 to 1800 Ma), organic matter gradually transformed into graphite through prograde metamorphism and accumulated to form the graphite deposits in the Liaohe Group.
... Fluids exsolved from a crystallizing granitic melt are generally thought to be H 2 Orich with negligible to moderate CO 2 contents whereas more CH 4 -N 2 -rich fluids are interpreted as ultimately metamorphic in origin that formed in equilibrium with graphite and NH 4 -containing micas and/or feldspars in the pegmatite country rocks [13][14][15][16][17]23]. CH 4 -rich fluids may originate from magmatic CO 2 -rich fluids under changing conditions, nevertheless, CO 2 -rich fluids are less likely to have evolved from differentiated granitic magma due to the very low solubility in such magma [17,24]. ...
Fluid inclusions (FIs) and associated solids in host minerals garnet, tourmaline, spodumene, and quartz from six pegmatite fields of Permian origin at Koralpe (Eastern Alps) have been investigated. Although pegmatites suffered intense Eoalpine high-pressure metamorphic overprint during the Cretaceous period, the studied samples originate from rock sections with well-preserved Permian magmatic textures. Magmatic low-saline aqueous FIs in garnet domains entrapped as part of an unmixed fluid together with primary N2-bearing FIs that originate from a host rock-derived CO2-N2 dominated high-grade metamorphic fluid. This CO2-N2 fluid is entrapped as primary FIs in garnet, tourmaline, and quartz. During host mineral crystallization, fluid mixing between the magmatic and the metamorphic fluid at the solvus formed CO2-N2-H2O–rich FIs of various compositional degrees that are preserved as pseudo-secondary inclusions in tourmaline, quartz, and as primary inclusions in spodumene. Intense fluid modification processes by in-situ host mineral–fluid reactions formed a high amount of crystal-rich inclusions in spodumene but also in garnet. The distribution of different types of FIs enables a chronology of pegmatite host mineral growth (garnet-tourmaline/quartz-spodumene) and their fluid chemistry is considered as having exsolved from the pegmatite parent melt together with the metamorphic fluid from the pegmatite host rocks. Minimum conditions for pegmatite crystallization of ca. 4.5–5.5 kbar at 650–750 °C have been constrained by primary FIs in tourmaline that, unlike to FIs in garnet, quartz, and spodumene, have not been affected by post-entrapment modifications. Late high-saline aqueous FIs, only preserved in the recrystallized quartz matrix, are related to a post-pegmatite stage during Cretaceous Eoalpine metamorphism.
... Fluids were present in the metamorphic rocks during the M 2 and M 3 metamorphic events. Compositions of fluid inclusions in quartz veins show that reducing conditions prevailed (Huff and Nabelek 2007). During M 2 , the fluids were dominated by variable proportions of CH 4 , CO 2 , and N 2 . ...
... Application of the Andersen and Lindsley (1988) oxygen barometer to Mn-bearing ilmenite and magnetite-ulvöspinel pairs in some garnet-grade samples suggests that f O2 was 4.6 ± 1.1 log units below the fayalite-magnetite-quartz oxygen buffer. Graphite in the schists ranges from poorly ordered in the garnet zone to well-ordered within the sillimanite zone in the HPG contact aureole (Huff and Nabelek 2007). Fluids in the aureole of the HPG had ~25% of carbonic components. ...
... Well-ordered graphite commonly occurs along the margins of quartz veins and host rocks to the veins (Duke et al. 1990a). In the samples described here, graphite is highly ordered with area ratios of "disordered/ordered" Raman peaks between 0 and 0.1, and fluid inclusions in the quartz vein have >90% CH 4 (Huff and Nabelek 2007). ...
Tourmaline is a common mineral in granites and metamorphic rocks in collisional orogens. This paper describes graphite-bearing, metasomatic tourmalinites in sillimanite-zone schists of the Proterozoic Black Hills Orogen, South Dakota. The tourmalinites bound quartz veins and beyond about 1 m grade into schists with disseminated tourmaline, and ultimately tourmaline becomes only a trace, intrinsic phase in the schists. Next to the quartz veins, tourmaline has almost completely replaced schist minerals, including biotite, muscovite, and plagioclase. The tourmaline is generally anhedral and follows the original foliation direction of the schist. However, tourmaline is euhedral in quartz veinlets cutting through the tourmalinites. Tourmaline is compositionally zoned from having about 22 to 2% of apparent Al occupancy on the Y sites. There are very good negative correlations of Y(Fe2++Mg2+), XCa2+, and YTi4+ with YAl3+, and a very good positive correlation of X-site vacancies with YAl3+. Mg# [molar Mg2+/(Mg2++Fe2+)] is fairly invariant at approximately 0.5, which is somewhat higher than that in the precursor biotite. This is in contrast to tourmaline in the neighboring peraluminous Harney Peak leucogranite where the range of Y site occupancy of Al is small at about 20%, but the Mg# ranges from 0.12 to 0.5.
The compositional trends in the metasomatic tourmaline are dominated by the exchange X☐ + 4 YAl3+ = XCa2+ + 3 Y(Fe2++Mg2+) + YTi4+. Mass-balance calculations suggest the metasomatizing fluid brought in H+ and B(OH)3 and removed K+, SiO2, and some Fe2+ during tourmalinization. Other elements in the tourmaline largely reflect the bulk composition of the replaced schist. The calculations show that silica in the quartz veins was locally derived, not brought in by the metasomatizing fluid. Interstitial graphite in the tourmalinites shows precipitation of carbon from the methane-bearing fluid. The study demonstrates an important effect of boron transfer by fluids during metamorphism and magmatism in the Earth's crust.
... Most volatile-rich fluids were produced during the HT-LP M2a stage under regional metamorphism (Bastoul, 1992;Delchini et al., 2018). The production of H 2 O-CO 2 -CH 4 rich fluids in this P-T range results typically from water and graphite equilibrium under reduced conditions close to Q-F-M buffer which constitutes a rather good proxy of the redox conditions in metamorphic series (Huizenga, 2001;Huff and Nabelek, 2007). Additional local sources are needed to explain the mixing trends among volatiles: i) a mixing trend between N 2 rich fluids and CH 4 rich fluids, and ii) a mixing trend between a CO 2 rich fluid end-member and the N 2 -CH 4 mixed fluids. ...
The Jbel Haïmer copper-sulphide mineralisation occurs at 20 km north of Marrakesh in the Variscan Jebilet
massif, Morocco. Most of the ores (up to 3.9 wt% Cu, ≤38 ppm Ag, and up to 2.9 ppm Au) occur as impregnations
of NE-SW fault/fracture zones and related tectonic breccia. Two independent stages of fluid circulation and
mineral deposition are distinguished. First, Late Variscan high temperature-low pressure metamorphism synchronous
of granite intrusion induced percolation of C–H-O-N hydrothermal fluids throughout faults and shear
zones. The drop in pressure from lithostatic down to hydrostatic values at temperatures around 350 ± 50 ◦C
triggered quartz precipitation associated with minor Sn-As-(Co-Ni) deposits and finally brecciation. The second
stage, more recent than Triassic, consists in the deposition of quartz + carbonates, followed by Cu-(Pb-Zn)
sulphides (±Ag-Au alloys) in fractures crosscutting 240 Ma microdiorite dikes. Mixing of evaporitic brines likely
coming from Triassic formations with low salinity aqueous fluids was responsible for Cu-sulphide deposition at
temperatures of around 220–280 ◦C at a depth of 4–5 km. These base metal-rich brines are similar to those from
the nearby Roc Blanc Ag-deposit and several other silver and base metal deposits in Morocco, considered as
having circulated during the Central Atlantic Ocean opening.
... Therefore, our preferred model is coprecipitation of uraninite and graphite from a single reduced fluid. CH 4 is the most dominant species of carbon in such highly reduced fluid (e.g., Huizenga, 2011) and crystallization of graphite from such a CH 4bearing fluid can take place by simple cooling via the reaction: CH 4 → C + 2H 2 (Huff and Nabelek, 2007;Luque et al., 2009a;Nabelek et al., 2003). It is possible that graphite in the spatially associated carbonaceous biotite schist was the source of this CH 4 in the fluid. ...
The Khetri Copper Belt (KCB), located in the northwestern part of the Aravalli-Delhi Fold Belt, western India, is famous for Cu mineralization and known for Au ± Ag ± Co ± Fe ± REE ± U ± P occurrences. The present study conducted in and around the Madan-Kudan-Kolihan-Chandmari Cu deposits of the KCB integrates the mode of occurrence, mineralogical association, textural relation, and chemistry of hydrothermal minerals, and in situ chemical dating of uraninite. We propose that the U mineralization, represented by Type 1 to Type 6 uraninites, has evolved through six successive stages: U-mineralization (Type 1 uraninite) of uncertain origin → U-mineralization (Type 2 uraninite) during Fe-Mg alteration → U-mineralization (Type 3 uraninite) during Ca-Na alteration → Cu-Fe-Co-REE-U mineralization (Type 4 uraninite) during Na-Ca-K alteration → U-mineralization (Type 5 uraninite) during chloritization (Fe-Mg alteration) → Cu-Co-REE-U mineralization (Type 6 uraninite) during K-Fe-Mg alteration. The chemical ages of uraninite suggest that the hydrothermal mineralization associated with Type 2 to Type 5 uraninites formed during a hitherto unknown older event (compared to the previously reported age of the mineralization in the KCB i.e. ~ 850 Ma), which initiated during the second phase of metamorphism of ~ 1.40–1.30 Ga (M2) and terminated well before the third phase of metamorphism of ~ 985–920 Ma (M3). The K-Fe-Mg alteration and the associated mineralization most likely is time-equivalent of the known alteration-mineralization event of ~ 850 Ga. The chlorite and biotite thermometry in tandem with U/Th ratios of uraninite suggest that uraninites crystallized at high temperature (> 390 °C) in all the hydrothermal stages. The common presence of magnetite and ilmenite, the occasional presence of graphite, and the Fe³⁺/(Fe³⁺+Fe²⁺) ratios of the co-genetic gangue minerals such as amphibole, biotite, and chlorite suggest reduced environment, below the haematite-magnetite buffer, during the crystallization of uraninite in all the hydrothermal stages. Based on the composition of gangue minerals (apatite, amphibole, biotite, chlorite, and scapolite) in alteration assemblages/veins and physicochemical characters of the fluids, we discuss the possibility of transportation of U as U⁴⁺-chloride and -fluoride complexes. The high temperature and reduced nature of the fluids, high Th contents and low U/Th ratios of most of the uraninites, similar age of mineralization (Type 2 to Type 5 uraninite) and M2 metamorphism, and the absence of concomitant magmatic activity collectively suggest that hydrothermal mineralization related to Type 2 to Type 5 uraninites took place from metamorphic fluids. We report, for the first time, a unique uraninite-graphite association in the KCB, which can be best explained by their co-precipitation from a hydrothermal fluid during the earliest Fe-Mg alteration.
... The Laser Raman spectrum results showed that a certain amount of N 2 existed in the fluid of the prograde skarn in the Zhuxi deposit. N 2 -rich inclusions have been observed in quartz from black shales submitted to contact metamorphism in several localities (Kreulen and Schuiling, 1981), and N 2 portentially could have be released from micas and feldspars during metamorphism and stored in these minerals and can be liberated at high temperatures during the diagenesis of organic-bearing sediments (Cepedal et al., 2013;Huff and Nabelek, 2007;Kreulen and Schuiling, 1981;Dubessy and Ramboz, 1986;Mullis, 1979). Actually, in the three ore-related granites in the Zhuxi deposit, mica and feldspar were the major ore-forming minerals and mostly had been altered (Pan et al., 2018), potentially indicating that the granitic rocks have presented the principal source. ...
... Journal of Asian Earth Sciences xxx (xxxx) xxxx current observations also showed that the garnet-pyroxene skarn had formed by the contact metasomatism of the biotite granite stock and granite porphyry dikes with the carbonate rocks , the contribution of wall rocks could not be excluded. This potential origin is also demonstrated by the presence of few methane and ethene in the fluid inclusions of the prograde stage detected by Laser Raman Spectrum (Fig. 8), because methane and ethene in the fluid from the graniterelated ore deposits have been proven to be derived from organic matter sources (Cepedal et al., 2013;Huff and Nabelek, 2007;Dubessy et al., 1989;Shepherd et al., 1991;Roedder, 1984) through assimilation of CH 4 -N 2 from metasedimentary host rocks with fluids related to Sn-W mineralization in granites (Pohl and Günther, 1991;Wilkinson, 1990). Moreover, one of the H-and O-isotope data was close to the metamorphic water and the Neoproterozoic Shuangqiaoshan metasedimentary rocks (Fig. 10), further hinting the small contribution of metamorphosed rocks and carbonate rocks to the fluid from the prograde skarn. ...
Scheelite mineralization accompanied by traces of chalcopyrite occurs in skarn systems in the giant Zhuxi deposit in the Taqian area, Northeastern Jiangxi province, South China. Three paragenetic stages of skarn with ore deposition have been recognized: the prograde skarn, retrograde skarn and hydrothermal quartz-sulfide stages. Microthermometer data showed that the prograde skarn were formed at relatively high temperatures (450–>500 °C) and pressures (0.97–1.38 kbars) and low oxidation to weak reduction conditions. The Raman microprobe data demonstrated that the fluid of the stage was H2O–NaCl/KCl/CaCl2 ± CH4/C2H4 system. The retrograde skarn alteration formed at 1.24 kbars and relatively medium temperatures (280–320 °C), and the ore-forming fluid was H2O–NaCl/KCl/CaCl2 system. During the hydrothermal quartz-sulfide stage, the fluids were methane-bearing aqueous, low-salinity (0.9–8.0 wt% NaCleqv) and low homogeneous temperature (160–240 °C). Correspondingly, the minimum fluid pressures were evaluated between 75 and 252 bars.
The H- and O-isotopic values from the prograde and retrograde stages implied that the mineralizing fluids were derived principally from magmatic water. The mineralizing fluids in the quartz-sulfide hydrothermal stages were mingled with magmatic water with some meteoric water as well as minor contributions of wall rocks. The sulfur and lead isotopes indicated that ore-forming materials including sulfur, lead, copper, zinc and iron in the Zhuxi deposit were derived from local magmatic and sedimentary sources. Geological, fluid inclusion and isotopic data supported that the Zhuxi deposit is a typical skarn-type W(Cu) deposit related to ilmenite-series granitic rocks and formed in a compressional tectonic environment.
... Because most shales are deposited in deep ocean basins in anoxic waters, organic material is commonly preserved. The organic material eventually turns into graphite on metamorphism and N 2 , CH 4 and CO 2 are released (Duke et al. 1990a;Huff & Nabelek 2007). f O 2 in schists may remain below the fayalite-magnetitequartz (FMQ) buffer, buffered by the assemblage Ms + Mt + Qz = Ann + Sil. ...
Leucogranites are a characteristic feature of collisional orogens. Their generation is intimately related to crustal thickening and the active deformation and metamorphism of metapelites. Data from Proterozoic to present day orogenic belts show that collisional leucogranites (CLGs) are peraluminous, with muscovite, biotite and tourmaline as characteristic minerals. Isotopic ratios uniquely identify the metapelitic sequences in which CLGs occur as sources. Organic material in pelitic sources results in f O 2 in CLGs that is usually below the fayalite–magnetite–quartz buffer. Most CLGs form under vapour-poor conditions with melting involving a peritectic breakdown of muscovite. The low concentrations of Mg, Fe and Ti that characterize CLGs are largely related to biotite–melt equilibria in the source rocks. Concentrations of Zr, Th and rare earth elements are lower than expected from zircon and monazite saturation models because these minerals often remain enclosed in residual biotite during melting. Melting involving muscovite may limit the temperatures achieved in the source regions. A lack of nearby mantle heat sources in thick collisional orogens has led to thermal models for the generation of CLGs that involve flux melting, or large amounts of radiogenic heat generation, or decompression melting or shear heating, the last one emphasizing the link of leucogranites and their sources to crustal-scale shear zone systems.
