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Scheelite-bearing calc-silicate rock (clinozoisite/zoisite,
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Stratabound tungsten mineralization in regional metamorphic calc-silicate rocks of probably Lower Paleozoic age is described from the polymetamorphic Austroalpine Crystalline Complex (ACC) of the Eastern Alps. Scheelite-bearing calc-silicate rocks which are often associated with marbles and tourmalinites are intercalated conformably with metaclasti...
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... chlorite, ap- atite, pyrite, pyrrhotite as accessoric minerals. Scheelite is either present as disseminated grains and porphyroblasts or in scheelite-quartz mobilisates. The latter must have formed prior to the D2 deformation as they are involved in D2 isoclinal folding and are crosscut by synmetamor-phic clinozoisite/zoisite mobilisates (Fig. 2). Tourmalin- ites containing scheelite in s-parallel quartz veins have undergone the same acts of metamorphism and deforma- tion (Raith ...
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Citations
... However, the majority of subeconomic tungsten occurrences in the Eastern Alps lack such spatial and temporal connection to igneous intrusions. Instead, they form stratabound scheelite mineralization in regional metamorphic metacarbonate or calc-silicate rocks (Wenger 1964;Haditsch and Mostler 1983;Raith 1991). Their stratabound appearance in early Paleozoic volcano-sedimentary sequences led to the postulation of the submarine-exhalative "Sb-W-Hg formation" model, assuming syngenetic/syndiagenetic mineralization associated with mafic volcanism (Maucher 1965;Höll et al. 1972). ...
A peculiar type of stratabound tungsten mineralization in metacarbonate rocks was discovered and explored at Mallnock (Austria) during the late 1980s. It is the only tungsten occurrence in the Eastern Alps in which scheelite is associated with wolframite (96 mol% ferberite). The tungsten prospect is located in the Austroalpine Drauzug-Gurktal Nappe System recording polyphase low-grade regional metamorphism. Raman spectroscopy of carbonaceous material yield maximum metamorphic temperatures of 296 ± 27 °C and 258 ± 27 °C, which are assigned to Variscan and Eoalpine metamorphism, respectively. Scheelite and ferberite occur as polyphase stockwork-like mineralization in Fe-rich magnesite in the northern ore zone (Mallnock North), whereas in the western ore zone (Mallnock West), scheelite-quartz veinlets are exclusively hosted in dolomitic marbles. LA-ICP-MS analyses of scheelite and ferberite yield low contents of Mo, Nb, Ta, and rare earth elements, but high contents of Na and Sr. Uranium is particularly high in scheelite (up to 200 µg/g) and makes this mineral a suitable target for U–Pb dating. In situ U–Pb dating of scheelite yielded an early Permian age (294 ± 8 Ma) for Mallnock West and a Middle Triassic age (239 ± 3 Ma) for Mallnock North. A monzodioritic dike close to Mallnock yielded a U–Pb apatite date of 282 ± 9 Ma and supports the polyphase formation of this mineralization. The U–Pb scheelite ages indicate that a model for tungsten metallogeny in the Eastern Alps must also consider remobilization of tungsten by metamorphic fluids. In the Alps, the Permian to Triassic period (ca. 290–225 Ma) is characterized by an overall extensional geodynamic setting related to the breakup of Pangea. Lithospheric thinning caused higher heat flow, low-P metamorphism, and anatexis in the lower crust, which led to enhanced crustal fluid flow in the upper crust. These processes were not only responsible for the formation of metasomatic hydrothermal magnesite and siderite deposits in the Eastern Alps but also for this unique magnesite-ferberite-scheelite mineralization at Mallnock.
... The mineralization in the Dahutang tungsten deposit is characterized by (1) disseminated-/ veinlet-type tungsten mineralization in the Jiuling biotite granodiorite (∼95% of the total reserve), which is associated with the roof of the porphyritic biotite granite stock (Fig. 2b, 3l); (2) cryptoexplosive breccia ores with the occurrence of wolframite, scheelite, chalcopyrite, and molybdenite (∼4%) ( Fig. 3f and i); and (3) quartz veins and stockworks of wolframite-scheelite (∼1%) (Fig. 2b, 3a-h). The ratio of scheelite to wolframite is approximately 1, unlike the Nanling tungsten province that contains carbonate-hosted scheelite-or wolframite-dominant deposits (Appel, 1994;Beran et al., 1985;Neinavaie et al., 1989;Plimer, 1994;Raith, 1991;Thalhammer et al., 1989). ...
The giant Dahutang tungsten deposit has total reserves of more than 1.31 Mt of WO3 with a scheelite/wolframite ratio of ~1 and is mainly hosted by the Neoproterozoic Jiuling granodiorite batholith (~820 Ma). The deposit is characterized by four types of alteration, including biotite alteration, phyllic alteration, greisenization and silicification. Whole-rock geochemical analyses showed that the elements Ti, Ni, V, Sc, and Lu exhibited immobility during the four alteration processes. The mobile element geochemistry effectively differentiated among four distinct hydrothermal alteration styles. During the biotite mineralization, there were mass gains in Al2O3, Fe2O3, MnO, MgO, K2O, P2O5, and W and depletions in SiO2, CaO, and Na2O. The phyllic alteration exhibited mass gains in SiO2, Fe2O3, MgO, and W and depletions in CaO, Na2O, and K2O, but Al2O3, MnO, and P2O5 were immobile. The weak greisenization exhibited mass gains in SiO2, Fe2O3, K2O, P2O5 and W and depletions in Na2O, MgO, and CaO, whereas Al2O3 and MnO remained immobile. The silicification exhibited mass gains in SiO2 and W and depletions in Al2O3, Fe2O3, MgO, CaO, Na2O, and K2O, but MnO exhibited immobility. These alterations were related to at least three major hydrothermal fluid systems. Firstly, a hydrothermal fluid caused biotitization zones and Fe + Mn ± W mineralization (mostly biotite) at temperatures ranging from 560 to 450°C, and the magmatic hydrothermal fluids were derived from the Jurassic porphyritic biotite granite (~150 Ma) and characterized by alkaline, oxidized, moderate-pressure, and low-salinity features. Secondly, a hydrothermal fluid was formed by the mixing of magmatic fluid with meteoric water and was responsible for the phyllic/weak greisenization alteration zones at temperatures ranging from 440 to 450°C and characterized by alkaline, weakly oxidized, moderate-pressure, and low-salinity features. Thirdly, a hydrothermal fluid caused greisenization and silicification zones at temperatures ranging from 440 to 160°C, which were characterized by acidic, reduced, high-pressure, and moderate- to low-salinity features, derived from the Cretaceous fine-grained biotite granite (~144 Ma), and associated with the main W mineralization at Dahutang.
The characteristics of Fe-enriched biotite in the biotitized and greisenized rock – decreasing temperature, high pressure, and high log(fH2O/fHCl) – could facilitate the formation of scheelite deposits, but the high F suppressed it. The decreasing temperature and f(O2) and the Fe-Mn released from biotite contributed to the formation and precipitation of wolframite. During alkaline alteration, biotite and apatite acted as storage places for Fe-Mn and Ca, which were subsequently released by acidic alteration to form scheelite and wolframite. There was no enough Ca was released from biotitized rock for the acidic alteration to provide the WO42－ to form scheelite. Meanwhile, Fe was added, and Mn was released to form the scheelite + wolframite deposit. Based on all the results, we have developed a genetic model for tungsten mineralization including superimposed alteration processes (alkaline overprinted by acidic alteration), which led to the gain and loss of elements, and corresponding to two magmatic events, the Jurassic porphyritic biotite granite and the Cretaceous fine-grained biotite granite. The superposition of alterations played an important role in the mineralization of the Dahutang giant tungsten deposit.
... O metassomatismo de alta temperatura é responsável pelo zoneamento mineral de assembleias compostas principalmente por granadas proximais, piroxênios distais e minerais como wollastonita, vesuvianita, scheelita ou sulfetos maciços e/ou óxidos mineralizados em contato com a frente de mármore encaixante (Robb, 2005). Essas formações somam 95% das ocorrências escarníticas conhecidas, sendo esta a gênese responsável pelos depósitos economicamente mais interessantes de scheelita no mundo (Raith, 1991). A formação de escarnitos relacionados ao metamorfismo de contato pode ser consideravelmente mais complexa envolvendo uma evolução iniciada pela intrusão plutônica, seguida de cristalização, alteração retrógrada e resfriamento do plúton. ...
During minerals research performed in Rio de Janeiro state, in the counties of Parati, Rio Claro and Piraí in the early 80 detected the presence of scheelite in concentrate panning from drains of Monumento/Cacaria area. Until this study, the lithology source responsible for this occurrence was unknown. In order to define the source and characterize the genesis of the tungsten mineralization, there were panned-concentrate drainage sampling in streams of the area, geological mapping in detailed scale (1:25.000) and collect of rock samples for characterization in analytic methods. The study area is located in the evolution context of Ribeira Belt, characterized by precambrian gneisses and the mineralization was classified as a stratabound scheelite, calcisilicate hosted. © 2016 Universidade Federal do Rio de Janeiro. All rights reserved.
... Tourmalinites have also been recognized to occur in association with stratabound tungsten mineralization where they are also assumed to be related to submarine volcanogenic-exhalative processes (e.g. Barnes, 1983;Appel, 1986;Raith, 1988Raith, , 1991Leake et al., 1989. Consequently, information on tourmalinites associated with tungsten deposits can give insights into the origin and evolution of these types of exhalative deposits. ...
Tourmalinites that are distally associated with tungsten deposits of the Pampa del Tamboreo area, San Luis, Argentina, contain tourmalines retaining evidence for its origin and evolution. Tourmaline grains uncommonly contain small grains of detrital tourmaline. Analysis of a single detrital tourmaline grain reveals that it is a Ca-rich "oxy-dravite". Proximal to the detrital cores there are inner domains of asymmetric tourmaline overgrowths that developed during low grade metamorphism. Volumetrically dominant tourmaline overgrowths in the outer domain are concentrically zoned aluminous dravite and "oxy-dravite" with Al/(Al + Fe + Mg) = 0.71-0.74 and Mg/(Mg + Fe) = 0.64-0.71. Variability of Al is primarily controlled by the deprotonation substitution R + OH- = Al + O2- (where R = Fe + Mg), and is a function of the activity of H2O. A likely evolutionary scenario is one in which volcanogenic material is altered by hydrothermal fluids in the sea floor resulting in an aluminous and magnesian residuum. With further hydrothermal circulation and incipient metamorphism, boron-rich fluids are expelled from metasedimentary and metavolcanic basement rocks and develop Mg-rich tourmalinites in the aluminous, magnesian host rocks. The tourmalinization process occurs over a range of metamorphic conditions and with fluids of variable activity of H2O. (C) 2009 Elsevier Ltd. All rights reserved.
... intermediate-P (600-700 • C and 4.0-6.0 kbar ∼ 12-18 km) during regional and/or contact metamorphism (e.g., Raith, 1991;Pan and Fleet, 1992;Mueller et al., 2004). The occurrence of garnet-diopside assemblage associated with ductile structures such as shear zones, tectonic boudins, and mylonitic foliations indicate that this assemblage was formed during the prograde stage of the regional amphibolite-facies metamorphism. ...
The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt consists dominantly of variably deformed and metamorphosed mafic to ultramafic flows (basalts to picrites). In addition, there are minor serpentinites, gabbros, clinopyroxene-rich cumulates, and volcaniclastic and siliciclastic sedimentary rocks. Primary volcanic structures such as pillows and volcanic breccia are well preserved in low strained zones. The belt underwent intense metasomatic hydrothermal alteration between 3075 and 2961 Ma. An early stage of calc-silicate metasomatism (stage-I) resulted in the formation of epidosites in pillow cores, pillow interstitials, and intrusive margins of gabbroic dykes. This alteration appears to have resulted from sea-floor hydrothermal alteration. A second stage of calc-silicate metasomatism (stage-II) formed centimeter- to meter-scale layers concordant to discordant relative to the regional foliation. These layers consist of diopside + garnet + epidote + plagioclase + quartz + titanite ± vesuvianite ± calcite ± actinolite ± scheelite. The second stage calc-silicate rocks are associated with shear zones and their origin is attributed to interaction of reactive fluids with mafic and ultramafic rocks during regional metamorphism.
... . Raith & Prochaske, 1995, Raith, 1991Holl, 1975Holl, , 1976( و اســـــتراليا مســـــيف بـوهـمــيـــــن و هيل بروكـن .) Maucher, 1976Plimer, 1987, 1994Kwak,1987;Barnes, 1983 Plimer,1994;Plimer, 1987;Kwak,1987;Barnes, 1983 ...
... Tourmalinites are defined as rocks with more than 20% tourmaline according to Slack (1982Slack ( ,1996.Tourmalinites have increasingly been recognized to occur in association with diverse types of stratabound deposits, in particular in SEDEX and VMS mineral deposits (Slack, 1996, Henry andDutrow, 1996). They have been also recognized to occur in association with tungsten mineralization (Barnes, 1983, Appel, 1986, Raith, 1988, 1991, Leake et al. 1989 This paper deals with the chemical composition of the tourmalines from tourmalinites in the Pampa del Tamboreo, San Luis Province. The Sierra de San Luis is part of the Sierras Pampeanas Orientales and is composed of Neoproterozoic-Early Paleozoic metamorphic and igneous rocks which has been subdivided in several complexes ( fig.1). ...
... Tourmalinites are defined as rocks with more than 20% tourmaline according to Slack (1982Slack ( ,1996.Tourmalinites have increasingly been recognized to occur in association with diverse types of stratabound deposits, in particular in SEDEX and VMS mineral deposits (Slack, 1996, Henry andDutrow, 1996). They have been also recognized to occur in association with tungsten mineralization (Barnes, 1983, Appel, 1986, Raith, 1988, 1991, Leake et al. 1989 This paper deals with the chemical composition of the tourmalines from tourmalinites in the Pampa del Tamboreo, San Luis Province. The Sierra de San Luis is part of the Sierras Pampeanas Orientales and is composed of Neoproterozoic-Early Paleozoic metamorphic and igneous rocks which has been subdivided in several complexes ( fig.1). ...
... Plimer 1987). Syngenetic/diagenetic, sedimentary-exhalative genetic models, which may include an evaporite-derived¯uid component, have been proposed for the latter (HoÈ ll 1977;Raith 1991;Plimer 1994). ...
Both stratiform/stratabound and granite-related models have been used to explain the genesis of W(Mo) deposits in the Okiep
copper district in western Namaqualand, South Africa. Apparently, stratabound mineralization (Fe-rich wolframite with accessory
molybdenite) occurs in foliation-parallel quartz veins in high-grade (∼750 °C, 5–6 kbar) metapelites of the Wolfram Formation,
and less commonly in small bodies of silicified leucogranites and pegmatites. Six Re–Os ages for molybdenites from four deposits
(Nababeep Tungsten Far West, Kliphoog, Narrap, Tweedam) range between 1000 ± 4 and 1026 ± 5 Ma. These molybdenites define
a well-constrained 187Re–187Os isochron with an age of 1019 ± 6 Ma, which is interpreted as the age of W(Mo) mineralization. This age is significantly
younger than Proterozoic protolith ages for supracrustal rocks and the emplacement ages for the main intrusive suites, but
geologic evidence requires overlap with a period of high-grade metamorphism. We suggest that W(Mo) mineralization is genetically
linked to intra-crustal magmatic processes at ∼1020 Ma, thereby precluding the ∼1060 Ma Concordia granite as the source for
mineralizing fluids. A narrow range of positive δ34S compositions (+3.6 to +4.5‰) for eight molybdenites from five W(Mo) mines is consistent with a SO2-rich fluid and a granite-related genetic model. Post-peak metamorphic deformation and metamorphism of W(Mo) ores is most
likely related to the retrograde stage of the Namaquan orogeny, which overlaps emplacement of late-orogenic, evolved granites
and pegmatites, and the formation of W(Mo) deposits in western Namaqualand. Therefore, the effects of retrograde Namaquan
metamorphism extend at least to ∼1020 Ma or, alternatively, these W(Mo) veins were affected by a poorly constrained later
event (e.g. early Pan-African).
... In metamorphic terranes where primary sedimentary textures commonly are not preserved, the presence of exhalites is an important criterion for stratiform and strata-bound tungsten deposits (James and Incson, 1993). Some of the most common exhalites found in association with stratabound massive sulfide and tungsten deposits are tourmalinites (Slack et al., 1984;Plimer, 1987;Raith, 1988). Banded ironformations, stratiform massive sulfides, coticules, or fluorinerich rocks are other relatively common rocks of exhalative origin that could be expected with sedimentary exhalative deposits. ...
Several tungsten deposits occur in the Okiep copper district, South Africa, which is part of a high-temperature, low-pressure granulite terrane. The W-Mo deposits are spatially and genetically associated with the 1.1 Ga Concordia granite, a silica-rich (70-76 wt %), peraluminous leucogranite with subalkaline monozonitic magma characteristics. More fractionated cogenetic intrusions are interpreted as separated residual granitic liquids. Mineralized pegmatites, replacement orebodies, and exo- and endogranitic veins are distinguished. Metapelites (Wolfram schist) hosting S2 subparallel exogranitic veins are characterized by M2 upper amphibolite-lower granulite facies assemblages. The facts that late to postorogenic granites and the W-Mo deposits are deformed, metamorphic ore textures are preserved, and ore deposit, specific hydrothermal low-temperature alteration is absent, suggest that the second M3 late-Kibaran metamorphic overprint postdated mineralization. -from Authors
... THERE are many known cases of often granite-unrelated scheelite mineralization in high-grade and/or highly deformed metamorphic rocks that have been classified as strata-bound ore deposits (Denisenko and Rundkvist, 1977;Kwak, 1987;Plimer, 1987;Cheilletz, 1988). Some of these deposits, especially those in the eastern Alps, have been interpreted as having been formed by syngenetic sedimentary exhalative processes (H611 andMaucher, 1967, 1976;H611, 1975) high-grade metamorphic Austroalpine crystalline basement (Neinavaie et al., 1985;Raith, 1988Raith, , 1991, and low-grade metamorphic rocks of the lower Austroalpine tectonic unit (H611, 1977;Raith, 1990). ...
... THERE are many known cases of often granite-unrelated scheelite mineralization in high-grade and/or highly deformed metamorphic rocks that have been classified as strata-bound ore deposits (Denisenko and Rundkvist, 1977;Kwak, 1987;Plimer, 1987;Cheilletz, 1988). Some of these deposits, especially those in the eastern Alps, have been interpreted as having been formed by syngenetic sedimentary exhalative processes (H611 andMaucher, 1967, 1976;H611, 1975) high-grade metamorphic Austroalpine crystalline basement (Neinavaie et al., 1985;Raith, 1988Raith, , 1991, and low-grade metamorphic rocks of the lower Austroalpine tectonic unit (H611, 1977;Raith, 1990). ...
... Syngenetic-syndiagenetic concentration of tungsten has been discussed for Tux and other deposits in the eastern Alps (H611 and Maucher, 1967;H611, 1977;Raith, 1988Raith, , 1990Raith, , 1991 and tungsten preconcentration in sedimentary carbonate-rich environments is usually explained with sedimentary exhalative hydrothermal processes. Alternative syngenetic-syndiagenetic models involving formation of tungsten mineralization in evaporitic environments (plus exhalative hydrothermal processes) have been proposed for some Australian strata-bound calcsilicate scheelite deposits (Broken Hill, N.S.W., Plimer, 1994; Halls Creek, Western Australia, Ririe, 1989); tentatively the latter type of strata-bound scheelite deposits could represent metamorphosed equivalents of tungsten concentration in a recent evaporitic hot spring environment at Searles Lake, California (Carpenter and Garett, 1959). ...
The Tux-Lanersbach magnesite-scheelite deposit is one of several small strata-bound scheelite deposits situated in low-grade metamorphic lower Paleozoic sequences of the lower Austroalpine Innsbruck quartz phyllite zone. A polymetamorphic evolution of these volcanosedimentary and sedimentary series is indicated by Ar-Ar dating. The dominant M 2-D 2 event is of Eoalpine (Cretaceous) age and the retrograde M 3-D 3 event, of late Alpine (Tertiary) age. Scheelite was produced as a by-product of magnesite and is hosted by various chlorite-rich phyllites and black schist-rich metaclastic rocks and mainly by metacarbonate rocks. The C-O isotope composition of carbonate rocks allows the distinction of three major groups. Although 13C values of scheelite-free carbonate rocks still reflect sedimentary marine values, scheelite-bearing dolomites exhibit 13C depletion. Oxygen isotopes indicate disequilibrium between magnesites and dolomitic host rocks and support an epigenetic model of spar magnesite formation. The present data do not support either a syn- or epigenetic concentration for the primary tungsten. -from Authors
