Skarn deposits of China
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Skarn deposits are one of the most common deposit types in China. The 386 skarns summarized in this review contain ~8.9 million tonnes (Mt) Sn (87% of China’s Sn resources), 6.6 Mt W (71%), 42 Mt Cu (32%), 81 Mt Zn-Pb (25%), 5.4 Mt Mo (17%), 1,871 tonnes (t) Au (11%), 42,212 t Ag (10%), and ~8,500 Mt Fe ore (~9%; major source of high-grade Fe ore). Some of the largest Sn, W, Mo, and Zn-Pb skarns are world-class.
The abundance of skarns in China is related to a unique tectonic evolution that resulted in extensive hydrous magmas and widespread belts of carbonate country rocks. The landmass of China is composed of multiple blocks, some with Archean basements, and oceanic terranes that have amalgamated and rifted apart several times. Subduction and collisional events generated abundant hydrous fertile magmas. The events include subduction along the Rodinian margins, closures of the Proto-Tethys, Paleo-Asian, Paleo-Tethys, and Neo-Tethys Oceans, and subduction of the Paleo-Pacific plate. Extensive carbonate platforms developed on the passive margins of the cratonic blocks during multiple periods from Neoarchean to Holocene also facilitated skarn formation.
There are 231 Ca skarns replacing limestone, 15 Ca skarns replacing igneous rocks, siliciclastic sedimentary rocks, or metamorphic silicate rocks, 113 Ca-Mg skarns replacing dolomitic limestone or interlayered dolomite and limestone, and 28 Mg skarns replacing dolomite in China. The Ca and Ca-Mg skarns host all types of metals, as do Mg skarns, except for major Cu and W mineralization. Boron mineralization only occurs in Mg skarns. The skarns typically include a high-temperature prograde stage, iron oxide-rich higher-temperature retrograde stage, sulfide-rich lower-temperature retrograde stage, and a latest barren carbonate stage. The zoning of garnet/pyroxene ratios depends on the redox state of both the causative magma and the wall rocks. In an oxidized magma-reduced wall-rock skarn system, such as is typical of Cu skarns in China, the garnet/pyroxene ratio decreases, and garnet color becomes lighter away from the intrusion. In a reduced intrusion-reduced wall-rock skarn system, such as a cassiterite- and sulfide-rich Sn skarn, the skarn is dominated by pyroxene with minor to no garnet. Manganese-rich skarn minerals may be abundant in distal skarns.
Metal associations and endowment are largely controlled by the magma redox state and degree of fractionation and, in general, can be grouped into four categories. Within each category there is spatial zonation. The first category of deposits is associated with reduced and highly fractionated magma. They comprise (1) greisen with Sn ± W in intrusions, grading outward to (2) Sn ± Cu ± Fe at the contact zone, and farther out to (3) Sn (distal) and Zn-Pb (more distal) in veins, mantos, and chimneys. The second category is associated with oxidized and poorly to moderately fractionated magma. Ores include minor porphyry-style Mo and/or porphyry-style Cu mineralization ± Cu skarns replacing xenoliths or roof pendants inside intrusions, zoned outward to major zones of Cu and/or Fe ± Au ± Mo mineralization at the contact with and in adjacent country rocks, and farther out to local Cu (distal) + Zn-Pb (more distal) in veins, mantos, and chimneys. Oxidized and highly fractionated magma is associated with porphyry Mo or greisen W inside an intrusion, outward to Mo and/or W ± Fe ± Cu skarns at the contact zone, and farther to Mo or W ± Cu in distal veins, mantos, and chimneys. The final category is associated with reduced and poorly to moderately fractionated magma. No major skarns of this type have been recognized in China, but outside China there are many examples of such intrusions related to Au-only skarns at the contact zone. Reduced Zn-Au skarns in China are inferred to be distal parts of such systems. Tungsten and Sn do not occur together as commonly as was previously thought.
The distal part of a skarn ore system may transition to carbonate replacement deposits. Distal stratabound mantos and crosscutting veins/chimneys may contain not only Zn-Pb but also major Sn, W, Cu, Mo, and Au mineralization. The Zn-Pb mineralization may be part of either an oxidized system (e.g., Cu, Mo, Fe) or a reduced system (e.g., Sn). In China, distal Zn-Pb is more commonly related to reduced magmas. Gold and W may also be related to both oxidized and reduced magmas, although in China they are more typically related to oxidized magma. There are numerous examples of distal mantos/chimneys that continuously transition to proximal skarns at intrusion-wall-rock contact zones, and this relationship strongly supports the magmatic affiliation of such deposits and suggests that distal skarns/carbonate replacement deposits systems should be explored to find more proximal mineralization. Carbonate xenoliths or roof pendants may host the majority of mineralization in some deposits. In contact zones, skarns are better developed where the intrusion shape is complicated. The above two skarn positions imply that there may be multiple skarn bodies below drill interceptions of intrusive rocks. Many of the largest skarns for all commodities in China are related to small or subsurface intrusions (except for Sn skarns), have multiple mineralization centers, are young (<~160 Ma), and have the full system from causative intrusion(s) to distal skarns or carbonate replacement extensions discovered.
Chinese skarn deposits fall in several age groups: ~830, ~480 to 420, ~383 to 371, ~324 to 314, ~263 to 210, ~200 to 83, ~80 to 72, and ~65 to 15 Ma. They are typically associated with convergent plate boundaries, mostly in subduction settings but also in collisional settings. Seven major skarn metallogenic belts are recognized based on skarn geographic location and geodynamic background. In subduction settings, skarns may form in a belt up to 4,000 km long and 1,000 km inland, with skarns continuously forming for up to 120 m.y., e.g., the eastern China belt. In most other belts, skarns form in 5- to 20-m.y. episodes similar to the situation in South America. In collisional settings, skarns may form up to 50 m.y. after an ocean closure, and the distance to the collisional/accretionary boundary may extend to ~150 km inland. The size of collision-related skarns may be as large as the largest skarns related to oceanic crust subduction. Older suture zones may be favorable sites for younger mineralization, for example, the Triassic Paleo-Tethys suture between the North and South China blocks for the younger and largest skarn cluster of the Middle-Lower Yangtze belt in the eastern China belt, and the Triassic sutures in southwestern China for Cretaceous to Tertiary mineralization.Cite
Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sediment-hosted Au deposits in increasingly peripheral locations; and superjacent high- and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ~100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer.
The alteration and mineralization in porphyry Cu systems, occupying many cubic kilometers of rock, are zoned outward from the stocks or dike swarms, which typically comprise several generations of intermediate to felsic porphyry intrusions. Porphyry Cu ± Au ± Mo deposits are centered on the intrusions, whereas carbonate wall rocks commonly host proximal Cu-Au skarns, less common distal Zn-Pb and/or Au skarns, and, beyond the skarn front, carbonate-replacement Cu and/or Zn-Pb-Ag ± Au deposits, and/or sediment-hosted (distal-disseminated) Au deposits. Peripheral mineralization is less conspicuous in noncarbonate wall rocks but may include base metal- or Au-bearing veins and mantos. High-sulfidation epithermal deposits may occur in lithocaps above porphyry Cu deposits, where massive sulfide lodes tend to develop in deeper feeder structures and Au ± Ag-rich, disseminated deposits within the uppermost 500 m or so. Less commonly, intermediate-sulfidation epithermal mineralization, chiefly veins, may develop on the peripheries of the lithocaps. The alteration-mineralization in the porphyry Cu deposits is zoned upward from barren, early sodic-calcic through potentially ore-grade potassic, chlorite-sericite, and sericitic, to advanced argillic, the last of these constituting the lithocaps, which may attain >1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sulfides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the litho-caps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them. Magmatic-hydrothermal breccias may form during porphyry intrusion, with some of them containing high-grade mineralization because of their intrinsic permeability. In contrast, most phreatomagmatic breccias, constituting maar-diatreme systems, are poorly mineralized at both the porphyry Cu and lithocap levels, mainly because many of them formed late in the evolution of systems.
Porphyry Cu systems are initiated by injection of oxidized magma saturated with S- and metal-rich, aqueous fluids from cupolas on the tops of the subjacent parental plutons. The sequence of alteration-mineralization events charted above is principally a consequence of progressive rock and fluid cooling, from >700° to <250°C, caused by solidification of the underlying parental plutons and downward propagation of the lithostatic-hydrostatic transition. Once the plutonic magmas stagnate, the high-temperature, generally two-phase hyper-saline liquid and vapor responsible for the potassic alteration and contained mineralization at depth and early overlying advanced argillic alteration, respectively, gives way, at <350°C, to a single-phase, low- to moderate-salinity liquid that causes the sericite-chlorite and sericitic alteration and associated mineralization. This same liquid also causes mineralization of the peripheral parts of systems, including the overlying lithocaps. The progressive thermal decline of the systems combined with synmineral paleosurface degradation results in the characteristic overprinting (telescoping) and partial to total reconstitution of older by younger alteration-mineralization types. Meteoric water is not required for formation of this alteration-mineralization sequence although its late ingress is commonplace.
Many features of porphyry Cu systems at all scales need to be taken into account during planning and execution of base and precious metal exploration programs in magmatic arc settings. At the regional and district scales, the occurrence of many deposits in belts, within which clusters and alignments are prominent, is a powerful exploration concept once one or more systems are known. At the deposit scale, particularly in the porphyry Cu environment, early-formed features commonly, but by no means always, give rise to the best ore-bodies. Late-stage alteration overprints may cause partial depletion or complete removal of Cu and Au, but metal concentration may also result. Recognition of single ore deposit types, whether economic or not, in porphyry Cu systems may be directly employed in combination with alteration and metal zoning concepts to search for other related deposit types, although not all those permitted by the model are likely to be present in most systems. Erosion level is a cogent control on the deposit types that may be preserved and, by the same token, on those that may be anticipated at depth. The most distal deposit types at all levels of the systems tend to be visually the most subtle, which may result in their being missed due to overshadowing by more prominent alteration-mineralization.
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Abstract: The skarns and genesis were studied of the Huanggang Fe‐Sn deposit and the nearby Sumugou Zn‐Pb deposit in Inner Mongolia, China. In the Huanggang mine, Nos. 1 to 4 Fe ore bodies are arranged along a calcareous horizon from proximal to distal in this order to a granite intrusion named Luotuochangliang, while Sn ore body is situated near another granite intrusion named 204. According to the distance from the granitic intrusions, mineral assemblages in skarns are systematically changed. Garnet is the most predominant skarn mineral throughout the deposit. Hastingsitic amphiboles, however, predominate in the proximal skarns. Fluorite is common in the proximal skarns, while instead calcite is common in the distal skarns. Chlorite is characteristically present only in No. 3 ore body, and chlorite geothermometry gives near 300C for the mineralization of later stage. When garnet crystal shows zonal structure, isotropic andraditic garnet occupies the core, and is surrounded with anisotropic less‐andraditic garnet. The presence of white skarn along the boundary between main skarns and host sedimentary rocks confirms relatively reducing environment prevailing as a whole in the studied area. However, the compositional relation between coexisting garnet and clinopyroxene demonstrates that relatively oxidizing condition was achieved for garnet skarn and magnetite ore in the distal, Nos. 2 to 4 Fe ore bodies and Sumugou deposit, compared to that for garnet skarn in the proximal, No. 1 and Sn ore bodies. Preliminary study on the tin content of garnets in the studied area revealed a certain degree of contribution brought from granitic intrusives since the early stage of skarn formation, irrespective of proximal or distal. Oxygen isotope study on garnet, magnetite, quartz and skarn calcite, as well as hydrogen isotope study on hastingsitic amphibole, demonstrates mainly meteoric water origin for the skarn– and ore‐forming solutions. The occurrence of Sn, W, Mo and F minerals indicates that those elements were mainly supplied to the deposit later than the formation of skarns and iron ores, overlapping to them. These constraints allow to delineate the formation model of the deposit as follows (Fig. 10): At the time of late Jurassic to early Cretaceous, felsic activity occurred in this region as a part of Yanshanian magmatism, and formed granitic intrusions as well as thick volcanic piles on the surface. The circulation of meteoric water was provoked by the heat brought by the intrusions. By this circulation, much amount of iron was extracted from andesites of the Dashizhai Formation, and precipitated as skarns and magnetite ores along calcareous horizons near the bottom of the Huanggangliang Formation. Subsequently, volatile‐rich fluids with Sn, W and Mo were expelled from the solidifying granitic magmas, and precipitated these metals in the pre‐existing skarns and ores.
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Research Article| September 01, 2017 Composition and Evolution of Fluids Forming the Baiyinnuo'er Zn-Pb Skarn Deposit, Northeastern China: Insights from Laser Ablation ICP-MS Study of Fluid Inclusions* Qihai Shu; Qihai Shu 1EGRU (Economic Geology Research Centre) and Academic Group of Geosciences, College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia2State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China3Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China Search for other works by this author on: GSW Google Scholar Zhaoshan Chang; Zhaoshan Chang † 1EGRU (Economic Geology Research Centre) and Academic Group of Geosciences, College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia †Corresponding author: e-mail, zhaoshan.chang@jcu.edu.au Search for other works by this author on: GSW Google Scholar Johannes Hammerli; Johannes Hammerli 1EGRU (Economic Geology Research Centre) and Academic Group of Geosciences, College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia4Centre for Exploration Targeting, School of Earth and Environment, University of Western Australia, Perth, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Yong Lai; Yong Lai 3Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China Search for other works by this author on: GSW Google Scholar Jan-Marten Huizenga Jan-Marten Huizenga 1EGRU (Economic Geology Research Centre) and Academic Group of Geosciences, College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia5Department of Geology, University of Johannesburg, Auckland Park, Johannesburg 2006, South Africa Search for other works by this author on: GSW Google Scholar Economic Geology (2017) 112 (6): 1441–1460. https://doi.org/10.5382/econgeo.2017.4516 Article history accepted: 31 Mar 2017 first online: 25 Aug 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Qihai Shu, Zhaoshan Chang, Johannes Hammerli, Yong Lai, Jan-Marten Huizenga; Composition and Evolution of Fluids Forming the Baiyinnuo'er Zn-Pb Skarn Deposit, Northeastern China: Insights from Laser Ablation ICP-MS Study of Fluid Inclusions. Economic Geology 2017;; 112 (6): 1441–1460. doi: https://doi.org/10.5382/econgeo.2017.4516 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The Baiyinnuo'er skarn deposit is one of the largest Zn-Pb deposits in northeastern China, with 32.74 million metric tons (Mt) resources averaging 5.44% Zn, 2.02% Pb, and 31.36 g/t Ag. The deposit formed in three stages: the preore stage (prograde skarn minerals with minor magnetite), the synore stage (sulfides and retrograde skarn minerals including calcite and minor quartz), and the postore stage (late veins composed of calcite, quartz, fluorite, and chlorite; cutting the above mineral assemblages). In this study we analyzed the composition of single fluid inclusions using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to (1) determine the composition of the fluids and the evolution through the stages, (2) infer the fluid and metal sources, and (3) explore the metal deposition mechanisms.The preore fluids trapped in pyroxene have higher homogenization temperatures (432°–504°C), higher salinity (36.5–46.1 wt % NaCl equiv), and higher concentrations of Zn (~0.9 wt %), Pb (~1.4 wt %), and other elements (e.g., Na, K, Li, As, Rb, Sr, Cs, Ba, Cl, and Br) than synore mineralizing fluids (<370°C, <10 wt % NaCl equiv, ~450 ppm Zn, and ~290 ppm Pb). The postore fluids show lower temperatures (<250°C) and a rather dilute composition (<4 wt % NaCl equiv, ~33 ppm Zn, and ~24 ppm Pb). Geochemically, the fluids of all paragenetic stages in Baiyinnuo'er have magmatic signatures based on the element mass ratios, including elevated K/Na, Zn/Na, and Rb/Na ratios, lower Ca/K ratios, and combined Cl/Br-Na/K ratios, which are distinctively different from basinal brines. Inclusion fluids in preore stage show little variation in composition between ~510° and ~430°C, indicative of a closed cooling system. In contrast, the major components of the syn- and postore fluids, including Cl, Na, and K, decrease and correlate with a drop of homogenization temperatures from ~370° to ~200°C, indicating a dilution by mixing with groundwater. The Baiyinnuo'er mineralizing fluids (trapped in sphalerite) have higher Ca/K mass ratios (avg ~0.78) than other proximal magmatic hydrothermal systems (0.06–0.52) but lower than that of the distal El Mochito skarn (avg ~6.4), probably reflecting a gradually weakened magmatic signal away from the causative intrusions.The metal contents in preore fluids are significantly higher than those in synore fluids, but no mineralization occurred. This confirms that the early fluids were, although enriched in metals, not responsible for ore precipitation, most likely due to their high temperature and high salinities. One important factor controlling Zn-Pb mineralization was mixing with groundwater, which resulted in temperature decrease and dilution that significantly reduced the metal solubility, thereby promoting metal deposition. Another main driving force was the interaction with carbonate wall rock that buffered the acidity generated during the breakdown of Zn and (Pb)-Cl complexes and the precipitation of sulfides. Phase separation occurred in both the preore and the early part of the synore stages, but no evidence indicated that it caused metal deposition.The prograde minerals and retrograde minerals (including ore minerals) coexisting in the same samples could have been caused by two (or more) successive pulses of hydrothermal fluids released from residual melts of a progressively downward crystallizing magma. Each fluid produced a series of proximal high-temperature prograde to distal low-temperature assemblages, with the lower temperature assemblages of later fluids overprinting the higher temperature assemblages at most locations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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Summary Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≈ Rb ≈ (≈ Tl) ≈ Ba(≈ W) > Th > U ≈ Nb = Ta ≈ K > La > Ce ≈ Pb > Pr (≈ Mo) ≈ Sr > P ≈ Nd (> F) > Zr = Hf ≈ Sm > Eu ≈ Sn (≈ Sb) ≈ Ti > Dy ≈ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs. In detail, minor differences in element ratios correlate with the isotopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. Niobium data indicate that the mantle sources of MORB and OIB are not exact complementary reservoirs to the continental crust. Subduction of oceanic crust or separation of refractory eclogite material from the former oceanic crust into the lower mantle appears to be required. The negative europium anomalies observed in some EM-type OIBs and the systematics of their key element ratios suggest the addition of a small amount (⩽1% or less) of subducted sediment to their mantle sources. However, a general lack of a crustal signature in OIBs indicates that sediment recycling has not been an important process in the convecting mantle, at least not in more recent times (⩽2 Ga). Upward migration of silica-undersaturated melts from the low velocity zone can generate an enriched reservoir in the continental and oceanic lithospheric mantle. We propose that the HIMU type ( eg St Helena) OIB component can be generated in this way. This enriched mantle can be re-introduced into the convective mantle by thermal erosion of the continental lithosphere and by the recycling of the enriched oceanic lithosphere back into the mantle.
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The effects of the chemistry of ore-forming fluids on the sulfur and carbon isotopic compositions of hydrothermal minerals are quantitatively evaluated from available thermochemical data and isotopic fractionation factors.The isotopic composition of both sulfur and carbon in hydrothermal minerals is strongly controlled by the f (sub O 2 ) and pH values of hydrothermal fluids as well as by the temperature and the isotopic composition of sulfur and carbon in the fluids (delta S 34 (sub Sigma S) and delta C 13 (sub Sigma C) values). For example, at 250 degrees C and within geologically important f (sub O 2 ) -pH regions, an increase in f (sub O 2 ) value by 1 log unit or in pH by 1 unit can cause a decrease in delta S 34 values of sulfur-bearing minerals by as much as 20 per mil. An increase in f (sub O 2 ) by 1 log unit or in pH by 2 units can cause a decrease of about 30 per mil in delta C 13 values of carbon-bearing minerals. Large variation in the delta S 34 values or in the delta C 13 values of hydrothermal minerals, which often have been interpreted as an indication of biogenic sulfur or carbon, could also be caused by slight variation in the f (sub O 2 ) and/or pH of ore-forming fluids during ore deposition.The concentrations in an ore solution of sulfur (or f (sub S 2 ) ) and of carbon (or f (sub CO 2 ) ) place limits on possible delta S 34 and delta C 13 values for hydrothermal minerals. Sulfur-bearing minerals and carbon-bearing minerals precipitating from sulfur- and carbon-rich solutions can have wider ranges of delta S 34 and delta C 13 values than those minerals precipitating from sulfur- and carbon-poor solutions.Sulfide minerals which precipitated in equilibrium with magnetite, hematite, or sulfate minerals, and carbonate minerals which precipitated in equilibrium with graphite, could exhibit isotopic compositions markedly different from those of the depositing fluids. Therefore, sulfides with delta S 34 values near zero per mil or carbonates with delta C 13 values near -6 per mil do not necessarily indicate a magmatic origin for the sulfur or the carbon.The mode of variation on the delta S 34 values of sulfide minerals and in the delta C 13 values of carbonate minerals in a given deposit may indicate the relative oxidation states of ore-forming fluids: variable delta S 34 + uniform delta C 13 values may suggest that the minerals were precipitated under relatively high f (sub O 2 ) conditions; uniform delta S 34 + uniform delta C 13 values, under intermediate f (sub O 2 ) conditions; and uniform delta S 34 + variable delta C 31 values suggesting deposition under relatively low f (sub O 2 ) conditions.Sulfur and carbon isotopic data, combined with geological and mineralogical data of ore deposits, may define the physico-chemical parameters (T, f (sub O 2 ) , f (sub S 2 ) , f (sub CO 2 ) , m (sub Sigma S) , m (sub Sigma C) ) and the origin (delta S 34 (sub Sigma S) and delta C 13 (sub Sigma C) values) of ore-forming fluids as well as the mechanisms of ore deposition.
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