The gold content of volcanogenic massive sulfide deposits

Volcanogenic massive sulfide deposits contain variable amounts of gold, both in terms of average grade and total gold content, with some VMS deposits hosting world-class gold mines with more than 100?t Au. Previous studies have identified gold-rich VMS as having an average gold grade, expressed in g/t, exceeding the total abundance of base metals, expressed in wt.%. However, statistically meaningful criteria for the identification of truly anomalous deposits have not been established. This paper presents a more extensive analysis of gold grades and tonnages of 513 VMS deposits worldwide, revealing a number of important features in the distribution of the data. A large proportion of deposits are characterized by a relatively low gold grade (<2?g/t), with a gradual decrease in frequency towards maximum gold grades, defining a log-normal distribution. In the analysis presented in this paper, the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of VMS deposits based on gold grade, especially when comparing deposits within individual belts and districts. The geometric mean gold grade of 513 VMS deposits worldwide is 0.76?g/t; the geometric standard deviation is +2.70?g/t Au. In this analysis, deposits with more than 3.46?g/t Au (geometric mean plus one geometric standard deviation) are considered auriferous. The geometric mean gold content is 4.7?t Au, with a geometric standard deviation of +26.3?t Au. Deposits containing 31?t Au or more (geometric mean plus one geometric standard deviation) are also considered to be anomalous in terms of gold content, irrespective of the gold grade. Deposits with more than 3.46?g/t Au and 31?t Au are considered gold-rich VMS. A large proportion of the total gold hosted in VMS worldwide is found in a relatively small number of such deposits. The identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in VMS. At the district scale, the gold-rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes. The gold-rich VMS are commonly associated with transitional to calc-alkaline intermediate to felsic volcanic rocks, which may reflect a particularly fertile geodynamic setting and/or timing (e.g., early arc rifting or rifting front). At the deposit scale, uncommon alteration assemblages (e.g., advanced argillic, aluminous, strongly siliceous, or potassium feldspar alteration) and trace element signatures may be recognized (e.g., Au?CAg?CAs?CSb ± Bi?CHg?CTe), suggesting a direct magmatic input in some systems.     

Geological setting of the Rapu Rapu gold-rich volcanogenic massive sulfide deposits,Albay Province,Philippines

Gold-rich Fe–Cu–Zn volcanogenic massive sulfide deposits occur within strata of probable Jurassic age on Rapu Rapu Island in Albay Province, Philippines. Massive sulfides at the Ungay Malobago and Hixbar deposits are spatially associated with dacitic volcanic rocks within a highly-deformed sequence of mafic volcanic and quartzofeldspathic sedimentary rocks. The massive sulfide deposits formed at the stratigraphic contact between footwall dacites and hangingwall mafic volcanic and quartzofeldspathic rocks. The deposits and their host strata have undergone regional metamorphism with strong penetrative deformation. Metamorphic mineral assemblages and textural evidence suggest that peak metamorphism was upper-greenschist to lower-amphibolite grade and syn-D₁ deformation. Based on the age of regional metamorphism, deformation is inferred to be mid-Tertiary in age. Deformation at Rapu Rapu resulted in reorientation of the strata into a broad antiform with strong shallow-plunging elongation fabrics, overturning of the volcanic sequence that hosts the Ungay Malobago deposit, and complex folding of the mineralized zones. The present highly linear form of the Ungay Malobago deposit is mainly a product of this ductile strain.Immobile element ratios for a given lithology generally remain constant in saprolitic samples, and thus provide an effective identification tool even in strongly weathered rocks. Lithogeochemical data define a bimodal volcanic suite that is comparable to bimodal assemblages that occur in several modern back-arc basins in the southwestern Pacific Ocean, including those behind the Vanuatu and the New Britain arcs. On Rapu Rapu, the dacitic rocks are enriched in light REE and have high Zr/Y ratios, which indicates a calc–alkaline affinity and suggests a mature island-arc setting. The quartzofeldspathic sedimentary rocks are more widespread than the dacites and have notably lower Zr/Y ratios; they may have been derived from erosion of a distant volcanic arc. The mafic volcanic rocks are dominantly low-K arc tholeiites of basaltic to andesitic composition, but with modest enrichment in the light REE; comparable rocks can be found in the Vanuatu and New Britain back-arc basins.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00126-003-0349-0An erratum to this article can be found at Editorial handling: O. Christensen     

Cyclic ore formation of some volcanogenic massive sulfide deposits in the skellefte district,Sweden

The Näsliden and Rävliden deposits in the Skellefte field consist of stratiform massive sulfide ores associated with submarine volcanic and clastic rocks. The ores are pretectonic. Consequently, the orebodies are considered to have formed syngenetically with deposition of the host rocks. Banding and interlayering with host sediments are common features. Cu : Zn and Zn : Pb ratios of the ores show stratigraphically and laterally defined trends. Cu : Pb : Zn ratios correspond with those found in other deposits of volcanogenic origin. Nonstratiform breccia Cu mineralizations occur directly under the massive stratiform ores in the footwall rocks where hydrothermal alteration is strongest. Ore formation took place intermittently resulting in clusters of ore systems occurring at slightly different stratigraphical levels within each deposit.     

Formation of volcanogenic massive sulfide deposits: The Kuroko perspective

The main objective of this paper is to identify the geochemical, hydrological, igneous and tectonic processes that led to the variations in the physical (size, geometry) and chemical (mineralogy, metal ratios and zoning) characteristics of volcanogenic massive sulfide deposits with respect to space (from a scale of mining district size area to a global scale) and time (from a < 10 000 year time scale to a geologic time scale).All volcanogenic massive sulfide deposits (VMSDs) appear to have formed in extensional tectonic settings, such as at mid ocean spreading centers, backarc spreading centers, and intracontinental rifts (and failed rifts). All VMSDs appear to have formed in submarine depressions by seawater that became ore-forming fluids through interactions with the heated upper crustal rocks. Submarine depressions, especially those created by submarine caldera formation and/or by large-scale tectonic activities (e.g., rifting), become most favorable sites for the formation of large VMSDs because of hydrological, physical and chemical reasons.The fundamental processes leading to the formation of VMSDs include the following six processes:

1. (1) Intrusion of a heat source (typically a 10³ km size pluton) into an oceanic crust or a submarine continental crust causes deep convective circulation of seawater around the pluton. The radius of a circulation cell is typically 5 km. The temperature of fluids that discharge on the seafloor increases with time from the ambient temperature to a typical maximum of 350°C, and then decreases gradually to the ambient temperatures in a time scale of 100 to 10 000 years. The majority of sulfide and sulfate mineralization occurs during the waxing stage of hydrothermal activity.

2. (2) Reactions between low temperature (T < 150°C) country rocks with downward percolating seawater cause to precipitate seawater SO²⁻₄ as disseminated gypsum and anhydrite in the country rocks.

3. (3) Reactions of the “modified” seawater with higher-temperature rocks at depths during the waxing stage cause the transformation of the “seawater” to metal- and H₂S-rich ore-forming fluids. The metals and sulfide sulfur are leached from the county rocks; the previously formed gypsum and anhydrite are reduced by Fe²⁺-bearing minerals and organic matter, providing additional H₂S. The mass of high temperature rocks that provide the metals and reduced sulfur is typically 10¹¹ tons ( 40 km³ in volume). The roles of magmatic fluids or gases are minor in most massive sulfide systems, except for SO₂ to produce acid-type alteration in some systems.

4. (4) Reactions between the ore-forming fluids and cooler rocks in the discharge zone cause alteration of rocks and precipitation of some ore minerals in the stockwork ores.

5. (5) Mixing of the ore-forming fluids with local seawater within unconsolidated sediments and/or on the seafloor causes precipitation of “primitive ores” with the black ore mineralogy (sphalerite + galena + pyrite + barite + anhydrite).

6. (6) Reactions between the “primitive ores” with later and hotter hydrothermal fluids cause transformation of “primitive ores” to “matured ores” that are enriched in chalcopyrite and pyrite.

Variations in the mineralogical and elemental characteristics, the geometry, and the size of submarine hydrothermal deposits are controlled by the following four parameters:

1. (A) The chemical and physical characteristics of seawater (composition, temperature, density), which depend largely on the geographical settings (e.g., equatorial evaporating basins),

2. (B) The chemical and physical characteristics of the plumbing system (lithology, fractures),

3. (C) The thermal structure of the plumbing system, which is determined largely by the ambient geothermal gradient, and the size and temperature of the intrusive, and

4. (D) The physical characteristics of the seafloor (depth, basin topography).

For example, the submarine hydrothermal deposits developed in basaltic plumbing systems are generally poor in Pb and Ba compared to those developed in felsic plumbing systems. The lower temperature systems are generally poorer in sulfides, but richer in iron oxides and sulfates. The higher temperature and larger hydrothermal systems tend to produce chalcopyrite and pyrite rich ores. Contrasts in the metal ratios between the Noranda-type Archean VMSDs and the younger VMSDs reflect the differences in the geothermal gradient of the plumbing systems. The submarine hydrothermal deposits developed in the near equatorial regions tend to form large continuous bedded type ores because of the likeliness of creating large stratified basins.The basic processes of submarine hydrothermal mineralization have remained essentially the same throughout the geologic history, from at least 3.5 billion year ago to the present.     

What processes at mid-ocean ridges tell us about volcanogenic massive sulfide deposits

Episodic seafloor spreading, ridge topography, and fault movement at ridges find (more extreme) analogs in the arc and back-arc setting where the volcanogenic massive sulfide (VMS) deposits that we mine today were formed. The factors affecting sulfide accumulation efficiency and the extent to which sulfides are concentrated spatially are the same in both settings, however. The processes occurring at mid-ocean ridges therefore provide a useful insight into those producing VMS deposits in arcs and back-arcs. The critical observation investigated here is that all the heat introduced by seafloor spreading at mid-ocean ridges is carried out of the crust within a few hundred meters of the ridge axis by ??350°C hydrothermal fluids. The high-temperature ridge hydrothermal systems are tied to the presence of magma at the ridge axis and greatly reduce the size and control the shape of axial magma intrusions. The amount of heat introduced to each square kilometer of ocean crust during its formation can be calculated, and its removal by high-temperature convection allows calculation of the total base metal endowment of the ocean basins. Using reasonable metal deposition efficiencies, we conclude that the ocean floor is a giant VMS district with metal resources >600 times the total known VMS reserves on land and a copper resource which would last >6,000?years at current production rates.     

Geology and volcanic stratigraphy of the Canatuan and Malusok volcanogenic massive sulfide deposits,southwestern Mindanao,Philippines

The Canatuan and Malusok massive sulfide deposits are located near Siocon, Zamboanga del Norte, in southwestern Mindanao, Philippines. The Canatuan–Malusok area is underlain by the Jurassic–Cretaceous Tungauan schists, which form much of the Zamboanga Peninsula. The volcanic strata at Canatuan and Malusok can be traced for >7 km along strike and is host to at least three discrete massive sulfide bodies: Canatuan, Malusok and SE Malusok. Basal basaltic andesite volcanic rocks are generally chemically uniform and show only moderate alteration. The massive sulfide deposits occur in overlying rhyolitic to rhyodacitic volcanic rocks that are altered to a schistose assemblage of quartz, sericite, chlorite and pyrite. The alteration is texturally destructive but graded clastic beds are locally observed. Despite tropical saprolitic weathering, four lithogeochemical subunits of the felsic package are identified. Stratigraphic interleaving, however, has made correlation of these units over any significant distance difficult. The sulfide lenses are overlain by a few metres of felsic schists which locally contain manganese-bearing silicates and oxides that serve as a stratigraphic marker. Hangingwall andesitic volcaniclastic rocks are discontinuously preserved, although where present, they consist of regularly bedded mafic volcanic sandstones. The lateral continuity of a manganese-bearing marker and flanking felsic volcaniclastic intervals indicate that locally the volcanic strata form a homoclinal sequence. The Canatuan Au–Ag–Cu–Zn deposit consists of a gossan overlying a massive sulfide lens. The sulfides and gossan are flat lying and hosted within felsic volcanic rocks. The gossan is gold–silver-rich, and was formed by a combination of oxidation and volume collapse of the original sulfide lens. The sulfide minerals present below the current water table, are auriferous massive pyrite with base metal sulfides, with some supergene chalcocite. The transition from gossan to sulfides is very sharp, occurring at the water table. Massive sulfide deposits at Malusok are hosted in the same felsic sequence as Canatuan and they have similar base and precious metal contents. Only limited gossan has been found at Malusok. The bimodal nature of the volcanic rocks at Canatuan, together with their low HFSE contents, near-flat REE patterns and tholeiitic affinities, suggest that they formed in an intra-oceanic arc setting above a depleted mantle source. Mafic and felsic volcanic rocks of similar composition have been recovered from the Tonga-Kermadec and Izu-Bonin-Marianas island-arc systems in the western Pacific. Mafic rocks at Canatuan show no evidence for LILE enrichment that characterizes melts derived from metasomatized mantle under more mature arcs, suggesting that they are the product of a nascent, rather than a mature arc. There is no evidence from the REE, or other incompatible trace elements, that continental crust or evolved arc crust was involved in the generation of the Canatuan-Malusok volcanic rocks. Although it has been proposed that the Zamboanga metamorphic complex comprises microcontinental fragments of Eurasian affinity, our data do not support an evolved crustal setting for the Canatuan-Malusok volcanic rocks, which we suggest were derived from an intra-oceanic arc and subsequently accreted to the eastern Mindanao terrane.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00126-003-0350-7Editorial handling: R.R. Large     

A sulfur isotope study of volcanogenic massive sulfide deposits of the Eastern Black Sea province,Turkey

Kuroko-type massive sulfide deposits of the Eastern Black Sea province of Turkey are related to the Upper Cretaceous felsic lavas and pyroclastic rocks, and associated with clay and carbonate alteration zones in the footwall and hangingwall lithologies. A complete upward-vertical section of a typical orebody consists of a stringer-disseminated sulfide zone composed mainly of pyrite and chalcopyrite; a massive pyrite zone; a massive yellow ore consisting mainly of chalcopyrite and pyrite; a black ore made up mainly of galena and sphalerite with minor amounts of chalcopyrite, bornite, pyrite and various sulfosalts; and a barite zone. Most of the deposits in the province are associated with gypsum in the footwall or hangingwall. The paragenetic sequence in the massive ore is pyrite, sphalerite, chalcopyrite, bornite, galena and various sulfosalts, with some overlap between the mineral phases. Massive, stringer and disseminated sulfides from eight kuroko-type VMS deposits of the Eastern Black Sea province have a ³⁴S range of 0–7 per mil, consistent with the ³⁴S range of felsic igneous rocks. Sulfides in the massive ore at Madenköy (4.3–6.1 per mil) differ isotopically from sulfides in the stringer zone (6.3–7.2 per mil) suggesting a slightly increased input of H₂S derived from marine sulfate with time. Barite and coarse-grained gypsum have a ³⁴S range of 17.7–21.5 per mil, a few per mil higher than the ³⁴S value of contemporaneous seawater sulfate. The deposits may, therefore, have formed in restricted basins in which bacterial reduction of sulfate was taking place. Fine-grained, disseminated gypsum at Kutlular and Tunca has ³⁴S values (2.6–6.1 per mil) overlapping those of ore sulfides, indicating sulfide oxidation during waning stages of hydrothermal activity.     

Correlation between compositions of ore and host rocks in volcanogenic massive sulfide deposits of the Southern Urals

The geology and typification of volcanogenic massive sulfide (VMS) deposits of the Southern Urals are considered. The mineralogical-geochemical types of these deposits correlate with the composition of the underlying igneous rocks: Ni-Co-Cu deposits correlatedwith serpentinites (Ivanovka type); (Co)-Cu deposits, with basalts (Dombarovka type); Cu-Zn deposits, with basalt-rhyolite and basalt-andesite-rhyolite complexes (Ural type); and Au-Ba-Pb-Zn-Cu deposits, with basalt-andesite-rhyolite complexes with predominance of andesitic and felsic volcanics (Baimak type). The Ural-type deposits are subdivided into three subtypes: I, underlain by basalts (Zn-Cu deposits); II, hosted in felsic volcanic rocks of bimodal complexes (Cu-Zn deposits); and III, hosted in felsic volcanic rocks of continuously differentiated complexes (Zn-Cu deposits with Ba, Pb, and As). The above types and subtypes bearing local names are compared with global types of VMS deposits (MAR, Cyprus, Noranda, and Kuroko), to which they are close but not identical.     

Quartz precipitation and fluid inclusion characteristics in sub-seafloor hydrothermal systems associated with volcanogenic massive sulfide deposits

Results of a numerical modeling study of quartz dissolution and precipitation in a sub-seafloor hydrothermal system have been used to predict where in the system quartz could be deposited and potentially trap fluid inclusions. The spatial distribution of zones of quartz dissolution and precipitation is complex, owing to the fact that quartz solubility depends on many inter-related factors, including temperature, fluid salinity and fluid immiscibility, and is further complicated by the fact that quartz exhibits both prograde and retrograde solubility behavior, depending on the fluid temperature and salinity. Using the PVTX properties of H₂O-NaCl, the petrographic and microthermometric properties of fluid inclusions trapped at various locations within the hydrothermal system have been predicted. Vapor-rich inclusions are trapped as a result of the retrograde temperature-dependence of quartz solubility as the convecting fluid is heated in the vicinity of the magmatic heat source. Coexisting liquid-rich and vapor-rich inclusions are also trapped in this region when quartz precipitates as a result of fluid immiscibility that lowers the overall bulk quartz solubility in the system. Fluid inclusions trapped in the shallow subsurface near the seafloor vents and in the underlying stockwork are liquid-rich with homogenization temperatures of 200?C400°C and salinities close to that of seawater. Volcanogenic massive sulfide (VMS) deposits represent the uplifted and partially eroded remnants of fossil submarine hydrothermal systems, and the relationship between fluid-inclusion properties and location within the hydrothermal system described here can be used in exploration for VMS deposits to infer the direction towards potential massive sulfide ore.     

Mineralogy and geochemical behavior of trace elements of hydrothermal alteration types in the volcanogenic massive sulfide deposits,NE Turkey

Volcanogenic massive sulfide (VMS) deposits of the Eastern Pontides, Turkey, are hosted by the Maastrichtian–Eocene dacite and rhyodacite series, accompanied by lesser andesite and basalts, as well as their pyroclastic equivalents, with tholeiitic to calc-alkaline affinity. The ore mineral assemblages are chalcopyrite, sphalerite, galena, chalcocite, covellite, bornite, and tetrahedrite. Potassic-, phyllitic- (sericitic), argillic- (kaolinitic and smectitic), silicic-, propylitic- and hematitic-alteration is commonly associated with these deposits.HFSE, LILE, TRTE and REE contents show strong variability in different alteration types resulting from interaction with acid or alkaline fluids. Sample groups showed chondrite-normalized enrichment of LREE relative to HREE and sub-parallel trends, except for the hematitic- and phyllitic-alteration types. MREE are strongly depleted in the zones of most intense silicification and kaolinization. Most sample groups have strongly- to slightly-negative Eu anomalies, ranging from 0.35 to 0.88 (mean); hematitic- (1.45) and propylitic-altered rocks (1.11) have slightly- to moderately-positive anomalies. The negative Eu anomalies indicate the low temperatures of fluids (< 200 °C). In contrast, the positive Eu anomalies result from high-temperature hydrothermal conditions (> 200 °C). No Ce anomaly was observed, except for phyllitic alteration where a slight positive anomaly was noted. The chondrite-normalized trace and REE patterns of the altered rocks are similar to each other, suggesting that they were derived from a common felsic source. The alteration groups formed from acid, intermediate, and alkaline hydrothermal solutions. Some transition, base and precious metals and volatile elements were clearly enriched, especially in the hematitic-, silicic-, kaolinitic- and phyllitic-altered samples. The other elements exhibit different behaviors in different sample groups. REE behavior is relatively immobile in the silicic-, hematitic-, kaolinitic- and partially in moderately- and propylitic-altered rocks, based on mass-balance calculations. LILE and HFSE appear mobile in the altered sample groups, except in the propylitic-altered rocks. TRTE behave as relatively immobile in most of samples, except in some of the silicic- and phyllitic-altered rocks, and especially in the hematitic-altered samples. HFSE, most of the transition (W, Mo, Cu, and Sb) and some other trace elements (Pb, As, Hg, Bi, Se and Tl), are enriched in the hematitic-altered samples and in the some silicic-altered samples. The highest As, Bi, Mo, Se and Hg concentrations in the hematite-altered samples can be used to distinguish other alteration types and may be a useful indicator in a prospect-scale base metal exploration.     

Effects of intrusions on grades and contents of gold and other metals in volcanogenic massive sulfide deposits

The reason some VMS deposits contain more gold or other metals than others might be due to the influence of intrusions. A new approach examining this possibility is based on examining the information about many VMS deposits to test statistically if those with associated intrusions have significantly different grades or amounts of metals. A set of 632 VMS deposits with reported grades, tonnages, and information about the observed presence or absence of subvolcanic or plutonic intrusive bodies emplaced at or after VMS mineralization is statistically analyzed.Deposits with syn-mineralization or post-mineralization intrusions nearby have higher tonnages than deposits without reported intrusions, but the differences are not statistically significant. When both kinds of intrusions are reported, VMS deposit sizes are significantly higher than in the deposits without any intrusions. Gold, silver, zinc, lead, and copper average grades are not significantly different in the VMS deposits with nearby intrusions compared to deposits without regardless of relative age of intrusive. Only zinc and copper contents are significantly higher in VMS deposits with both kinds of intrusive reported. These differences in overall metal content are due to significantly larger deposit sizes of VMS deposits where both intrusive kinds are observed and reported, rather than any difference in metal grades.     

对北祁连山火山喷溢型贱金属硫化物矿床区域成矿的探讨

北祁连山加里东优地槽褶皱山系由厚层海相火山岩系和沉积建造组成。其内已经发现数十个火山岩型块状硫化物矿床,可划分为三种类型,即Cu(Fe)型(或红沟型)、Cu-Zn型(或蛇绿岩套型)及Cu-Pb-Zn型(或白艰厂型)。不同类型矿床分别形成于不同地质环境且趋向于在特定时-空范围产出:Cu(Fe)型矿床集中分布在南部达坂山成矿带,成矿与晚奥陶世双峰态细碧角斑岩系有关,矿床形成于弧间或弧后盆地环境;Cu-Zn型矿床分布在北部九个泉—错沟、猪嘴哑吧一银硐沟矿带,与早—中奥陶世蛇绿岩套有关,矿床形成于大洋扩张构造环境;Cu-Pb-Zn型矿床集中分布在祁连、白银成矿区,矿床产出与中寒武世中酸性石英角斑凝灰岩有关,形成于优地槽发展早期阶段裂谷岛弧环境。     

Naturally acidic and metalliferous waters at unmined volcanogenic massive sulfide deposits in the Bonnifield mining district, Alaska Range, east-central Alaska

The Bonnifield district hosts 26 tmmined volcanogenic massive sulfide （VMS） occurrences. Environmental geochemical samples of water and stream sediment were collected at several occurrences, concentrating on the two best-exposed and largest deposits, Red Mountain （RM） and Sheep Creek （SC）. Limited samples were also collected at the poorly exposed WTF deposit. The deposits are Late Devonian to Early Mississippian, and are hosted by felsic metavolcanic and carbonaceous schist members of the Totatlanika Schist or Keevy Peak Fm. Spring and stream waters at RM and SC have pH values commonly 〈3.5 （as low as 2.4 at RM and 2.5 at SC）, high conductivity （up to 11000 μS/cm）, and very high （Is to 100s mg/L） dissolved contents of Al, Cd, Co, Cu, Fe, Ni, and Pb. Waters at RM are characterized by extremely high REE contents （summed REE median 3200 μg/L, n=33）. At both RM and SC, pyrite oxidation and dissolution produce low pH waters that interact with and dissolve bedrock minerals, resulting in acidic, metal-laden, naturally degraded streams that are mostly devoid of aquatic life. Ferricrete is common. In contrast, WTF barely produces a surficial environmental footprint, mostly due to topography and relief. RM and SC are well exposed in the areas of relatively high relief, and both exhibit extensive areas of quartz-sericite-pyrite-alteration. While WTF shares many of the same deposit-and alteration characteristics, it is concealed by tundra in a large, nearly flat area. Surface water at WTF is absent and outcrops are sparse. Even though WTF is roughly the same size as Red Mountain （both around 3 million tonnes） and has similar base- and precious-metal grades, the surficial geochemical manifestation of WTF is minimal. However, exposure through mining of the altered, mineralized rock at WTF potentially could initiate the same processes of pyrite oxidation, acid generation, and mineral dissolution that are observed naturally at RM and SC.     

新疆阿舍勒块状硫化物矿床成矿特征及形成环境

阿舍勒块状硫化物矿床位于阿尔泰华力西地槽系南缘。容矿岩石为中、下泥盆统富钠的火山岩系，为双峰式火山岩组合，系弧后扩张背景下的产物。矿床具双层结构，并具明显的垂向分带和侧向分带。矿体下盘火山岩发生了强烈地蚀变作用，形成由石英＋绢云母＋绿泥石±黄铁矿组成的半整合蚀变带。同位素研究表明，硫由海水硫酸盐和岩石中硫化物所提供，铅具深源的特征。通过对比，认为阿舍勒矿床与矿区阿尔泰的块状硫化物矿床相似     

青海南部熔积岩的发现:对寻找VMS型矿床的重要启示

熔积岩指的是侵入、混合到未固结或弱固结的湿沉积物中的熔浆分解、原位形成的一类特殊岩石。正确地认识该类岩石,有利于增进人们对岩浆-水(沉积物)相互作用过程的理解,恢复古环境。在青海南部沱沱河地区发现了一套角砾为撕片状、锯齿状及浑圆状的安山岩,胶结物为铁硅质组合的特殊熔积岩。研究表明,该熔积岩的角砾为岩浆遇水后快速淬火、裂解的产物,铁硅质组合为海底喷气沉积形成的含铁建造;且安山岩与含铁建造发生混合时,含铁建造尚未固结。该套熔积岩的发现,改变了长期以来对开心岭铁矿为火山热液交代安山岩而形成的认识,对于在矿区寻找VMS型矿床、区域内寻找海底热水喷流沉积型矿床具有重要的启示意义。     

Metamorphism of volcanogenic massive sulphide deposits in the Urals. Ore geology

The Urals VMS province comprises a broad spectrum of variably metamorphosed deposits, from unmetamorphosed to those without any primary ore textures, which are the results of high-grade metamorphic processes. Contact metamorphism near large granite and granodiorite plutons caused the most significant changes of ores, with coarse-grained to pegmatoidal ores with magnetite closest to its contact with the intrusion, followed by pyrrhotite-enriched copper ores, and more distal zinc (± Pb ± Ag) mineralisation. Koktau, Tarnyer and Vesenneye deposits are metamorphosed to the hornblende-hornfels and pyroxene-hornfels facies (t = 400–800 °C, P = 1–6 kbar). Metamorphism of Tash-Yar, Dzhusinskoe and Krasnogvardeiskoe deposits corresponds to the greenschist and albite-epidote-hornfels facies (t = 250–450 °C, P = 1–4 kbar).The regional metamorphism of VMS ores varies from prehnite-pumpellyite facies (t = 150–300 °C, P = 0.5–4 kbar) in the South Urals to the epidote-amphibolite and amphibolite facies (t = 400–600 °C (up to 700 °C), P = 1–6 kbar) in the Karabash area in the Middle Urals. In the Magnitogorsk zone, the metamorphism of host rocks and VMS bodies increases to the north, reaching its peak near the Ufa promontory of the East European platform. With increased metamorphism, the morphology of orebodies evolves from gently dipping thick lenses (Alexandrinskoe and Uzelga fields), to subvertical and folded (Uchaly and Novo-Uchaly deposits) and pseudomonoclinal steeply-dipping vein-like bodies (Karabash district).The massive sulphide transformation in PTX-gradient fields led to partial redistribution of ore material. An enrichment in Cu, Zn, Ag and Au, ± Pb occur in the uppermost parts of large steeply-dipping massive sulphide lenses in wide tectonic zones (e.g., Gai deposit) or as gold-sulphide disseminated bodies near large metamorphosed VMS lenses, distal to a granite pluton (Tarnyer deposit). Partial melting probably occurred in some highly metamorphosed deposits (Tarnyer, Koktau and Mauk). Redeposition of base metals sulphides (chalcopyrite, tennantite, sphalerite, ± bornite, galena), as well as the presence of “visible” gold and tellurides, took place during retrograde metamorphism, which produced a transfer of ore matter towards the low stress areas, such as the outer parts of shear zones, the uppermost parts of steeply-dipping ore lenses, pressure shadows, hinge zones of small folds, and small extension fractures (i.e., Alpine-type veins) in deformed ore body or its immediate surroundings.