Occurrences and distribution of “invisible” precious metals in sulfide deposits from the Edmond hydrothermal field,Central Indian Ridge

Here, we report the first documented occurrences of “invisible” gold and silver in seafloor sulfide deposits from an active hydrothermal system on the Central Indian Ridge. A detailed mineralogical and geochemical study of polymetallic sulfides from the Edmond vent field was conducted in order to identify controls on the distribution of precious metals. Bulk samples (N = 18) contain up to 18.7 ppm Au and 1450 ppm Ag, with average concentrations of 2.3 ppm Au and 218.9 ppm Ag. Among them, several Zn-rich chimney fragments and anhydrite-dominated ore samples have higher contents of precious metals than Fe-Cu-rich massive sulfides and silica-rich hydrothermal precipitates. Native gold grains are mainly associated with sphalerite, anhydrite, barite and Fe-oxyhydroxides. Abundant submicroscopic Au-Ag alloys tend to occur along grain boundaries between Cu-Fe sulfides and tennantite, or close to the rims of Fe-poor sphalerite. In contrast to primary electrum with high Ag/Au ratios, the absence of detectable silver in high-purity gold indicates that secondary Au enrichment has probably occurred after a direct co-precipitation with Zn-rich mineral assemblages upon cooling and mixing of vent fluids with cold seawater. A suite of late-stage Ag-rich phases, including argentotennantite, pearceite and acanthite, occur as crack-filling veinlets and patches in low-temperature fahlores, or as tiny inclusions enclosed by pyrite, chalcopyrite and colloform sphalerite. By using HRTEM combined with HAADF-STEM imaging, we have found out that silver is also present in significant quantities as discrete colloidal nanoparticles in tennantite. Minor native copper is closely associated with altered chalcopyrite, sphalerite and covellite, exhibiting signs of dissolution, recrystallization and reprecipitation. Extensive hydrothermal reworking resulted from a long history of high-temperature venting in this field, together with post-depositional supergene replacement processes (involving oxidation, leaching or coupled dissolution-reprecipitation mechanisms facilitated by a permeable porosity generated in primary Cu-Fe sulfides) are considered to be important for the remobilization and local reconcentration of early-formed precious metals, and may have been responsible for the formation of relatively coarse-grained native gold or silver within recrystallized massive sulfides and chimney debris.     

Trace metal nanoparticles in pyrite

Hydrothermal pyrite contains significant amounts of minor and trace elements including As, Pb, Sb, Bi, Cu, Co, Ni, Zn, Au, Ag, Se and Te, which can be incorporated into nanoparticles (NPs). NP-bearing pyrite is most common in hydrothermal ore deposits that contain a wide range of trace elements, especially deposits that formed at low temperatures. In this study, we have characterized the chemical composition and structure of these NPs and their host pyrite with high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), analytical electron microscopy (AEM), and electron microprobe analysis (EMPA). Pyrite containing the NPs comes from two types of common low-temperature deposits, Carlin-type (Lone Tree, Screamer, Deep Star (Nevada, USA)), and epithermal (Pueblo Viejo (Dominican Republic) and Porgera (Papua New-Guinea)).EMPA analyses of the pyrite show maximum concentrations of As (11.2), Ni (3.04), Cu (2.99), Sb (2.24), Pb (0.99), Co (0.58), Se (0.2), Au (0.19), Hg (0.19), Ag (0.16), Zn (0.04), and Te (0.04) (in wt.%). Three types of pyrite have been investigated: “pure” or “barren” pyrite, Cu-rich pyrite and As-rich pyrite. Arsenic in pyrite from Carlin-type deposits and the Porgera epithermal deposit is negatively correlated with S, whereas some (colloform) pyrite from Pueblo Viejo shows a negative correlation between As + Cu and Fe. HRTEM observations and SAED patterns confirm that almost all NPs are crystalline and that their size varies from 5 to 100 nm (except for NPs of galena, which have diameters of up to 500 nm). NPs can be divided into three groups on the basis of their chemical composition: (i) native metals: Au, Ag, Ag–Au (electrum); (ii) sulfides and sulfosalts: PbS (galena), HgS (cinnabar), Pb–Sb–S, Ag–Pb–S, Pb–Ag–Sb–S, Pb–Sb–Bi–Ag–Te–S, Pb–Te–Sb–Au–Ag–Bi–S, Cu–Fe–S NPs, and Au–Ag–As–Ni–S; and (iii) Fe-bearing NPs: Fe–As–Ag–Ni–S, Fe–As–Sb–Pb–Ni–Au–S, all of which are in a matrix of distorted and polycrystalline pyrite. TEM-EDX spectra collected from the NPs and pyrite matrix document preferential partitioning of trace metals including Pb, Bi, Sb, Au, Ag, Ni, Te, and As into the NPs. The NPs formed due to exsolution from the pyrite matrix, most commonly for NPs less than 10 nm in size, and direct precipitation from the hydrothermal fluid and deposition into the growing pyrite, most commonly for those > 20 nm in size. NPs containing numerous heavy metals are likely to be found in pyrite and/or other sulfides in various hydrothermal, diagenetic and groundwater systems dominated by reducing conditions.     

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.     

Massive sulfides of Mount Jourdanne along the super-slow spreading Southwest Indian Ridge and their genesis

Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35 wt.%) and are characterized by high concentrations of Pb (≤ 3.5 wt.%), As (≤ 1.1 wt.%), Ag (≤ 0.12 wt.%), Au (≤ 11 ppm), Sb (≤ 967 ppm), and Cd (≤ 0.2 wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40 cm high; ~ 10 cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300 °C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 °C. The late-stage mineralization (below 200 °C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.     

Indium in cassiterite and ores of tin deposits

The results obtained with LA-ICP-MS by less abundant lighter ¹¹³In isotope and EPMA show that in cassiterite of cassiterite–quartz veins the indium contents do not exceed 160 ppm, while cassiterite from Sn–sulfide veins is characterized by higher indium contents from 40 to 485 ppm; sulfides of Sn–sulfide veins unlike sulfides of cassiterite–quartz veins also have the highest indium contents: Fe-sphalerite (100–25,000 ppm), chalcopyrite (up to 1000 ppm), and stannite (up to 60,000 ppm). Indium contents in the Sn–sulfide ore of the Tigrinoe and Pravourmiiskoe deposits obtained using SR-XRF, ICP-MS and atomic absorption methods range from 10 to 433 ppm with average values of 56–65 ppm. Indium-rich Sn–sulfide mineralization in five large Sn–Ag ore districts of the Far East Russia (Khingansky, Badzhalsky, Komsomolsky, Arminsky, Kavalerovsky) provides the impetus for further exploration of deposits with Sn–sulfide mineralization as the most promising indium resources in Russia. Empirical observations from geology and geochronology of cassiterite–quartz and Sn–sulfide mineralization show that the combined contribution from granite and alkaline–subalkaline mafic sources and multistage ore-forming processes doubled indium resources of deposits being the main factors in the formation of high grade indium mineralization.     

柿竹园和香炉山W多金属矿床中硫化物微量元素特征:来自原位LA-ICP-MS分析

华南包括两个世界级的W矿带,分别是南岭和江南造山带W成矿带。柿竹园W多金属矿床位于南岭地区,香炉山W矿床位于江南造山带东北部。两个矽卡岩W矿床都发育硫化物成矿阶段。但硫化物和成矿元素组成存在显著的差异。前者由含Pb、Zn、Ag硫化物和黝铜矿、银黝铜矿、含Ag斜方辉铅铋矿和铁硫锡铜矿硫盐组成;后者主要为磁黄铁矿。柿竹园远接触带Pb-Zn-Ag矿脉中硫化物(闪锌矿、黄铜矿、方铅矿和磁黄铁矿)较富集B、Mn、Cr、Sb、Sn和Hg,香炉山似层状矽卡岩和硫化物-白钨矿矿体中硫化物(磁黄铁矿、黄铜矿和闪锌矿)较富集W、Se和Bi。两个矿床中黄铜矿、闪锌矿和方铅矿较富集Ag,黄铜矿、闪锌矿富集In和Sn,闪锌矿还富集Cd。两个矿床中的硫化物微量元素分析表明与矽卡岩W矿成矿相关的硫化物可载有多种微量元素。这些元素参与到硫化物中程度由多种因素控制。具体如下,硫化物中B含量高低与成矿相关岩体中B含量相关;在相对高温和还原条件下,硫化物中W含量较高;闪锌矿中Mn和Cd与Zn发生取代作用; Cr可以一定程度进入到硫化物中,并受成矿流体中Cr含量影响; Se与S发生了一定程度的取代进入硫化物,并受流体中它的含量控制; Bi在闪锌矿与黄铜矿易形成固溶体;硫化物中Sb含量受初始流体中它的含量影响,方铅矿中易包裹一定的辉锑矿(Sb_2S_3)或含Sb的硫盐矿物; Ag是否形成独立的矿物相和进入哪些硫化物中,取决于流体中Ag的初始含量和硫化物的沉淀次序;硫化物中Hg的含量受温度影响。     

Variation of copper isotopes in chalcopyrite from Dabu porphyry Cu-Mo deposit in Tibet and implications for mineral exploration

The study presents copper (Cu) isotope data of mineral separates of chalcopyrite from four drill core samples in the Miocene Dabu porphyry Cu-Mo deposit formed in a post-collisional setting in the Gangdese porphyry copper belt, southern Tibet. Copper isotope values in hypogene chalcopyrite range from –1.48‰ to +1.12‰, displaying a large variation of up to 2.60‰, which demonstrates Cu isotope fractionation at high-temperature during hydrothermal evolution. The majority of measured chalcopyrite isotopic compositions show a gradual increasing trend from –1.48‰ to +1.12‰ with the increase of drilling depth from 130m to 483m, as the alteration assemblages change from potassic to phyllic. Similarly, the other δ⁶⁵Cu values (δ⁶⁵Cu = ((⁶⁵Cu/⁶³Cu)_sample/(⁶⁵Cu/⁶³Cu)_standard − 1) × 1000) of the chalcopyrite show a gradual increasing trend from −1.48‰ to +0.59‰ with the decrease of drilling depth from 130 m to 57 m, as the alteration assemblages change from potassic, phyllic, through argillic to relatively fresh. These observations suggest a genetic link between Cu isotope variation and silicate alteration assemblages formed at different temperatures, indicative of a Rayleigh precipitation process resulting in the large variation of δ⁶⁵Cu values at Dabu. In general, samples closest to the center of hydrothermal system dominated by high-temperature potassic alteration are isotopically lighter, whereas samples dominated by low-temperature phyllic alteration peripheral to the center are isotopically heavier. The predicted flow pathways of hydrothermal fluids are from No. 0 to No. 3 exploration line, and the lightest δ⁶⁵Cu values are the most proximal to the hydrothermal source. Finally, we propose that the northwest side of the No. 0 exploration line has high potential for hosting undiscovered orebodies. The pattern of Cu isotope variation in conjunction with the features of silicate alteration in porphyry system can be used to trace the hydrothermal flow direction and to guide mineral exploration.     

Actively forming Kuroko-type volcanic-hosted massive sulfide (VHMS) mineralization at Iheya North,Okinawa Trough,Japan

Modern seafloor hydrothermal systems provide important insights into the formation and discovery of ancient volcanic-hosted massive sulfide (VHMS) deposits. In 2010, Integrated Ocean Drilling Program (IODP) Expedition 331 drilled five sites in the Iheya North hydrothermal field in the middle Okinawa Trough back-arc basin, Japan. Hydrothermal alteration and sulfide mineralization is hosted in a geologically complex, mixed sequence of coarse pumiceous volcaniclastic and fine hemipelagic sediments, overlying a dacitic to rhyolitic volcanic substrate. At site C0016, located adjacent to the foot of the actively venting North Big Chimney massive sulfide mound, massive sphalerite-(pyrite-chalcopyrite ± galena)-rich sulfides were intersected (to 30.2% Zn, 12.3% Pb, 2.68% Cu, 33.1 ppm Ag and 0.07 ppm Au) that strongly resemble the black ore of the Miocene-age Kuroko deposits of Japan. Sulfide mineralization shows clear evidence of formation through a combination of surface detrital and subsurface chemical processes, with at least some sphalerite precipitating into void space in the rock. Volcanic rocks beneath massive sulfides exhibit quartz-muscovite/illite and quartz-Mg-chlorite alteration reminiscent of VHMS proximal footwall alteration associated with Kuroko-type deposits, characterized by increasing MgO, Fe/Zn and Cu/Zn with depth. Recovered felsic footwall rocks are of FII to FIII affinity with well-developed negative Eu anomalies, consistent with VHMS-hosting felsic rocks in Phanerozoic ensialic arc/back-arc settings worldwide.Site C0013, ∼100 m east of North Big Chimney, represents a likely location of recent high temperature discharge, preserved as surficial coarse-grained sulfidic sediments (43.2% Zn, 4.4% Pb, 5.4% Cu, 42 ppm Ag and 0.02 ppm Au) containing high concentrations of As, Cd, Mo, Sb, and W. Near surface hydrothermal alteration is dominated by kaolinite and muscovite with locally abundant native sulfur, indicative of acidic hydrothermal fluids. Alteration grades to Mg-chlorite dominated assemblages at depths of >5 mbsf (metres below sea floor). Late coarse-grained anhydrite veining overprints earlier alteration and is interpreted to have precipitated from down welling seawater as hydrothermal activity waned. At site C0014, ∼350 m farther east, hydrothermal assemblages are characterized by illite/montmorillonite, with Mg-chlorite present at depths below ∼30 mbsf. Recovered lithologies from distal, recharge site C0017 are unaltered, with low MgO, Fe₂O₃ and base metal concentrations.Mineralization and alteration assemblages are consistent with the Iheya North system representing a modern analogue for Kuroko-type VHMS mineralization. Fluid flow is focussed laterally along pumiceous volcaniclastic strata (compartmentalized between impermeable hemipelagic sediments), and vertically along faults. The abundance of Fe-poor sphalerite and Mg-rich chlorite (clinochlore/penninite) is consistent with the lower Fe budget, temperature and higher oxidation state of felsic volcanic-hosted hydrothermal systems worldwide compared to Mid Ocean Ridge black smoker systems.     

The muscovite granites: Parental rocks to the Nanling Range tungsten mineralization in South China

Muscovite granites (MGs) in the Nanling Range (South China) occur as satellite intrusions within or surrounding batholitic biotite monzogranites (BMs). The MGs are massive and fine-grained with a porphyritic texture, and contain quartz, K-feldspar and albite in nearly equal portions. The accessory minerals in the MGs include alumina-rich minerals (e.g., Mn- and Fe-rich garnet, andalusite, topaz, and tourmaline), anatase, rutile, wolframite, cassiterite, xenotime, chalcopyrite, molybdenite, and volatile-rich minerals (e.g., microlite, topaz, tourmaline, fluorite, and calcite). Compared with the BMs, the MGs are geochemically enriched in major elements of Si, K, and Na, and incompatible trace elements of Rb, Cs, Y, U, Nb, Ta, W, Sn, Pb, Bi, Li, and Be, and depleted in major elements of Fe, Mg, Ca, Ti, and P, and compatible trace elements of Ba, Sr, Co, Ni, Cr, Cd, V as well as Zr and Hf. The chondrite-normalized REE patterns of the MGs are flat with large negative Eu anomalies. The mineralogical and geochemical features of the MGs indicate that they crystallized from highly fractionated granitic magmas. Zircons separated from the MG samples, which were collected from six different tungsten deposits, show characters of hydrothermal origin according to their morphologies, chemical compositions and inclusions. In-situ U–Pb dating of the zircons yields a weighted mean ²⁰⁶Pb/²³⁸U age of 133.4 ± 1.0 Ma. This age is similar to the mean age of the zircons from wolframite-bearing quartz veins (WQVs) in the Nanling Range (133.7 ± 1.3 Ma) reported from our previous study. Zircon Hf isotopes also reveal that the MGs and the WQVs are homologous. These mineralogical, geochemical and zirconological features indicate that the MGs are the parental rocks of the tungsten deposits in the Nanling Range. This study provides a new guidance for the exploration of magmatic-hydrothermal tungsten deposits.     

A magmatic source of hydrothermal sulfur for the Prominent Hill deposit and associated prospects in the Olympic iron oxide copper-gold (IOCG) province of South Australia

The Prominent Hill deposit is a world-class iron oxide copper–gold (IOCG) deposit in South Australia, characterized by a high Cu/S ratio of the dominant Cu-(Fe) sulfides hosted by hematite breccias. It contains a total resource of 278 Mt of ore at 0.98% Cu and 0.75 g/t Au. Prominent Hill is one of several IOCG deposits and numerous prospects in the Olympic IOCG province that are temporally associated with the 1603–1575 Ma Gawler Range Volcanics, a large igneous province including co-magmatic granitoid intrusions of the Hiltaba Suite. Globally, IOCG deposits share many similar features in terms of their geological environment and mineral association. However, it is not yet clear whether sulfur and copper originate from the same source rocks and which hydrothermal redox processes created the characteristic iron oxide enrichment. Highly variable sulfur isotope compositions of sulfides and sulfates in IOCG deposits have previously been interpreted in terms of diverse sulfur sources that may include contributions from magmatic, sedimentary, seawater or evaporitic sulfur. In order to test these alternatives, we performed a detailed sulfur isotope study of Cu-(Fe) sulfides from Prominent Hill and IOCG prospects nearby. The Prominent Hill deposit shows a wide range in δ³⁴S_V-CDT between − 33.5‰ and 29.9‰ for Cu-(Fe) sulfides, and a narrower range of 4.3‰ to 15.8‰ for barite. Iron sulfides (pyrite, pyrrhotite) show a narrow range in sulfur isotope composition, whereas Cu-bearing sulfides show a much wider range, and more negative δ³⁴S_V-CDT values on average. We propose a two-stage sulfide mineralization model for the IOCG system in the Prominent Hill area, in which all hydrothermal sulfur is ultimately derived from a magmatic source that had a composition of 4.4 ± 2‰. The diversity in sulfur isotope composition can be produced by different fluid evolution pathways along reducing or oxidizing trajectories. A reduced sulfur evolution pathway is responsible for stage I mineralization, when intrusion-derived magmatic-hydrothermal fluids produced early pyrite and minor chalcopyrite at Prominent Hill, and iron ± copper sulfides in regional magnetite skarns and in some pervasively altered volcanic rocks of the Gawler Range Volcanics. Shallow-venting magmatic-hydrothermal fluids and subaerial volcanic gases that became completely oxidized by reaction with atmospheric oxygen produced sulfate and sulfuric acid with a sulfur isotope composition equal to their magmatic source. This highly oxidized ore fluid probably consisted dominantly of water from the hydrosphere, but contained magmatic solute components, notably sulfate, acidity and Cu. Sulfate reduction produced hydrothermal Cu sulfides with a wide range in sulfur isotope compositions from very negative to moderately positive values. Partial reaction of the Cu-rich stage II fluid with earlier stage I sulfides resulted in mixing of sulfur derived from sulfate reduction and from sulfides deposited during stage I. Modeling of the sulfur isotope fractionation processes in response to reducing and oxidizing pathways demonstrates that the entire spectrum of sulfur isotope data from stage I and stage II mineralization can be explained with a single, ultimately magmatic sulfur source. Such a magmatic sulfur source is also adequate to explain the complete spectrum of sulfur isotope data of other IOCG prospects and deposits in the Olympic province, including Olympic Dam. The results of our study challenge the conventional model that suggests the requirement of multiple and compositionally diverse sulfur sources in hematite-breccia hosted IOCG style mineralization.     

Geology,geochemistry and fluid inclusions of the Bianjiadayuan Pb–Zn–Ag deposit,Inner Mongolia,NE China: Implications for tectonic setting and metallogeny

The Bianjiadayuan Pb–Zn–Ag deposit in the Southern Great Xing'an Range consists of quartz-sulfide vein-type and breccia-type mineralization related to granite. Vein orebodies are localized in NW-trending extensional faults. Hydrothermal alteration is well developed and includes silicification, potassic alteration, chloritization and sericitization. Three stages of mineralization are recognized based on field evidence and petrographic observation and are marked by assemblages of quartz–arsenopyrite–pyrite (stage I), quartz–pyrrhotite–chalcopyrite–sphalerite (stage II) and quartz–galena–silver minerals (stage III). The granite, with a zircon age of 143.2 ± 1.5 Ma (n = 14, MSWD = 0.93), is subalkaline, peraluminous and is classified as A2-type granite originating in a post-orogenic extensional setting during the opening of suture zone between the North China Craton and the Siberia Craton from the Late Jurassic to the Early Cretaceous. The δ³⁴S_CDT values of sulfides, ranging from 3.19 to 10.65‰, are not consistent with the majority of magmatic hydrothermal deposits in the SGXR, possibly implying accessory source in addition to magmatic source. Microthermometric measurements show that ore minerals were deposited at intermediate temperatures (347.8–136.4 °C) with moderate salinities (2.9–14.4 wt.% NaCl). Ore-forming fluids were derived largely from magmatic hydrothermal processes, with the addition of meteoric water in late stage. Successive precipitation of Pb, Zn and Ag occurred with changes of physicochemical conditions. Overall considering mineralization features, ore-forming fluids and materials and tectonic setting and comparing with adjacent deposits, the Bianjiadayuan deposit is a mesothermal magmatic hydrothermal vein-type Pb–Zn–Ag deposit controlled by fractures and related to A2-type granite in response to the tectonic/magmatic/hydrothermal activity in late Jurassic. Besides, the explosive breccias in the west area require more attention in future exploration.     

The Blagodatnoe gold-sulfide deposit (Yenisei Ridge,Russia): the nature of geophysical anomalies and the succession and causes of formation of petrophysical zoning

Data on geophysical fields and petrophysical heterogeneity, parageneses and the thermodynamic conditions and age of their formation, and fluid inclusions were used for the genetic reconstruction of petrophysical zoning at the Blagodatnoe gold-sulfide deposit. Petrophysical associations of the preore and ore stages of the deposit formation are clearly reflected in anomalies of the magnetic and natural electric fields and the aureoles of radioactive elements. At the early preore stage (752 Ma), reduced solutions with high activity of K, enriched in U, Th, and, probably, Au, were supplied to intensely foliated tectonic zones. Their interaction with initial metasedimentary rocks gave rise to contiguous zones of quartz–muscovite and chlorite metasomatic rocks. Accompanying graphitization led to a high electrochemical activity of the metasomatic rocks, which generated anomalies of up to –300 mV in the natural electric field; the most intensely carbonized zones became enriched with U (up to 6.5 × 10^–4%) and, probably, Au. The quartz–muscovite metasomatic rocks accumulated Th and K (up to 29 × 10^–4% and 4%, respectively), whereas the chlorite metasomatic rocks accumulated rock-forming elements (particularly Fe), which led to the compaction of these rocks and the acceleration due to gravity in local positive anomalies. The nonmagnetic character of the fresh pre-ore metasomatic rocks suggests the predominantly pyritic composition of early sulfides. At the ore stage (698 Ma), the minerals were deposited from H₂O–CO₂–As–S solutions at 560 to 315 °C. The activity of these solutions caused a redistribution of radioactive elements and a high petrophysical differentiation of the ore-bearing structure. The amplitudes of the anomalies above this structure vary from 500 to 80 nT in the magnetic field and from –130 to + 10 mV in the natural electric field. It has been found that the hydrothermal fluid hardly affected the polarization properties of graphitized rocks at the maximum temperatures but caused an intense removal of U and the development of magnetic pyrrhotite after pyrite. The temperature decrease in the mineral-forming system was favorable for the formation of siderite. Carbonaceous schists which experienced carbonatization lost their electrochemical activity. The binding of carbon dioxide in the solid phase influenced the migration capability of trace elements and their zonal distribution. With this evolution of the solution, Th accumulated at the lower levels of the mineralized zone, whereas the upper levels of the deposit became enriched with U. Productive gold–arsenopyrite–pyrite–pyrrhotite paragenesis with anomalous magnetic susceptibility evolved at the ore stage. The late galena–sphalerite–chalcopyrite paragenesis (365 Ma) was of strictly local occurrence and reduced the magnetic susceptibility of ores.     

Application of pyrite trace element chemistry to exploration for SEDEX style Zn-Pb deposits: McArthur Basin,Northern Territory,Australia

Sedimentary pyrites in black shales contain abundant trace elements that provide information on the chemistry of the seawater at the time of sedimentation. This study focuses on the Barney Creek Formation (~ 1640 Ma) in the McArthur Basin in the Northern Territory of Australia, which is host to one of the world's largest SEDEX Zn-Pb-Ag deposits, and several smaller deposits. Fine-grained sedimentary pyrite has been sampled from three drill holes through the Barney Creek Formation at various distances from SEDEX mineralisation. Samples were selected through the stratigraphy of each hole and analysed by LA-ICPMS for a suite of 14 trace elements. The data show that sedimentary pyrite at the base of the Barney Creek Formation, closest (within 1 km) to SEDEX mineralisation, is strongly enriched in Zn and Tl by one to two orders of magnitude compared to the global average for sedimentary pyrite. In contrast sedimentary pyrite from the hole furthest from SEDEX mineralisation (~ 60 km) contains mean Zn and Tl values equal to, or less than, the global average. Based on the three drill hole pyrite data sets it is concluded that trace elements that are contributed to the basin during hydrothermal exhalation, and adsorbed into contemporaneous sedimentary pyrite, are principally Zn, Tl, Cu, Pb, Ag and As. In contrast, trace elements that are adsorbed into sedimentary pyrite from background seawater are principally Mo, Ni, Co, Se and As. These differences have enabled the development of a SEDEX fertility diagram for sedimentary basins, based on the composition of sedimentary pyrite, that distinguish high Zn, but barren shales, from high zinc SEDEX-related shales. In parallel with the increase in Zn and Tl in sedimentary pyrite approaching mineralisation there is a decrease in Ni, Co and Mo. This means that the ratios Zn/Ni and Tl/Co are particularly good pyrite vectors to SEDEX mineralisation in the McArthur Basin, varying over 4 to 6 orders of magnitude from barren shales to mineralised shales. It is speculated that the reason for the reverse relationship between Ni, Co and Zn, Tl may be caused by hydrothermal exhalations into the water column that effect the ion-exchange pyrite surface complexation processes that alter the uptake of these elements into sedimentary pyrite.Another important conclusion of this study is that hydrothermal exhalations into a sedimentary basin may affect the redox sensitive trace element chemistry of sedimentary pyrite and therefore the trace element chemistry of pyritic black shales. Nickel, Co and Mo all decrease in proximity to hydrothermal vents that form SEDEX deposits, whereas Zn, Tl and Pb increase. Selenium and bismuth are the only redox sensitive trace elements that appear to be unaffected by hydrothermal activity in the McArthur Basin. This has implications on how trace element concentrations of black shales and pyrite are used to reflect past global ocean chemistry.     

Genesis of the Huangshannan high-Ni tenor magmatic sulfide deposit in the Eastern Tianshan,northwest China: Constraints from PGE geochemistry and Os–S isotopes

The Huangshannan magmatic Ni-Cu sulfide deposit is one of a group of Permian magmatic Ni-Cu deposits located in the southern Central Asian Orogenic belt in the Eastern Tianshan, northwest China. It is characterized by elevated Ni tenor (concentrations in recalculated 100% sulfide) in sulfide within ultramafic rocks (9–19 wt%), with values much higher than other deposits in the region. Sulfides of the Huangshannan deposit are composed of pentlandite, chalcopyrite, and pyrrhotite and the host rock is relatively fresh, indicating that the high-Ni tenor is a primary magmatic feature rather than formed by alteration processes. It is shown that sulfides with high-Ni tenor can be generated by sulfide-olivine equilibrium at an oxygen fugacity of QFM +0.5, for magmas containing 450 ppm Ni and 20% olivine. Ores with >10 wt% sulfur have relatively low PGE and Ni tenors compared to other ores, R factor (mass ratio of silicate to sulfide liquid) modeling of Ni indicates that they formed at moderate R values (150–600). Based on this constraint on R values, ores with <10 wt% sulfides in the Huangshannan deposit can be segregated from a similar parental magma with 0.05 ppb Os, 0.023 ppb Ir, and 0.5 ppb Pd at R values between 600 and 3000. This, coupled with the supra-cotectic proportions of sulfide liquid to cumulus silicates in the Huangshannan ores imply mechanical transport and deposition of sulfide liquid in a magma pathway or conduit, in which sulfides must have interacted with large volumes of silicate magma. Platinum and Pd depletion relative to other platinum group elements (PGEs) are observed in fresh and sulfide-rich samples (S > 4.5 wt%). As sulfide-rich samples are also depleted in Cu, and as interstitial sulfides in those samples are physically interconnected at a scale of several cms, the low Pt and Pd anomalies are attributed to solid Pt and Pd phases crystallization and retention with the monosulfide solid solution (MSS) and Cu-rich sulfide liquid percolation during MSS fractionation. This finding indicates that Pt anomalies in sulfide-rich rocks from magmatic Ni-Cu deposits in the Eastern Tianshan are the result of sulfide fractionation rather than a hydrothermal effect. ¹⁸⁷Os/¹⁸⁸Os_(278Ma) values of the lherzolite samples vary from 0.27 to 0.37 and γOs_(278Ma) values vary from 110 to 189, indicating significant magma interaction with crustal sulfides, rich in radiogenic Os. Well constrained γOs values and δ³⁴S values (−0.4 to 0.8‰) indicate that crustal contamination occurred at depth before the arrival of the magma in the Huangshannan chamber. Regionally, deposits with high-Ni tenor have not been reported other than the Huangshannan deposit; however, many intrusions with high-Ni contents in olivine are present in NW China, such as the Erhongwa, Poyi and Poshi intrusions. Those intrusions are capable of forming high-Ni tenor sulfides due to olivine-sulfide-silicate equilibrium and relative high-Ni content in parent magma, making them attractive exploration targets.     

Isocubanite-chalcopyrite intergrowths in the Mid-Atlantic Ridge 26°S hydrothermal vent sulfides

Petrographic, SEM, and EPMA analyses are used to study the micro-textures and mineralogical composition of samples collected by a TV-grab from the 26°S SMAR (southern Mid-Atlantic Ridge) hydrothermal field. The investigated samples include the outermost chimney walls and sulfide debris. Isocubanite-chalcopyrite intergrowths are the major Cu-Fe sulfide phase in the chimney wall samples. These intergrowths include normal chalcopyrite, anomalous chalcopyrite (Cu-poor, Zn- and Fe-rich), normal isocubanite with Cu/Fe < 0.50, and Cu-rich isocubanite with Cu/Fe > 0.50. Anomalous chalcopyrite and Cu-rich isocubanite represent the intermediate phases between stoichiometric chalcopyrite and isocubanite in the Cu-Fe-S system. Anomalous chalcopyrite occurs as cores or thin rims bordering isocubanite, which associated with sphalerite. While Cu-rich isocubanite commonly associates pyrite. Based on textural relationships and microanalytical data of both phases, we interpret the abundant anomalous chalcopyrite and Cu-rich isocubanite as metastable or as high-temperature (~300 °C) rapidly precipitated hydrothermal sulfides. This interpretation advocates the SMAR 26°S hydrothermal field as an immature and short-living system.     

Sulfidic and non-sulfidic indium mineralization of the epithermal Au–Cu–Zn–Pb–Ag deposit San Roque (Provincia Rio Negro,SE Argentina) — with special reference to the “indium window” in zinc sulfide

At San Roque in Patagonia's Rio Negro Province, Argentina, an In–Au–Cu–Zn–Pb–Ag mineralization (< 0.24 wt.% In, < 7 ppm Au, < 0.45 wt.% Cu, < 14.1 wt.% Zn, < 0.55 wt.% Pb, < 60 ppm Ag) is bound to lava, and volcaniclastics of Triassic through Jurassic age. The polymetallic sulfidic and non-sulfidic indium mineralization is attributed to the low-sulfidation (LS) to intermediate sulfidation (IS) epithermal type of mineralization. Its vein-type and stockwork mineralization developed at 39.2 bars under hydrostatic conditions, corresponding to a depth of 400 m below the water level of the paleoaquifer. In the redox-controlled hypogene mineralization, the temperature increased from 130 °C up to as much as 250 °C at depth, while the pH regime changed from slightly acidic near surface to more alkaline conditions around pH 8 at a depth of approximately 150 m. The monophase mineral associations composed of sphalerite, Ag–Bi-enriched and inclusion-free galena (< 1.7 wt.% Ag, < 3.7 wt.% Bi), chalcopyrite, pyrite, gold, silver, digenite, various In–Cu- and Pb–Zn–Ag “intermediate products”, wittichenite, roquesite, sakuraiite, dzhalindite, brochantite, antlerite, cerussite, and “manganomelane” in a quartz and muscovite-rich gangue have been subdivided into three different stages: (1) Stockwork mineralization of LS to IS epithermal type (hypogene), (2) quartz vein mineralization (hypogene), and (3) salar mineralization (supergene–hypogene).Salt–mud flats controlled the youngest mineralization with Mn, Li, Ca, Mg, V, Sr, Cu, Ag and In bound to oxides, hydroxides, sulfates and subordinate carbonates. The quartz vein mineralization is made up of oxides, hydroxides prevailing over sulfides and containing W, Fe, Au, As, Pb, In, and Cu. It formed at the passage from the vadose into the phreatic zones under oxidizing to slightly reducing conditions. The level marks the boiling level of the hydrothermal solutions involved in the mineralizing process. The hypogene stockwork mineralization is exclusively made up of sulfides containing Zn, Pb, Cu, In, Ag and Bi in the phreatic zones. It developed under reducing conditions. Indium is present at all levels within the volcanic rocks and has been derived from sphalerite rich in Cd (< 1.6 wt.% Cd), In (< 7.3 wt.% In) and Cu (< 7.2 wt.% Cu) while the Fe contents are moderate in sphalerite (< 6.8 wt.% Fe). Indium reached economic grade only through the segregation of a Cu–In–S phase in the “indium window” which is defined by a Cd content of sphalerite in the range 0.2–0.6 wt.% Cd. This concentration of In is controlled by the crystal morphology and the lattice parameters of the minerals involved. It is described as a two-stage process with interdiffusion processes in an Fe-enriched system (stage I) and zoned replacement in an Fe-poor system enriched in indium (stage II). Cu-bearing sphalerite decomposed into sphalerite poor in trace elements and into Cu–In-bearing sphalerite. Further indium concentration took place, when roquesite and sakuraiite decomposed along with an increase in oxygen pressure under hypogene and supergene conditions into dzhalindite. The physical–chemical conditions of the mineralogy and chemical changes in the system In–Cu–Zn–Cd observed in nature have been approximated based upon the results obtained during laboratory studies in material sciences that were focused on solar energy.     

Precious metal and telluride mineralogy of large volcanic-hosted massive sulfide deposits in the Urals

Summary The study focuses on the mode of occurrence of Au, Ag and Te in ores of the Gaisk, Safyanovsk, Uzelginsk and other volcanic-hosted massive sulfide (VHMS) deposits in the Russian Urals. Minerals containing these elements routinely form fine inclusions within common sulfides (pyrite, chalcopyrite and sphalerite). Gold is mostly concentrated as ‘invisible’ gold within pyrite and chalcopyrite at concentrations of 1–20 ppm. Silver mainly occurs substituted in tennantite (0.1–6 wt.% Ag). In the early stages of mineralization, gold is concentrated into solid solution within the sulfides and does not form discrete minerals. Mineral parageneses identified in the VHMS deposits that contain discrete gold- and gold-bearing minerals, including native gold, other native elements, various tellurides and tennantite, were formed only in the latest stages of mineralization. Secondary hydrothermal stages and local metamorphism of sulfide ores resulted in redistribution of base and precious metals, refining of the common sulfides, the appearance of submicroscopic and microscopic inclusions of Au–Ag alloys (fineness 0.440–0.975) and segregation of trace elements into new, discrete minerals. The latter include Au and Ag compounds combined with Te, Se, Bi and S. Numerous tellurides (altaite, hessite, stützite, petzite, krennerite etc.) are found in the massive sulfide ores of the Urals and appear to be major carriers of gold and PGE in VHMS ores.     

中国台湾龟山岛热液自然硫中微观包体的元素富集特征

台湾东北部的龟山岛浅海热液体系产生大量的热液自然硫.为了理解微量元素在自然硫中的富集规律和机制,采用激光剥蚀等离子体质谱仪（LA-ICPMS）对龟山岛自然硫进行了元素含量分析.结果显示,硫磺基底仅含有As、Se和Te等岩浆脱气产生的挥发性亲铜元素.Fe、Mn、Co、Ni等亲铁元素主要来自于安山岩基岩,富集于富铁或含硅包体中.Al、Zn、Ba、Pb、La、Ce、Au、Ag等元素显著富集于含硅包体中,表明这些元素受硅酸盐矿物控制.富铜包体具有最高的Hg、Pb、Zn等亲铜元素的单位富集程度.首次对龟山岛热液自然硫中的微量元素分布进行了原位微区分析,有助于理解微量元素在热液活动中的来源、分布和分配等地球化学行为.      

Mineralogical evolution of the Las Cruces gossan cap (Iberian Pyrite Belt): From subaerial to underground conditions

The Las Cruces VMS deposit is located at the eastern corner of the Iberian Pyrite Belt (SW Spain) and is overlain by the Neogene–Quaternary sediments of the Guadalquivir foreland Basin. The deposit is currently exploited from an open pit by Cobre Las Cruces S.A., being the supergene Cu-enriched zone the present mined resource. The Las Cruces orebody is composed of a polymetallic massive sulfide orebody, a Cu-rich stockwork and an overlying supergene profile that includes a Cu-rich secondary ore (initial reserves of 17.6 Mt @ 6.2% Cu) and a gossan cap (initial reserves of 3.6 Mt @ 3.3% Pb, 2.5 g/t Au, and 56.3 g/t Ag).The mineralogy of the Las Cruces weathering profile has been studied in this work. Textural relationships, mineral chemistry, deposition order of the minerals and genesis of the Las Cruces gossan are described and discussed in detail. A complex mineral assemblage composed by the following minerals has been determined: carbonates such as siderite, calcite and cerussite; Fe-sulfides including pyrite, marcasite, greigite and pyrrhotite; Pb–Sb sulfides and sulfosalts like galena, stibnite, fulöppite, plagionite, boulangerite, plumosite, and the jordanite–geocronite series, Ag–Hg–Sb sulfides and sulfosalts including miargyrite, pyrargyrite, sternbergite, acanthite, freibergite, cinnabar, Ag–Au–Hg amalgams; and Bi–Pb–Bi sulfides and sulfosalts such as bismuthinite, galenobismutite, others unidentified Bi–Pb-sulfosalts, native Bi and unidentified Fe–Pb–Sb-sulfosalts. Remains of the former oxidized assemblage appear as relicts comprised of hematite and goethite.Combining paragenetic information, textures and mineral chemistry it has been possible to derive a sequence of events for the Las Cruces gossan generation and subsequent evolution. In that sense, the small amount of Fe-oxyhydroxides and their relict textures replaced by carbonates and sulfides suggest that the gossan was generated under changing physico-chemical conditions. It is proposed that the Las Cruces current gossan represents the modified residue of a former gossan mineralization where prolonged weathering led to dissolution and leaching out of highly mobile elements and oxidation of the primary sulfides. Later, the gossan was subject to seawater-gossan interaction and then buried beneath a carbonated-rich cover. The basinal fluids-gossan interaction and the equilibration of fluids with the carbonated sediments brought to the carbonatization and sulfidation of the gossan, and thus to the generation of Fe-carbonates and Pb–Sb-sulfides.The Las Cruces mineral system likely represents a new category within the weathering class of ore deposits.     

Trace element geochemistry of magnetite from the giant Beiya gold-polymetallic deposit in Yunnan Province,Southwest China and its implications for the ore forming processes

The Beiya gold–polymetallic deposit is one of the largest gold deposits in China and is considered to be a typical porphyry-skarn system located in the middle of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt. Massive magnetite is widespread in the Beiya ore district but its genesis is still the subject of debate. Five representative magnetite types are present in the Beiya deposit, namely magmatic magnetite (M1) from the ore-related porphyry, disseminated magnetite (M2) from the early retrograde alteration, massive magnetite (M3) from the early quartz-magnetite stage, massive magnetite (M4) from the middle quartz-magnetite stage and magnetite (M5) from the late quartz-magnetite stage. Compared with the M1 magnetite, the magnetites from stages M2 to M5 are depleted in Ti, Al and high field strength elements, implying a hydrothermal origin, distinct from the magmatic accessory magnetite in the ore-related porphyry (M1). The concentrations of cobalt in the hydrothermal magnetites decrease gradually from M2 to M5, and can be used to discriminate the magnetite types. The Al + Mn and Ti + V contents of the successively precipitated magnetite grains (M2–M5) suggests that the ore forming temperature decreased from M2 to M4, but increased from M4 to M5, possibly as the result of a new pulse of magma entering the chamber, which may have triggered the gold mineralization. The V content in the hydrothermal magnetite suggests that the oxygen fugacity increased from M2 to M4 but decreased as soon as the sulfides entered the system (M5).