Fe-poor Sphalerite Research Articles

Genesis and evolution of the Natividad Au-Ag(-Ge) epithermal deposit in southern Mexico: Unravelling the final chapters of the Sierra Madre del Sur metallogeny

The final magmatic arc—Miocene in age—of the long-lived Sierra Madre del Sur igneous province in southern Mexico hosts several epithermal deposits that have hitherto received little attention. The Natividad Au-Ag(-Ge) epithermal deposit is one of them and holds a mining record of > 200 years. Here, we present the first petrogenetic and metallogenic study on the Natividad deposit, in which we use a multi-methodological approach to assess the genesis and evolution of the deposit and its associated igneous rocks. Natividad is mostly hosted by Oligocene–Miocene arc-related dacites (U-Pb zircon dates of 22.8–24.7 Ma), whose geochemical features suggest lower-crustal differentiation (i.e., involvement of garnet) at the base of a thickened continental crust. The mineralization occurs in three multi-stage quartz + carbonate veins and consists of Fe-poor sphalerite (<5 mol. % FeS), galena, chalcopyrite, acanthite, and marcasite (sulfide-dominated stage) overprinted by pearceite-polybasite, pyrargyrite-proustite, tetrahedrite-group minerals, electrum, and argyrodite (Ag8GeS6; Ag-sulfosalt-dominated stage). Geothermometry and fluid inclusion data for ore-bearing assemblages reveal fluid temperatures of 170°–400 °C and salinities of 14.6–19.5 wt% NaCl equiv. δ18O from 0.8 ‰ to 7.5 ‰ in mineralizing fluids suggests mixtures of magmatic brines and meteoric waters, while δ13C from –8.4 ‰ to 2.2 ‰ indicates the recycling of organic carbon from the meta-sedimentary basement. Further, δ34S from –3.2 ‰ to –0.3 ‰ in sulfides attest to magmatic S. These results align with an intermediate-sulfidation epithermal model, whereby upwelling magmatic ore-bearing brines precipitated the ores due to conductive cooling, dilution, and, locally, boiling. Our study highlights the metallogenic potential of Miocene magmatism in the eastern Sierra Madre de Sur.

Multi-stage magmatic fluid recharge and fluid mixing developed the Gongdongchong intermediate-sulfidation type epithermal Pb-Zn deposit, North Huaiyang, China: Constraints from petrography, fluid inclusion and in situ geochemistry studies of sphalerite

The Gongdongchong (GDC) lead and zinc deposit is located in the North Huaiyang (NHY) metallogenic belt, northern part of the Dabie orogen. Its Pb-Zn orebodies are predominately in the breccia pipe hosted by the Early Paleozic Foziling Group. Three stages of mineralization could be divided according to replacement relationships and petrography, and the ore and gangue mineral assemblages at the main base metal stage were recognized as combination of Fe-poor sphalerite + galena + pyrite + chalcopyrite + tetrahedrite with quartz and calcite. Three successive generations of sphalerite were distinguished through detailed petrographic observation on crystal-scale, namely Spc (core), Spm (mantle), and Spr (rim). Fluid inclusion petrography result shows that two-phase liquid-rich fluid inclusions are the dominant type in sphalerite. Microthermometric results show the homogenization temperatures and salinities of Spc ranged from 233 °C to 268 °C and 6.6 to 10.4 wt% NaCl equiv. While fluid inclusions in the Spm display homogenization temperatures of 241 °C to 284 °C, with salinities of 8.7 to 11.3 wt% NaCl equiv. This increasing trend may imply a magmatic fluid recharging from core to mantle. However, fluid inclusions in the Spr have homogenization temperatures of 231–254 °C, with salinities of 6.3–9.1 wt% NaCl equiv. A trend of mixing with meteoric water is manifested by the decrease of temperatures with decreasing salinities from mantle to rim. It suggests the combination of the magmatic fluid recharging and mixing of meteoric water should be the key mechanism responsible for the sphalerite precipitation at the GDC deposit. Meanwhile, the GDC deposit shows a similar range of homogenization temperatures and salinities with typical intermediate-sulfidation epithermal deposits, and these homogenization temperatures also correspond well with the geological thermometer results acquired by trace element concentrations of sphalerite. In addition, the sphalerite geochemical results obtained from trace elements as Mn, Co, In and Ge illustrate that the GDC Pb-Zn deposit shares a good consistence with epithermal Pb-Zn deposit.Based on the evidences presented above, combined with the geological and geochemical features, the GDC deposit can be classified as an intermediate-sulfidation epithermal deposit. Intermediate-sulfidation epithermal deposits usually share spatial and genetic relationships with porphyry deposits. This may provide new implication for the mineral exploration of porphyry deposits at depth in the NHY metallogenic belt.

Mineralogy and genesis of the Pb-Zn-Sb-Ag vein H32A in the Příbram uranium and base-metal district, Bohemian Massif, Czech Republic

A detailed paragenetic, electron microprobe, fluid inclusion and S,C,O-isotope study was conducted on Pb-Zn-Sb-Ag mineralization of the vein H32A, Háje deposit, Příbram uranium and base-metal district, Czech Republic. The vein is hosted by folded Neo-Proterozoic sandstones and siltstones of the Teplá-Barrandian unit in exo-contact of the Central Bohemian Plutonic Complex of the Variscan age (354–335 Ma). The ore zone is close to a crustal-scale tectonic zone dividing two distinctly different basement blocks of the Bohemian Massif. A rich mineral assemblage consisting of 44 mineral phases formed during two major mineralization stages (siderite-sulphidic and calcite-sulphidic) widespread in the Příbram area. A complex history of the vein is evidenced from the presence of seven mineralization sub-stages and widespread repeated metasomatic replacement and dissolution of older vein during younger mineralizing events. The vein is dominated by carbonates (especially siderite-rhodochrosite, less frequently dolomite-ankerite-kutnohorite, rarely calcite), minor constituents are quartz, illite-muscovite, and chamosite (locally with up to 1.52 apfu Sb, 0.53 apfu Zn and 0.38 apfu Pb). Ore minerals are dominated by Ag-poor galena. The Fe-poor sphalerite, pyrrhotite, löllingite, arsenopyrite, Pb-Sb, Pb-Sb-Ag and Cu-Ag-Sb sulphosalts are subordinate phases and dyscrasite, native antimony and native arsenic are accessories. The fluid inclusion study revealed the wide ranges of homogenization temperatures (210–<100 °C) and salinities (0.0–30.5 wt% NaCl eq.) of exclusively aqueous fluid inclusions. General decrease of both parameters occurred during evolution of the vein. Sulphur isotope disequilibrium was found between co-existing galenas and sphalerites. The calculated fluid δ13C values range between −9.0 and −12.3 ‰ V-PDB, implying for a well-mixed source of carbon, or its significant re-cycling during processes of dissolution-reprecipitation of vein carbonates. The calculated fluid δ18O values are highly positive for early siderite (+7.2 to +9.6 ‰ V-SMOW), and near-zero for later dolomites and calcites (−2.9 to +3.2 ‰ V-SMOW). The siderite fluids likely represent deeply circulated waters, which underwent a significant isotope exchange with hot crustal rocks. Late low-salinity fluids were likely sourced from the Permian partly evaporated freshwater piedmont basins. The high-salinity Ca-Na-Cl brines rarely recorded in secondary fluid inclusions hosted by late calcite likely represent either local “shield brines” or basinal brines of marine provenance. The study site covers a metallogenetically significant portion of the Late Variscan fluid history within an active crust-scale tectonic zone hosted by basement of the Bohemian Massif. A pronounced Ag enrichment of this vein is mainly caused by widespread occurrence of inclusions of late-stage Ag minerals (dyscrasite) in the vein, which form rich concentrations in the shallower parts of the Háje deposit.

Geological, geochemical and fluid inclusion features of Kömürlükdere and Göçükdibi Cu-Zn ore (Central Pontides, Turkey): Implications for their genesis

The Kömürlükdere and Göçükdibi Cu-Zn ores are located in the Central Pontide orogenic belt, where Besshi-type deposits (such as Hanönü, Zeybek, Sayyayla [Kastamonu]) have been discovered in last two decades. The Göçükdibi and Kömürlükdere ores are hosted in metabasites and quartz schist that belong to the Middle Jurassic Kunduz metamorphic rocks in the accretionary complex in the Central Pontides. The ore bodies show stratiform features, parallel to schistosity, within an alternation of metabasite and quartz schist succession. The average thicknesses of the ore zone and ore levels within the ore zone are 12 m and 3 cm, respectively. The ore bodies contain chalcopyrite, sphalerite, and magnetite, with dominant pyrite formed during the ore formation phase. Meanwhile, hematite, covellite, malachite, and goethite minerals formed during the supergene processes.Microprobe studies showed that the Fe and Cd content of sphalerite varies from 0.08 to 1.12 wt%, indicating Fe-poor sphalerite, and 0.08–0.27 wt%, respectively. The Zn/Cd ratios (average 274.4 for Kömürlükdere, 288.6 for Göçükdibi) of the sphalerite are comparable to those of the worldwide volcanogenic-massive sulfide (VMS) ore system related to andesitic-basaltic source rocks. The Co/Ni ratio (mean 3.2) of pyrite shows volcanogenic pyrite.The average δ34S of the stratiform pyrites is 3.9 ‰ (ranging from 2.06 ‰ to 5.34 ‰), indicating that the sulfur comes from a large homogeneous source, possibly magmatic. The average homogenization temperature (Th) and salinity of fluid inclusions obtained from quartz and sphalerite are 313 °C and 7.7 % equiv. NaCl, respectively, and similar to those of the global VMS deposits.The metabasites contain an average of 164 ppm Cu, 127 ppm Zn, and 2.2 ppm Sb, which shows enrichment several times greater than the background value of the basalts. Meanwhile the ore levels contain an average 0.23 % and 0.83 % Cu and Zn values, respectively. The trace metal enrichment of associated metabasites and the ore zones is evident for elements such as Cu, Zn, Cd, As, and Sb, indicating that they both precipitated in the same basin as syngenetic, and that there was repeated pulses of metal-rich fluids exhaled into the basin.Field observations and analytical data (mineral chemistry, sulfur isotope, fluid inclusion, etc.) show that the Kömürlükdere and Göçükdibi Cu-Zn ore bodies occurred as Besshi-type deposits within the Middle Jurassic Central Pontide Supercontinent, which developed in the marine environment appropriate to the accretionary complex located along the southern margin of Eurasia.

The Maluntou Au deposit: A transitional mineralization type between low- and intermediate-sulfidation epithermal styles

The Maluntou Au deposit is located in Southeast Coastal Volcanic Belt in South China. Its orebodies are hosted by the Cretaceous intermediate to silicic volcanic rocks and controlled by tensional NW-trending faults. The types of ore-related wall rock alterations consist of silicification, argillization, pyritization, and weak chloritization. Based on detailed field and microscopic petrography observation, three mineral paragenetic stages can be divided, i.e. PbZn stage, AuAg stage and post-ore stage.Electron microprobe analysis reveals slightly different composition of metal sulfides between PbZn stage and AuAg stage. The Fe content of Maluntou sphalerite is generally <2 %, indicating a typical Fe-poor sphalerite. Fluid inclusions microthermometric analysis of the early PbZn mineralization stage and late AuAg stage yielded homogenization temperatures (Th, 205–260 °C, 138–234 °C) and salinities (1.0–4.0 wt% NaCl equiv., 0.3–3.4 wt% NaCl equiv.), respectively. The low-moderate Th and low salinity ranges indicate an epithermal mineralization environment. From early stage to late stage, δDV-SMOW values show similar ranges from −69.4 ‰ ~ −64.3 ‰ to −68.2 ‰ ~ −64.9 ‰, with δ18OH2O‰ values ranges from −4.6 ‰ ~ −2.6 ‰ to −5.6 ‰ ~ −4.3 ‰, indicating ore-forming fluids derived from a magmatic and meteoric mixed source. The microthermometric data and H − O isotopic compositions of ore fluids suggest fluid mixing contributed to metal precipitation. The δ34SV–CDT values of sulfide minerals (i.e. pyrite, sphalerite, galena, chalcopyrite; −3.1 to 3.4 ‰) indicate a magmatic sulfur source. The relatively homogeneous lead isotopic compositions of the ore minerals (206Pb/204Pb = 18.4203–18.4814, 207Pb/204Pb = 15.6712–15.6853, and 208Pb/204Pb = 38.7730–38.8636) suggest a crustal origin.All the above results imply that the Maluntou Au deposit is a transitional type epithermal deposit between low- and intermediate-sulfidation styles which occurred distal to the magmatic hydrothermal system. Considering the close time and space relationship of this type deposit with other epithermal type and porphyry type mineralization, our results also suggest a possible exploration potential for the epithermal-porphyry type mineralization in the surrounding altered volcanic rocks in Zhenghe–Jian'ou area.

Geology and genesis of the Chomalu polymetallic deposit, NW Iran

The vein-type Chomalu polymetallic epithermal deposit, located in the Tarom-Hashtjin Metallogenic Province (THMP), western Alborz, formed in two separate mineralized zones controlled by fault zones within andesite and olivine basalt host rocks. The deposit occurs adjacent to the Varmarziar quartz monzonite, quartz monzodiorite, and monzosyenite intrusions. Ore mineralization consists of three stages; (i) an early stage dominated by gold-bearing breccia veins mainly consisting of quartz, pyrite, arsenopyrite, chalcopyrite, minor magnetite and bornite assemblages, (ii) a main stage, which is divided in three sub-stages I, II and III. Sub-stage I is dominated by Pb-Zn-Cu-Ag-rich mineral assemblages including galena, Fe-poor sphalerite, minor chalcopyrite, tetrahedrite, and pyrite. Sub-stage II is only represented by galena and Fe-poor sphalerite. Sub-stage III is defined by Fe-Mn-Zn-Ca-Mg carbonate minerals. The late supergene stage (iii) is characterized by malachite, covellite, chalcocite, cerussite, and Fe-oxide and hydroxides. Microthermometry of primary fluid inclusion assemblages indicate homogenization temperatures (Th) of 253° to 305 °C and salinities of 3.5–4.82 wt% NaCl equivalent in the early stage. The main stage indicates homogenization temperatures (Th) of 200° to 280 °C and 180° to 235 °C with salinities of 2.18–4.96 and 0.53–2.90 wt% NaCl equivalent for the sub-stages I and II, respectively. Ore precipitation was possibly caused by simultaneous dilution and cooling of hydrothermal fluids. The epithermal mineralization in the Chomalu deposit may be classified as an E-type intermediate sulfidation epithermal deposit in the extensional back-arc regime.

Distribution of indium, germanium, gallium and other minor and trace elements in polymetallic ores from a porphyry system: The Morococha district, Peru

We report indium, germanium, gallium, and other minor and trace elements contents in sphalerite, chalcopyrite, galena, and tetrahedrite-tennantite occurring in skarn and skarn-free (“Cordilleran”) polymetallic mantos and vein ore bodies in the Miocene porphyry-related Morococha District, Central Peru. Among the investigated minerals, LA-ICP-MS measurements indicate that In and Ga concentrate mostly in sphalerite (Inter-Quartile Range [IQR] 217–2.7 ppm and up to 4608 ppm In; IQR 61–2.0 ppm and up to 2137 ppm Ga) and chalcopyrite (IQR 109–32 ppm and up to 1070 ppm In; IQR 62–1.5 ppm and up to 630 ppm Ga). In coeval generations of sphalerite and chalcopyrite, the contents of In and Ga in sphalerite are at least two times higher than in chalcopyrite. Germanium content is generally low in the four analyzed minerals (IQR 1.2–0.19 ppm), although late Fe-poor sphalerite may yield much higher values (IQR 129–74 ppm).Certain trace element contents appear to correlate with (i) the evolving characteristics of the hydrothermal fluids during individual mineralization events, and (ii) the location of the studied ore bodies relative to the hydrothermal feeders. The highest In values in sphalerite are found in high-sulfidation assemblages in Cordilleran polymetallic veins and, with lower amounts, in low-sulfidation assemblages in skarn bodies. In intermediate-sulfidation assemblages in Cordilleran mineralization, In content decreases from early to late generations of sphalerite, while that of Ge increases. Spatial trace-element trends in Cordilleran veins and replacement bodies formed during the so-called “Morococha district-scale polymetallic event” include, from porphyry-distal to porphyry-proximal locations: i) In and Cu, and to a lesser extent Ga, enrichment in sphalerite; ii) Se and Hg enrichment and Sn and Ag depletion in chalcopyrite; iii) In enrichment in galena; and iv) Ag depletion in tetrahedrite-tennantite.Our dataset suggests that In is incorporated in the sphalerite crystal lattice via coupled substitutions involving Cu and subordinately also Sn and Ag. Availability of Cu in the mineralizing fluids is therefore key to In enrichment in sphalerite. Progressive dilution of metal-rich magmatic-hydrothermal fluids and Cu precipitation probably account for the progressive In depletion in distal-to-porphyry Zn-Pb-Ag and Ag-Pb Cordilleran polymetallic mineralization and in late sphalerite generations in intermediate-sulfidation assemblages.

Ore genesis of Qingyunshan Cu-Au deposit in the Dehua-Youxi area of Fujian Province, southeastern China: Constraints from U-Pb and Re-Os geochronology, fluid inclusions, and H-O-S-Pb isotope data

The Qingyunshan Cu-Au deposit, located in the Dehua-Youxi area (Fujian Province, southeastern China), is a vein-type deposit that occurs along fractured zones in the Late Jurassic volcanic-sedimentary rocks and Early Silurian intrusions. Three mineral paragenetic stages are identified, including the pyrite-quartz veins (stage I), polymetallic sulfide-quartz-calcite veins (stage II), and calcite (±siderite)-chalcedony-comb quartz veins (stage III). The stage II is the main mineralization stage, dominated by pyrite, chalcopyrite, and galena as well as two generations of Fe-poor sphalerite with average Fe content of 0.84 wt% in the early sub-stage and 0.31 wt% in the late sub-stage. Fluid inclusion studies indicate that the stage I has a temperature of 220–240 °C and salinity of 3.00–3.50 wt% NaCleq., whereas the stage II has lower temperature (140–160 °C), but similarly low salinity (2.50–3.00 wt% NaCleq.), suggesting it is an intermediate-low temperature epithermal deposit. Hydrogen and oxygen isotope data indicate the fluids of stage I has a δD value of −72.5 to −69.5‰ and δ18Ow value of −2.96 to −0.46‰, whereas the stage II fluids show similar or slightly higher δD value (−68.0 to −66.5‰), but significantly lower δ18Ow value from −6.96 to −6.26‰, which suggest meteoric water predominated in the ore-forming fluid and shows an increasing trend from stage I to II. The δ34S values of sulfide minerals are between −3.7 and −2.3‰, consistent with a major magmatic sulfur source. The lead isotope data show a relatively narrow range with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.392–18.513, 15.642–15.758, and 38.497–39.043, respectively. These Pb-isotope data are similar to those of the Late Jurassic intrusions, but quite different from those of the surrounding rocks of Early Silurian quartz diorite. Pyrite from the ores yielded a Re-Os isochron age of 158.1 ± 9.3 Ma, which is similar to the zircon U-Pb age (162.0 ± 1.0 Ma) of the host dacite crystal tuff in the Nanyuan Formation. Therefore, we concluded that the Late Jurassic magmatic activity (ca. 160 Ma) has a genetic relation with formation of the Qingyunshan vein-type Cu-Au deposit, for which the ore metals were mainly derived from the magma, but ore-forming fluids evolved from a mixing of magmatic fluids and meteoric water with the later playing a major role in the main stage of ore formation.

Formation of highly Zn-enriched sulfide scale at a deep-sea artificial hydrothermal vent, Iheya-North Knoll, Okinawa Trough

Artificial hydrothermal vents, created by boreholes that discharge hydrothermal fluids and useful for observing secular changes in mineral precipitates and the chemical compositions of hydrothermal fluids, are periodically cleaned of scale deposits. Here, we report petrographic and geochemical features of hydrothermal scale with a concentric structure and extreme enrichment in Zn, recovered as an intact plug from an artificial hydrothermal vent pipe in the Okinawa Trough. The scale consists of sphalerite with accessory galena and chalcopyrite, and minor cotunnite (PbCl2), barite, an unidentified Zn sulfate, and Bi-rich minerals. It comprises at least five concentric layers alternating between thin, reddish-brown porous layers composed of relatively Fe-rich sphalerite accompanied by galena and chalcopyrite, and coarse-grained, dark gray layers dominated by relatively Fe-poor sphalerite. Cotunnite occurs only in the innermost reddish-brown layer, and barite occurs only in the uppermost and innermost layers. The scale is composed of > 50 wt% Zn, several wt% Fe and Pb, and < 1 wt% Cu, Mn, and Cd, a composition consistent with the solubility of Zn and Cu in a hydrothermal fluid at 304–311 °C and pH 4.7–5.0. We suggest that the concentric layers are related to periodic scale removal operations through which (1) mostly clogged pipe conditions and weak hydrothermal discharge alternate with (2) fully open pipe conditions and vigorous hydrothermal discharge, thus affecting sulfur fugacity and [Cl−] and [SO42−] activities in the hydrothermal fluid and leading to the formation of concentric layers of precipitated minerals.

Mineralogy, hydrothermal alteration, fluid inclusion, and O–H stable isotopes of the Siah Jangal-Sar Kahno epithermal gold deposit, SE Iran

Siah Jangal-Sar Kahno deposit is located in the northern part of Taftan volcano in the Sistan and Balouchestan provinces, southeast of Iran, and is an example of a vein-type epithermal gold system with related stockwork and shear zone mineralization. The veins are hosted by flysch facies rocks of the Makran zone and subvolcanic dioritic porphyry. The NE-SW fault systems played an essential role in the genesis of alteration and mineralization in the area. Diorite porphyry ranges from alkali (Na2O + K2O) content of 4.1–6.66 wt%, and plot in the calc-alkaline to high-K calc-alkaline fields. The chondrite-normalized REE patterns for least altered porphyry diorite rocks, altered host rocks, and silica-carbonate vein show a LREE/HREE ratios of 10.40, 4.03, 4.00, and 2.66, respectively. Positive Eu anomalies in the silica-carbonate veins indicate the Ca-bearing minerals, such as plagioclase decomposition causing release of Eu into hydrothermal fluid and subsequent precipitation in silica-carbonate veins. Mineralization consist of quartz, adularia, calcite, pyrite, arsenopyrite, marcasite, Fe-poor sphalerite, galena, chalcopyrite, and native gold. Later supergene mineral assemblages consists of Fe-oxide and hydroxides, covellite, cerussite, and scorodite. Hydrothermal alteration is generally well developed enveloping the ore-bearing hydrothermal breccia and subdivided into prograde inner quartz-chlorite-pyrite-muscovite, and outer argillic alteration zones, with a regional barren, widespread near-surface supergene (blanket) advanced argillic alteration zone. Chemical discrimination by means of cationic R1-R2 diagram indicates that R1 increases, whereas R2 decreases with increasing argillic alteration. Microthermometry of fluid inclusions in quartz crystals from silica-carbonate vein show the homogenization temperatures (Thv-l) of 167°–332 °C with salinities in the range of 0.21–4.24 wt% NaCl eq. The O and H isotopic compositions of quartz from hydrothermal vein and argillic alteration simply show a low sulfidation epithermal environment with meteoric waters as the main fluid. Due to a narrow range in salinity of the fluids, very low sulfide diversity, sulfide volume, and presence of adularia suggest dominantly meteoric water in the deposit, supporting classification as a low-sulfidation epithermal system.

High $${f_{{{\rm{H}}_2} - }}{f_{{{\rm{S}}_2}}}$$ Conditions Associated with Sphalerite in Latala Epithermal Base and Precious Metal Deposit, Central Iran: Implications for the Composition and Genesis Conditions of Sphalerite

This paper presents the properties of fluid inclusions found in sphalerite from Latala epithermal base and precious metal deposit (Central Iran), which is hosted in Cenozoic volcanic-sedimentary host-rocks. The Latala Deposit represents an example of vein type, base metal deposits in the Miduk porphyry copper deposits (PCDs) in southern Urumieh-Dokhtar magmatic belt (UDMB). Mineralization in Latala epithermal base and precious metal vein type formed in 3 stages and sphalerite-quartz veins occur in stages 2 and 3. Stage 2 quartz-sphalerite veins are associated with chalcopyrite and zoned sphalerite, along with quartz+hematite, and Stage 3 quartz-sphalerite veins contain galena+sphalerite+ chalcopyrite and quartz with overgrowth of calcite. Mineralization in Stage 3 occurs as replacement bodies and contains Fe-poor sphalerite without zoning in the outer parts of the deposit. This paper focuses on fluid inclusions in veins bearing sphalerite and quartz. The fluid inclusion homogenization temperatures and salinity in sphalerite (some with typical zoning) range from 144 to 285 °C and from 0.2 wt.% to 7.6 wt.% NaCl eq. Sphalerite and fluid inclusions of the Latala base and precious metal deposit formed from relatively low-T and low-salinity solutions. Raman spectroscopy analyses indicate a high percentage of CO2 in the gas phase of fluid inclusions in Fe-poor sphalerites, as expected with melting temperature for CO2 of −56.6 °C, and significant amounts of H2. Lack of reduced carbon species (methane and lighter hydrocarbons) was confirmed in the petrographic study using UV light and Raman spectroscopy. High amounts of H2 in fluid inclusions of Fe-poor sphalerite can be the result of different intensities of alteration and diffusion processes. The common occurrences of CO2 in fluid inclusions have originated from magma degassing and dissolution of carbonates. The δ34S values for sulfide minerals in galena of sphalerite bearing veins vary between −9.8‰ and −1.0‰, and the δ34S values calculated for H2S are between −7.1‰ and +0.6‰. These values correspond to magmatic sulfur whit possible interaction with wall rocks. Magmatic fluids were successively diluted during cooling and continuous ascent. Secondary boiling would lead to variable amounts of potassic or prophylactic alteration and the hydrogen diffusion into the inclusions hosted in sphalerite of Latala.

Geology and genesis of the Early Paleozoic Zhengguang intermediate-sulfidation epithermal Au-Zn deposit, northeast China

Zhengguang is a partly eroded (about ≥500 m being eroded), structurally controlled intermediate sulfidation (IS) epithermal gold-zinc deposit, characterized by wide distribution of base metal sulfides, Fe-poor sphalerite and Mn-calcite, hosted by the Late Cambrian-Early Ordovician basaltic-andesitic volcanic and volcano-sedimentary rocks in northeast China. The deposit is located 4 and 8 km from the Early Ordovician Tongshan (including several IS veins about ~500 m away in the east called East Tongshan) and Duobaoshan porphyry copper deposits, respectively. A 484.8 ± 8.7 Ma (MSWD = 198) of Re-Os isochron age on pyrite indicates that it is the most ancient intermediate sulfidation deposit that has been dated.Four stages of veins have been discerned at Zhengguang. Early magnetite ± chalcopyrite ± epidote ± chlorite and K-feldspar ± pyrite ± chalcopyrite veins (stage I) were associated with restricted K-feldspar ± epidote (locally with chlorite) alteration and propylitic (epidote ± chlorite ± calcite) assemblages. Two primary epithermal gold stages developed at Zhengguang: pyrite-quartz ± Fe-poor sphalerite ± chalcopyrite ± galena ± electrum ± petzite ± hessite ± tetrahedrite/tennantite ± adularia veins (stage II) and (Mn-)calcite-quartz-pyrite ± Fe-poor sphalerite ± chalcopyrite ± galena ± hessite ± native gold (stage III), plus a late barren stage characterized by little sulfides (calcite ± chlorite ± hematite ± quartz, stage IV). Gold occurs chiefly as micro-inclusions of electrum and petzite in pyrite and sphalerite of stages II and III.Stable isotope analyses and fluid inclusion results indicate a magmatic-hydrothermal component in the ore fluids. Fluid inclusion data from stage I yielded the highest salinity (∼6.9 wt% NaCl) and homogenization temperature (average 264 °C). Calculated oxygen isotope composition of fluid (δ18Owater up to 4.9‰) equilibrated with quartz indicates a magmatic-hydrothermal source during stage I. A progressive addition of meteoric water component is suggested from stage I to IV of Zhengguang based on the average δ18Owater values equilibrated with quartz and homogenization temperatures (stage I: δ18Owater = 3.3‰, Th = 264 °C; stage II: δ18Owater = −1.4‰, Th = 182 °C; stage III: δ18Owater = −3.4‰, Th = 154 °C; stage IV: δ18Owater = −6.3‰, Th = 121 °C).Our new pyrite Re-Os dating result shows that Zhengguang formed at the same time with Tongshan and Duobaoshan within errors. Comparable sulfur isotopic compositions of pyrite from Zhengguang and Tongshan, analogous low-Fe content in sphalerite and similar mineral assemblage and alteration pattern between Zhengguang and East Tongshan IS veins collectively indicate a genetic connection between Zhengguang and Tongshan, which may derive from fluids exsolved from the same magma chamber. High-temperature assemblages (e.g., K-feldspr ± pyrite ± chalcopyrite) at Zhengguang indicate that there is potential for the discovery of porphyry copper–gold mineralization below the current level of diamond drilling. The confirmation of the Zhengguang as an Early Paleozoic epithermal deposit implies a good preservation and exploration potential of ancient epithermal deposits in eastern Central Asian Orogenic Belt.

The granite-related, high-tonnage Sn-Li deposit of Argemela, central Portugal

The Argemela Sn-Li quartz vein stockwork, east of the Panasqueira tungsten mine, is hosted in Cambrian slates and greywacke. An underlying Variscan granitic cupola is inferred from spotted slates and albitic microgranite dykes, the last including a thick modified albitic microgranite, enriched in F and Li, exposed some 500 m away, on the hill top. Inferred resources for shallowest deposit portion are 20.1 million tonnes (Mt) at 0.1-0.2% Sn, 0.2% Li and 0.1% (estimate) Rb, but the 650-m vertical-extent of the deposit suggests a resource of &gt;200 Mt (with identical grades). The hydrothermal paragenetic sequence is amblygonite-montebrasite (mostly montebrasite) (Stage I)–quartz I-II–cassiterite (with columbite-tantalite inclusions)─arsenopyrite I─carbonate I-white mica I ─chlorite I–fluorite–apatite–rutile (Stage II)– white mica II–molybdenite– tourmaline– carbonate II-quartz III–arsenopyrite II–sphalerite–stannite–chalcopyrite–pyrite– pyrrhotite-chlorite II (Stage III)–covellite– vivianite–goethite/lepidocrocite (Stage IV). Amblygonite-montebrasite is the main Li carrier; Sn is evenly distributed between cassiterite and stannite; Rb is mostly in white mica (with 0.25-1.23 wt % Rb2O in the hill-top albitic microgranite). Primary aqueous, 1-3 um-wide fluid inclusions in the deposit in quartz I, carbonate I, apatite and cassiterite growth zones yield overall salinities and homogenisation temperatures of 7.2-19.1 wt % NaCl equiv. and 290-360ºC, respectively. The trace concentrations (electronic microprobe analysis) in quartz vein cassiterite reach 1.95 wt % Nb, 0.39 wt % Fe, 0.13 wt % Ti, and low/negligible values of Sb, Zn, As, Ag and Bi showing its granite-hydrothermal affiliation. Fe-poor and Fe-rich sphalerite (lower-intermediate and upper deposit parts) contain 1.0-1.6 and 7.9-9.4 wt % Fe, 64.3-66.0 and 55.9-57.2 wt % Zn, 0.4-0.5 and 0.9-1.1 wt % Cd, respectively. The sphalerite-stannite geothermometer yields temperatures of 245-297ºC. Following higher temperature amblygonite-montebrasite deposition (Stage I), hydrothermal fluids (aCl-=0.25 m), related to the hidden granitic cupola, at a mean pressure-corrected (50 MPa) temperature of 350ºC, were responsible for Stage II minerals deposition. Calculated cassiterite deposition from Sn chloride complexes occurred likewise, from probable magmatic-hydrothermal fluids, at fO2 = 10-34 -10-32 atm and pH=3.5-4. Cassiterite deposition mechanisms were oxidation, mixing, neutralisation, possible aCl- increase, and cooling. Later Fe-poor sphalerite (+kesterite/ferrokesterite) and Fe-rich sphalerite (+stannite) deposited at higher and lower fS2, respectively, the latter probably at a higher fO2 (Stage III). The uniqueness of Argemela system with abundant amblygonite-montebrasite in hydrothermal quartz tin veins may be related to an extreme fractionated F-, Li- and P-rich granitic magma. After the emplacement of the granite/albitic microgranite dykes, an emerging pegmatitic fluid was unable, possibly due to insufficient depth, to form pegmatites but only modified the hill-top albitic microgranite. As a consequence, the system, where mixing of high- and low-salinity magmatic fluids probably occurred, remained very enriched in F, Li and P and by the time the hydrothermal stockwork developed amblygonite-montebrasite (Stage I) was the first mineral to deposit abundantly before Stage II minerals deposition in those Argemela Sn-Li quartz veins.

Ore geology, fluid inclusions and O-S stable isotope characteristics of Shurab Sb-polymetallic vein deposit, eastern Iran

The Shurab Sb-polymetallic mineralization is a subvolcanic rock-hosted epithermal deposit and located in north Lut Block, eastern Iran. It is one of the most important deposits of the Iranian East Magmatic Assemblage (IEMA) in which numerous Middle-Cenozoic precious and base metals deposits occur. The main lithological units in the area are Paleogene subvolcanic intrusions and minor Jurassic sedimentary rocks. Mineralization occurs as veins in a series of NW-SE and E-W trending faults and fractures in the Eocene-Oligocene dacite and andesite subvolcanic rocks. Mineralization at the Shurab deposit can be subdivided into four stages: pre-ore stage, Cu-Zn-Pb ore stage, Sb-Ag ± As ore stage and post-ore stage. The total sulfide content of the veins in the area is variable, ranging from 1 to 50%, and is dominated by stibnite, chalcopyrite, galena, Fe-poor sphalerite and pyrite with minor chalcostibite, Ag-tetrahedrite and bournonite; gangue minerals are mainly quartz and calcite. Silicic, argillic, propylitic, and sericitic, are the most obvious wall rock alterations. Microthermometric measurements of primary liquid-rich fluid inclusions in quartz and sphalerite indicate that the veins were formed at temperatures between 115 and 290 °C from fluids with salinities between 0.7 and 16.2 wt% NaCl eq., suggesting an epithermal origin. The δ34S values of pyrite, chalcopyrite and galena vary between -2.5 and 0.8‰, and δ18O values of quartz range between 12.5 and 14.8‰. It is inferred that the Shurab mineralization is of epithermal origin, related to an Eocene-Oligocene magmatic geothermal system involving fluids of magmatic and meteoric origin.

Geology, mineral paragenesis and fluid inclusion studies of the Yueyang Ag-Au-Cu deposit, South China: implications for ore genesis and exploration

The Yueyang epithermal Ag-Au-Cu deposit is located in the Zijinshan ore district in western Fujian Province, South China. Orebodies are predominately hosted by the Jurassic Zijinshan granite batholith and controlled by a group of NW-trending faults. Roughly all minerals were deposited in a single extended period, and three stages can be further defined: (1) the early sphalerite stage; (2) the base metal-silver stage; and (3) the post-mineralization stage. Microthermometric measurements on quartz- and sphalerite-hosted, liquid-rich fluid inclusions indicate that mixing and dilution of the ore forming fluids took place from early to late stages. However, fluid boiling may locally occur and lead to silver participation, as suggested by the presence of fluid inclusion assemblage consisting of coexisting liquid-rich and vapour-rich inclusions, and also indicated by adularia in Ag-bearing veins and the breccia type ore of bonanza grade. Compared with typical low-sulphidation epithermal deposits, the higher Ag/Au ratios and fluid salinities, Fe-poor sphalerite and large proportion of sulphide minerals suggest that the Yueyang deposit is best classified as an intermediate-sulphidation epithermal deposit. Since intermediate-sulphidation epithermal deposits favour a magmatic affinity and usually exhibit spatial and temporal association with high-sulphidation and porphyry deposits, mineral exploration at the adjacent area of the Yueyang deposit is promising.

Micro-scale sulfur isotope and chemical variations in sphalerite from the Bleiberg Pb-Zn deposit, Eastern Alps, Austria

The Bleiberg Pb-Zn deposit in the Drau Range is the type locality of Alpine-type carbonate-hosted Pb-Zn deposits. Its origin has been the subject of on-going controversy with two contrasting genetic models proposed: (1) the SEDEX model, with ore forming contemporaneously with sedimentation of the Triassic host rocks at about 220 Ma vs. (2) the epigenetic MVT model, with ores forming after host rock sedimentation at about 200 Ma or later. Both models assume that, on a deposit or even district scale, a fixed paragenetic sequence of ore minerals can be established. The results of our detailed petrographic, chemical and sulfur isotope study of two key ore-samples from two major ore horizons in the Wetterstein Formation at Bleiberg (EHK02 Erzkalk horizon and Blb17 Maxer Bänke horizon) demonstrate that there is no fixed paragenetic sequence of ore minerals. Small-scale non-systematic variations are recorded in textures, sphalerite chemistry and δ34S. In each sample, texturally different sphalerite types (colloform schalenblende, fine- and coarse-grained crystalline sphalerite) co-occur on a millimeter to centimeter scale. These sphalerites represent multiple mineralization stages/pulses since they differ in their trace element inventory and in their δ34S. Nonetheless, there is some correspondence of sphalerite micro-textures, sulfur isotope and chemical composition between the two samples, with microcrystalline colloform schalenblende being Fe-rich, having high Fe/Cd (15 and 9, respectively) and a light sulfur isotope composition (δ34S −26.0 to −16.2‰). Cadmium-rich and Fe-poor sphalerite in both samples has relatively heavier sulfur isotope composition: in sample EHK02 this sphalerite has Fe/Cd of ∼0.5 and δ34S from −6.6 to −4.6‰; in sample Blb17 Fe/Cd is ∼0.1 and δ34S ranges from −15.0 to −1.5‰. Barite, which is restricted to sample EHK02, has δ34S ≈ 17‰. The large variations in δ34S recorded on the mm to cm-scale is consistent with variable contributions of reduced sulfur from two different sulfur reservoirs. The dominant reservoir with δ34S values <−20‰ likely results from local bacteriogenic sulfate reduction (BSR), whereas the second reservoir, with δ34S about −5‰ suggests a hydrothermal source likely linked with thermochemical sulfate reduction (TSR). Based on this small- to micro-scale study, no simple, deposit-wide paragenetic and sulfur isotope evolution with time can be established. In the Erzkalk ore (sample EHK02) an earlier Pb-Zn-Ba stage, characterized by heavy sulfur isotope values, is succeeded by a light δ34S-dominated Zn-Pb-F stage. In contrast, the several mineralization pulses identified in the stratiform Zn-Pb-F Maxer Bänke ore (sample Blb17) define a broad trend to heavier sulfur isotope values with time. The interaction documented in these samples between two sulfur reservoirs is considered a key mechanism of ore formation.

Geology, S–Pb isotopes, and 40Ar/39Ar geochronology of the Zhaxikang Sb–Pb–Zn–Ag deposit in Southern Tibet: implications for multiple mineralization events at Zhaxikang

Several Au, Sb, Sb–Au, Pb–Zn, and Sb–Pb–Zn–Ag deposits are present throughout the North Himalaya in southern Tibet, China. The largest Sb–Pb–Zn–Ag deposit is Zhaxikang (18 Mt at 0.6 wt% Sb, 2.0 wt% Pb, 3.5 wt% Zn, and 78 g/t Ag). Zhaxikang veins are hosted within N–S trending faults, which crosscut the Early–Middle Jurassic Ridang Formation consisting of shale interbedded with sandstone and limestone deposited on a passive continental margin. Ore paragenesis indicates that Zhaxikang mineralization occurred in two main phases composed of six total stages. The initial phase was characterized by assemblages of fine-grained Mn–Fe carbonate + arsenopyrite + pyrite + sphalerite (stage 1), followed by relatively coarse-grained Mn–Fe carbonate + Fe-rich sphalerite + galena + pyrite (stage 2). The second phase was marked by assemblages of quartz + pyrite + Fe-poor sphalerite and Ag-rich galena + tetrahedrite + sericite (stage 3), quartz + Sb–Pb sulfosalt minerals mainly composed of boulangerite and jamesonite (stage 4), quartz + stibnite ± cinnabar (stage 5), and quartz ± calcite (stage 6). Sulfides of stage 2 have δ34SV–CDT of 8.4–12.0‰, 206Pb/204Pb ratios of 19.648 to 19.659, 207Pb/204Pb ratios of 15.788 to 15.812, and 208Pb/204Pb ratios of 40.035 to 40.153. Sulfides of stage 3 have similar δ34SV–CDT of 6.1–11.2‰ and relatively more radiogenic lead isotopes (206Pb/204Pb = 19.683–19.792). Stage 4 Sb–Pb sulfosalt minerals have δ34SV–CDT of 5.0–7.2‰ and even more radiogenic lead (206Pb/204Pb = 19.811–19.981). By contrast, stibnite of stage 5 has δ34SV–CDT of 4.5–7.8‰ and less radiogenic lead (206Pb/204Pb = 18.880–18.974). Taken together with the geological observations that the Pb–Zn-bearing Mn–Fe carbonate veins were crosscut by various types of quartz veins, sphalerite and galena of stage 2 underwent dissolution and remobilization, and that Sb–Pb(−Fe) sulfosalts formed at the expense of Pb from stage 2 galena and of Fe from stage 2 sphalerite, we argue that the early Pb–Zn veins were overprinted by later Sb-rich fluids. Stage 2 fluids were likely acidic and oxidized and leached lead from high-grade metamorphic rocks of the Greater Himalayan crystalline complex (GHC) and sulfur from reduced rocks, such as slate of the Ridang Formation, along N–S trending faults, leading to precipitation of Pb–Zn sulfides and Mn–Fe carbonate and formation of solution collapse breccias. Later Sb-rich fluids leached Pb from the GHC and the pre-existing sulfides and deposited Fe-poor sphalerite, Ag-rich galena, tetrahedrite, Sb–Pb sulfosalts, and stibnite in quartz veins that cut pre-existing Pb–Zn-bearing Mn–Fe carbonate veins. The Sb-rich fluids also likely leached Pb from Early Cretaceous gabbro and formed stibnite at shallow levels where early Pb-Zn-bearing Mn-Fe carbonate veins are absent. A sericite 40Ar–39Ar plateau age of 17.9 ± 0.5 Ma from stage 3 veins represents the timing of the onset of stage 3 mineralization.

Ore petrology, hydrothermal alteration, fluid inclusions, and sulfur stable isotopes of the Milin Kamak intermediate sulfidation epithermal Au-Ag deposit in Western Srednogorie, Bulgaria

The Milin Kamak gold-silver deposit is located in Western Srednogorie zone, 50km west of Sofia, Bulgaria. This zone belongs to the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt. The deposit is hosted by altered trachybasalt to andesitic trachybasalt volcanic and volcanoclastic rocks with Upper Cretaceous age, which are considered to be products of the Breznik paleovolcano. Milin Kamak is the first gold-silver intermediate sulfidation type epithermal deposit recognized in Srednogorie zone in Bulgaria. It consists of eight ore zones with lengths ranging from 400 to 1000m, widths from several cm to 3–4m, rarely to 10–15m, an average of 80–90m depth (a maximum of 200m) and dip steeply to the south. The average content of gold is 5.04g/t and silver – 13.01g/t. The styles of alteration are propylitic, sericite, argillic, and advanced argillic. Ore mineralization consists of three stages. Quartz-pyrite stage I is dominated by quartz, euhedral to subhedral pyrite, trace pyrrhotite and hematite in the upper levels of the deposit. Quartz-polymetallic stage II is represented by major anhedral pyrite, galena, Fe-poor sphalerite; minor chalcopyrite, tennantite, bournonite, tellurides and electrum; and trace pyrrhotite, arsenopyrite, marcasite. Gangue minerals are quartz and carbonates. The carbonate-gold stage III is defined by deposition of carbonate minerals and barite with native gold and stibnite.Fluid inclusions in quartz are liquid H2O-rich with homogenization temperature (Th) ranging from 238 to 345°C as the majority of the measurements are in the range 238–273°C. Ice-melting temperatures (Tm) range from −2.2 to −4.1°C, salinity – from 3.7 to 6.6wt.% NaCl equiv. These measurements imply an epithermal environment and low- to moderate salinity of the ore-forming fluids.δ34S values of pyrite range from −0.49 to +2.44‰. The average calculated δ34S values are 1.35‰. The total range of δ34S values for pyrite are close to zero suggesting a magmatic source for the sulfur.

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, 33.1ppm Ag and 0.07ppm 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, ∼100m 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, 42ppm Ag and 0.02ppm 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 >5mbsf (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, ∼350m farther east, hydrothermal assemblages are characterized by illite/montmorillonite, with Mg-chlorite present at depths below ∼30mbsf. 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.

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 18.7ppm Au and 1450ppm Ag, with average concentrations of 2.3ppm Au and 218.9ppm 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.