Generations Of Pyrite Research Articles

Vein-type gold formation during late extensional collapse of the Eastern Desert, Egypt: the Gidami deposit

Orogenic gold deposits, though construed to focused fluid flow during orogenesis, commonly post-date the main accretionary events. Several lines of evidence indicate that orogenic gold formation in the Arabian–Nubian Shield continued through the orogen collapse stage and associated rapid exhumation and thermal re-equilibration. The Gidami gold deposit in the Eastern Desert of Egypt is associated with post-foliation, brittle-ductile shear zones that deformed a weakly foliated tonalite-trondhjemite massif dated as ~ 704 Ma (U–Pb zircon age). Gold-sulfide quartz veins exhibit textural features indicative of repeated mylonitization, recrystallization, and muscovite crystallization. New 40Ar/39Ar ages of muscovite flakes from the auriferous quartz veins and from the altered wallrock overlap within analytical uncertainty at ~ 583 Ma, which corresponds to the climax of extension-related wrenching and rapid exhumation in the region (~ 596 to 582 Ma). Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data coupled with microtextural characteristics suggest that early formed pyrite generations experienced substantial fluid-mediated recrystallization, and that a set of metals was remobilized by later fluids. A late generation of fibrous pyrite, ubiquitous in microfractures, deposited while the veins re-opened and deformed. The occurrence of free gold particles along with a late-paragenetic assemblage of galena-sphalerite-chalcopyrite(± hessite ± cervelleite) was related to influx of low salinity, metalliferous H2O-NaCl-CO2-CH4 fluids as indicated by the fluid inclusion laser Raman spectroscopy and microthermometry results. Au-mobilization and redeposition at T ≤ 350 °C and P ~ 1 to 1.7 kbar, triggered by intermittent fluid pluses and thermal re-equilibration, were most likely stimulated by extensional structures and within-plate magmatism. Coincident province- and deposit-scale pressure–temperature-time data highlight the pivotal role of the orogenic collapse tectonics in gold endowment in the Central Eastern Desert’s crust.

Metallogenesis of the Bakoshi-Kundila gold deposit in northern West Nigerian Subshield: Insights from pyrite chemical and sulfur isotopic compositions and zircon U-Pb geochronology

The Bakoshi-Kundila gold deposit, located in northern West Nigerian Subshield, in the southern trans-Saharan Orogenic Belt of West Africa, is a recent discovery and artisanally mined deposit. Like other Nigerian gold deposits, the mechanism and timing of gold precipitation remains unknown. In this study, we report the results of an integrated study of pyrite chemical and isotopic compositions and U-Pb on zircon geochronology to determine the gold precipitation mechanisms, fluid sources, and formation age of the gold mineralization. Two mineralization stages are recognized: (i) the Au-pyrite-quartz vein-type mineralization, including two generations of pyrite referred to as Py1a and Py1b, and (ii) wall rock disseminated-type Au-pyrite mineralization, comprising three pyrite types, Py2a, Py2b, and Py3. Py1 is Au-rich and As-poor pyrite and contain lattice-bound Au (Au+), nanoparticle Au (Au0), and native Au grains adsorbed on Py1b surface. Associated with Py1 are Ag-Te-Au bearing minerals. In contrast, Py2 and Py3 are As-rich and are less in Au; they contain only lattice-bound Au. Py1 grains have higher contents of Ag, Pb, Bi, Sb, Tl, and Cu which correlate with Au compared to those from Py2 and Py3. Py1 generations has lower δ34SV-CDT from –5.43 to –2.11 ‰ compared to the higher values of +3.63 to +5.47 ‰ obtained for the Py2 and Py3. These sulfur isotopes data are within the δ34S values of 0 ± 5 ‰ of the magmatic reservoir. U-Pb on zircon from Au-pyrite-quartz vein stage yielded older ages of 644.5 ± 2.2 Ma and 681.5 ± 1.8 Ma, compared to younger age of 606. 4 ± 1.8 Ma yielded by zircon grains from wall rock-type mineralization. Additionally, zircon grains from Au-bearing Tourmalinite yielded ages of 679 ± 1.3 Ma and 609.6 ± 7.1 Ma. We propose that Au mineralization at the Bakoshi-Kundila occurred during two periods in the Neoproterozoic: (i) an early ∼ 682 Ma (Cryogenian), possibly related to the emplacement of 683 Ma Yettiti granite and (ii) a second-stage Au disseminated in wall rock of granites and might have experienced 606–610 Ma Ediacaran metamorphism during the late tectonic events in West Nigerian Subshield.

Multi-stage ore forming history of the Variscan porphyry Mo-Cu-W Myszków deposit (Poland): Evidence from trace elements of pyrite

Four generations of pyrite (Py I-IV) from the porphyry-type Mo-Cu-W Myszków deposit are investigated using electron-probe microanalysis and laser ablation inductively coupled plasma mass spectrometry. Pyrite-I, representing skarn-forming stage of mineralization associated with magma intrusion activity, was formed in a relatively high-temperature environment. It has high contents of Co (up to 3966.11 ppm), Ni (up to 2552.62 ppm), Mn (up to 70.32 ppm), and Se (up to 103.94 ppm), but is depleted in As, Te, V, and devoid of Sb. Pyrite-II, representing the main hydrothermal stage of ore mineralization under the vigorous boiling conditions, contains elevated levels of Co (up to 1962.31 ppm), Ni (up to 1080.86 ppm), and Se (up to 153.03 ppm) with a high Se/Te ratio of 28.30. Pyrite-III, formed under vigorous to gentle boiling conditions, is also enriched in Co (up to 3312.65 ppm), Ni (up to 1469.09 ppm), Se (up to 184.24 ppm), and Te (up to 117.50 ppm), but depleted in As, Mn, V. The latest, low-temperature generation of pyrite, Py-IV is characterized by the highest contents of As (up to 3331.79 ppm), Mn (up to 141.91 ppm), the elevated levels of Te (up to 62.51 ppm), but depletion in Co, Ni, Se, V. Cu (mostly Py-I and Py-II), Pb (mainly Py-II and Py-IV), Bi (mainly Py-IV), Ag and Au (mainly Py-IV) are found as trace elements of solid micro-sized inclusions hosted by various generations of pyrite. The results of the study seem to demonstrate the sequence of metal precipitation in the ore system. At the relatively high-temperature conditions (the contact metamorphism down to hydrothermal stage), the deposition of Co, Ni, Mn, and later Se in pyrite occurred. Additionally, cobalt and nickel concentrations might suggest a contribution from magmas of mafic composition. Copper was mobilized and formed solid micro-inclusions in the host pyrite. Later, along with the evolution of the ore-forming system, and lower temperature rate, tellurium entered the structure of pyrite, when the redox condition temporarily changed from oxidizing to more reducing. With the further temperature drop and likely rising oxidation, arsenic entered the pyrite structure in the most recent episode of the main hydrothermal ore-mineralization stage. Also, the highest budget of Bi, Pb, and Ag with traces of Au was deposited as micro-inclusions in pyrite during this period. The concentration of these elements can be related to the same mechanism, as revealed by their positive correlations, i.e. Bi vs Pb in Py-IV (R = 0.95) Ag vs Pb in Py-IV (R = 0.94), Ag vs Bi in Py-IV (R = 0.97).

Discriminating Between Primary and Secondary Au Events in a Paragenetically Complex Archean Lode-Gold Deposit, Wawa Gold Corridor, Ontario, Canada

AbstractThe Wawa gold corridor, located in the Michipicoten greenstone belt of the Superior province, Canada, comprises Au-bearing shear zones that crosscut the 2745 Ma Jubilee stock and that evolved during protracted deformation (D1-D3). Numerous generations of sulfide minerals crystallized before, during, and after these deformation events, and gold is associated with D1 arsenopyrite, D2 pyrite, and Bi-Te phases and chalcopyrite in assemblages that crosscut D3 veins. Observations of porosity and inclusions in D1 arsenopyrite and D2 pyrite suggest these sulfides underwent coupled dissolution-reprecipitation reactions. By coupling these textural observations with trace element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), it is evident that such replacement reactions generated gold from Au previously in solid solution. Conversely, textural relationships among paragenetically late gold and Bi-Te minerals are consistent with the precipitation of these phases from Bi-rich polymetallic melts. Mass balance calculations involving comparisons of the mass of Au in sulfides and the total mass of Au in their associated host rocks indicate that only D1 arsenopyrite contained enough Au to account for whole-rock Au content and overall deposit grade. Although D1 arsenopyrite is less volumetrically abundant than the various pyrite generations present in the deposit, it is often replaced by the later pyrite types, which is compatible with higher initial volumes of arsenopyrite than what is presently observed. It is concluded that the D1 Au + arsenopyrite event was the principal Au-mineralizing event in the Wawa gold corridor and that the other gold-bearing assemblages (i.e., gold + D2 pyrite, gold + Bi-Te phases + chalcopyrite) largely represent secondary mobilization of this primary enrichment. Given that LA-ICP-MS sulfide chemistry is regularly used in orogenic Au research, the approach outlined herein to assess the relative impact of distinct Au- and sulfide-mineralizing events could easily be applied to the study of other Au deposits in which complex hydrothermal parageneses are recognized.

In-situ trace element and S isotope compositions of sulfides from the Tonggou Cu deposit, Eastern Tianshan Orogen: Implication for ore-forming process

The Tonggou deposit is located in the western Bogda Orogen, the northern margin of Eastern Tianshan. Porphyry Cu and vein-type Cu-Zn mineralization are both developed in the Tonggou orefield. This well-preserved porphyry-vein system, therefore offers an excellent opportunity to evaluate the genetic relationship and ore-forming process between porphyry Cu and vein-type Cu-Zn mineralization. Porphyry mineralization consists of magnetite-quartz (P1) and chalcopyrite-quartz (P2) stages, whilst vein-type mineralization includes pyrite-quartz (V1), polymetallic sulfide-quartz (V2), and pyrite-calcite (V3) stages. Four pyrite generations are identified, including porphyry Cu ore-related (Py1) and vein-type Cu-Zn ore-related (Py2, Py3, and Py4) ones. In most cases, Py1 (stage P2) occurs as anhedral grains, Py2 (stage V1) as fine anhedral grains, Py3 (stage V2) as euhedral-subhedral grains, and Py4 (stage V3) as anhedral aggregates. The Sb content first decreases from Py1 to Py2, then increases from Py2 to Py3, and finally decreases from Py3 to Py4. Cobalt and Ni contents show opposite trend to that of Sb. The relatively high Sb but low Co-Ni contents in Py1 and Py3 indicate that the main ore stage (P2 and V2) environment was high oxygen fugacity and low sulfur fugacity. Moreover, the contents of Cu (Py1: avg. 4108 ppm, Py2: avg. 735 ppm, Py3: avg. 284 ppm, Py4: avg. 149 ppm) and Ag (Py1: avg. 204 ppm, Py2: avg. 11.1 ppm, Py3: avg. 6.29 ppm, Py4: avg. 2.98 ppm) gradually decrease from Py1 to Py4, indicating that the initial ore fluid was Cu-Ag rich. The δ34S values obtained are 4.6–6.8 ‰ (avg. 5.9 ‰; Py2), 5.7–7.4 ‰ (avg. 6.6 ‰; Py3), and 7.3–8.8 ‰ (avg. 8.1 ‰; Py4), which indicate that the sulfur of vein-type mineralization was initially derived from felsic magma, and subsequently mixed with strata sulfur. Furthermore, the similar δ34S range of Ccp1 (4.7–5.3 ‰) from porphyry ore and Ccp2 (3.3–4.8 ‰) from vein-type ore indicates that they have a similar felsic-magma-derived sulfur source. Combining with principal component analysis (PCA) of pyrite trace elements and REE patterns, the different pyrite generations can be divided into porphyry pyrite and vein-type pyrite, albeit with similar fluid source.Consequently, we suggest that the Tonggou porphyry and vein-type ores have similar ore-fluid source, and may belong to the same porphyry mineralization system with different ore-forming processes. Redox change may have played an important role in the metal enrichment and precipitation at Tonggou.

Ore genetic implications of pyrite and sphalerite compositions fromRajpura‐Daribaand ZawarmalaPb‐Zndeposits, Northwestern India

Pb–Zn mineralization at Rajpura‐Dariba and Zawarmala, India, is hosted in the Palaeoproterozoic meta‐volcano‐sedimentary sequence of Aravalli‐Delhi Belt. We have studied different generations of pyrite (Py‐I, II and III) and sphalerite (Sph‐I, II and III), associated with ore mineralization and remobilization stages, from both the deposits. In Rajpura‐Dariba, high concentrations of the majority of trace elements in syngenetic Py‐I and Sph‐I suggest their formation from trace element enriched hydrothermal fluid in SEDEX environment. Enrichment of lattice bound elements in Py‐II (As, Co, Ni) and Sph‐II (Mn, Hg and Cd) during metamorphic recrystallization of early pyrite and sphalerite indicates their local derivation from host rocks. The Pb, Tl, Ag and Sb rich Py‐III and Sph‐III in discordant ore indicate their crystallization from low melting‐point chalcophile elements enriched sulfide melt. In Zawarmala, the trace element poor natures of diagenetic banded Py‐I and Sph‐I suggest that the initial ore‐forming fluid was depleted in trace elements. Enrichment of trace elements in Py‐II (As, Mn, Tl, Cu) and Sph‐II (Mn, Hg, As, Ga) in sphalerite‐pyrite vein ore signify their derivation from carbonate host rocks. The high abundance of trace elements in Py‐III and Sph‐III indicates their precipitation at lower temperatures from a trace element enriched hydrothermal fluid during the massive galena‐sphalerite ore formation. Pyrite and sphalerite from global SEDEX are trace elements enriched as compared to MVT deposits, where their compositions have remarkably correlation with host rocks. Our study highlights the influence of host rock in pyrite and sphalerite compositions and their ore genetic implications.

Two-stage Cu[sbnd]Pb[sbnd]Zn mineralization of the Baoshan deposit in southern Hunan, South China: Constraints from zircon and pyrite geochronology and geochemistry

The Baoshan CuPbZn deposit is one of the representative polymetallic deposits in the middle of the Nanling Range, the western part of the Qin–Hang ore belt. In order to better understand the magmatic activity (granodiorite porphyry and porphyritic granodiorite) and mineralization in the Baoshan deposit, in situ UPb and LuHf isotope studies of zircons and trace element compositions of two generations of pyrite (ore stage: Py I and post-ore stage: Py II) have been carried out. This constrains the geochronology, magma source, fluid composition, and the origin of the ore-forming materials. The zircon UPb dating results from two types of intrusions show two geochronological populations: (i) ~180 Ma for the Cu (PbZn) mineralization that is related to the porphyritic granodiorite, and (ii) ~160 Ma for the CuPbZn mineralization which is associated with the granodiorite porphyry. The similar REE patterns, Hf/U, Nb/Ta, and Y/Ho ratios along with Hf isotopic characteristics of both granite types indicate that these rocks were sourced from the partial melting of lithospheric mantle and lower crust. Zircons from the granodiorite porphyry have higher Nb, Ta, Lu, and Hf contents, but lower Ti contents and Th/U ratios than those from the porphyritic granodiorite, suggesting that the magma-forming granodiorite porphyry had lower temperature, higher oxygen fugacity, and probably experienced strong crystal fractionation. Py I and Py II are associated with the porphyritic granodiorite and are related to the mineralization that occurred at ~180 Ma. The composition of pyrite in the two stages indicates the contribution of granite and limestone to mineralization. The higher contents of metals (Cu, Pb, Zn, Bi, Ag, except Co and Ni) in Py I than in Py II indicate the cooling and mixing process of ore-forming fluid with meteoric water. The geochemical characteristics of the pyrite generations and UPb dating of zircons suggest that the small-scale mineralization occurred at ~180 Ma under a relatively high-temperature and lower oxidized magmatic environment, whereas the major metallogenic event occurred at ~160 Ma under a low-temperature, medium oxidized, and strongly fractionated magmatic environment. This study reveals that the multi-stage magmatic and mineralization processes mainly occurred during the Early to Late Jurassic in South China.

Metallogenic model of the Fengyan stratabound Zn-Pb deposit in Fujian of southeastern China: Constraints from fluid inclusions, C[sbnd]O[sbnd]S-Pb isotopes, and pyrite chemistry

The Fengyan stratabound Zn-Pb deposit (total resources: 24.7 Mt of ore @ 4.09 % Zn and 1.92 % Pb) is hosted by Neoproterozoic marble and metavolcanic rocks in the Meixian ore field of southeastern China. Hitherto, the genesis of this deposit has been a matter of debate, including a Neoproterozoic volcanogenic massive sulfide genesis (VMS) or an Early Cretaceous magmatic-hydrothermal origin. Based on fluid inclusion data from various hydrothermal stages, stable isotope data of hydrothermal minerals, and in-situ trace element analyses of poly-stage pyrite (Py1-3), the deposit can be classified as a distal skarn-type. A complex paragenesis reflects four hydrothermal stages: stage I (pyroxene + garnet + Py1), stage II (epidote + hematite + magnetite + Py2), stage III (quartz + sphalerite + galena + Py3a + Py3b), and stage IV (calcite). The prograde skarn comprises andradite-rich garnet (on average Ad57Gr34Py9) and pyroxene (on average Hd58Di10Jo32) with high Mn contents. Fluid inclusion data reveal salinity and temperature ranges for the prograde and retrograde skarn fluids as 11.5 to 14.6 wt% NaCl equiv. at 278 to 338℃ and 7.5 to 11.2 wt% NaCl equiv. at 235 to 275℃, respectively. The entrapment pressure is calculated as 130 bars. The sulfide ore minerals of stage III were precipitated at lower temperatures (186 to 259℃) from aqueous fluids with lower salinities (<6.6 wt% NaCl equiv.). Late-stage calcite was deposited from a more dilute (<2.2 wt% NaCl equiv.) and cooler (<200℃) fluid with extremely depleted δ18Ofluid values of −10.1 to −2.0 ‰ (V-SMOW), consistent with a meteoric origin. A mean δ34SV-CDT of 1.7 ± 0.9 ‰ of sulfide minerals points to a magmatic sulfur source. Lead isotopic compositions of sphalerite separates (206Pb/204Pb = 18.295–18.381, 207Pb/204Pb = 15.644–15.662, and 208Pb/204Pb = 38.494–38.724) are similar to those of the Yanshanian granitic bodies in the region but different from those of the ore-hosting marble and metavolcanic rocks. Calcite in the late stage has δ13CV-PDB values of −5.4 to −1.5 ‰, consistent with a predominant magmatic origin. Variations of Co, Ni, Se, and As in pyrite of different generations are interpreted to reflect changes in temperature during hydrothermal evolution. The Co/Ni ratios in all generations of pyrite, mainly between 1 and 10, indicate a magmatic-hydrothermal source. Overall, our new data indicate progressive mixing of a granite-derived magmatic fluid with meteoric waters, as is expected in a distal skarn deposit.

Genesis of the Danping bauxite deposit in northern Guizhou, Southwest China: Constraints from in-situ elemental and sulfur isotope analyses in pyrite

The super large bauxite deposit known as the Danping deposit is hosted in the Dazhuyuan formation, Lower Permian, and is located in northern Guizhou (Southwest China). The geochemical signatures of five generations of pyrite from Danping have been identified, and their genesis has been constrained by analyzing their geochemical signatures. Oolitic pyrite (Py-O), which has two sub-generations, occurs in the upper part of the oolitic bauxite. Typically, Py-O2 has a core and rim structure, where the core may contain altered primary Py-O1. While Py-M appears as occurs in the form of interstitial material in the lower part of the oolitic bauxite, Py-C is cubic in shape and is reported in the earthy bauxite. Moreover, Py-Q is found in the Qixia formation. Py-M has a Co/Ni ratio of ∼ 1 and a δ34SV-CDT value of ∼ 0 ‰, thus suggesting a magmatic hydrothermal origin. The primary Py-O1 has a uniform geochemical composition. The reformed Py-O1 and the core of Py-O2 have considerably lower δ34S values of −19.15 ‰ to −4.72 ‰, indicating that a brief pulse of seawater injection can result in the replacement of Py-O1 and the formation of Py-O2. Py-M, Py-O and Py-Q all have positive Ce anomalies, while Py-C has negative Ce anomalies. These contrasting characteristics demonstrate that the original aluminous rock series was largely deposited in an oxidic environment, while the earthy bauxite was formed in a reducing environment. Lithium, Sc and Ga are positively correlated with one another, reflecting their similar geochemical behavior during sedimentary–weathering processes. Py-M has higher contents of Li, Sc and Ga, implying that magmatic fluids contributed to the presence of critical metals even in the weathering conditions.

Episodic ore-forming fluid evolution processes in the Jiudian gold deposit, Jiaodong Peninsula: Constrains from texture, trace element and S isotope composition of pyrite

Jiudian is a representative quartz vein-type gold deposit in the Jiaodong world-class gold province, southeast of the North China Craton. Four stages and ten pyrite generations can be identified based on the paragenetic relationships: (1) pyrite (Py1)-milky quartz, (2) pyrite (Py2-1 and Py2-2)-smoky grey quartz, (3) siderite-pyrrhotite-pyrite (Py3, Py3-1 and Py3-2)-quartz, (4) quartz-polysulfide-siderite-marcasite (Py4-mc)-pyrite (Py4-1, Py4-2 and Py4-3), suggesting the complex and multistage ore-forming processes.The course-grained euhedral Py1 from the pre-ore stage 1 quartz veins is enriched in lattice-bound Co, Ni, and Se with relatively low δ34S values (+4.7 to + 5.5‰), precipitated from the equilibrated fluid environment with higher temperature (ca. 400 ℃). The dissolution-reprecipitation textures are characterized by the pristine As-rich Py2-1 as parent phase and porous Py2-2 as product phase hosting abundant microscale galena enriched in low-melting chalcophile elements (LMCE, e.g., Pb, Bi, Ag, Te, and Sb) and minor electrum. Both of Au-HS and Ag-Cl complexes destabilized by decompression would result in the precipitation of electrum with low gold fineness (672 to 713). Py3 is a poor host for majority of trace elements coexisting with pyrrhotite, precipitated from the late second pulse fluid.Py3 was overprinted by the third ore fluid pulse and replaced by siderite into sieve-shaped Py3-1 and anhedral aggregates Py3-2. Subsequently, fluid oxidation caused by pyrite replacement and meteoric water influx would result in the precipitation of marcasite (Py4-mc). Furthermore, euhedral pyrite aggregates were directly deposited from this ore-forming fluid, characterized by the Co-rich core (Py4-1) with abundant inclusions of LMCE-dominant sulfosalt (lillianite homologues) and galena, overgrown by pristine As-rich rim (Py4-2). The decoupled As and Co in Py4-1 and Py4-2 were probably attributed to abrupt temperature drop due to meteoric water influx. Nevertheless, the precipitation of visible gold with higher gold fineness in siderite or intergrown with Py4-mc was primarily resulted from fluid oxidation which has significant effect on the stabilities of Au-HS complexes but little on those of Ag-Cl complexes. The last generation Py4-3 was the post-oxidation product, evidenced by the extremely negative δ34S values (-34.3 to −28.4‰).Hence, the textural and geochemistry characteristics of different pyrite generations of Jiudian have revealed the presence of three fluid pulses as well as the distinctive evolution processes and changes of physicochemical conditions leading to the characteristic mineral assemblages and multiple-stage gold mineralization, which could provide implications for the genesis of siderite-rich gold deposits in the Jiaodong district.

Testing the global significance of the sulfur isotope record of the ca. 2.0 Ga Zaonega Formation: A micro-scale S isotope investigation

The Paleoproterozoic metasedimentary rocks of the Zaonega Formation (Onega Basin, NW Russia) are important archives of inferred global environmental change following the initial oxygenation of the Earth’s atmosphere and oceans. However, the geochemical signals preserved in these exceptionally organic-and pyrite-rich metasedimentary rocks and their environmental meaning remain contested. In particular, the Zaonega Formation’s unusually high pyrite sulfur isotope ratios (δ34S) have been explained by either global or local forcings acting on sulfur cycling processes. We tested former interpretations of the Zaonega Formation’s sedimentary pyrite record by integrating bulk and micro-scale δ34S analysis to discriminate the isotopic signatures of different generations of pyrite and determine the underlying mechanisms contributing to δ34S variability. We show that the prolonged genesis of pyrite occurred via multiple stages and included precipitation from early diagenetic fluids, organic matter pyritization, and late-stage alteration fluids. Our results demonstrate that early-stage pyrite typically carries more variable and lower δ34S values than late-stage pyrite. Although the early pyrite captures pore water S isotope signatures least evolved from the seawater, their contribution to the bulk δ34S results can be dwarfed by the greater volume of late-stage coarse pyrite. Consequently, determining the sequence of pyrite precipitation and δ34S characteristics of individual generations in any given sample are fundamental to interpreting bulk δ34S records. Our micro-scale results suggest that previous estimates based on bulk pyrite data (ca. 6 to 18‰) should not be related to the original seawater sulfate’s isotopic composition. These results demonstrate that a thorough understanding of the geological context and mechanisms associated with S-cycling, and pyrite formation is necessary to interpret bulk δ34S records accurately.

Sediment-hosted disseminated gold deposits in orogenic belts: An example from the giant Jiagantan gold deposit in the West Qinling orogen, China

Sediment-hosted disseminated gold deposits in orogenic belts share many similarities to both epizonal orogenic and Carlin-type gold deposits, leading to a lot of difficulties in their genetic classification. The giant Jiagantan gold deposit was newly discovered in the West Qinling orogen, central China, and was selected to provide a better understanding of this issue. Gold mineralization at Jiagantan is hosted within sandstone and silty slate, and the gold is intimately associated to disseminated pyrite and arsenopyrite. Three generations of pyrite (Py0, Py1, and Py2) and two generations of arsenopyrite (Apy1 and Apy2) are recognized and used to perform in situ textural, chemical, and sulfur isotopic analyses.The diagenetic Py0 is framboidal and porous, and contains elevated concentrations of As, Sb, Co, Ni, Cu, Ti, and V. The early mineralization stage Py1 and Apy1 are disseminated within sandstone and silty slate, and have the highest average Au concentrations of 7.7 ppm and 12.6 ppm, respectively. The intermediate mineralization stage Py2 and Apy2 are hosted by quartz veins and veinlets, coexisting with stibnite, chalcopyrite, and minor amounts of other sulfides. Gold mineralization mainly took place during the early mineralization stage. Microscopic observations and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) output graphs confirm the majority of gold may reside in the crystallographic structures of Py1 and Apy1.The diagenetic Py0 grains show negative δ34S values of −25.2 to −20.1‰, implying the derivation of sulfur by bacterial reduction of marine sulfate. The hydrothermal Py1, Py2, Apy1, and Apy2 have higher but still negative δ34S values ranging from −16.4 to −5.0‰, suggesting an origin of sulfur from metamorphism of the underlying Devonian sedimentary rocks.The Jiagantan gold deposit can best be classified as an epizonal orogenic gold deposit owing to the possible metamorphic origin of Au, As, S, and other associated elements. The source of ore-forming materials is the key to discriminating orogenic gold deposits from Carlin-type gold deposits, while the type of host rocks, the style of mineralization, and the occurrence state of gold may not be the effective indicators.

Trace elements and in situ sulfur isotopes of pyrite from the Baiyunpu Au deposit in central Hunan, South China: Implications for gold mineralization

The Central Hunan metallogenic province, located in the southeastern part of the Yangtze Block, South China, is one of the most important Sb–Au metallogenic belts in China. The Baiyunpu gold deposit is one of the important Carlin‐type gold deposits occurring in Devonian sedimentary strata in Central Hunan. Optical microscopy and in situ laser ablation (multi‐collector) inductively coupled plasma mass spectrometry (LA‐[MC]‐ICP‐MS) are used to determine the texture, trace element compositions and sulfur isotope for pyrites from the pre‐ore and syn‐ore stages to constrain the sources of reduced sulfur and metals and the mechanism of gold precipitation. Four generations of pyrite were identified by petrography and pyrite compositions. Pre‐ore Py1 is characterized by relatively low concentrations of As, Au, Sb and Cu and high concentrations of Co, Ni, Bi and Pb. Py1 has positive δ34S values of 6.5–10.1‰, which we ascribe to a bacterial reduction of marine sulfate in closed marine systems, or from weak Rayleigh fractionation by bacterial sulfate reduction (BSR) or thermochemical sulfate reduction (TSR) during sedimentary‐diagenetic processes. Pre‐ore Py2 presents as rims of Py1 and contains relatively high As (69,530 ppm), Sb (123.2 ppm) and low Au (4.89 ppm). Compared with Py2, Py3 has relatively high Au (194.4 ppm) and Cu (24.6 ppm) and low As (40,801 ppm). We interpret that Py2 and Py3 could have precipitated from an Au‐free but As‐rich early hydrothermal fluids or from low‐Au and As‐rich fluids at the beginning of the ore stage. The δ34S values of Py2 and Py3 in the Baiyunpu deposit are concentrated in a narrow range of −1.2 to 1.2‰, suggesting the involvement of magmatic sulfur. Syn‐ore pyrites (Opy) are enriched in Au (517.8 ppm), As (39,719 ppm), Cu (261.9 ppm) and Sb (171.4 ppm). Irregular boundaries between Py1 and Opy suggest that the replacement may have been important for the formation of pyrites at the syn‐ore stage. The variation of As concentration in Opy1, Opy2 and Opy3 appear to have recorded fluctuations in the chemical composition of ore fluids. The δ34S values of Opy (0.1–5.9‰) are slightly higher than Py2 and Py3 due to mixing with sedimentary components with elevated δ34S values in late‐stage hydrothermal fluids. Profile analyses for Baiyunpu auriferous pyrite grains suggest that Au was positively correlated with Cu, but not with As. The correlation between Au, Cu and As in Opy may be dominated by their concentrations of ambient evolving fluids.

Diagenesis of clastic ores of the Ishkininо Co-bearing massive sulfide deposit (Southern Urals): Mineralogical-geochemical data and thermodynamic modeling

Research subject. The transformed clastic ores (ore diagenites) of the Ishkinino Co-bearing massive sulfide deposit hosted by serpentinites of the Main Uralian Fault Zone.Materials and methods. The structures and textures of the ores were stu died. The trace element contents of sulfides and oxides were determined using LA ICP MS. The physical and chemical modeling of the diagenetic formation of accessory As minerals was conducted using the Selektor program package. Results. The clastic ores are transformed gravelites with angular and rounded clasts of serpentinites, sulfides and chromite in the psammitic matrix of the same mineral composition. No hydrothermal minerals remain in gravelites; they are replaced by crystalline pyrite-2, porous pyrite-3, anhedral pyrite-4, pyrrhotite, chalcopyrite and magnetite. Chalcopyrite and magnetite replace all sulfides, sulfarsenides, chromite and gangue minerals. Chromite occurs as fragmented crystals or inclusions into serpentinite clasts. The matrix hosts euhedral cobaltite crystals with nickeline, gersdorffite and native gold inclusions. Crystalline pyrite-2 is characterized by higher Mn, Co, Ni, Cu and Zn contents. Porous pyrite-3 exhibits higher Co, Cu and Se contents. Anhedral pyrite-4 is enriched in most trace element contents in comparison with other sulfides and pyrite generations. Chalcopyrite is characterized by higher contents of Zn and Se. Pyrrhotite contains the highest Ni and hi gher Co contents.Conclusions. The main trace elements in the ores of the deposit (Co and Ni), as well as Cu, Zn and Mn, are hosted not only in sulfides, but also in oxides. Thus, chromite contains Zn and Ni, while magnetite contains Mn and Cu. Selenium occurs in all sulfides in similar quantities. Tellurium is mostly concentrated in pyrite-4. A comparative analysis of our results with those reported on other massive sulfide deposits showed that the serpentinite-sulfide gravelites of the Ishkinino deposit had been intensely transformed during diagenesis, which resulted in low trace element contents in diagenetic sulfides. The diagenetic alteration of clastic ores led to the formation of authigenic cobaltite, gersdorffite, nickeline and native gold as a result of trace element release from primary hydrothermal minerals. Thermodynamic mode ling showed the possibility of formation of As-bearing minerals (in particular, nickeline) at temperatures of 200°C and below.

Thermoelectric Properties of Pyrite in the Supra-Ore Level of Gold Mineralization (Ukrainian Carpathians)

The thermoelectric properties of different-aged generations of pyrite from Lostun (Chyvchyny ore region) Tukalo and Kamin-Kliovka (Лостунь, Тукало, Камінь-Кльовка) (Rakhiv ore region) ore manifestations are investigated. The research included traditional geological observations with the collection of samples of various hosting ores, together with mineralogical analysis measuring their reflective power and the thermo electro-motive force of pyrite. Two pyrite generations (pyrite I and pyrite II) have been revealed by the investigation’s results. The crystals belonging to the generations differ morphologically quite vividly (pyrite I has the form of a pentagonal dodecahedron, while pyrite II takes the form of a cube) and have different thermoelectrical properties. Pyrite I testifies to the fact that in the direction from the central parts of crystals with a pentagonal-dodecahedron tendency to its surface, the thermoelectrical properties essentially change. In particular, the central parts of pyrite I crystals have electron conductivity while its faces are mainly hole ones. Such essential changes of the pyrite thermoelectrical properties from the central parts of the crystals to their peripheral ones are probably mostly caused by quantitative changes of element admixtures in the crystalline lattice. However, the pyrite II thermoelectrical properties investigation results testify that this mineral has only hole-conductivity. Thus, in terms of general thermo-e.m.f. (electromagnetic field) as well as selections range, the thermoelectric properties of the pyrite from the Lostun and Tukalo ore manifestations and the Sauliak (Сауляк) auriferous deposit are similar. The comparative character of the pyrite thermoelectric properties from the investigated ore manifestations, the Sauliak deposit and other auriferous deposits testify to the supra-ore level of the gold mineralization in Tukalo and Lostun objects and make it possible to assume that erosion shear of the gold mineralization in Tukalo ore manifestation is similar to the Sauliak deposit erosive shear and is deeper in comparison to the Lostun ore manifestation.

Пирит зон сульфидизации терригенных комплексов Яно-Колымского орогенного пояса (Северо-Восток России): генерации, типохимизм, минеральные ассоциации

Finely disseminated sulfide mineralization in terrigenous carbon-bearing strata is known to have a certain metal-bearing potential and to be an additional source of ores for deposits. In the zones of finely disseminated sulfide mineralization in the Debinsky, Chay-Yuryinsky and Orotukan-Srednekansky faults of the Yana-Kolyma orogenic belt, three generations of pyrite have been identified and studied: sedimentogenic, hydrothermal-metamorphogenic, and tentatively ore-hydrothermal with different sets of mineral associations. The studies were carried out in the Late Triassic and Early Jurassic sediments adjacent to the faults in the basins of the Spokoyny-Matrosova Creek, the Chay-Yurya River, the Ozyorny Creek, the Khara-Yuryakh Creek, the Nera River, and the Pravy Srednekan River. It was found that the sulfide mineralization had been formed in several stages. Morphological and genetic varieties of pyrite permit to distinguish sedimentary and metamorphogenic pyrite from ore pyrite. According to the quantitative analysis performed on a Camebax microanalyzer with an EDS detector X-Max Oxford, the main trace impurities in pyrite are As, Co, and Ni.

Textures, trace element geochemistry and in-situ sulfur isotopes of pyrite from the Xiaojiashan gold deposit, Jiangnan Orogen: Implications for ore genesis

The northeastern Hunan region in the Jiangnan Orogen (South China) is endowed with many important gold deposits, whose genesis remains controversial. The Xiaojiashan is a representative gold deposit (7.77 t Au @ 2.88 g/t) in NE Hunan, and is characterized by multi-stage pyrite formation. Its mineralization can be divided into 3 stages: (I) quartz-ankerite-pyrite-gold; (II) quartz-ankerite-polymetallic sulfide-gold; (III) quartz-ankerite stage. Three pyrite generations were identified: fine-grained porous Py1 and coarse-grained Py2 in stage I, and core-rim-textured Py3 in stage II. Py1 and Py2 are enriched in Co, Ni, Se and Te, but depleted in As and Au. Comparatively, Py3a and Py3b have higher As, Au, and Zn, but lower Co, Ni, Se and Te contents, indicating the compositional variations of ore-forming fluids from stage I to stage II. The Au- and As-poor Py1 and Py2 have similarly low δ34S values (Py1: −33.30 to − 16.23 ‰; and Py2: −25.41 to − 15.45 ‰), indicating that the sulfur of Py1 and Py2 may have been derived from metamorphism of sedimentary strata, such as Neoproterozoic Lengjiaxi Group. Meanwhile, both the core (Py3a) and rim (Py3b) of the Au-As-rich Py3 have high δ34S values (Py3a: −3.44 to − 1.72 ‰; and Py3b: −1.00 to − 0.99 ‰), resembling typical magmatic sulfur. The trace element compositions and sulfur isotopes of pyrite in stages I and II suggest a distinct shift of ore-forming fluids source from metamorphic (stage I) to magmatic (stage II). Therefore, we propose that the Xiaojiashan gold mineralization was likely associated with early metamorphism and late magmatic-hydrothermal overprinting, and its multistage and complex ore-forming process had recorded the complexity of gold mineralization in NE Hunan.

The Formation of Highly Positive δ34S Values in Late Devonian Mudstones: Microscale Analysis of Pyrite (δ34S) and Barite (δ34S, δ18O) in the Canol Formation (Selwyn Basin, Canada)

The sulfur isotope composition of pyrite in marine sedimentary rocks is often difficult to interpret due to a lack of precise isotopic constraints for coeval sulfate. This study examines pyrite and barite in the Late Devonian Canol Formation (Selwyn Basin, Canada), which provides an archive of δ34S and δ18O values during diagenesis. Scanning electron microscopy (SEM) has been combined with microscale secondary ion mass spectrometry (SIMS) analysis (n = 1,032) of pyrite (δ34S) and barite (δ34S and δ18O) on samples collected from nine stratigraphic sections of the Canol Formation. Two paragenetic stages of pyrite and barite formation have been distinguished, both replaced by barium carbonate and feldspar. The δ34Sbarite and δ18Obarite values from all sections overlap, between +37.1‰ and +67.9‰ (median = +45.7‰) and +8.8‰ and +23.9‰ (median = +20.0‰), respectively. Barite morphologies and isotopic values are consistent with precipitation from diagenetically modified porewater sulfate (sulfate resupply &amp;lt;&amp;lt; sulfate depletion) during early diagenesis. The two pyrite generations (Py-1 and Py-2) preserve distinct textures and end-member isotopic records. There is a large offset from coeval Late Devonian seawater sulfate in the δ34Spyrite values of framboidal pyrite (-29.4‰ to -9.3‰), consistent with dissimilatory microbial sulfate reduction (MSR) during early diagenesis. The Py-2 is in textural equilibrium with barite generation 2 (Brt-2) and records a broad range of more positive δ34SPy-2 values (+9.4‰ to + 44.5‰). The distinctive highly positive δ34Spyrite values developed from sulfate limited conditions around the sulfate methane transition zone (SMTZ). We propose that a combination of factors, including low sulfate concentrations, MSR, and sulfate reduction coupled to anaerobic oxidation of methane (SR-AOM), led to the formation of highly positive δ34Spyrite and δ34Sbarite values in the Canol Formation. The presence of highly positive δ34Spyrite values in other Late Devonian sedimentary units indicate that diagenetic pyrite formation at the SMTZ may be a more general feature of other Lower Paleozoic basins.

Deciphering multiple ore-forming processes of the Shuangqishan orogenic gold deposit, Southeast China by in situ analysis of pyrite

Gold deposits are characteristically formed via multiple mineralization and remobilization events. Inferences on the complex formation history of such deposits from ore textures can be ambiguous in the lack of chemical and isotopic evidence as exemplified by the Shuangqishan orogenic gold deposit in Southeast China. We, therefore, conducted LA-ICP-MS spot analysis coupled with LA-MC-ICP-MS sulfur and lead isotope analysis on texturally complex gold-bearing pyrite from the Shuangqishan deposit. Gold distribution in different syn- to late-ore pyrite generations indicate initial evenly deposition of nano- to micro-inclusions of Au-Ag-Pb-Bi tellurides within pyrite grains and subsequent Au remobilization following brittle deformation and fluid-mediated coupled dissolution-reprecipitation (CDR) reactions. Gold dissolved from the pyrite during the reworking event became re-concentrated and re-precipitated as visible gold either as inclusions in pyrite or larger free gold grains within microfractures of pyrite. The distribution of Bi-Te-Pb-Ag assemblage is comparable to that of Au, illustrating that these trace metals became redistributed in a similar fashion. Early, undeformed pyrite has the least radiogenic Pb isotopic compositions. Late, porous and inclusion-rich pyrite, brecciated pyrite, and recrystallized Te-Bi minerals have variable but in general more radiogenic Pb isotope ratios (higher 206Pb/204Pb and 207Pb/204Pb ratios), which are attributed to modification and precipitation from a more evolved crustal fluid during the re-precipitation of native gold. The Pb isotopic signature of the younger pyrite generations was likely inherited from Pb released during modification of earlier proto-pyrite and a second, crustal lead source that was involved in the hydrothermal system during later remobilization. The δ34S values for the early proto-pyrite and the reworked pyrite generations within the individual vein stage are broadly similar. The variations in sulfur isotope compositions reflect the change in physicochemical conditions (temperature and oxygen fugacity) during proto-ore formation. Our study highlights the importance of metal recycling from early proto-auriferous pyrite during later reworking and gold remobilization, which led to visible gold and high-grade ore shoot formation. The extensive variations of trace element concentrations and S-Pb isotope compositions of proto and reworked pyrites record the complicated Au mobilization and deposition processes and help to understand how gold ores evolved.

Micro-textural and chemical fingerprints of hydrothermal cobalt enrichment in the Jingchong Co-Cu polymetallic deposit, South China

The Jiangnan Orogen, located at the margin of the southeastern Yangtze Block, has Co reserve more than 20,000 t, in which Co occurs mainly along with Cu deposits, with minor as independent Co deposits. As for Co enrichment in the Jiangnan Orogen, it remains unclear whether Co was enriched by the same mineralizing episodes as that precipitating Cu ores or from other processes. The Jingchong Co-Cu polymetallic deposit as a representative was chose to illuminate this issue, based on the integrated TIMA, EBSD, EPMA, LA-ICPMS and LA-MC-ICPMS analyses. The results show that cobaltiferous sulfides have complex textural and compositional zoning patterns. Four generations of pyrite (i.e., PyI, PyII, PyIII and PyIV) corresponding to four different ore stages (i.e., barren stage I, Cu-rich stage II, Co-rich stage III, and Pb-Zn-rich stage IV) were identified. The PyIII which consists of PyIII-1 (0.02–0.79 wt% Co and 0.16–3.08 wt% As) rimmed by PyIII-2 (0.19–13.66 wt% Co and 0.20–7.42 wt% As), arsenopyrite consisting of Apy-1 (up to 0.90 wt% Co and 39.70–42.06 wt% As) and Apy-1 (up to 0.60 wt% Co and 42.42–45.61 wt% As), and cobaltite-alloclasite (18.84–34.98 wt% Co) of stage III dominate the Co occurrence. These inhomogeneous features were explained by the fluid-mediated coupled dissolution-reprecipitation reactions (CDR), and the super-enrichment of the Co metal budget at the interface of PyIII-2 with PyIII-1 was caused by the non-equilibrium process at the advancing reaction front. In combination with the high Co and As contents and Co/Ni ratios (>1) at stage III, as well as the δ34S ranges (−4.47‰ to 3.57‰) similar to that of magmatic sulfur, Co enrichment in the Jingchong deposit could be ascribed to the interaction of a Co– and As-rich magmatic-hydrothermal fluid pulse with wall rock (including the early ores), later than Cu mineralization. The decreasing temperature together with increasing sulfur and oxygen fugacity serve as the critical factors controlling Co precipitation from solutions. This study provides a detailed mineralogical insight into Co enriching process in magmatic-hydrothermal Cu deposits. Finally, a significant mineral indicator (i.e., the coexistence of fine-grained pyrite and arsenopyrite) for Co ore exploration and one more suggestion (i.e., crushing sulfides ores into fine pieces, smaller than 15–20 μm) for efficient cobalt recovery were proposed.