Generations Of Pyrite Research Articles

Influence of fluid-rock interaction on gold mineralization in the Dongwan deposit, East Qinling, China: Constraints from systematic sulfur isotope and trace element geochemistry

The Dongwan gold deposit is located in the Xiong'ershan area, East Qinling, China, with gold ore bodies hosted in NE-trending hydrothermal alteration zone and quartz + sulfides veins in structures. Here we present systematic field investigation, petrographic observations, in-situ trace elements and sulfur isotope of pyrite, and sulfur isotope of galena and barite to elucidate the genesis and effect of fluid-rock interaction during hydrothermal evolution of the Dongwan gold deposit. Four types of pyrite are recognized based on their occurrences in different hydrothermal veins, structures and paragenetic sequences, as follows: i) Py1 in the stage I quartz-pyrite vein is composed of coarse-grained cubic pyrite (Py1-1) and medium-grained cubic pyrite (Py1-2); ii) Py2 is characterized by fine-grained disseminated pyrite in stage II vein; iii) Py3 is represented by pyrite that occurs together with galena, sphalerite and chalcopyrite in stage III vein. The early stage Py1-1 and Py1-2 are characterized by high Co/Ni ratios and low contents of As, Au and Ag. The main ore-forming stages represented by Py2 and Py3 show lower Co/Ni ratios and higher concentrations of As, Sb, Au, Ag, Pb and Cu. The Ni contents of all pyrite types are < 10 ppm, indicating that the ore-forming fluid was derived from felsic rocks. The δ34S values of the different pyrite generations range between −16.0‰ and −7.4‰, which are attributed to the fractionation between barite and sulfide minerals. The sulfur isotopic composition of the hydrothermal fluid calculated from co-genetic barite and pyrite is 1.2‰, suggesting that the ore-forming materials were possible derived from mantle source, and were correlated with the Late Mesozoic granitic magmatism. The main mechanisms of gold precipitation are fluid-rock interaction and decrease of temperature, which promote the Fe2+ rich Xiong’er Group wall rocks to reduce the hydrothermal fluid and disequilibrate the gold-sulfur complex causing the precipitation of gold. The overall trace elements and sulfur isotopic signatures suggest that the pyrite is of magmatic-hydrothermal origin, and that the ore-forming materials of the Dongwan gold deposit are probably related to post-magmatic fluids derived from the Early Cretaceous granitoid magmatism in the region.

Distal gold mineralization associated with porphyry system: The case of Hongzhuang and Yuanling deposits, East Qinling, China

The Hongzhuang and Yuanling gold deposits are located in the Shiyaogou ore field within the Xiong'ershan area, East Qinling, China, where the ore bodies are hosted in Xiong'er Group and mainly controlled by EW-trending and NE-trending faults. The gold mineralization mechanism and the possible genetic link with the porphyry magmatism and hydrothermal events remain unclear. Here we present results from systematic field investigation, petrographic observation, in situ trace elements and sulfur isotope of pyrite to elucidate the genesis of gold mineralization in these deposits. Based on the occurrences of pyrite in different hydrothermal veins, three types of pyrite are identified from each deposit, including: i) coarse-grained cubic pyrite (HZ-Py1 and YL-Py1) in stage I milky quartz vein; ii) medium- to fine-grained pyrite (HZ-Py2 and YL-Py2) in stage II polymetallic sulfides veins; iii) coarse-grained pyrite (HZ-Py3 and YL-Py3) symbiotic with calcite in stage III quartz-calcite vein. The LA-ICP-MS trace element analyses of pyrite show that Au occurs as invisible nanoparticles or nano-sized inclusions in pyrite through absorption-chemisorption during the growth of pyrite or as nano-sized Au-bearing mineral inclusions. The δ34S values of different generations of pyrite in the Hongzhuang and Yuanling gold deposits range from 3.92‰ to 6.43‰ and 2.82‰ to 4.46‰, respectively, indicating that the ore-forming materials were mainly derived from mantle-related source with affinity to the Late Mesozoic granitic magmatism. The Hongzhuang and Yuanling gold deposits are spatially and temporally correlated with the Shiyaogou pluton and they show consistent material sources. We propose that the hydrothermal Au mineralization in these deposits were the distal products generated from the post-magmatic fluids of the Shiyaogou porphyry system. The stretching and thinning of the early Cretaceous lithosphere led to the upwelling of magma and migration of fluid, forming the Au mineralization in fault structures in the shallow crust.

Silver enrichment and trace element deportment in hydrothermal replacement reactions: Perspective from the Nageng Ag-polymetallic deposit, East Kunlun Orogen, NW China

Mineral replacement reactions (dissolution-reprecipitation and solid-state diffusion) have been reported in various types of hydrothermal deposits. However, the metal transfer and partitioning between the parent and daughter minerals and the role of different replacement reactions in silver enrichment remains poorly understood. Here we present the petrographic textures, major and trace elements, and sulfur isotopes of different generations of pyrite and marcasite associated with replacement reactions from the Nageng epithermal Ag-polymetallic deposit, East Kunlun Orogen (EKO, NW China). The mineralization includes the pyrite-quartz (I), quartz-siderite-sulfides (II), quartz-fluorite-rhodochrosite-sulfides-sulfosalts (III), and quartz-calcite (IV) stage. This deposit is characterized by a metal zonation from deep-level Cu-Pb-Zn mineralization to shallow-level Ag-Pb-Zn mineralization, which correspond to main ore stages II and III, respectively. Stage II ores contain the colloform pyrite (Py1) and porous pyrite aggregate (Py2), both of which have higher Co, Ni, and W contents than stage III pyrite (Py3 and Py4) and marcasite (Mc1 and Mc2). In contrast, stage III pyrite/marcasite are enriched in Ag and other ore metals (e.g., Pb, Zn, Sb, Mn, and Sn). The sharp contact between Py3 and Py4/Mc1, together with the porosity in Py4/Mc1, suggests that Py3 and Py4/Mc1 represent the parent and daughter phase of dissolution and reprecipitation. The crystallographically-oriented and metallic inclusion-rich Mc1 has higher Ag concentrations (median 246 ppm) than Py3 (median 180 ppm), and commonly occurs in breccia-type ores related to hydraulic fracturing. This suggests that (i) the dissolution-reprecipitation reaction may have remobilized and concentrated silver and associated ore metals, and (ii) the fluid oxidation related to hydraulic fracturing may contribute to dissolution-reprecipitation reaction. However, the randomly-oriented Mc2 is porous and has homogeneous compositions. This, together with the prevailing occurrence with rhodochrosite in vein-type ores, indicates that Mc2 was transformed from Mc1 via Mn-rich fluid-driven solid-state diffusion under relatively mild physicochemical changes. Mc2 has the most homogeneous and highest Ag concentrations (avg. 1142 ppm) and other ore meals among all the studied Fe disulfides, suggesting that the marcasite has higher trace element compatibility than pyrite, and that the solid-state diffusion reactions promoted Ag enrichment more efficiently than dissolution-reprecipitation reactions. The mostly positive δ34S values (−1.09 to 8.50‰) of the Nageng pyrite and marcasite are consistent with a magmatic origin. The δ34S variations among different pyrite and marcasite generations are attributed to the fluctuations between episodic replenishment of magmatic fluids and subsequent oxidation in respond to hydraulic fracturing and mixing with meteoric water. Our findings reveal higher Ag compatibility of marcasite over pyrite, and that replacement reactions (especially solid-state diffusion) greatly promote ore metal enrichment.

Diversity of Pyrite-Hosted Solid Inclusions and Their Metallogenic Implications—A Case Study from the Myszków Mo–Cu–W Porphyry Deposit (the Kraków–Lubliniec Fault Zone, Poland)

Pyrite from the central part of the Myszków porphyry deposit in Poland was investigated using a combination of reflected and transmitted polarizing microscopy, back-scattered imaging with energy-dispersive X-ray spectroscopy, and Raman micro-spectroscopy. Five generations of pyrite (I–V) found in hydrothermal veins were distinguished, differing in morphology, microtexture, and the types and amounts of solid inclusions. In general, pyrite hosts a diversity of mineral inclusions, including both gangue and ore phases, i.e., chlorite, quartz, monazite, cerianite-(Ce), xenotime, K-feldspars, albite, sericite, barite, magnetite, chalcopyrite, galena, sphalerite, bastnaesite (Ce), bismuthinite, native silver, cassiterite, rutile, anatase, and aikinite-group species. The presence of inclusions is good evidence of various stages of the evolution of the hydrothermal lode system ranging from high- to low-temperature conditions. During the formation of stockworks, some fluctuations in the physicochemical conditions of mineralizing fluids were indicated by the occurrence of cassiterite formed from acidic, reducing solutions, and hematite hosted in xenotime or REE phases found in pyrite, which signal more oxidizing conditions. Periodically, some episodes of boiling in the hydrothermal, porphyry-related system were recorded. They were mainly evidenced by the presence of (1) lattice-bladed calcite found in the close vicinity of pyrite II, (2) irregular grain edges of pyrite I, (3) clustered micropores in pyrite I, and (4) the variety of mineral inclusions hosted in I and II generations of pyrite.

In situ trace elements and sulfur isotopes of sulfides in the Dabaiyang Te-Au deposit, Hebei Province, China: Implications for Au remobilization from pyrite

Coupled dissolution–reprecipitation (CDR) reactions and low-melting point chalcophile elements (LMCE) melt scavenging are effective mechanisms for gold remobilization and are important for the formation of Te-Au deposits. The Dabaiyang deposit is a typical Te-Au deposit in the Zhangjiakou district and contains tellurides, including altaite, hessite, petzite, tetradymite and tellurobismuthite. Two generations of pyrite have been recognized in the deposit: early pyrite without fractures or alteration (Py1) and later pyrite with more porosity, inclusions and fractures (Py2), and Py2 could be separated into Py2a that containing many fractures without mineral inclusions and Py2b that containing microfractures, micropores and mineral inclusions. Pyrite containing large amounts of mineral inclusions and free of microfractures (Py-MI) has also been recognized, but timing relationships between Py-MI and Py1 (or Py2) is hard to establish. The Pyrite textures indicate that Py2a underwent brittle deformation and that Py2b underwent CDR reactions and Te-melt scavenging. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses show that Py2a contains trace elements similar to Py1, while Py2b contains higher Au, Ag, Te and other trace elements, indicating that brittle fracturing has no effect on element mobilization and reprecipitation, and porous pyrite has Au-Ag-Te concentrations. High Co/Ni ratios and Te contents and low Se contents show that the Dabaiyang deposit has a genetic relationship with magmatic activity. In situ δ34S values of sulfides range from −15.77‰ to −6.09‰ (mostly from −13.89 to −10.06‰), which is consistent with bulk sulfide δ34S values. The negative δ34S values more likely resulted from sulfur isotope fractionation in high fO2 hydrothermal fluids. CDR reactions liberated Au, Te, Ag and other trace elements from pyrite and formed porous textures. Then, Te-rich melts scavenged Au from fluid and wallrocks during migration. Finally, the melt precipitated as mineral inclusions in pores or fractures in pyrite. CDR reactions and LMCE melt scavenging played an important role in upgrading the ores and the occurrence of visible native gold in the Dabaiyang gold deposit, as well as other Te-Au deposits in the Zhangjiakou district.

Intrusion-related orogenic gold deposit in the East Kunlun belt, NW China: A multiproxy investigation

The Wulonggou gold district is one of the most important gold producers of the East Kunlun metallogenic belt in China. Due to its complex geological background and limited investigations, the age of mineralization and ore-forming process remain unclear. Here, we focus on the Yanjingou gold deposit which is the largest and most typical deposit in the Wulonggou gold district, with a view to investigate the metallogenic mechanism and timing of ore formation with a view to evaluate the ore-forming processes and sources through a comprehensive study of the ore mineralogy, monazite and zircon U-Pb dating, in situ trace element analysis and mapping, and in situ S isotopes. Our results show that the magmatism and mineralization were coeval, during 239 Ma and 244 Ma in the Middle Triassic. Four stages of mineralization are identified with distinct textures, mineral assemblages, trace element characteristics and S isotopes. Stage 1 is represented by euhedral pyrite bearing quartz veins, which originated from deep metamorphic fluid, and was rarely affected by magmatic hydrothermal fluids. Stage 2 is characterized by the occurrence of abundant oriented arsenopyrite, which originated from the mixture of deep metamorphic fluid and magmatic hydrothermal fluid. Stage 3 is characterized by the occurrence of polymetallic sulfide of copper, with two generation of pyrite (stage 3 Py1 and Py2). Stage 3 Py1 formed from magmatic hydrothermal fluids whereas Py2 originated from deep metamorphic fluid and was also slightly influenced by magmatic hydrothermal fluids. Stage 4 is represented by late calcite and pyrite combination, which originated from another stage of deep metamorphic fluid. Stage2 and 3 are the main gold mineralization stages, and Au has a close relationship with As, and an obvious inverse correlation with Co and Ni. Combined with the trace element characteristics, we infer that the denudation degree of the Yanjingou gold deposit is very shallow with good prospects for exploration. Through multi-proxy investigation of the different stages and types of pyrite, we postulate that the Yanjingou gold deposit is an orogenic gold deposit related to intrusive rocks formed during Middle Triassic compressional transformation.

Mineralogical and geochemical evidence for biogenic uranium mineralization in northern Songliao Basin, NE China

The sandstone-hosted uranium mineralization areas in the Sanzhao Sag of the northern Songliao Basin have been newly identified. The target stratum is the Upper Cretaceous Sifangtai Formation and the uranium mineralization mainly occurs in the bottom of Sifangtai Formation, corresponding to channel sand bodies in meandering river system, characterized by medium to fine-grained sandstone. This study proposes the uranium metallogenic model through petrographic observation, whole rock geochemistry, mineralogical study of uranium occurrence form (SEM), organic matter rock–eval pyrolysis analysis (REP) and in-situ sulfur isotope determination of different generations of pyrite by LA-MC-ICP-MS. Compared with the sandstones collected in barren reduction and oxidization zones, the mineralized sandstones show obvious increase in the contents of TOC, total sulfur, Y and U. Petrographic observations indicate that organic matters are mainly inherited from land plants. REP data display that the organic matter (OM) disseminated in the sandstone has very low hydrogen index (HI) from around 0 to 21 mg HC/g TOC and varied oxygen index (OI) from 44 to 115 mg CO2/g TOC, corresponding to Type Ⅳ kerogen (degraded kerogen). There are two types of coffinite with different grain size, micro-particles (μm-sized) and large aggregates (generally up to 100 μm) respectively. The coffinite micro spherules exhibit short rod-like or worm-like morphology occurring in clay matrix and cell cavities in degradofusinite or around subidiomorphic-idiomorphic pyrite. The coarse-grained coffinite contains other mineral facies (e.g. pyrite, quartz) and some of large coffinite aggregates display thrombolite-type microbial structures. The irregular pyrite relict particles in coarse-grained colloidal coffinite have light sulfur isotope compositions characterized by δ34S values from –39.96‰ to –49.89‰. The δ34S values of colloidal pyrite in replacement of OM or of the sub-idiomorphic FeS2 cement filling in the cavities of OM range from –52.77‰ to –13.88‰. Some of sub-idiomorphic pyrite cement and idiomorphic crystal have the heavier signature from – 27.06‰ to + 14.23‰. The light sulfur isotope signature suggests that the sulfur originates from bacterial sulfate reduction (BSR). The OM replacement by pyrite and the highest OI values recorded by REP in uranium mineralized samples are lines of evidence of biodegradation. Bacteria use the organic matter as food source and produce isotopically light reduced sulfur species. Oxygenated uranium-bearing waters infiltrated through the denudated windows at Daqing placanticline into the porous reduced sandstones deposited in the Sanzhao Sag. Uranium was indirectly reduced by BSR-derived iron disulfides or directly reduced by sulfate-reducing bacteria.

Multistages mineralization and transformation of terrigenous rocks in the Vyun ore field, Yana-Kolyma metallogenic belt, Northeast Asia: insight from the sedimentary, diagenetic and hydrothermal sulfides and geochemistry of ore-hosting rocks

The article presents the results of studying the sulfidization zone of the Charky-Indigirka thrust fault within the Vyun ore field in the Upper Adycha sector of the Yana-Kolyma metallogenic belt. The purpose of the research is to study the composition and distribution of basic and trace elements in terrigenous rocks of the Upper Triassic and Middle Jurassic, as well as in distal metasomatites on the territory of the Vyun ore field. The petrochemical features of weakly altered terrigenous rocks, conditions of their formation and changes of composition during epigenetic processes were analyzed. Three generations of pyrite were identified: diagenetic Py1, metamorphogenic Py2 and metasomatic Py3. Typomorphic trace elements and variations of their distribution in pyrites were determined. Composition analyses of weakly altered sedimentary rocks of the Upper Triassic (V/(V+Ni)=0.5-0.8, V/Cr=0.1-2.9 and Ni/Co=2.5-10.3) and Middle Jurassic (V/(V+Ni)=0.7-0.9, V/Cr=0.2-2.0 and Ni/Co=1.3-8.8) yielded the conclusion that changes in oxygen conditions to disoxic and anoxic, as well as the enrichment of terrigenous material with ore elements, lead to the formation of authigenic sulfide mineralization at the early stages of the sedimentary strata formation. The subsequent multistage development of the territory was accompanied by an active migration of chemical elements, their input and redistribution.

Evidence of fluid evolution of Baoshan Cu−Pb−Zn polymetallic deposit: Constraints from in-situ sulfur isotope and trace element compositions of pyrite

In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements. Three generations of pyrite (Py I, Py II, and Py III) in the skarn-type ores and pyrite in the carbonate-hosted sulfide ores from central, western, and northern (C_Py, W_Py, and N_Py) mining districts are selected for comparison. Compared with Py I and Py III, the contents of most elements in Py II are apparently higher. The As and Se contents are high within a wide range and are decoupled in the growth band of the C_Py. The highest As, Se, and Pb contents were found in W_Py and N_Py. These results indicate the drastic changes in the temperature and fluid mixing during the mineralization. The occurrence of fluctuation and change in temperature and f(O2) was triggered by intermittent pulses of magmatic-hydrothermal fluids, mixing with meteoric water, and water−rock interactions. The sulfur isotopes of all species of pyrite indicated the magmatic source. The change in the f(O2) conditions caused slight differences in the sulfur isotope compositions. Consequently, a metallogenic model was proposed to explain the ore-forming processes.

In situ multiple sulfur isotopes and chemistry of pyrite support a sedimentary source-rock model for the Linwang Carlin-type gold deposit in the Youjiang basin, southwest China

The Linwang gold deposit is a representative example of Carlin-type gold deposits in Youjiang basin, southwest China. High-grade ores are hosted in silicified and brecciated siltstone, sandstone, and mudstone of the Middle Triassic and are controlled by high-angle reverse faults. Optical microscopy pyrite texture, in situ laser ablation-inductively coupled mass spectrometry (LA-ICP-MS) trace elements, and secondary ion mass spectrometry (SIMS) multiple sulfur isotopes analyses are used to examine the different types of pyrites to constrain the sources of reduced sulfur and metals for the Linwang deposit.Petrography and pyrite chemistry studies distinguished three generations of pyrite: Pre-ore pyrite (Py 1) and ore pyrites (Py 2 and Py3). Pre-ore pyrite is framboidal, anhedral to euhedral pyrite with highest concentrations of Co, Ni, and Pb and is interpreted to have a sedimentary (diagenetic) origin. Ore pyrites were formed by hydrothermal fluids via sulfidation of Fe-bearing minerals in the host rocks. They commonly rimed and partially replaced the pre-ore pyrite and have an As-rich inner rim (Py 2) and an Au-rich outer rim (Py 3) with lowest contents of Co, Ni, and Pb. All pyrites contain Au, As, Sb, Cu, Tl, and Se, with increasing concentrations from Py 1 to Py 3.In situ SIMS multiple S isotope analyses show that all pyrites in the Linwang deposit have narrow ranges of δ34S values, with average of +5.13‰ for Py 1, +4.84‰ for Py 2, and +4.53‰ for Py 3, and near zero of Δ33S values (−0.02‰ to +0.03‰), suggesting that the S within the Linwang deposit was most likely sourced from the Triassic sedimentary rocks that host the deposit. A near zero Δ33S signature in all pyrites indicates no record of the assimilation of Archean sulfur, implying the deep basement of Archean rocks beneath the basin were not involved the formation of the Linwang deposit.Oxygen and hydrogen isotope compositions of ore fluids (δ18OH2O = +11.7‰ to +16.5‰, δD = −71‰ to −57‰) indicate a metamorphic origin. Based on these data, we propose a sedimentary source-rock model for the Linwang deposit in which the ore fluids were generated by release of previous Au-bearing sedimentary pyrites during metamorphism of sedimentary rocks. The stress relaxation of Yanshanian orogeny resulted in the ore fluids flowed upward along the fault zones into structural highs where they reacted with Fe-bearing minerals in the host rocks to deposit Au-rich pyrite. The preconcentration of Au, As, and Sb in sedimentary pyrite and gold deposition process are key to the formation of the Linwang deposit and may apply to the genesis of other Carlin-type gold deposits in the Youjiang basin.

Mineralogy and geochemistry of tellurides and pyrite from the Laowan Au−Ag−Te deposit, Qinling−Dabie orogenic belt, central China: Implications for ore genesis

The Laowan Au − Ag − Te deposit (containing greater than 100 t Au), located at the center of the Qinling − Dabie orogenic belt in central China, represents a breakthrough in gold prospecting in the Tongbai district. A tunnel geological survey and microscope-based mineral identification, combined with EMPA/EDS mapping and LA-ICP-MS analysis, were used in this study to determine the mineral types present. The sequence of formation and symbiosis were determined using the Au-hosting mineral geochemical element typomorphism to provide a basis for Au enrichment and the sources of material and ore − forming fluids. The results indicate that: (1) Tellurides were widespread in the main metallogenic auriferous pyrites, consisting of petzite, calaverite, tellurobismuthite, tetradymite, volynskite, and hessite. The vertical zonation of different telluride combinations indicates that mineral distribution shows the vertical zoning characteristics of upper Ag and lower Bi. (2) Petrographic analyses indicate that 5 generations of pyrite formed during the ore-forming stage (Py1, Py2, Py3, Py4, and Py5). LA-ICP-MS analytical data showed that Py3 and Py4 were rich in Au − Ag − Bi − Te, with a correlation between gold and tellurium. Auriferous pyrites were rich in both As and Te, and the enrichment of Au was unrelated to As. Te is an important scavenger of gold, the effect of As is not obvious. (3) From 250 °C to 200 °C, logfTe2 and logfS2 decreased from − 13.0 to − 8.3 and − 14.7 to − 8.6 to − 15.2 to − 11.2 and − 16.7 to − 10.5, respectively. fTe2, fS2 and temperature were the conditions controlling variations in the telluride combination. (4) The occurrence of tellurides, the correlation of Au − Ag − Bi − Te elements and enrichment of Te and Bi, combined with previous isotopic geochemical data, indicate that the ore-forming fluids and metals might be stemmed from the mantle-derived magmatic system, which could have provided materials, sufficient heat energy, volatiles, and components for the gold mineralisation.

Multistage ore-forming processes and metal source recorded in texture and composition of pyrite from the Late Triassic Asiha gold deposit, Eastern Kunlun Orogenic Belt, western China

The Asiha vein-type gold deposit, located in the Eastern Kunlun Orogenic Belt, provides an excellent opportunity for deciphering sources of metals and origins of orogenic intrusion-related gold systems. Within this deposit, four types of pyrite have been distinguished in three stages of hydrothermal activities. Pyrite (Py1) occurs in quartz-pyrite veins (stage I); pyrite (Py2), consisting of core (Py2a) and rim (Py2b), occurs in quartz-polymetallic sulfide veins (stage II); pyrite (Py3) occurs in quartz-pyrite-chalcopyrite veins (stage III). Py1 contains high concentrations of As (median of 2090 ppm) and Au (0.1 ppm). Py2a is enriched in Co (43.1 ppm) and Ni (50.9 ppm), but depleted in As and Au. By contrast, Py2b is enriched in As (7894 ppm) and Au (0.5 ppm), but depleted in Co and Ni. Although, Py3 shows enrichment in Co (1319 ppm) and Ni (1783 ppm), it is usually accompanied with chalcopyrite and visible gold. Three generations of gold-associated pyrite indicate three stages of hydrothermal mineralization, and the variation of metals in pyrite suggest that the ore-forming materials were predominantly derived from felsic magma mixed with different proportion of mafic-volcanic host rocks. U-Pb dating on hydrothermal monazite from stage III constrains the mineralization age at 227 ± 7 Ma, which is coeval with the concealed granite porphyry (228 Ma). The δ34S values of the pyrites vary from +4.8‰ to +8.9‰, which are slightly higher than magmatic pyrite in porphyry (+4.2‰ to +5.6‰). We tentatively propose that the ore-forming materials are closely related to the granite porphyry and the evolved magmatic hydrothermal fluids.

In situ chemical and isotopic analyses and element mapping of multiple-generation pyrite: Evidence of episodic gold mobilization and deposition for the Qiucun epithermal gold deposit in Southeast China

Abstract Gold deposits are often the result of complex mineralization and remobilization processes. Interpretation of bulk geochemical and sulfur isotope data of the gold deposits is frequently hampered by complex zoning in pyrite, which calls for in situ determination of geochemical and sulfur isotope composition of sulfide minerals. The Qiucun deposit is a good representative of epithermal gold deposits in the Mesozoic Coastal Volcanic Belt of southeastern China. It represents a complex mineralization history, comprising three hydrothermal stages: (I) early stage of pyrite-quartz-chalcedony; (II) main ore stage of quartz-polymetallic sulfide; and (III) post-ore stage of quartz-carbonate. Detailed backscattered electron imaging (BSE) and in situ trace element and sulfur isotope analyses using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and LA-multicollector (MC)-ICP-MS were applied to reveal the gold mineralization and remobilization history of this deposit. Four texturally distinct generations of pyrite were identified, all of which host invisible gold: Py1a and Py1b in Stage I and Py2a and Py2b in Stage II. A detailed study of the texture, chemistry, and sulfur isotopic composition as well as hydrothermal evolution of auriferous pyrite from the Qiucun deposit revealed the behavior of gold in the course of pyrite evolution. Pyrite of Stages I and II contains invisible gold, whereas later-stage visible native gold and re-enrichment in invisible gold is associated with alteration rims around the primary pyrite grains. Py1a is rich in silicate inclusions, enriched in Co and Ni, and depleted in As and Au relative to later pyrite generations. This redistribution is attributed to the alteration of biotite in the sub-volcanic host rocks that effectively destabilized gold in the ore fluid during Py1a deposition. Py1b and Py2a show oscillatory zoning with bright bands having elevated As and Au contents. The oscillatory zoning is interpreted to reflect pressure fluctuations and repeated local fluid boiling around the pyrite crystals. These three pyrite generations (Py1a, Py1b, Py2a) record a narrow range of δ34SV-CDT values between –3.6 and 4.6‰, consistent with a magmatic sulfur source. Gold and some trace elements (As, Ag, Sb, Pb, Tl, and Cu) that were initially incorporated into Py2a became partially exsolved and remobilized during the replacement of porous and invisible gold-rich Py2b. This replacement was likely due to coupled dissolution and re-precipitation reactions triggered by oxidation of the mineralizing fluids. Fluid oxidation is further supported by a general decrease trend of δ34SV-CDT from Py2a (–3.2 to 4.6‰) to Py2b (–15.2 to –2.3‰). Last, previously formed auriferous pyrite underwent post-mineralization fracturing, causing local pulverization of pyrite. Thus, newly created porosity facilitated fluid circulation, hydrothermal alteration of the pyrite, and remobilization of invisible gold, which re-precipitated with pyrite in the form of electrum as small inclusions or as larger grains within fractures. Our study emphasizes that pressure-driven hydrothermal processes play a vital role in the initial enrichment and re-concentration of gold and some other trace metals during episodic deposition, replacement, and hydrothermal alteration of gold-bearing pyrite in epithermal gold deposits, ultimately forming visible gold and high-grade ore shoots as exemplified by the Qiucun deposit.

Gold accumulation in the metavolcanic-hosted orogenic gold deposit constrained by pyrite paragenesis coupled with in-situ trace elements and sulfur isotope: The Sarekuobu example in the Chinese Altay Orogen

Origin and accumulation process of gold in the metavolcanic-hosted orogenic gold deposits is still open to debate. Approximately fifteen gold-bearing deposits are hosted in the metamorphosed volcanics of the Chinese Altay Orogen, NW China. Among them, the representative Sarekuobu gold deposit, occurs as lodes in a Devonian volcanic-sedimentary succession that was deformed into a series of multiple overturned synclines and metamorphosed to (garnet)-biotite-chlorite schists. In previous studies, little attention has been paid to pyrite varieties and their in situ geochemistry to constrain their genetic understanding. Herein, five types of pyrite with distinct textures and mineral assemblages at Sarekuobu are divided into four generations based on the crosscutting and replacing relationship. The earliest pyrite (PyI) occurs as magnetite-pyrite parallel laminated layers comparable to those in VMS deposits, and some of its beddings are crosscut by PyⅡ that is scattered in foliation of the host greenschists and likely formed during syn-deformation. The colloidal PyIIIa and inclusion-rich PyIIIb are present in the same auriferous quartz veins continuously cutting across the PyⅡ-rich schists. It is notable that PyIIIb acts as the most important gold-bearing pyrite containing some micro-mineral inclusions such as visible gold and chalcopyrite. The final inclusion-poor PyⅣ with coarse and euhedral grains replaces or envelops all above three pyrite generation. The highest gold concentrations are presented in PyIIIa and PyIIIb by LA-ICP-MS spot analysis, with the maximum values up to 16 ppm and 426 ppm, respectively. In contrast to the substituted invisible Au nano-particles in lattice structures with time-resolved LA-ICP-MS signal parallel to Fe, the visible Au occurs as sizeable micro-inclusions in PyIIIb revealed by highly variable LA-ICP-MS signal spectrum. Further LA-ICP-MS trace element mapping show Au and other trace elements (e.g., Cu, Pb, Zn, Bi, Sb and Ag) are unevenly distributed in PyIIIb but barren in coexisting PyⅣ, in agreement with the microscopic textures of inclusion-rich PyIIIb and inclusion-poor PyⅣ. Another mapping displays these trace elements are homogeneously distributed along colloidal layers in PyIIIa but depleted in the coexisting PyI. Collectively, PyIIIb is believed to experience relatively longer-time crystallization co-precipitating with native gold and chalcopyrite, whereas PyIIIa is rapidly deposited from the same auriferous ore fluids without sufficient time for crystallization and captures some clay minerals and organic matters. In-situ δ34SV-CDT values of four pyrite generations by fsLA-MC-ICP-MS range from +2.34 to + 10.14‰, and gradually decrease from PyI (mean, +9.59‰), through PyⅡ (+8.67‰), PyIIIa (+6.16‰) and PyIIIb (+4.97‰), to final PyⅣ (+3.66‰). In combination with published sulfur isotope composition of host rocks (maximum, +18.7‰), the formation of the auriferous fluids and deposition of Au in pyrite at Sarekuobu might be attributed to the sulfur pathway of progressively enhanced thermal sulfate reduction (TSR) in the Devonian marine strata. Thus, two process including the Devonian seafloor sedimentation and Triassic orogeny-related metamorphism are critical for formation of the Sarekuobu gold deposit.

Geochemistry of Pyritic Mudstones from the Singa Formation, Malaysia: Insights into Gold Potential, Source of Sulfur and Organic Matter

Major trace element analyses, including pyrite chemistry of pyritic mudstones of shallow-marine Singa Formation of Pennsylvanian–Early Permian age have been carried out to assess gold potential, the source of sulfur and organic matter. Regionally, Singa Formation spatially correlates with the Bohorok Formation (Sumatra, Indonesia), the Kaeng Krachang group (Thailand), and the Lebyin group (Burma or Myanmar). In Southeast Asia, this formation is important because it has a record of glacial processes that occurred along the northern margin of Gondwana in the Late Paleozoic age. This study has revealed that mudstones of the Singa Formation, which contain lonestones of glacial origin, deposited under suboxic–oxic conditions in shallow marine environment during Pennsylvanian–Early Permian time. The black mudstones contain total organic carbon which ranges from 0.1 to 0.7 wt.%, and gold content varying from 40 to 62 ppb, making them gold source rocks. This study has revealed diagenetic gold presence in the early pyrite generations (pyrites 1, 2, and 3) in these mudstones with gold content ranging up to 1.6 ppm Au which is indicative of early enrichment of gold. Conversely, late generations of pyrite (pyrites 4, 5, and 6) in these mudstones record low gold content up to 0.5 ppm Au. The δ34S values for pyrite grains range from −24.6‰ to +6.2‰ likely indicate a combination of magmatic and biogenic source of sulfur. Organic carbon isotope composition of the pebbly mudstone samples shows a wide range from −23.9‰ to −5.8‰ indicating a mixed terrestrial and marine source.

Occurrence and remobilization of gold in the Dayingezhuang deposit in Jiaodong, North China Craton: Evidence from textural and geochemical features of pyrite

The Dayingezhuang gold deposit in the Jiaodong district, eastern margin of the North China Craton is hosted in Mesozoic granitic rocks and consists of quartz-sulfide veins/veinlets and sulfide disseminations in alteration envelopes. Previous studies mainly focused on the geochronology, sources of ore-forming fluids and metals to investigate the ore genesis. However, enrichment mechanism of Au and other associated trace metals remain unclear. In this study, we present detailed textures and in-situ LA-ICP-MS trace-element compositions of different generations of pyrite, as well as EMP analysis of Au-bearing minerals to discuss the occurrence and enrichment mechanism of Au at this deposit.Three generations of pyrite (Py1, Py2 and Py3) formed during three hydrothermal ore stages (I, II, and III) at Dayingezhuang. Py1 occurs as disseminations in sericitic alteration assemblages and is characterized by low Au (mean 0.15 ppm), Ag, As and Te contents. The time-resolved depth-concentration profiles indicate that Au in Py1 mainly occurs as nanoparticles and/or micron-sized inclusions. Py2 can be further divided into the early undeformed Py2a and later Py2b, which is the product of deformed Py2a with different degrees of brittle to plastic deformation and recrystallization. Py2a in pyrite-siderite-quartz veins is relatively enriched in invisible Au (mean 0.41 ppm), Ag, As, and Te compared to Py1, and contains numerous micron-sized Au inclusions. In contrast, Py2b contains lesser invisible Au (0.21 ppm) and host abundant gold minerals along the grain boundaries and microfractures. Py3 in polymetallic sulfide veins has little Au. As a whole, Au in pyrite is positively correlated with Ag and Te, which is consistent with the results of EMP analysis showing the occurrence of Au as electrum, native gold and minor petzite in pyrite. Such evidences show that the deformation and recrystallization of auriferous Py2a potentially caused local remobilization of Au (mainly as micron-sized inclusion Au) via solid-state ductile flow and subsequent reconcentration of Au in microfractures of Py2b. The pyrite deformation and Au remobilization events were suggested to be related to the continuous reactivation of the regional Zhaoping Fault contemporaneous with gold mineralization. Our study highlights the importance of remobilization and reconcentration of Au triggered by syn-ore tectonic activities at Dayingezhuang and possibly other Au deposits in the Jiaodong district.

SHRIMP 4-S isotope systematics of two pyrite generations in the 3.49 Ga Dresser Formation

The 3.49 Ga Dresser Formation has been considered to host evidence of the earliest microbes metabolising sulfur species on Earth. However, previous bulk analyses and in situ measurements conclude disparate metabolisms based on opposite ΔS. This study first established the generations of pyrite growth, and then measured the multiple sulfur isotopes in situ using Sensitive High Resolution Ion MicroProbe-Stable Isotope analyses. Two main generations of pyrite were revealed based on core-rim textures and multiple sulfur isotopic compositions: ΔS-positive Generation One (G1) and δS- and ΔS-negative Generation Two (G2). In the chert-barite unit, the diluted ΔS-positive and ΔS-negative photochemical products were mainly sequestered in G1 and barite, respectively. G2 were formed via the sulfide pathway with sulfur derived from sulfate reduction and magmatic HS. The δS-ΔS-ΔS systematics suggests an abiological origin for G1, and thermochemical and possible (minor) microbial sulfate reduction for G2.

The trace and rare earth element contributions to the understanding of Chouichia iron-copper deposits in Northern Tunisia: metal sources interrelated with magmatism and metamorphism

The Chouichia ore deposits are one of the most important polymetallic Cu-Fe-rich mineralizations located in the front of the thrust zone of the Tunisian Tellian belt. This mineral occurrence is carried by veins and breccias hosted by the Upper Cretaceous to Oligocene-Lower Miocene sediments in the Fej Et Tamer tectonic corridor. Geochemical work carried out on host rock and mineral samples shows an enrichment and fractionation of REEs with Eu negative anomalies due to interactions of hydrothermal fluids with Eu-depleted magmatic rocks presumably lying in the subsurface. Co/Ni ratios help distinguish three pyrite generations. Pyrite I disseminated in the host rock is sedimentary-syngenetic, formed at low temperature (Co/Ni 1 and confirmed by varying Y/Ho ratios (range 19.625 to 36.5). Trace element amounts normalized to the average contents of trace metals in primitive mantle testify to a metal source from the upper crust and upper mantle with high enrichments of ore bodies in As, Sb, Cu, Pb, Ag, Au, W, and Mo. Marked depletions in Hf, Zr, and Sc indicate their high fractionation degree in both mineralizing and magma fluids and/or igneous rock/fluid interaction effects in the subsurface. Positive anomalies of magmaphile trace element markers such as Mo and W support high-temperature mineralizing fluids driven by magmatism. These geochemical characters easily allow the classification of Chouichia veins as a hydrothermal affiliation deposit type where fluids are imprinted by magmatism and metamorphism. Deep-rooted faults in the Fej Et Tamer tectonic corridor have had an essential role in metal transfer, fluid conveying to the surface, and mineral formation.

Disseminated Gold–Sulfide Mineralization in Metasomatites of the Khangalas Deposit, Yana–Kolyma Metallogenic Belt (Northeast Russia): Analysis of the Texture, Geochemistry, and S Isotopic Composition of Pyrite and Arsenopyrite

At the orogenic gold deposits of the Yana–Kolyma metallogenic belt (northeast Russia) both Au–quartz-sulfide mineralization with native gold and disseminated sulfide mineralization with invisible Au developed. The textural and mineralogical-geochemical features, isotope-geochemical characteristics of gold-bearing sulfides from proximal metasomatites, and possible forms of Au occurrence in pyrite and arsenopyrite have been studied using electron microprobe, atomic absorption, LA-ICP-MS trace element, isotope analysis, and computed microtomography. Four generations of pyrite (Py1, diagenetic; Py2, metamorphic; Py3, metasomatic; Py4, veined) and two generations of arsenopyrite (Apy1, metasomatic; Apy2, veined) have been identified at the Khangalas deposit. In the proximal metasomatites, the most common are Py3 and Apy1. Studying their chemical composition makes it possible to identify the features of the distribution patterns of typochemical trace elements in pyrite and arsenopyrite, and to establish the nature of the relationship between Au and these elements. In Py3 and Apy1, structurally bound (solid solution) Au+ prevails, isomorphically entering the crystal lattice or its defects. Isotope characteristics of hydrothermal sulfides (δ34S = −2.0 to −0.6‰) indicate that mantle/magmatic sulfur was involved in the formation of the deposit, though the participation of sulfur from the host rocks of the Verkhoyansk clastic complex cannot be ruled out. The Khangalas deposit has much in common with other gold deposits of the Yana–Kolyma metallogenic belt, and from this point of view, the results obtained will help to better reveal their gold potential and understand their origin.

Alkalinity Production Coupled to Pyrite Formation Represents an Unaccounted Blue Carbon Sink

AbstractBlue carbon ecosystems, including mangroves, saltmarshes, and seagrasses, mitigate climate change by storing atmospheric carbon. Previous blue carbon research has focused on organic carbon stocks. However, recent studies suggest that lateral inorganic carbon export might be equally important. Lateral export is a long‐term carbon sink if carbon is exported as alkalinity (TAlk) produced via sulfate reduction coupled to pyrite formation. This study evaluates drivers of pyrite formation in blue carbon ecosystems, compares pyrite production to TAlk outwelling rates, and estimates global pyrite stocks in mangroves. We quantified pyrite stocks in mangroves, saltmarshes, and seagrasses along a latitudinal gradient on the Australian East Coast, including a mangrove dieback area, and in the Everglades (Florida, USA). Our results indicate that pyrite stocks were driven by a combination of biomass, tidal amplitude, sediment organic carbon, sediment accumulation rates, rainfall, latitude, temperature, and iron availability. Pyrite stocks were three‐times higher in mangroves (103 ± 61 Mg/ha) than in saltmarshes (30 ± 30 Mg/ha) and seagrasses (32 ± 1 Mg/ha). Mangrove pyrite stocks were linearly correlated to TAlk export at sites where sulfate reduction was the dominant TAlk producing process. However, pyrite generation could not explain all TAlk outwelling. We present the first global model estimating pyrite stocks in mangroves, giving a first‐order estimate of 197 Mg/ha (RMSE = 24 Mg/ha). In mangroves, estimated global TAlk production coupled to pyrite formation (∼3 mol/m2/y) is equal to ∼24% of their global carbon burial rate, highlighting the importance of including TAlk export in future blue carbon budgets.