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Stratabound ore has been recognized as an end-member of porphyry copper systems, but pyrite chemistry has not been widely applied to linking stratabound ore with the related porphyry and skarn system. Stratabound ore is commonly developed around porphyry-skarn systems in eastern China, and is characterized by abundant colloform pyrite; however the origin of the colloform pyrite has been contentious. Xinqiao deposit is ideal for study of pyrite geology and geochemistry with the aim of elucidating formation of the stratabound ore and to decipher the evolution of pyrite compositions in a porphyry-skarn environment. The colloform pyrite paragenesis and S isotopes indicate that it formed during early skarn mineralization, based on its occurrence in stockwork veins cutting skarn minerals, and that it is replaced by later hypogene sulfides; the δ34S of colloform pyrite (average 6.12‰) is close to the δ34S value of both porphyry- (average 5.06‰) and skarn-type pyrite (average 4.65‰). The colloform texture formed as an aggregate of nanometer- or micrometer-sized (<0.2 μm) pyrite cubes produced by rapid crystallization from a high-fS2, low-temperature, and supersaturated fluid. Supersaturation of the fluid was probably produced by rapid decompression that triggered fluid boiling and cooling when the magmatic-hydrothermal fluid (derived from Cretaceous magma) flowed along the Devonian-Carboniferous unconformity. Subsequently, the colloform pyrite was replaced by later stage pyrite with distinctive trace elements (Co, Ni, and Se), indicating that the stratabound ore at Xinqiao formed from multiple pulses of magmatic-hydrothermal fluids derived from an Early Cretaceous stock. Co, Ni, and Se enrichment in porphyry- and proximal skarn-type pyrite suggests they formed at relatively high temperature, whereas the colloform pyrite shows trace element contents (Cu, Pb, Zn, Ag, and Bi) similar to those in distal skarn pyrite, suggesting that they may have formed in the same fluid environment. The trace element variations in pyrite from stratabound, skarn and porphyry ore probably resulted from decreasing fluid temperature and increasing pH away from the source. Our data, combined with previous studies, show that Co and Ni in pyrite increase toward porphyry and skarn ore, whereas As, Sb, Pb, Ag, and Bi are enriched in pyrite in distal stratabound ore, which extends for 1–2 km away from the intrusion. A plot of As/Se vs. Co discriminates the three ore types that occur associated with porphyry-skarn Cu systems in the Middle and Lower Yangtze belt (MLYB). These results indicate pyrite chemistry can be effective in discriminating the genesis of different deposit types related to porphyry-skarn systems and can potentially be used as a vectoring tool during exploration in the MLYB and elsewhere. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porphyry- and epithermal-style mineralization is associated with ∼ 130 Ma magma event. • The mineralizing fluids were predominantly magmatic water with addition of meteoric water. • Metal deposition resulted from cooling, sulfidation, neutralization, and boiling of fluids. The Naozhi deposit in the Yanbian district of northeastern China contains polymetallic epithermal veins and subeconomic porphyry-style Cu mineralization within 2 km of each other. These two mineralization styles are genetically associated with 130–126 Ma andesites and dioritic–granitic intrusions. Isotopic ages determined on sericite (128.2 ± 2.9 Ma; 40Ar–39Ar plateau age) and sulfide (124.6 ± 2.7 Ma; Rb–Sr isochron) associated with the epithermal mineralization constrain the hydrothermal activity to at approximately 128 Ma. Three types of fluid inclusions, including halite-bearing, vapor-rich, and liquid-rich inclusions were trapped in quartz from porphyry-style veinlets associated with an assemblage of K-feldspar–biotite–magnetite. Based on microthermometry and the homogenization behavior of halite-bearing inclusions, they were trapped at lithostatic pressures of > 500 bars and at temperatures of ≥ 350 °C, whereas the vapor- and liquid-rich inclusions were trapped at pressures and temperatures of 110 ± 35 bars and ≤ 350 °C. Epithermal mineralization comprises four vein stages, which, from oldest to youngest, are quartz–pyrite, quartz–base metal sulfide, quartz–precious metal, and quartz–carbonate. The ore assemblage precipitated from low-salinity fluids (<10 wt% NaCl equiv.) at temperatures and pressures of ≤ 350 °C and ≤ 100 bars. The δ18O H2O (2.5 to −2.4 ‰) and δD H2O (−85 to −114 ‰) compositions of fluids related to porphyry- and epithermal-style mineralization indicate a mixture of magmatic and meteoric waters. The δ34S H2S (−3.1 to 4.5 ‰) values of fluids become isotopically heavier from the quartz–pyrite stage to the quartz–base metal sulfide stage, reflecting continuous reduction during epithermal mineralization. The mineral assemblage and chemical composition of sulfide minerals indicate a transition from oxidizing, high sulfidation porphyry-style fluids to reducing, intermediate–low sulfidation epithermal fluids, with log ƒO 2 values ranging from −31 to > −33, and log ƒS 2 values ranging from −7.0 to ≤ −13.4 during the epithermal veining stage. Metal deposition in the Naozhi magmatic–hydrothermal system resulted from cooling, sulfidation, neutralization, and boiling of predominantly magmatically sourced hydrothermal fluids that mixed with meteoric water. [ABSTRACT FROM AUTHOR]

The Zhuangzi Au deposit in the world-class Jiaodong gold province hosts visible natural gold, and pyrite as the main ore mineral, making it an excellent subject for deciphering the complex hydrothermal processes and mechanisms of gold precipitation. Three types of zoned pyrite crystals were distinguished based on textural and geochemical results from EPMA, SIMS sulfur isotopic analyses and NanoSIMS mapping. Py0 has irregular shapes and abundant silicate inclusions and was contemporaneous with the earliest pyrite-sericite-quartz alteration. It has low concentrations of As (0-0.3 wt.%), Au and Cu. Py1 precipitated with stage I mineralization shows oscillatory zoning with the bright bands having high As (0.4-3.9 wt.%), Au and Cu contents, whereas the dark bands have low contents of As (0-0.4 wt.%), Au and Cu. The oscillatory zoning represents pressure fluctuations and repeated local fluid phase separation around the pyrite crystal. The concentration of invisible gold in Py1 is directly proportional to the arsenic concentration. Py1 is partially replaced by Py2 which occurs with arsenopyrite, chalcopyrite and native gold in stage II. The replacement was likely the result of pseudomorphic dissolution-reprecipitation triggered by a new pulse of Au-rich hydrothermal fluids. The δ34S values for the three types of pyrite are broadly similar ranging from + 7.1 to + 8.8‰, suggesting a common sulfur source. Fluid inclusion microthermometry suggests that extensive phase separation was responsible for the gold deposition during stage II mineralization. Uranium-Pb dating of monazite constrains the age of mineralization to ca. 119 Ma coincident with a short compressional event around 120 Ma linked to an abrupt change in the drift direction of the subducting Pacific plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyrite-bearing veins at Qulong can be divided into seven subclasses. • The contents of Co and Ni and the ratios of Co/Ni and Ni/Se in pyrite can be used to investigate the evolution of fluid composition, temperature and oxygen fugacity. • Changes in trace elements and S isotopes in pyrite can be used to investigate the evolution of magmatic-hydrothermal fluids. The post-collisional Qulong porphyry Cu-Mo deposit is the largest in the Gangdese Cu belt, southern Tibet. Despite many previous studies, the evolution of ore-forming fluids in the Qulong deposit remains controversial. Pyrite-bearing veins at Qulong can be divided into seven subclasses, including Mt-type, Bt-type, A-type, B-type, C-type, D-type, and E-type veins. To decipher the evolution of magmatic-hydrothermal fluids at Qulong, in situ LA-ICP-MS trace element and sulfur isotope compositions of pyrites from different veins were analyzed. The δ34S values (+1.01‰ to + 4.28‰) for pyrites indicate a magmatic sulfur source and the high Se/S ratios of pyrite at Qulong are consistent with hydrothermal fluids being mainly magma-derived. The low Co/Ni ratio (0.01–0.1) of pyrite in Mt-type vein suggests that the earliest magmatic-hydrothermal fluids may have contributed from mafic magma injection. From Mt- to Bt- to A-type veins, the δ34S values in the hydrothermal fluids decrease as the temperature decreases, whereas the Cu and Co contents increase and the As and Ni contents decrease. In B- and C-type veins, the relatively high and stable Co and Ni contents and the range of δ34S isotope values in pyrite indicate the existence of multiple-stages of magmatic-hydrothermal fluids during the main mineralization period. During the late stages of mineralization, the decrease of Co, Ni and As contents and increase of Cu in pyrite in D- and E-type veins, as well as the narrow range of δ34S values, may be due to decreasing temperature as a result of fluid dilution caused by mixing with meteoric waters. The slightly negative δ34S fluid values for chalcopyrite (-1.56‰ to −0.75‰) in sample Q711-1968 also suggests the addition of external water at Qulong. [ABSTRACT FROM AUTHOR]

[Display omitted] • Six types of pyrite formed in two overprinting gold-mineralizing events. • Monazite U-Pb dating constrains the age of early mineralization to ca. 429 Ma. • Distinct δ34S values suggest early metasedimentary and late magmatic origin of sulfur. The Tanjianshan goldfield is the most important gold producer in the North Qaidam, NW China. Genesis of gold deposits in Tanjianshan is enigmatic, primarily because of uncertainties as to timing, mineralization processes and fluid sources. We investigate these uncertainties through a comprehensive study of the texture and geochemistry (LA-MC-ICPMS trace elements and sulfur isotopes) of pyrite and in-situ U-Pb dating of monazite from the Qinglonggou gold deposit. Six types of pyrite with distinct textures, trace element contents and sulfur isotopes have been identified, and provide constraints on two overprinting gold-related hydrothermal events. Stage I consists of Py1, occurring as veinlets parallel to S1 deformation in a schist, is characterized by extremely low Co/Ni ratios with high contents of Ni, and high δ34S values (+14.9 ‰ to +16.1 ‰), and were likely derived from metamorphism of the sedimentary strata in the Tanjianshan and Wandonggou Group. In stage II, Py2 occurs in the pyrite-quartz veins that cut Py1 veinlets. They have similar δ34S (+13.1 ‰ to +17.8 ‰) to Py1, indicating that sulfur was likely derived from the dissolution of Py1. The stage I and II veins formed during an early gold pre-concentration event, which is constrained at 429.1 ± 5.9 Ma by in-situ U-Pb dating of monazite that coexists with Py1. Stage III includes Py3 and Py4 which occur in the altered carbonaceous schist and accompanying quartz veins. Trace metals are highest in Py3 (Ag, Au, Sb, and Bi) which represent the most economic ore stage in the deposit, whereas the following Py4 shows low concentrations of most trace elements due to abundant Py3 precipitation. In contrast, trace elements contents increase in Py5 to similar levels as those seen in Py3, suggesting a new pulse of fluid in stage IV. Minor Py6 grains precipitated in the youngest quartz-calcite veins associated with stage V, and contain low concentrations of trace elements. The δ34S values of Py3 (+5.2 ‰ to +6.0 ‰) and Py4 (+4.2 ‰ to +6.1 ‰) are within the range of magmatic sulfur, suggesting a dominantly magmatic source. The δ34S values increase from Py3-4 to Py5 (+6.3 ‰ to +7.4 ‰), and to Py6 (+8.7 ‰ to +9.6 ‰), probably due to increasing contribution from the host rocks, as well as decreasing f O 2 , through incremental fluid-rock interaction. Stages III and IV represent a late gold-mineralizing event during Late Paleozoic to Early Mesozoic, while stage V is post-mineralization. The overprinting gold pre-concentration and mineralization events in the Tanjianshan goldfield correspond to orogenic evolution of the Proto-Tethys Ocean and Paleo-Tethys Ocean, respectively. [ABSTRACT FROM AUTHOR]