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From integrated textural and compositional studies of auriferous and barren pyrite/marcasite in the epithermal Axi gold deposit, China, we have identified a relationship between multiple gold mineralizing events, mafic magma recharge, and fluid-rock reactions. Three generations of pyrite (Py1–3) and four generations of marcasite (Mar1–4) record episodic gold mineralizing events, followed by silver-copper-lead-zinc-cadmium enrichment. The gold mineralizing events are recorded by high concentrations of subnanometer-sized gold in Py1, Py3, and Mar3 (max. = 147, 129, and 34 ppm, med. = 39, 34, and 12 ppm). Based on previous Re-Os age determinations of pyrite and U-Pb zircon ages of the andesitic wallrock, these gold events slightly postdate pulsed mafic magma recharge and represent the incursion of Au-As-S-rich magmatic volatiles into circulating meteoric water. Silver-Cu-Pb-Zn-Cd enrichment in Py2, Mar2, and Mar4 are consistent with quiescent degassing and gradual Ag-Cu-Pb-Zn-Cd enrichment in an evolved felsic magma. Barren Mar1 records the dominance of meteoric water and a limited magmatic fluid contribution. High-Co-Ni-V-Cr-Ti contents in porous cores of Py1 and Mar2 are attributed to wall rock alteration and dissolution-reprecipitation. The results provide convincing evidence that the metal budget (especially for Au, Ag, Cu, Pb, Zn, Sb) of the hydrothermal fluids and sulfides in epithermal systems are controlled by the influx of magmatic fluids and associated magma, whereas the enrichment of certain fluid-immobile elements, such as Co, Ni, V, Cr, and Ti, is caused in part by fluid-rock interaction. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Pyrite and arsenopyrite display complex textural and compositional evolution. • Pyrite incorporates significant amounts of refractory Au, up to 1.02 wt.%. • Arsenopyrite incorporates significant amounts of refractory Au, up to 1.75%. Apy3 was formed at 325–385 °C based on arsenopyrite geothermometer. Abstract The Axi deposit is the largest low-sulfidation epithermal gold deposit in Chinese Western Tianshan, Central Asian Orogenic Belt. In this contribution, combined petrological observations, electron microprobe analysis (EMPA) and X-ray backscattered electron images (BSE) have been conducted on Fe-S-As minerals to reveal their textural and compositional evolution. Pyrite and arsenopyrite are ubiquitous. Their texture and composition show gradual changes with time. Four generations of pyrite can be identified, named Py1, Py2, Py3 and Py4 from early to late. The coarse-grained, euhedral to subhedral Py1 (mostly 100–300 μm) from the quartz-chalcedony stage is the earliest, and predates gold mineralization. Sometimes they contain silicate and arsenopyrite (Apy1) inclusions. Compositionally, they are enriched in Pb (up to 0.60 wt%), but depleted in As (0.06–7.61 wt%, mostly <0.30 wt%) and Au (0.01 wt%–0.25 wt%, mostly <0.10 wt%). Subhedral to anhedral Py2 grains (50–1000 μm) coexist with other sulfides such as chalcopyrite, sphalerite, galena and tetrahedrite in the quartz-polymetallic sulfides stage. They are unusually rich in Au (with a mean value of 0.06 wt%), Ag (with a mean value of 0.04 wt%), Cu (with a mean value of 0.21 wt%) and As (with a mean value of 3.06 wt%), implying a syn -mineralization feature. Subsequent Py3 occurs as very fine-grained disseminations of euhedral crystals (10–50 μm) in quartz-polymetallic sulfides stage and carbonate-quartz stage. They display clear oscillatory zoning and contain arsenopyrite (Apy3), sphalerite and Sb-Te mineral inclusions. Their Au content vary greatly from 0.02 wt% to 1.02 wt%, with corresponding As content varying from 0.07 wt% to 8.28 wt%. The post-mineralization Py4 crystals (30–5000 μm) mainly occur as foliated, sheaf, or radiaxial aggregates in carbonate-quartz stage. They have the lowest Au (with a mean value of 0.04 wt%), As (with a mean value of 0.32 wt%), Co (with a mean value of 0.04 wt%) and Ni (with a mean value of 0.04 wt%) concentrations, although dramatically high S contents (with a mean value of 52.72 wt%). Correspondingly, there are three generations of arsenopyrite: Apy1 (20–50 μm) and Apy3 (3–15 μm) mainly occur as inclusions in Py1 and Py3, respectively, whereas the latest Apy4 (<5–60 μm) can occur either as serrated grains surrounding Py4 or overgrowth Py1 and Py3, or as individual euhedral to sub-euhedral grains. They also contain considerable, but much higher Au contents than pyrite, with the values of 0.6 wt%–1.1 wt% for Apy1, 0.18 wt%–1.32 wt% for Apy3 and 0.50 wt%–1.75 wt% for Apy4, respectively. Besides, they also contain considerable amounts of trace elements such as Co, Zn, Pb, Sb and Se. Arsenopyrite geothermometer constrains the ore-forming temperature responsible for Apy3 formation to 325–385 °C. Our result reveals that significant invisible gold accommodated by sulfides is the main cause of refractory ores at the Axi deposit. [ABSTRACT FROM AUTHOR]

The Xiaoqinling gold field in central China is the second largest orogenic Au province in China. In the Xiaoqinling area, the Dahu Au-Mo deposit is typical because it is one of the five early-discovered large gold deposits, but also unique for its northernmost location and Mo-association. This study shows that the deposit is a fault-controlled lode system formed by a three-stage hydrothermal process. The early-stage pyrite-quartz veins are structurally deformed and broken. The middle-stage molybdenite-pyrite-quartz stockworks (mostly coaxial) infill the cracks of the early-stage veins and minerals. The late-stage open-space filling quartz-carbonate veinlets show a comb-like texture. The early- and late-stage quartz only contains the fluid inclusions of CO2-H2O and H2O-NaCl types, respectively, suggesting an evolution from CO2-rich to CO2-poor; whereas the middle-stage quartz contains fluid inclusions of CO2-H2O, H2O-NaCl, pure CO2 and daughter mineral-bearing types, supporting a boiling fluid system, because they can occur in a microscopic domain of a single crystal, homogenize divergently at similar temperatures clustering between 293 and 410 °C, and show contrasting salinities of <13.6 wt.% and >26.3 wt.% NaCl equiv. The inclusions in early-stage quartz are homogenized at 402-503 °C, with salinities of 4.5-10.4 wt.% NaCl equiv.; and those in late-stage quartz are homogenized at temperatures of <251 °C, with salinities of 14.4-14.8 wt.% NaCl equiv. The trapping pressures of inclusions are estimated to be 138-331 MPa in the early stage and 78-237 MPa in the middle stage, implying that the fluid system alternately fluctuated from lithostatic to hydrostatic, which was controlled by a fault-valve mechanism at depths of >11 km and ~7.8 km, respectively. Hydrogen and oxygen isotope signatures indicate that the fluids originated from metamorphic devolatilization in the early stage, then mixed with meteoric water in the middle stage, and finally replaced by meteoric water in the late stage. Hence, it is concluded, that metal precipitation at the Dahu deposit was mainly caused by fluid boiling, followed by fluid mixing, along with a trans-compressing at the transitional zone from a magmatic arc to back-arc basin, which resulted from the Triassic northward subduction of the Mian-Lue oceanic slab. © 2014 The Authors. Geological Journal published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

[Display omitted] • CL images of quartz are dark in Tokuzbay orogenic gold deposit. • PC, C-type FIs are trapped from initially carbon-rich metamorphic fluids. • Organic carbon in the sediments significantly contributed to the carbon in the fluids. • Carbon isotopes of carbon-rich water-poor fluids are light in orogenic gold deposits. Carbon-rich or carbonic fluids are identified in some orogenic-type gold deposits worldwide. Their nature, origin, evolution, and relations with gold mineralization are still poorly understood. The Tokuzbay large-size orogenic-type gold deposit in Chinese Altai is characterized by enormous CO 2 -rich fluid inclusions (FIs), providing an ideal case to investigate the genetic relationship between carbon-rich hydrothermal systems and orogenic-type gold mineralization. The mineralization process in the Tokuzbay includes four stages: (1) stage I quartz-magnetite veins; (2) stage II quartz-pyrite veins; (3) stage III quartz-polymetallic sulfide veins; and (4) stage IV quartz-carbonate veins. Based on the microscopic investigation, cathodoluminescence (CL) imaging, Raman spectrum analysis, and mircothermometric measurements, three types of FIs are identified in the veins, including the N 2 -bearing carbonic or CO 2 -rich inclusions (PC-type), the CO 2 -H 2 O inclusions (C-type), and the H 2 O-dominated or aqueous inclusions (W-type). The FIs in the stage I minerals are dominated by PC- and C-types, with minor amount of W-type, and occur as primary and pseudosecondary within quartz grains. These inclusions show a salinity of 5.0—9.5 wt% NaCl eqv. and homogenize to liquid phase during 272℃ to 399℃, indicating their entrapment from an initially homogeneous carbon-rich CO 2 -H 2 O-NaCl metamorphic fluid system. From early to late stages, the PC- and C-type FIs are getting infertile, while the W-type FIs become more abundant, indicating the escapes of CO 2 and compositional transition from CO 2 -rich to H 2 O-rich system. Moreover, the decreasing in temperature (272–399 ℃, 238—326 ℃, 173—267 ℃ and 135—182 ℃ from stages I to IV, respectively) and salinity (5.0—9.5, 2.6—9.2, 2.3—7.8 and 1.4—4.3 wt% NaCl eqv. from stages I to IV, respectively), together with the decrease of the δ18O values, suggests an input of meteoric water during mineralization. In the main mineralization stages (II and III), some FIs show divergent homogenization direction (liquid vs vapor) at similar homogeneous temperatures, yielding quite different salinities. For example, the coexisting W-type and C-type FIs yield similar homogenization temperatures, and the liquid-rich and vapor-rich FIs divergently homogenize to liquid and vapor at similar temperatures with different salinities. This indicates that the fluid effervescence drove phase separation and caused the CO 2 escape from the fluid system which promoted the gold precipitation at the ductile-to-brittle transition zone that revealed by the depth (8—11 km) calculated by the C-type FIs of the immiscible inclusion assemblages. The δ13C values of the CO 2 extracted from fluid inclusions range from –7.6 to –22.8‰, suggesting that the CO 2 might be derived from the hydrolysis of organic matter in the source sediments during metamorphism, rather than simply sourced from magma or the mantle. This understanding is supported by the widespread observation of the low δ13C values from most of orogenic-type gold deposits hosted in sedimentary rocks worldwide. [ABSTRACT FROM AUTHOR]

• At Jingxi-Yelmand, there are two main pulses of magmatism at 370 Ma and 365–362 Ma. • Gold mineralization occurred no later than 293 Ma. • Periodic injection of mafic magma trigger volcanic eruption and gold mineralization. The Dahalajunshan Formation volcano-volcanoclastic rocks in Chinese Western Tianshan host specific Paleozoic epithermal gold deposits as well as volcanogenic Fe-Cu mineralization. Although numerous studies have been taken to constraint its geological, geochemical, geochronological features as well as petrogenesis, the link between volcanism and mineralization is not well constrained. In this contribution, accessory zircon was collected from the intermediate to felsic volcanic rocks outcropped at the Jingxi-Yelmand gold deposit. Detailed cathodoluminescence imaging illustrates ubiquitous resorption surfaces and embayments, and in situ LA-ICPMS trace element analysis further indicates periodic recharge of magma chamber by mafic magma input from depths. U-Pb geochronology constrains two main pulses of magmatism at ~370 Ma and 365–362 Ma, respectively. The duration of magmatic activity in the magma chamber is estimated to 52 ± 6 Myrs, using the U-Pb age of the oldest zircon antecryst (406.9 ± 5.4 Ma) and the youngest zircon autocryst (354.6 ± 3.0 Ma) as cutting edge and taking the analytical uncertainty into consideration. (U-Th)/He dating of zircon from the first pulse yields an age of 354 ± 15 Ma, which is identical to U-Pb age within analytical uncertainty. However, zircons from the second pulse of volcanic rocks yield much younger (U-Th)/He centered at 292.6 ± 7.6 Ma due to significant post-eruption reheating events. We propose that the intermediate to acid volcanic rocks are constructed by incremental addition of small magma batches. The periodic injection of more mafic magma and subsequent mixing may act as important trigger of not only volcanic eruption but also epithermal mineralization. Gold mineralization at the deposit should be no later than 292.6 Ma. [ABSTRACT FROM AUTHOR]