Mineralogy and Geochemistry of Pyrite and Arsenopyrite from the Zaozigou Gold Deposit in West Qinling Orogenic Belt, Central China: Implications for Ore Genesis

Abstract

The Zaozigou gold deposit lies in the West Qinling orogenic belt, Gansu Province, China. It is one of the largest gold deposits, and the orebodies are hosted in fine‐grained slates intercalated with limestone of the Middle‐Triassic Gulangdi Formation and varied dykes. The gold orebodies are strictly controlled by the NE‐, NW‐, and SN‐trending tensional and shearing faults with high dipping angle. The mineralogy and geochemistry of pyrite and arsenopyrite are measured by electron microprobe. Pyrite has up to 0.12 wt.% Au, and arsenopyrite contains up to 0.17 wt.% Au. The antithetic correlation between S and As indicates the substitution of As for S in pyrite, and arsenic occurs in anionic As1− state in the pyrite structure under the reduced conditions. Pyrite has relatively high Co (~364–2248 ppm) but relatively low Ni (~109–497 ppm) contents, with Co/Ni ratios ranging from ~1.63 to 10.50, indicating that the deposit originated from a volcanogenic fluid and remobilized by hydrothermal fluid. Au in arsenopyrite occurs as cationic Au in solid solution, whereas Au in pyrite is in solid solution and metal nanoparticles (Au0). The texture characteristics and trace element geochemistry among cores, transition zones, and rims of pyrites demonstrate that there are at least four pulses of fluid participating in the generation of pyrite in the deposit. The calculated formation temperatures of the Zaozigou deposit vary from 148°C to 304°C, with an average temperature of 213°C based on Au contents in pyrite. The Pb isotopic compositions of pyrite samples suggest that the metallogenic materials of the Zaozigou deposit were derived from the mantle and upper crust. All the characteristics above lead us to draw the conclusion that the Zaozigou gold deposit is classified as an epithermal deposit.

The Gold Mineralization of the Baranyevskoe Au-Ag Epithermal Deposit in Central Kamchatka

“…For instance, the content of As in pyrite at the Zaozigou Gold Deposit (Central China) is 4.1 wt. % [37], it is 4.5 wt. % in pyrite of the Roudný deposit, Bohemian Massif [38], while As in pyrite from El Valle gold deposit (Spain) is the most abundant (up to 9.5 wt.…”

A magmatic‐hydrothermal origin of the Xinfang gold deposit, Liaodong Peninsula, China, revealed by in‐situ S–Pb isotopes and trace element analyses of pyrite

“…Previous studies reported that pyrite can contain visible and invisible gold (e.g., Cook and Chryssoulis, 1990; Palenik et al ., 2004; Reich et al ., 2005; Ciobanu et al ., 2012; Tang et al ., 2019). In the Xinfang gold deposit, pyrite represents the dominant Au‐bearing mineral and can be distinguished into three generations (Py1, Py2, and Py3) according to size, textures, and paragenesis.…”

Trace Element Characteristics of Pyrite and Arsenopyrite from the Golden Ridge Gold Deposit, New Brunswick, Canada: Implications for Ore Genesis

“…In arsenopyrite, arsenic and sulphur show a strong negative correlation regardless of the arsenopyrite type (Figure 15f), with a variable As/S ratio ranging from 0.72 to 0.82. The high Au contents in this low arsenic arsenopyrite (Appendix C, Table A4) are related to its non-stoichiometry [82], i.e., As concentrations between 27.52 and 29.60 at.%, compared to 33 at.% as the stoichiometric value [83]. These variations, a common feature in arsenopyrite, lead to disorder in the host lattice and allow the incorporation of gold [84].…”