Geochemistry of pyrite and its implications for exploration of the Jiuzhanggou gold deposit in western Henan

Objective Pyrite is a common auriferous mineral in gold deposits. Its mineral geochemistry not only plays a significant role in elucidating ore genesis, but also provides important information for the exploration of deposits. The Jiuzhanggou gold deposit in western Henan Province is a gold deposit typical of tectonically altered rocks in the Xiong'ershan gold ore cluster, and it is an ideal deposit to study the genetic indications and prospecting signs of pyrite in gold deposits. Methods In this study, the tectonically altered zones of the Jiuzhanggou gold deposit were investigated, and 8 samples of tectonically altered rocks were collected over a vertical depth of 280 m, from +260 m to −20 m. Electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite from the altered rocks were carried out, and the characteristics and variations of the element contents in pyrite of differently altered zones were obtained, revealing the indications of pyrite for ore genesis and prospection at greater depth. Results The interval between the +260 m and −20 m levels of the Jiuzhanggou gold deposit can be divided into four altered zones. Microscopic observation of the altered rocks shows that pyrite was formed during the metallogenic period. Given its Fe and S contents, most of the pyrite is sulfur-depleted. Cluster analysis shows that Au, Cu, As, Sb, Zn, Ag, Te, Se and Pb in pyrite belong to a group of hypothermal-mesothermal elements. Conclusion The Co/Ni ratio (1～10) and the Co-Ni-As diagram indicate a magmatic hydrothermal origin of pyrite. The Au in pyrite is positively correlated with Cu, As, Sb, Zn, Ag, Te, and Pb. The contents of these elements gradually decrease in the 1st～3rd altered zones, but increase in the 4th zone. It is speculated that the 1st～3rd altered zones are the product of the same hydrothermal mineralization activity, while the 4th altered zone is the product of another hydrothermal mineralization activity. According to the vertical extent of the 1st～3rd altered zones, it is speculated that the 4th altered zone may reach −60 meters. At least one level (40 m) can be explored at depth, which has a good prospecting potential. Significance The contents of Au, Cu, As, Sb, Zn, Ag, Te, Se, and Pb and the ratios of Au/As, Au/Ag, and Co/Ni in pyrite reflect the vertical mineralization zoning. These trace elements in pyrite are essential markers for prospecting targets in the deeper parts of gold deposits.