TYPOMORPHIC CHARACTERISTICS OF ARSENOPYRITE IN GOLD DEPOSIT AND OCCURRENCE OF GOLD: A case study of gold deposits in Hunan Province

As-bearing gold deposits in Hunan Province are broadly distributed, with large reserves and multiple types. The main As mineral is arsenopyrite, which in most of gold deposits contains Au (generally 120×10^-6 to 250×10^-6). The Au content in arsenopyrite is two to five times higher than that in the coexisting pyrite or more. The Au distribution rate in arsenopyrite is up to 64.3%-94.05%. The arsenopyrite was formed in two stages. It is chemically enriched in S and depleted in As, with rich Sb (Se), Ni and Co, poor Mn, and increased of unit cell parameter (a₀). Most of the Au-bearing arsenopyrite contains invisible gold, which cannot be found even by electron microprobe. The invisible Au in arsenopyrite mostly occurs as nanometer fine grains.