Texture and geochemistry of pyrite from the Gaoche gold deposit in South China: Implications of ore-forming processes

Abstract

The Gaoche lode-type gold deposit is hosted in the Neoproterozoic metasedimentary rocks at the northeastern Cathaysia Block in South China. The deposit comprises three ore-bodies that are controlled by the NE-trending faults. Four generations of pyrite and associated paragenesis minerals have been identified. The Py0, formed in the early sericite-quartz alteration period unrelated to the gold mineralization, contains abundant silicate inclusions and has low Au (0–0.03 ppm), Ag (0.79–6.4 ppm) and As (0.93–402 ppm). The Py1 shows oscillatory zonings and has high invisible Au (0.01–1.8 ppm), Ag (0.01–106 ppm) and As (0.46–1163 ppm), representing the first stage mineralization. The Py2 also has high invisible Au (0.08–8.9 ppm), Ag (0.06–37 ppm) and As (5.5–10275 ppm), reflecting pseudomorphic dissolution of the Py1 and reprecipitation at the second stage mineralization. The Py3 lacks mineral inclusions but is chemically similar to the Py2. Available δ34S values for the mineralization-related pyrites range from −11.4‰ to +7.2‰, and their variation suggests the fluids were originally released from magmas followed by fluid-rock interaction under redox states at shallow depth. In addition, the Py1 and Py2 show high lead isotope compositions which lie above the orogen curve in the Pb-Pb isotope plots, indicating that the ore-forming materials were probably sourced from the metamorphic basement rocks. In combination with the regional geology and mineralization, the Gaoche gold deposit is suggested to have been genetically associated with regional metamorphism and deformation in relation to the western subduction of the paleo-Pacific oceanic slab during the Mesozoic.