Genesis of the Sanshiliuwan Sn-Pb-Zn-Sb deposit in the Xianghualing ore district (Southern Hunan, South China): Constraints from geology, fluid inclusion analyses, and geochronology

Abstract

Tin (Sn) and antimony (Sb) deposits commonly formed in distinctive environments and thus the coexisting of Sn and Sb mineralization in a single deposit is rarely recognized worldwide and the genesis of this type of deposit remains poorly understood. The newly discovered Sanshiliuwan Sn-Pb-Zn-Sb deposit in the Xianghualing ore district of Southern Hunan has metal reserves of 44,000 t Sn, 291,000 t Pb + Zn, and 20,000 t Sb and average grades of 0.39 % Sn, 4.91 % Pb + Zn, and 1.00 % Sb, and thus offers an ideal window for prospecting the genesis of the Sn-Pb-Zn-Sb deposit. The orebodies in the deposit were mainly hosted in Cambrian and Devonian sequences and occurred as veins. Three mineralization stages were recognized including the cassiterite-sulfide, Pb-Zn-Sb sulfide, and carbonate. The fluid inclusions in the quartz from the cassiterite-sulfide stage (QtzI) have homogenization temperatures of 418–244 °C (typically 400–320 °C) and salinities in the range of 0.87–10.11 % NaClequiv. While the fluid inclusions in the quartz from the Pb-Zn-Sb sulfide stage (QtzII) have the homogenization temperatures of 253–141 °C (typically 250–180 °C) and salinities in the range of 0.18–9.86 % NaClequiv. The fluid inclusions in quartz from different mineralization stages have low Na+/K+ ratios in the range of 0.05–0.96 and clustered Cs/Rb ratios of 2–5, indicating that the ore fluids of the deposit were likely to have been exsolved exclusively from a magmatic source. Cassiterite U-Pb dating suggested that the Sanshiliuwan deposit formed ca. 155 Ma, which is well coincided with the concealed granites (formed ca. 156 Ma). Therefore, the genetic model for this deposit would demonstrate that evolved fluids from Jurassic granites invaded the faults and deposited Sn and Sn-Pb-Zn ore veins in the granite periphery. Thence, Sn-depleted but Pb-Zn-rich fluids interacted with the Sb-rich Cambrian sequence and leached it to create Sb-rich fluids. In response to fluid cooling and boiling, Pb-Zn-Sb-rich fluids then deposited Pb-Zn-Sb sulfide ore veins at favorable structural sites.