Genesis of Caoziwa Pb–Zn Deposit in Tengchong Block, SW China: Constraints from Sulfur Isotopic and Trace Elemental Compositions of Sulfides

Abstract

The Caoziwa Pb–Zn deposit is one of the typical vein-type Pb–Zn deposits in the western part of the Tengchong block. Due to limited research, the genesis of these deposits is unknown. In this study, the sulfur isotopic and trace elemental compositions of sulfides from the Caoziwa Pb–Zn deposit were analyzed to trace the sources of ore-forming materials, and to reveal the genetic type of this deposit. The results show that abundant Co, Ni, As, and Se, and less Cu, Zn, Ag, Cd, Sn, Sb, Te, Pb, and Bi could enter pyrite by isomorphic substitution. Elemental Mn, Fe, Cd, Co, and Ni could substitute Zn to enter sphalerite, while the contents of Ag, Sn, and Sb are mainly controlled by the Pb-rich inclusions in sphalerite. Elemental Bi, Sb, Cd, Sn, Ag, and Tl mainly enter the galena grains via an isomorphic substitution mechanism of (Bi, Sb)3+ + (Cd, Sn)2+ + (Ag, Tl)+ ↔ 2Pb2+. Both sulfur isotopic compositions and trace elemental compositions indicate that the ore-forming materials and fluids of the Caoziwa Pb–Zn deposit mainly originate from magmatic hydrothermal fluid related to Paleocene granitic magmatism. Combined with the geological facts that some skarnizations developed in the northern part of the ore field near the Paleocene granite, the Caoziwa Pb–Zn deposit is suggested to be a magmatic hydrothermal vein-type deposit that probably belongs to a distal part of a skarn mineralization system developed by the intrusion of Paleocene granitic magmatism in the western part of the Tengchong block.