Mineralogy of tin-sulfides in the Zijinshan porphyry–epithermal system, Fujian Province, China

Abstract

The Zijinshan orefield is a Cu–Au–Mo–Ag porphyry–epithermal mineralization system of Cretaceous age in southeastern China, comprising the Zijinshan high-sulfidation (HS) Au–Cu deposit, Luoboling porphyry Cu–Mo deposits, Yueyang low-sulfidation Au–Ag–Cu deposit, and Wuziqilong and Longjiangting intermediate-sulfidation (IS) Cu deposit. A number of Sn-(W)-sulfides occur in the Zijinshan orefield, including kiddcreekite, hemusite, colusite, vinciennite, stannoidite, mawsonite and kësterite. The occurrence represents the first report of hemusite, colusite and vinciennite in China. The relative abundance and diversity of Sn-(W)-sulfide-bearing assemblages make the Zijinshan orefield possibly unique in the world, and carries implications for the evolution of the mineralizing environment. Detailed electron probe studies of the Sn-minerals reveal that kiddcreekite, hemusite, mawsonite, stannoidite and kësterite have compositions close to ideal formulae. In contrast, colusite displays grain-scale zoning expressed by W, Sn and As. Vinciennite displays compositional variation depending on mineralization style: an average composition of Cu10.74Fe3.88Sn(As0.85,Sb0.08)S15.4 in the Zijinshan HS deposit, Cu10.71Fe3.9SnAs0.85S15.34 in the Wuziqilong Cu deposit and Cu10.76Fe3.7Sn1.02 (As0.5,Sb0.45)S15.54 with higher Sb contents (3.32%) in the adjacent Longjiangting Cu deposit.In the Zijinshan HS Au–Cu deposit, the main Cu-mineral assemblage varies from bornite-rich to digenite- to covellite-rich with increasing depth. Correspondingly, tin mineralogy varies from kësterite at upper levels to stannoidite-dominant at mid-to-upper levels of the copper orebody, to vinciennite- and mawsonite-dominant at depth, implying an increase in sulfidation and oxidation state downwards. Moreover, kiddcreekite is always partially replaced by wolframite and (hypogene) covellite at depth, also indicating overprinting by high-fO2 and -fS2 fluids in the covellite stage of mineralization. Kiddcreekite, along with a primary chalcopyrite–pyrite mineral association, occurs widely in the Zijinshan orefield (Zijinshan, Yueyang, Luoboling, Wuziqilong, Longjiangting and Dayanli), and is likely indicative of the early IS stage of epithermal system. Analogous with published data, kiddcreekite most commonly occurs in porphyry-style mineralization, implying the presence of the mineral has potential as an indicator of porphyry systems. Vinciennite-bearing Cu–Sn–As mineral associations occur in a specific position in the Zijinshan HS Au–Cu, Wuziqilong and Longjiangting Cu deposits, indicative of a transitional zone between porphyry and HS epithermal-style mineralization. The occurrence of the identified Sn-(W)-sulfide-bearing assemblages has considerable potential implications for understanding the architecture of a complex porphyry–epithermal environment and for exploration for underlying porphyry copper deposits. There is potential for discovery of a subjacent porphyry Cu deposit within the Zijinshan orefield.