Metallogenic discrimination by sphalerite trace element geochemistry: An example from the Fengyan Zn-Pb deposit in central Fujian, SE China

Abstract

Central Fujian is an important polymetallic (Zn-Pb-Ag-Cu-Mo-Au) mineral province in southeastern China, yet its mineralization is still disputed with proposed genetic models ranging from Proterozoic volcanogenic massive sulfide (VMS) to Mesozoic skarn-type mineralization. The Fengyan stratabound Zn-Pb deposit is mainly hosted in marble of the Meso-Neoproterozoic Longbeixi Formation. The deposit contains two types of ore-stage sphalerite (Ⅰ and II) distinguishable based on their paragenetic relations and associated mineral assemblages. Sphalerite I generally occurs as solitary crystals characterized by black to red internal reflections. Sphalerite II is commonly associated with galena and chalcopyrite, and has yellow internal reflections. Sphalerite I has lower concentrations of Co, Cd, Cu, Pb, Ag, and Bi, but higher concentrations of Fe, Mn, and In compared to sphalerite II. Both sphalerite types have very low contents of Ga, Ge, and Sn. According to a large, global sphalerite geochemical database of well-studied VMS and skarn deposits compiled as part of this study, skarn-hosted sphalerite is characterized not only by a broader range of contained trace element contents than its VMS-hosted equivalent but also by higher concentrations of Fe, Ga, Ge, and Ag and lower Mn, Cd, In, and Co. Trace element geochemistry and metal concentrations can thus be used to distinguish VMS and skarn deposits. Overall, the two sphalerite types from Fengyan have similar trace element compositions to those of skarn-hosted (but not VMS-hosted) sphalerite. In addition, the two types of sphalerite and their coexisting minerals have a narrow in-situ δ34S range (-1.6 to 4.1 ‰, mean 2.3 ‰), indicating a magmatic source. The elemental and isotopic geochemical evidence suggests that Fengyan is best classified as a stratabound, distal Zn-Pb skarn deposit. Our work highlights the effectiveness of sphalerite trace element geochemistry for differentiating ore deposit types, thereby presenting a possible tool in support of both Zn-Pb ore exploration and research.