Mineralization processes at the giant Jinding Zn–Pb deposit, Lanping Basin, Sanjiang Tethys Orogen: Evidence from in situ trace element analysis of pyrite and marcasite

Abstract

The giant Jinding Zn–Pb deposit is in the Mesozoic–Cenozoic Lanping Basin of southern China and hosted by sandstone in the Early Cretaceous Jingxing Formation and limestone breccia and sandstone and gypsum in the Palaeocene Yunlong Formation. Mineral associations at the deposit are early (Stage 1) marcasite–sphalerite(–pyrite) and galena–quartz; through (Stage 2) pyrite–sphalerite–galena(–arsenopyrite) and marcasite–celestite–carbonate–gypsum; and the late (Stage 3) galena–sphalerite–pyrite–sulfate–carbonate(–celestite), gypsum, and barite. Pyrite and marcasite have higher Pb, Zn, Ag, Bi, As, Se, and Tl and lower V, Cr, Co, Ni, Cu, and Sn assays in orebodies hosted by sandstone and brecciated limestone. The concentration of these elements progresses from the early to late stages with increasing Cu, Zn, Ag, Bi, V, Cr, Co, Ni, and Se; decreasing Tl and As; and constant Pb, Sn, and Sb. This chemical characteristic of the pyrite and marcasite indicates that their source is basinal brine with minor contribution from the host rocks. During the early and middle stages, pyrite and marcasite contain higher concentration of Pb, Tl, and As, which is related to mineralized basinal brine and H2S‐rich fluids at a low pH during relatively higher temperature conditions. During the late stage mineralization, pyrite and marcasite contain the highest concentrations of Cu, Zn, Ag, Sb, Pb, Bi, and Se, which is associated with metal‐rich basinal brine and meteoric water at a near‐neutral pH and lower temperature conditions.