Textural and geochemical analysis of celestine and sulfides constrain Sr-(Pb-Zn) mineralization in the Shizilishan deposit, eastern China

Abstract

Breccia-hosted Sr-(Pb-Zn) mineralization from the Shizilishan deposit (Edong district, eastern China) is located at the contact between a Lower Cretaceous (∼139 Ma) quartz diorite porphyry stock and Triassic evaporite-bearing limestone/dolomite sequences. Backscatter electron imaging, electron probe microanalysis, and laser ablation (multicollector-) inductively coupled-plasma mass spectrometry constrain ore genesis based on the textural evolution and trace element and isotope geochemistry in multiple stages of celestine and sulfides (pyrite and marcasite). Complex growth and/or dissolution and/or recrystallization textures of celestine and superposition of pyrite and marcasite are suggestive of evolving fluid compositions and physicochemical conditions during which pH first decreased (favorable for marcasite precipitation) and then increased, facilitating precipitation of Ba-rich celestine and As-rich pyrite. Sphalerite is characterized by enrichment in structurally-bound Sb, Cu, Ag, As, and Tl. Celestine displays Sr and S isotope signatures comparable to Middle Triassic seawater, indicating derivation of both elements from evaporite sequences. Decreasing δ34S in sulfides through the paragenetic sequence may reflect multiple sulfur sources produced by thermochemical reduction of sulfate and/or bacterial sulfate reduction processes. This research highlights that low to moderate salinity fluids, expected to carry significant concentrations of Sr, are able to form large celestine deposits through extensive water–rock interaction when fluid flow is either protracted, or there are superimposed episodes of fluid introduction with high Sr/Ba ratios and moderate dissolved sulfate. The Shizilishan deposit shares some alteration features and geochemical signatures with low-temperature Carlin-type Au deposits (e.g., relative enrichment in As and Tl in ore-stage pyrite) and Fe-poor MVT-type Pb-Zn ores (e.g., high content of Ga and Ge but low Fe, Mn, and In in sphalerite).