Determining the ore-forming processes of Dongshengmiao Zn-Pb-Cu deposit: Evidence from the linear discriminant analysis of pyrite geochemistry

Abstract

The orogenic base metal deposits gain more and more attentions in recent years. The ore-forming fluids associated with these deposits are enriched in reduced sulfur and have low salinity. Since this kind of fluid has low affinity to transport base metals, pre-enrichment of sulfide should take place during the formation of orogenic base metal deposits. The Dongshengmiao Zn-Pb-Cu deposit, which is located in the northern margin of the North China Block, was considered as orogenic base metal deposit, and a two-stage mineralization process was proposed by previous researchers, but other researchers proposed that the Dongshengmiao is a typical sedimentary exhalative (SEDEX) deposit. Even though the tectonic environment, fluid inclusion, geochronology and isotopic geochemistry have been widely investigated in the Dongshengmiao, its genesis is still under debate, and new data or proof should be presented to decipher the genesis model of the Dongshengmiao deposit. In this study, linear discriminant analysis (LDA), one of the commonly used machine learning methods, was employed to discriminate the genesis of pyrite in the Dongshengmiao deposit based on the trace element concentrations analyzed by LA-ICP-MS. The LDA results demonstrate that nearly all the early-stage fine-grained pyrites (Py1) show the same geochemical features as the pyrites from volcanic hosted massive sulfide (VHMS), whereas most of the late-stage recrystallized pyrite (Py2) is of orogenic origin. The Mesoproterozoic submarine volcanic activities resulted in pre-enrichment of sulfide with VHMS geochemical signature in the rocks hosting Dongshengmiao deposit. The pre-enriched sulfides were subsequently remobilized during the subsequent metamorphism in the early Cretaceous, leading to the formation of giant an orogenic base metal deposit.