Textures, trace elements and Pb isotopes of pyrite from the Donggushan tungsten polymetallic deposit, eastern China: Deciphering the source of a skarn tungsten polymetallic deposit

Abstract

The Donggushan tungsten polymetallic deposit is located near the northern margin of one of the most important ore deposit belts in China; the Middle - Lower Yangtze Metallogenic Belt (MLYB). The source and genesis of mineralization in the Donggushan deposit is poorly understood and is investigated using pyrite textures and geochemistry. Two types of pyrite and two subtypes were recognized, based on the location within the ore body, mineral assemblages, textures and geochemistry. Pyrite 1a occurs in the cores of pyrite crystals in the tungsten orebody, at depth within the deposit, near the intrusive rocks. It is characterized by high Ni and low contents of other trace elements and is overgrown by Py1b which has low Ni and higher trace elements. Pyrite 2a is characterized by moderate As and higher trace elements than those in Pyrite 1. It occurs in the cores of pyrite crystals in the shallow zinc-lead orebody. This pyrite is overgrown by Pyrite 2b characterized by higher trace elements. The trace elements, textures and inclusions in these pyrites suggest a progressive decrease in temperature, with Pyrite 1a forming at 350 °C through to Pyrite 2b forming at < 250 °C. The Pb isotopic compositions in the pyrites indicate that Pb in the deep tungsten ore body was derived from Yangtze upper crust (Dongling basement) but that Pb in the shallower ore body was sourced from the Dabie Orogen lower crust. The data supports a model whereby intra-continental subduction was the main geodynamic process controlling the mineralization of the Donggushan deposit.