In situ trace elements and sulfur isotopes of sulfides in the Dabaiyang Te-Au deposit, Hebei Province, China: Implications for Au remobilization from pyrite

Abstract

Coupled dissolution–reprecipitation (CDR) reactions and low-melting point chalcophile elements (LMCE) melt scavenging are effective mechanisms for gold remobilization and are important for the formation of Te-Au deposits. The Dabaiyang deposit is a typical Te-Au deposit in the Zhangjiakou district and contains tellurides, including altaite, hessite, petzite, tetradymite and tellurobismuthite. Two generations of pyrite have been recognized in the deposit: early pyrite without fractures or alteration (Py1) and later pyrite with more porosity, inclusions and fractures (Py2), and Py2 could be separated into Py2a that containing many fractures without mineral inclusions and Py2b that containing microfractures, micropores and mineral inclusions. Pyrite containing large amounts of mineral inclusions and free of microfractures (Py-MI) has also been recognized, but timing relationships between Py-MI and Py1 (or Py2) is hard to establish. The Pyrite textures indicate that Py2a underwent brittle deformation and that Py2b underwent CDR reactions and Te-melt scavenging. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses show that Py2a contains trace elements similar to Py1, while Py2b contains higher Au, Ag, Te and other trace elements, indicating that brittle fracturing has no effect on element mobilization and reprecipitation, and porous pyrite has Au-Ag-Te concentrations. High Co/Ni ratios and Te contents and low Se contents show that the Dabaiyang deposit has a genetic relationship with magmatic activity. In situ δ34S values of sulfides range from −15.77‰ to −6.09‰ (mostly from −13.89 to −10.06‰), which is consistent with bulk sulfide δ34S values. The negative δ34S values more likely resulted from sulfur isotope fractionation in high fO2 hydrothermal fluids. CDR reactions liberated Au, Te, Ag and other trace elements from pyrite and formed porous textures. Then, Te-rich melts scavenged Au from fluid and wallrocks during migration. Finally, the melt precipitated as mineral inclusions in pores or fractures in pyrite. CDR reactions and LMCE melt scavenging played an important role in upgrading the ores and the occurrence of visible native gold in the Dabaiyang gold deposit, as well as other Te-Au deposits in the Zhangjiakou district.