Comparison of vein- and breccia-type Au-mineralization in the giant Jiapigou mining district of Northeast China

Abstract

The Jiapigou mining district (JMD) in China, known as a world-famous gold-producing district, contains a dozen lode gold deposits (greater than 180 t Au), including vein-, disseminated-, and breccia-type ores. Among them, the vein- and breccia-type gold deposits show differences in mineralization style, sulfide content and ore-controlling structure, but have many similarities, such as hydrothermal alteration, mineral assemblage and mineralizing age. Here we present an integrated study involving detailed geology, petrography, fluid inclusions (FI), and H–O–S–Pb isotopes for the Liupiye (vein-type) and Binghugou (breccia-type) deposits in the JMD to elucidate the sources, mineralizing mechanism, genetic relationship of the two mineralization types, and evaluate preservation of the Au-mineralization. The results show the following: (1) ores are mainly hosted in auriferous quartz veins at Liupiye, and in cements of rounded breccia facies at Binghugou; (2) three hydrothermal stages have been identified in the two deposits: the early (quartz–pyrite), main (quartz–polymetallic sulfides) and late (quartz–carbonate) stages; (3) native gold was mainly deposited in the main stage; and (4) the FI studies of the two deposits indicate that the ore-fluid system evolved from a CO2–H2O–NaCl system to a CO2–H2O–NaCl system from the early to late stage, with gradually decreasing temperature and salinity. These FI results indicate that fluid boiling occurred during the main stage, and is considered to be a key control on the precipitation of gold and sulfides. The H–O–S–Pb isotopic results suggest that initial ore-fluids were predominantly derived from the synchronic deep-seated magma, while metals mainly originated from a mixed source between lower crustal and enriched mantle materials. The ore-fluids at Binghugou are more volatile-rich, higher temperature (i.e., CO2 and H2O), higher pressure, more sulfides (≥35–95 %), and more high-temperature minerals (i.e., bornite) than those of the Liupiye deposit. The differences in ore-controlling structure and ore-fluid composition lead to the formation of the two different styles of mineralization. Regionally, combined with previous observations, the breccia-type gold deposits were formed at deep level, while the vein-type gold deposits were formed at shallow level in the entire mineralization system. Considering the depth of regional post-ore exhumation has been estimated to be 4.07 ∼ 5.5 km, the gold deposits in the JMD have higher formation depth of 4–12 km than exhumation depth, which indicate that the gold deposits in this district are relatively well preserved.