Characteristics and genesis of Kanggur gold deposit in the eastern Tianshan mountains, NW China: evidence from geology, isotope distribution and chronology

Abstract

The Kanggur gold deposit lies in East Tianshan mountains, eastern section of Central Asia orogenic belt. The gold mineralization occurs on the northern margin of the Aqishan–Yamansu island arc in the Tarim Plate. It is mainly hosted in Lower Carboniferous volcanic rocks, and controlled by syn-tectonic intrusions and the ductile shear zone. The host rock is a calc-alkaline volcanic rock series consisting of andesite, dacite, tuff and subvolcanic rocks. The gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation. Ore-controlling structure is EW-trending normal brittle–ductile shear zone. The gold ore bodies are composed of Au-bearing altered rocks and a few Au-bearing sulfide-quartz veins. The mineralization shows vertical zonation in which Au was enriched in the upper orebodies, Au–Pb–Zn were enriched in the middle and Au–Cu were enriched in the lower orebodies. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification, chloritization, pyritization and magnetization zone (major ore body); pyrite-phyllic rock and/or sericite alteration zone; and sericite–chlorite alteration zone. Five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins. The δ 34S values of sulfide in the ores range from −0.9‰ to +3.3‰, similar to those of the volcanic and subvolcanic rocks (−3.21∼+1.3‰), indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur. The lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks. The initial 87Sr/ 86Sr ratios of the ores vary between 0.7077 and 0.7106, similar to those of the host rocks (0.7079–0.7125). According to the Sr, S and Pb isotopic data, it is indicated that the ore-forming materials were derived from the surrounding volcanic rocks and feature deep source. The δ 18O values of the ore fluids vary from +3.83‰ to −1.77‰ and the δ D values from −46‰ to −66‰. The δ 18O vs. δ D and δ 18O vs. 87Sr/ 86Sr diagrams indicate that ore fluids were derived from dynamic metamorphic water, magmatic water and meteoric water. The ore-forming ages of Kanggur gold deposit are determined by Rb–Sr and Sm–Nd isochron methods. The results show that the main ore-forming stages of Kanggur gold deposit are 290–282 Ma, secondary mineralization stages are 275–254 Ma. Studies on regional geology, ore geology, isotope geochemistry and ore-forming ages have proved that the Kanggur gold deposit was formed in the compression–extension transition stage during the latest Paleozoic continental collision, and is characterized by orogenic gold deposits.