Geology, geochemistry and metallogenic epoch of the Katebasu large-sized gold deposit, Western Tianshan Mountains, Xinjiang

Abstract: The Asian gold belt extends into Western Tianshan Mountains, showing great prospecting foreground and potentiality. The Katebasu gold deposit is a newly-discovered large-sized deposit, with 87t gold reserves and 3.84 g/t average gold grade. The deposit is situated in a deformation band near the north Nalati fracture on the northern margin of the Middle Tianshan Mountains. Gold orebody, lenticular or tabular in form, is controlled by the alteration zone along with the brittle and ductile fracture zone in the monzonite granite. The center of the gold orebody is silicified rock with gold-bearing pyritization, and the edge is sericite chlorite epidote altered rock with gold-bearing pyritization. The pyrite and chacopyrite are main gold carriers, with ionic gold in pyrite, while embedded-gold and fissure-gold constitute the main forms in chacopyrite. The geological bodies of the Katebasu large-sized gold deposit consist of monzonite granite, with a (346.3±3.3) Ma zircon U-Pb concordia age, suggesting Early Carboniferous. The isochron age of the ore-bearing pyrite is (310.9±4.2) Ma, implying Late Carboniferous, appximately 35 Ma later than monzonite granite. The key to gold mineralization was the tectonic fluidization caused by the closure of South Tianshan Ocean and the collision of Tarim plate with Middle Tianshan landmass. Ore-forming fluids of gold were mesothermal to hyperthermal (270~390 °C) and low-middle?salinity (7%?16% NaCl eq.) ones rich in CO2, with the data δ18OH2O(V?SMOW)=1.6‰?6.4‰ and δD H2O(V?SMOW)=?64‰ ?107‰, showing characteristics of deep metamorphism fluids. The average (187Os/188Os)i of the pyrite in gold ore is 1.449±0.052, and the REE patterns and Pb isotope (206Pb/204Pb=18.129?18.773, 207Pb/204Pb=15.459?15.554, 208Pb/204Pb=37.707?38.123) have similarity or relevance to the earth crust of the Middle Tianshan Mountains, suggesting that the metallogenic material was derived form the earth crust. The δ34S values of the sulfide are 6.92‰?12.15‰, implying that the S of the ore came from Thermochemical Sulfate Reduction (TSR) of the marine strata of Paleozoic. The Katebasu gold deposit was controlled by the shatter tectonic stresses between the Tarim plate and the Middle Tianshan zone in Late Carboniferous epoch, produced by the structure-altered Tianshan rock and belonging to the collision-orogeny gold deposit. The results achieved by the authors provide valuable guide for the continuous prospecting breakthrough in Western Tianshan Mountains of Xinjiang.