Genesis of the late Ordovician Kukaazi Pb-Zn deposit in the western Kunlun orogen, NW China: New insights from in-situ trace elemental compositions of base metal sulfides

Abstract

The Kukaazi Pb-Zn deposit was recently discovered in the western Kunlun orogen (WKO), NW China. This deposit consists of three ore blocks (KI to KIII) hosted in Mesoproterozoic metamorphosed rocks. Ores are mainly composed of sphalerite, galena, chalcopyrite and scheelite. Here we present in-situ LA-ICP-MS trace elemental compositions of sphalerite and galena of sulfide ores from ore blocks KI and KII, to shed light on the ore formation and its regional tectono-metallogenic implications. Sphalerite from ore block KI contains higher contents of Fe, Mn, Co, Cu, Bi, Sn, and Sb than sphalerite from ore block KII. Nonetheless, sphalerite from the two ore blocks has compositions similar to the sphalerite from typical skarn deposits. Galena from ore block KI is compositionally different from galena from ore block KII, and has relatively high Ag, Cd and Tl contents and low Sb content. Such differences are probably due to different ore-forming temperatures in these two ore blocks. Based on the Cd partition coefficient between the co-existing sphalerite-galena pairs, sulfide ores in ore block KI may have formed under higher temperatures (265–387 °C) than those in ore block KII (229–251 °C).Combined with previous studies, we propose that the Pb-Zn mineralization at Kukaazi was distal skarn related and formed in a continental arc setting. Discovery of this deposit implies that WKO is a promising area for future porphyry/skarn-related Pb-Zn (-Cu-W) mineral exploration in northwestern China.