Geological characteristics and genesis of the Ulan Uzhur porphyry copper deposit in Qinghai

Abstract：The Ulan Uzhur copper deposit, situated on the western margin of the Qaidam basin is a porphyry copper deposit controlled by granite porphyry dikes. The major element, rare earth element (REE) and trace element characteristics indicate that ore-controlling granite porphyry and its wall rock plagiogranite (porphyritic) belong to the calc-alkaline series characterized by enrichment of LREE, pronounced negative Eu anomalies and depletion of Sr, Ba and Ca. They formed in a syncollisional orogenic environment and are related to the subduction-collision and closing of the late Variscan-Indosinian Songpan-Garzê Paleo-Tethys ocean. The ore-controlling granite porphyry and its wall rocks underwent strong hydrothermal alteration and show apparent alteration zoning. The main hydrothermal alteration includes potassic, phyllic and porphyritic alteration. The core of the granite porphyry is usually marked by a zone of potassic and silicic alteration superimposed by phyllic alteration, and the wall rocks adjacent to the granite porphyry are phyllic zones, and those distal to the granite porphyry are propylitic zones. The intensity of mineralization is apparently positively correlated to the intensity of alteration. The spatial distribution, attitude and size of the copper orebodies are also controlled by granite porphyry. The mineral assemblage, hydrothermal alteration, sulfur and oxygen isotopic compositions and results of microthermometric measurements of fluid inclusions—all suggest that the Ulan Uzhur copper deposit formed at high to medium temperatures and that the ore-forming fluids and materials were derived from magma. So the deposit is a porphyry copper deposit related to hypo- and mesothermal processes.