Geology and metallogenesis of the Tiegelongnan Cu-Au-Ag deposit, Duolong ore district, Tibet

The Tiegelongnan deposit is a giant deposit (> 10 million tons Cu resources with an average grade of 0.53%) located in the west of the Bangong Co-Nujiang metallogenic Belt, where typical porphyry and epithermal types of alteration and mineralization are developed. A compilation of geological features and mineralogical studies revealed that the Tiegelongnan deposit developed two stages of hydrothermal alteration. The early stage was related to porphyry emplacement, developing potassic, phyllic and propylitic alterations, telescoped by the late advanced argillic alteration in the shallow levels. Correspondingly, two stages of mineralization occurred, the early porphyry-type mineralization being overlapped by the late high-sulfidation epithermal mineralization. Due to differences in pH, log fO(2), K+ activity and temperature of ore-forming fluids, distinct sulfide minerals of low to extremely high sulfidation states, such as chalcopyrite, tennantite, enargite and covellite, precipitated throughout the entire hydrothermal process. The Tiegelongnan deposit is a complex porphyry metallogenetic system of 'multiple structures'. The Early Cretaceous andesitic volcanic rocks of the Meiriqiecuo Formation exposed on the surface act as a cap for the ore body, beneath which an oxidizing-leaching zone lies. Under the cap and the oxidizing-leaching zone, a porphyry ore body is remoulded by high-grade high-sulfidation epithermal hydrothermal mineralization, which gradually transitions to continuous porphyry-type mineralization at depth.