Multiple tectonic-magmatic Mo-enrichment events in Yuleken porphyry Cu-Mo deposit, NW China and its’ implications for the formation of giant porphyry Mo deposit

Abstract The Yuleken porphyry Cu-Mo deposit located in the Chinese Altay-East Junggar, a section of the Central Asian Orogenic Belt, the world's largest Phanerozoic subduction-accretionary orogens, and witnessed the multistage tectonic-magmatic and mineralization of porphyry Cu and Mo deposit systems from arc to syn- and post-collision environments in this region over a time span of about 52 Ma. Four types of molybdenite have been distinguished: (1) primary magmatic-hydrothermal, undeformed molybdenite in porphyry, (2) recrystallized molybdenite associated with ductile deformation, (3) recrystallized, intrafoliational molybdenite, and (4) fracture-related hydrothermal molybdenite, and are characterized by decreasing Re abundances from magmatic to hydrothermal conditions. Individual molybdenite types are non-stoichiometric and exhibit the following negative correlation between the Mo and Re contents: Re (apfu) = – 0.0026 Mo (apfu) + 0.00268. This trend reflects successive stages of tectonic-hydrothermal events from a magmatic island arc to a post-collisional setting. These repetitive mineralization events produced Mo enrichment and higher overall Mo grade of the Yuleken deposit, and are recorded in progressively decreasing Re concentrations in molybdenite. Statistical evaluation of Mo and Re abundances in giant to small porphyry deposits worldwide also indicates that decreasing Re in molybdenite will lead to lower overall Re resource (in a single deposit) and to greater overall Mo resource (in the same deposit). Multiple mineralization processes related to repetitive tectonomagmatic episodes in large porphyry Mo deposits that display Re depletion in molybdenite suggest that reworking of mantle-derived porphyry systems by successive events of crustal growth may be the responsible for Mo enrichment and higher overall Mo ore grade, and eventually produce giant porphyry molybdenum deposits.