Metallogenic Mechanism Of The Indosinian Huomaidi Porphyry Copper-molybdenum Deposit, West Qinling

Huomaidi copper-molybdenum deposit lying in the intersection of North Qilian orogenic belt and West Qinling orogenic belt, is a typical porphyry deposit in the northern section of West Qinling. Based on detailed study of geological and geochemical characters of the Huomaidi deposit, we recognized the spatial distribution character and the alteration zonation of the deposit, identified the magmatic and hydrothermal vein events which caused the alteration and mineralization, figures out geochemical characters of the ore-bearing porphyries, figured out the dating of diagenesis and metallogeny. And it discusses the source the ore-forming fluids and ore-forming material, and discusses the minerogenetic mechanism.1. Huomaidi copper-molybdenum deposit displays a typical alteration- mineralization pattern. From the center to the edge, it respectively develops potassic alteration, phyllic alteration, argillic alteration and propylitic alteration. The ore body are mainly in the phyllic alteration zone.2. The deposit mainly has three phase hydrothermal fluids vein, from early to late: granular-Kfeldspar-biotite-lesser veins(A veins), quartz-chalcopyrite-molybdenite- pyrite sphalerite veins(B veins), Pyrite-quartz-lesser chalcopyrite veins(D veins).3. Analytical studies on the isotope geochemistry(including H, O and S isotopes) shows that δ18OH2O values vary from 8.6‰ to 13.6 ‰,δDH2O values vary from-50‰ to-85 ‰, which suggest that the ore-forming fluids were mainly magmatic water with meteor water mixed. The δ34S values vary from 0.02‰ to 5.9‰, suggest that mineralized elements should be mainly from lower crust and exchanged material with the upper mantle.4. The ore-bearing porphyries belong to potash rich cal-alkali and quasialuminumperaluminous rock series, enrich in LREE and LILE, and relatively deplet in HFSE of Ta, Nb, P, Hf, Ti; The zircon isotopic Lu-Hf data implies that the ore-bearing granitic magma was derived from partial melting of the ancient Mesoproterozoic to Neoproterozoic continental crust. The LA-ICP-MS zircon U-Pb isotopic dating shows that,the ore-bearing porphyries emplaced at 226.6 Ma to215.0 Ma,. The molybdenum Re-Os isotopic dating shows the ore mineral precipitated at ca. 210 Ma. Combined with the tectonic evolution history of the west Qinling orogenic belt, geochemical features of ore-bearing porphyry, diagenetic and mineralization age show that tectonic regime transformed from syn-collision to post-collision caused in the ancient lower crustal rocks partial melted and with mantle material to joined in, the magma carried ore-forming materials intruded along the fault, then the ore-forming fluid differentiated from the magma carried elements such as Cu, Mo, S migrated along cracks filled and replaced the surrounding rock.To sum up, Huomaidi copper-molybdenum deposit was formed in the collisional orogenesis of The north China plate and south China platetectonic dynamics background, and it is a porphyry copper-molybdenum deposit formed in tectonic regime transformation from syn-collision to post-collision.