| The Duobuza copper deposit is discovered by the Fifth Geological Brigade of Tibet Provincial Bureau of geological prospecting in super large ore deposits with prospects.In this paper, based on the existing research, the application of modern analytical techniques and metallogenic theory, systematic research on the metallogenic geological background, geological and geochemical and isotopic chronology of deposits and other aspects, in-depth analysis of the formation mechanism of the deposit, the main results are as follows:(1)The Duobuza copper deposit is tectonically belonging to the Qiangtang-Sanjiang composite plate,combining with Bangonghu-Nujiang and Gangdese-Nyainqentanglha plate, experienced the Qiangtang terrane, Lhasa terrane, cracking, the polymerization and reclamation, orogenic evolution processes. In the mining area tectonic magmatic activity is frequent and intense fluid interaction, both magmatic activities, and volcanic eruptions, and has a multi cycle and multi sources and the characteristics of the diversity, from the Variscan, Indosinian, until Yanshan period magmatic activity, for a long time.Cross together within the mining area to the North East to what F2 and F10 two regional deep faults, as increased migration to minerals and fluid and in the porphyry emplacement provided favorable conditions. This condition is conducive to the mantle fluid and provide rock forming minerals, but also conducive to building a good environment of ore.(2)The granodiorite porphyry aremainly calc alkaline series, enriched in LREE, HREE loss, ?Eu positive Eu anomaly, the relative enrichment of Cs, Rb, Th, K, La, Sr, Hf, Tb and other elements, and relatively depleted in Ba, U, Ta, Nb, Ti and other elements of the ore bearing porphyries of earth; these geochemical characteristics and chemical characteristics of the typical porphyry copper deposits are similar, indicated that the felsic magma derived from the mantle diapir caused crustal remelting, and the ore bearing mantle fluid metasomatism diagenetic processes associated with magmatic rock ore. The granodiorite porphyry and metamorphic sandstones are intrusive contact relationship, both in the rock contact zone, mineralization alteration metamorphic sandstone with more enhanced, mineralization and the alteration is mainly potassic, phyllic alteration, silicification, propylitization, clay and so on; porphyry metallogenic ore bearing rock development requirements a closed condition of local fracture system, in favor of the ore-forming fluid percolation and metasomatism, and does not make the ore-forming hydrothermal rapid loss of or escape, and the area of metamorphic sandstone just to meet such conditions, effectively promote the alteration of sufficient and uniform, resulting in the whole rock mineralization strong alteration zone. The granodiorite porphyry, metamorphic sandstone and basaltic andesite with similar right inclined REE patterns, on the whole show LREE enrichment, REE wide range of features, composed of granodiorite porphyry and metamorphic sandstone, basalt andesite, REE shows the characteristics of gradually rising, this shows that in the mineralization process with REE elements to bring out into the mantle fluid with uniform mixing; EU negative staining and metasomatism are reduced or offset the crystallization differentiation of prospecting, and its proportion and the strength is increased and the formation of positive Eu anomaly, suggesting that ore-forming fluid properties with diversity; The Duobuza copper deposit distribution pattern of rare earth elements in various types of rocks and ores show the complexity, diversity and complexity of mineralization process of minerals; metallogenic characteristics of the diversity and complexity in one, suggesting that metallogenic unified subject to the ore bearing mantle fluid and the crust mantle mixing and multi mineral superposition. Granodiorite porphyry vein quartz, gypsum mineral ?Eu negative Eu anomaly, is a porphyry by late diagenetic oxidation leaching results; while the biotite minerals ?Eu positive Eu anomaly, is a sign of ore bearing mantle fluid with magmatic crystallization diagenesis mineralization metasomatic rock.(3)The magmatite in the mining area were analyzed by LA-ICP-MS and SHRIMP zircon U-Pb isotopic dating, indicating the Duobuza copper tectonic magmatic activity in the area took place at about 120 Ma or so, there are many times during the magmatic activities. Re-Os isotopic dating of Molybdenite mineralization age represents, indicating the mineralization took place at about 118 Ma or so; potassic zone the forming age of 119.2 + 1.1Ma, and the metallogenic age, show that the mineralization occurs in potassium alteration stage; sericite Ar-Ar dating results was 115.8 + 1.4Ma, on behalf of the late hydrothermal alteration mineralization; variable and ore-forming ages slightly later than the intrusion of magma, the diagenetic and metallogenic ages are basically the same, with the diagenesis mineralization lasted about 4Ma. Diagenesis and metallogenesis are concentrated in the Yanshan period, the period is between the Lhasa block and the Qiangtang block Nujiang ocean basin closed, with a large number of collision granite mantle derived magmatism, diorite porphyry magma emplacement age, that the formation of the deposit structure and the District of Yanshan period magmatic fluid activity.(4)Porphyry in S, Cu, Au content significantly positive correlation, suggesting that S, Cu, Au may be of the same origin, mainly from the mantle; Pb isotope composition show that it has the characteristics of crust mantle mixing and subduction zone lead; granodiorite porphyry and pyrite samples of initial value of Sr is higher than the global mantle source the mafic rock Sr isotopic average of 0.70350, lower than the silicon aluminum shell source rock Sr isotopic average 0.720 + 0.005, that is a mixture of mantle and crust source Sr; hafnium isotopic characteristics indicate the ore bearing rock should be experienced different source of magma mixing process, there are many components involved in the rock forming and ore-forming process in the main, to mantle source. Carbon and oxygen isotope composition of porphyry indicate that ore-forming fluids are mainly derived from the mantle of carbon; hydrogen and oxygen isotope studies show that the ore bearing mantle fluid in the felsic magma contamination of crustal remelting process of formation, mixed with some precipitation and show a certain degree to drift phenomenon, so as to promote the precipitation of ore-forming and aggregation; helium argon isotope show that the ore-forming fluids is a mixture of two element model of typical mantle fluids and crustal fluid, and by the mantle source based; analysis of silicon and oxygen isotopes show that the ore-forming fluids mainly come from the primitive mantle. Comprehensive research shows that, the ore bearing mantle fluid in mantle diapir caused by crustal felsic magma formed by remelting and crystallization process with diagenetic metasomatic rocks and granodiorite porphyry with the crust mantle contamination and metallogenic characteristics.(5) A comprehensive study of the genesis of the deposit of the mantle fluid metasomatism caused by crust mantle mixing mechanism with superposition mineralization. Due to the collision between the closure of Qiangtang block and Lhasa block Nujiang of oceanic crust, subduction of oceanic crust in the Qiangtang block to the south of Bangonghu-Nujiang, makes the Bangonghu-Nujiang suture zone in the development of large-scale thrusting and strike slip faults and the deep geological process. With this process, the primitive mantle gradually to the metasomatic enriched mantle transformation and partial melting, forming silica undersaturated mafic magma and alkaline magma and the properties of slurry ore bearing mantle fluid. Then drive the mantle underplating, the hot rise, cause deep crustal melting to form a silicon rich felsic magma.They further mixed, multiphase molten form of crust mantle mixing, and along the deep fault passage upward emplacement. As a kind of transmagmatic fluid, the ore bearing mantle fluid can not only with the silicon rich alkaline magma crystallization diagenetic processes synchronize account and energy conversion of alteration mineralization, but also out of the rock magma or separation, along the passage into the favorable ore rock interface or with secondary crack closure conditions, and fracture interaction between surrounding rock caused by crust mantle exchange between matter and energy, and promote the crust mantle contamination superimposed mineralization, resulting in the formation of the Duobuza copper deposit. |
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