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Inner Mongolia Ao Lun Spend Porphyry Molybdenum Deposit Magmatic Evolution And Mineralization Mechanism

Posted on:2013-01-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:T ZouFull Text:PDF
GTID:1110330374465686Subject:Mineral prospecting and exploration
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The Aolunhua Mo deposit, Inner Mongolia, located on the southern of the Daxingling Magmatic Belt, which belongs to the southern portion of Xing-Meng Orogenic Belt that between Siberia plate and North China Craton. The recently discovered Xilamulun Mo-Cu belt, which contains many porphyry deposits, has been focused by lots of geologist. Based on detailed studies in geology, geochemistry and geochronology of the Aolunhua porphyry deposit, we determine the rock/ore-forming mechanism and built the metallogenetic model, and provide theoretical support for further prospecting in the Xilamulun Mo-Cu belt or the Daxingling Orogen belt. The results include the following:1. Wallrock alterations associated with Mo mineralization are similar to a porphyry system, including K-feldspathization, silicification, and sericitization.2. The zircon from the Aolunhua pluton, mafic enclave, rhyolite porphyry and diorite porphyry yielded U-Pb isotopic isochron age of134.1±1.4Ma,133.6±1.0Ma,127.7±0.9Ma and125.2±0.7Ma, respectively, which show that the magmatism have been lasted about9Ma in Aolunhua deposit.3. Based on detailed studies in lithology, lithogeochemistry and geochronology of the first discovered mafic enclaves in Aolunhua porphyry deposit, we propose that the mafic enclave is the direct evidence for the underplating of mantle-derived magmas in this area. The injection of mantle-derived magmas is an effective way to obtain ore-forming material, i.e., metal and sulfur.4. According to study of lithogeochemistry, three types of plutons can be identified:(1) Granodiorite porphyrys, the intrusion with high Sr/Y ratios is composed of Aolunhua granite and granodiorite porphyry dike, which resulted from remelting of the crust induced by underplating of mantle-derived magmas;(2) Acid dikes, the intrusion with low Sr/Y ratios consist of quartz porphyry dike and rhyolite porphyry dike, which formed by mixing between the source of the high Sr/Y intrusions and continental crustal materials;(3) The late intermediate-basic dikes, the intrusion comprised of dacite porphyry, diorite porphyry and diabase, which maybe evolve from the mixing between acid magma from acid dikes and mantle-derived magma.5. Coexistence of melt inclusions and liquid inclusions in vein dikes and together with previous results of discovery of the prophyritic quartz, which suggest that the initial ore-forming fluids were not derived from a single hydrothermal fluid but magmatic fluid through boiling of deep-sourced magma.6. As revealed by C-H-O isotope data, the ore-forming fluids evolved from magmatic to meteoric in origin, which is a common feature of the porphyry deposits in various parts the world. The S-Pb isotope data indicate that ore-forming metals derived from magma. The comparison of Pb isotopes show the molybdenum is observably affected by magma mixing, which suggest magma mixing of Aolunhua pluton links to the origin of porphyry deposit.7. According to fluid inclusion study, we conclude that the initial ore-forming fluids were derived from high-temperature, high-salinity fluid magmatic hydrothermal. The ore-forming fluid evolved from initial boiling, through fluid boiling, fluid mixing and water-rock reaction. Boiling-related escape of volatile such as CO2made the fluids condensed or oversaturated, resulting rapid precipitation of ore-forming materials such as MoS2. The ore-forming is also slightly influenced by the water-rock reaction and fluid mixing.
Keywords/Search Tags:porphyry molybdenum deposit, Aolunhua, magma mixing, magmaevolution, mineralization mechanism
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