(Geochemistry And Genesis Of Feimo Cu-Mo Polymetal Deposit On Ailaoshan Orogenic Zone, Yunnan, China)

Ailaoshan orogenic belt is the important composition unit of the southwest "Sanjiang" metallogenic belt, part of the Tethyan metallogenic domain. It is also the great potential polymetallic metallogenic belt of copper, gold, molybdenum, tungsten and tin.Supported by the cooperation of school and enterprise, the author has made the documentary on the subject of "discussion on the geochemistry and genesis characteristics of Feimo Cu-Mo polymetalic deposit in Ailaoshan orogenic belt". Guided by regional metallogeny and the metallogenic theory of orogen belts, subject to the absorption and drawing upon the former achievements on the Ailaoshan exploration and research, doing widely field geological investigation and indoor synthetic analysis at the mining districts and its surrounding area, this article was at the forefront of the geostatistics and geological exploration in our country. Achievements obtained are as follows:(1)Feimo Cu-Mo polymetalic deposits are located in the medium-deep dark colored metamorphic rock of Ailaoshan belt. The evolution progress of tectonic and the Yangtze plate triggered toward by the Indian Ocean plate make a series of northwest blocks and discordogenic fault; Honghe fault and Ailaoshan fault which determined the development, evolution and spatial distribution of the medium-deep Ailaoshan metamorphic rock belt, the distribution pattern of the series of fracture and fold structure that paralleled to the main structure line, and the magmatic action of this area; all of those are finally formed the Ailaoshan polymetallic metallogenic belt and the Cu-polymetalic metallogenic belt in connection with metabasite and deep igneous activity.(2) The medium-deep metamorphic rock in Ailaoshan belt is the ore-bearing rock series of Feimo Cu-Mo polymetalic deposit, and it is also the ore-forming material source of the deposit. The deposit is hosted in the medium-deep dark colored metamorphic rock of Ailaoshan belt. The ore-bearing wellrock are diopside marble in Feimo section Along Fm Ailaoshan group. Ailaoshan group composed chiefly of1800-800Ma Paleoproterozoic to Neoproterozoic tectonic microlithon, and its host rock should be formed in1600～1300Ma by the structural deformation and dynamothermal metamorphism,1000～800Ma by Jinning movement. The reconstruction of metamorphic rocks protoliths in Ailaoshan showing that its protoliths was basic volcanic rock and sediment limestone, mudstone, dolomitic sandstone in early proterozoic. Geochemical characteristics showing that the dark colored metamorphite schists, granulites are characterized by obvious macroion lithophile K, Rb enrichment, significantly, depletion of HFSE Nb, Ta, P and Ti. Th and Sr distinctly negative anomaly; chondrite-normalized patterns are showing minor fractionation with flat to strongly HREE-depleted patterns, characterized by obvious fractionation of REE, with not obvious Eu and Ce anomalies; trace elements and rare earth elements suggest that they are having the similar characteristics with basic rock and basic volcanic tuff. Marble are characterized by obvious Rb, U enrichment, significantly depletion of Nb, Ta, P and Ti, strong negative Ba and Sr anomalies; chondrite-normalized patterns showing minor fractionation with flat to strongly HREE-depleted patterns, characterized by obvious fractionation of REE, with obvious Eu anomalies; trace elements and rare earth elements suggest that they are having the similar characteristics with carbonatite like dolostone and limestone.(3)Dapijia small intrusions was first researched its rock geochemical characteristics, its lithology are dimicaceous monzonitic granite. The average w (SiO2) is72.42%, A/CNK (molecular ratio)>1.1(1.17on average), the average K2O/Na2O is2.18, the rittman index (σ) is1.76～4.19(3.02on average), the differentiation index (DI) is90～92, ΣREE is between103.34×10-6and247.39×10-6, ΣLREE/ΣHREE is between1.16and7.45, obvious Eu positive anomalies; in the curves of the trace element distribution patterns normalized by the primitive mantle, they are K, Rb, Ba, U-rich and Nb, P, Ti-depletion, have the characterics of crystallization differentiation. Geochemical characteristics of rock-body have similarity with crust-mantle mixed type of magma, high silica, excess aluminum, and calc-alkaline granite. Various diagrams for discrimination of protolith reveal that Dapijia rock-body was collisional orogeny granite, which were formed in collide and post_orogenic extensional structural environment. The ore-forming age of the rock-body is57.72Ma; which is slmilar to the age of large-scale Diagenesis-mineralization in Himalayan Epoch with large-scale inner deforming. Part of the metallogenic materials are supplied by the rock-body, especially Mo.(4)Feimo Cu-Mo polymetalic deposit was first researched its Re-Os isotopic data of molybdenite, attained the age of47.81+0.71Ma, which is slmilar to the age of Zhenyuan, Mojiang, Daping gold deposits in Alaoshan Cu-polymetalic(50Ma±on average). Bulge-extrusion in Himalayan movement, large scale tectono-magmatic thermal event by granite intrusion in Ailaoshan, actived by the magmatic explosion, ore-forming fluid and the volatile component, The act of gathering in large numbers of metallogenic element, and their cosmical mineralization interaction in mineralization period, forming the large-middle Cu-Au polymetalic deposit. The time framework of Feimo Cu-Mo polymetalic deposit is that:the original mineralized layers are the basic volcanic rock (the original mineralized layers that contains copper) which were formed approximately in Proterozoic era (1800-1600Ma), and the concentration, reformation by the action of the metamorphism in Mesoproterozoic-Neoproterozoic (1600-900Ma) then the Jinning movement (900-800Ma), and the reforming in Cu-polymetalic deposit by the strike slipping and overthrusting mylonitization in the Indosinian movement (260Ma), the modification of thermal fluid by the granite intrusive in Yanshan movement (160-80Ma), the bulging-extrusion in Himlayan movement (65-1OMa), and the subversive acts of the large scale tectono-magmatic thermal event by granite intrusion bring the new metallogenic material and become the main mineralizing stages of the deposit.(5) Research on the geochemical characteristic of the deposit showing that, the isotopic data of elements H, O, S, Pb and rare-earth element, trace element are all reach an agreement that the mineralizing matter of the deposit are mainly from deep, the aquatic medium of the metallogenic fluids is magmatic water meteoric on the supplying. Combine with the tectonic setting of the deposit, the types of the wall rock alteration, the ore-controlling factors and the characteristics of isotope, they are showing that the dark-colored metamorphic series in the host strata of the Feimo Cu-Mo polymetalic deposit provided with part of the metallogenic material, the hypomagma, the continental basements of the convectional circulation and the wallrock by igneous intrusion provided with another part of the metallogenic material. Research on the genetic type of the deposit is showing that the discordogenic fault and the path of magma are conducive to the deep material upwelling; the granite intrusive in Himalayan Epoch is the fixation phase of the deposit, the mineralizing fluid are magmatic hydrothermal by granite intrusive which mixed with heated the ground water; the metallogenic material are composed of the deep material and the materials of the process of layer extracting by the hot water. The genetic type of the deposit belongs to sedimentary-metamorphic-superposition of magmatic hydrothermalism reworked Cu-Mo polymetalic deposit.(6) The article summarized the geological and geochemical characteristic of the Feimo Cu-Mo polymetalic deposit and the regularity of ore formation; illustrated the time-space relationship and the genetic relation of the Cu-Mo polymetalic orebody, Ailaoshan metamorphic series and Dapijia granite body; constructed the metallogenic model of Feimo Cu-Mo polymetalic deposit on the genetic type and the time-space distribution pattern of the deposit Cu、Mo、Au、Ag; and summarized the seven critical indicators for deposit, structure, lithology, magmatite, alteration, aeromagnetic survey, physical geography and geochemical anomaly. By the mineral-bearing granite vein, exposed mineralization in granite body, we conclude that the deep level of ore deposit has a good prospect for large scale of porphyry type and contact metasomatic Cu-Mo polymetalic deposit.