| Wenquan Molybdenum Deposit,a large porphyry molybdenum deposit located within the Wushan County of Gansu,was discovered by Bureau of Geology and Exploration for Non-ferrous Metals in 2000. Aiming at the Wenquan Molybdenum Deposit,guilded by the theory of regional metallogeny and prospecting engineering,and starting from the relationship between granitic geochemistry and mineralization,and with the thread of magma-structure-fluid mineralization,this paper makes some studies on the mineralize condition,deposit geology,geochemistry, ore-forming mechanism and laws,etc.and especially sets up the metallogenetic model and predicts metallogenetic prospect.The following are main progress and conclusions:1.Within central orogenic zone(Dabie-Qinling-Qilian-Kunlun),the previous geological works indicate that not only granitic molybdenum resource,but molybdenum deposits possessed to a certainty scale were only distributed in East Qinling region,which led to the formation of a porphyry molybdenum belt of 52%molybdenum reserves in China and the second largest molybdenum zone in the world,only being second to Climax-Henderson porphyry molybdenum belt in west America.In 2000, however,the discovery of Wenquan molybdenum ore broke the distribution pattern of the Qinling molybdenum belt,west extending this belt by over 400 kilometers,and pointed out the ore-hunting direction in whole central orogenic belt.2.Its regional setting,deposit geology,lithology feature,deposit geochemistry are systematic described in this paper.The studies show that it is a porphyry molybdenum deposit with an average deposit-forming age of 214±7.1Ma,Mesozoic Trias at the Indosinian movement stage.Detailed survey of 15th-32th Lines(0.3km2) in Chenjiadawan finished in June,2007 included the drilling engineering controlled by exploratory density of 100×100～80m and tunnel exploring at 2025m Lever and 2065m Lever,which explored the molybdenum ore reserves of 7805 WT(0.053×10-2).Furthermore,42 mineral occurrences (mineralized points) in Wenquan rock mass occuring its outside area covering 260km2.These show a large-scale molybdenum mine exploration potential of Wuquan Molybdenum Deposit.3.Consisting of medium-grain porphyritic-like monzonitic granite, the intruded rock system of Wenquan granitic batholith include the high greenschist facies volcanic-metasediment of Qinling group, middle-Lower Proterozoic Era,low greenschist facies volcanic-metasediment of Liziyuan group of lower paleozoic,and carbonate, sandstone,shale of Liba-Dacaotan group,middle-upper devonian Era. This batholith is also controlled by the junction location between Baoji-Tianshui-Linxia fracture zone(south side) and Wudu-Tianshui hiddened huge faulting(west side).The ore-bearing rock body is Chenjiadawan porphyry stock,a complement body of Wenquan batholith, and the emplacement epoch of the former is posterior to the later.The metallogenetic age could be dated 214±7.1Ma,Mesozoic Trias at the Indosinian movement stage.4.At present,there are 34 projects to control ore body,a single body length of 50～650 meters thick 5～24.4m,the top depth of 38.5～516.5m.Mineralization styles include the fracture altered rock, microfissuring quartz vein-net type and disseminated type.Usually ore bodies are produced at the place where the micro-veins densely occur,so the boundary between ore body and host rock is not obvious and is delineated by chemical analysis.The ore is mainly composed of molybdenite and quartz,and the secondary minerals include pyrite, chalcopyrite,blende,scheelite,arsenopyrite,Tetrahedrite,galena,bornite, feldspar and mica and others.Wall-rock alteration include kalium silicification,silicification,zeolitization,red argillization and others except propylitization.5.The mean content of SiO2 is 71.21%,K2O is 4.91%,K2O+Na2O is 8.22%,K2O is much greater than Na2O,Rittmann index(σ) is 2.45,which indicate the ore bearing porphyry belongs to potash-rich cal-alkali rock series.These features are similar to inclusive molybdenum porphyry (Si02 70%～77%,K2O+Na2O 8%～9%,and K2O is greater than Na2O), show its potential for good mineralization.Compared with Vickers value, the ore-bearing porphyry is high in Mo,Cu,As,Ag,poor in Bi,Hg,Ba,Au,and the contents of Pb,Zn,Sb,Co,Ni,Cr,V are equal to Vickers'.The mean contents of Mo is up to 45×10-6 and Cu is up to 142×10-6,which indicate ore-bearing porphyry magma is the basic substance source for the mineralization.6.Respectively,theΣREE of medium-grain porphyritic-like adamellite,fine-grain porphyry adamellite,dark inclosure and quartz vein are 126×10-6,148×10-6,167×10-6 and 26.8×10-6,which indicate that the three formers are from the congenetic magma and the latter is the crystallized product of post-secondary hydrothermal fluid.The LREE/HREE value can reach 4.5～5.6,and are 4～5 times higher than those of general granite(1.0～1.2),which shows obvious LREE enrichment.The(La/Sm)N value is about 4.6,indicating satisfactory fractionation degree and LREE enrichment,whereas the(Gd/Yb)N value vary from 1.97 to 2.53,and are obviously higher than those of shell type granite[(Gd/Yb)N≈1],which indicate poor fractionation degree.The rate of partition curve(La/Yb)N is 15.13～24.06,rapidly dips rightwardly.The distribution pattern figure of rare earth shows similar variation of curve shape among granite,opaque-color inclosure and quartz vein,which indicates their REE homologue.With growing magmatic differentiation degree,the 5Eu value is decreasing accompanied by more violence europium depletion,theδEu value is 0.66～0.68,negative abnormality and europium depleted type,having features of crust remelting regenerated granite and mantle original granite,which show mantle resource intermingle into it during the period of crust remelting,and which is also the best explanation for basic rock wall(mantle resource) associating with micro-fine grain mafic inclusion intergrowth.The valueδCe is 0.83～0.90,belonging to ceriumdepleted type and weak negative abnormality.7.The dynamics mechanism of the main ore-bearing fault is the intrusion of granitic magma,which results in faulting fractured zone and joint fissure system and finally became the principal host structures.The genetic model of deposit could be supposed as the following:In Indo-Chinese epoch,due to continental plate action and mantle current action,granitic magma intruded along the junction between Baoji-Tianshui fracture zone and Wudu-Tianshui fracture belt,and then became granite batholith.As the evolution and intrusion of the magma,a high pressure fluid phase riching in ore-bearing substance has been formed when the intrusion of Chenjiadawan porphyry stock happened. While it continuely raised and permeated along the available passageways, and led to a high vein-bearing rate and permeability region around the porphyry stock.For long-time convective circulation of groundwater and hydrothermal fluid and water-rock reaction caused by magmatic thermal current,veinlet-disseminated shaped molybdenum mineralization took place in the wall rock along both sides of fracture zone and micro-fissure of the upper wall.On the other hand,due to the varies of fluid pressure and rupture and opening-closing of the host rock time after time,the orebearing hydrothermal fluid sedimentate,and came into being interlaced ore-bearing quartz net-vein.8.The indications of ore include kalium silicification,silicification, zeolitization,red argillization,pyritization and malachitization,etc.If the silicification is more intensive,the net-vein quartz vein is more concentrated and the single vein is more wider and its color is more deep, the metallogenic condition is more favorable.Usually,the ore exist on the zeolitization alteration zone,the superposed location between red argillization and dike,and at some places where isseminated or filmily-shaped pyritization and malachitization are well developed.The favourable metallogenic element combination is composed of Mo,Cu,Ag,As.In minefield,key points for ore prospecting could be the deep parts along the exploratory line in NEE direction,while in the Wenquan rock mass,42 molybdenum mineralization points as well as the intersection of F32,F16 and F20 Could be layed emphases on.Regionally, the Indo-Chinese granitic masses exposured area adjacent to discordogenic fault zone and Precambrian basement could be the ore-hunting prospecting area.
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