The Study Of Metallogenic Conditions Of The Gold Polymetallic Deposit In Are-bengge Ore Belt, Shangri-La,Yunnan Province

Sanjiang region(the three rivers: Jinsha, Lancang and Nujiang), is affected bythe Indian ocean plate and Eurasian plate and Pacific plate each other, going throughthe formation and evolution of tethys, and India-Eurasia collision and the plateauuplift, the process of the Sanjiang tectonic is conducive to mineralization and animportant metallogenic province metal. The Yidun Island Arc Belt is one of theimportant tectonic units in the archipelagic arc-basin system in the Sanjiang Area, andis the important metallogenic belt of the polymetal as copper, lead, zine, silver, gold,tungsten, tin, molybdenum, and so on, with a great resources potential.The study area is located in Zhongdian arc on the southern tip of YiDun islandarc belt, Zhongdian arc is an important mineral area and the geologists at home andabroad have very focused on regional metallogenic conditions, the area is anotherimportant mineral base related to the porphyry copper deposits since the Yulongporphyry copper belt discovered. For a long time, it was considered as alkaline-richporphyry related to strike-slip shear caused by India-Asia continental collision, itseastern and southern Ganzi-Litang suture zone, the west is Xiangcheng-Gezan deepfault.Deposit is located at the confluence of two faults, Alteration types mainlyinclude silicification and chloritization, and sericitization and clay minerals, themineralization is mainly in long porphyry development, Minerals include pyrite,arsenopyrite, chalcopyrite, sphalerite, etc. Wall rock alteration or mineral group showthe characteristics of the low temperature hydrothermal ore-forming fluid, oredeposit types should be related to alkaline rock of hypabyssal hydrothermal golddeposit in low temperature. Late orthophyre intrusion may be the main causes ofmineralization in the Bengge regione.Gold deposit types in the northwest Yunnan(the gold polymetallic deposit) iscollision orogenic type ore deposit.The regional tectonic evolution laid thefoundation of space and material basis for Himalayan rich alkali magmatic activityand the formation of related metallogenic system in the regione.The goldpolymetallic mineralization is close related to rich alkali magmatic activit in thespace and time and causes. Mineralization is mainly related to rich middle-lateproduct of alkaline magma evolution, and together produce in space.Magmatic rocks in the area of gold deposits mainly include Triassic syenite andorthophyre. SiO2content between53.90%～68.38%broadly consistent with that ofintermediate-acidic intrusive rocks in northwest yunnan indosinian period and Cenozoic alkali rich porphyry in western yunnan. And the SiO2content is close to thelatter.All types of rock shows the characteristics of the high potassium rich alkali,the alkali content is higher.Na2O+K2O change in range of4.83%～12.98%, K2Ocontent up to9.27%, the lowest content was3.31%, the extreme value, average>3%,K2O/Na2O ratio great range (1.45～27.57), that is similar to characteristics ofrich alkali rock mass associated with gold. Both ph and total alkali content of Benggerock mass accord with the requirement of mineralization of ore-forming.So rich alkalirock mass in the mining zone is very good for gold mineralization.Combined with rock geochemical analysis research，Bengge rocks belongs tothepotassium basalt series, it is high Mg#, Cr and Ni that show the characteristics ofmantle source.The trace element analysis of Bengge rock mass shows enrichment ofLarge ion lithophile elements such as Sr, K, Rb, Ba, Th, and light rare earth andrelative loss of high field strength elements such as Ta, Nb, Hf, Ti, P that indicateBengge rock mass is formed in tectonic environment related to island arc.Ore-forming elements analysis shows that Cu,Ag,Pb,Au,Zn are not positivelyrelated to the SiO2, but Au,Ag are positively related to alkali. Gold and otherore-forming elements of Bengge rock mass do not mainly come from the magmaitself, but are closely related to deep ore fluid containing silicon. Strong mineralizedsamples are rich in Ore-forming elements such as Ag, Cu, Pb, Zn which showmetallogenic potential in deep.The Langdeng gold polymetallic deposit develop in Are main and secondaryfaults stratum in the mining area is the Triassic’s Tumugou group(T3t1);Rock mass tothe Permian system in the target group of basalt.In broken belt, Luo ji group basaltand basalt and tuffaceous basalt touching part’s groove group is an ideal area to findgold.Main elements data of basalt of the mining area in Langdeng shows that SiO2content of basalt samples is mostly between43.54%~52.17%, and belong to thescope of basic rock. Rittmann index σ is between1.18~8.46. This rock belong tocalc-alkaline-alkali rock series; Na2O and K2O content is between2.93%~2.93%which is an alkaline. With the increasing of silica content, the content of FeO andMgO in the fall, K2O levels rising, Na2O and CaO is negatively related to the silicacontent that shows the possibility of basalt of spilitization is the largest in later stages;increasing Al2O3content indicate basalt is normally evolved from magma; Thecontent of H2O+is between2.07%~5.51%which show the possibility ofhydrothermal activity is in diagenesis and after diagenesis．Luoji group basalt REE analysis data in Langdeng area show total content ofREE very changed; from the rare earth distribution patterns, it overall display tiltedto the right; light rare earth concentration degree is a bit high, heavy rare earthconcentration degree is relatively low. But, data overall reflect features of the transition from T-MORB to P-MORB.The spider diagram of trace element ratio of basalt in Landdeng show that LILEin basalt samples (e.g., Cs and Ba) concentration is obvious, volatile which implythe possibility of hybridization of basalt is very large；LILE (Rb, K) shows the loss isobvious which imply basalt of spilitization; the loss of HFSE (Nb, Ta) suggests thatbasalt is likely formed in volcanic arc environment and is chose related to platesubduction; obvious positive Pb anomaly of samples imply that basalt is altered oraffected by the mineralization; the loss of Sr largely suggests the influence of thealteration or the mantle metasomatism.Ore-forming elements analysis data show Au content of Luoji group basalt is74×10-6that is nearly20times than the global basalt gold content (4×10-6); the goldcontent of silicide basalt is higher than no silicide; the gold content of limonite evenreached the industrial grade. The content of polymetallic elements such as Cu, Pb,Zinc is more several times than that of global basalt which suggests basalt providedthe ore-forming material in the metallogenic process.From degree of enrichment of ore-forming elements of surrounding rock,mineral-containing come from T3t1and part from volcanic rocks inT3t.Comprehensive analysis of ore, Genetic types of Langdeng gold point may bemagmatic hydrothermal gold deposit.Point out the fault fracture zone is a Are-bengge region to find the best parts ofthe gold deposits.