| Southwest Sanjiang(Nu river, Lancang river, Jinsha river)region is located in theeastern Tibetan Plateau, also is part of Alpinei-Himalayan orogen. The deposit occurseastern of Tethyan tectonic which is the connection position by Indian plate andEurasian plate, spreading from NNW to SN trending. The ares has experienced aseries of tectonic events, such as oceanic subduction, continental-arc collision andintracontinental with the characteristics of long-term acticities. In the tectonic region,magmatic activity is frequent and intense, meatllogenic condition is superior with richmineral resources, is one of China’s major nonferrous metals and precious metalsdeposits with the formation of large, super-large deposits having giant prospectingpotential.Shaxi silver polymetallic deposit is located in middle zone of Yidun island arc foldbelt which is in north of southwest Sanjiang area, with frequent magmatism, developedfolds and faults. In addition the deposit has been the second oversized silverpolymetallic deposit after Gacun deposit (volcanogenic massive sulphide deposits),Xiasia silver polymetallic deposit in Yidun island arc. The exposed strata is PresinianChias group Sinian and Paleozoic, Triassic strata is widely distributed and thickgeosynclinal sedimentary. Southwest Sanjiang (Nujiang, Lancang and Jinsha River)region located in the eastern Tibetan Plateau, is part of Alpine-Himalayan Orogen, andits geotectonic is in the eastern Tethyan tectonic domain of the binding site of theEurasian plate and Indian plate eastern domain, with direction NNW spread to nearlySN. Since the early Paleozoic the area has experienced oceanic crust subduction,continental-arc collision and intracontinental tectonic convergence and a series ofevents, with the characteristics of long-term activities. Magmatic activity is frequentand intense, metallogenic condition is superior, with rich mineral resources in this area which is one of the China’s biggest concentrated non-ferrous metals, precious metalsdeposits, with the formation of large, ultra-large polymetallic deposit conditions andhuge prospecting potential.This paper analyzes Shaxi silver lead-zinc deposit on mineralization geologicalbackground, geological characteristics, ore geochemistry, mineral material sources andmineralization model systematicly, and explores the occurrence of the deposit arearocks, magmatic rocks and mineralization relationships, revealing a mineral depositsources and formation process, as well as polymetallic mineralization rules. All thesestudies lead to in-depth study of the genesis of the deposit to provide new information,further guide and promote this type silver prospecting, exploration profoundly in Yidunarea. Such deposits are closely related to the middele-acidic magmatite intrusion rolewith form of biotite granite and rock tumors, but no rock outcrop within the deposit.Due to the impact of external deep rock, ore hydrothermal alteration are well developed.The ore body is controlled by tectonic fracture zone (shear zone) and hydrothermalalteration. Furthermore, the deposit has the following characteristics:(1) the ore body occurs in the form of vien, lenticular and cystic of Shaxi silverpolymetallic deposit, which is controlled by two faults cutting by Thum strata groupand its staggered position, one fault is NNW trending, and another is NW trending.The main minerals are composed of galena, sphalerite, chalcopyrite, pyrrhotite,containing a small amount of chalcopyrite, arsenopyrite, pyrite. These minerals arerepresented in a very high temperature conditions as pyrrhotite, but also under lowtemperature conditions as galena, sphalerite, indicating that the formation of the depositexperienced different mineralization periods.(2) Gabbros’ major and trace elements point out that the deposit occurs in intraplatealkali basalts formed in extensional environment.(3) the analysis on treace element Ti in quartz shows that the deposit is formed inlow-temperature environment, and ore-bearing quartz and non-ore-bearing quartz areformed at different hydrothermal fluids. while ore-bearing quartz is formed in differenthydrothermal fluids, in addition the formation of former may not be related tomagmatic hydrothermal. Calcite and fluorite have the same source material, and theformation of calcite and fluorite is not derived from magmatic hydrothermalhydrothermal fluid. Ore-bearing wall rock slate and gabbro have a similar trace elementcomposition indicating the latter are likely to provide hydrothermal fluids. Thesimililarity on REE of single material and Rong Yicuo rock shows that the rockpossible provides driving force migration for ore-bearing hydrothermal fluids but does not offer ore-forming elements directly.(4) the value of calcite and oxygen isotope analysis displays that the genesis of of thedeposit is closely connected with hydrothermal alteration and re-deposition carbonaterocks.(5) the mineral deposits of the metal source is not from Rong Yicuo granite and gabbroin the area, partly Pb, Zn element may be provided by ore-bearing wall rock-TuMugou group layer. The main mineralizing hydrothermal fluids may be from othersfluids forming magma chamber containing Rong Yicuo rock and gabbro that mayprovide ore hydrothermal fluid migration driving force, but does not directly provideore-forming elements. The appearing of gabbro in mining area indicates the depositundergo extensive stretching stress before the intrusion of gabbro resulting in tensionaltectonic fracture zone which not only for basic magma in deep crust or mantle providesa good channel, also provides a migration path for the deep hydrothermal fluidmigration. Meanwhile, for the sake of gabbro from the deep crust or mantle magma, sogabbro dykes cannot be isolated, it was an indication of the deep mines has largeconcealed basic rock, outcropping gabbro dyke is likely to be sticks in deep concealedrock. Deep hydrothermal fluid migration would be to occur, we must have migrationchannels, but also need transport power, the formation of mafic rock mining of deepmagma chamber can provide a large number of thermal power sources for deephydrothermal fluid migration... |
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