| Tibet in the east of Tethys-Himalayan metallogenic belt, the superior of porphyrycopper metallogenic geological conditions, geochemical conditions and porphyryfavorable for mineralization characteristics. Now we have found three porphyrycopper belt in Tibet: Yulong, Gangdese and Duolong metallogenic belt, where rich inresources, is the main copper source in our country. This article based on previousresearch, to analyzed the several typical porphyry copper deposits, through the orerock, wall rock alteration, mineralization characteristics and metallogenic epoch of thediscussion, the following results and understanding:Tibet porphyry copper deposits are mainly distributed the south of Gangdesevolcanic magma belt, both sides of Bangong-Nujiang suture zone and north ofSanjiang metallogenic belt. Regional magmatic activity is strong, and mainly in lateyanshanian and Himalayan intermediate-acid intrusive rocks, Intrusive rocks arebanded distribution of compound batholith, rock strain and dike output; Strongtectonic activities, extruding orogenesis formed a series of nearly east-westdistribution of double fold, large-scale thrust fault of nearly east-west distributiongroups, north east and north west subprime compression shear fracture, that providesgood tectonic conditions for magmatic activity and ore, metallogenic hydrothermalmigration.Area of the ore-bearing rock mass generally is multiple phase hypabyssalcomplex massif emplacement, emplacement age more concentration in lateyanshanian and Himalayan period, mostly rock strain or rock dendritic output, surfaceexposed area and irregular shape. Ore-bearing rock mass to invade surrounding rockno specific selectivity, but may have some affinity to limestone(such as Yulong andQulong).Judging from the geochemical characteristics of the ore-bearing porphyry, Tibetan areas associated with mineralization porphyry in acid rock, ore-bearingporphyry potassium-rich, LREE-enriched, HREE-lossed, loss of HFSE. The collisionorogen environment mineralized porphyry is shoshonitic series, showing the adakiteaffinity, it is different to island arc environment.Tibet porphyry type copper mine has the center type surface wall rock alterationzoning: Centering on the ore-bearing porphyry body, potassium silicate salinizationalteration occur in the core of mineralized magma fluid(the core of the depositpotassic alteration has an extremely important role for the precipitation of copperenrichment); out with phyllic belt(phyllic alteration closely related to mineralizationin some deposits); the edge with propylitization. In addition, some ore spot at the topof the rock mass is development has a strong clay mineralization belt (Qulong, etc.)and hydrothermal breccia (Qulong, Yulong, etc.). The huge range of alteration toporphyry body several times or even ten times (such as Qulong).There are some differences in mineralization type, ore-bearing porphyry intrudedin the early granite batholith in veinlet mineralization-based; mineralized porphyryintrusive carbonate rocks or volcanic sedimentary rocks in veinlets stratiformmineralization. The morphology of ore body plane is in oval ring belt andCross-sectional in upright irregular columnar. Ore structure mainly is Euhedral crystaland account structure, ore structures based on veinlet and stockwork structure. Themineral assemblages in primary ore mostly is pyrite, chalcopyrite and molybdenite; inthe oxidized ore, the typical mineral assemblage may include malachite azurite andred copper ore. Ore grade is low, ore-forming elements give priority to Cu element,associated Mo, Au, Ag and other useful elements. Porphyry copper ore in island arcenvironment containing gold is higher (Duolong, Xiongcun), when Continentalmargin of the porphyry copper ore containing higher molybdenum (Qulong, Yulong).Tibet porphyry copper metallogenic epoch mainly in Himalayan period andyanshan period, due to the mineralization depth more shallow, be preserved depositsformed in the period of the Mesozoic and Cenozoic deposits. Duolong metallogenicbelt in porphyry copper deposits formed in early cretaceous; Yulong copper ore belt inporphyry copper deposits formed in the Eocene; Gangdese eastern section of theporphyry copper deposits formed in the Miocene, Xiongcun in western section ofcopper may be formed in the Early and Middle Jurassic.There is a basic similar porphyry copper deposit metallogenic system in Tibetarea, adak magma formed by partial melting who derived in the collision zone maficlower crust or Calcium alkaline magma formed by partial melting who derived from subduction zone mantle wedge emplacement formed deep magma chamber, somemagma continued emplacement to form a shallow magma chamber; With thecondensation crystallization of the magma, cryptoexplosion and boiling happened, inthe mineralized porphyry body and its surrounding rock formation of the stockworkfine cracks and hydrothermal breccia, the high-temperature gas-liquid fluidcondensation rock account of reactions leading to potassic and phyllic, themineralization metal precipitation and enrichment of a porphyry copper (molybdenum,gold) mineralization, porphyry bodies near the surrounding rock developedpropylitization under the action of hydrothermal lithification; degraded alterationduring the process of mineralization system of cooling effect lithification (claylithification); rise in the earth’s crust erosion, oxidation leaching forming secondaryenrichment zone. |
PDF Full Text Request