摘要
西藏甲玛铜多金属矿床位于特提斯-喜马拉雅构造域冈底斯-念青唐古拉(地体)板片中南部,主矿体(矽卡岩型矿体)赋存于甲玛弧后盆地上侏罗统多底沟组灰岩、大理岩与下白垩统林布宗组砂板岩、角岩的层间构造带内,矿体受继承于层间构造的区域性推覆构造、矿区滑覆构造及其所产生的次级褶皱控制。矿体走向北西西,倾向北北东,整个矽卡岩型矿体走向方向长约3000米,倾向方向延伸大于2000米,矿体呈层状、厚板状、似层状、透镜状,整体形态呈上陡下缓的“椅状”。主矿体位于47-0-56线之间,为甲玛矿区矽卡岩型矿体的核心部位。通过矿石组构、矿物共生组合、矿物成分等特征的研究,将该矿床成矿期划分为岩浆期、矽卡岩期、热液成矿期和表生期,其中热液成矿期又划分为铜钼硫化物阶段、铜硫化物-硫盐矿物阶段、铜铅锌硫化物阶段及金成矿阶段,形成一套典型的岩浆期后热液的成矿组合,矿物组合从高温组合到低温组合。
甲玛铜多金属矿床是冈底斯中段产出的重要矿床,由于其品位富,矿床规模大,长期来受到众多地质学家的关注。该矿床的成因问题一直以来是众多学者争论的焦点,前人提出的成矿理论观点主要集中在喷流成因与岩浆热液交代成矿理论。本文通过对甲玛铜多金属矿矿床地球化学特征的研究,详细研究了岩矿石的岩石地球化学特征、微量元素地球化学特征、同位素地球化学特征、流体包裹体地球化学特征、成岩成矿年代学特征等,提出矿床类型为斑岩-矽卡岩型,而非海底喷流沉积成因的认识,矿床形成于中新世后碰撞晚阶段地壳伸展与断陷时期(<18Ma),与冈底斯成矿带中主要斑岩型铜钼矿床有着相同的地球动力学背景,以上认识为区域找矿指明了方向。
The Jiama polymetallic copper deposit locates in mid-south of Gangdese-Nyainqentanglha plate ,Tethys-Himalayan tectonic megaprovince, Tibet. Main(Skarn ore body) ore body is hosted in stratiform structural zone between limestone、marble of the upper Jurassic and sandy slate、chert of the low Cretaceous, and is controlled by sub-fold produced regional thrust nappe structure and ore field gliding nappe structure. The length is over 3000m in strike with NWW and over 2000m in dip with NNE. The morphology of ore body is stratiform、thick plated、beded、lenticular ,and the whole form is“chair”.Main ore body located in line 47-0-56 is hard core of skarn ore body in Jiama ore field. Metallogenic epoch can be setted off magmatic、skarn、thermal metallogenic epoch which also can be setted off Cu-Mo sulphide phase、Cu sulphide-sulphate phase、Cu-Pb-Zn sulphide phase and Au metallogenic phase、supergene metallogenic epoch, through studying texture and structure of ores、paragenesis of minerals and mineral components, and forms a typical thermal metallogenic combination.
The Jiama polymetallic copper deposit was regarded as high grading and big scale. Genetic problem of the deposit was being a controversy focus which focus on sedimentary exhalative metallogenic theory and magmatic contact metasomatic metallogenic theory. The article puts forward that Jiama polymetallic copper deposit is not a Sedex deposit,but a porphyry-skarn deposit, through the study of rock geochemical characteristic、trace element geochemical characteristic、stable isotope geochemical characteristic、??d inclusion geochemical characteristic、metallogenic chronology and so on, and that the deposit formed The crust extension and rifting occurring in the late post_collisional stage since Miocen (<18Ma) ,holding the same dynamical background to earth with mian porphyry Cu-Mo deposits in Gangdese metallogenic zone. Their cognitions point out the way of finding similar deposits in region.
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