玻利维亚Laurani斑岩-浅成低温热液矿床地质特征及控矿因素

Laurani矿床是玻利维亚Altiplano盆地内典型的高硫化浅成低温热液矿床,发现和开采历史悠久,但研究程度低,控矿因素和找矿潜力不清。通过矿床地质特征精细解剖,文章查明了该矿床控矿因素,分析了深部找矿潜力。研究表明,构造-岩浆作用为其主导性控矿因素。火山穹窿构造与环状断裂约束了矿床的定位,侵入接触构造、爆破角砾岩筒和NE向断裂裂隙控制了矿体(脉)的形成和展布。岩浆岩为二长花岗斑岩、英安岩/英安斑岩和凝灰岩组合,属于高钾钙碱性、钾玄岩系列,具有较一致的锆石U-Pb年龄(约7.5 Ma),反映它们为晚中新世同期岩浆活动的产物。该矿床发育斑岩型Au-Cu、爆破角砾岩型Au-Cu、接触带型Cu-Au-Ag和热液脉型Au-Ag-Cu-Pb-Zn四类不同产出特征的矿(化)体。成矿元素组合分带显著,平面上Huari Humana断裂上盘为Au-Ag-Cu-Pb-Zn组合,下盘为Ag-Pb-Zn组合;垂向上深部为Au-Cu元素组合,浅部为Au-Ag-Cu-Pb-Zn元素组合。热液蚀变强且分带明显,平面上以英安斑岩为中心,从内至外依次为黄铁绢英岩化带→青磐岩化带→碳酸盐化带,泥化带不同程度地叠加在黄铁绢英岩化带和青磐岩化带内,石英-明矾石化-重晶石化主要沿热液脉型矿体及其旁侧分布;垂向上从深至浅依次为黄铁绢英岩化带→青磐岩化带→泥化带;钾硅酸盐化带目前尚未揭露,可能产在深部。成矿后弱构造作用使矿床得以较好保存,结合钻孔揭露深部存在斑岩型、爆破角砾岩型矿化,笔者认为Laurani矿床深部具有寻找斑岩型矿体的较大潜力。

Geological characteristics and ore-controlling factors of Laurani porphyryepithermal deposit,Bolivia

Laurani deposit is a typical high-sulfidation epithermal deposit in the Altiplano basin, Bolivia. The deposit has a long history of discovery and exploitation, but the research degree is low, and its ore-controlling factors and prospecting potential are still unclear. Through detailed analysis on geological characteristics of the deposit, we summarized ore-controlling factors and provided insight into prospecting potential of the Laurani deposit. Tectonism and magmatism are the dominate ore-controlling factors. The volcanic dome and ring faults constrain the location of the deposit. The intrusion contact zones, explosive breccia pipes, NE-trending faults and fractures control the formation and distribution of ore-bodies(-veins). The igneous rocks comprise monzogranite porphyries,dacites, dacite porphyries and tuffs, belong to high-K calc-alkaline and shoshonite series, and have a relatively consistent zircon U-Pb ages(~7.5 Ma), which indicates they are the products of the same magmatic event in the late Miocene. The Laurani deposit develops four types of mineralization with different occurrence characteristics: Porphyry-type Au-Cu, explosive breccia-type Au-Cu, contact-type Cu-Au-Ag and hydrothermal vein-type Au-Ag-Cu-Pb-Zn. There is a clear element zonation, horizontally the Au-Ag-Cu-Pb-Zn and Ag-Pb-Zn occur respectively in hanging wall and footwall of the Huari Humana fault;vertically the Au-Cu forms mainly in the deep part and Au-Ag-Cu-Pb-Zn develops well in the shallow part. The Laurani deposit has extensive hydrothermal alterations with significant zonation. Centered with dacite porphyries, the horizontal zoning of alteration varies outwards from phyllic to propylitic and carbonate alteration. Widespread argillic alteration overprints on the phyllic and propylitic zones to varying degrees in the shallow. Quartz-alunite-barite distribute mainly within the hydrothermal vein-type ore-bodies and their adjacent areas. Vertically, the alteration zoning varies from phyllic to propylitic and argillic from the deep to the shallow. The absence of the potassic zone in the Laurani deposit, is likely due to its possible existence in deep and has not been exposed. The deposit is well preserved resulted from weak post-mineral tectonism, combined with the interception of porphyry-type and explosive breccia-type mineralization in the deep by drilling, we suggest there is great upside potential for porphyry-type ore-bodies in the deep of the Laurani deposit.