老挝班康姆铜金矿床火山-侵入杂岩地球化学特征及地质意义

Geochemical characteristics of the volcanic intrusive complex in the Pangkuam copper-gold deposit of Laos and its geological significance

班康姆铜金矿床是近年来新发现的大型铜金矿床。前人研究初步表明研究区成矿作用与古特提斯洋壳俯冲消减所产生的岩浆作用密切有关,但是缺乏岩石地球化学证据。笔者于研究区地表、钻孔采集了13件火山岩-侵入岩新鲜岩石,开展了主量元素、微量元素、稀土元素分析测试。研究表明该区安山质-侵入杂岩具有岛弧钙碱性火山岩的地球化学特征,构造环境判别图显示该套岩石属于大洋弧环境,形成于大洋消减带,与洋壳板片俯冲有关。安山质-侵入杂岩来源于地幔楔,并经历了结晶分异作用,而煌斑岩形成于板片消减而富集的地幔部分熔融。通过与黎府构造带矿床稀土、微量元素特征对比,证实班康姆矿区与Chatree矿区火山岩及金矿床形成于同一期构造岩浆成矿作用,进一步表明了黎府构造岩浆带在晚二叠世—早三叠世发生了一次重要的区域成矿作用。

The Pangkuam deposit is a large-sized copper-gold deposit newly discovered in Laos. Previous studies held that the gold mineralization in the study area was closely related to the magmatic activity with the subduction of the Paleo-Tethys oceanic plate and crust vanishing; nevertheless, such an argument has not been supported by convincing geochemical evidence. In the study area, 13 samples of volcanic rock and intrusive rock were collected in order to analyze the content of main elements, trace elements and rare earth elements （REE）. The research result shows that the andesitic intrusive rocks have the geochemical features of calc-alkaline volcanic rocks in an island arc environment. Tectonic discrimination diagram indicates that the rocks belong to an oceanic arc environment, related to the subduction of the oceanic plate. The formation process occurred in an oceanic subduction zone. The magma of volcanic rock and intrusive rock originated from the mantle wedge with crystallization differentiation. The lamprophyre was formed by the mantle melting, which was enriched during the plate subduction. Based on a comparison with the geochemical features of REE and trace elements of several deposits in Chatree magmatic belt, the authors hold that volcanic rocks and gold deposits in the two mining areas originated from the same stage of tectonomagmatic mineralization process. The result has further demonstrated that there existed an important regional mineralization process at the Loei tectonic magmatic belt in the Late Permian-Early Triassic period.