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苏门答腊北部的沃伊拉(WOyla)河重砂中,含有低银自然金、铂—铁、锇—铱、铜—锌、铜—锡合金及辰砂,这种典型的组合在苏门答腊北部及中部其他河流中也可找到。这里的自然金是非常纯的,银的含量仪为0.7—9.7％,并含微量铜。相似的矿物组 合在加里曼丹东南部的同一构造单元的延长部分也有发现。低银自然金和铂在苏门答腊中部的花岗闪长岩侵入石灰岩及互层火山岩地层的矽卡岩接触变质带中,以前也发现过。有人认为这种矿化作用可能是苏门答腊低银自然金和自然铂砂矿的来源。加迪斯(Gadis)河也含有来自较晚脉状矿化作用的高银自然金。铜—锌和铜—锡合金是非常罕见的,如果它们确实是天然形成的,那么这些物相的来源仍存在问题。重矿物是从苏门答腊的五个砂金矿区收集的,并经电子探针检查,以确定贵金属矿物组合特征,并提供了作为这些矿床来源区特征的地球化学指示剂。样品是由地质科学研究所(现为英国地质调查所)和印度尼西亚万隆矿物资源理事会在最近完成的北苏门答腊地质和地球化学填图五年计划期间收集的。所研究的样品位置及矿物组合列在表1中。这次工作的结果首次在这里作一报导,是初步的总结,还有待进一步研究。
In the heavy sand of the WOyla river in northern Sumatra, it contains low silver natural gold, platinum-iron, osmium-iridium, copper-zinc, copper-tin alloy and cinnabar. This typical combination is found in northern and central Sumatra Can also be found in the river. Natural gold here is very pure, silver content meter is 0.7-9.7%, and contains trace amounts of copper. Similar mineral assemblages have also been found in the extension of the same tectonic units in southeastern Kalimantan. Low silver natural gold and platinum in Central Sumatra, the central granodiorite intrusive limestone and interbedded volcanic rock skarn contact metamorphic belt, also found before. Some believe that this mineralization may be a source of low-silver natural gold and natural platinum placer deposits in Sumatra. The Gadis River also contains high silver natural gold from later vein-mineralization. Copper-zinc and copper-tin alloys are very rare, and if they are indeed formed naturally, the source of these phases is still problematic. Heavy minerals were collected from five gold and gold mines in Sumatra and were electronically probed to determine the characteristics of the precious metal mineral assemblages and provide geochemical indicators that characterize the source areas of these deposits. The samples were collected by the Institute of Geological Sciences (now the British Geological Survey) and the Bandung Mineral Resources Council of Indonesia during the recently completed North Sumatra Geological and Geochemical Mapping Five Year Plan. The studied sample locations and mineral assemblages are listed in Table 1. For the first time, the result of this work is reported here. It is a preliminary conclusion yet to be further studied.