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Diamonds in volcaniclastic komatiite from French Guiana

机译：法属圭亚那火山碎屑科马提岩中的钻石

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The world's main sources of non-alluvial diamonds are found in ultrapotassic kimberlite or lamproite diatremes (pipes filled with explosive volcanic debris), most of which have Phanerozoic ages and are located in stable Precambrian cratons. Diamond exploration has therefore tended to focus on such deposits. Microdiamonds are known to occur in metamorphic rocks such as gneiss and eclogite that have equilibrated deep in the mantle and were then tectonically transported to the surface, but such deposits are thought to have little commercial potential. Here we report a new type of diamond occurrence from the Dachine region in French Guiana for which the host rock is volcaniclastic komatiite—an unusual type of volcanic rock whose composition and origin are quite unlike those of kimberlite and lamproite. These komatiites form part of a Proterozoic island-arc sequence, a tectonic setting distinct from that of all other currently exploited diamond deposits. The discovery of diamonds in volcaniclastic komatiite has implications not only for diamond exploration, but also provides strong evidence that these komatiite magmas originated at depths of 250 km or greater within the Earth.
机译：世界上非冲积钻石的主要来源存在于超钾金伯利岩或菱铁矿（充满爆炸性火山碎屑的管道中），其中大多数具有生代时代，并位于稳定的前寒武纪克拉通中。因此，钻石勘探往往集中于此类矿床。众所周知，微金刚石存在于变质岩中，例如片麻岩和榴辉岩，这些变质岩在地幔深处达到平衡，然后以构造方式运到地表，但这种沉积被认为具有很小的商业潜力。在这里，我们报告了一种来自法属圭亚那Dachine地区的新型钻石，其中的宿主岩为火山碎屑科马提岩，这是一种不寻常的火山岩，其成分和成因与金伯利岩和锂锰矿完全不同。这些科马铁矿构成了元古代岛弧序列的一部分，其构造背景不同于目前所有其他开采的钻石矿床。在火山碎屑科玛替岩中发现钻石不仅对钻石勘探具有影响，而且还提供了强有力的证据表明这些科玛替岩岩浆起源于地球内部250 km或更大的深度。

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