The Uitkomst intrusion and Nkomati Ni-Cu-Cr-PGE deposit, South Africa: trace element geochemistry, Nd isotopes and high-precision geochronology
The Uitkomst intrusion and Nkomati Ni-Cu-Cr-PGE deposit, South Africa: trace element geochemistry, Nd isotopes and high-precision geochronology
复制标题
南非 Uitkomst 岩体和 Nkomati Ni-Cu-Cr-PGE 矿床：微量元素地球化学、Nd 同位素和高精度地质年代学
DOI：
10.1007/s00126-017-0716-x
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发表时间：
2017
影响因子：
4.8
通讯作者：
T. Gomwe
中科院分区：
文献类型：
--
作者：
W. Maier;S. Prevec;J. Scoates;C. Wall;S. Barnes;T. Gomwe
Uitkomst侵入体是一个管状镁铁质-超镁铁质层状岩体，承载着南非最大的镍-铜-铬-铂矿之一--恩科马蒂矿床。硫化物矿石以块状透镜的形式赋存于紧邻的石英质下盘中，并以侵入橄榄岩的形式存在。铬铁矿矿石在侵入体的下部形成了一层厚达∼10米的岩层。Uitkomst通常被解释为一条岩浆管道，可能与布什维尔德事件有关。在这里，我们给出了一个新的高精度的锆石U-Pb定年，其年龄为2057.64 Ma±0.69 Ma，与布什维尔德杂岩的Merensky礁的年龄重叠，从而证明了两个侵入岩之间的同时代关系。根据不相容的微量元素和氧、钕同位素数据(εND−4.5~−6.2)，我们认为乌特科姆斯特母岩浆在侵位前被太古代上地壳混染了20%，在侵位过程中混染了15%的白云质围岩。Nkomati的成矿主要得益于白云岩底板岩石的大量演化和剥离，导致结晶泥在下沉侵入体及其底盘的槽状中心滑落期间，导致硫化物和铬铁矿的流体动力浓缩。
The Uitkomst intrusion is a tubular mafic-ultramafic layered body that hosts one of South Africa’s largest Ni-Cu-Cr-PGE deposits, Nkomati. The sulphide ore occurs in the form of massive lenses in the immediate quartzitic footwall and as disseminations within peridotite. The chromite ore forms an up to ∼10-m-thick layer in the lower portion of the intrusion. Uitkomst has generally been interpreted as a magma conduit, possibly related to the Bushveld event. Here, we present a new high-precision U-Pb zircon date of 2057.64 ± 0.69 Ma that overlaps with the age of the Merensky Reef of the Bushveld Complex and thus demonstrates a coeval relationship between the intrusions. Based on incompatible trace elements as well as O- and Nd isotope data (εNd −4.5 to −6.2), we show that the Uitkomst parent magmas were contaminated with up to 20% Archean upper crust prior to emplacement, and with up to 15% dolomitic country rock during emplacement. Ore formation at Nkomati was critically aided by substantial devolatisation and removal of dolomitic floor rocks leading to hydrodynamic concentration of sulphide and chromite during slumping of crystal mushes into the trough-like centre of the subsiding intrusion and its footwall.