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Base metal sulphide geochemistry of southern African mantle eclogites (Roberts Victor): Implications for cratonic mafic magmatism and metallogenesis
Lithos ( IF 3.5 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.lithos.2020.105918 Hannah S.R. Hughes , Charlie Compton-Jones , Iain McDonald , Ekaterina S. Kiseeva , Vadim S. Kamenetsky , Gavyn Rollinson , Judith A. Coggon , Judith A. Kinnaird , Grant M. Bybee
Lithos ( IF 3.5 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.lithos.2020.105918 Hannah S.R. Hughes , Charlie Compton-Jones , Iain McDonald , Ekaterina S. Kiseeva , Vadim S. Kamenetsky , Gavyn Rollinson , Judith A. Coggon , Judith A. Kinnaird , Grant M. Bybee
Abstract Platinum-group elements (PGE) display a chalcophile behaviour and are largely hosted by base metal sulphide (BMS) minerals in the mantle. During partial melting of the mantle, BMS release their metal budget into the magma generated. The fertility of magma sources is a key component of the mineralisation potential of large igneous provinces (LIP) and the origin of orthomagmatic sulphide deposits hosted in cratonic mafic magmatic systems. Fertility of mantle-derived magma is therefore predicated on our understanding of the abundance of metals, such as the PGE, in the asthenospheric and lithospheric mantle. Estimations of the abundance of chalcophile elements in the upper mantle are based on observations from mantle xenoliths and BMS inclusions in diamonds. Whilst previous assessments exist for the BMS composition and chalcophile element budget of peridotitic mantle, relatively few analyses have been published for eclogitic mantle. Here, we present sulphide petrography and an extensive in situ dataset of BMS trace element compositions from Roberts Victor eclogite xenoliths (Kaapvaal Craton, South Africa). The BMS are dominated by pyrite-chalcopyrite-pentlandite (± pyrrhotite) assemblages with S/Se ratios ranging 1200 to 36,840 (with 87% of analyses having S/Se 〈10,000). Total PGE abundance in BMS range from 0.17 to 223 ppm. We recognise four end-member compositions (types i to iv), distinguished by total PGE abundance and Pt/Pd and Au/Pd ratios. The majority of BMS have low PGE abundances ( 100 ppm) and are characteristically enriched in Os, Ir, Ru and Rh. Nano- and micron-scale Pd-Pt antimonide, telluride and arsenide platinum-group minerals (PGM) are observed spatially associated with BMS. We suggest that the predominance of pyrite in the xenoliths reflects the process of eclogitisation and that the trace element composition of the eclogite BMS was inherited from oceanic crustal protoliths of the eclogites, introduced into the SCLM via ancient subduction during formation of the Colesberg Magnetic Lineament c. 2.9 Ga and the cratonisation of the Kaapvaal Craton. Crucially, we demonstrate that the PGE budget of eclogitic SCLM may be substantially higher than previously reported, akin to peridotitic compositions, with significant implications for the PGE fertility of cratonic mafic magmatism and metallogenesis. We quantitatively assess these implications by modelling the chalcophile geochemistry of an eclogitic melt component in parental magmas of the mafic Rustenburg Layered Suite of the Bushveld Complex.
中文翻译:
南部非洲地幔榴辉岩的贱金属硫化物地球化学 (Roberts Victor):对克拉通基性岩浆作用和成矿作用的影响
摘要 铂族元素 (PGE) 表现出亲硫行为,主要由地幔中的贱金属硫化物 (BMS) 矿物承载。在地幔部分熔化期间,BMS 将它们的金属预算释放到产生的岩浆中。岩浆源的肥力是大型火成岩省 (LIP) 矿化潜力的关键组成部分,也是克拉通基性岩浆系统中的正岩浆硫化物矿床的起源。因此,地幔源岩浆的肥沃性取决于我们对软流圈和岩石圈地幔中金属(如铂族元素)丰度的理解。上地幔中亲硫元素丰度的估计基于对地幔包体和钻石中 BMS 包裹体的观察。虽然之前对橄榄岩地幔的 BMS 组成和亲硫元素预算存在评估,但关于榴辉岩地幔的分析相对较少。在这里,我们展示了来自 Roberts Victor 榴辉岩包体(南非卡普瓦尔克拉通)的硫化物岩石学和广泛的 BMS 微量元素组成的原位数据集。BMS 以黄铁矿-黄铜矿-戊铁矿(± 磁黄铁矿)组合为主,S/Se 比范围为 1200 至 36,840(87% 的分析具有 S/Se <10,000)。BMS 中的总 PGE 丰度范围为 0.17 至 223 ppm。我们识别出四种端元成分(i 至 iv 型),以总 PGE 丰度和 Pt/Pd 和 Au/Pd 比率区分。大多数 BMS 具有低 PGE 丰度 (100 ppm),并且特征性地富含 Os、Ir、Ru 和 Rh。纳米和微米级 Pd-Pt 锑化物,观察到碲化物和砷化物铂族矿物 (PGM) 在空间上与 BMS 相关。我们认为,捕虏体中黄铁矿的优势反映了榴辉岩化的过程,榴辉岩 BMS 的微量元素组成继承自榴辉岩的海洋地壳原岩,在科尔斯伯格磁线 c 形成过程中通过古代俯冲引入 SCLM。 . 2.9 Ga 和 Kaapvaal 克拉通的克拉通化。至关重要的是,我们证明榴辉岩 SCLM 的 PGE 预算可能大大高于先前报道的,类似于橄榄岩成分,对克拉通基性岩浆作用和成矿作用的 PGE 富集性具有重要意义。
更新日期:2021-02-01
中文翻译:
南部非洲地幔榴辉岩的贱金属硫化物地球化学 (Roberts Victor):对克拉通基性岩浆作用和成矿作用的影响
摘要 铂族元素 (PGE) 表现出亲硫行为,主要由地幔中的贱金属硫化物 (BMS) 矿物承载。在地幔部分熔化期间,BMS 将它们的金属预算释放到产生的岩浆中。岩浆源的肥力是大型火成岩省 (LIP) 矿化潜力的关键组成部分,也是克拉通基性岩浆系统中的正岩浆硫化物矿床的起源。因此,地幔源岩浆的肥沃性取决于我们对软流圈和岩石圈地幔中金属(如铂族元素)丰度的理解。上地幔中亲硫元素丰度的估计基于对地幔包体和钻石中 BMS 包裹体的观察。虽然之前对橄榄岩地幔的 BMS 组成和亲硫元素预算存在评估,但关于榴辉岩地幔的分析相对较少。在这里,我们展示了来自 Roberts Victor 榴辉岩包体(南非卡普瓦尔克拉通)的硫化物岩石学和广泛的 BMS 微量元素组成的原位数据集。BMS 以黄铁矿-黄铜矿-戊铁矿(± 磁黄铁矿)组合为主,S/Se 比范围为 1200 至 36,840(87% 的分析具有 S/Se <10,000)。BMS 中的总 PGE 丰度范围为 0.17 至 223 ppm。我们识别出四种端元成分(i 至 iv 型),以总 PGE 丰度和 Pt/Pd 和 Au/Pd 比率区分。大多数 BMS 具有低 PGE 丰度 (100 ppm),并且特征性地富含 Os、Ir、Ru 和 Rh。纳米和微米级 Pd-Pt 锑化物,观察到碲化物和砷化物铂族矿物 (PGM) 在空间上与 BMS 相关。我们认为,捕虏体中黄铁矿的优势反映了榴辉岩化的过程,榴辉岩 BMS 的微量元素组成继承自榴辉岩的海洋地壳原岩,在科尔斯伯格磁线 c 形成过程中通过古代俯冲引入 SCLM。 . 2.9 Ga 和 Kaapvaal 克拉通的克拉通化。至关重要的是,我们证明榴辉岩 SCLM 的 PGE 预算可能大大高于先前报道的,类似于橄榄岩成分,对克拉通基性岩浆作用和成矿作用的 PGE 富集性具有重要意义。