New lithological and whole rock compositional data show that the main platinum-group element (PGE) horizons of the Flatreef succession show strong compositional similarities to the Merensky and Bastard reefs of the western Bushveld Complex (WBC), notably in terms of many immobile and incompatible minor and trace elements such as TiO 2 , Zr, Y, and REE. However, Al 2 O 3 , CaO, and Na 2 O contents are markedly lower in the Flatreef, whereas MgO contents are higher. In view of broadly similar silicate mineral compositions in the Flatreef and the WBC reefs, we suggest that the major element compositional differences between the rocks are largely due to higher modal proportions of orthopyroxene and olivine and lower proportions of plagioclase in the Flatreef. The thickness of the mineralised interval is much greater in the Flatreef than in the WBC (several 10 s of m vs ~ 1 m) and the abundance of sulfides in the Flatreef is typically somewhat higher (on average ~ 1.5% vs ~ 1%). These data, complemented by textural observations, are interpreted to reflect enhanced hydrodynamic crystal sorting accompanied by percolation of sulfide melt through incompletely solidified cumulates. Further genetic constraints are provided by metal data: The concentration of Ni (~ 3000 ppm) in the Flatreef is broadly similar to that in the Merensky Reef of the WBC, but Cu contents are markedly higher (average ~ 1500 ppm vs 700 ppm in the WBC). The concentrations of most PGE are slightly lower (Flatreef ~ 1.5–2 ppm Pt, ~ 100–150 ppb Rh; WBC MR 3.7 ppm Pt, 240 ppb Rh), but Pd has broadly similar contents (Flatreef ~ 1.2–2 ppm; WBC MR 1.54 ppm). The relatively high Cu content of the Flatreef is interpreted as a result of assimilation of Cu sulfides from the sedimentary floor rocks. The reason for the enrichment of Pd relative to Pt, especially in the basal rocks, remains unclear. It could reflect mobilisation of Pd via a fluid phase from the country rocks or the interior of the intrusion, relatively enhanced partitioning of Pd into the sulfides, or relative Pt depletion of the earliest magma pulses in response to Pt alloy fractionation triggered by contamination with reducing country rocks.

中文翻译：

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通过流体动力和水岩浆过程在布什维尔德北部形成 Flatreef 矿床

新的岩性和全岩成分数据表明，Flatreef 序列的主要铂族元素 (PGE) 层位与西部 Bushveld 杂岩体 (WBC) 的 Merensky 和 ​​Bastard 礁具有很强的成分相似性，特别是在许多不动和不相容的方面TiO 2 、Zr、Y 和 REE 等微量元素和微量元素。然而，Flatreef 中的 Al 2 O 3 、CaO 和 Na 2 O 含量明显较低，而 MgO 含量较高。鉴于 Flatreef 和 WBC 珊瑚礁中的硅酸盐矿物组成大致相似，我们认为岩石之间的主要元素组成差异主要是由于 Flatreef 中斜辉石和橄榄石的模态比例较高以及斜长石的比例较低。Flatreef 中矿化层的厚度比 WBC 大得多（几 10 s 的 m vs ~ 1 m），并且 Flatreef 中硫化物的丰度通常略高（平均 ~ 1.5% vs ~ 1%） . 这些数据与结构观察相辅相成，被解释为反映了增强的流体动力学晶体分选，伴随着硫化物熔体通过不完全固化的累积物的渗透。金属数据提供了进一步的遗传限制：Flatreef 中 Ni 的浓度（~ 3000 ppm）与 WBC 的 Merensky Reef 中的大致相似，但 Cu 含量明显更高（平均~ 1500 ppm vs 700 ppm）白细胞）。大多数 PGE 的浓度略低（Flatreef ~ 1.5-2 ppm Pt，~ 100-150 ppb Rh；WBC MR 3.7 ppm Pt，240 ppb Rh），但 Pd 的含量大致相似（Flatreef ~ 1.2-2 ppm；WBC MR 1.54 ppm）。Flatreef 相对较高的铜含量被解释为同化沉积底板岩石中的硫化铜的结果。Pd 相对于 Pt 富集的原因，尤其是在基岩中，仍不清楚。它可以反映 Pd 通过来自围岩或侵入体内部的流体相的流动，Pd 相对增强的分配到硫化物中，或者最早岩浆脉冲的相对 Pt 消耗，以响应由污染触发的 Pt 合金分馏乡村岩石。