Bushveld杂岩北部底板PGE矿化侵入体的岩石成因

IF 1.2 4区 地球科学 Q2 GEOLOGY
W. Maier, A. Brits, D. Grobler
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引用次数: 1

摘要

Bushveld杂岩北角的底板岩石上有几个类似岩床的镁铁质-超镁铁质岩体。在本文中,我们评估了勘探公司为位于Mokopane北部的Townlands、Amatava、Uitloop、Turfspruit和Rietfontein农场的岩床生成的全岩数据,以限制岩床的起源及其矿化。主要观察结果包括:(i)岩床与下带(LZ)或下临界带(LCZ)具有地球化学亲和力。(ii)相对于大多数其他LZ和LCZ堆积体,大多数岩床富含硫化物和铂族元素(PGE)。(iii)大多数PGE矿化侵入岩已侵位在碳质泥质Duitschland组中。(iv)岩床在空间上与Mokopane重力异常有关,可能代表Bushveld杂岩的主要补给带。(v) 岩床显示了沉积宿主岩同化的证据,其形式为局部升高的δ34S、不相容的微量元素含量以及碳质和泥质围岩捕虏体的存在。(vi)PGE丰度与地壳污染指标之间没有相关性。基于这些数据,我们提出,在假定的Mokopane补给带附近,相对肥沃的、未演化的岩浆最初以岩脉的形式上升穿过地壳。当与相对易裂变的Duitschland组相交时,岩浆侵位模式转变为岩床侵位模式。这促进了富含硫化物和石墨的碳酸盐和页岩的污染,引发硫化物熔体饱和。硫化物在沉淀之前在岩床内局部夹带和升级,可能在流动动态圈闭内。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Petrogenesis of PGE mineralised intrusions in the floor of the northern Bushveld Complex
The floor rocks of the northern lobe of the Bushveld Complex host several sill-like mafic-ultramafic bodies. In the present paper we evaluate whole rock data generated by exploration companies for sills on the farms Townlands, Amatava, Uitloop, Turfspruit and Rietfontein, located to the north of Mokopane, in order to constrain the origin of the sills and their mineralisation. Key observations include: (i) The sills have geochemical affinities to the Lower Zone (LZ) or Lower Critical Zone (LCZ). (ii) Most sills are enriched in sulphides and platinum-group elements (PGE) relative to most other LZ and LCZ cumulates. (iii) Most PGE mineralised intrusives have been emplaced into the carbonaceous-pelitic Duitschland Formation. (iv) The sills are spatially associated with the Mokopane gravity anomaly, possibly representing a major feeder zone to the Bushveld Complex. (v) The sills show evidence for assimilation of the sedimentary host rocks in the form of locally elevated δ34S, incompatible trace element contents and the presence of carbonaceous and pelitic country rock xenoliths. (vi) There is no correlation between PGE abundance and indicators of crustal contamination. Based on these data we propose that in the vicinity of the putative Mokopane feeder zone relatively fertile, unevolved magmas ascended through the crust initially as dykes. When intersecting the relatively fissile Duitschland Formation the mode of magma emplacement changed to one of sills. This facilitated contamination with sulphide- and graphite-rich carbonate and shale, triggering sulphide melt saturation. The sulphides were locally entrained and upgraded within the sills before precipitating, likely within flow dynamic traps.
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来源期刊
CiteScore
3.60
自引率
5.60%
发文量
18
审稿时长
>12 weeks
期刊介绍: The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.
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