Early Neoproterozoic rare metal (Sn, Ta, W) and gold metallogeny of the Central Africa Region: A review
Early Neoproterozoic rare metal (Sn, Ta, W) and gold metallogeny of the Central Africa Region: A review
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中部非洲地区新元古代早期稀有金属（Sn、Ta、W）和金成矿：综述
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
Bernd Lehmann
中科院分区：
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作者：
Walter L. Pohl;M. Biryabarema;Bernd Lehmann
在中非或大湖区具有重要经济意义的四种金属，即金、锡、钽和钨，是一个复合成矿系统的一部分，其年龄约为980±20 Ma。主要驱动力为过铝钛铁矿系列花岗岩岩浆作用，与克拉通挤压作用同步，并与超大陆Rodinia的最终融合有关。花岗岩熔体侵位于≥2kbar(≥8千米)的侵位水平；侵入岩表现出不同的、往往是先进的分馏程度，包括丰富的锡-钽-锂-铍-Rb-Cs伟晶岩，并与富含锡、钨和/或金的热液系统有关。根据过去的累积产量和目前的金属价格，热液石英脉中的金是主要的大宗商品，其次是稀有金属伟晶岩中的锡或片状热液石英脉中的锡。该省许多矿床赋存于母花岗岩之上的硅质碎屑变沉积或变玄武岩顶板岩石中；主要在其西部，矿化带伸展到花岗岩顶板。通常在第一种情况下，非正规场所充当流体逃逸带，碳质或变质玄武岩作为钨和金的化学陷阱。文中较详细地列举了伟晶岩和岩浆热液矿床的实例，以说明矿床的特征和成因控制，并支持本文提出的成矿假说。阻碍战略勘探的是，已发表的理解Kibara带演化和矿化的要素相互矛盾，缺少必要的联系，最重要的是对肥沃花岗岩1 Ga爆发的理解。为了解决这一难题，我们认为，解决这一难题的关键是地幔岩石圈和致密的镁铁质下地壳的剥离，以及大量1.38Ga花岗岩熔体提取后的残余。在泛罗丹期造山事件期间，坦桑尼亚克拉通的坦噶尼卡旋回起到了压痕的作用，其影响导致了早期基巴拉岩石圈的下沉。随后软流圈热的涌入引发了大规模的地壳熔融，形成了锡花岗岩。应力状态主要是压缩的，但可能会被短期或局部的伸展活动打断。地质演化与成矿的相关性证实了基巴拉成矿域的正式识别，该成矿域由两个单元组成：中元古代(1·4Ga)卡班加-穆松加蒂镍(±铜、钴、铂)省和新元古代早期(1Ga)基巴拉稀有金属金矿省是本文的主要研究对象。目前对运作成矿系统的认识仍然有限。关于现代概念和技术的应用，该省的开发严重不足。
The four metals of economic significance in the Central Africa or Great Lakes region, i.e. gold, tin, tantalum and tungsten, are part of one composite metallogenic system that operated about 980±20 Ma. The main driving agent was peraluminous ilmenite-series granite magmatism, synchronous with intracratonic compression and associated with the final amalgamation of the supercontinent Rodinia. The granitic melts were emplaced at intrusive levels of ≥2 kbar (≥8 km); the intrusions display a variable and often advanced degree of fractionation, including abundant Sn–Ta–Li–Be–Rb–Cs pegmatites, and are associated with hydrothermal systems enriched in tin, tungsten and/or gold. Based on cumulative past production and present metal prices, gold in hydrothermal quartz veins is the major commodity, followed by tin either in rare metal pegmatites or in sheeted, hydrothermal quartz veins. Many deposits in the province occur in siliciclastic metasedimentary, or metabasaltic roof rocks above parental granites; mainly in its western part, the zone of mineralisation retracts into the granite roof. Typically in the first case, antiformal sites acted as fluid escape zones, with carbonaceous or metabasaltic rocks as chemical traps for tungsten and gold. Examples of pegmatitic and magmatic–hydrothermal deposits are presented in some detail in order to illustrate characteristics and genetic controls, and to support the metallogenic hypothesis here advanced. Impeding strategic exploration, published elements of understanding the evolution and mineralisation of the Kibara belt are contradictory and essential links are missing, foremost an understanding of the 1 Ga flare up of fertile granites. Towards solving this conundrum we suggest that the key is delamination of the mantle lithosphere and dense mafic lower crust, residual after extraction of voluminous 1·38 Ga granitic melts. During pan-Rodinian orogenic events, the Tanganyika spur of the Tanzania craton acted as an indenter whose impact caused foundering of the early Kibaran lithosphere. Consequent influx of asthenospheric heat triggered large-scale crustal melting that resulted in the tin granites. The stress state was largely compressive but possibly punctuated by short or local extensional events. The correlation of geological evolution and mineralisation substantiates the formal recognition of a Kibara Metallogenic Domain, which is composed of two units: The Mesoproterozoic (1·4 Ga) Kabanga-Musongati nickel (±copper, cobalt, platinum) province; and the early Neoproterozoic (1 Ga) Kibara rare metal and gold province that is the main subject of this paper. The present understanding of the operating metallogenic systems remains limited. Regarding the application of modern concepts and technologies, this province is drastically underexplored.