Significance of diagenesis for the origin of Witwatersrand-type uraniferous conglomerates
Significance of diagenesis for the origin of Witwatersrand-type uraniferous conglomerates
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成岩作用对Witwatersrand型含铀砾岩成因的意义
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发表时间：
1979
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通讯作者：
E. Dimroth
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作者：
E. Dimroth
对黄铁矿的岩相研究可能是了解威特沃特斯兰德（南非）金铀矿床的关键：威特沃特斯兰德超群的沉积物至少含有九种类型的黄铁矿，即（1）层状黄铁矿层； (2) 页岩中的黄铁矿结核； (3)石英岩、砾岩中的黄铁矿结核； (4) 碳质丝上生长的黄铁矿； (5)黄铁矿填充孔隙，置换碎屑； (6)黄铁矿置换碎屑磁铁矿； (7)层状黄铁矿同种异体碎片； (8) 黄铁矿结核的同种异体碎片； (9)粗粒黄铁矿的同种异体碎片。 1-6 型可能是在沉积物成岩作用过程中由于硫酸盐还原菌的活性而形成的； 7型和8型是成岩黄铁矿的搬运碎片； 9 型可能有多种来源，但也可能部分是成岩黄铁矿的迁移碎片。黄铁矿岩相学表明矿石富集的多阶段历史：在含有机质的沉积物中金、铀矿和黄铁矿的成岩沉淀，随后是侵蚀，矿石矿物的同种异体碎片短距离迁移，以及在河道底部和不整合面的滞后砾石中富集。风化作用、风化溶液的成岩降水、侵蚀、轻微搬运和再沉积的反复循环可能导致上威特沃特斯兰德超群主要不整合面上的矿石异常富集。
A petrographic study of pyrite may be the key to the understanding of the Witwatersrand (South Africa) gold-uranium deposits: the sediments of the Witwatersrand Supergroup contain at least nine types of pyrite, namely (1) Laminated pyrite seams; (2) pyrite nodules in shales; (3) pyrite nodules in quartzite and conglomerate; (4) pyrite as overgrowths on carbonaceous filaments; (5) pyrite filling pore spaces and replacing clasts; (6) pyrite replacing detrital magnetite; (7) allogenic fragments of laminated pyrite; (8) allogenic fragments of pyrite nodules; and (9) allogenic fragments of coarse-grained pyrite. Types 1-6 probably formed during diagenesis of the sediment due to the activity of sulphate-reducing bacteria; types 7 and 8 are transported fragments of diagentic pyrite; type 9 may be of diverse origin, but may also in part be transported fragments of diagenetic pyrite. Pyrite petrography suggests a multi-stage history of ore enrichment: diagenetic precipitation of gold, uraninite and pyrite in sediments containing organic matter, followed by erosion, transport of allogenic fragments of ore minerals for short distances, and concentration in lag gravels at channel bottoms and unconformities. Repeated cycles of weathering, diagenetic precipitation from weathering solutions, erosion, minor transport and redeposition may have caused the extraordinary enrichment of the ores on major unconformities in the Upper Witwatersrand Supergroup.