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首页> 外文期刊>South African journal of geology >The Delmas silica deposit, Transvaal - A mega-sinkhole filled with beach sand during the Pretoria Group transgression
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The Delmas silica deposit, Transvaal - A mega-sinkhole filled with beach sand during the Pretoria Group transgression

机译：特尔瓦瓦尔（Dervaal）的Delmas硅土矿床-比勒陀利亚（Pretoria）组侵袭期间充满海滩沙子的巨型污水池

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The Delmas silica deposit forms a kidney-shaped, 800 x 400 x 200 m pod of pure quartzite overlying argillitic rock and chert breccia. The latter represents residual material left after dissolution of siliceous dolostone from the Malmani Subgroup of the Transvaal Supergroup during the pre-Pretoria Group karst event. The residual material and the quartzite are interpreted as the filling of a mega-sinkhole. From the sedimentological and structural relations between the residual material and the quartzite, it is suggested that the latter could be correlated with the basal, transgressive marine beds of the Pretoria Group. It is proposed that during this transgression, due to progressive subsidence, a mega-sinkhole was filled with pure arenitic quartz beach sand that had been washed and sorted by tidal action. The sand was later transformed into quartzite by low-grade metamorphism.
机译：Delmas硅土矿床形成了一个肾形，800 x 400 x 200 m的荚状纯石英岩，上面覆盖着阿胶质岩石和石角砾岩。后者表示在比勒陀利亚前岩溶事件期间，特瓦斯瓦尔超群的马尔玛尼亚群溶解硅质白云岩后留下的残留物质。残留的材料和石英岩被解释为一个巨大的污水坑的填充物。从残余物质与石英岩之间的沉积学和结构关系，可以认为后者可能与比勒陀利亚群的基底海侵海床有关。有人提出，在这种海侵过程中，由于逐渐沉陷，一个大型的污水坑里充满了纯的砂质石英沙滩，这些沙滩已经通过潮汐作用进行了洗涤和分选。沙子随后通过低等变质作用转变为石英岩。

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