Some features of placer formation under tropical climate conditions

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• 作者：Sukhoroslov ; V.L. ; Yablokova ; S.V.
• 刊名：Quaternary International
• 出版年：2001
• 出版时间：August, 2001
• 年：2001
• 卷：82
• 期：1
• 页码：75-85
• 全文大小：761 K

文摘

Features of formation of gold placer under tropical climate conditions were analyzed with the Nindi River placer (Southern Tanzania) considered as a case in point. The structure and composition of unconsolidated deposits were studied. The governing role of chemical weathering has been demonstrated. It was shown that the placer forming process consisted of three stages: (1) downcutting stage, including the formation of bedded and gold ingress; (2) formation of overbank alluvial deposits and concentration of heavy resistant minerals (ilmenite, zircon and gold); and (3) formation of sheetwash deposits. Autochthonous and allochthonous gold concentrations were distinguished in the river valley along its course. Based on a set of typomorphic characteristics of gold, it is suggested that the main gold suppliers to the placer are mineralized zones of metasomatic silicification in ultramafic rocks located not far from the autochthonous segments of the placer. Tropical climate obviously provides favorable conditions for intense corrosion leaching of gold with its subsequent redeposition and forming of peculiar ‘envelope-like’ and ‘sandwich-like’ gold grains in allochthonous segments of the placer.