Portal de Periódicos da CAPES

Major Element Geochemistry of the Host Rocks in Some Sediment-Hosted Copper Deposits

1986; Springer Nature; Linguagem: Inglês

10.1007/978-3-642-70902-9_32

0723-8835

B. Moine, L. Guilloux, D. Audeoud,

Geochemistry and Elemental Analysis

The chemical compositions of fine-grained sedimentary rocks provide important genetic indications when their mineralogical significance is brought out. The chemical approach is essential when the primary features have been obliterated by metamorphic crystallization. Recent progress in the geochemistry of shales and marls from evaporite-bearing series is of special interest with regard to sediment-hosted copper deposits.Two major chemical characteristics are obvious in the environment of the Ore-Shale deposits in the Zambian Copperbelt based on comparison of 378 analyses on systematically chosen samples from drill holes and cross-sections in Konkola, Chingola, Chambishi, Mindola, Rokana, and Luanshya (metamorphism from greenschists to lower amphibolite facies) with shales and marls from common platform series. Firstly, the relatively high Mg (and Li) contents are characteristic of magnesian clay minerals, in the early members of evaporitic sequences. This is an ubiquitous feature whereas anhydrite is only of local occurrence. Secondly, primary (premetamorphic) fine-grained rocks with very high K- feldspar and comparatively low quartz contents (around 63% feldspar, 10% quartz and 27% chlorite-rich clays) are inferred from extremely high K2O concentrations (often ≥10%) and K/Al ratios in the Ore-Shale Formation. These compositions cannot be obtained by sedimentary processes only and a large part of the feldspar is probably of diagenetic/hydrothermal origin.In Shaba (Kamoto, Kambove) the Cu and Co concentrations are carbonate- hosted. However, very uncommon chemical compositions are exhibited by the Mg-chlorite-quartz-dolomite rocks of the underlying RAT formation (32 analyses): high Mg, Li and low alkali contents. They could partly derive from felsic-volcanic glass altered by reaction with Ca- and Mg-rich and alkali-poor brines. Such brines have been observed in fluid inclusions related to U-mineralization which occurs at the top of the formation.In contrast, the German Kupferschiefer (Mansfeld district, 22 analyses) does not show major element compositions different from those of common black shales.