Metallogeny of the Boschhoek base metals occurrence and its geological context with respect to the polymetallic mineralization of the Stavoren Fragment of the Bushveld Complex, South Africa
Date
2024
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Abstract
The Boschhoek Prospect is an epigenetic mesothermal copper, lead, zinc and silver deposit within repeatedly fractured Nebo granite of the Lebowa Granite Suite. The Prospect is exposed as hilly gossanous bodies that grade vertically downwards into siderite-calcite-quartz veins system. Similar deposit occurred at Mutue Fides Tin deposit comprising predominantly of tin and fluorite within miarolitic Bobbejaankop granite. These deposits are associated with local scale structures and they are spatially separated by a regional sinistral strike-slip Wonderkop Fault. The study examines the spatial relationships and possible structural control the Wonderkop Fault bears on local scale structures. It investigates metallogeny of base metals and evaluates the petrological character of the Boschhoek Prospect in relation to the Mutue Fides deposits. Extensive fieldwork characterising tectonic structures and structural analysis in the study areas suggest strong link between the Wonderkop Fault and the local scale structures. In syn- and post-BIC intrusion period, the northeast-southwest striking Wonderkop Fault underwent a compressional event directed at northwest-southeast that resulted in splay morphologies on the Transvaal inliers and the felsic plutonic bodies along the fault. Several warping events and rheological failures in response to this reactivation created small-scale faults and veins adjacent to the fault that are associated with polymetallic deposits. The local scale structures mimic morphologically and geodynamically the regional scale Wonderkop Fault. Petrographic studies show pervasive sericitization of the Nebo granite is characteristic of mineralised zones. The varied nature of siderite-calcite-quartz-hematite veins suggest metalliferous fluids emanate from numerous sources including the LGS, the nearby inliers and the connate waters. Greisenization and albitization characterises the mineralised zones in the Bobbejaankop granite. The metals source emanate from magmatic-hydrothermal fluids concentrated in cupolas. Geochemistry results suggest that the Nebo and Bobbejaankop granite are cogenetic and possibly share the same continental source as ascertain by normalised La/Yb ratios. The Bobbejaankop granite experienced higher fractionation degrees accompanied by intensive magmatic-hydrothermal alterations as ascertain by TEDI (Ba x (Sr/Rb)), Zr/Hf versus Y/Ho, Yb/Nb ratios and normalised REE plots. Normalised iv REE plots and petrographic studies suggest that Bobbejaankop granite melt assimilated the Stavoren granophyre and gave rise to the granophyric and the hydrothermally unaltered variety of the Klipkloof granite.
Description
A research report submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Geosciences, University of the Witwatersrand, Johannesburg, 2023
Keywords
Metallogeny, Polymetallic mineralization, Epigenetic mesothermal copper