Abstract
This study was conducted at the Bathopele Platinum Mine, Bushveld omplex. This aims of this study were two-fold. The first aim was to determine the structural geological aspects of the pegmatite veins in relation to the UG2 chromitite layers which include: their shape, orientation and relation to fault sets, and characterization of these pegmatite veins based on geochemistry, microstructures and spatial distribution, as well as formation mechanism(s).
Pegmatite veins were classified into five categories: (i) pegmatite veins that are layer bound, (ii) pegmatite veins that are fault related, (iii) pegmatite veins partly cross-cutting UG2 chromitite layers, (iv) pegmatite veins that crosscut entirely UG2 chromitite layers and (v) pegmatite veins with irregular shapes. The concepts of rock engineering such as (i) principal stress rotation upon meeting the horizontal contact, (ii) elastic mismatch and material toughness, and (iii) Cook-Gordon debonding were applied on the pegmatite veins at the Bathopele Platinum Mine to assess the spatial association of the pegmatite veins with the UG2 chromitite layer. These factors were used to explain the development mechanisms of each pegmatite vein category and explain why some of the pegmatite veins are arrested at the upper and lower contact of the UG2 chromitite layer.
The geometry of the pegmatite veins and the tensile strength of their host rocks allowed an estimation of the magma pressure ratio, absolute value of the differential stress and magmatic overpressure of the pegmatite veins. The mineralogy and microstructures showed that pegmatite veins in the study were formed by a single episode magma and were later altered by hydrothermal fluids. Whole-rock geochemical data of the pegmatite veins and pod-like bodies of vein material have indicated that the source of the magmas falls under metaluminous granites.
The second aim was to determine the potential influence the pegmatite veins can have on the recovery of the PGEs at the vicinity as well as away from the UG2. The results from metallurgical test work indicated that channel samples 1 m away from pegmatite veins (i) milled slower than channels that incorporate pegmatite veins, (ii) have lower mass pull than channels that incorporate pegmatite veins and (iii) have higher grades and recoveries than channels incorporating pegmatite veins. In addition, the results show that high cumulative mass pull % from ore which incorporates pegmatite veins implies high 6PGEs + Au while low mass pull % in ore with minimal pegmatite
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veins means high indicate recoveries of 6PGEs + Au. Therefore, cumulative mass pull % can be used to indicate recoveries of 6PGEs + Au at Bathopele Platinum Mine. The Pt/Pd ratios are preserved between ore samples with pegmatite veins and those without.
When the two aspects of this study are combined, the results imply that pegmatite veins dilute the recovery and grade of the ore. The result indicated that the intrusion of pegmatite veins caused a cm-scale remobilization of metals. These metals are Ni, Cu, Co, V, Pb and Zn and were enriched in the outer selvages and depleted in the inner selvages.