The geology of the Unki platinum-base metal deposit, Selukwe subchamber, great dyke, Zimbabwe

Murahwi, Charley Zvinaiye (1996) The geology of the Unki platinum-base metal deposit, Selukwe subchamber, great dyke, Zimbabwe. Masters thesis, Rhodes University.

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This thesis focuses on platinu'm group element (PGE) mineralization in the Unki Section of the Selukwe Subchamber of the Great Dyke (Zimbabwe), and is based on drill hole intersections and underground and surface exposures of the Main Sulphide Zone (MSZ) which hosts significant concentrations of PGE. The petrological and geochemical data presented are part of a broader study currently underway and the present are restricted to the 2m section of the PGE-rich MSZ encountered in drill hole MR126. The PGE-rich MSZ at Unki is unique in having a shear, locally referred to as the Footwall Shear, developed at or close to its base . It is however, similar to the other PGE occurrences on the Great Dyke (MSZ) in having its hanging-wall restricted to within 1m of the websterite/bronzitite contact. Slight axial tilting to t he west is indicated by steeper dips on the eastern flank. The sulphide concentration wit hin the MSZ can be used as a rough guide to the PGE-rich zone, but is not sufficiently precise to be used in stope control. The visual identification of the potentially mineable zone remains a problem that is unlikely to be solved. Based on petrological evidence, the bulk of the sulphides with which the PGE are associated, are cumulus in status. This provides unequivocal evidence for an orthomagmatic origin of the MSZ. The dominant platinum group mineral (PGM) phase is the Arsenide/Sperrylite group which is most commonly found at the contact zones between base metal sulphides (BMS) and gangue. The PGM range up to 90 ~m in length. Geochemical evidence from the analyses of cumulate orthopyroxenes through the 2m PGE-rich MSZ interval at Unki reveals a trend of arked Fe enrichment upwards which corresponds to an enrichment in sulphide. This indicates that precipitation of sulphide was caused by fractionation with lowering of temperature in the magma. The Fe enrichment is followed by a reversal in Mg# of orthopyroxene which corresponds to the decrease in sulphide content, suggest i ng that the termination of the PGE-rich MSZ was due to an increase in temperature associated with an influx of new magma. Coupled with these magmatic events are a complex interplay of chemical and physical processes occurring at a critical stage in the overall fractionation of the Great Dyke magma chamber. The overall persistence and continuity of t he PGE zone as observed in the Unki area is consistent with the inferred orthomagmatic origin of the mineralization

Item Type:Thesis (Masters)
Uncontrolled Keywords:Platinum, Ores, Zimbabwe, Unki
Subjects:Q Science > QE Geology
Divisions:Faculty > Faculty of Science > Geology
ID Code:3798
Deposited By: Mrs Carol Perold
Deposited On:24 Oct 2012 08:23
Last Modified:24 Oct 2012 08:23
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