Gold mineralisation potential of the Kraaipan granite- greenstone terrane, southern Botswana
Date
2023
Authors
Mdze, Manelisi
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Abstract
The Kraaipan granite-greenstone terrane, which straddles the North West province of South Africa and the Southern district of Botswana, is comprised of four linear, north-south trending greenstone belts namely, Stella, Kraaipan, Madibe and Amalia. Banded iron formation (BIF)- hosted gold mineralisation is present within the Kraaipan Greenstone Belt (KGB) in South Africa at the currently producing Kalahari Goldridge mine, as well as other defunct mines and historical occurrences. There are no known gold deposits along the Botswana extension of the KGB where the belt has a strike length of over 40 km.
A review of historical data suggests that the KGB is largely unexplored in Botswana, with most of the belt covered by younger strata (Transvaal Supergroup and Kalahari Group). To evaluate the gold potential of the KGB in Botswana, field mapping and observations were integrated with historical geological and exploration datasets to produce an updated geological interpretation of the KGB.
A Kalahari sediment thickness map was constructed from historical borehole data, to differentiate between areas of thicker and thinner cover. Thicker cover complicates mineral
exploration, in particular the interpretation of soil geochemistry results and mining. Satellite imagery was used effectively for geological and regolith mapping. High-resolution Bing
imagery was particularly effective at accurately mapping rock fabric, folds, and faults in areas of outcrop and sub-crop. Landsat 8 data was used to identify reflectance signatures associated with various types of regolith from which provenance predictions can be used to understand the nature and source of soil geochemical anomalies.
Magnetic data is the most effective geophysical dataset for mapping the KGB lithologies, including the high-interest gold-bearing BIF, due to a distinct magnetic response relative to the encompassing granitic rocks. Ultra-high-resolution magnetic data collected over part of the study area was used to: better resolve the extension of the KGB into the study area; accurately delineate lithological contacts and structures and to identify high-interest exploration target areas.
Down-hole multi-element data was evaluated from four drill-holes which historically intersected elevated gold mineralisation. In all instances the gold mineralisation was associated
with greater than 15 weight-percent iron, confirming gold affinity with strongly iron-oxidised rocks. Silver, copper, nickel, arsenic, antimony, selenium and bismuth displayed excellent
down-hole correlations with gold, therefore their usefulness as gold pathfinder elements in this geological setting should not be disregarded.
Description
A research report submitted in partial 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