1. 10th Inkaba yeAfrica/!Khure Africa (AEON) Conference/Workshop
Lord Milner Hotel, Matjiesfontein - Karoo
29 September – 3 October 2014
The use of chemostratigraphy and geochemical vectoring as an exploration tool for platinum group metals in the Platreef, Bushveld Igneous Complex, South Africa:
A case study on the Sandsloot and Overysel farms.
By Tshipeng Mwenze
Supervisors: C. Okujeni, R. Bailie, A-M. Siad
Department of Earth Sciences
University of the Western Cape 1

2. Introduction
Fig. 1 Geological map of the Northern limb of the Bushveld Igneous Complex after Kinnaird and McDonald (2005), modified from Van der Merwe (1978) and Ashwal et al. (2005).

3. Introduction
The Platreef is a 10 to 400 m thick mafic package that occurs at the base of the igneous sequence in the northern Bushveld Complex overlies different floor rock units (Fig. 1) (Holwell and McDonald, 2006).
The PGE mineralisation in the Platreef occurs at different depths; i.e. top, middle and bottom, and in different host rocks varying with depth and along strike.
In addition, the PGEs are hosted within metamorphosed/ metasomatised-derived floor rocks varying as well with depth and along strike (Armitage et al., 2002; Kinnaird et al., 2005; Holwell and McDonald, 2006).
The objectives of this study are:
To identify and distinguish processes based on mineralogical/ geochemical signatures, which may be useful in stratigraphic correlation and characterizing the nature and styles of PGE mineralisation across the strike and with depth of the Platreef and its metamorphosed floor rock.
To investigate the possible use of geochemical vectoring as a tool to locate the PGE mineralisation within the studied rocks.
Fig. 2 Schematic longitudinal section through the Platreef over the entire strike length, after Kinnaird et al. (2005)

4. Methodology
Boreholes OY 482 and SS 330 (Fig. 2), located at the Overysel and Sandsloot farms respectively (Fig. 1), were logged, and a total of 119 quarter cores were sampled for petrographic studies. The elemental contents in the rocks were determined by XRF and ICP-OES analyses and were evaluated using various statistical and mass balance techniques.
Fig. 3 Stratigraphic log of studied boreholes.

5. Results Fig. 4 The Geochemical classification of rocks.
Fig. 6 The Geochemical characterisation of the studied rocks.
Fig. 5 Median gains and losses pattern for selected oxides in wt % for the clinopyroxenites (CP) in (a) and olivine clinopyroxenites (OCP) in (b).

6. Results
Fig. 7 Ternary diagram illustrating the relationship between the BMS (Cu+Ni) mineralisation and the lithogeochemical indices. CP: Clinopyroxenites; OCP: olivine clinopyroxenites.
Fig. 8 Downhole lithogeochemical variations in the studied boreholes. Ca/Mg= CaO/(MgO+CaO); Mg/Fe=MgO/(Fe2O3+MgO); PGE index= (Cu/Zn) x (Ni/Co).

7. Conclusions
The two boreholes studied show contrasting petrographic and geochemical attributes. This dissimilarity is mainly due to the fact that borehole OY 482 comprises Platreef magmatic rocks whereas borehole SS 330 intersected metamorphic/ metasomatic rocks.
The suggested base metal index [(Cu/Zn) x (Ni/Co)] correlates with the Pt+Pd in the BMS-rich zones. This is not always the case in zones of low BMS contents which may reflect changes in the mineralogy of the BMS.
References
Armitage, P.E.B., McDonald, I., Edwards, S. & Manby, G. 2002, "Platinum-group element mineralization in the Platreef and calc-silicate footwall at Sandsloot,
Potgietersrus District, South Africa", Applied Earth Science: Transactions of the Institutions of Mining and Metallurgy: Section B, vol. 111, no. 1, pp
Ashwal, L.D., Webb, S.J. & Knoper, M.W. 2005, "Magmatic stratigraphy in the Bushveld Northern Lobe: continuous geophysical and mineralogical data from the 2950 m
Bellevue drillcore", South African Journal of Geology, vol. 108, no. 2, pp
Harris, C. & Chaumba, J.B. 2001, "Crustal contamination and fluid–rock interaction during the formation of the Platreef, northern limb of the Bushveld Complex, South
Africa", Journal of Petrology, vol. 42, no. 7, pp
Holwell, D.A. & McDonald, I. 2006, "Petrology, geochemistry and the mechanisms determining the distribution of platinum-group element and base metal sulphide
mineralisation in the Platreef at Overysel, northern Bushveld Complex, South Africa", Mineralium Deposita, vol. 41, no. 6, pp
Kinnaird, J.A., Hutchinson, D., Schurmann, L., Nex, P. & de Lange, R. 2005, "Petrology and mineralisation of the southern Platreef: northern limb of the Bushveld
Complex, South Africa", Mineralium Deposita, vol. 40, no. 5, pp
Kinnaird, J.A. & McDonald, I. 2005, "An introduction to mineralisation in the northern limb of the Bushveld Complex", Applied Earth Science: Transactions of the
Institutions of Mining and Metallurgy: Section B, vol. 114, no. 4, pp
Van der Merwe, M. 1978, The geology of the basic and ultramafic rocks of the Potgietersrus limb of the Bushveld Complex, .

8. Acknowledgements I would like to thank:
Inkaba yeAfrica for funding this project.
Anglo platinum at Mogalakwena mine (Limpopo) for providing the research materials.