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Waterberg Project - Bushveld Complex |
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Limpopo (Northern) Province, South Africa |
| Main commodities:
PGE PGM Pt Pd Au Rh Cu Ni
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Super Porphyry Cu and Au
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The Waterberg platinum project is located ~85 km north of Mokopane in the Limpopo province, within a concealed section of the Bushveld Complex, north of the known exposures of the Northern Limb of the complex (#Location 23° 22' 01"S, 28°49' 42"E).
This deposit was initially discovered in November 2011, to the north of the Hout River Shear Zone which was previously believed by many to mark the northern termination of the Northern Limb of the Bushveld Complex. A Pre-Feasibility Study was completed in 2016 and a Definitive Feasibility Study announced in September 2019 concluding it represented a low-cost, shallow, bulk mineable project with significant scale and growth potential (Platinum Group Metals web page, sighted Nov. 2020). The host succession has a number of contrasts to Bushveld stratigraphy elsewhere, including the presence of economic grades of PGE mineralisation in a gabbro-norite dominated sequence that could be correlated with Main Zone rocks of the Complex (Kinnaird et al., 2017).
For detail on the regional setting and a geological map see the Bushveld Complex overview record.
The exposed northern limb of the 2.06 Ga Palaeoproterozoic Bushveld Complex is oriented north-south with a sinuous 100 x 15 km outcrop, extending from the Zebediela fault in the south, to the Hout River Shear Zone in the north. With this extension below Waterberg Group cover, it is regarded as part of a much larger, at least 160 x 125 km lobe of the Complex, as indicated by aeromagnetic and gravity data (Kinnaird, et al., 2005; Finn et al., 2015). The concealed section hosting the Waterberg mineralisation and host ultramafic-mafic succession extends ~24 km NE from the Hout River Shear Zone.
The succession in this area is typically ~1 km thick and dips at 34 to 38°W. It comprises a basal Ultramafic sequence, a troctolite-gabbronorite-anorthosite sequence and an Upper zone. These are overlain by the ~2.05 to ~1.93 Ma red beds of the Waterberg Group.
The basal Ultramafic Sequence comprises a lower <60 m of orthopyroxenite overlying Archaean granite gneisses with an intervening agmatite (a breccia textured xenolithic migmatite), which is interpreted to represent remobilised footwall gneiss within a pyroxenite. The upper portion of the Ultramafic sequence is composed of serpentinised harzburgite.
The troctolite-gabbronorite-anorthosite sequence is <850 m thick, dominated by gabbronorites with minor anorthosites at the top, with thick troctolite layers that are generally <50 m thick and locally pegmatoidal, toward the base. The contact with the Upper zone is defined by an increase in cumulus magnetite, as reflected in increased magnetic susceptibility.
The Upper Zone is composed of ferrogabbro and magnetite gabbronorite, and varies from 0 to 500 m in thickness. Disseminated magnetite is ubiquitous within this zone, although magnetitite layers characteristic of the Upper zone elsewhere in the Bushveld Complex are absent, except in the
extreme south of the project.
Two main PGE-Cu-Ni-Au mineralised intervals are differentiated, a lower F zone hosted within pyroxenite and harzburgite of the Ultramafic Sequence, and an upper T zone at the top of the troctolite-gabbronorite-anorthosite sequence, just below the contact of the overlying Upper zone. Both zones vary from 3 to 60 m in thickness. The T zone is restricted to the southern section of the deposit area, whilst the F zone, which is persists for ~17 km along strike. In both there is a correlation between visible chalcopyrite and pentlandite abundance, and the PGE grade.
The F Zone is typically <10 m thick, although in its central section, the 'Super F zone', it thickens to 60 m true thickness, with grades of 2 to 4 g/t 2PGE + Au over this interval. The basal pyroxenite has variable grades, but when of better grade, the overlying harzburgite also has better levels. Mineralisation generally comprises blebs, net-textured to disseminated pyrrhotite, chalcopyrite and pentlandite with accessory chromite, chalcocite and pyrite. Chromite crystals are often enclosed in silicates, while chromite itself may host sulphide inclusions and rare chromitite stringers. Magnetite often replaces sulphides and chromite. Platinum group minerals (PGM) are dominated by sperrylite with lesser Pt-Pd bismuthotellurides, Au-Ag alloys, Pd arsenides, and Pt-Rh sulphoarsenide with a grade of <7 g/t Pt + Pd + Au. The precious metal budget comprises 64% Pd, 30% Pt, 1% Rh, and 5% Au with associated 'ore' grades of 0.16% Ni and 0.07% Cu.
The T Zone at its shallowest is at a depth of 130 m, subcropping below the Waterberg Group sedimentary rocks. In the south, it is ~30 m thick but expands northward, but is still <50 m. It is characterised by its lithologic variability which includes anorthosite, pegmatoidal gabbros, pyroxenite, troctolite, harzburgite, gabbronorite and norite. The T zone is subdivided into two mineralised intervals, the lower T2 unit and the upper T1 layer which can be traced for several kilometres along strike. T2 is hosted in homogeneous gabbronorite/gabbro that is locally pegmatoidal. The latter is characterised by distinctive, elongated, <1 cm milky-white plagioclase crystals, and may grade into a feldspathic pyroxenite. T2 ranges from 2 to 15 m in thickness and contains disseminated and blebby pyrrhotite, pentlandite, chalcopyrite and pyrite with minor millerite, sphalerite and bornite. The PGM are less varied than in the F zone and are dominated by Pt-Pd bismuthotellurides. Both T1 and T2 have a consistent and unusually gold-enriched metal ratio of ~49% Pd, ~29% Pt, 1% Rh and 21% Au, with 0.08% Ni and 0.16% Cu. T2 passes downward into an unmineralized gabbronorite/norite unit. The middling between the T2 and T1 is not always present, but when there, varies from ~20 cm to 35 m in thickness and comprises pegmatoidal leucogabbro or a vari-textured pegmatoidal anorthosite that is compositionally similar to the 0 to 20 m thick pegmatoidal anorthosite in the T1 hanging wall. The middling and hanging-wall units locally contain good grade. The T1 mineralised zone varies from 3.5 to 5 m in thickness is hosted in a variety of rock types, including troctolite, which may grade into a feldspathic harzburgite or sometimes to an olivine-bearing feldspathic pyroxenite. All show minor chlorite alteration and serpentinite development in olivine-bearing intervals. Sulphides are common, occurring as blebby to net-textured chalcopyrite and pentlandite, with minor disseminated pyrrhotite, as flame-textured pentlandite in pyrrhotite and pyrite, as pyrite replacing magnetite and pyrrhotite, or rimming earlier sulphides.
Neither the T nor F zones has direct correlatives in other limbs of the Bushveld Complex, with significant differences in thickness and lithologies, geochemistry and mineralization of this arcuate intrusion of the Waterberg segment, compared to the eastern, western and northern limbs of the Bushveld Complex, suggesting the Waterberg ultramafic-mafic body may represent a structurally controlled separate compartment north of the Hout River Shear Zone.
Published Ore Reserves and Mineral Resources (Platinum Group Metals web page, sighted Nov. 2020) were:
Proved + Probable Ore Reserves: 187 Mt @ 3.24 g/t 4E or 606 tonnes of 4E.
Measured + Indicated Mineral Resources: 242 Mt @ 3.38 g/t 4E or 808 t of 4E.
Reserve and Resource estimates are based on a 2.5 g/t 4E cut-off.
JORC compliant Mineral Resources (Platinum Asset Management Limited, 2016; quoted by Kinnaird et al., 2017) at a cut-off grade of 2.5 g/t 4E and to a depth of 1250 m, as of 4 Sept. 2019 were:
T Zone
Indicated Mineral Resources - 31.540 Mt @ 1.13 g/t Pt, 1.90 g/t Pd, 0.81 g/t Au, 0.04 g/t Rh, 0.16% Cu, 0.08% Ni;
Inferred Mineral Resources - 19.917 Mt @ a similar grade.
Precious metal ratio: Pt 29:Pd 49:Au 21: Rh 1.
F Zone
Indicated Mineral Resources - 186.725 Mt @ 1.05 g/t Pt, 2.23 g/t Pd, 0.17 g/t Au, 0.04 g/t Rh, 0.07% Cu, 0.16% Ni;
Inferred Mineral Resources - 77.295 Mt @ a similar grade.
Precious metal ratio: Pt 30:Pd 64:Au 5: Rh 1.
This summary is drawn from Kinnaird et al.(2017).
The most recent source geological information used to prepare this decription was dated: 2017.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Waterberg Project centre
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Selected References:
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Huthmann, F.M., Yudovskaya, M.A., Frei, D. and Kinnaird, J.A., 2016 - Geochronological evidence for an extension of the Northern Lobe of the Bushveld Complex, Limpopo Province, South Africa: in Precambrian Research v.280, pp. 61-75.
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Huthmann, F.M.,. Yudovskaya, M.A., Kinnaird, J.A., McCreesh, M. and McDonald, I., 2018 - Geochemistry and PGE of the lower mineralized Zone of the Waterberg Project, South Africa: in Ore Geology Reviews v.92, pp. 161-185.
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Kinnaird, J.A., Yudovskaya, M.A, McCreesh, M., Huthmann, F. and Botha, T.J., 2017 - The Waterberg Platinum Group Element Deposit: Atypical Mineralization in Mafic-Ultramafic Rocks of the Bushveld Complex, South Africa: in Econ. Geol. v.112, pp. 1367-1394.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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