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Pering |
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North West Province, South Africa |
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Zn Pb
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The Pering carbonate hosted zinc-lead mine is located 18 km NE of Reivilo, and 150 km NNW of Kimberley, in the North West Province of South Africa (#Location: 27° 26' 12"S, 24° 16' 18"E).
Ore occurs as an outer cylindrical shell to a poorly developed collapse structure in the Ghaap Group dolomites of the late Archaean to Lower Proterozoic Transvaal Supergroup.
The Lower Proterozoic Transvaal Supergroup and the underlying late Archaean Ventersdorp Supergroup were deposited in a generally arcuate trough, trending from E-W to the east to NE-SW in the SW. The depository is divided into two preserved sections by a central block of Ventersdorp Supergroup. The eastern section, known as the Transvaal Basin is located generally to the north of Johannesburg. The south western section, the Griqualand West Basin, which hosts the Pering Deposit, extends from Vryburg, which is 70km to the NE of Pering, to the Brakbos-Copperton Shear Zone 250km to the SW, which separates it from the Kheis Mobile Belt and the Namaqualand Metamorphic Complex.
The host Steekdorings Member of the Reivilo Formation is characterised by a series of nine thin, black, carbonaceous shale bands, each of up to 0.5m in thickness, and eight stromatolitic dolomite zones which are generally of from 2 to 10m thick.
The carbonaceous shales are black, fine grained and well laminated on around a 1mm basis. The stromatolitic dolomite zones comprise columnar stromatolites, with mega-domes which have 'wavelengths' of 1 to 3m and 'amplitudes' of 10 to 30cm. Within the dolomitic units the drusestones which are vuggy have textures that are interpreted as being evaporitic.
As well as the carbonaceous shales, the stromatolitic dolomite zones are also carbonaceous, although less so.
A small circular, basin like downwarp, approximately 2 km in diameter encircles the Pering Mine area. Regionally dips are sub-horizontal, but within the basin rise to 15 degrees inward. Detailed mapping of the downwarp has revealed two oval 'rubble breccias' in the core, each of approximately 200x300m in size at surface. A third has been detected in drilling, but does not outcrop. The three are roughly aligned in a north-south direction, with the northern being blind, and the southern being most broadly exposed at the surface. The northern blind breccia zone has undisturbed dolomites at the surface, but which between depths of 130 and 150m shows evidence of collapse, while below 150m becomes a 'rubble breccia'. These three breccias zones cross cut the stratigraphy, both vertically and horizontally.
These breccia form the core of the larger subsidence pipe, within the bulk of which brecciation is not obvious in the open pit. Within the centre of the pit, which is of the order of 500m across, individual beds subside by up to 15m, the majority of which occurs on the outer margins. This subsidence defines the main 'pipe'. Within the pit at any point brecciation is not obvious, although on a broad scale it is possible to see differences in attitude of bedding by up to 40 degrees within adjacent small and large blocks of dolomite, without seeing the margins of the clasts. The smaller blocks may be 10x1 to 4cm with bedding obvious in part, surrounded by massive dolomite of the same grey colour and grain size as the bedded portions. Larger blocks are up to tens of metres across. In the 'matrix' there is also often white dolomite lenses/veins which may be 10 to 20cm across and a few metres long, while there are also vugs up to 10cm across containing coarse quartz (crystals up to 1 to 2cm long) and calcite. The calcite often carries 'drops' 1 to 2 x 2 to 4mm of hydrocarbons.
Within the 'rubble breccia' calcite veining is more intense, outlining the rotated clasts and making the brecciated texture more obvious. The clasts in the 'rubble breccia' are 1mm to 2cm and may be up to several metres across and are randomly oriented. The matrix in a good specimen is a little darker than the clasts.
There is little evidence of faulting within the Pering mine, although a strong north-south trending fault is known approximately 750m to the west of the orebody, while another east-west fault crosses 1 km to the north. The latter fault provides some evidence of syn-sedimentary movement.
At Pering there are two principal and intimately associated types of zinc-lead mineralisation. The first of these is a broadly sub-horizontal, conformable style following the stromatolitic dolomite zones and a second style comprisingtransgressive sub-vertical zones associated with the subsidence breccias.
The main ore is within the subsidence 'pipe'/breccia, where it occurs as both stromatolitic and breccia hosted mineralisation. Although the stromatolitic zones carry 'high grade' mineralisation within the 'pipe' zone they only carry low grade away from it, with anomalous values of 100 to 200ppm Zn persisting up to 5km from the 'pipe' (in contrast to a background of 25ppm Zn). Within the 'pipe' the sandy facies and algal mats between the stromatolitic dolomite zones and the carbonaceous shales carry low grade mineralisation, being highest grade on the rims of the 'pipe' where the change in dip of the bedding is most pronounced in response to the subsidence. Away from the 'pipe' these same facies are barren. These relationships provide a cross section through the pipe which is broadly ladder shaped, being continuous through the flat lying sequence on the margins of the 'pipe', but only represented on the stromatolitic dolomite 'rungs' within the pipe, and for a short distance outside. The thickness of mineralisation, as well as grade increases within the stromatolitic dolomite bands as the pipe margin is approached, from both within and without. The better mineralisation away from the 'pipe' is generally found closest to an adjacent carbonaceous shale band. Similarly within the ore zone the stromatolitic dolomite zones, where developed adjacent to a carbonaceous shale are often vuggy at the contact, where they also carry the best mineralisation. Within the 'pipe' the other facies, while mineralised, are only 'low grade'.
Sphalerite, galena, minor pyrite and traces of chalcopyrite are the only metallic minerals within the deposit. These are generally disseminated in a gangue of calcite and dolomite.
Resource to 100 m depth in 1992 (mine staff, pers. comm.) - 18 Mt @ 3.6% Zn, 0.6% Pb.
The most recent source geological information used to prepare this decription was dated: 1996.
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.
Pering
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Selected References:
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Gutzmer J 2006 - The Paleoproterozoic carbonate-hosted Pering Zn-Pb deposit, South Africa: I. Styles of brecciation and mineralization: in Mineralium Deposita v40 pp 664-685
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Huizenga J M, Gutzmer J, Banks D and Greyling L 2006 - The Paleoproterozoic carbonate-hosted Pering Zn-Pb deposit, South Africa. II: fluid inclusion, fluid chemistry and stable isotope constraints: in Mineralium Deposita v40 pp 686-706
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Southwood M J 1986 - The mineralogy of the Pering zinc-lead deposit, Cape Province, with special reference to supergene alteration: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 875-889
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Wheatley C J V, Whitfield G G, Kenny K J, Birch A 1986 - The Pering carbonate-hosted zinc-lead deposit, Griqualand West: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 867-874
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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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