Zn 3.0% Sulphide Rosh Pinah NA

Description

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AMIS0157 Zinc Lead sulphide, 3.03% Zn, 0.3% Pb, Rosh Pinah, Namibia

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Origin of Material: AMIS0157 was supplied by Exxaro from their Rosh Pinah mine situated 800km south of Windhoek in Namibia.  The Rosh Pinah Zinc-lead deposit is hosted by the Rosh Pinah Formation of the Late Proterozoic Gariep Belt, which is an arcuate north trending tectonic unit some 400km long by 80km wide. This belt consists of sediments deposited in association with late pre-Cambrian continental rifting, which resulted in the formation of sedimentary basins. These basins are commonly sites for sedimentary exhalative (“SEDEX”) base metal mineralisation, which involves hot, metal-rich brines from depth rising along the extensional faults before emerging from the sea floor and interacting with the cold seawater. This results in the deposition of metal sulphides into topographic lows along with other sediments. Compressive tectonic processes resulted in the obliteration of the extensional features, folding of the strata and the development of thrust faulting.

The current geological interpretation of the Rosh Pinah deposit is that it represents a single layer of SEDEX sulphide mineralisation subsequently deformed by tectonic processes. The original strata have undergone varying degrees of deformation ranging from broad folding in the northern extremity of the deposit to isoclinal folding with associated faulting to the south. Ductile deformation has resulted in the attenuation of the mineralised zone along the limbs of the folds with general thickening in the fold hinges. Shearing along fault planes sub-parallel to fold axes has enhanced thinning of some of the mineralised zones. The result of this has been the development of a series of discrete, sub-linear orebodies resident primarily on the crests and troughs of folds, but which typically extend into one or both of the fold limbs. These individual orebodies range in size from several tens of metres to as much as 200m in length along the axes, with thicknesses of the order of less than 1m to as much as 60m. The degree of geometric variability in section is substantial over distances of only 10m to 15m, with changes to the ore thickness of 50% or more commonly encountered within these distances.

Mineral and Chemical Composition: The mineralisation consists of sphalerite and galena with pyrite and minor chalcopyrite along with a suite of other minor accessory minerals. Sphalerite and galena are the economically important minerals with gold, silver and copper providing minor contributions to value. The upper contacts of the orebodies as defined by mineralisation are very sharp with little or no mineralisation beyond the hangingwall. The lower horizons show varying degrees of mineralisation, largely in the form of fracture-filling sulphides between breccia clasts and in fractures developed in late-stage brittle deformation. The grades developed in this “footwall” are generally less than 2% zinc equivalent and so are not currently of economic interest.

Recommended Concentrations and Limits

(at two Standard Deviations)

Certified Concentrations

Provisional Concentrations