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Skorpion

Namibia

Main commodities: Zn
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The Skorpion non-sulphide zinc deposit is located in southern Namibia, some 25 km to the north of Rosh Pinah and 85 km NE of Oranjemund at the Atlantic Ocean mouth of the Orange River.

Like the Rosh Pinah sediment and volcanic hosted massive sulphide deposit, it is hosted by the Neoproterozoic to Palaeozoic Gariep Complex mixed sediments and volcanics deposited in a continental rift setting between the Rio de la Plata and Kalahari cratonic blocks.   The volcanics of the sequence have been dated at 751.9 ±5.5 Ma (see the Rosh Pinah record for more detail).

Deposition of the siliciclastics and carbonates of the host sequence was controlled by a series of horsts and half grabens in an extensional environment and varies throughout the basin from shallow to deeper water environments.   These rocks were subsequently influenced by the Pan Africa-Brasiliano orogenic cycle at 550 to 545 Ma producing greenschist facies metamorphism and intense folding, thrusting and faulting.

The immediate hosts to the mineralisation comprise arkosic meta-arenites and subordinate volcaniclastic meta-sediments.   Four lithologic units are recognised in the deposit area, from bottom to top of:  i). mafic metavolcanics with hyaloclasitic, volcaniclastic, siliciclastics and subordinate carbonate intercalations,  ii). dark grey marble (predominantly calcitic) with minor intercalations of siliciclastics - this lithological association is generally devoid of either sulphide or non-sulphide mineralisation,  iii). mainly siliciclastics with minor hyaloclastics, pyroclastics and carbonate lenses  iv). felsic meta-rhyolites.   All of the volcanics in this succession were deposited sub-aqueously.

The orebody and mineralisation is irregular in shape and transgresses sedimentary layering, but is generally confined to the siliciclastic dominated lithotypes.   It has a flat top and is concealed below un-mineralised calcrete, boulder beds and recent sand dunes, while the base of mineralisation is defined by a relatively sharp contact (gradational over around 2 m) with underlying barren marble on the south and east.   The deposit occurs to the west and north of a prominent NNW plunging anticline of un-mineralised underlying marble and has a gradational boundary within the host siliciclastics down dip on the limbs.

The principal ore mineral is a Zn-smectite, sauconite with substantial amounts of hemimorphite and smithsonite and lesser scholzite, tarbuttite, atacamite, hydrozincite and hetearolite occurring as euhedral and subhedral crystals and open space pore fillings of intergranular voids, breccias and fractures, as well as by replacement of feldspar and micas.

The host metsediments contain abundant evidence of pre-existing sulphides in the form of gossanous developments and iron and Mn hydroxide pseudomorphs after disseminated and stringer sulphides and after rare semi-massive sulphide layers.   These indications are more prevalent to the west and north-west.   Calcite cement has been removed from the hosts in the mineralised interval, while detrital albite-rich plagioclase and orthoclase have been broken down accompanied by silicification and deposition of barite.

While weak pre-metamorphic sulphide mineralisalisation (pyrite, pyrrhotite, sphalerite, minor chalcopyrite and galena, with secondary chalcocite and colloidal sphalerite) are found in meta-rhyolites and feldspar hyaloclastic rocks below the non-sulphide orebody, the latter is clearly of post metamorphic origin.

The orebody will be mined from an open pit, leached under atmospheric conditions, with the zinc being extracted by SX-EW to produce 150 000 tpa of zinc metal over a 15 year period. The zinc in the ore is readily soluble in sulphuric acid, and has low contaminants, with silica being the major impurity (about 60% of the gangue)

The resource in 2002 was:   24.6 Mt @ 10.6% Zn.
Remaining Ore Reserve and Mineral Resources at the end of 2018 (Vedanta Resources Annual Report, 2018) were:
    Proved + Probable Reserve - 2.74 Mt @ 9.88% Zn;
    Measured + Indicated Resource - 2.92 Mt @ 9.12% Zn;
    Inferred Resource - 1.84 Mt @ 8.65% Zn.
  NOTE: Reserves are additional to resources.

The deposit was discovered by Anglo American in 1976. Reunion Mining gained a 60% interest by conducting a feasibility study, after which Anglo American purchased Reunion to gain 100% ownership. Anglo American subsequently sold to Vedanta Resources in 2010.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2001.    
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.


  References & Additional Information
   Selected References:
Anonymous  1999 - Namibia Base Metals - Skorpion Process will Use SX Technology: in    Mining in Southern Africa Quarterly, 1999, 1st Quarter    pp 21, 23
Borg G, Karner K, Buxton M, Armstrong R, van de Merwe S W  2003 - Geology of the Skorpion supergene zinc deposit, southern Namibia: in    Econ. Geol.   v98 pp 749-771
Frimmel H E, Jonasson I R, Mubita P,  2004 - An Eburnean base metal source for sediment-hosted zinc-lead deposits in Neoproterozoic units of Namibia: Lead isotopic and geochemical evidence: in    Mineralium Deposita   v39 pp 328 - 343


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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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