Summary:
The Norasa Project uranium deposits fall within the Pan African Damara Orogen on the inland branch (the Damara Belt) which stretches from the Namibian coast north-eastwards through to Zambia.
The Norasa project comprises two uranium deposits of the alaskite type at Valencia and at Namibplaas in central western Namibia. The Valencia and Namibplaas deposits are situated in the same regional structural setting; the socalled Khan Syncline which is underlain by Karibib marbles located just west of the Khan River and east of Valencia and west of the Khanberge.
The Norasa deposits of Valencia and Namibplaas all fall into category 2 of the list above, i.e., hightemperature, late magmatic or “intrusive type” uranium mineralisation. The sub-types at Valencia and Included in this type are those deposits associated with intrusive rocks including alaskite, granite, pegmatite and monzonites. All of these uranium deposits are associated with alkaline leucogranites that comprise massive stock-like bodies, dykes of varying thickness, sill like bodies or veins and veinlets, which can be either conformable with or transgressive to their host rocks.
The Valencia and Namibplaas deposits lie adjacent to the tightly folded Abbabis inlier (old “Joly zone” or Valencia North on Valencia, and Area A on Namibplaas).
Metamorphic gradients vary between these zones and are highest (granulite facies) in the southern portion of what is termed the Central Zone. The Zone is deeply eroded toward the coastal region in the west, exposing Proterozoic basement rocks and the alaskite type uranium deposits.
Primary uranium mineralisation of economic significance is limited to this southern Central Zone. Large volumes of U-bearing leucogranite intrude a limited stratigraphic range, occasionally crosscutting into basement rocks but mainly cross-cutting into stratigraphic units directly above and below the Nosib Group and Swakop Group unconformity.
Valencia Deposit
The Valencia deposit (or Valencia Main) is approximately 4 km southeast of the Khan River Valley and approximately 23 km northeast of the Rössing Mine. U-mineralisation is hosted in leucogranites that have invaded the local Damara succession in stockwork-like fashion along NNE/SSW structural weakness zones, preferential utilising the fold plane of a characteristic Z shape fold.
The syncline is a regional scale fold with a core of refolded Kuiseb schists. The fold hinge trending NE-SW. The synform is refolded south of the Rössing deposit where the hinge trend changes to roughly N-S. The eastern limb of the syncline at Valencia is attenuated and a secondary fold provided the weakness pathway for the mineralised intrusives in a saddle-reef style.
The uranium mineralisation at Valencia is hosted only by alaskites, and occasionally in a narrow halo within the immediate country rock contacts. The alaskites, which comprise massive stock-like bodies, dykes and sills of varying thickness, and narrow veins, are either conformable with or transgressive to the metamorphic fabric in the metasedimentary host rocks.
Uranium mineralisation at Valencia has been identified over an area of 1,100 m north-south by 500 m east-west. The mineralisation dips at approximately 35° to the south and has been identified by diamond (DDH) drilling to a depth of 499 m below surface (drillhole VA26-152). Approximately 6 km to the northeast, the Namibplaas deposit extends approximately 2,500 m along a NE-SW trend and is exposed on surface with a width of approximately 400 m.
Namibplaas
Airborne uranium anomaly maps, produced by the Namibian Geological Survey in 1997 pointed out the presence of two prominent uranium anomalies on farm Namibplaas; one in Abbabis basement and the other in Damaran metasediments.
Similar to at the Valencia deposit area, the lowermost Damaran unit present at Namibplaas is the Etusis formation. The Etusis, Khan, Rössing, Chuos, Karibib and Kuiseb formations are present throughout with the Khan formations and the Kuiseb formations bordering the anomaly along the regional SW-NE strike of the country rocks. The Khan formation forms the surface geological limit on the northwestern part of the radiometric anomaly and the Kuiseb on the southeastern part.
At Namibplaas, mineralisation is confined to syn- to post-tectonic leucogranites which are similar in texture and mineralogy to the ones at the Valencia deposit. In addition to the usual D-type mineralised alaskite, Namibplaas has mineralised magnetite rich Ctype alaskites. This type is confined to the northern portion of the deposit and locally unique.