Geelwal Karoo deposit, Geelwal Karoo Farm, Matzikama Local Municipality, West Coast District Municipality, Western Cape, South Africai

Regional Level Types
Geelwal Karoo deposit	Deposit
Geelwal Karoo Farm	Farm
Matzikama Local Municipality	Municipality
West Coast District Municipality	District
Western Cape	Province
South Africa	Country

Heavy mineral concentrates in a raised beach deposit. The deposit was first prospected in 1954 using 50 grab samples and later in 1983 by Trans Hex Group Limited using grid-based drilling. The heavy-mineral sands are present on the foreshore and the backshore and are between 0.5 and 12 m thick, with an average thickness of 2 m. The heavy minerals are present in seaward dipping layers between several millimetres and 1.2 m thick and are hosted by fine-to medium-grained, well sorted, quartzose sand. Garnet is the most abundant heavy mineral comprising up to 40 % of the total sand mass. Other minerals are ilmenite, rutile, zircon, magnetite, augite, tourmaline, leucoxene, haematite, actinolite and calcite.

The heavy-mineral sands overlie gravel or bedrock of the Gifberg Group with the gravel being up to 2.5 m thick and diamondiferous in places. Both the sand and gravel abut against bedrock or Neogene sediments at the base of a cliff face up to 80 m high. The Neogene sediments include gravel and heavy-mineral-bearing sands that rest on the middle Pliocene “27 m terrace”. These sands probably provided the bulk of the heavy minerals to the present Holocene beach sands.

The “27 m terrace” heavy-mineral sands were derived from the Namaqualand Metamorphic Province (section 2.1) through several cycles of sedimentation that involved fluvial transport to the Olifants River mouth and northward littoral transport along the coast. Some of the zircon may have been sourced from the Table Mountain Group.

Trans Hex Group Limited calculated an ore resource of 10 Mt grading at 24% heavy minerals, but the heavy mineral fraction was not disclosed. A grab sample taken by the author yielded the following results: 64% garnet; 17% quartz; 10% ilmenite; 4% zircon; 2% calcite; 1% haematite; 1% halite; 1% potassium feldspar; 1% plagioclase feldspar. The ratio of ilmenite + rutile + zircon to gangue minerals is between 1:3 and 1:6 and a 4:1 ratio of ilmenite to rutile + zircon is present. Thus, an ilmenite resource of 1.3 Mt, a rutile resource of 0.15 Mt and a zircon resource of 0.14 Mt can be inferred. The average TiO2 content of ilmenite is 50.8 %.

The deposit has not been exploited due to high costs relative to the small size of the deposit (Cole, 2013).

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References