Rare-Earth Element and Thorium Potential of Heavy Mineral Deposits Along the West Coast of South Africa With Special Reference to the Namakwa Sands Deposit

Abstract

The west coast of South Africa is well known for its Cenozoic unconsolidated marine and aeolian placer deposits. The gem-quality diamond deposits have been effectively depleted; however, the significant heavy mineral concentrations are actively exploited at Namakwa Sands. This world-class mineral sand has an inferred resource of some 900 million tons at a grade of ~10% total heavy minerals (THMs) from which high-grade concentrates of zircon, rutile and leucoxene are extracted and titanium slag and pig iron are produced. Gangue minerals consist of garnet, pyroxene, kyanite, amphibole, apatite and monazite. Several other resources including satellite deposits proximal and distal to the mine area, extensive diamond mine dumps and present-day beach placers demonstrate the vast heavy mineral potential along the west coast. The increased global demand for the rare-earth elements (REEs) uranium and thorium has initiated interest in the economic potential of gangue minerals from these placer deposits. The present quantitative mineral distribution and mineral chemistry study has shown that monazite, impure zircon, leucoxene and garnet are common constituents that host significant concentrations of the REEs uranium and thorium. The total estimated resources in the Namakwa Sands deposit amount to 250 kt REEs, 4.7 kt uranium and 10.5 kt thorium. Monazite is the most significant contributor to the total thorium and light REE resource, whereas zircon is a heavy REE and U-enriched. Garnet and leucoxene show low concentrations of these elements and make a minor contribution to the total resources. Results from the Namakwa Sands deposit suggest that the west coast of South Africa as a whole presents a vast untapped resource for these elements. Considering the anticipated increasing demand for rare earths and possibly thorium, these resources could be produced as a low-cost by-product from existing and future ilmenite–zircon–rutile producers, thereby increasing the in situ value of the placers and ultimate revenue.