Beneficiation and appraisal of a beach placer sand deposit from Malawi

Abstract

Heavy mineral sands of Monkey bay on the Cape Maclear peninsula of Lake Malawi occur as an active placer deposit. The heavy minerals are mainly ilmenite, garnet, magnetite and zircon, with small amounts of sphene, monazite and rutile. The sands are sderived from the surounding Precambrian basement which is composed of high-grade paragneiss and microsyenitic dykes and granite ring complexes. Beneficiation of a typical sand was carried out using gravity, magnetic and electrostatic separation in an attempt to produce concentrates of ilmenite, zircon, rutile and monazite. Individual grains were identified using the Link system of an Hitachi SEM. An ilmenite concentrate grading 78% and with a recovery of 75% was produced by combining the 'conductive magnetics' products, which also represent half of the heavy minerals present. Combining the non-magnetic products gave a concentrate containing 49% zircon (recovery of 92%), 6.5% monazite (recovery of 78%) and 5.9% rutile (recovery of 66%). These results are directly applicable to industrial scale processing. Although ilmenite is highly magnetic and conductive and concentrated as expected into the appropriate product, monazite, which is moderately magnetic, was found to concentrate in the non-magnetic products. Monazite grains from all the processing products were therefore analysed by electron microprobe in an attempt to determine the relation between chemistry and separation. Elemental mapping was carried out to determine the REE distribution within the monazites and detect the presence of inclusions. This work formed part of the ODA/BGS R&D project "Minerals for Development" and was partly carried out by M. Anuar for his MSc. in Industrial Mineralogy