Mineralogy of beneficiation problems involving fluorspar concentrates from carbonatite-related fluorspar deposits

摘要

The World's three largest producers of fluorite fromcarbonatite-related fluorspar ore deposits are located at Okorusu(Namibia), Amba Dongar (India), and Mato Preto (Brazil).Beneficiation problems involving fluorite concentrates from thosethree deposits share similar characteristics that are directly relatedto the mineralogy and textures of the ores. The most important ofthese beneficiation problems involves their phosphorus, silica, andlime contents. Because the fluorite-depositing hydrothermal fluids were partlyor largely derived from carbonatite sources, and carbonatitestypically are rich in phosphorus, carbonatite-related fluoritedeposits would be expected to be characterized by significantamounts of phosphorus mineral in the form of apatite. In thebeneficiation products from those ore deposits, apatite occurs asfree particles and especially as particles locked with fluorite. Thepresence of apatite in fluorite concentrates may contributesignificant amounts of phosphorus, a deleterious constituent influorspar concentrates used in the steelmaking industry.Fluorite concentrates from some carbonatite-related fluorspardeposits are characterized by significant amounts of silica. Thesilica occurs especially in the form of quartz, potash feldspar, andsericite. Quartz occurs in both free particles and in particles whereit is locked with fluorite. Quartz was deposited late in theparagenetic sequence and typically fills small vugs between thefluorite crystals. Potash feldspar formed during early potassicfenitization associated with the magmatic carbonatite emplacement.Potassic feldspar forms intricate intergrowths with fluorite thatresult in locked feldspar-fluorite particles in the fluorsparconcentrates. The potash feldspar is intensely altered to sericite.Fluorite deposits that occur within a carbonatite host, such asthose deposits at Amba Dongar and some deposits at Mato Preto,may have the grades of their fluorite concentrate diluted by thepresence of calcite. The calcite commonly is present as binarylocked calcite-fluorite particles in those fluorspar concentrates.Although the beneficiation problems concerning fluoriteconcentrates from carbonatite-related fluorspar deposits may beeffectively studied by petrographic and ore microscopic techniques,cathodoluminescence microscopy has been found to be uniquelysuited to rapid mineral recognition and the study of those mineralsinvolved in fluorspar beneficiation problems.