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Deposit variability |
Mineral Resource Consultancy, 12 Thornhill Road, Ickenham, Uxbridge, Middlesex UB10 8SF, UK
Phosphate rock in the mineral industry refers to the marketable, usually beneficiated, product. Geologically, however, the term embraces a very wide variety of rock types, of both sedimentary and igneous origin, as well as their weathering derivatives. Phosphate deposits thus form in markedly different geological environments and ore characteristics are so varied that a combination of nearly identical factors applicable to their evaluation seldom exists. In spite of this diversity, the phosphate component in most deposits is a member of the apatite group represented by the two end members: fluorapatite, the main mineral in crustal igneous rocks, and carbonate fluorapatite or francolite, by far the most important phosphate component of commercial sedimentary deposits. The identification of the correct apatite composition is important in assessing the quality of marketable phosphate concentrates.
Evaluation usually begins with a detailed mineralogical, petrographical, and chemical study of a representative sample of prospective phosphate ore to determine the principal constituents in the ore and their mode of occurrence. The data obtained establish the grade (P2O5 content) of the rock and its chemical quality and, hence, the method and degree of beneficiation required to provide a commercially acceptable phosphate concentrate. Beneficiation technology is such that often the most difficult ore types (e.g. siliceous, dolomitic and Fe-Al-rich) can be upgraded satisfactorily, but the problems become more acute when impurities occur as substitutions in the apatite lattice. Quality rather than grade is often the deciding factor in determing the viability of a given deposit, in addition to other technical and economic factors.
