Mineral liberation study in the Huanuni mine, Bolivia.

Abstract

The Huanuni ore deposit in the central part of the eastern Andes is a representative tin vein type ore deposit in Bolivia, The veins consist of cassiterite as a economic mineral, being associated mainly with pyrite, pyrrhotite, quartz, tourmaline and rutile.In this study, the species, grain sizes, shapes of the grains, types of intergrowth, compositions of grains, etc., of each mineral were characterized to assess the liberationcharacteristics of the ore. Observation on polished specimens under the microscope, heavy liquid separation, powder X-ray diffraction and chemical analysis by ICP were the techniques used to accomplish the mineral liberation study.Samples collected from the feed in the Huanuni's beneficiation plant were ground and classified into 6 size fractions from mesh Nos. 2 to 200. Each fraction was then separated according to their densities into 8 ranks from+3.20g/cm3 to -2.05 g/cm3.The density spectrum has been distributed into two fraction groups, one of +3.20 g/cm3 and the other of -2.90g/cm3, with lack of intermediate density fractions between them.X-ray diffraction and microscope analysis have revealed that the heavy group was characterized by the presence of predominant sulfides-cassiterite, and the light one by predominant quartz. The results were confirmed by the chemical analysis of tin and iron. Detailed particle counting under the microscope indicated that about 70% of total cassiterite was liberated by grinding the raw ore to sizes of -100 +200 ineshes. However, some “liberated” cassiterite particles, even in the finer fraction (-150 +200) still contained inclusions of about 3 pm to 15 pm of tourmaline, pyrrhotite, pyrite and rutile.