Applications of Ore Microscopy to Beneficiation



Fine-grained framboidal pyrite partially coated by later coarser grained crystalline pyrite (Py; bright yellow) and contained within calcareous shale (Gg). Carlin gold ores, Nevada. Gold contained in fine-grained pyrite is readily leached, but gold entrained in coarser pyrite is more difficulty to leach. Ore microscopy, reflected light, high magnification.



Extremely fine-grained pyrite (light yellow)-sphalerite (gray) ores with gangue (black) from MacArthur River, Australia. The fine-grained (pyrite grains average about 6 µm) intergrowth has prevented treatment of these ores by normal beneficiation techniques. Ore microscopy, reflected light, high magnification.



Four locked sphalerite (Sl)-dolomite (Dolo) particles in zinc concentrate from the Magmont mine, Viburnum Trend, Southeast Missouri. The locked particles carry deleterious magnesium into the zinc concentrates and cause most of the zinc concentrates from the district to be treated with sulfuric acid to dissolve the dolomite and remove the magnesium. A single pyrite (white) grain (upper left) also is locked with dolomite. The mineral particles are enbedded in plastic (dark gray). Ore microscopy, reflected light, low magnification.



Thick coating of siegenite (Sg; pinkish yellow; top) deposited on chalcopyrite (Cp; deep yellow; bottom). Irregular replacement remnants of chalcopyrite within the siegenite indicate that siegenite was also deposited partly by replacement of the chalcopyrite. The cobalt content of the lead-zinc ores in the Frederictown subdistrict average about ten times greater than that of ores in the Viburnum Trend subdistrict. Efforts to recover cobalt have been hampered by the intergrowth between siegenite and other minerals, especially chalcopyrite, and by the strong tendency for siegenite to float with chalcopyrite during flotation. Madison mine, Fredericktown subdistrict, Southeast Missouri Lead District. Ore microscopy, reflected light, low magnification.