Many of the major copper ore bodies throughout the world contain chalcocite (79.9% Cu) as the principal copper mineral, yet the grades of copper concentrates produced from these ores rarely exceeds 25 to 28% Cu and in one known instance went as low as 13%. The low grade has traditionally been attributed to the presence of “activated pyrite” and/or chalcopyrite, and the universal approach has been excessive regrinding with all of its inherent effects-high capital, energy and maintenance costs, excessive sliming, and concentrate filtration difficulties (high moisture content).
Rimmed pyrite particles at a minus 65 mesh grind are usually observed in two forms:
In many instances, these rims are one micron or less, with mono or dimolecular films being invisible at 400 to 600 magnification. Thus, the rims responsible for major lowering of grade represent a very small fraction of the total copper content (1 to 3%).
Summary of American Cyanamid Investigations
Rougher concentrates from several major copper mills were examined under the microscope. In most cases pyrite rimmed with varying thicknesses of copper sulfides was present. Assay-size analyses of the rougher concentrates were made and theoretical surface areas calculated. On the average, the