Accessory minerals in rocks, ores and mine tailings can represent valuable, but in many cases unrecognized resources for the minerals industry (notably platinum-group minerals (PGM), native gold, silver, diamonds and other rare minerals). In addition, they can also provide unique opportunities for scientific research.
The new technique for the concentration of "heavy" minerals (here meaning minerals with density higher than that of the host rock) from ores, rocks and tailings uses a combination of electric-pulse disaggregation (EPD) for crushing of geological/mineral samples and concentration of comminuted heavy minerals by means of a hydroseparator (HS).
Electric-pulse disaggregation yields a perfect separation of the mineral constituents, since the crushing occurs primarily along grain boundaries and fractures in the sample (boundaries between domains with different physical properties). The technique largely preserves crystals and mineral grains of the sample providing a unique possibility of observing the crystal shape, morphology, primary grain sizes and internal texture of individual mineral grains. Furthermore, alteration products are effectively removed from mineral surfaces producing unusually clean mineral grains. In cases, where mineral associations contain important information for the accessory minerals, the crushing is done by careful use of a shatter box instead of by EPD.
The extraction of "heavy" minerals is done by using a hydroseparator with practically no loss of mineral grains. In different tests, mineral concentrates had 100 to 10,000 times the original proportions of the desired minerals. The technique has been applied successfully to samples having as low as 0.1-1.0 ppm of the phase forming elements of the desired minerals. The technique has been tested on many types of samples which are difficult to separate using normal techniques, and some examples include:
- PGM in chromite ores;
- PGM-Au bearing low-sulfide ores of layered intrusions and tailings;
- disseminated Cu-Ni ores;
- black shales;
- carbonatites;
- tailings from orthomagmatic sulphide deposits;
- native gold ores;
- Pt-bearing phases in ocean Mn-Fe crusts on basalts;
- kimberlites (to define diamond indicator minerals);
- low grade Ni-PGE ores.
- study the crystal morphology, mineralogy and mineral chemistry of PGM and gold of different rock types containing low concentrations of these minerals;
- enhance the chances of finding accessory minerals for study by the Scanning Electron Microscope and the Electron Microprobe for identification and characterization of accessory heavy minerals (e.g., PGM, gold, zircon, baddeleyite, etc);
- carry out prospecting and technological mapping at a phase level from small samples (100-200 g);
- detect the occurrence of useful minerals and elements in possible secondary mineral deposits (process products such as mine tailings, industrial slags, etc);
- produce ultraclean separates of accessory minerals (e.g., zircon, baddeleyite) for geochronology without using toxic chemicals and reactants which may leach the minerals or crush desired minerals;
- separate intact crystals and/or crystal fragments of various precious and semi-precious stones.
- determine the identity of accessory minerals, their grain-size distribution, and their mineral associations, important information for economic evaluation and extraction;
- contribute to better understanding of the paragenesis of deposits through detailed studies of accessory minerals;
- separation of zircon, baddeleyite and PGE-mineral concentrates for age determinations;
- analysis of losses in tailings of concentration mills;
- analysis of Au & PGM in placers and source host rocks;
- study of products from different stages of mineral processing;
- study of environmental pollution — heavy-metal pollutants in solid phases.
Short course on EPD+HS and other methods of process mineralogy
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