Platinum-group element distribution in the oxidized Main Sulfide Zone, Great Dyke, Zimbabwe |
| |
| Authors: | Marek Locmelis Frak Melcher Thomas Oberthür |
| |
| Institution: | (1) Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hannover, Germany;(2) Present address: ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC), Department of Earth and Planetary Sciences, Macquarie University, Sydney, Australia; |
| |
| Abstract: | In the Great Dyke mafic/ultramafic layered intrusion of Zimbabwe, economic concentrations of platinum-group elements (PGE)
are restricted to sulfide disseminations in pyroxenites of the Main Sulfide Zone (MSZ). Oxidized ores near the surface constitute
a resource of ca. 400 Mt. Mining of this ore type has so far been hampered due to insufficient recovery rates. During the
oxidation/weathering of the pristine ores, most notably, S and Pd are depleted, whereas Cu and Au are enriched. The concentrations
of most other elements (including the other PGE) remain quite constant. In the oxidized MSZ, PGE occur in different modes:
(1) as relict primary PGM (mainly sperrylite, cooperite, and braggite), (2) in solid solution in relict sulfides (dominantly
Pd in pentlandite, up to 6,500 ppm Pd and 450 ppm Pt), (3) as secondary PGM neoformations (i.e., Pt–Fe alloy and zvyagintsevite),
(4) as PGE oxides/hydroxides that replace primary PGM as the result of oxidation, (5) hosted in weathering products, i.e.,
iron oxides/hydroxides (up to 3,600 ppm Pt and 3,100 ppm Pd), manganese oxides/hydroxides (up to 1.6 wt.% Pt and 1,150 ppm
Pd), and in secondary phyllosilicates (up to a few hundred ppm Pt and Pd). In the oxidized MSZ, most of the Pt and Pd are
hosted by relict primary and secondary PGM; subordinate amounts are found in iron and manganese oxides/hydroxides. The amount
of PGE hosted in solid solution in sulfides is negligible. Considerable local variations in the distribution of PGE in the
oxidized ores complicate a mineralogical balance. Experiments to evaluate the PGE recovery from oxidized MSZ ore show that
using physical concentration techniques (i.e., electric pulse disaggregation, hydroseparation, and magnetic separation), the
PGE are preferentially concentrated into smaller grain size fractions by a factor of 2. Highest PGE concentrations occur in
the volumetrically insignificant magnetic fraction. This indicates that a physical preconcentration of PGE is not feasible
and that chemical, bulk-leaching methods need to be developed in order to successfully recover PGE from oxidized MSZ ore. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
