REPLY TO: “NANOMETER-SIZED PLATINUM-GROUP MINERALS (PGM) IN BASE METAL SULFIDES: NEW EVIDENCE FOR AN ORTHOMAGMATIC ORIGIN OF THE MERENSKY REEF PGE ORE DEPOSIT, BUSHVELD COMPLEX, SOUTH AFRICA: DISCUSSION” by Louis J. Cabri: Fig. 1

2013 ◽  
Vol 51 (6) ◽  
pp. 941-943
Author(s):  
Richard Wirth
Keyword(s):  
South Africa ◽  
Base Metal ◽  
Bushveld Complex ◽  
Metal Sulfides ◽  
Ore Deposit ◽  
Merensky Reef ◽  
Platinum Group Minerals ◽  
Base Metal Sulfides ◽  
Platinum Group ◽  
New Evidence

Platinum-Group Elements and Gold in Base Metal Sulfides, Platinum-Group Minerals, and Re-Os Isotope Compositions of the Uitkomst Complex, South Africa

2018 ◽  
Vol 113 (2) ◽  
pp. 439-461 ◽  
Author(s):  
Jakub Trubač ◽  
Lukáš Ackerman ◽  
Christoph Gauert ◽  
Jana Ďurišová ◽  
Tomáš Hrstka
Keyword(s):  
South Africa ◽  
Base Metal ◽  
Platinum Group Elements ◽  
Metal Sulfides ◽  
Platinum Group Minerals ◽  
Base Metal Sulfides ◽  
Platinum Group ◽  
Os Isotope

Laboratory-Based Bacterial Weathering of the Merensky Reef and Its Impact on Platinum Group Mineral Migration

2021 ◽  
Author(s):  
Ling Tan ◽  
Thomas Jones ◽  
Jianping Xie ◽  
Xinxing Liu ◽  
Gordon Southam
Keyword(s):  
Base Metal ◽  
Mineral Dissolution ◽  
Metal Sulfides ◽  
Acidithiobacillus Thiooxidans ◽  
Thin Sections ◽  
Secondary Minerals ◽  
Merensky Reef ◽  
Fe Oxides ◽  
Base Metal Sulfides ◽  
Platinum Group

Abstract Weathering of the Merensky reef was enhanced under laboratory conditions by Fe- and S-oxidizing bacteria: Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans. These bacteria preferentially colonized pyrrhotite and pyrite, versus pentlandite and chalcopyrite (all of which were common within the rock substrate), promoting weathering. Weathering of base metal sulfides resulted in the precipitation of Fe oxides, Fe phosphate, and elemental sulfur as secondary minerals. Fe pyroxene weathered readily under acidic conditions and resulted in mineral dissolution, while other silicates (orthopyroxene and plagio-clase) precipitated Fe phosphate spherules or coatings on their surface. The deterioration of the platinum group metal (PGM) matrix (base metal sulfides and silicates) and the occurrence of a platinum grain associated with platinum nanoparticles observed in the biotic thin sections demonstrate that biogeochemical acid weathering is an important step in the active release of intact PGM grains. A platinum grain embedded in secondary Fe oxides/phosphate that had settled by gravity within the weathering solution demonstrates that secondary minerals that formed during weathering of PGM-hosting minerals also represent targets in PGM exploration by trapping and potentially slowing PGM migration. Dispersion halos surrounding or occurring downstream from PGM occurrences will likely produce two physical target classes—i.e., grains and colloids—under surficial weathering conditions.

Supergene mobilization and redistribution of platinum-group elements in the Merensky Reef, eastern Bushveld Complex, South Africa

2021 ◽  
Vol 59 (6) ◽  
pp. 1381-1396
Author(s):  
Maximilian Korges ◽  
Malte Junge ◽  
Gregor Borg ◽  
Thomas Oberthür
Keyword(s):  
South Africa ◽  
Platinum Group Element ◽  
Bushveld Complex ◽  
Platinum Group Elements ◽  
Element Distribution ◽  
Group Element ◽  
Recovery Rates ◽  
Merensky Reef ◽  
Platinum Group Minerals ◽  
Platinum Group

ABSTRACT Near-surface supergene ores of the Merensky Reef in the Bushveld Complex, South Africa, contain economic grades of platinum-group elements, however, these are currently uneconomic due to low recovery rates. This is the first study that investigates the variation in platinum-group elements in pristine and supergene samples of the Merensky Reef from five drill cores from the eastern Bushveld. The samples from the Richmond and Twickenham farms show different degrees of weathering. The whole-rock platinum-group element distribution was studied by inductively coupled plasma-mass spectrometry and the platinum-group minerals were investigated by reflected-light microscopy, scanning electron microscopy, and electron microprobe analysis. In pristine (“fresh”) Merensky Reef samples, platinum-group elements occur mainly as discrete platinum-group minerals, such as platinum-group element-sulfides (cooperite–braggite) and laurite as well as subordinate platinum-group element-bismuthotellurides and platinum-group element-arsenides, and also in solid solution in sulfides (especially Pd in pentlandite). During weathering, Pd and S were removed, resulting in a platinum-group mineral mineralogy in the supergene Merensky Reef that mainly consists of relict platinum-group minerals, Pt-Fe alloys, and Pt-oxides/hydroxides. Additional proportions of platinum-group elements are hosted by Fe-hydroxides and secondary hydrosilicates (e.g., serpentine group minerals and chlorite). In supergene ores, only low recovery rates (ca. 40%) are achieved due to the polymodal and complex platinum-group element distribution. To achieve higher recovery rates for the platinum-group elements, hydrometallurgical or pyrometallurgical processing of the bulk ore would be required, which is not economically viable with existing technology.

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