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CRYPTIC VARIATION OF CHROMITE CHEMISTRY, PLATINUM GROUP ELEMENT AND PLATINUM GROUP MINERAL DISTRIBUTION IN THE UG-2 CHROMITITE: AN EXAMPLE FROM THE KAREE MINE, WESTERN BUSHVELD COMPLEX, SOUTH AFRICA

2014; Volume: 109; Issue: 3 Linguagem: Inglês

10.2113/econgeo.109.3.795

1554-0774

Malte Junge, Thomas Oberthür, Frank Melcher,

Clay minerals and soil interactions

Research Article| May 01, 2014 CRYPTIC VARIATION OF CHROMITE CHEMISTRY, PLATINUM GROUP ELEMENT AND PLATINUM GROUP MINERAL DISTRIBUTION IN THE UG-2 CHROMITITE: AN EXAMPLE FROM THE KAREE MINE, WESTERN BUSHVELD COMPLEX, SOUTH AFRICA Malte Junge; Malte Junge † Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany †Corresponding author: e-mail, malte.junge@bgr.de Search for other works by this author on: GSW Google Scholar Thomas Oberthür; Thomas Oberthür Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany Search for other works by this author on: GSW Google Scholar Frank Melcher Frank Melcher Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Malte Junge † Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany Thomas Oberthür Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany Frank Melcher Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany †Corresponding author: e-mail, malte.junge@bgr.de Publisher: Society of Economic Geologists Received: 11 Jun 2013 Accepted: 01 Oct 2013 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2014 Society of Economic Geologists. Economic Geology (2014) 109 (3): 795–810. https://doi.org/10.2113/econgeo.109.3.795 Article history Received: 11 Jun 2013 Accepted: 01 Oct 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Malte Junge, Thomas Oberthür, Frank Melcher; CRYPTIC VARIATION OF CHROMITE CHEMISTRY, PLATINUM GROUP ELEMENT AND PLATINUM GROUP MINERAL DISTRIBUTION IN THE UG-2 CHROMITITE: AN EXAMPLE FROM THE KAREE MINE, WESTERN BUSHVELD COMPLEX, SOUTH AFRICA. Economic Geology 2014;; 109 (3): 795–810. doi: https://doi.org/10.2113/econgeo.109.3.795 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The UG-2 chromitite of the Bushveld Complex in South Africa contains the world's largest resources of platinum group elements (PGEs). However, only limited work has been conducted on the fine-scale chemical variation of chromite, and the distribution of PGEs and platinum group minerals (PGMs) within the UG-2. In the present study, one drill core (155 cm long) covering the sequence of the UG-2 chromitite at the Karee mine in the western Bushveld Complex was studied in detail.Geochemically, Pt correlates well with Pd, but not with Ni, Cu, and S, and Pt and Pd show high concentrations at the bottom and in the center of the main UG-2 layer. The mineral chemistry of chromite is characterized by distinct cryptic variation, leading to the division of the UG-2 sequence into 10 distinct sublayers. From bottom to top (with exception of the basal sublayer), each sublayer is defined by an upward decrease of Mg# combined with increases of Cr# and TiO2. It is proposed that these trends reflect magmatic differentiation of individual chromitite entities, which coalesced to form a massive chromitite seam. Sulfides (pentlandite, chalcopyrite) interstitial to chromite grains are rare, and associated PGM grains are mainly Pt-Fe alloy, laurite, and cooperite-braggite. The PGEs are bimodally distributed in the UG-2. Platinum and the IPGE (Os, Ir, Ru) are dominantly present as discrete PGMs, whereas large proportions of Pd and Rh are hosted in the crystal lattice of pentlandite. Palladium and rhodium contents of pentlandite reach a maxima of 2.2 wt % Pd and 3.0 wt % Rh.The present data suggest that a succession of chromitite sublayers formed due to magmatic differentiation and segregated sequentially on top of each other, finally forming a massive chromitite seam. Contemporaneously with chromite segregation, PGE-rich magmatic sulfides segregated with chromite grains, but large proportions of these sulfides were subsequently removed mainly by reaction of sulfide with chromite, thereby upgrading the PGE contents of the remaining sulfides. Upon cooling, the PGE-bearing sulfide droplets recrystallized, leading to a bimodal distribution of the PGEs in the UG-2. The bulk of the Pd and Rh is hosted in pentlandite, whereas Pt and the IPGEs, apparently incompatible in the remaining sulfides, formed a distinct suite of discrete PGMs. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.