Geochemistry and origin of ?platinum-nuggets? in lateritic covers from ultrabasic rocks and birbirites of W. Ethiopia

The calculated solubility of platinum and gold in oxygen-saturated fluids and the genesis of platinum-palladium and gold mineralization in the unconformity-related uranium deposits

“…The possibility of transporting PGE in relatively lowtemperature ore fluids was indicated by Ottemann and Augustithis (1967) who discussed the mineralogy and genesis of platinum-bearing nuggets from lateritic cover over ultramafic rocks in W. Ethiopia. Fuchs and Rose (1974) have drawn attention to the behaviour of platinum and palladium during weathering and have discussed the relative mobility of these two elements in the soil profile.…”

The activation energy values estimated by the Arrhenius equation as a controlling factor of platinum-group mineral formation

“…However, there is a debate as to whether all PGM grains in placer deposits represent transported minerals or they have formed either in the weathered rock or in placers, due mostly to the paucity of large PGM in the parent rocks and differences in the chemical composition of PGM (Ottemann and Augustithis, 1967;Cabri and Harris 1975;Cousins and Kinloch 1976;Bowles, 1981Bowles, , 1986Bowles, , 1988Burgath, 1988;Cabri et al, 1996;Bowles et al, 2000;Johan et al, 2000;Tsintsov, 2001;Weiser, 2002;Hattori et al, 2004;Oberthü r et al, 2004;Oberthü r and Melcher, 2005;Tolstykh et al, 2005). Laurite (RuS 2 ), with a size ranging from 700 to 1100 lm (average 900 lm), from the sediments in the main channel of the river Pontyn River and Tambanio River, Borneo, exhibit inclusions, such as Ca-Al amphibole, chalcopyrite, bornite, pentlandite, heazlewoodite.…”

“…More specifically, the origin of coarse-grained platinum-group minerals (PGM) located in many placers associated with ultramafic-mafic complexes, such as Ural/ Alaskan-and ophiolitic-type and in laterites related with the Freetown layered gabbro, Sierra Leone and many other deposits worldwide, have been a subject of debate for several years, due to the paucity of coarse-grained PGM in parental rocks. Some authors have suggested that coarsegrained PGM have formed at low-temperature, during the weathering of mafic rocks and sedimentation in placers (Augustithis, 1965;Ottemann and Augustithis, 1967; 0016-7037/$ -see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2008.12.009 Cousins and Kinloch, 1976;Bowles, 1986;Barker and Lamal, 1989;Bowles et al, 2000) whilst others suggested that such coarse-grained PGM have crystallized at relatively high temperature, in a magmatic environment (Cabri and Harris, 1975;Hattori and Hart, 1991;Johan et al, 1991;Slansky et al, 1991;Cabri et al, 1996;Johan et al, 2000;Malitch and Thalhammer, 2002;Hattori et al, 2004;Tolstykh et al, 2005).…”

Formation des latérites nickélifères et mode de distribution des éléments du groupe du platine dans les profils latéritiques du complexe de Musongati, Burundi /

“…Les possibilités de concentration résiduelle des EGP dans un environnement supergène ont été déjà étudiées par Ottemann et Augustithis (1967). Ces auteurs suggèrent que les pépites riches en EGP de la couverture latéritique des roches ultramafiques en Ethiopie, forment des agglutinations résiduelles au cours de la latéritisation.…”