South African Journal of Geology; March 2009; v. 112; no. 1;
p. 47-64; DOI: 10.2113/gssajg.112.1.47
© 2009 Geological Society of South Africa
Alteration and metasomatism of the UG2 melanorite and its stratiform pegmatoids, Bushveld Complex, South Africa –characteristics, timing and origins.
R.J. Voordouw and
N.J. Beukes
Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, 2006, South Africa e-mail: ron.voordouw{at}gmail.com, nbeukes{at}uj.ac.za
The UG2 chromitite at Two Rivers Platinum Mine (eastern limb, Bushveld Complex) is fully enclosed within a UG2 melanorite that is here divided into five sub-units, all of which crystallised from the same parental magma. From top to bottom, these sub-units are the upper distal, upper stratiform pegmatoid, upper split, lower split and lower stratiform pegmatoid. The upper distal and lower split sub-units exhibit the most primary characteristics whereas hydrothermal fluids and/or hydrous melts infiltrated the remaining three sub-units, as well as the UG2 chromitite. Within the stratiform pegmatoid sub-units, network veins of amoeboidal troctolite, high abundances of secondary silicates, enrichment in incompatible elements and the coarsening of grain sizes indicate this infiltration of fluids and/or melts. The upper split sub-unit is chromite-rich and locally altered to amphibolite. This fluid- and melt-induced alteration/metasomatism occurred at high temperatures and is pervasive along at least 7 km of strike length, suggesting magmatic origins. These magmatic fluids are probably related to the compaction of underlying cumulates or the intrusion of chromite crystal slurries.
Copyright © 2010 by Geological Society of South Africa
