Mineralogy and chemistry of podiform chromite deposits of the Medellín dunites, Antioquia, Colombia
DOI:
https://doi.org/10.32685/0120-1425/bolgeol33.1-3.1993.230Keywords:
Ophiolites, Chromite, Banded schlieren, Cortical levels, peridotites, Magmatic accumulation, Relict cumulus texture
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Copyright (c) 1993 Servicio Geológico Colombiano
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Abstract
The podiform chromite deposits of the Medellín tectonite dunites are characteristic of ophiolites. The chromite ores are of the disseminated, schlieren banded, lenticular, and irregular type. The chemical variations of these ores, determined by electron microprobe, indicate that they are magnesium aluminous chromites, which, although related to other high Al chromites belonging to the typical Ornan and Grecia ophiolites, have higher aluminum and magnesium contents. Microscopic studies showed that the chromite ores have relict cumulus textures, are generally cataelastic, and are altered to ferricromite and magnetite. Based on the existing information, their origin is preliminarily interpreted as a product of magmatic accumulation, from basaltic magmas, in a narrow chamber and in the lower part of the transitional sequence of an ophiolite. These deposits may have undergone plastic deformation of varying intensity in the mantle forming some accumulations parallel to the foliation and undergoing tectono-metamorphic processes after cortical levels.
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