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Porphyritic-nodular, nodular, and orbicular chrome ores from the Sakhakot-Qila complex Pakistan, and their chemical variations

Published online by Cambridge University Press:  05 July 2018

Zulfiqar Ahmed
Zulfiqar Ahmed*
Affiliation:
Department of Geology, University of London, King's College, London WC2R 2LS
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Abstract

A new kind of chromitite texture—a porphyritic nodular texture, found in an alpine-type complex in Pakistan, is described. The chromite from phenocrystic nodules and that from their disseminated chromitite groundmass show comparable trivalent elements and postcumulus to subsolidus Mg−Fe2+ variations, which are also recorded from ‘normal’ nodular ore samples. The nodular ores differ from all other textural types of chromitite from this complex in an unusual, though slight, increase in Cr/(Cr+Al) with Mg/(Mg+Fe2+) between stratigraphically different desposits, which is caused by magmatic differences. The implications of major element variations in chromites and olivines of nodular chromirites are discussed and a cumulus origin is supported. Temperatures of final chromite-olivine equilibration ranged from 750 to 900 °C the individual nominal values being higher for chromitite with coarser chromite crystals and, or, higher chromite:silicate ratio.

Type
Research Article
Information
Mineralogical Magazine , Volume 45 , Issue 337 , 1982 , pp. 167 - 178
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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Footnotes

*

Permanent address: Institute of Geology, University of the Punjab, New Campus, Lahore, Pakistan.

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