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Structure of veins in a gold–pyrite deposit in banded iron formation, Amalia greenstone belt, South Africa

Published online by Cambridge University Press:  01 May 2009

J. R. Vearncombe
J. R. Vearncombe
Affiliation:
Department of Geology, Rand Afrikaans University, P.O. Box 524, Johannesburg 2000, Republic of South Africa
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Abstract

Fibrous quartz veins in deformed banded iron formation of the Amalia greenstone belt, southwestern Transvaal, are spatially related to gold–pyrite mineralization in both wallrock and vein inclusions. Poles to quartz vein orientations show a general parallelism with mineral elongation and fold plunges of the principal deformation in the wallrock. Quartz vein fibres show a consistent anticlockwise rotation, late components being subparallel to the elongation lineation, suggesting veining was probably synchronous with the principal deformation. Antitaxial fibrous veins, which dominate the mineralized banded iron formation, formed by the process of crack–seal which channelled mineralizing fluids along the vein walls, increasing the potential for fluid–wallrock interaction. Gold mineralization in quartz veins occurs in wall-parallel slivers of banded iron formation which have been plucked off the vein wall during antitaxial fibre growth. Mineralization can be explained by a process of fluid–wallrock interaction with sulphidation and gold precipitation.

Type
Articles
Information
Geological Magazine , Volume 123 , Issue 6 , November 1986 , pp. 601 - 609
Copyright
Copyright © Cambridge University Press 1986

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