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Post-recrystallisation mobilisation phenomena in metamorphosed stratabound sulphide ores

Published online by Cambridge University Press:  05 July 2018

F. M. Vokes  and
J. R. Craig
F. M. Vokes
Affiliation:
University of Trondheim, Norwegian Institute of Technology, H6gskoleringen 6, N-7034 Trondheim-NTH, Norway
J. R. Craig
Affiliation:
Virginia Polytechnic Institute and State University, Department of Geological Sciences, Blacksburg, VA 24061, U.S.A.
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Abstract

Metamorphosed stratabound iron- and base-metal sulphide deposits often exhibit microtextures in which fractures in cataclastically-deformed pyrite porphyroblasts are filled with matrix sulphides; chalcopyrite, sphalerite, pyrrhotite or galena. Discussions of such textures have mostly centred on whether solid-phase or fluid-phase mechanisms were responsible for the movement of the matrix sulphides.

The small Zn-Cu sulphide body at Gressli, in the central Norwegian Caledonides, shows these textural features to an extreme degree. Both chalcopyrite and sphalerite show heavy replacive relations to the cataclastically deformed metablastic pyrite, along fracture walls and grain boundaries. They also occur injected along the opened-up triple junctions of foam-textured pyrite. In addition, parts of the ore show patchy quartz with clear replacive relationship to all three sulphides, a feature not often reported from such ores. Such textures can be interpreted to support a mobilisation sequence chalcopyrite-sphalerite-quartz within the Gressli ore. Their extent and degree of development indicate that fluid-phase mobilisation of the three minerals must have played a dominant role. Chalcopyrite and sphalerite are most likely derived from within the ore-mass itself; an external source for the SiO2 seems most probable, in the form of metahydrothermal solutions moving along retrograde shear zones at or near ore-walls.

Keywords

metamorphismsulphide oresmicrotexturesGressliNorway
Type
Research Article
Information
Mineralogical Magazine , Volume 57 , Issue 386 , March 1993 , pp. 19 - 28
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1993

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