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Sulfidation and Oxidation Haloes as Guides in the Exploration for Metamorphosed Massive Sulfide Ores

By
Paul G. Spry
Paul G. Spry
Department of Geological and Atmospheric Sciences, 253 Science I, Iowa State University, Ames, Iowa 50011-3212
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Published:
January 01, 1998

Abstract

The effects of sulfidation and oxidation on country rocks enclosing metamorphosed massive sulfide deposits constitute an exploration guide to ore. Sulfur and oxygen from the sulfide deposit react with the Fe component of ferromagnesian silicates (e.g., garnet, staurolite, chlorite, biotite, and amphibole) or oxides (e.g., gahnite and högbomite) to produce more Mg- or Zn-rich silicates or Zn-rich oxides with proximity to ore. This halo of Mg-rich or Zn-rich minerals can be superimposed onto zones of premetamorphic alteration or can be developed around ore deposits where signs of alteration are apparently absent. Corresponding zonation patterns are also observed for minerals in the system Ca-Ti-Fe-S-O (e.g., titanite, ilmenite, and rutile). The compositions of ferromagnesian silicates and Zn-rich minerals, as well as the distribution members of the system Ca-Ti-Fe-S-O, are dictated by bulk-rock composition and by a variety of physicochemical conditions including T, P, forumla, forumla, and forumla. Sulfidation-oxidation haloes are most prominent where a large forumla-forumla gradient is apparent around an ore deposit. The presence of pyrrhotite, pyrite, and magnetite (high forumla-forumla conditions) in a metamorphosed orebody that is enveloped by graphite (low forumla conditions)-bearing country rocks ensures such a gradient. The proximity and abundance of graphite in part dictate the width of the sulfidation-oxidation halo to the orebody. Where graphite occurs adjacent to an orebody, the halo will be narrow but if graphite occurs tens to hundreds of meters from sulfide mineralization the likelihood of a wider halo is increased.

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Contents

Reviews in Economic Geology

Metamorphic and Metamorphogenic Ore Deposits

Frank M. Vokes
Frank M. Vokes
Volume Editor
Department of Geology and Mineral Resource Engineering Norwegian University of Science and Technology Trondheim, Norway
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Brian Marshall
Brian Marshall
Volume Editor
Department of Applied Geology University of Technology Sydney NSW 2007 Australia
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Paul G. Spry
Paul G. Spry
Volume Editor
Department of Geological and Atmospheric Sciences Iowa State University Ames, Iowa 50011 USA
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Society of Economic Geologists
Volume
11
ISBN electronic:
9781629490182
Publication date:
January 01, 1998

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