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Ruthenium-chromium variation; a new lithogeochemical tool in the exploration for komatiite-hosted Ni-Cu-(PGE) deposits

M. L. Fiorentini, S. W. Beresford and M. E. Barley
Ruthenium-chromium variation; a new lithogeochemical tool in the exploration for komatiite-hosted Ni-Cu-(PGE) deposits
Economic Geology and the Bulletin of the Society of Economic Geologists (April 2008) 103 (2): 431-437

Abstract

We present a new lithogeochemical method to target prospective komatiites that may host Ni-Cu-(PGE) deposits. The new methodology is based on the geochemical properties of ruthenium (Ru) and chromium (Cr), elements that are immobile under most conditions; it relies on a restricted number of carefully selected representative samples and is applicable in highly altered terrains. Ruthenium is a platinum-group element (PGE) that exhibits contrasting geochemical behavior in sulfide-saturated and sulfide-undersaturated komatiites. Similarly to other PGEs, Ru shows highly chalcophile behavior in magmas that equilibrate with an immiscible sulfide phase. However, Ru is also compatible in chromite in sulfide-undersaturated systems. If we consider Cr concentration as an index of chromite abundance in chromite-saturated komatiites, we observe that Ru increases or decreases systematically with increasing Cr according to the sulfide saturation state of the magmatic system. In rocks that crystallized from sulfide-saturated melts, Ru contents decrease with increasing Cr. Conversely, in rocks that crystallized from sulfide-undersaturated melts, Ru contents increase with increasing Cr. As a result, on the basis of the Ru-Cr variation it is possible to discriminate whether a komatiite melt equilibrated with a sulfide liquid during crystallization. The strength of this method compared to previous PGE-based lithogeochemical techniques derives from combining the traditional use of the geochemical properties of a highly immobile and chalcophile element that records the ore-forming process (ruthenium) with the occurrence of a mechanically and chemically resistant mineral phase (chromite), which is generally preserved in highly altered komatiites.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 103
Serial Issue: 2
Title: Ruthenium-chromium variation; a new lithogeochemical tool in the exploration for komatiite-hosted Ni-Cu-(PGE) deposits
Affiliation: University of Western Australia, School of Earth and Geographical Sciences, Crawley, West. Aust., Australia
Pages: 431-437
Published: 200804
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 44
Accession Number: 2008-104094
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Annotation: A digital suppl. to this paper is available at http://www.geoscienceworld.org, or for members and subscribers on the SEG website http://www.segweb.org
Illustration Description: illus. incl. sketch map
S30°00'00" - S30°00'00", E118°00'00" - E118°00'00"
Secondary Affiliation: Monash University, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200836
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