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Cu-Ni-PGE mineralization in the South Filson Creek area, South Kawishiwi Intrusion, Duluth Complex; mineralization styles and magmatic and hydrothermal processes

Benedek Gal, Ferenc Molnar and Dean M. Peterson
Cu-Ni-PGE mineralization in the South Filson Creek area, South Kawishiwi Intrusion, Duluth Complex; mineralization styles and magmatic and hydrothermal processes
Economic Geology and the Bulletin of the Society of Economic Geologists (May 2011) 106 (3): 481-509

Abstract

The South Filson Creek mineralization occurs above the basal units of the South Kawishiwi intrusion and represents an uncommon geologic setting of Cu-Ni-platinum-group element (PGE) mineralization within the Duluth Complex. Unlike other mineralization of economic interest in the basal heterogeneous troctolite units along the lower contact, it is located at an approximate stratigraphic height of 1,000 m above the contact with the footwall granitoids in the usually unmineralized homogeneous troctolite unit. Magmatic sulfide mineralization forms disseminated fine-grained patches and pockets in an area of approximately 1/2 km (super 2) of homogeneous troctolitic rocks in the northeastern part of the South Kawishiwi intrusion. Pyrrhotite, chalcopyrite, pentlandite, and cubanite are the main sulfide minerals with subordinate amounts of other copper-bearing phases (bornite, covellite, talnakhite). Cu/Pd ratios for unaltered mineralization indicate that sulfides were formed from multiple injections of magma that segregated sulfides with different R factors or having different initial compositions. Variation in the halogen contents of apatite from pegmatoids within troctolitic rocks revealed that a fluid has segregated from the crystallizing melt into which fluid Cl and rare earth elements partitioned. Amphibole, chlorite, sericite, prehnite, pumpellyite, and carbonate are associated with alteration along brittle structures and isolated patches in the area. The hydrothermal fluid-rock interaction has affected the composition of primary magmatic sulfide mineralization and is also responsible for mineralization in the anorthositic hanging wall of the South Kawishiwi intrusion. Hydrothermal alteration resulted in a slight Pd depletion in magmatic sulfide mineralization, which might indicate remobilization of precious metals to an unknown location. The hanging-wall mineralization is characterized by relative Cu enrichment in comparison to the magmatic sulfide mineralization with no PGE enrichment. Partial remobilization of platinum group elements (PGE) has also occurred as a result of a separate alteration event, on the evidence that platinum group minerals (PGM) are also associated with serpentinization of olivine and Ca enrichment of plagioclase along grain boundaries with sulfides. This alteration was probably effective on a very local scale.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 106
Serial Issue: 3
Title: Cu-Ni-PGE mineralization in the South Filson Creek area, South Kawishiwi Intrusion, Duluth Complex; mineralization styles and magmatic and hydrothermal processes
Affiliation: Eotvos Lorand University, Department of Mineralogy, Budapest, Hungary
Pages: 481-509
Published: 201105
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 61
Accession Number: 2011-050390
Categories: Economic geology, geology of ore depositsIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 7 tables, geol. sketch maps
Secondary Affiliation: University of Minnesota-Duluth, USA, United States
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: 201128
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