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Titolo:
Threading the eye of the needle: Lessons from the search for another Voisey's Bay in Labrador, Canada
Autore:
Kerr, A; Ryan, B;
Indirizzi:
Geol Survey Newfoundland & Labrador, Dept Mines & Energy, St Johns, NF A1B4J6, Canada Geol Survey Newfoundland & Labrador St Johns NF Canada A1B 4J6J6, Canada
Titolo Testata:
ECONOMIC GEOLOGY AND THE BULLETIN OF THE SOCIETY OF ECONOMIC GEOLOGISTS
fascicolo: 4, volume: 95, anno: 2000,
pagine: 725 - 748
SICI:
0361-0128(200006/07)95:4<725:TTEOTN>2.0.ZU;2-0
Fonte:
ISI
Lingua:
ENG
Soggetto:
CU-CO DEPOSIT; INTRUSION; NAIN; GEOCHRONOLOGY; COMPLEX; SULFIDE; GEOLOGY;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
57
Recensione:
Indirizzi per estratti:
Indirizzo: Kerr, A Geol Survey Newfoundland & Labrador, Dept Mines & Energy, POB 8700, St Johns, NF A1B 4J6, Canada Geol Survey Newfoundland & Labrador POB 8700St Johns NF Canada A1B 4J6
Citazione:
A. Kerr e B. Ryan, "Threading the eye of the needle: Lessons from the search for another Voisey's Bay in Labrador, Canada", ECON GEOL B, 95(4), 2000, pp. 725-748

Abstract

Magmatic sulfide mineralization is present in three of the four compositional groupings in the Mesoproterozoic Nain Plutonic Suite and in compositionally similar Paleoproterozoic rocks. Anorthosite-hosted mineralization appeals to be spatially linked to small gabbronorite bodies, where sulfide liquids separated from silicate magmas to variable degrees, depending on the wall-rock conditions. Sulfide metal contents are low (0.2-1.0% Ni) and the Ni/Cu ratio is variable, although sulfide Ni values remain fairly consistent within individual occurrences. Pyroxenite-hosted mineralization is essentially restricted to minor intrusions, and locally, has higher sulfide metal contents (up to 2% Ni) and less variable Ni/Cu. There are similarities between pyroxenite- and anorthosite-hosted mineralizations, and they may form part of a broad continuum. Ferrodiorite-hosted disseminated sulfide mineralization is associated with abundant iron oxides, and typically, has low amounts of Ni in the sulfide (<0.5%) and Ni/Cu <<1. Gabbro-troctolite-hosted mineralization contains the most variable and metal-enriched sulfides, containing from 1 to 7 percent Ni, and showing consistent Ni/Cu greater than or equal to 1. The best examples are associated with the Voisey's Bay intrusion (dominantly troctolite) and the Pants Lake intrusion (dominantly olivine gabbro). Significantly, these are the only Nain Plutonic Suite mafic intrusions that were emplaced into or in close proximity to sulfide-bearing paragneisses; exploration of gabbroic and troctolitic rocks within Archean orthogneisses has not yet revealed significant mineralization. The Pants Lake intrusion has intriguing geologic similarities to the Voisey's Bay intrusion and supports some aspects of genetic models for the latter. However it has lower sulfide Ni contents (around 2%) and relatively elevated Cu and Co, suggesting differences in the source magmas and/or conditions of sulfide segregation. The different styles of mineralization can be integrated with petrogenetic models For the Nain Plutonic Suite and similar plutonic suites. Anorthosite-hosted sulfide mineralization is interpreted to be derived from residual mafic magma that coalesced and migrated during ascent of semicrystalline anorthositic magmas, and ferrodiorite-hosted mineralization is interpreted to be derived from late Fe-enriched differentiates of deep-seated maficchambers. In both cases, the source magmas were fractionated, which limitstheir potential for metals. Crustal sulfur from paragneisses may have played a role in sulfide saturation in both cases but does not appear to be a critical ingredient. Some pyroxenite-hosted mineralization is akin to anorthosite-hosted types, but other examples may be linked to silicic contamination of more mafic magmas. Gabbro-troctolite-hosted mineralization is associated with mafic magmas that rose from deep crustal chambers prior to extensive fractionation; these were richer in Ni, Cu, and Co when they ascended into the upper crust. Sulfide-bearing paragneisses apparently played a critical role in inducing sulfide saturation in the magmas. The lessons from the search for nickel in Labrador are mostly familiar from other ar-eas; the regional metallogeny of the Nain Plutonic Suite underlines the critical rolesof a relatively unevolved host magma and crustal contamination processes, possibly involving addition of externally derived sulfur. It emphasizes theimportance of identifying and prioritizing these two key factors in the exploration of similar anorthosite-dominated plutonic suites elsewhere in theworld.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 23/10/20 alle ore 10:07:34