DESCRIPTIVE MODEL OF SYNOROGENIC-SYNVOLCANIC Ni-Cu

MODEL 7a

By Norman J Page

APPROXIMATE SYNONYMS Gabbroid class (Ross and Travis, 1981), gabbroid associated (Marston and others, 1981).

DESCRIPTION Massive lenses, matrix and disseminated sulfide in small to medium sized gabbroic intrusions in greenstone belts.

GEOLOGICAL ENVIRONMENT

Rock Types Norite, gabbro-norite, pyroxenite, peridotite, troctolite, and anorthosite forming layered or composite igneous complexes.

Textures Phase and cryptic layering sometimes present, rocks usually cumulates.

Age Range Archean to Tertiary, predominantly Archean and Proterozoic.

Depositional Environment Intruded synvolcanically or during orogenic development of a metamorphic terrane containing volcanic and sedimentary rocks.

Tectonic Setting(s) Metamorphic belts, greenstone belts, mobile belts.

Associated Deposit Types Komatiitic Ni-Cu, dunitic Ni-Cu, talc-carbonate Ni-Au (no model available).

DEPOSIT DESCRIPTION

Mineralogy Pyrrhotite + pentlandite + chalcopyrite ± pyrite ± Ti-magnetite ± Cr-magnetite ± graphite--by-product Co and PGE.

Texture/Structure Predominantly disseminated sulfides; commonly highly deformed and metamorphosed so primary textures and mineralogy have been altered. Deformation about the same age as the deposit.

Ore Control Sulfides commonly are in the more ultramafic parts of the complex and near the basal contacts of the intrusion.

Weathering Lateritic.

Geochemical Signature Ni, Cu, Co, PGE.

EXAMPLES

Sally Malay, AUWA (Thornett, 1981)

Rana, NRWY (Boyd and Mathiesen, 1979)

Moxie pluton, USMA (Thompson and Naldrett, 1984)