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TitlePetrology and economic geology of the Dumont Sill: an archean intrusion of komatiitic affinity in northwestern Quebec
AuthorDuke, J M
SourceGeological Survey of Canada, Economic Geology Report 35, 1986, 56 pages, (Open Access)
PublisherGeological Survey of Canada
Mediapaper; on-line; digital
File formatpdf
NTS31M; 31N; 31O; 31P/03; 31P/04; 31P/05; 31P/06; 31P/11; 31P/12; 31P/13; 31P/14; 32A/03; 32A/04; 32A/05; 32A/06; 32A/11; 32A/12; 32A/13; 32A/14; 32B; 32C; 32D; 32E; 32F; 32G; 32H/03; 32H/04; 32H/05; 32H/06; 32H/11; 32H/12; 32H/13; 32H/14; 32I/03; 32I/04; 32I/05; 32I/06; 32I/11; 32I/12; 32I/13; 32I/14; 32J; 32K; 32L; 41O/01; 41O/02; 41O/07; 41O/08; 41O/09; 41O/10; 41O/15; 41O/16; 41P; 42A; 42B/01; 42B/02; 42B/07; 42B/08; 42B/09; 42B/10; 42B/15; 42B/16; 42G/01; 42G/02; 42G/07; 42G/08; 42G/09; 42G/10; 42G/15; 42G/16; 42H; 42I; 42J/01; 42J/02; 42J/07; 42J/08; 42J/09; 42J/10; 42J/15; 42J/16
AreaDumont Area
Lat/Long WENS-83.0000 -73.0000 51.0000 47.0000
Subjectseconomic geology; igneous and metamorphic petrology; sills; intrusive rocks; komatiites; ultramafic rocks; petrogenesis; nickel; sulphides; mineralization; lavas; peridotites; dunites; mafic intrusive rocks; archean; Dumont Sill; Abitibi Belt; Precambrian
Illustrationslocation maps; geological sketch maps; cross-sections; photomicrographs
Released1986 06 01; 2016 03 11
AbstractThe komatiiti c, synvolcanic Dumont Sill occurs within a sequence of iron-rich tholeiite lavas in the Abitibi greenstone belt. Its Ultramafic Zone comprises the Lower Peridotite Subzone, an olivine+chromite cumulate, the Dunite Subzone, an olivine ±sulphide cumulate, and the Upper Peridotite Subzone, an olivine+chromite cumulate. The overlying Mafic Zone comprises the Clinopyroxenite Subzone, a clinopyroxene cumulate, the Gabbro Subzone, a clinopyroxene+plagioclase cumulate, and the Quartz Gabbro which includes plagioclase + pyroxene cumulates as well as noncumulate gabbros. The parent magma was a peridotitic komatii te liquid (27 .5% MgO) that carried 12.5% olivine crystals in suspension. The Lower Peridotite formed by the settling and accumulation of these intratelluric phenocrysts whereas the overlying cumulates accumulated by a bottom crystallization process. Olivine+sulphide cumulate layers occur in the Dunite and formed by the accumulation of olivine and molten sulphide in their "cotectic" proportions. Sulphide saturation occurred when fractionated, sulphur-enriched intercumulus liquid was expelled upward by filterpressing of the partially molten Lower Peridotite and mixed with less evolved liquid at the floor of the magma chamber. The intrusion is pervasively altered with the development of lizardite+brucite+magnetite+diopside+chlorite in the Ultramafic Zone and actinolite+epidote+chlorite assemblages in the Mafic Zone. The secondary textures and assemblages are indicative of nonequilibrium, retrograde, low-temperature alteration which probably resulted from an influx of water during initial cooling of the sill.