Quantitative modelling of the segregation of magmatic sulphides: an exploration guide

Abstract The segregation of magmatic sulphides from mafic and ultramafic silicate magmas, in many circumstances, leaves the magma with a lower-than-normal Ni/MgO ratio, which is characteristic of both lavas erupted from the magma chamber and olivine crystallizing within it. Two end members of the segregation process are discussed; i) batch segregation and ii) fractional segregation.
In the former, the critical factor is the magma/sulphide ratio. Computer modelling suggests that where this ratio has been less than 1000, the magma will be recognizable as anomalously low in Ni, due to sulphide segregation, and thus a good target for exploration. In fractional segregation, the critical factors are the proportion of sulphide to silicate being segregated and the degree of fractionation.
Samples believed to represent the liquid portion of komatiitic lava flows from a series of unmineralized sequences in the Abitibi greenstone belt, Canada, Belingwe belt, Zimbabwe, and Barberton Mountain/and, South Africa coincide with the sulphide-free fractionation model. They are in marked contrast to samples from the ore-bearing districts of Kam-balda and Scotia, Western A ustralia in which distinct Ni depletion, corresponding to fractionation of olivine plus sulphide in a ratio of between 100 and 200:1 is recognizable. Ni-depleted olivines a/so mark the sulphide-bearing Dumont intrusion of the Abitibi belt.
The Moxie intrusion of northern Maine has distinctly Ni-depleted olivines, as does the nearby and petrologically related Katahdin body. In both of these intrusions, the composition of the olivine allows reasonable predictions to be made of the Ni tenors of sulphide showings within them. At Katahdin, the Ni depletion is so widespread that little hope is help out for the presence of economic concentrations of sulphide. At Moxie, the olivine compositions suggest that the best chance of economic sulphides lies in the southern lobe of the intrusion. Ni-depleted olivines also characterize certain rock units within intrusions of the Insizwa complex, Transkei, Southern Africa. Many millions of tonnes of Ni have apparently been removed by sulphides from these rock units, many more than are contained within the single mineralized occurrence so far identified at Waterfall Gorge.
Keywords: Mineral exploration, Quantitative modelling, Magmatic sulphides, Chalcophile elements, Batch equilibration, Fractional segregation
Full Access to Technical Paper
PDF version for $20.00
Search
Sort By:  Relevance
Showing results 1 - 5
Text
Summary: On February 15, 1984 Finance Minister Lalonde presented to Parliament a budget heavily flavoured with the current consultative mood of the Government. Notably absent from the budget was the typically long list of tax changes of immediate effect. Instead, the bulk of the budget papers consisted of a wide variety of white papers on significant topics that would have afar reaching impact on the future of all Canadians.This month, Tax Notes examines the highlights of Mr. Latonde's budget.
Publication: CIM Bulletin
Author(s): ROBERT B. PARSONS
Issue: 864
Volume: 77
Year: 1984
Text
Summary: In order to establish some links between the 22 specimens found on the site of Les Forges du St. Maurice, their slag inclusions have been analyzed by electron microprobe. Comparison between their contents of various specific oxides allowed us to segregate them into two major groups and even to isolate two sub-groups possibly characterized by some equilibrium between their oxides and/or the type of ores used.
In all probability, limestone coupled systematically with a soil rich in hydrated...
Publication: CIM Bulletin
Author(s): M. FISET, T. VO VAN, A. GALIBOIS
Keywords: Slags, Wrought iron, Bloomery process, Pig iron, Charcoal finery
Issue: 864
Volume: 77
Year: 1984
Text
Summary: The McClean uranium deposits are in northern Saskatchewan, 11 km west-northwest of the Rabbit Lake mine. Their average grade is 1.8% U3O8 and they contain 6,350 tonnes of uranium oxide in seven pods of variable grade and mineral assemblage. They are hosted by both basal Athabasca Group and the regolith developed on the underlying crystalline basement. The major mineral fades are: sulphide, arsenide, 'bleached', and hematite, with the important uranium minerals being coffinite, uraninite and...
Publication: CIM Bulletin
Author(s): R.H. WALLIS, N. SARACOGLU, J.J. BRUMMER
Keywords: Mineral exploration, Geology, McClean deposits, Uranium, Saskatchewan, Athabasca Group, Mineralization
Issue: 864
Volume: 77
Year: 1984
Text
Summary: Besshi-type Cu-Zn (-Ag-Au±Co) deposits are tabular, stratiform volcanogenic sulphide bodies which are usually associated with mafic volcanic rocks of oceanic or intra-plate geochemistry, but which can also be found locally with ultra-mafic volcanics or subvo/canic mafic intrusions. A thick sequence of continental/y-derived clastic sediment usually encloses both the mafic volcanics and the ore. Besshi-type deposits form subaqueously, in epicratonic rifting environments, more-or-less...
Publication: CIM Bulletin
Author(s): U.S. FOX
Keywords: Mineral exploration, Besshi-type deposits, Massive sulphides, Sanbagawa belt, Blue Ridge belt, Trondheim region, Outokumpu region, Mafic volcanics, Continentally-derived sediment, Lead isotopes, Epicratonic rift environment, Guaymas basin
Issue: 864
Volume: 77
Year: 1984
Text
Summary: Most of the Paleozoic section of the Williston Basin is a thick accumulation of numerous carbonate to evaporite, shallowing-upward, cyclic sequences. These sediments were deposited in broad epeiric seas, and the deposition of the evaporite fades marked the final stage of each cycle. Many of the sequences display a pervasive replacement dolomite in the uppermost portion of the carbonate units. This secondary dolomitization is, at least in part, an early diagenetic event, synchronous with...
Publication: CIM Bulletin
Author(s): ALF HARTLING
Keywords: Mineral exploration, Williston Basin, Hydrocarbon reservoirs, Dolomitization, Sedimentation, Oungre Zone, Red River 'C' Zone.
Issue: 864
Volume: 77
Year: 1984
Powered by Coveo Enterprise Search