Nickel sulphide mineralization associated with Archean komatiites
- Authors: Lane, Monica Leonie
- Date: 1992
- Subjects: Nickel sulfide , Geology, Stratigraphic -- Archaean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4982 , http://hdl.handle.net/10962/d1005594 , Nickel sulfide , Geology, Stratigraphic -- Archaean
- Description: The distribution of Archean Nickel sulphide deposits reflects tectonic controls operating during the evolution of the granitoid greenstone terrains. Important deposits of komatiitic-affinity are concentrated within, and adjacent to, younger (∼2.7 Ga), rift-related greenstone belts (e.g. Canada, Western Australia and Zimababwe). Two important classes of Archean Nickel sulphide deposits exist, formerly known as "Dunitic" and "Peridotitic", these are now referred to as Group I and Group II deposits, based on their characteristic structure and composition. Mineralization varies from massive and matrix to disseminated, and is nearly always concentrated at the base of the host unit. Primary ores have a relatively simple mineralogy, dominated by pyrrhotite-pentlandite-pyrite, and to a lesser degree millerite. Metamorphic grades tend to range from prehnite-pumpellyite facies through to lower and upper amphibolite facies. Genesis of Group I and II deposits is explained by the eruption of komatiites into rift-phase greenstone belts, as channelized flows, which assimilated variable amounts of footwall rocks during emplacement. Sulphide saturation was dependent on the mode of emplacement and, the amount of sulphidic sediments that became assimilated prior to crystallization. This possibly accounts for variations in ore tenor. The Six Mile Deposit (SMD) in Western Australia, is an adcumulate body of the Group IIB-type, exhibiting disseminated mineralization. The ore has been "upgraded" due to hydration and serpentinization. A profound weathering sequence exists, which was subsequently utilized during initial exploration. Exploration techniques has been focused on Western Australia, as it is here that the most innovative ideas have emerged.
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- Date Issued: 1992
Economic geology of sulphide nickel deposits
- Authors: Harrison, P A
- Date: 1983
- Subjects: Nickel sulfide , Ore deposits , Geology, Economic , Silicate minerals , Geochemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5022 , http://hdl.handle.net/10962/d1006349
- Description: From Chapter 1: It has been a long standing belief that many nickel sulphide ores are derivatives of magmatic processes in ultramafic and mafic rocks, and that they segregate from these magmas as immiscible sulphide droplets which are then concentrated into an orebody by gravitational settling either during intrusion or extrusion, or during the early stages of crystallization of the magma (Naldrett, 1981). Some geologists however, have suggested alternative mechanisms to explain the concentration of nickeliferous sulphides in the mafic and ultramafic hosts. These include hydrothermal replacement (Fleet, 1977), exhalative volcanic processes (Lusk, 1976), or major metamorphic upgrading of low grade, initially magmatic deposits (Barrett et al., 1977). It is not the purpose of this study to verify or disprove these hypotheses, but in so far as the initial concentration of sulphides in most deposits is concerned, these effects are relatively unimportant (Naldrett, 1981). The nickel sulphide ores associated with these mafic and ultramafic host rocks, invariably consist of nickeliferous pyrrhotite as the dominant phase, together with lesser, but variable, amounts of magnetite, pentlandite, chalcopyrite, cubanite, and platinum group elements (Reynolds, 1982).
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- Date Issued: 1983