METAMORPHISM AND SUPERGENE ALTERATION OF
Four principal types of sulfide ore are recognized at the Thiegry'mine, located in the Uchi volcanic belt (Superior Province), northwestern Ontario. These are: disseminated Cu-Ni-Fe sulfides, breccia ore, mylonite ore and bornite ore. The sulfides are interpreted to be of magmatic origin, but modified by strong shearing to produce mylonite and breccia ore. The bornite ore represents enrichment in Cu of blocks of amphibolite schist in the mylonite. Supergene alteration removed iron from the iron-nickel sulfides to produce iron oxides and sulfides, especially violarite enriched in cobalt and nickel. Violarite (Ni-Fe-rich) appears to coexist with pentlandite where it formed from pentlandite. Violarite (Ni-Co-rich) generated as the result of metamorphism does not coedst with pentlandite. This strongly suggests that cobalt plays a major role in defining the lowtemperature stability fields and explains the two conflicting interpretations of assemblages involving violarite in the system Fe-Ni-S. The modification, during deformation and metamorphism, of primary magmatic sulfides of subeconomic grade to an ore deposit at Thierry and other areas implies that an ulfiamafic-gabbroic body in an intensely metamorphosed and deformed terrane might offer a better target for er<ploration than ore in lower-grade rocks. Furthermore, the enrichment of platinum-group elements @GE) in mylonite and bornite ores at Thierry indicates that mobilization into shear zones could produce PGE deposits.
The geology of the Thierry Cu-Ni mine, northwestern Ontario
The Thierry Cu-Ni mine is located in the Uchi Volcanic Belt, Superior Structural Province, 450 kilometres northwest of Thunder Bay, Ontario, near the town of Pickle Lake. The regional geology consists of an east-west-trending belt of Archean metavolcanic rocks, predominantly pilowed mafic flows with minor felsic volcanic and metasedimentary rocks. These have been intruded by granitoid stocks and mafic to ultramafic rocks that range in composition from gabbro to peridotite. Four main types of Cu-Ni sulfides are recogflized: breccia ore, mylonite ore, bornite ore and disseminated sulfides. The regional metamorphic grade is middle amphibolite facies; mineral and chemical data suggest that temperature and pressure reached approximately 600oC and 5.5 kbar. These rocks have undergone late dynarnic metamorphism, which produced a shear zone and a system of conjugate faults. Where mafic and ultramafic rocks were sheared, a mylonite was produced consisting of fragrnents of hornblende in a matrix of chlorite and biotite. Chemical alteration is associated with the dynamic metamorphism; whole-rock data indicate that Ca, Na and Si have been removed from the mylonite, and K was added. The sulfides are of magmatic origin, but their distribution within the mine was modified by dynamic metamorphism. Both mylonite and breccia ores were emplaced during the mylonitic event. The bornite ore was formed by the enrichment in copper of amphibolite-schist blocks in the mylonite.
Solutions, Minerals and Equilibria
Fluid-mineral Equilibria in Hydrothermal SystemsOn the Origin of the Black Pyritic Slates from the Iron Mineral Deposits of Iron River District of MichiganPetrogenesis of Metamorphic RocksSolutions, Minerals, and EquilibriaHandbook of Soil Sciences (Two Volume Set)Contact MetamorphismGeochemistry and Mineral Formation in the Earth SurfaceGeochemistry, Groundwater and PollutionThermodynamic Modeling of Geologic MaterialsWater ResearchMineral ExplorationHydrochemical Balances of Freshwater SystemsMontmorillonite Genesis in Soils as Influenced by the Activities of Monosilicic Acid and Various Cations in the Matrix SolutionWater-resources InvestigationsThermodynamics in Earth and Planetary SciencesSolution ChemistryCourses and DegreesMineral Equilibria at Low Temperature and PressureAqueous Environmental GeochemistrySoil Solutions, Minerals, and EquilibriaProceedings of the Fourth International Symposium on Electrochemistry in Mineral and Metal ProcessingThermodynamics of Minerals and MeltsSulfide Mineralogy and GeochemistryIncomplete SolutionPhysical GeographyPHREEQEStockholm Contributions in GeologyPetrogenesis of Metamorphic RocksSolutions, Minerals, and EquilibriaEquilibres des minéraux et de leurs solutions aqueusesPhosphate MineralsSolutions, Minerals, and EquilibriaBulletin de MinéralogieEquilibrium Activity DiagramsThe American Journal of ScienceCharacterization of Metamorphism through Mineral EquilibriaSOLUTIONS, MINERALS & EQUILIBRIA.Composition of Holocene Sands of Mull and Adjacent Offshore AreasGeochemistry InternationalOxidation of Pyrite in Alkaline Solutions and Heterogeneous Equilibria of Sulfurand Arseniccontaining Minerals in Cyanide Solutions This book offers thorough, up-to-date coverage of controls on the chemical quality of surface and