GEOSCAN, résultats de la recherche


TitreHigh-grade sperrylite zone reveals primitive source in the Sudbury impact structure
AuteurAmes, D E; Hanley, J; Tuba, G; Jackson, S
SourceMineralogical Magazine vol. 77, no. 5, 2013 p. 587
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140555
ÉditeurEuropean Association of Geochemistry
Mediapapier; numérique; en ligne
Lat/Long OENS -81.5000 -80.5000 46.7500 46.2500
Sujetscratères; cratères météoriques; brèches; épidote; quartz; petzite; galène; cassitérite; rapports strontium-strontium
ProgrammeÉtude des gîtes magmatiques de Ni-Cu-EPG, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
Earth's largest impact craters had transient craters that penetrated 30 -40 km depth and collapsed to form ~200 km impact craters with perturbations of the Moho [1]. The Sudbury impact structure is the eroded remnant of a larger 150-200 km multi-ring crater and uniquely revealing at present-day surface the crustal impact structures in the crater floor below the igneous complex [2].
The Paleoproterozoic Broken Hammer Cu-Ni-PGE deposit, is hosted by impact-induced pseudotachylitic breccias in the crater floor within Neoarchean gneiss and granites. A high-grade PGE-only zone is composed of major coarse epidote-quartz, minor chlorite-sperrylite-merenskyite, with sperrylite crystals up to 4 mm, and trace michenerite. Isolated sperrylite grains in epidote or quartz contain inclusions of gold, petzite, galena and aleskite, whereas complex intergrowths of Pd-, Bi-and Ag-tellurides are associated with specular hematite and cassiterite, suggesting high fO2 conditions. in situ trace element analyses of euhedral epidote and chlorite precipitated long growth zones in hydrothermal quartz reveal increasing Mg, Zn, Fe and Ni towards the rims. Late-stage Cpy-millerite penetrates the core of extensional epidote-quartz-sperrylite veins.
Early formed epidote that hosts coarse sperrylite analyzed by TIMS yielded a narrow range of low age corrected 86 Sr/86Srratios from 0.705948 to 0.706457 with a primitive non-radiogenic source supporting a mantle origin [3,4]. This implies that initial impact destabilized the crust -mantle boundary resulting in rapid fluid-gas release and transport of precious metals from the mantle along deep-seated faults to
the footwall environment of the SIC.
In situ LA-MC-ICP-MS Sr isotope analysis of epidote and calcite in early syn-PGE ore, later Ni-Cu and Cu-PGE vein ores and post-mineralization phases will be used to trace the evolution of fluids in the Sudbury crater.