Electron Microprobe Analysis of Sudbury Breccia from the Creighton and Coleman Mines, Sudbury Ontario: Constraints on the Extent of Hydrothermal Modification of Magmatic Footwall Ni-Cu-PGE Sulphide Mineralisation.
Jonathan O'Callaghan1, Gordon R Osinski
2, Robert Linnen
2 and Peter C Lightfoot
3, (1)University of Western Ontario, Department of Earth Sciences, London, ON, Canada, (2)University of Western Ontario, Earth Sciences, London, ON, Canada, (3)Vale, Sudbury, ON, Canada
Contact First Author: Jonathan O'Callaghan; jocalla@uwo.ca
English Abstract:
The Sudbury Igneous Complex (SIC) represents the remains of a ~200-km diameter impact crater, formed 1.85 billion years ago. Ore deposits associated with the impact structure can be subdivided into contact, footwall and offset types, and represent the end products of magmatic and hydrothermal processes. Footwall Ni-Cu-PGE deposits are hosted within zones of Sudbury breccias (pseudotachylitic), near to contact ore deposits at the margin of the SIC. Our study focuses on the application of ICP-MS and electron microprobe analyses of a suite of Sudbury breccia samples collected proximal to active mines in the North and South Ranges of the Sudbury Basin. We investigate subtle geochemical variations to mineralogy in barren and mineralised breccia matrix from different lithologies, and use this information to constrain the relative roles of magmatic and hydrothermal processes in the modification of primary Sudbury breccia and better understand the footwall ore deposits.
Our research has identified ilmenite-magnetite with titanite rims within breccia <10cm from footwall mineralisation in the McCreedy East 153 orebody at Coleman Mine. This assemblage is consistent with both high ƒO2 and high ƒH2O conditions. Samples from near the footwall orebodies at Creighton Mine contain heterogenous titanite that may be associated with later metamorphic alteration. In Sudbury breccia samples from Creighton mine, we also observe evidence of partial assimilation of host granite in hand-specimen and have identified two species of titanite, one showing Al/Fe substitution indicative of the presence of F-OH at the time of formation, and a second low Ti, low Al/Fe variety that may have been derived from the host granite. For the first time we also report chlorine zonation in amphibole at Creighton mine, similar to zonation features reported in the Fraser mine in the North Ranges.
