The McDougall-Despina Fault Set, Noranda, Quebec: Evidence for Fault-Controlled Volcanism and Hydrothermal Fluid Flo

Exploration & Mining Geology, Vol. 4, No. 4, 1995

Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada, N6A 5B7, H.L. GIBSON, Mineral Exploration Research Centre, Laurentian University, Sudbury, Ontario, Canada, P3E 2C6, J.J. WATKINS P.O. Box 3127, Courtenay, British Columbia, Canada, V9N 5N4

The McDougall-Despina fault set in the Noranda district of northwestern Quebec de?nes the eastern margin of the Despina cauldron, nested within the district-scale Noranda cauldron. The faults are stratabound in that they displace stratigraphy of the cauldron ?ll, but do not offset the cauldron cover. The faults are occupied by dikes that acted as eruptive centers to volcanic members of the cauldron-?lling sequence. Measurable displacement across the McDougall-Despina fault set is greater than 750 m, and coincident with post-cauldron volcanism. Feeder dikes cross-cut each other and are typically depleted in Na2O and CaO, and enriched in MgO, K2O, Fe2O3 and MnO relative to fresh ?ows. Economic and subeconomic massive sul?de deposits occur adjacent to the McDougall-Despina fault set at different levels over a stratigraphic thickness of 3000 m. These include the Corbet deposit, the subeconomic D-68 Zone deposits, and the subeconomic stringer zones of South Rusty Hill and Bedford Hill. Numerous copper occurrences and abundant hydrothermal alteration occur in and immediately adjacent to the fault set. The McDougall, Despina, and adjacent, parallel, ancillary faults de?ne a synvolcanic fault set which controlled the location of magmatism, hydrothermal alteration and mineral deposition during the early evolution of the Noranda cauldron. Signi?cant sul?de mineral deposition commonly occurred in proximity to the intersection of the McDougall-Despina fault set with northeast-trending synvolcanic faults. Recognition of synvolcanic faults is therefore a major objective of exploration programs for volcanic-associated massive sul?de deposits.

Keywords: Fault-controlled Volcanism, Hydrothermal fluid flow, Stratisgraphy, synvolcanic faults.