|Auteur||Taylor, B; Goutier, J; Mercier-Langevin, P; Ross, P S; Gibson, H; Hannington, M; Dion, C; Martin, L; Rigg, D; Dubé, B|
|Résumé||(disponible en anglais seulement)|
The nature and style of magmatic-centered and ore-forming hydrothermal activity varied in the Blake River Group (BRG) over the course of some 22 m.y. of
synvolcanic to syntectonic intrusive history. Associated styles of mineralization included Cu-Zn and Zn-Cu VMS deposits, Au-rich VMS deposits and veins, porphyrystyle deposits. Oxygen isotope mapping of the 'footprints' of the principal,
paleo-magmatic-hydrothermal systems in the BRG (based on several projects spanning a number of years, plus published studies; ca. 2140 whole-rock analyses), reveals a range of system size, style, isotopic systematics, and number of related stages.
All studied hydrothermal systems are marine in nature, but differences in system size and heat budget, longevity, tectonic setting, nature and timing of magmatism, depth and temperature between centres across the BRG are reflected by the isotopic
characteristics of each system. Intrusive centres and/or mining camps compared here include, from west to east in the BRG: the Clifford Stock, Monsabrais Pluton, Flavrian Pluton (FP), central Noranda camp, Powell Pluton, Horne-Quemont deposits,
Clericy Pluton, Mooshla Pluton, and Doyon-Bousquet-LaRonde (DBL) camp. Not all of these intrusions, or phases of these intrusions (e.g. Late leucotonalite, FP), supported large marine hydrothermal systems. The younger intrusive centres (e.g.
Monsabrais and Clifford) exhibit only weak hydrothermal activity and mineralization associated with single-stage systems. The FP and the central Noranda camp deposit-bearing volcanic wall rocks were tilted eastward during the regional deformation.
d18O mapping in this sector provides an oblique, cross-sectional view of the largest, and little deformed, hydrothermal footprint, which is a composite of the effects of at least four hydrothermal episodes. In contrast, strain has markedly shortened
the altered rocks in the DBL camp, and removed evidence for magma chamber(s) related to the wide-spread paleo-hydrothermal alteration and sources of the felsic flows. Synvolcanic faults played key roles in the development, organization, maintenance,
and longevity of hydrothermal systems; long-lived hydrothermal conduits are responsible for several VMS deposits in the central Noranda camp. Systematics evident from this multi-phase system, and evident on reduced scales in other, simpler systems
(e.g. Clericy), provide useful exploration guides. Hydrothermal activity associated with FP was contained within the Noranda cauldron; there is no mappable evidence for synchronous paleo-hydrothermal activity along larger, caldera-like structures.
Contrasting tectonic/ geographic settings are reflected by differing isotopic systematics: marked 18O depletion associated with deeper, multiple high-heat flow systems in the central Noranda camp to 18O enrichment in lower heat-flow, perhaps
shallower systems of the DBL camp.