Effects of greenschist-facies metamorphism and related deformation on the Mobrun massive sulfide deposit, Qu�bec, Canada

Abstract

Abstract. The Mobrun Zn-Cu-Ag-Au deposit in the Noranda mining camp is hosted by Archean mafic and felsic submarine volcanic rocks. The deposit comprises three massive sulfide complexes: the Main and Satellite Lenses near surface, and the 1100 orebody at depth. The rocks have been subjected to lower greenschist-facies metamorphism and related deformation, which resulted in changes in ore textures, development of shear zones and veins systems, remobilization of gold, and formation of a new mineral (electrum) within the orebodies. Both mechanical and chemical processes operated to produce secondary textures and structures resulting from brittle deformation, ductile deformation, and annealing. The specific deformation mechanisms include brittle failure and cataclastic flow, dislocation glide, dislocation creep and solution-precipitation creep. The Main and Satellite Lenses are characterized by excellent preservation of primary sulfides deposited from and reworked by synvolcanic hydrothermal fluids. These orebodies were affected to a limited degree by mechanical processes of deformation. In contrast, the 1100 orebody is characterized by a higher degree of development of textures and structures related to metamorphism and deformation, especially those formed by chemical processes. The differences may be due to the greater depth of the 1100 orebody relative to the other lenses, as regional metamorphic isograds are subhorizontal, and more extensive interaction between metamorphic fluids and the 1100 Lens.Deformation experiments on natural polycrystalline sulfides have provided information on their mechanisms of deformation. Under greenschist-facies metamorphic conditions, pyrite deforms exclusively by cataclasis (Atkinson 1975;Cox et al. 1981). In contrast; chalcopyrite and * Present address: Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada sphalerite deform ductilely, by intragranular (dislocation) sliding and deformation twinning (Clark and Kelly 1973;Kelly and Clark 1975;Roscoe 1975). Pyrrhotite, which undergoes brittle deformation at low temperature and pressure, deforms ductilely by twin-gliding at temperatures above 250~ (Clark and Kelly 1973). Interpretation of deformation textures may be made difficult by the fact that evidence of ductile deformation in sulfides may be obliterated by subsequent static (postdeformational) recrystallization or thermal annealing. This is especially common in pyrrhotite.Examining the effects of deformation on monominerallic sulfide aggregates is useful, as it provides information about the relative importance of diffusion, slip, and intergranular deformation (Poirier 1985). However, the behaviour of individual sulfide minerals during metamorphism and related deformation of massive sulfide deposits may vary greatly, depending on temperature, strain rate, confining pressure, fluid pressure, differential stress, permeability within the zone of deformation, and the nature of adjacent or matrix-forming sulfides (Ashby and Verrall 1973;Kelly an...

Metamorphic textures and geochemistry of the Cyprus-type massive sulfide lenses at Zurabad, Khoy, Iran

“…Some lenses have textures of primary deposition and sedimentary reworking of sulfides. Similar preserved primary sulfide textures have been reported in greenschist to lower amphibolite facies metamorphism at Matagami, Canada (Aftabi, 1980;Aftabi, 1989;MacLean and Aftabi, 1982;MacGeehan et al, 1981;MacLean, 1984), and at Noranda, Canada (Liaghat et al, 1993;Larocque and Hodgson, 1995). The rounded detrital grain of pyrite ( Fig.…”

Mineralogy and mineral chemistry of the ABM replacement-style volcanogenic massive sulfide deposit, Finlayson Lake district, Yukon, Canada

“…In many ancient deposits, however, distinguishing textural features of emplacement origin and zone refining are commonly obscured due to post-VMS overprinting, metamorphism, and deformation (Lafrance et al 2020 ). This creates a unique challenge in VMS deposit research: recognition of primary exhalative- and replacement-related textures versus those imposed by subsequent post-VMS formation events (e.g., Craig and Vokes 1992 ; Larocque and Hodgson 1995 ; Lafrance et al 2020 ).…”

“…Past studies have been successful in identifying replacement-style VMS mineralization in the ancient record, including documenting the mineralizing fluid evolution, metal sources, and the impact of metamorphic and structural overprinting (Larocque and Hodgson 1995 ; Genna et al 2014 ; Brueckner et al 2016 ; Vikentyev et al 2017 ). However, the effects of metamorphism on VMS mineralization, even at low metamorphic grades, have not been yet fully resolved.…”