Summary:
Local Geology of the Murray Brook Deposit Area
The Murray Brook deposit is hosted by sedimentary rocks of the Charlotte Brook Member in the lower part of the Mount Brittain Formation. The upper felsic volcanic member of the Mount Brittain Formation hosts the Restigouche deposit, 10 km to the west of Murray Brook. The Mount Brittain Formation is considered to be equivalent of the Spruce Lake Formation, which hosts the Caribou mine, 10 km to the east.
Deposit Geology, Alteration and Mineralization
The Murray Brook deposit is elliptical in plan with a strike length of approximately 350 m and a maximum thickness of up to 100 m. The deposit dips approximately 40° to the northwest with a dip extent of >350 m. It plunges moderately to the north and appears to pinch out at depth and to the east. The geometry of the deposit was probably lens-shaped, but the up-dip portion of the body has been eroded and pre-Pleistocene weathering produced the gossan that was historically mined for silver and gold.
Structurally, the massive sulphides occupy the core of an F1/F2 synform (sheath fold) that is deformed by F3 folds, such that the hangingwall and footwall are part of the same unit. Although the Murray Brook deposit is a single body of massive sulphide with good continuity, in-fill drilling indicates that it consists of two connected lenses or lobes. The western, deeper lobe is richer in zinc and lead and the eastern, shallower lobe is richer in copper. Given that zoned volcanogenic massive sulphide (VMS) deposits tend consist of copper-rich lower zones and zinc-lead-rich upper zones, it appears possible that the Murray Brook deposit may be overturned.
The Murray Brook deposit is enclosed in a 1 to 3 m wide halo of chloritized sedimentary rocks containing disseminated pyrite. The hangingwall is moderately chloritic and locally intensely deformed. The footwall consists of fine grainedfelsic tuff and tuffaceous sedimentary rocks with moderate to strong chlorite and sericite alteration.
The Murray Brook deposit sulphides are massive to semi-massive, locally banded, and pyrite-rich. The sulphides are mainly fine-grained, massive, weakly laminated pyrite with disseminated and banded sphalerite, chalcopyrite, and galena, and minor tetrahedrite, covellite, marcasite and arsenopyrite.
Deposit Classification
The Murray Brook sulphide mineralization is classified as a volcanogenic massive sulphide (VMS) deposit hosted in sedimentary rocks. VMS deposits are well-studied and documented, and are a major global source of zinc, lead, copper, silver, gold, and other metals (Galley, 2007; Franklin, 2007; Shanks et al., 2009). Although VMS deposits tend to be hosted volcanic rocks, some of those in the Bathurst mining camp are hosted in sedimentary rocks proximal to felsic volcanic-sedimentary interfaces (Franklin et al., 1981). However, at Murray Brook and elsewhere in the Bathurst mining camp, the original depositional and stratigraphic relationships are obscured by the overprinting effects of postdepositional metamorphism and polyphase deformation.