Summary:
The Bul River deposit has been described as a Churchill-type vein copper-silver deposit (Lefebure, 1996). The deposit type displays characteristics of relatively low tonnage (typically range from 10Kt to 1Mt) but high grade (typically range from 1% to 4% Cu). Frequently occurring in Proterozoic-age extensional sedimentary basins, Churchill-type deposits are associated with rifting can comprise single vein to complicated vein systems that vary from centimetres to tens of metres in width, and can extend hundreds of metres along strike and down dip. Commonly hosted in clastic meta-sediments, veins and vein systems are often spatially associated with mafic dykes and sills. The veins are generally associated with major faults related to crustal extension that controls the ascent of hydrothermal fluids to favorable sites for metal deposition. Fluids are believed to be derived from those mafic intrusives that are associated with the vein systems. (Snowden 2013).
Mineralization in Churchill-type deposits is predominantly chalcopyrite, pyrite, and chalcocite with subordinate pyrrhotite, galena, bornite, tetrahedrite, argentite, and covellite and is generally younger than the host lithology.
The GBRM deposit is hosted within poorly exposed graded turbidite beds of the middle Aldridge Formation of the Middle Proterozoic Purcell Supergroup. Interbedded quartzites, siltstones, and argillites make up a turbidite sequence whose bedding plane strikes approximately east-west and dips 20° to 30° to the north (Baldys, 2001). The host rocks of the deposit are a northward pinching series of anticlines and synclines (de Souza, 2000).
The GBRM mineralized zones comprise a vertical to sub-vertical network of sulphide-bearing quartz carbonate veins striking approximately east-west hosted in sheared and brecciated Aldridge Formation sediments. Mineralization consists of pyrite, pyrrhotite, and chalcopyrite with minor local galena, sphalerite, arsenopyrite, and cobaltite and traces of tetrahedrite and native gold. Sulphides range from massive, irregular bodies within the vein system to thin discontinuous veins, veinlets, and disseminations in the host rock (Höy et al., 2000). Gangue mineralogy of the veins is variable, with the eastern parts of the deposit consisting of quartz and siderite. The western part of the vein system is dominated by siderite (Baldys, 2001).