Summary:
Mineralization
Buchans Area
Mineralization in the Buchans area is associated with the three main genetically related mineral deposit types: 1) massive in situ sulphide; 2) transported sulphide clasts; and 3) stockwork and stringer sulphides.
The Lucky Strike and Oriental #1 deposits are the best-known examples of the in situ sulphide style of mineralization, contain the highest metal grades mined in the Buchans area and occur on the Property (Thurlow and Swanson, 1981). Massive in situ sulphides exhibit various textures, but massive, finegrained, streaky texture is most common and occurs in aggregates of sphalerite, galena, barite and lesser chalcopyrite. Thurlow et al. (1975) reported presence of trace amounts of enargite, native silver and argentite, ruby silver and gold tellurides, in addition to native silver and gold in this style of mineralization. Minor sulphides also include tetrahedrite-tenantite, chalcocite and bornite. Pyrite forms a relatively minor part of the massive sulphide assemblage but is more common in association with stockwork sulphides (Thurlow and Swanson, 1981). The paragenetic sequence of mineral deposition is complex and includes resorption, fracturing and re-deposition. Pyrite appears to be the first mineral deposited and sphalerite, chalcopyrite and galena are thought be deposited at the same time. However, chalcopyrite is also seen as blebs, lamellae and veins (Strong, 1981).
Transported mineralization occurs as elongate, tabular accumulations of discrete fragments of high-grade sulphides (Thurlow and Swanson, 1981). These deposits reflect transport by density flows that were controlled by paleo-topographic lows that extended down slope from in situ sulphide zones. The MacLean, Rothermere, Clementine and Oriental #2 deposits are examples of transported sulphide styles of mineralization. Together with the massive style, they represent 98% of the production from Buchans deposits. The transported mineralization occurs as mechanically transported sulphide breccia lenses composed of sulphide bearing fragments derived from in situ sulphide zones (Thurlow and Swanson, 1981). These deposits potentially demonstrate transport of as much as 2 km from source areas. Sulphide fragments range from angular to sub-rounded and display streaky textures, with sphalerite, galena, chalcopyrite and barite being the main minerals. Unlike the in situ sulphide ore deposits, these deposits have no associated stockwork zone. Stockwork mineralization is typically associated spatially with in situ sulphide zones and the best example on the Property is the Lundberg Zone.
Mineralization is also found in association with high-grade clasts noted from drilling within the Buchans area and their source is not clearly understood. Clasts range in size from grains and pebbles to 30 cm boulders of high-grade sulphide mineralization. The clasts contain galena, sphalerite, pyrite, chalcopyrite and gold and silver and are similar in metal grades to the in situ Buchans ores. They occur in polylithic conglomerates within the same stratigraphic horizon as the in situ ore but also at distances of up to 6.7 km away from any known in situ ore body (Thurlow and Swanson, 1981).
Lundberg and Engine House Zones
The Lundberg Zone sits below the former Lucky Strike orebody and consists of sulphide veins and veinlets plus disseminated sulphide mineralization predominantly hosted by strongly altered felsic to intermediate volcanics and to a lesser extent footwall mafic volcanics correlated with the Ski Hill Formation (Moore et al., 2023). The stockwork mineralization comes to surface on the eastern edge of the zone and forms an elongate, wedge-shaped body that is 250 m deep on the western end. The highest concentration of sulphide mineralization lies in close proximity to the Lucky Strike massive sulphide zone and mineralization is more diffuse away from the zone. Unlike the in situ sulphides, fine- to coarse-grained euhedral pyrite is the dominate sulphide and occurs with varying amounts of chalcopyrite, sphalerite, galena and barite (Thurlow and Swanson, 1981). Current drilling has defined the Lundberg Zone stockwork to measure approximately 800 m in length, 400 m in width, and between a few metres to over 250 m in true thickness.
A second zone of stockwork mineralization is associated with the Engine House Zone, located immediately south of the Lucky Strike deposit, and this zone has a higher proportion of chalcopyrite. This stockwork mineralization comes to surface in the eastern edge of the zone and forms a tabular, sheet-like body that occurs at a depth of 125 m below surface at its western end. Current drilling has defined the Engine House Zone stockwork as measuring 300 m in length, 200 m in width and between a few metres and over 30 m in true thickness.
Deposit Type
The Buchans area deposits and showings are classified as being of VMS association, primarily comprised of base-metal sulphides and barite and show strong similarities to the Kuroko style deposits of Japan (Thurlow, 1981).
The Buchans deposits include three distinct but genetically related deposit types, and occur as in situ sulphides, mechanically transported sulphides, and stockwork sulphides (Thurlow and Swanson, 1981). The high-grade in situ and transported styles were the focus of historic mining in the area and the stockwork style, associated with lower grade sulphide mineralization at the Lundberg Deposit, has been the focus of exploration programs by BMC.
The zoned massive sulphides of the in situ deposits are interpreted to have formed in close proximity to volcanic discharge zones. They consist of thick lenses of high-grade sulphide and form the largest deposits in the Buchans area. The in situ sulphides are overlain by a cap of massive barite that is characteristic of the historically mined Buchans deposits and may provide an important lithogeochemical exploration tool. The felsic volcanics also host lower grade, base metal enriched sulphide systems of hydrothermal alteration that manifest as stockwork mineralization (Thurlow et al., 1975).
The largest known concentration of stockwork and disseminated mineralization is the Lundberg Zone that underlies the Lucky Strike deposit. Stockwork mineralization consists of a network of sulphide veins and veinlets that cut strongly altered and sulphide-impregnated hosts rocks. The stockwork mineralization has a higher ratio of pyrite to base metal sulphides than the in situ sulphide zones and is typified by presence of fine- to coarse-grained pyrite with lesser amounts of chalcopyrite, sphalerite, galena and barite. This mineralization occurs within felsic volcanic rocks of the Buchans River Formation below the Lucky Strike deposit and extends well into the underlying Ski Hill Formation, where sulphide-bearing stockwork mineralization occurs at tens to hundreds of metres below the deposit (Jambor, 1987). In that instance, mineralization thins and feathers out into lower grade, semi-conformable zones of alteration (Moore, pers. com., 2013).
Transported sulphide deposits are coarser grained and are interpreted to be debris flows originating from the in situ deposits that have accumulated in paleo-channels and other downslope regions. The transported sulphide deposits at Buchans are elongate, tabular accumulations of high-grade massive sulphide fragments and lithic fragments that most commonly occur within paleo-topographic channels. Six of these channels, containing at least seven economic and sub-economic sulphide deposits have been recognized in the Buchans area including the former Two-Level/North orebody (Lucky Strike), Rothermere, Oriental #2, MacLean-MacLean Extension orebodies, as well as the undeveloped Clementine and Sandfill prospects.