Summary:
The Black Butte Copper Project contains two zones, the Johnny Lee Upper Copper Zone (UCZ) and the Johnny Lee Lower Copper Zone (LCZ). Both of these zones are characterized as being high-grade, flatlying and with relatively narrow widths. All deposits have anomalous Silver (Ag) and Cobalt (Co) mineralization. However Cu is the only economic product considered in the FS.
The majority of the Black Butte Project area is underlain by gentle to moderately southward-dipping rocks of the Belt Supergroup. The Belt Supergroup lithofacies are juxtaposed against gently south-dipping Cambrian sedimentary rocks along the VVFZ. To the north of the Project area, Belt Supergroup rocks are also exposed, below the basal Cambrian unconformity. Intermediate to mafic, Early Tertiary intrusive dykes and sills occur within the Belt Supergroup. Late Tertiary sedimentary lithofacies unconformably overlie all other units in the area.
Potentially economic Cu mineralization has been identified in the Newland Formation at the UCZ and the LCZ. The mineralization in both of these deposits is largely hosted by massive sulphide units referred to as the USZ and LSZ, respectively. Although not included in the MOP application, Cu mineralization also occurs at Lowry situated 3 km SE of the Johnny Lee deposit. Mineralization at Lowry is hosted by the LSZ and the MSZ. In order to discriminate between Johnny Lee and Lowry, the MSZ and LSZ at Lowry are herein referred to as Lowry Middle Sulphide Zone (LMSZ) and Lowry Lower Sulphide Zone (LLSZ). Mineralization at Lowry that occurs in these zones is referred to as the Lowry Middle Copper Zone (LMCZ) and Lowry Lower Copper Zone (LLCZ).
Johnny Lee Lower Copper Zone
The LCZ occurs at depths of 340 to 520 m below surface, strikes approximately EW and dips at 15° to 30° to the south. Mineralization in the LCZ is primarily hosted by the LSZ located in the FW of the VVFZ and HW of the Buttress Fault. The LSZ is overlain by a unit comprising interlayered shale and conglomerate and is underlain by a conglomerate unit. The LCZ deposit comprises three lenses of mineralization termed the East, Central, and West Lenses. These lenses are defined by the outer limit of >2.0% Cu mineralization which extend outside of the LSZ into the HW intercalated conglomerate and shale unit. Minor Cu mineralization also occurs in the conglomerate below the LSZ but does not exceed 2.0% Cu.
Johnny Lee Upper Copper Zone
The north-eastern corner of the UCZ is exposed on surface and the top of the mineralized zone extends to a depth of 210 m below surface. The high-grade portion of the UCZ (>1.2% Cu) is entirely encapsulated by the USZ although >0.25% Cu Halo mineralization extends into the shale that is located in the HW and FW of the USZ. The UCZ is gently folded by a W/NW plunging syncline-anticline pair such that strike is variable and dip ranges between 0° and 20°. With the exception of its extreme north-eastern corner, the UCZ is situated below the level of surficial oxidation. Acidic groundwater, preferentially focused along a layer parallel, brittle-ductile shear zone, resulted in localized supergene alteration of copper sulphides below the base of oxidation. The volume of supergene altered copper sulphide minerals along the shear zone is generally low, except at the junction of the shear zone with Fault 1.
Lowry Middle Copper Zone
The LMCZ is hosted by a succession of ferruginous sediment (massive sulphide and ferruginous shales) with interbedded conglomerate, carbonaceous shale and shale lithofacies. Three zones of >1.2% Cu mineralization occur in the LMCZ, termed LMCZ Vein 1 – LMCZ Vein 3. These mineralized zones dip to the south at 25 - 30°. The >1.2% Cu zones are surrounded by a zone of >0.25% Halo mineralization. The northern tip of the LMCZ occurs at 245 m below surface and the southern tip occurs at 755 m below surface. The LMCZ is situated below the depth of surficial oxidation. The LMCZ has plan view dimensions of 830 m (NS) by 280 m (EW). The maximum true thickness of the LMCZ is 45 m and it progressively reduces in width and pinches out to the north, south, east, and west.
Mineralization in the LMCZ occurs in both massive sulphide and the interlayered clastic sediment. Pyrite + Marcasite concentrations of typical mineralized intersections range from 9.1 – 45.2% and gangue mineral contact ranges from 38.7 – 76.0% (McArthur, 2019). Copper sulphide mineralization is predominantly chalcopyrite (8.3 – 17.0% in typical mineralized intersections) with minor tennantite (0.01 – 0.23%) observed in 30% of mineralogical samples studied to date (McArthur, 2019). The amount of primitive pyrite in the LMCZ ranges from 10.4 – 60.0% (average 49.1%) which is lower than that of the northern part of the UCZ (average 62.7%) indicating that the amount of recrystallization in the LMCZ is higher than that of the northern part of the UCZ.
Lowry Lower Copper Zone
The LLCZ occurs in the FW of the VVFZ and both the host and mineralization is truncated in the SE by the Volcano Valley FW Fault. The LLCZ is hosted by a succession of ferruginous sediment (massive sulphide and ferruginous shales) with interbedded shale and conglomerate lithofacies. Two bedding-sub-parallel zones of >1.2% Cu mineralization occur within the LLCZ: LLCZ Vein 1 and LLCZ Vein 2.
The Black Butte Copper Project deposits exhibit attributes of both Sedimentary Exhalative sulphide deposits (SEDEX deposits, e.g. Emsbo et al, 2016) and Sediment-hosted Stratabound Copper (SSC) deposits (SSC deposits, e.g., Hayes et al, 2015).