Summary:
Deposits of the Crean Hill Project include Contact Type and Footwall Type deposits.
The Property straddles the South Range of the Sudbury Igneous Complex (SIC). From 1906-2002 a total of 20,370,000 tonnes of ore grading 1.09% Cu, 1.31% Ni, 1.56 g/t TPM (total precious metals) was produced from the Main, Intermediate and 9400 zones. The Property hosts part of a large trough structure at the base of SIC which contains several previously mined ore deposits including Crean Hill Main Orebody, Crean Hill Intermediate Orebody, Crean Hill West (9400) Orebody, Ellen Mine, and Lockerby Mine, each sitting in embayments within the larger trough. The embayments largely control the distribution of Ni-Cu mineralization. Much of the historic mining activity on the property exploited Contact Type deposits. Mineralization includes blebby to massive accumulations of sulphide, including pyrrhotite > chalcopyrite > pentlandite concentrated within embayment depressions along the base of the SIC, both within the contact sublayer and in the immediately adjacent footwall (FW) Breccia.
A significant portion of the mineralization, such as the 109 FW (footwall) Zone, the 101 FW Zone, and part of the 9400 Zone, are hosted in the footwall rocks. The host rocks are dominated by metamorphosed basalt (historically mapped and logged as greenschist), but also include gabbro, andesite, rhyolite, and sedimentary units (arkosic quartzite and meta-pelite) of the Huronian supergroup, Elsie Mountain Formation. The main mineralized zones from east to west are as follows:
• Main
• 109 FW
• Intermediate
• 101 FW
• 99 Zone
• 9400
9400 Zone
The 9400 Zone mineral envelope, as currently defined, is 1,970 ft (600 m) in depth extent, up to 820 ft (250 m) in strike length, and ranges from 10 ft to 130 ft (3 m to 39 m) thick. The envelope extends from 10,470 ft elevation down to 8,500 ft elevation, or from 450 ft to 2,460 ft (150 to 750 m) below surface.
The zone occurs primarily down-dip of the historic Crean Hill West Orebody, as well as mineralization to the west of the mined stopes. It is a tabular body that curves to the south at depth, and thickens from east to west, branching into two to three apophyses at the western margin of the zone. The Ni-Cu rich and PGM poor eastern part of the 9400 Zone is in contact with the SIC, trending obliquely away from the contact into the FW to the west. Mineralization at the eastern part consists mostly of semi-massive to massive Contactstyle pyrrhotite, pentlandite, and chalcopyrite.
Toward the west, into the FW, the PM grades increase whereas the Ni and Cu grades decrease. Here, the sulphide mineralization occurs as stringers, fracture-controlled within quartz / carbonate veins, disseminations within the host rock, and disseminations within quartz / amphibole veins / patches that are interpreted to be partial melts. The majority of the 9400 Zone is composed of this type of FW mineralization. FW sulphide mineralization is dominated by chalcopyrite and pyrrhotite. Other minor sulphide/arsenide minerals include pentlandite, pyrite, gersdorffite, and trace minerals identified primarily in thin section sphalerite, galena, bornite, chalcocite, cobaltite, sperrylite, michenerite, and merenskyite (Baker et al., 2017). This style of mineralization changes to the west, gradually becoming lower in sulphide and shifting to higher Pt, Pd, and Au grades.
The upper half of 9400 Zone remains open to the west and to surface.
109 FW Zone
The Crean Hill 109 FW zone rests in the immediate FW of the main embayment structure, which hosted what was the Crean Hill Mine Main zone but now includes the 109 HW zone. There is little or no separation between the norite-hosted, semi-massive to massive mineralization of the 109 HW, and the much lower sulphide Pt-Pd-Au mineralization in the FW, hosted primarily in metabasalt.
The mineralization is often associated with partial-melt veinlets, thought to be a thermal effect from the emplacement of the SIC, and occurs with veinlets of chalcopyrite-pyrrhotite and local pentlandite near the SIC contact. Fine to 1-cm-thick quartz-carbonate veinlets are found throughout the deposit, often hosting pyrrhotite and local chalcopyrite. Fine disseminations and veinlets of gersdorffite are found locally.
Where present, metasediments and felsic metavolcanics are not as prospective as the metabasalt unit. The deposit has the morphology of an open fold with thin limbs and a thickened axial hinge in the FW of the apex of the Crean Hill embayment. However, the deposit is understood to be located by two shears running parallel to the limbs, concentrating a PGE-Au mineralization halo around the contact mineralization. The mineralization is particularly concentrated in the hinge at the intersection of the two limb shears.
Mineralization can be extremely low in sulphide toward the FW margin of its known envelope. The mineralization is not necessarily hosted in noticeably sheared rock, but rather the sheared areas define the mineralized corridors. The shearing may have prepared the host rock to receive—or acted as a conduit for—mineralizing fluids (Baker et al., 2015).
The 109 FW zoneone remains open below the current extent to depth, along within the FW to the Main zone.
Main Zone
The Main Zone remnants are the unmined Ni-Cu rich contact sulphide mineralization of the historic Main orebodies. They are concentrated at or near the base of the SIC or within embayment structures, and associated with sublayer norite and quartz-rich norite phase of the SIC. Generally, these zones become more Cu rich the further the mineralization is from the main contact mineralization. The main sulphide assemblages are massive to net-textured pyrrhotite, pentlandite, and chalcopyrite mineralization, where pentlandite is the main Ni-bearing mineral, and chalcopyrite is the main Cu-bearing mineral.
101 Zones
The 101 Zones have been modeled as narrow mineralized structures extending out from the SIC contact from near surface to approximately 400 m depth and up to 200 m southwest, perhaps exploiting weakness along lithological contact in the footwall rocks. The orientation and metal ratios are curious for this zone. Unlike most of the mineralized zones which are near parallel to the SIC contact or following identified embayment trends, the strike orientation of the 101 Zones is oblique to the main mineralized trend. Also peculiar is the high Ni/Cu of the zone despite extending so far into the footwall. The 101 Zones remain partially open along to the southwest to depth.
99 FW Zone
The 99 FW Zone has been modeled as three sub-parallel mineralized zones, are oriented sub-parallel to the SIC contact, and have a strike extent of over 1,800 m and a depth extent of over 700 m within the Property boundary. The largest and most continuous of the three zones is located at the SIC basal contact and two smaller zones are interpreted to be within the footwall. The thickest part of these zones has been interpreted to be plunging shallowly to southeast along a secondary embayment structure. There is a lower confidence in the interpretation of the 99 FW Zone because of the limited number of drillhole intercepts and the high angle at which the drilling completed was oriented relative to the zones.