Summary:
Disseminated awaruite (Ni3Fe) forms an unusual nickel deposit type, with occurrences on the Decar Property comprising the most advanced projects of this type in the world (Britten, 2016). Terrestrial awaruite was first described in heavy black sand from the South Island of New Zealand (Frost, 1985; Ulrich, 1980) and has since been found as a minor component in altered ultramafic rocks all over the world. It forms during serpentinization of peridotite, whereby nickeliferous olivine is altered to serpentine minerals and awaruite + magnetite under conditions of low oxygen fugacity (Frost, 1985).
The Decar Property lies entirely within the Cache Creek terrane of British Columbia, with awaruite mineralization hosted by the Trembleur ultramafite unit and correlated to increased serpentinization. This alteration is best developed in association with NW-striking shear zones defined by a core of cataclasite, mylonite, and/or fault breccia that passes symmetrically outwards into decreasing intensities of penetrative deformation fabric. The Baptiste Deposit, Sid target, and Van target, for example, are all elongated along a NW-SE direction and bound by subvertical, NW-SE striking, 50-100 m wide, belts of strong penetrative deformation fabric. This relationship suggests that NW-striking structures channeled the fluids that caused serpentinization of the Trembleur ultramafite and resultant awaruite mineralization. The surface expression of the Baptiste Deposit also suggests a possible secondary NE-directed control.
Serpentinization and Mg-Fe carbonate alteration are the predominant alteration types within the Trembleur ultramafite. Serpentinization is the most widespread, with all ultramafic rocks within the Trembleur unit estimated to be 60-100% serpentinized. On the Decar Property, serpentinization is defined by the replacement of olivine and orthopyroxene with antigorite and lizardite, with magnetite and awaruite forming as part of the serpentinization process.
Awaruite deposits are formed by the serpentinization of magmatic olivine that leads to the liberation of nickel and iron and subsequent formation of awaruite. Awaruite occurs as disseminated grains throughout the entire extent of the peridotite on the Decar Property, but four zones of more abundant mineralization and larger grain size have been identified and named: Baptiste, Sid, B, and Van. The Baptiste Deposit and Van target are the most advanced of these zones, with both tested by numerous drill holes. The Sid and B targets are defined through surface mapping, sampling and/or diamond drilling, with three holes drilled at Sid target and one drilled at B target. High-grade awaruite zones trend NW-SE, parallel to lithological contacts and older fault structures.
The Baptiste Deposit is currently defined for approximately 3,000 m in a west of northwest to east of southeast direction, and for 400-1,500 m from north-northeast to south-southwest. Diamond drilling shows that mineralization typically extends to vertical depths of at least 200-300 m, with 13 of 28 holes drilled deeper than 300 m and ending in mineralization. The Deposit is in fault contact with Sitlika metavolcanic rocks to the southwest and grades into massive peridotite with lower-grade mineralization to the north and northwest.
The Van target lies 7.4 km north of the Baptiste Deposit and has a surface expression of approximately 2,200 x 700 m, with the eastern part of this target defined by 2021 and 2022 drilling (1,000 x 700 m) and the western half by rock sampling (1,200 x 700 m). The Van target is fault bound by Sowchea metasediments to the northeast and along part of its southwest boundary, with the remaining southwestern boundary formed by massive peridotite.
The Sid and B targets occur 3.0 km north-northwest and 4.5 km northwest of the Baptiste Deposit, respectively, and were also initially defined by rock sampling. Drill holes in both targets are sufficient only to demonstrate that Baptistelike mineralization occurs there as well, but insufficient to determine the length, width, depth, and continuity of the mineralization.
Exploration for listwanite-hosted gold deposits peaked in 1990-1994, with 1,541 m of diamond drilling over 22 holes to test the most prospective zones (Mowat, 1990, 1991, 1994). By 1994, drilling had identified at least 17 listwanite zones on or around the current Decar Property. Pathfinder elements for listwanite-hosted gold occurrences include iron, arsenic, lead, copper, zinc, nickel, cobalt and antimony. Possible origins of the gold-listwanite association include (1) carbon dioxide and hydrogen sulphide immiscibility with attendant gold deposition, (2) reduction of the mineralizing fluid by gold deposition, (3) sulphide precipitation promoted by Fe-rich lithologies, and (4) precipitation of silica, pyrite, arsenide and gold when an acidic gold-bearing solution enters reduced and alkaline carbonatized rocks (Kerrich, 1989; Dussel, 1985).
Mapping by the GSC identified nine chromite pods in the Trembleur ultramafic rocks within or near the Decar Property, with follow-up work suggesting these pods are generally too small to be economic. These occurrences are examples of podiform chromite that formed in the ultramafic part of an ophiolite complex.