Summary:
Limited areas of the Wicheeda claim group have been covered by reconnaissance and/or gridbased bedrock mapping. The REE-enriched carbonatites located at the project are part of a narrow elongate, south-trending intrusive carbonatite-syenite complex cutting or occupying a structural panel within calcareous siltstones and limestones of the Cambrian to Ordovician Kechika Group. Some of the geological contacts observed in core are intrusive while others are almost certainly structural. The carbonatite complex extends southward from the south end of Wicheeda Lake for approximately 13 km.
Outcrop on a moderately steep, west-facing slope south of Wicheeda Lake, an area that coincides with part of the former ‘George’ grid, consists of a sequence of interbedded limestone, calcareous argillite and argillite with consistent northwest-trending attitudes and sub-vertical dips (Betmanis, 1987). A small intrusion cuts the sedimentary rocks in the southern part of the grid, just north of ‘A’ Creek. This feature was mapped as syenite in 1986 by Betmanis (1987), although during a reevaluation of the area (including trenching) the following year, it was concluded that the intrusion was a carbonatite (Lovang and Meyer, 1988).
Three types of narrow (0.5 m to 1.5 m), northwest-trending dikes were also observed in the gridded area, including: a K-feldspar phyric type with a fine-grained albite matrix and abundant Fe-rich biotite; a blue sodalite-rich (as phenocrysts and matrix) type, and; a feldspar and augite-phyric intermediate type with aphanitic groundmass that appears to be the youngest of the three varieties (Mader and Greenwood, 1988).
Outcrop in the area covered by the former ‘Lake’ grid is rare, but consists of strongly weathered, medium to coarse-grained calcite carbonatite, a band of fresh, fine-grained calcite carbonatite and related syenite were exposed in trenches (Mader and Greenwood, 1988).
The Wicheeda Carbonatite is comprised mainly of dolomite carbonatite, xenolithic dolomite carbonatite with varieties of matrix to clast-supported fenite breccia where dolomite carbonatite occurs as the dominant matrix component, and minor calcite carbonatite. This carbonatite body intrudes into syenite and minor mafic dikes, limestone and calcareous sedimentary wall rocks. The upper part of the complex consists mainly of dolomite carbonatite, brecciated dolomite carbonatite and lesser calcite carbonatite with minor fenitized limestone, mafic dike and syenite xenoliths whereas the lower part of the complex is weakly constrained by drilling and mainly consists of xenolithic varieties of brecciated dolomite-carbonatite, fenitized limestone, syenite and country wall rocks.
The geometry of the Wicheeda Carbonatite was originally interpreted to be sub-circular in plan (Lovang and Meyer, 1988; Greenwood and Mader, 1988). Subsequent modeling of the carbonatite body following diamond drilling showed a more oblong or lens-shaped with a long axis that is approximately north-south (Lane, 2009; 2010), a subvertical dip and a plunge to the northwest. The main carbonatite body was intersected over the extent of 215 m thick and is in fault contact with unaltered metasedimentary rocks of the Kechika Group on its western edge, and in intrusive contact with fenitized argillaceous limestones of the Kechika Group on is eastern margin (Betmanis, 1987). As defined by drilling, the carbonatite body stretches over 360 m along a north-south strike, 160 m east-west width and up to 250 m deep in the central down-dip portion of the body.
In their study of the Wicheeda Carbonatite on the Wicheeda project, Trofanenko et al. (2016) proposed a preliminary model in which the carbonatite magma exsolved a fluid which fenitized the host metasediments near the intrusion to potassic fenite and heated formational water distal to the intrusion, altering the metasedimentary rocks to sodic fenite. The REE were concentrated by magmatic hydrothermal fluids, which partially dissolved the carbonatite, altered the dolomite, and lead to deposition of compositionally zoned dolomite and later bastnäsite-(Ce) and monazite-(Ce) in veins and vugs in response to cooling and an increase in pH.
REE mineralization at the Wicheeda Carbonatite is zoned into high, moderate and low grade. High REE mineralization is directly related to dolomite-carbonatite, xenolithic dolomite carbonatite where country rock xenoliths are less than 20%, and around mafic dike xenoliths where columbite and pyrochlore is observed. Moderate REE mineralization is typically associated with mixed zones where xenolithic dolomite carbonatite, fenitized limestone, syenite and mafic dike xenoliths exceed 30% and are less than 70%. These mixed zones have the potential to add size to the deposit with more modest grades. Low REE mineralization is typically encountered in fresh and fenitized limestone, calcareous sedimentary rocks, syenite and fresh, weakly brecciated mafic xenoliths.
Field observation of REE mineralization includes disseminated to clotty dark grey-bluish columbite, disseminated, inclusion and fractured pyrochlore, rare fluorite and sphene/rutile and a combination of bastnäsite-parasite and monazite observed as aggregates and patches in veins and vugs. Veintype mineralization was commonly noted in amorphous to coarse-grained dolomite-carbonate intersecting earlier fine-grained, dolomite carbonatite with disseminated fine-grained REE mineralization and proximal to strongly altered – brecciated mafic dike xenoliths. Vein-type mineralization range in width from a few centimeters to over a meter wide. On the other hand, vuggy and disseminated REE- mineralization was noted in all lithologies, except the fresh limestone and calcareous sedimentary rocks, in variable percentages throughout the drill core.
Production
The production schedule mines 26 million tonnes of mill feed over a period of 16 years. The assumption is that for the first four years, the concentrate produced by the mill is sold directly. During this period a hydrometallurgical plant is assumed to be built and from Year 5 onwards, a mixed REE precipitate is the product sold.
| Commodity | Units | Avg. Annual |
|
REE
|
t
| 25,423 |
All production numbers are expressed as oxide.