The AT9-North target lies 1.4km northwest of Eagle’s Nest and 400m northwest of the AT9 target (figure 1). It is represented by a 200m long discrete magnetic anomaly. Past drilling has intersected 470m of mafic-ultramafic intrusive rocks cutting the footwall tonalite on the edge of large gravity anomaly. Mineralization intersected to date is limited to narrow PGEs, however, a significant surface EM anomaly associated with the target has been identified and has yet to be fully tested.
A northwest trending Proterozoic(?) mafic dyke occurs proximal to AT9 and AT9-North (figure 1) and may map out long-lived Archean structures which facilitated emplacement of Muketei-age mafic-ultramafic intrusions such as Eagle’s Nest.
The AT5 target is located 1km east of Eagle’s Nest. It is an ultramafic body measuring 500m wide x 800m long with Eagle’s Nest type chemistry (figure 2). The intrusion is hosted by the footwall tonalite, and its southern margin is truncated by the Triple-J fault. 2008 VTEM surveying over the target identified several weak conductors coincident with the magnetic response. To date 6 holes (4,128m) have been drilled into the target. Like the East Dyke, drilling at AT5 has intersected wide intervals of dunite, peridotite and pyroxenite, but mineralization to date is limited to low-grade PGEs and very narrow low-grade Ni-Cu-PGE mineralization along the northwest margin of the intrusion (interpreted basal contact). Further work will include detailed geological modelling and possible drilling of a platform geophysical hole.
The AT3 target is located 3km southwest of Eagle’s Nest, along strike and to the west of the Blackbird intrusion (figure 3). It is a large ultramafic body measuring 600m wide x 2000m long. The magnetic response of AT3 is the strongest of any ultramafic body in the Ring of Fire. Coupled with a very strong gravity response the target is believed to have the greatest depth extent of the ultramafic sills in the area. Like the Blackbird intrusion, the northern margin of AT3 is truncated by the Triple-J fault.
To date 18 drill holes (5,772m) have been drilled into the target returning ultramafic and mafic lithologies (dunite, peridotite, gabbro). Sporadic low-grade Ni-Cu-PGEs have been intersected dominantly in the centre of the intrusion, however, the chemistry of AT3 appears to be different than Eagle’s Nest, with higher Fe abundance and lower Mg abundance relative to other ultramafic intrusions in the area.
Work to date by the OGS and GSC in the Ring of Fire have identified two sub-suites of mafic-ultramafic rocks in the Ring of Fire, i) the Koper Lake ultramafic sub-suite (host to Eagle’s Nest and all chromite deposits) and the ii) Ekwan River ferrogabbro sub-suite (host to Fe-Ti-V occurrences). The chemistry at AT3, plus other areas in the Ring of Fire (e.g. Butler East, McFaulds South), suggests the possibility of a third ferropicritic sub-suite. If true, what is the Ni potential of this group? Globally, ferropicritic magmas can host significant Ni-Cu-PGE deposits (e.g. Pechenga, Russia). Additional work at AT3 will include 3D geological modelling and review of existing surface and borehole geophysics.
Area 7 is a 0.5km wide x 22km long northeast trending corridor defined by a series of discrete magnetic anomalies in the footwall tonalite northwest of Eagle’s Nest (figure 4). One of the anomalies (7I) was drilled in 2010 and intersected 260m of peridotite-pyroxenite from surface with chemistry similar to the Eagle’s Nest peridotite. In 2017 Noront utilized a track mounted rotary air blast (RAB) drill to test the bedrock surface at many of these anomalies. Of the 15 targets drilled, 12 returned ultramafic-mafic lithologies (peridotite, dunite, pyroxenite, olivine-gabbro, gabbro). While no sulfide mineralization was encountered, most holes only penetrated the top 10m of the bedrock surface.
One of the more intriguing anomalies, 7E, displays a ring-like structure along its margin and is coincident with a pronounced airborne gravity anomaly suggesting potential for depth continuity. A fence of three RAB holes into this anomaly from west to east returned gabbro, ferrogabbro, and olivine gabbro suggesting a possible fractionated sequence. Anomaly 7G, immediately southwest of 7E, returned 0.4g/t PGE over 6.1m within dunite.
Many of the Area 7 anomalies have a similar size magnetic footprint to Eagle’s Nest. Their alignment over a 22km long corridor suggests their ascent through the crust along a pre-existing structure. Further work should test the potential for Ni sulfide mineralization down-plunge at each anomaly.
The AT11 target is located 15km west-southwest of Eagle’s Nest, along the north margin of the WSZ (figure 5). The area is defined by several discrete magnetic anomalies within a broad gravity high. Some of the magnetic anomalies have coincident airborne EM conductors. Limited drilling to date has intersected mafic intrusive rocks of Muketei age (2734Ma), though the strongest magnetic anomalies have yet to be drill-tested. A string of conductors immediately south of the target area reflect formational sulfides of the Victory assemblage.
Further work at AT11 including core re-logging, 3D modelling and ground geophysics is warranted given the occurrence of Muketei age mafic-ultramafic intrusive rocks in the vicinity of sulfide-bearing country rocks.
The Bay target is located 6.8km east of Eagle’s Nest, and immediately northwest of the McFaulds South target, at the terrane boundary between the Victory and Muketei Assemblages (figure 6). It is represented by a 450m long x 200m wide magnetic anomaly whose long axis is perpendicular to the regional magnetic trend suggesting a cross-cutting relationship into surrounding sulfide-bearing volcanic rocks and iron-formation. The anomaly encompasses at least 9 low conductance airborne EM anomalies, some of which fall off the northeast regional trend. Past drilling (2 holes, 306m) along the western margin of the anomaly failed to properly test the target. The presence of a coincident gravity anomaly in the area suggests more significant mafic-ultramafic rocks than is presently known.
Given its location at a major terrane boundary, coincident magnetic-gravity anomalies, and the presence of abundant country rock sulfides, the Bay target presents an attractive Ni target which warrants additional work.
The McFaulds South target is located 11km east of Eagle’s Nest, immediately south of the terrane boundary between the Victory and Muketei Assemblages (figure 7). It is represented by a 10km long x up to 1km wide pronounced magnetic-gravity anomaly. The target represents a potentially large UM sill or komatiite flow. Limited drilling along the eastern and western margins has confirmed the presence of ultramafic rocks with elevated Ni content, including a 590m intersection in MCF-11-84 averaging 20% MgO (up to 27% MgO) from 60-650m depth. No significant Ni mineralization has been intersected to date, though the exploration maturity of the target is early. Of note is a 1,200m long string of weak airborne EM conductors parallel to the northern margin of the intrusive (along its inferred base) which has yet to be tested.
Given the size and inferred depth continuity of the target, coupled with the presence of untested conductors along the inferred base of the ultramafic sequence, further work at McFaulds South is justified and should target mineralization at depth, starting down dip of the identified conductor axis, and utilizing 3D inversions of existing magnetic and gravity data. Relogging and additional sampling of historic drill core would aid in better reconciling the stratigraphy of the ultramafic body.
The Muketei North target is located 28km north-northeast of Eagle’s Nest, roughly half way between the Thunderbird and Sanderson ferrogabbro intrusions. It is represented by a circular magnetic-gravity high 1km in diameter (figure 8) situated on the edge of a regional Proterozoic(?) dyke. The northern margin of the target was drilled in 1996 during early diamond exploration. The drill log reports strongly magnetic mafic gneiss which is interpreted by the OGS to be mafic-ultramafic intrusive rock given the well-defined boundaries of the target. No assays were reported.
Further work on the target may include soil sampling and ground geophysics designed to test for bedrock conductors at depth.
The Pinay target (Ojicree for partridge, given the shape of the anomaly) is located 43km north-northeast of Eagle’s Nest, in the footwall to the Sanderson ferrogabbro sill. The target is a 4.5km long x up to 800m wide magnetic-gravity anomaly similar in form and size to the BTIC (figure 9). Its stratigraphic position in the footwall to the Big Mac ferrogabbro is also similar to the BTIC which lies in the footwall to the Thunderbird ferrogabbro intrusion. A 2017 detailed airborne magnetic survey over the target outlines what looks like two prominent limbs or feeders to an 800m thick main body with an internal magnetic fabric reflecting possible magmatic layering (figure 8).
In 2018 Noront executed a four-hole (1,351m) drill program designed to test the two limbs and main body of the anomaly. Drilling intersected moderate to strongly magnetic ferrogabbro, gabbro and lesser pyroxenite. Fractionation trends in hole PN-18-03 suggest stratigraphic tops to the east. No significant Ni-Cu-PGE mineralization was encountered in the drilling, though much of the target remains untested. Further work to better resolve the age, stratigraphy and structural setting of the Pinay target is recommended.