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Hidden Lake Lithium Project


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Washington is increasingly viewing Canada as a kind of “51st State” for its critical mineral supply needs and plans to deepen financial and logistical partnerships with the country’s mining sector ”
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Foremost Lithium Hidden Lake Lithium project consists of 5 contiguous claims, totaling 4100 acres/1,659hectares (Figure 2). The property is just north of Highway 4 (Ingraham Trail) providing excellent access. The exploration targets on the property are lithium-bearing spodumene pegmatite dykes which are visible from aerial imagery as elongated white linear features visible through vegetation and soil due to their high reflectance. Hidden Lake hosts lithium-bearing pegmatite dykes that are part of the larger Yellowknife Pegmatite District which have been described as the largest lithium resource in Canada with a minimum of 55,000,000 US tons at 1.41% L2O primarily as spodumene. Extensive channel sampling and assays by previous workers documented significant lithium mineralization over substantial intervals for each of the four surveyed dykes, including a maximum value of 1.75% Li2O over 6.01 metres. The dykes have exposed strike lengths of up to 800 m and up to 20 m in width at surface but are concealed by overburden cover along strike..

foremostlithium sep 27 2

Current claim map, Hidden Lake Property, N.W.T.

Granitic Pegmatites 

These pegmatites intrude both the surrounding Burwash Formation and the granitic plutons and form the Yellowknife Pegmatite Field. Depending on their proximity to the granite intrusion, the pegmatite complexes commonly show regional zoning in their mineralization and can be rare element bearing. Lithium enrichment occurs in an outer zone typically 2 to 3 kms from the intrusion accompanied by Be, Ta, Nb and Ca enrichment (Sinclair, 1996).

The lithium bearing pegmatites that are targeted for exploration are white to light grey, coarse to very coarse-grained, and comprised of K-feldspar (microcline), plagioclase (albite), quartz, muscovite and spodumene with trace amounts of apatite, biotite, tourmaline, columbite and montebrasite. The dykes consist of long, discontinuous bodies oriented in an NNE-SSW direction (between 010° and 020°) and range from 3 to 11 m wide and 300 to 800 m long. The bodies are zoned and spodumene content typically ranges from 10% to 20% by volume, with up to 35% locally within the center of the bodies. Spodumene crystals were green to light greenish grey, up to 60 cm long and were typically oriented parallel to the dyke boundaries along the edges and perpendicular to the boundaries in the center of the dykes (Sinclair, 1996)

2016 Exploration 

Dahrouge Geological Consulting Ltd. (Dahrouge) undertook exploration work in 2016 and 2017 on behalf Patriot Battery Metals3 who is Foremost Lithium’s 40/60 partner on this property with Foremost owning the majority. This work consisted of prospecting, grab sampling, detailed mapping, and channel sampling. Only the results of the 2016 program are relevant to the Hidden Lake Property.

Subsequently a channel sampling program was completed between August 16th and September 7th, 2016. A total of 308 channel samples were collected from 61 channels cut across dykes D12, HL1, HL3 and HL4 Table 1.


Table 1: 2016 channel sampling details.

Pegmatite Length (m) Number of Channels Number of Samples
D12 350 15 85
HL1 690 16 65
HL3 800 15 89
HL4 400 15 69


In 2016 a total of 5 grab samples and 308 channel samples were collected during the two Hidden Lake field programs carried out in 2016. Five grab samples from dyke D12 assayed 1.63 – 3.06% Li2O. Channel sample results were presented as weighted averages for individual channels for each dyke. The thickest section of D12 was 11.58 m wide and returned a weighted average of 1.53% Li2O and included a 9.02 m section of 1.90% Li2O. A channel from the HL1 dyke assayed 1.26% Li2O over 8.72 m and an 8.78 m channel from the HL3 dyke assayed 1.58% Li2O. A 5.78 m channel from HL4 assayed the highest Li2O of 1.71% over 5.78 m. Significant grades of tantalum were recorded with an average of 54 pm Ta2O5 for the four dykes. The maximum value was 402 ppm.

2018 Exploration

Dahrouge also undertook an exploration program in 2018 on behalf of Foremost Lithium4. The purpose of the drilling was to test the vertical continuity of spodumene mineralization in the subsurface. This work took place between May 22nd and June 10th, 2018 and consisted of 1079.37 m of core drilled in ten drill holes on pegmatite dykes HL-001 through HL-003 and D-12 (Figure 4). A total of 197 core samples were collected and submitted for assay at SGS Mineral Services Lakefield facility. Intersected pegmatites were typically composed of quartz, plagioclase, feldspar, muscovite, spodumene and accessory minerals consisting of tourmaline and epidote.


Figure 4. Summary of drill hole locations and targets, Hidden Lake Lithium Property, N.W.T

Drill hole specific information including core samples collected for assay is provided in Table 2.

Hole ID Target Easting Northing Overburden Depth (m) EOH Depth (m) Pegmatite Intersection Sum (m)
HL18-001 D-12 374935 6936971 0.00 109.00 15.10
HL18-002 D-12 375023 6937090 4.23 101.34 10.98
HL18-003 D-12 374893 6936899 5.16 108.94 11.12
HL18-004 HL-1 373748 6936978 5.25 106.19 7.95
HL18-005 HL-1 373361 6937389 6.45 108.82 3.79
HL18-006 HL-4 373440 6937524 0.30 108.94 7.72
HL18-007 HL-4 373407 6937465 0.10 109.00 5.98
HL18-008 HL-4 373361 6937389 0.00 108.94 5.62
HL18-009 HL-3 373364 6937097 0.70 109.20 8.68
HL18-010 HL-3 373306 6937011 1.05 109.00 8.97
        Total: 10793.37 m 171.82 m

 Table 2: Pegmatite intersection and sample collection summary.


Pegmatites intersected in this drill program were marked by fine to very coarse grained spodumene crystals varying from 7-10 modal percent in dyke HL3 to 15-25% modal percent spodumene crystals in dyke D12.

All spodumene-bearing dykes tested during the 2018 drill program intersected high-grade 1.0-2.0% Li2O over individual widths that varied from 2.0 to 9.2 m or total widths of between 3.79 m and 15.10 m (Table 3; cf. September 10, 2018, news release). The assay results for 2018 drill core confirm the presence of high grade spodumene-bearing pegmatite dykes on the property and reflect the historic assay results from 2016 surface channel samples

Hole ID Li2O (%) Ta (ppm) Length (m)
HL18-001 1.5 33.4 9.0
HL18-002 1.7 34.0 5.0
HL18-003 1.6 32.4 9.2
HL18-004 1.6 24.4 7.0
HL18-005 1.2 41.8 2.0
HL18-006 1.4 21.5 7.0
HL18-007 2.0 43.6 5.2
HL18-008 1.3 42.5 3.8
 HL18-009 1.5 7.8 2.0
HL18-010 1.0 15.1 7.0

   Table 3. Summary of assay results, 2018 Hidden Lake drill program.


Pegmatite intersections in the drill core were sawn in half with one half of the sample collected for assay. The samples were shipped to Activation Laboratories (Ancaster, Ontario) digested with a sodium peroxide fusion followed by ICP-OES/MS analysis. Assay results are summarized in Table 3.

Future Exploration 

Future exploration is planned to expand the lithium resource at Hidden Lake with additional diamond drilling based on an integrated exploration plan using state-of-the-art drone assisted geophysical surveys and rock and soil geochemical techniques.

2: Morrison, M. 1978. Report on a trenching programme and geological survey of the LU3, 5, 8, 9 and 10 mineral claims, Yellowknife area. NWT assessment report 080847.
3: Goreham, J. 2018: 2016 and 2017 geological and geochemical exploration on the Hidden Lake property, Yellowknife, N.W.T. report for property owner 92 Resources Corp., 29p.
4: Wood, A. 2018: Summary memo for the 2018 Hidden Lake P1 drill program, Yellowknife area, N.W.T., 12p. Sinclair, W.D., 1996. Granitic Pegmatites; in Geology of Canadian Mineral Deposit Types, (ed.) O.R. Eckstrand, W.D. Sinclair and R.I Thorpe. Geological Survey of Canada, Geology of Canada. No. 8 p. 503-512.