*1.2. Surficial Geology*

The Izok Lake region was most recently glaciated during the Wisconsinan [32]. Regional surficial mapping in the Izok Lake region was carried out by Stea et al. [33], with large-scale ice flow reconstructions compiled by Dyke and Prest [34] and Dyke [35]. Recent ice flow indicator mapping in the region by Paulen et al. [36] built on the previous work to elucidate four ice flow phases that affected the region. Of these, an older southwest ice flow and younger northwest ice flow were determined to be responsible for the formation of most local glacial landforms and the palimpsest glacial transport of mineralized debris down ice [11,18]. These ice flows deposited a till cover that is relatively thin (<3 m thick) and consists mainly of silty sand till. The Izok Lake region is a permafrost terrain and, therefore, it is not practical to dig to appropriate till horizons by hand. All samples were collected at the surface from frost boils, small circular periglacial features formed by cryoturbation that bring till material from depth to surface [37].

The GSC carried out a reconnaissance-scale till geochemical survey in the Point Lake region, including the Izok Lake area, but geochemical analysis of the <0.002 mm and <0.063 mm till fractions did not indicate the presence of the mineralization at Izok Lake [38]. In 2009, a till geochemical survey was carried out around the Izok Lake deposit [17] along with a detailed bedrock and till indicator mineral survey. The <63 μm fraction of till, analyzed by aqua regia/inductively coupled plasma mass spectrometry (ICP-MS), yielded elevated values for Zn (<346 ppm), Cu (<322 ppm), Pb (<392 ppm), Fe (<1880 ppm), Ag (<1411 ppb), Cd (<1.36 ppm), Bi (<5.12 ppm), Hg (<247 ppb), Se (<0.5 ppm), In (<0.28 ppm), and Tl (<0.20 ppm) up to 6 km down ice to the northwest [11]. Also in 2009, a gossan containing sphalerite and referred to as the West Iznogoudh (WIZ) showing (Figure 2; [27]) was sampled. Oviatt [39] reported elevated contents of Zn, Ag, Cu, Hg, and Bi in the <63 μm fraction of till collected in the vicinity of the showing.

In addition to the till geochemical samples, bulk (10–15 kg) till and bedrock (1 kg) samples were collected around the Izok Lake deposit, concentrated to produce HMC and the >250 μm size fraction was examined for indicator minerals. That study identified gahnite, staurolite, chalcopyrite, sphalerite, pyrrhotite, and pyrite as indicator minerals. Gahnite dispersal was identified to be the broadest and farthest down ice of all of the indicator minerals identified, extending more than 40 km to the northwest with an older component to the southwest [11,18]. Significant abundances of sulfide minerals (chalcopyrite, galena, sphalerite, pyrite) were identified in the coarse fraction of only the most proximal down ice till sample to mineralization. Axinite, a potential indicator of hydrothermal alteration, was identified in bedrock thin sections and HMC, but was not identified in till HMC due to its lack of distinguishing visual characteristics [18,31].

**Figure 2.** Location of the four till samples used in this study. Arrows indicate relative ice flow chronology (1 = oldest) and vigor (arrow width) of flow events. Colored polygons depict the glacial dispersal fan for gahnite in the non-ferromagnetic 250–500 μm fraction of till heavy mineral concentrate (HMC), as interpreted by McClenaghan et al. [1]. Yellow polygon represents dispersal by the NW ice flow; blue represents dispersal by the older SW ice flow, and the question-marked border represents the terminal sampling distance beyond which data is not available.

#### **2. Materials and Methods**

Four till samples collected by Hicken et al. [18,31] were chosen for use in this study. They were selected based on their locations relative to mineralization and the indicator minerals identified in their coarse fraction of HMC, in particular gahnite. The four sample locations are shown in Figure 2, along with the gahnite dispersal fan identified by McClenaghan et al. [11]. Sample 09-MPB-060, located 1 km up ice of mineralization, was the farthest-up ice sample available, and was chosen to represent background values compared to down ice sample locations. However, this up ice sample site is still within the hydrothermal alteration halo surrounding the Izok Lake deposit [22], and may not represent true regional background for certain alteration indicator minerals. Sample 09-MPB-058, located 500 m down ice (west) of mineralization, was the only sample with a significant abundance of sulfide indicator minerals identified in the coarse fraction [18,31]. It is the most proximal down ice sample chosen for this study. Sample 09-MPB-075, located 3 km down ice of mineralization, represents the intermediate down ice sample chosen for this study. Previous work identified gahnite in the coarse fraction HMC of these till samples. Sample 12-MPB-902, located 8 km down ice of mineralization, represents the most distal down ice sample chosen for this study.

#### *2.1. Preparation of Heavy Mineral Concentrate (HMC) in Previous Geological Survey of Canada (GSC) Study*

In 2009, the four GSC till samples were processed to recover >3.2 SG HMC at Overburden Drilling Management Limited (ODM), in Ottawa, ON, Canada. Density concentration was carried out using a combination of wet screening and shaking table, followed by heavy liquid separation at 3.2 SG, acid-washing, and ferro-magnetic separation to produce coarse (>250 μm) non-ferromagnetic HMC (>3.2 SG) fraction. This fraction was visually examined, and indicator minerals were counted with results reported by Hicken [18] and McClenaghan et al. [11]. The archived byproduct of the sample

processing was the non-ferromagnetic <250 μm fraction. It is this fraction that forms this basis of the study reported here (Table 1).

**Table 1.** Sample processing weights indicating the original mass of bulk till sample prior to heavy mineral concentrate (HMC) production, the individual mass of each size fraction following sieving of the <250 μm HMC, and the mass of <250 μm HMC lost during sieving.


## *2.2. Sieving Methods*

The<250 μm HMC fraction of the four till samples was dry-sieved at the Queen's University Facility for Isotope Research (QFIR, Kingston, ON, Canada) into four smaller size fractions: (1) 185–250 μm, (2) 125–185 μm, (3) 64–125 μm, and (4) <64 μm. The sieving was carried out using single-use, nylon-screened sieves following the procedures developed by Lougheed et al. [40]. Table 1 contains the masses of <250 μm HMC prior to sieving, the masses of each resultant size fraction, and the mass loss of HMC material as a result of sieving.

#### *2.3. Epoxy Mounting of Mineral Grains*

The grain mounting method used in this study was modified after Blaskovich [41]. In our study, the entire mass of each of the 16 subsamples was mixed with vacuum-evacuated epoxy and poured into a 2.54 cm diameter plastic ring mold. Each ring mold was immediately placed into a vacuum chamber under full vacuum for 5 min. Vacuum impregnation eliminated air bubbles from liquid epoxy and drew epoxy into void spaces in mineral grains, maximizing the adhesion between epoxy and grains [42]. Following removal from the vacuum chamber, the mounts were allowed to cure for 24 h. The resulting grain mount was trimmed and vertically quartered using a Raytech Jemsaw 45 (Raytech Industries, Middletown, CT, USA) fitted with a diamond-impregnated blade. One quarter of each mount was archived. The other three quarter-pieces were remounted into a single plastic ring mold and set with epoxy (Figure 3) and cured for 12 h. Thus, one new epoxy mount containing three quarter slabs was prepared for each of the 16 subsamples. After polishing to 1 μm, these three slabs in the secondary mount were used for MLA analysis and examination of any settling effects or gradients that developed during mixing with epoxy and curing of the primary mount. Following polishing, the mounts were carbon coated using a Denton Vacuum Desk V carbon-coater (Denton Vacuum LLC, Moorestown, NJ, USA).

Grain mount preparation took ~30 min, followed by 12 h of curing time. Several samples were prepared simultaneously, with the limiting factor being the number of mounts that can be placed in the vacuum chamber.

**Figure 3.** Mounting schematic displaying the basal surface of the two mounting stages. The primary grain mount was quartered, and three quarters were reoriented and made into a second mount to display one basal surface and two cross-sectional surfaces for analysis. Cross-sectional surfaces are indicated by the black grey bar in left pane of figure.
