4.5.3. Epidote

Epidote was previously reported by Hicken [17], Nowak [26], and Hicken et al. [31] in bedrock PTS and till HMC. Nowak [26] and Hicken [17] identified epidote grains in bedrock. Nowak [26] divided bedrock into domains based on the degree of hydrothermal alteration of the protolith, and epidote was reported in metamorphosed bedrock corresponding to least- and weakly altered protolith, with coarser-grained epidote being found in the weakly altered (0.2–0.7 mm) assemblages than in the least-altered (0.1–0.3 mm) assemblages.

Hicken [17] reported epidote grains in four bedrock PTS samples. Two samples (diabase dyke and iron formation) were collected to the west of Iznogoudh Lake (>5 km down ice of the Izok Lake deposit), and two samples (schist and gneiss) were collected from metamorphic rocks <1.5 km from the Izok Lake deposit. Epidote in the two proximal bedrock samples was coarser-grained than in the two more distal samples. Green epidote abundance was estimated by ODM for the 0.250–0.500 mm fraction of till HMC for the four samples examined by this study (Geological Survey of Canada, unpublished data). The counts were only accurate to 10–100 grains, depending on the total number of epidote grains present, but indicate an increase in abundance overlying mineralization, peaking 3 km down ice at sample site 09-MPB-075 and diminishing at sample site 12-MPB-902, 8 km down ice (Table 4).

Epidote identified by this study increases in abundance in the most proximal till sample down ice of mineralization (09-MPB-058), and till samples 09-MPB-060 (1 km up ice) and 09-MPB-075 (3 km down ice) have relatively equal epidote abundance in all size fractions. Till sample 12-MPB-902, 8 km down ice of mineralization, has the lowest abundance of epidote in all size fractions examined. This suggests that till sample 09-MPB-060 is within the hydrothermal alteration halo of the Izok Lake deposit, which is supported by the extent of hydrothermal alteration described in Morrison [22], who describes a late-stage, widespread zone of calcic alteration containing epidote surrounding the deposit. Epidote has been previously identified as an important indicator in porphyry terranes [8], where epidote abundance and trace element composition can be used in tandem to identify hydrothermal carbonate and propylitic alteration halos and assess ore fertility in porphyry systems. However, the chemical changes associated with carbonate and propylitic alteration lead to bulk-rock compositions similar to those of calc-silicate rocks of sedimentary or metasomatic origin [59] and, therefore, epidote abundance will need to be identified along with other indicator minerals to serve as a vector to VMS mineralization. Future work is needed to investigate the utility of epidote as an indicator mineral for VMS deposits, with careful attention paid to collecting true regional background samples outside the potentially wide zone of propylitic alteration.
