The Mineral Resource Estimate (MRE) is predominately based on an unchanged geological model and methodologies utilized to calculate the 2021 MRE. The differences in the Current deposit relate to the incorporation of approximately 7,200 m of infill drilling within the Lower Bridge/Upper Beaver area and the corresponding reinterpretation of the infill drilling and incorporating updated metal prices and metallurgical and smelter recoveries.
The Thunder Bay North Critical Minerals Project 2021 PEA, while based largely on MSO analysis in continuous mineralized material within the indicated mineral resource category, is preliminary in nature and includes an economic analysis that is based in part on Inferred Mineral Resources. Inferred mineral resources are considered too speculative geologically for the application of economic considerations that would enable them to be categorized as Mineral Reserves and there is no certainty that the results will be realized. Mineral Resources do not have demonstrated economic viability and are not Mineral Reserves. Table 1 and 3 shows the MRE grades and Table 2 and 4 shows the MRE contained metals.
Table 1: Thunder Bay North Resource Estimate – Grade Summary (Effective Date November 1, 2021)
Note: Equivalency formula can be viewed in the following Link (Click Here)
Table 2: Thunder Bay North Resource Estimate – Contained Metals (Effective Date November 1, 2021)
Table 3: Thunder Bay North Resource Estimate – Grade Summary (Effective Date November 1, 2021)
Table 4: Thunder Bay North Resource Estimate – Contained Metals (Effective Date November 1, 2021)
Mineral Resource Estimate Notes
The cutoff value used for the mineral resource for Current deposit is US$93/tonne (CA$121/tonne) insitu contained value and the Escape deposit is US$100/tonne (CA$130/tonne) insitu contained value. The cutoff value is calculated based on estimations as follows: direct mining operating cost, onsite milling operating cost, tailings management facility operating cost, indirect operating cost, G&A cost, onsite milling metal recoveries, offsite smelting metal recoveries, and smelter metal payable percentages.
Estimated operating costs, onsite estimated mill metal recoveries, offsite estimated smelting metal recoveries and estimated smelter payable percentages used for mineral resource cutoff grade calculations are summarized in Table 5. For resource cutoff calculation purposes, a mining recovery of 100.0% and 0.0% mining dilution were applied.
Table 5: Mineral Resource Estimate Cutoff Grade Calculation
Clean Air Metals expects to complete a mineral resource update in 2022 on the greater than 35,000 m of step-out and delineation drilling that has been completed on the Escape deposit since the January 20, 2021 resource statement. Much of the inferred material in the present PEA mine plan has been a focus of infill drilling activity as previously disclosed and is expected to convert to indicated mineral inventory. Continuity of mineralization has been also demonstrated geophysically (using the Magnetometric Resistivity (MMR) technique). The additional drilling is expected to support the use of the MSO algorithm in a prefeasibility study.
The Current deposit drill hole database is comprised of 171,465 m from 767 diamond drill holes completed between 2006 and 2021. The Escape deposit drill hole database is comprised of 49,383 m from 137 drill holes completed between 2008 and 2020.
The 3D geological modelling integrates assay and geological data collected from diamond core drilling; surface geologic mapping; airborne magnetic; and radiometric geophysical surveys.
The Current and Escape deposit block models were estimated using nearest neighbours (NN), inverse distance squared (ID2), inverse distance cubed (ID3), and ordinary kriging (OK) interpolation methods for global comparisons and validation purposes. The OK method was used for the MRE; it was selected over ID2, ID3, and NN as the OK method was the most representative approach to controlling the smoothing of grades.
Zonal controls were used to constrain the grade estimates to within each low grade and high grade wireframes. These controls prevented the assays from individual domain wireframes from influencing the block grades of one another, acting as a “hard boundary” between the zones.
Search orientations were used for estimation of the block model and were based on the shape of the modelled mineral domains. A total of three nested searches were performed on all zones. The search distances were based upon the variography ranges.
Search ellipsoids defined by metal modelled variograms, which range from 130 to 140 m in the major axis, 100 m in the minor axis, and 9 to 18 m in the vertical axis. The MRE was estimated with 3 m composites utilizing ordinary kriging and local varying anisotropy. The search radius of the first search was based upon the first structure of the variogram, the second search is approximately two times the first search pass and the third search pass is 1.5 times the initial search. Search strategies for each domain used an elliptical search with a minimum and maximum number of composites. Unestimated blocks were left as absent and not reported in the MRE.
Tables 6 and 7 below illustrate the sensitivity of the MRE to different cutoff grades for a potential underground operation scenario with reasonable outlook for economic extraction. The reader is cautioned that the figures provided in these tables should not be interpreted as a statement of Mineral Resources. Quantities and estimated grades for different cutoff grades are presented for the sole purpose of demonstrating the sensitivity of the resource model to the choice of a specific cutoff grade.
Note: PtEq Grade = Total Metal Value in 1 Tonne ÷ Pt Price per Oz × 31.10348 g per Oz. For the MRE, total metal value includes 8 metals (Platinum, Palladium, Gold, Silver, Rhodium, Cobalt, Copper and Nickel)
Clean Air Metals has identified additional tradeoff opportunities at a prefeasibility level to enhance sustainability and overall project economics, including:
Table 6: Mineral Resource Sensitivity to Reporting Cutoff (Indicated)
Table 7: Mineral Resource Sensitivity to Reporting Cutoff (Inferred)
Figure 1: PtEq (g/t) Grade-Tonne Curve
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