Reserve and Resource Estimates

The Entrée/Oyu Tolgoi JV Property mineral reserve estimate for Hugo North Extension Lift 1 has an effective date of May 15, 2021.

Entrée/Oyu Tolgoi JV Property mineral reserves are contained within the Hugo North Extension Lift 1 block cave mining plan (see table below). The mine design work on Hugo North Lift 1, including the Hugo North Extension, was prepared by OTLLC and was used as the basis for OTFS20. The mineral reserve estimate is based on what is deemed minable when considering factors such as the footprint cut-off grade, the draw column shut-off grade, maximum height of draw, consideration of planned dilution and internal waste rock.

The mineral reserve estimate only considers mineral resources in the Indicated category and engineering that has been carried out to a Feasibility level or better to state the underground mineral reserve. There is no Measured mineral resource currently estimated within the Hugo North Extension deposit. Copper and gold grades for the Inferred mineral resources within the block cave shell were set to zero and such material was assumed to be dilution. The block cave shell was defined by a US$17.84/t net smelter return ("NSR"). Future mine planning studies may examine lower shut-offs. 

Hugo North Extension Lift 1 Mineral Reserves Statement

Entrée/Oyu Tolgoi JV Property – Mineral Reserve
Hugo North Extension Lift 1
Classification Tonnage NSR Cu Au Ag Contained Metal
(Mt) (US$/t) (%) (g/t) (g/t) Cu (Mlb) Au (Koz) (Ag(Koz)
Probable 40 96.97 1.5 0.53 3.6 1,340 676 4,613
  1. Mineral reserves have an effective date of May 15, 2021.
  2. For the underground block cave, all Indicated mineral resources within the cave outline were converted to Probable mineral reserves.  No Proven mineral reserves have been estimated.  The estimation includes low-grade Indicated mineral resource and Inferred mineral resource assigned zero grade that is treated as dilution.
  3. A column height shut-off NSR of US$17.84/t was used to define the footprint and column heights. The NSR calculation assumed metal prices of US$3.08/lb Cu, US$1,292.00/oz Au, and US$19.00/oz Ag.  The NSR was calculated with assumptions for smelter refining and treatment charges, deductions and payment terms, concentrate transport, metallurgical recoveries, and royalties using OTLLC’s Base Data Template 38. 
  4. Mineral reserves are reported on a 100% basis. OTLLC has a participating interest of 80%, and Entrée has a participating interest of 20%. Notwithstanding the foregoing, in respect of products extracted from the Entrée/Oyu Tolgoi JV Property pursuant to mining carried out at depths from surface to 560 metres below surface, the participating interest of OTLLC is 70% and the participating interest of Entrée is 30%.
  5. Numbers have been rounded as required by reporting guidelines and may result in apparent summation differences.

The Entrée/Oyu Tolgoi JV Property mineral resource estimates for the Hugo North Extension and Heruga deposits have an effective date of March 31, 2021. Mineral resources are reported inclusive of those mineral resources that were converted to mineral reserves. Mineral resources that are not mineral reserves do not have demonstrated economic viability.

Entrée/Oyu Tolgoi JV Property Mineral Resources

Entrée/Oyu Tolgoi JV Property – Mineral Resources 
Classification  Tonnage (Mt)  Cu (%)  Au (g/t)  Ag (g/t)  Mo (ppm)  CuEq (%)  Contained Metal 
Cu (Mlb)  Au (Koz)  Ag (Koz)  Mo (Mlb) 
Hugo North Extension (>0.41% CuEq Cut-Off) 
Indicated  120  1.70  0.58  4.3  ___  2.04  4,500  2,200  16,000  ___ 
Inferred  167  1.02  0.36  2.8  ___  1.23  3,800  1,900  15,000  ___ 
Heruga (>0.41% CuEq Cut-Off) 
Inferred  1,400  0.41  0.40  1.5  120  0.68  13,000  18,000  66,000  370 
  1. Mineral resources have an effective date of March 31, 2021.
  2. Mineral resources are reported inclusive of those mineral resources that were converted to mineral reserves. Mineral resources that are not mineral reserves do not have demonstrated economic viability.
  3. Metal prices used for copper equivalent (CuEq) and cut off grade calculation for both Hugo North Extension and Heruga are: US$3.08/lb Cu, US$1,292.00/oz Au and US$19.00/oz Ag. Metallurgical recoveries used for CuEq and cut-off grade calculation at Hugo North Extension are 93% for Cu, 80% for Au and 81% for Ag.  Metallurgical recoveries used for CuEq and cut-off grade calculation at Heruga are 82% for Cu, 73% for Au, 78% for Ag and 60% for Mo.
  4. Mineral resources at Hugo North Extension are constrained within a conceptual mining shape constructed at a nominal 0.50% CuEq grade and above a CuEq grade of 0.41% CuEq.  The CuEq formula is CuEq = Cu + ((Au * 35.7175) + (Ag * 0.5773)) / 67.9023 taking into account differentials between metallurgical performance and price for Cu, Au and Ag.
  5. The overall geometry and depth of the Heruga deposit make it amenable to underground mass mining methods.   Mineral resources are stated above a CuEq grade.  The CuEq formula is CuEq = Cu + ((Au * 37.0952) + (Ag * 0.5810) + (Mo * 0.0161)) / 67.9023 taking into account differentials between metallurgical performance and price for Cu, Au, Ag and Mo.
  6. A CuEq break-even cut-off grade of 0.41% CuEq for Hugo North Extension mineralization and covers mining, processing and G&A operating cost and the cost of primary and secondary block cave mine development.
  7. A CuEq break-even cut-off grade of 0.41% CuEq is used for the Heruga mineralization and covers mining, processing and G&A operating cost and the cost of primary and secondary block cave mine development.  
  8. Mineral resources are stated as in situ with no consideration for planned or unplanned external mining dilution.
  9. Mineral resources are reported on a 100% basis. OTLLC has a participating interest of 80%, and Entrée has a participating interest of 20%. Notwithstanding the foregoing, in respect of products extracted from the Entrée/Oyu Tolgoi JV Property pursuant to mining carried out at depths from surface to 560 metres below surface, the participating interest of OTLLC is 70% and the participating interest of Entrée is 30%.
  10. Numbers have been rounded as required by reporting guidelines and may result in apparent summation differences.

Last updated: June 2021