Example mine planning output
Seabridge Gold Inc (Seabridge Gold) is developing the Kerr-Sulpherets-Mitchell (KSM) project in northwestern British Columbia, Canada. The project consists of four orebodies within 1-2 km of each other, as shown in the figure below. The orebodies are a complex assemblage of porphyry deposits, and mineralization associated with intrusive phases and extensive alteration of country rock. Gold and copper are the dominant metals, but each orebody also contains silver and molybdenum.
Based on a 2020 feasibility study (Tetra Tech, 2020), the proposed mine development has about 2.1 billion tonnes of proven and probable reserves and a mine life of 53 years. It is one of the largest undeveloped gold deposits in the world.
The production rate was restricted to 130,000 tpd or 47.5 Mtpa due to an anticipated limitation on the power supply. However, that limitation no longer exists and a higher production rate is possible. It is not an optimum production rate because the report states (p. 16-1) that the project NPV could be improved by increasing mill throughput to more than 130,000 tpd.
The size and spatial distribution of the deposits provides flexibility in the manner in which they are developed and mined. A combination of open pit and underground mining and stockpiling is used to achieve the goals of paying back capital, minimizing waste, and providing a constant feed rate to the mill during the mine life. The development scheme is illustrated below.
Initially, the lower cost open pit mines at Kerr, Sulphurets, and Mitchell are mined. The Mitchell and Sulphurets pits are mined out by year 20, after which waste rock from the Kerr pit is used to backfill the Sulphurets pit. The Kerr pit is mined out by year 30. Underground mining (block caving) is used beneath the Mitchell pit after year 20 and at Iron Cap after year 30 to minimize waste production. Low to mid-grade ore from the open pits is stockpiled and processed after year 30 to maintain the feed rate to the mill.
In addition to financial goals, there are geotechnical and environmental conditions and constraints that govern the design and sequencing of the mines in this project. These are discussed in Chapter 16 of the feasibility study.
The production schedules are plotted in the next figure.
For the open pit mine, knowing the amount of waste and ore being mined at each point in time, the time history of the strip ratio over the mine life may be computed as shown in this figure.
