VANCOUVER (miningweekly.com) – Northern Ontario-focused gold producer Detour Gold has optimised and de-risked the life-of-mine (LoM) plan for its flagship Detour Lake gold mine, adding about three years to the mine life and lifting LoM gold output by 1.8-million ounces to 15.1-million ounces.

"We are very pleased to report this new life-of-mine plan. For the first time, the technical report was prepared by Detour Gold's technical team. We were successful in delivering a gold production profile above 650 000 oz/y and a mine plan that significantly reduces the front-end strip ratio.

“This was possible by integrating West Detour, formerly known as Block A. We now have an increased reserve and mine life and a significantly de-risked operation which yields a higher net present value,” stated Detour COO Pierre Beaudoin.

Under the new 23-year mine plan, the operation would maintain an average output of about 655 000 oz/y, with 617 000 oz/y expected over the next three years.

Compared with the previous February 2014 mine plan, the updated plan entailed some operational improvements, including a reduction in the maximum mining rate from 140-million tonnes to 124-million tonnes and a reduced waste-to-ore strip ratio for the first nine years from 4.8:1 to 4:1 – a reduction of 160-million tonnes of waste. It also incorporated a second feed from the West Detour deposit.

Plant throughput capacity would increase to 23-million tonnes after 2018, from 22.3-million tonnes post-2017. Mill throughput would rise from 56 000 t/d currently, to 63 000 t/d in 2019.

In incorporating a second feed source, Detour had reallocated a portion of capital in the next nine years to the West Detour openpit. The operation would now also process one-million tonnes of fines from the low-grade stockpiles starting in 2019.

Detour noted that mining the Detour Lake pit in parallel with the West Detour pit resulted in an optimal mine production plan and, through processing low-grade fines of between 0.4 g/t and 0.5 g/t, the operation would add a third source of ore and contribute to achieving maximum plant throughput, albeit at a slightly reduced recovery rate.

The new mining plan entailed mining 2.21-billion tonnes of waste, compared with 1.96-million in the previous plan, producing 490-million tonnes of ore at an average grade of 0.99 g/t, as opposed to the previously planned grade of 1.03 g/t.

The most significant change from the prior study is an increase in mining costs over the LoM (C$2.76/t vs C$2.60/t mined), mainly as a result of lower assumed productivities and increased operating costs for the smaller-sized West Detour fleet. About 75% of operating costs were based in Canadian dollars while 25% would have US dollar exposure.

Capital costs over the LoM were estimated at C$1.1-billion (excluding closure costs), of which C$104-million was for West Detour. Capital costs over the next three years were estimated at C$314-million, of which C$80-million was for West Detour. About 60% of capital costs were based in Canadian dollars while 40% had US dollar exposure and were variable depending on the delivery of the US dollar-denominated mining fleet.

Total site costs between 2016 and 2018 and over the LoM were projected to average $812/oz and $690/oz produced, respectively.

The new National Instrument 43-101-compliant proven and probable openpit reserves increased by 10% over the previous estimate to 16.4-million ounces of contained gold.