Open-pit miners now consider going underground

According to a recent report in The Northern Miner, Capstone Mining is considering developing an underground mine at its Minto copper-gold site 240 km north of Whitehorse that would produce a higher-grade feed of between 1000-2000 tonnes per day.

  Production at the high-grade open pit mine will average 45 million pounds of copper per year over an eight-year mine life, starting January 2010. To increase production, Capstone is considering increasing mill capacity to 7500 tonnes per day and would focus on mining resources from outside the current proposed open-pit limits.

  The underground option is proving more attractive from an investment perspective, the company says, and it plans to make the option a priority. The new net present value of the project is estimated at $199 million after tax, using a 7% discount and a copper price of US$2.25 per lb.

 Reserves have been increased more than 30% to 10.9 million tonnes grading 1.64% copper, 0.64 grams gold per tonne and 5.9 grams silver, containing 395 million lbs copper, 224,000 oz gold and 2 million oz silver.

  The mine was brought into production in 2007