- Types of Mines

Open Pit mines

Open pits have become the favoured mining method in recent years. This has been driven by major advances in the size and efficiency of large mobile equipment. Large equipment moves rock cheaply and as a result lowers the cutoff grades at which gold mineralization becomes profitable.

This virtuous circle has contributed to mines being developed (and value created) where gold grades were previously too low. In the case of oxide gold mines, this process has been further helped by the low-cost heap leaching treatment method.

This treatment method avoided the need for a large upfront capital investment in a conventional mill and thus further lowered the pay limit (and probably, more importantly, the risk) for new mine developments.  Consequently, what were previously marginal gold resources became profitable.

Mobile equipment has advanced in size over the last 20 years. Initially trucks carried about 70 tons and the shovels that loaded them were optimal if they delivered about a third or 25 tons per pass. Now with trucks typically carrying 250tons and some 500 tonners arriving, the loaders have also jumped in size. The limiting factor on the trucks has been tyre size, and in particular the challenge of getting economic lives out of tyres. In early designs tyres became very hot, greatly shortening the life of the tyres.

Underground mining

Underground mining methods are far more variable than open pit mining; the approach used must be the most cost effective one that fits in with the configuration of the ore zones, the strength of the ore, and the surrounding rock.