This kind of mining is done when the rock or mineral is on the side of a mountain. This makes it an easy, cheaper way to mine. Minerals that are mined with draft mining are gold, coal etc. with slope mining, the coal or mineral bed is located very deep and parallel to the ground. It is called a slope mine because the shafts are slanted.
Besides allowing the extraction of gold this process allows the recovery of virtually any other metal found associated with Black shales including rare earth elements. For just gold mining this process would obviate the use of cyanide or mercury for the extraction of gold. By fine tuning the process any number of other metals can be extracted.