Ore reserves suitable for surface mining can be classified initially as; * Relatively horizontal stratified reserves with a thin or thick covering of overburden * Stratified vein-type deposits with an inclination steeper than the natural angle of repose of the material so that waste cannot be tipped inside the pit * Massive deposits, deep and very large laterally such that dumping of the waste within the pit is not possible.
When any ore body lies a considerable distance below the surface, the amount of waste that has to be removed in order to uncover the ore through surface mining becomes prohibitive, and underground techniques must be considered.
Biomining is an application of biotechnology in recovery of various minerals from ore. Biomining is defined as extracting mineral ores or enhancing the mineral recovery from mines using microorganisms instead of traditional mining methods. Copper was the first metal extracted using microorganisms in the ancient past in the Mediterranean region. Biomining is becoming popular because it is cheap, reliable, efficient, safe, and environmentally friendly, unlike traditional mining methods. The efficiency of biomining can be increased either by finding suitable strains of microorganisms or by genetically modifying existing microorganisms, made possible due to rapid advances in the field of biotechnology and microbiology. Ores of high quality are rapidly being depleted and biomining allows environmentally friendly ways of extracting metals from low-grade ores (ores that have small amounts of valuable metals scattered throughout).
Biomining includes two different chemical processes called bioleaching and biooxidation. Thus, biomining is an application of biotechnology and is also known as microbial leaching or alternately, biooxidation