in mining, gangue / ɡæŋ / is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. it is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body that are displaced during mining without being processed, and from tailings, which is rock .
mineral resource classification is the classification of mineral resources based on an increasing level of geological knowledge and confidence. mineral deposits can be classified as: mineral resources that are potentially valuable, and for which reasonable prospects exist for eventual economic extraction.; mineral reserves or ore reserves are valuable and legally, economically, and technically .
volcanogenic massive sulfide ore deposit at kidd mine, timmins, ontario, canada, formed 2.7 billion years ago on an ancient seafloor. a cross-section of a typical volcanogenic massive sulfide vms ore deposit as seen in the sedimentary record. volcanogenic massive sulfide ore deposits, also known as vms ore deposits, are a type of metal .
hard rock gold mining extracts gold encased in rock, rather than fragments in loose sediment, and produces most of the world's gold. sometimes open-pit mining is used, such as at the fort knox mine in central alaska.
gossan eiserner hut or eisenhut is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. in the classic gossan or iron cap all that remains is iron oxides and quartz , often in the form of boxworks which are quartz-lined cavities retaining the shape of the dissolved ore minerals .
hard rock ores have formed the basis of the majority of commercial gold recovery operations since the middle of the 20th century where open pit and or sub-surface mining techniques are used. once the ore is mined it can be treated as a whole ore using a dump leaching or heap leaching processes.
porphyry deposits represent an important resource of copper; however, they are also important sources of gold and molybdenum - with porphyry deposits being the dominant source of the latter. in general, porphyry deposits are characterized by low grades of ore mineralization, a porphyritic intrusive complex that is surrounded by a vein stockwork .
the two principal mines, campbell and red lake, both have historic ore grades averaging about 0.57 oz/ton au 22 g/tonne . the rocks and mineralization features in this district are complex. the host rock here is a metamorphosed tholeiitic basalt dating to 2.85 billion years early neoarchean .
after the end of the sierra leone civil war exploration of gold grew and by 2013 to 2015 new modern mines are expected to be in production. in 2010 cluff gold, a british company, found gold deposits in the rocks of the southern kangari hills and is planning to build a mechanised mine to extract it.
the mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. the samples of matter used by mohs are all different minerals. minerals are chemically pure solids found in nature. rocks are made up of one or more minerals.