Tungsten ore is usually mined underground. Scheelite and/or wolframite is frequently located in rather narrow veins which are slightly inclined and often widen with the depth. Open pit mines exist but are rare.Most tungsten orescontain less than 1.5% WO3 and ore dressing plants are always in close proximity to the mine.The ore is first crushed and milled to liberate the tungsten mineral crystals.Scheelite ore can be concentrated by gravimetric methods, often combined with froth flotation, whilst wolframite ore can be concentrated by gravity, sometimes in combination with magnetic separation.
Most tungsten ore flotation concentrates and some table concentrates are not of sufficiently high grade to meet the exacting specifications of the market. The principal diluents are phosphates and carbonates, which are difficult to depress sufficiently in flotation. The removal of these minerals is most frequently accomplished by leaching the concentrates with hydrochloric acid. Because of the relatively simple equipment required, the trend has been toward leaching at the flotation plant. However, a number of custom leaching plants are equipped to treat flotation concentrates from the smaller concentrators.