3. What is the chemistry of tungsten mineralisation?

There are two key naturally occurring ore minerals of tungsten: wolframite and scheelite.  In mining one or both these minerals are extracted from the ore and concentrated.  Ore grades are normally quoted as percentage of wolfram trioxide WO3, or percentage tungsten metal. 

Wolframite is an iron-manganese tungsten oxide (Fe, Mn) WO4. Wolframite is a black to grey/brown primary ore of tungsten, with a submetallic to resinous lustre. Wolframite is named after the German word wolfram which means "tungsten." The iron rich variety, called Ferberite, contains 76.3% WO3; the manganese rich variety is called Hubnerite and contains 76.6% WO3.

Scheelite is a calcium tungstate, CaWO4, named after the discoverer of tungsten, K. W. Scheele. Scheelite crystals are translucent, ranging in colour from white, yellow, through orange or greenish grey to brown, with an adamantine to greasy lustre, and fluorescence bright blue-white under ultraviolet light. Sheelite contains 80.5% WO3.