Manganese ore has been mined from the Peak Hill Gold- field since 1948 and from the Pi'lbaraGoldfield since 1954, and it is probable that some deposits- In and, near the Phillips River Goldfield will be mined at a future date', There are also several million tons of mariganiferous ;naterial which is too low in manganese. .co.ntent_ for . present requirements. The manganese depositsof Western Australia are mostly superficial. They hav' been formed during the Cainozoic Era by supergene enrichment 6f Precambbrian: manganiferoius sediments, and by deposition from -solution on, or'in caves in, the Cain- ozoic land surface. The manganese in solution was derived from the weathering of Precambrian manganifer.ous s.edimexsts, None of the deposits are of hydrothermal origin, nor are they related to igneous rocks in any war, other than as ultimate source rocks. There is ho evidence-'t.o.:sugge,st that meta- morphism has been responsible for.the emplacement of any deposit. The tenor of the ore varies'aec'ording'to the quantity of gangue in the orebody and- also to the nature of the part- icular ore minerals. The main ore.mine.rals are the oxides pyrolusite and cryptomelane and the 'o'xide-silicate braunite._x000D_
The main gangue minerals are hematite, limonite and quartz. The deposits of high grade ore(-above.45 per cent Mn) range in size from 50 tons to many thousands of tons but most of them are in the 500-5,000-tons r .nge .