how much mn?

Here is an exerpt from the Australian Government Geoscience website.

http://www.australianminesatlas.gov.au/education/fact_sheets/offshore_minerals.jsp

Extensions of onshore mineralisation

Probably the most common form of offshore exploration and mining occurs as an extension to mining onshore deposits. Examples of where mineralisation is known to extend offshore from onshore deposits, or where exploration has been carried out offshore for such extensions are:

Coal. At Newcastle in New South Wales, offshore seams have been mined by underground methods from onshore. The Gippsland Basin off the coast of Victoria has brown coal deposits.
Scheelite (tungsten). At King Island off Tasmania, mineralisation occurs in basement rocks of the continental shelf surrounding the island.
Manganese. At Groote Eylandt off the eastern Northern Terrritory rich manganese beds in the Lower Cretaceous are known to extend off the island.

So the Govt knows that it exists but anyone want to speculate on how much Mn GOT may have and what dollar value this may equate too?

Cheers