The Groote Eylandt manganese mine has been in operation since 1965, and has produced more than 115 million tonnes of manganese ore and concentrate to June 2018. The mine is operated by the Groote Eylandt Mining Company Pty Ltd (GEMCO), which is majority owned by South 32 Ltd.
The ore is mined by shallow open-cut mining methods and is transported by road to a nearby port. Production in 2020/21 totalled 5.88 Mt of manganese ore. The deposit comprises oolitic and pisolitic sedimentary manganese within the Cretaceous Carpentaria Basin.
The Bootu Creek mine is 110km north of Tennant Creek and commenced operation in 2005. The mine is operated by OM Manganese Ltd, a subsidiary of Singapore-based OM Holdings. In 2020, production of manganese concentrate (lumps and fines) totalled 0.74 Mt.
An ultrafines plant to process tailings at the mine was commissioned in March 2020.
The Bootu Creek deposit is a hydrothermally modified sedimentary deposit hosted in Palaeoproterozoic rocks of the Tomkinson Province.
Winchelsea Mining Pty Ltd has a granted exploration licence covering part of Winchelsea Island, off the northwest coast of Groote Eylandt, Carpentaria Basin. The company is a joint venture between the Anindilyakwa Advancement Aboriginal Corporation and AUS China International Mining. Drilling in 2019 and 2020 delineated a shallow mineralised zone covering an area ~1 km by 2 km. The mineralisation is the same style as the Groote Eylandt deposit.
In December 2020, the company submitted a referral document to the NT EPA for a staged open cut mine plan that targets an annual production rate of ~1.4 Mtpa with a potential mine life of 14 years. The mineral resource estimate for the project has not been publicly announced.
Further potential for sedimentary hosted manganese occurs in relatively unexplored regions of eastern Arnhem Land, along the western margin of the Carpentaria Basin, where manganese was precipitated during a Cretaceous marine regression on coastal terraces and troughs.
Sedimentary or secondary manganese deposits are also present in the Amadeus Basin (for example, Wangatinya), McArthur Basin (for example, South Rosie Creek), Georgina Basin and South Nicholson Basin.