NTGS Report 13 (2001) - manganese deposits

The following updated notes are derived from the abstract of Ferenczi PA, 2001. Iron ore, manganese and bauxite deposits of the Northern Territory. Northern Territory Geological Survey, Report 13. Contact the Information Centre (telephone +61 8 8999 6443 or email geoscience.info@nt.gov.au) for copies of this report, available free-of-charge.

Manganese occurrences in the Northern Territory have been classified into three types: sedimentary, hydrothermal and surficial. Sedimentary Mn deposits along the western margin of the Carpentaria Basin are the most prospective target. The well documented Groote Eylandt deposit with past production of 50 Mt @ 49% Mn and total resources of 212 Mt @ 47.5% Mn, consists of stratiform, massive to disseminated ore in a sheet-like body averaging 3 m in thickness. Manganese minerals were originally precipitated during an early Cenomanian (~95 Ma) marine regression on coastal terraces and troughs.

Exploration by BHP Ltd in places along the southern and western margins of the Carpentaria Basin has identified several mineralised areas, the largest being at South Rosie Creek. Areas within the Late Albian shoreline, which have shallow marine sediments but no airborne EM coverage, are considered highly prospective for Groote Eylandt-style Mn.

Hydrothermal (diagenetic) Mn mineralisation has been previously interpreted as surficial in the Renner Springs district (Tennant Region). This style of mineralisation appears as stratabound massive replacement deposits in Palaeoproterozoic shallow marine sediments. A 612 m-thick manganese horizon at the base of the Palaeoproterozoic Bootu Formation can be traced for 24 km around a faulted syncline. Small-scale mining on the western side of the syncline at Mucketty produced 13 300 t @ 42% Mn between 1955 and 1969. Drilling on the eastern side at Bootu 4 by BHP Ltd within a conductive GEOTEM zone, intersected massive Mn mineralisation to 75 m depth. The lower 2 m of the Mn horizon hosts low-silica (<10%), high-grade (>40% Mn) ore.

The Renner Springs deposits are hosted in siltstone and dololutite near the base of the Palaeoproterozoic Shillinglaw Formation. A percussion drillhole (W38RDH) by Key Resources NL intersected 9 m grading 36.7% Mn including 3 m @ 42.4% Mn from 63 m depth. The resource potential for this Mn horizon is essentially untested. Mn mineralisation at Wangatinya (Amadeus Basin) consists of a series of massive bedding-concordant lenses averaging about 44% Mn. Surficial manganese occurrences in the NT are widespread and numerous, but appear to be an insignificant resource.