Summary:
The manganese mineralisation at the Butcherbird Project with the most economic value occur where the manganiferous shales of the Ilgarari formation intersect the weathering profile and display a supergene overprint where deep chemical weathering has upgraded the grade of the manganese and partitioned the manganese mineralisation into discrete high-grade bands, resulting in an ore that is amendable to simple physical beneficiation.
The Project lies in the Bangemall Basin, near the eastern boundary of the Savory Basin in central Western Australia. The Bangemall Basin features three main rock units: the Backdoor Formation (shales, mudstone, and minor siltstone); the Calyie Sandstone (quartzite sandstone to the north) and the Ilgarrari Formation (grey/white shales, mudstone, and dolerite sills, containing the target manganiferous shales).
Locally, the Project comprises a stratiform sedimentary sequence hosted within the Ilgarrari Formation, which is mostly flat lying with some occurrences of gentle folding. Mineralisation occurs within a manganiferous surface cap, a supergene manganiferous laterite, and a basal shale. Where the hardcap material is mineralised, the mineralisation is from surface. The manganese occurs as sub-horizontal layers within bounding clays, and the average thickness of the mineralisation is approximately 5 metres. The dominant strike direction is east west.
The Butcherbird project consists of a number of stratiform sedimentary manganese deposits hosted within the Ilgarrari Formation, which is mostly flat lying with some occurrence of gentle folding.
The manganese mineralisation occurs within three primary ore zones;
- High grade manganiferous hardcap;
- Supergene enriched manganiferous shale;
- Basal shale.
There are five major lithologic units within the Project area capped by a thin botryoidal duricrust, with the duricrust ranging in thickness from 0.1 metres to 2 metres.
The lithological units are as follows:
- Cap Rock occurs intermittently across the Project area, particularly away from the Yanneri ridgeline. The cap rock is comprised predominantly of iron-rich calcretes and soils with minor occurrences of manganiferous bands with botryoidal and cemented textures. The economic cut-off grade for the Cap Rock for the October 2024 MRE is 25% Mn, as the intrinsic manganese may not be upgraded within the current process.
- Manganiferous Shale is the primary shale unit containing a supergene-enriched manganiferous sequence with an average thickness of 10m to 25m. The manganese layers are predominantly 1cm to 1m thick which are confined to distinct bands of cryptomelane within goethitic friable clays. There are also very minor interbedded red/brown shales intermixed within the clay bands. Botryoidal textures are a common characteristic observed within the manganese mineralisation zone, in particular the clay rich zone. The geological cut-off grade used for the October 2024 MRE for the manganiferous shale is 6% Mn. The economic cut-off grade for the manganiferous shale is 7% Mn. With the removal of the unmineralised clays the remaining manganese is economic. For the October 2024 MRE all basal shales were currently considered uneconomic and were designated as unclassified material.
- Dolerite Unit is a medium-grained weathered unit interbedded between the two basal shales which exhibits relatively parallel bedding that have undergone gentle folding.
- Basal shale: Lower Shale; capped by the weathered dolerite.
The combined extents of the four deposits (Coodamudgi, Mundawindi, Richies Find, and Yanneri) extends from approximately 769,500mE to 778,800mE, and 7,297,000mN to 7,299,500mN (GDA94 with projection MGA Zone 50).