Summary:
Bauxite deposits at Gove occur at a latitude slightly more than 12 degrees south of the equator. The bauxite appears to be a weathering product of Cretaceous marine sediments, which overlie Proterozoic basement rocks of the Arnhem Inlier. Uplift, weathering, and erosion of the sediments, as well as formation of the bauxite, took place during the Tertiary, but exact timing and detail of events remains uncertain. Marine reworking of weathered products is likely to have taken place, possibly more than once.
Pisolitic textures are dominant, with variable cementation. However, variably cemented coarser nodule horizons are also common. Some deeper bauxite, as well as underlying laterite, contain abundant interconnected solution cavities, which may have been created geochemically and/or biologically (associated with root channels). Modern day root channel structures and infill, in the upper part of the bauxite, are common. Gibbsite is the major ore mineral, with boehmite being of lesser significance.
Bauxite occurs on top of a gently undulating plateau at approximately 30 to 70m above sea level, over an area measuring approximately 20km east-west by 15km north-south as seen in the figure below. The plateau has been variably dissected by erosion into three main plateau areas. Main Plateau is the largest contiguous bauxite area, whilst Rocky Bay and Eldo are two adjacent smaller bauxite areas, figure below. The present day extent of the bauxite likely represents a fraction of what was originally present.
The bauxite horizon has historically been up to 10m thick but is more typically 2 m to 4 m in thickness. It comprises several distinct layers in either a dominantly cemented (“hard”) profile, or a dominantly poorly cemented to uncemented (loose or soft) profile. The latter tends to be thicker and occupies hollows in the plateau surface and is often considered to be a proximal erosion/deposition product of the “hard” profile bauxite.
Hard profile bauxite generally consists of footwall vuggy laterite (Lat), overlain by nodular bauxite (Lower Nodules – Nod), overlain by extremely vuggy “tubular” bauxite (Tub), overlain by strongly cemented pisolitic bauxite (Cemented Hard - CH), overlain by weakly cemented pisolitic bauxite (Cemented Soft - CS), overlain by a thin loose pisolite layer (LP), overlain by a thin overburden layer (OB) being a mix of loose pisolites and topsoil, figure on next page.
All of the lithologies described above are generally elevated in bauxitic alumina throughout the deposit plateau. The extent of the mineralisation described therefore depends on the chemical grade threshold and thickness limits applied.
The Gove deposits extend over an area approximately 20 km east-west by 15 km north-south that includes three separate lateritic bauxite plateaus (Main Plateau, Rocky Bay and Eldo). The bauxite horizon averages 3.5 m in thickness but can be up to 10 m thick and is typically 0.6 m (up to 8.5 m) below surface cover.
The Gove deposits extend over an area approximately 20 km east-west by 15 km north-south that includes three separate lateritic bauxite plateaus (Main Plateau, Rocky Bay and Eldo). The bauxite horizon averages 3.5 m in thickness but can be up to 10 m thick and is typically 0.6 m (up to 8.5 m) below surface cover.