Summary:
Silica sand mineralisation at Si2 Deposit occurs within the Cape Bedford / Cape Flattery Dune Field. The targeted silica sand deposits are the trailing arms and apex of elongate parabolic aeolian sand dunes.
The Cape Bedford / Cape Flattery Dune Field is one of several extensive areas of aeolian dunes which occur on the tropical east coast of Cape York Peninsula. The dune field covers an area of 700km2 and contains a variety of depositional and erosional landforms. The dominant source sand of the dune field is considered to be from the weathering of Mesozoic sandstone such as the Gilbert River Fm, and the Dalrymple Sandstone, however coastal granites and the Hodgkinson Fm are likely additional sources of sand.
As the Mesozoic sandstones are the aquifer units within the Laura Basin, they are likely to have been exposed to leaching while hosted within the sandstone, prior to exposure to erosional processes. Strong prevailing South-easterly winds appear to have been the consistent wind direction in the region, and still prevail today for most of the year. These winds are the energy source for the establishment and remobilisation of the sand dune systems.
The mineral resource is generally constrained to the trailing arms and apex of elongate parabolic dunes, which can be clearly defined using the surface LiDAR imaging. Drilling often intersects overlapped dunal features, which are not represented by LiDAR or aerial photography. Conversely, the interdunal areas are often devoid of thick aeolian sand and predominantly exhibit exposed B1 horizons, clays, bedrock, or other sediments. Where drilling has intersected obscured silica sand mineralisation, the sampled sand has been included in the geological model. There is an observable basement high on the topographic high towards the coastline on the western dunes.
The deposit style is an unlithified aeolian sand deposit, comprised of a series of complex parabolic and elongate parabolic dune systems repeatedly reworked and are superimposed upon older dune systems.
Geology
The Northern Silica Project is comprised of unlithified aeolian dune complexes. The Cape Flattery & Cape Bedford dune fields are aeolian dunes established in the Pleistocene epoch and regularly remobilised during the Pleistocene and Holocene epochs. The dune fields are situated on a coastal plain overlying the Hodgkinson Formation basement with Dalrymple Sandstone forming mesa on basement highs. Mineralisation is thought to be due to repeated eluviation and illuviation events on immobilised dune systems comprised of an existing quartzose sand source, with reactivated dune systems also exhibiting mineralisation. Intradunal valleys tend to be a surface expression of the B1 horizon, and typically are not considered mineralised. Deleterious metals are thought to have been eluviated by organic acids, which are transported by gravity through the stratigraphic column and illuviated either by binding to clay rich horizons, or transported away from the deposit through the water table.
Geological interpretation
Silica sand mineralisation at the Si2 Deposit occurs within the Cape Bedford / Cape Flattery Dune Field. The targeted silica sand deposits are the trailing arms and apex of elongate parabolic aeolian sand dunes. The mineral resource is generally constrained to the trailing arms and apex of elongate parabolic dunes, which can be clearly defined using the surface LiDAR imaging. Drilling often intersects overlapped dunal features, which are not represented by LiDAR or aerial photography.
Conversely, the interdunal areas are often devoid of thick aeolian sand and predominantly exhibit exposed B1 horizons, clays, bedrock, or other sediments. Where drilling has intersected obscured silica sand mineralisation, the sampled sand has been included in the geological model. There is an observable basement high coincident with the topographic high towards the coastline on the western dunes.
Dimensions
The Mineral Resource Estimate spans a total area of approximately 1400 hectares with varying dimensions: a maximum length along strike of 9.5 km and a width up to 2.7 km. The average thickness of the resource is ~11 metres, though it can reach up to 55 metres. The top of the resource varies in elevation from 22 mRL to 114 mRL, corresponding to the topography, while the bottom ranges from 16 mRL to 96.5 mRL, aligning with the water table or resource basement level.