What is this layer?
MnO/SiO2 content for all sample media included in the GSWA near-surface geochemistry datasets. This statewide dataset includes information from WACHEM, OZCHEM (the WA subset), CRCLEME-laterite and WAMEX (surface rock chip, stream, soil and shallow drillhole).
The MnO/SiO2 index demonstrates areas where MnO has been enriched relative to SiO2. This index is a proxy for enrichment of MnO in silica-rich sedimentary rocks via the removal of silica (e.g. supergene dissolution of quartz bands in banded iron-formation).
A unique legend and colour scheme has been chosen for this geochemical layer to best highlight geochemical trends, via a 3 × 3 cell mean neighbourhood statistics raster. Cell resolution is 0.05º (~5 km). Areas in red indicate a higher value.
The use of this ratio ‘normalizes’ disparate primary data sets obtained from different sample media, using a variety of laboratory methods, allowing their combination and comparison. Even so, all these indices will be sensitive to precursor rock chemistry and to the effects of overprinting events, such as weathering. These factors need to be taken into consideration when interpreting alteration indices.