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Department of Mines, Industry Regulation and Safety

MnO/(CaO + MgO) 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/(CaO + MgO) index demonstrates areas where MnO has been enriched relative the removal of CaO and MgO – a process that is potentially recorded in carbonate-rich rocks where dissolution of calcite and dolomite by fluids may result in the concentration of less soluble MnO.

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.

Legend Range Classification
MnO/(CaO + MgO) index TRAP 11.75 – 23.19 Manual breaks
  5.21 – 11.74 Manual breaks
  1.31 – 5.20 Manual breaks
  0.31 – 1.30 Manual breaks
  0.00 – 0.30 Manual breaks


GSWA near-surface geochemistry (Accelerated Geoscience Program data release)

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