Effective land-use
planning requires accurate knowledge of mineral resource potential. Mineral
companies during reconnaissance exploration, feasibility investigations and mine
development also use this type of analysis. The Institute of Geological and Nuclear Sciences is
undertaking a two-year project reviewing the resource potential of the West
Coast of the South Island of New Zealand. Spatial prospectivity models have been
developed as part of this resource assessment process, using computer based
statistical pattern recognition techniques to delineate areas that are
prospective for mineral deposits and to test deposit genesis models. Digital GIS
data-sets of mineral occurrence were correlated against geology and exploration
information. The distribution of mesotherrnal shear zone gold deposits in the
Reefton Goldfield, were examined against geological data-sets from both the
regional (QMAP) and local prospect-scale mapping. Weights of evidence analysis
generated a correlation matrix that highlights relationships and degrees of
association that might otherwise not normally be recognised.

Mesothermal shear zone
gold deposits have strong positive spatial correlations with Greenland Group
host rocks and areas with moderate to high quartz vein densities;
moderate-strong positive correlation with regions <500 m from folds, with>
regions <600 m from faults and five to eight kilometres from granite>
contacts; moderate correlations with Ntrending fault and fold segments; and
no/weak/poor correlations with fault intersections, fold-fault intersections,
bends in regional structures and magnetic and radiometric data. The regional and
prospect scale data sets give different results, with the more detailed prospect
scale mapping giving generally better correlations. This emphasises the value of
detailed geological mapping in the exploration process.

Maps
generated by prospectivity modelling consistently highlighted areas of known
mineralisation and generate targets where follow-up investigation is warranted.
The prospectivity per unit area provides a measurable value that should change
as new information comes to hand and, in addition to highlighting targets, can
be used to measure the impact of increased exploration expenditure and assess
the effectiveness of exploration investment.