There is a wealth of information to be found in some historical data. Even where it appears that previous sampling programs have sterilized the region for the presence of mineralization, compilations of existing data can often reveal hidden opportunities where previous sampling may have been ineffective. The adjacent catchment basin map demonstrates this point for northern Vancouver Island where it was determined through a review of previous stream sediment (moss mat) multi-element geochemical data that catchment basins greater than 10 km2 are likely to have experienced enough dilution to conceal evidence of exposed porphyry Cu mineralization within the catchments. The application of catchment analysis to an existing, publically available data set has revealed the extent of effectively sampled terrain on north Vancouver Island and indicates potential for further in-fill sampling.
Northern Vancouver Island, Canada
Catchment basins with areas greater than 10 km2 on northern Vancouver Island interpreted ti have been under-sampled (from Arne & Brown, 2014).
QUEST South Porphyry Cu-Au-Mo Percentile Gridded Image
Data from multiple map sheets have been compiled and corrected for the effects of metal scavenging onto secondary iron hydroxides. The data are overlain by regional structural trends, defined by the dark thin lines (from Arne & Bluemel, 2011).
QUEST South, BC, Canada
Other opportunities exist to add value to existing data set through the merging of data from different surveys to form regional compilations that reveal large-scale trends within the data. Data from different surveys may be levelled to remove analytical artefacts related to the use of different laboratories, digestion and/or analytical methods. Surficial geochemical data can further be levelled for the effects of background lithological variation or the effects of metal scavenging onto clays, organics or secondary iron or manganese hydroxides. Similar strategies can be pursued using lithogeochemical or other forms of geochemical data. The adjacent figure shows a percentile gridded additive image for Cu, Mo and Au in stream sediment data from the QUEST South study region of southern British Columbia, Canada following regression analysis to correct the data for the possible effects of scavenging of metals onto secondary iron hydroxides. The dark lines represent major structural lineaments from the geology map superimposed on the geochemical image. Geochemical patterns clearly follow major structural trends in some places, as well as reflecting known porphyry Cu deposits and occurrences. New targets unrelated to known deposits or occurrences are indicated in the gridded image based on the compilation and review of historical data.