The terrain of northern Vancouver Island is considered ideal for the automated generation of catchment basins, which help define the zone of geological influence on a specific stream sediment sample site. For this reason, this project is using stream sediment data collected as part of the Northern Vancouver Island Exploration Geoscience Project, a partnership between Geoscience BC and the Island Coastal Economic Trust.
Raw copper data in stream sediment samples obtained from moss mats on Northern Vancouver Island are dominated by the presence of mafic volcanic rocks of the Karmutsen Formation and, to a lesser extent, by the presence of diabase sills of the Mount Hall Gabbro. These units can effectively be traced using the first principal component from multivariate analysis of the raw geochemical data. High background copper in these lithological units potentially obscures copper anomalies associated with exposed copper deposits in the region.
By examining previously published geochemical data from 1725 samples from Northern Vancouver Island, and using copper as the demonstration element, this study illustrates that there are a variety of ways to process raw copper data in areas strongly influenced by a particular rock type. Nested catchments for the samples were delineated automatically from digital elevation data using a procedure developed by the B.C. Geological Survey.
A limited number of map products are included in Geoscience BC Report 2015-04, designed to illustrate the relative effects of different data processing options for copper. Digital data files that accompany the report contain the catchment polygons as well as the leveled and residual data for a number of elements.