CH2 – Geological Mapping – Property Scale – Yukon Territory, Canada


This example illustrates how bedrock geological maps and related mineral exploration models can be improved through use of airborne gamma ray spectrometric and corresponding magnetic data. The example is from a 1993, 500m line-spaced helicopterborne gamma ray spectrometric and magnetic survey over the Dawson Range, central Yukon-Tanana Terrane, where mid-Cretaceous plutonic rocks host copper occurrences. The survey overlies unglaciated terrain (rare in Canada) where deep weathering and lack of fresh bedrock exposures hinder conventional mapping and exploration.

GamX CH2 Field Spectrometric Measurement Photo

Combined with field study1 (photo) effectively focussed by the airborne survey results, the data were used to significantly revise local geology, identify geological units and alteration haloes spatially associated with mineral occurrences.

GamX CH2 Mapping Dawson Range Yukon

 

 

 

Figure 1: Pre-airborne survey geology shows younger, felsic intrusive phases in pink cutting older more mafic phases in orange, with oldest, volcanosedimentary rocks in grey-blue. Copper occurrences are shown. Four mafic dikes are outlined as rectangles. The related geological contacts have been overlain on all subsequent images, for comparison.

 

 

 

Figure 2: Airborne Potassium (%) clearly delineates the youngest, felsic intrusive phases via higher K concentrations; the older volcanosedimentary rocks have relatively lower K. Incorrectly mapped contacts are apparent in at least two locations (see white arrows). Alteration associated with the copper occurrences produces highest K, and lowest eTh/K ratios (not shown).

 

 

 

Figure 3: Residual magnetic total field (nT) shows the felsic intrusive phases have low magnetic values (as expected) and the patterns further support revised contacts. The mafic dikes are quite magnetic, and extend well beyond their previously mapped limits. Copper is also associated with this arcuate feature.

 

 

 

 

 

Figure 4: Post-airborne and ground surveys geology provides accurate location of the most prospective intrusive phases and increased strike length along the central, intrusive mafic dike system represent significant bedrock mapping improvements in this area of typically poor bedrock exposure. This, in turn, supports much better exploration focus for copper in the area.

 

 

 

 

 

 

 

 

 

 

 

  1. Johnston, S.T., and Shives, R.B.K., 1995. Interpretation of an airborne multiparameter geophysical survey of the northern Dawson Range, central Yukon: A progress report. In: Yukon Exploration and Geology, 1994. Exploration and Geological Services Division, Yukon. Indian and Northern Affairs Canada, p. 105-111.