Geological significance of high-resolution aeromagnetic and radiometric data in the area of the Naver and Ste. Marie plutons, central British Columbia: an example of remote predictive mapping (RPM)

Abstract

New aeromagnetic data collected at 400 m line spacing in the area of the Naver and Ste. Marie plutons, central British Columbia, provide images of the magnetic field at sufficiently high resolution to examine finer elements of the bedrock geology, which is largely hidden by ubiquitous Quaternary glacial cover. The data offer a wealth of information on the internal structure and lithological variations of many units defined by 1 : 250 000 scale geological mapping. Complementary airborne radiometric data collected in the same survey contribute to the analytical process and to an evaluation of the mineral potential in the area. One of the principal outcomes of the analysis is a picture of the detailed structural fabric of the area provided by images of vertical derivatives of the magnetic field that proxy as predictive maps. This fabric is an important framework for developing exploration strategies. Patterns and other characteristics of the magnetic field have been used to revise positions of some geological boundaries, delineate domains within the Naver and Ste. Marie plutons, map faults, and speculate on sources of magnetic anomalies having no apparent link with mapped geology, some of which are probably intrusions. Radiometric data have been used to supplement the magnetic interpretations in some cases, but their main utility has been in evaluating the area for its potential for copper-porphyry-type deposits. The characteristic potassium enrichment associated with these deposits can be manifested in radiometric data as potassium highs and, critically important, Th/K lows. Several such features of interest are discussed. An important conclusion based on radiometric data is that glacial transport in the area has been minimal, probably no more than a few kilometres. The significance of this, in this area of widespread glacial cover, is that radiometric signatures can be confidently interpreted to represent bedrock directly below them. The same confidence can be applied to geochemical data derived from glacial tills, and this is of considerable significance for mineral exploration.