GEOPHYSICAL CASE HISTORIES OF DISSEMINATED SULFIDE DEPOSITS IN BRITISH COLUMBIA

The growth of the mining industry in British Columbia in recent years has been mainly due to the development of large low‐grade disseminated sulfide deposits. The two problems faced by the geophysicist in the exploration for deposits of this nature are the difficulty of, one, detecting large volumes of rock containing a low‐percentage content of total sulfide mineralization and, two, obtaining some idea of the economic significance of the mineralization. Although the standard geophysical methods used in the search for disseminated sulfide deposits have been successfully applied, there are some aspects of the British Columbia deposits which create additional problems for the geophysicist. As illustrated by the Brenda, Valley Copper, and Lornex deposits, the lack of appreciable pyrite associated with the economic mineralization results in a low total sulfide content; this in turn makes it difficult to obtain a diagnostic anomalous geophysical response. Because of the rugged terrain and generally heavy forest growth, the more powerful geophysical methods, such as induced polarization, are high‐cost techniques. However, alteration and fracturing associated with the disseminated mineralization (Babine Lake area) may lower the overall resistivity of a deposit sufficiently to allow detection with electromagnetic (EM) methods. Although limited in application, the lower cost of EM methods in many situations renders their use practical, especially if airborne techniques can be employed.