Geochemical prospecting of an Appalachian porphyry copper deposit at Woodstock, New Brunswick

Abstract

A project to discover a porphyry copper deposit in New Brunswick commenced in 1965. In 1970, after five years of outcrop and boulder prospecting assisted by a major soil sampling survey, the discovery of ore-grade prophyry copper mineralization was made. The discovery area is mantled with 2–20 ft (0.6–6m) of soil. The mineralization occurs as chalcopyrite disseminations and fracture fillings within a Devonian age quartz diorite stock. The host Cambro-Ordovician quartzites and argillites have been sericitized and contain chalcopyrite disseminations and fracture fillings. Non-magnetic pyrrhotite and pyrite occur in amounts up to 10% by volume. Trace amounts of magnetite and molybdenite are present. More than a dozen significant soil Cu anomalies have been discovered within an area of 8 sq. miles (20 km 2). Nine of these have been trenched by 8 miles (13 km) of bulldozer trenches. Each anomaly was found to be underlain by copper mineralization in bedrock. Various amounts of drilling, induced polarization surveys and magnetometer surveys tested three major anomalies. Significant areas containing 0.3–1.0% Cu were discovered but no orebody has been outlined to date. It is shown that regional stream geochemistry, done in sufficient detail, would locate similar occurrences in Northern Appalachia. With the possible exception of traditional prospecting of boulders and outcrops, stream and soil geochemistry over well-selected geological targets are the best methods for discovering porphyry copper mineralization in this region. The existence of porphyry copper mineralization of economic interest in Northern Appalachia has been proved and the successful use of geochemistry in the discovery of such mineralization is demonstrated.