Mapping Bedrock Topography Beneath Glacial Overburden Near Cape Horn, South America

Placer gold mining operations were carried out on several of the small islands between Tierra del Fuego and Cape Horn in the late 1800’s, just before the Klondike gold rush. As soon as the Klondike rush was announced to the world many of the miners and prospectors working in this isolated region went north. The area was quiet for nearly a hundred years before there was any renewed interest in it. This was due to the dispute between Chile and Argentina over ownership of these islands. Although the Chilean government was eventually granted ownership of these islands it is only recently that any exploration activity has occurred. A placer gold exploration program that included surface sampling, geological mapping and bulk sampling was carried out in the early 1990’s. The project looked promising but there was difficulty in unravelling the glacial history and obtaining estimates of gravel thickness for tonnage calculations. Bemex Consulting International was asked to set up a program to map the bedrock topography and estimate gravel thickness. The project was carried out in two phases. The first phase was carried out during the summer season (December) to determine if time-domain EM soundings would provide the necessary accuracy to meet the above objectives. At the end of this phase the conclusion was the Geonics EM-47 system was capable of mapping the gravel thickness and bedrock topography. The second phase was conducted the following summer (January and February) and consisted of carrying out more than two hundred 40 m x 40 m loop soundings at the site. The results of this survey were verified with a series of manholes dug to depths varying from 15 m to more than 30 m. The depth to bedrock in these holes was consisted with the 1D interpretation provided from the Interpex software.