RESOLVING BURIED STRUCTURES WITHIN POLY-DEFORMED REGIONS: CONSTRAINED GEOPHYSICAL MODELLING OF THE BATHURST AND BAIE VERTE MINING DISTRICTS

The Bathurst Mining Camp (BMC), NB, and Baie Verte Peninsula (BVP), NL, represent two of the most important mining districts in the Canadian Appalachians. Although these districts host numerous deposits and occurrences, the great majority were discovered over fifty years ago and almost all because they directly outcrop at surface. As with many mature mining camps, the likelihood is that if there are significant deposits awaiting discovery, then they will be hidden or deeply buried. In spite of the structural complexities of poly-phase deformations and, with exception of the coastal portion of the BVP, both areas having poor outcrop control, the distribution of units at surface are reasonably well defined. However, the traces of these units to depth have mostly been very poorly constrained. Particularly for the BMC this is partially due to multi-phases of steeply dipping fabrics that do not necessarily reflect the overall enveloping surface of mineralised horizons. Detailed investigation and integration of geophysical and geologic data provides an improved understanding of the 3D geological structure, which in turn enhances the ability to vector in on mineralised horizons, even into areas that have hitherto been considered largely unprospective.

Reprocessing, inversion and integration of airborne geophysical surveys, ground gravity data, digital elevation models and physical property measurements on a series of transects across major structural and/or economically significant parts of these mining districts have been developed. For the BVP, these indicate that the economically very important Lower Pacquet Harbour Group tectonically underlies the Cape Brule Porphyry and that the Betts Cove Complex is a basinal structure segmented by listric faults. For the BMC, gravity models indicate: a) the Flat Landing Brook Formation is locally up to 10km thick, and b) to the southeast of the BMC there is an unexposed ophiolitic complex, for which the Tomogonops Formation is in part its cover, as opposed to it overlying the Little River Formation. Models also indicate that the Miramichi Group is tectonically emplaced as thin sheet over the younger Sheephouse Brook felsic volcanic rocks and the associated Chester ore horizon, effectively increasing the area of high mineral prospectivity by approximately 35%.