Innovations in Exploration Technology and Exploration Targeting
Muon geotomography, a novel geophysical exploration and imaging technology, uses cosmic rays to create three-dimensional (3-D) images of subsurface density distributions. The first controlled field test confirming the capability of muon geotomography for imaging a dense orebody in a complex geologic environment was conducted at the Price volcanic-hosted massive sulfide (VHMS) deposit, Vancouver Island, British Columbia, Canada. The semimassive and massive polymetallic mineralization of the Price deposit is situated in a Paleozoic stratigraphic package of rocks known as the Sicker Group including the Price, Myra, Thelwood, and Flower Ridge Formations, indicative of volcanic rocks formed in a rifted oceanic island-arc system. The field application involved placing a sensor with an active area of 1 m2 beneath the massive sulfide orebody in an underground tunnel for exposures of about two weeks at several locations. Muon flux data were inverted to recover a 3-D density image of the deposit. The inverted data were in good agreement with drill core data. However, some distortions of the image were observed due to the limitations imposed by the available tunnel which restricted the angular views available to the sensors. Muon geotomography works best when sensors are placed such that they can view the region under study from a range of different angles. The demonstrated ability to perform accurate forward model simulations makes the sensitivity of the technique predictable for specific survey situations. The results demonstrate the potential of muon geotomography for identification and characterization of orebodies located in complex geologic environments. Three-dimensional images from muon geotomography surveys may be used to guide drilling operations toward regions of high-density contrast, thereby significantly reducing costs and environmental impact associated with locating orebodies.