Bryson Burke Diamond Corporation: Diamond Exploration and Mining in Canada

7.0 GEOPHYSICS

Fresh kimberlites may contain five to 10 percent iron oxides that generate a strong magnetic signature. As near-surface material weathers it breaks down into an electrically highly-conductive clay-rich horizon.

A more modest, but still detectable conductivity anomaly in fresh kimberlites and lamproites is due to serpentinization of olivine. Ideally a kimberlite or lamproite will display a conductivity response coincident with a slightly smaller, strong magnetic response. Magnetic anomalies are not masked by overburden, but merely become broader and more diffuse as the sensor to source distance increases (Urquhart and Hopkins, 1993).

In the Central Gneiss Belt the recognition of magnetic anomalies attributable to kimberlite or lamproite bodies is hampered by the presence of complexly folded gneisses that commonly contain layers of magnetic schist, pyroxenite, and amphibolite. These rocks commonly form oblate masses on fold noses and other pod-like bodies causing magnetic signatures of a size and shape that could also be indicative of kimberlites or lamproites. The challenge in interpretation is not due to the absence of magnetic anomalies that are possibly indicative of kimberlite bodies, but an overabundance of such targets.

Other than the ground-magnetic profile surveys conducted by Bryson-Burke Resources and Burke which are both too restricted and too sparse to be meaningful, the only potentially-useful geophysical data available for the area of the Properties is the 250,000-scale Geological Survey of Canada airborne magnetic survey mapsheet NTS 31K. The data used to generate this map were collected on flight lines flown at 800-meter intervals. This line-spacing is too broad to be expected to detect magnetic bodies of a size reasonably attributable to kimberlite or lamproite intrusives. Despite this inherent limitation, the map does indicate the presence of a north-trending zone of high magnetic response that is at least in part at variance with the regional magnetic pattern that can confidently be attributed to the Grenville gneisses. (Figure 10)

This anomalous trend is parallel to and slightly east of the line of 77̊ West longitude, between 46̊ 15' and 46̊ 45' North latitude. The north end of this trend is a large circular feature that most probably reflects a domal gneiss structure in this area, but to the south, in the area of 46̊ 30' North, the magnetic response is equally intense and not self-evidently attributable to the gneisses. This portion of the anomalous northerly trend is coincident with Bryson Lake. The significance, if any, of this anomaly is not known and the coarseness of the data does not permit any greater level of inference, however, it does coincide with the postulated source-area for the indicator minerals found immediately south of Bryson Lake. The shaded-relief presentation of this data (Figure 11), appears to indicate a discrete north-trending linear through the axis of this larger magnetic anomaly, perhaps suggestive of a north-trending tectonic structure.

A circular magnetic low feature in the vicinity of Gerland Lake is of potential significance because it is proximal to the location of four samples from this area that contained indicator-minerals (Section 8.1, below).