Bryson Burke Diamond Corporation: Diamond Exploration and Mining in Canada

5.2 Property Geology

5.2.1 Rock Types

The local gneissic geology has no genetic relationship to the target kimberlite or lamproite intrusions which can be expected to be much younger and are structurally controlled. However, a brief description of the dominant lithologies within the Property area, taken mainly from Katz (1976), follows.

Quartzo-feldspathic and biotite-hornblende gneiss underlies more than 80 percent of the Property area (Figures 6a,b). The quartzo-feldspathic gneisses are leucocratic, fine to medium-grained, equigranular, quartz-feldspar-rich rocks that weather greyish-orange and are light-red to pink on fresh surface. The quartzo-feldspathic gneisses are frequently interlayered with dark amphibolites in undulous, discontinuous layers several centimeters thick. Accessory minerals may include ilmenite and magnetite.

The biotite and hornblende-gneisses are commonly fine-grained, equigranular rocks that weather to paleorange and yellowish-grey hues, and are greyish-blue on fresh surface. The biotite gneisses are conspicuously laminated or finely interlayered with alternating dark amphibolite and light quartzofeldspathic zones. These gneisses are commonly veined and injected by abundant pegmatitic material and display porphyroblastic textures. The hornblende gneisses are not commonly laminated but are interlayered with amphibolite. Accessory minerals include ilmenite-magnetite, locally in significant amounts.

Garnet gneiss underlies 10 to 15 percent of the property area. These gneisses are medium-grained bluish-white weathering rocks that are pale-pink on fresh surface, and contain conspicuous crystals of very dark-red garnet. Dark garnetiferous amphibolites are commonly associated with these gneisses. Notably, pale-pink garnet may be present in amounts up to 20 percent, and accessory minerals include ilmenite-magnetite.

Amphibolite occurs as lenses and pods interlayered with the gneisses, is dark greenish-grey to black, medium-grained, equigranular, and commonly rusty-weathering. Notable accessory minerals include ilmenite-magnetite.

With increasing metamorphic grade to the west, all of the above lithologies develop into granulites and charnokites.

The only known marble or calc-silicate unit in the area is exposed in the deeply-eroded Coulonge River valley and represents the westernmost calc-silicate band in the region. The marbles are friable, medium to coarse-grained rocks that may be white, bluish-grey, or orange-pink, depending upon the minormineral composition.

The only clearly post-tectonic intrusive rocks that have been recognized within the Properties are eaststriking diabase dykes that outcrop sporadically across the area; one crosses the south end of Lamb Lake, two are mapped between Branssat and Lynch Lakes, and one occurs at the east end of Gerland Lake, just north of Katz's (1976) map area.

An unusual ultramafic rock of websterite composition occurs just to the southwest of the Properties in two localities along the Jim Lake Road at about kilometer 70. Also, a small boulder of kimberlitic or lamproitic float was reportedly found in 1993 by Bryson-Burke Resources personnel along the west slope of the Coulonge River valley, in the southeastern portion of the present large Bryson-Branssat claim block (D. Burke, personal communication). This specimen, which was fine-grained and xenolith-free, was sent to Russia for identification and was not available for examination by the author.

The geology map for the former Ressources Dianor Block 1 Property shows several small outcrops of mafic to ultramafic rock (map unit 14) about 100 meters east of the eastern boundary of the property in the area southeast of Gerland Lake. These rocks are not discussed in the text of the report (GM52684), but are of potential interest because they occur in the vicinity of four anomalous indicator-mineral samples discussed below (Section 8.1).

5.2.2 Structure

The area has a complex structural history that commenced with early to mid-Proterozoic (probably Paleohelikian) orogeny, and involved deep burial followed by tight folding and over-thrusting causing general east-west compression and crustal thickening (Section 5.1.6). Dominant fold axes trend NNW near the Coulonge River in the eastern area of the Properties, NW across the Lynch Lake area in the western part of the Properties, and WNW beyond the properties to the southeast. These folds truncate and deform an earlier set of northeast-striking fold axes (Katz, 1976). Refolded folds along these earlier northeast structures are also common. (Figure 8)

The two main generations of folding have resulted in a regional basin-and-dome tectonic style. On a local and outcrop scale, folding is variable and complex. Tight isoclinal folds are most common, although fan, chevron and interference folds occur as well.

An anticlinal axis is interpreted by Katz to strike northwest through Lynch and Lamb Lakes. A branching, north-trending synclinal axis is interpreted in the northern part of Bryson Lake. The Coulonge River valley is thought to represent a doubly-plunging synform, which is better-developed to the north and south of this area. East of the Coulonge River, with the exception of the Wright Lake area, gneissosities dip generally steeply eastward.

Gneisses in the area of the Properties do not appear to have been significantly remetamorphosed during the Grenvillian Orogeny.

5.2.3 Tectonic Setting

Three separate studies of regional lineations have been completed including Sharma, et al.,1993, Charlton, 1993 (unpublished), and Gouchtchine, (1992-93, unpublished). Katz, (1976) limited his structural examinations to the Ottawa Graben. Four different sets of faults, probably related to four tectonic events, affect the area.

Northwest-striking lineations, parallel to regional fold trends, dominate the structural fabric. The majority of lineations are fold or lithology-related, however, Gouchtchine (1993) attempted to differentiate between the northwest striking fold/lithology-related features and thrust faults that developed along some of these, and interprets many long, northwest-striking thrust faults. These are probably old Proterozoic, late-phase orogenic structures that dip steeply east and northeast.

A set of northeast-striking faults is truncated by the northwest-striking faults.

The west-northwest to east-trending faults associated with formation of the Ottawa Graben are more numerous toward the south. The Graben was active from latest Proterozoic to post-Ordovician time and developed along extensional block faults. The Murtagh Creek Fault may represent the north flank of the Graben. The coincidence of this fault with the Early-Cretaceous track of the Great Meteor hotspot suggests that it may have been reactivated during that time. (Figure 8)

The youngest episode of faulting is possibly an early Cretaceous (?) period of uplift that may have been caused by passage of the area over the Great Meteor hotspot mentioned above. Only Gouchtchine (1993) has analyzed uplift in this area (Figure 9). The faulted boundaries of the differentially-uplifted blocks are, or represent, because of their mode of formation, crustal penetrative, extensional fractures.

5.2.4 Quaternary Glaciation and Drainage

Fluvial evidence studied by Gouchtchine et al. (1993) indicates that some recent reversals in drainage directions have occurred in the area and probably have resulted from recent isostatic rebound. The most pertinent reversal noted is that from Bryson Lake, which in the immediate post-glacial period drained toward the southeast from the southern end of Five Mile Bay into the Coulonge River. Bryson Lake now drains into the Coulonge River from the north.

The course followed by the post-glacial drainage is marked by a linear, southeast-trending valley that intersects the Coulonge River valley at the point where microdiamonds were first recovered in 1992, and where numerous (78) other microdiamonds were subsequently recovered by Bryson-Burke Resources (Section 7.2, TABLE 2).