Bryson Burke Diamond Corporation: Diamond Exploration and Mining in Canada

5.0 GEOLOGY

5.1 Regional Geology

5.1.1 Exploration Concept (Deposit Types)

The exploration targets on the Properties are diamondiferous, alkaline, ultramafic intrusions of kimberlitic or lamproitic composition. Distinctive indicator-mineral assemblages suggestive of both rock-types exist in the area of the Properties.

Kimberlite pipes tend to occur in clusters of a few to over forty individual bodies within an area of up to 50 kilometers in diameter. Emplacement of the pipes is controlled by deep-seated regional fractures and bears little relationship to host lithology. Kimberlite pipes are generally oval to elliptical in plan view, with long axes parallel to local structural lineaments, and range from less than 50m to more than 1500m in diameter. Contacts of a kimberlite pipe are steep-dipping (80 to 85̊). Dykes and sills occur within the deeper root zones.

Until the early 1990s, the Slave Province was thought to have limited potential to host kimberlite pipes with economic quantities of diamonds because recent glacial erosion would have resulted in significant erosion of these bodies. Moreover, no kimberlite or lamproite pipes had ever been discovered in that area. It is now known that kimberlite pipes containing economic quantities of diamonds do indeed occur, and that they have not necessarily undergone significant erosion. Approximately 90 percent of the kimberlite pipes discovered within the Slave Province are located beneath lakes.

Since diamonds, even in economic deposits, can be present in concentrations of less than 0.06 parts per million, it is common practice in diamondiferous kimberlite exploration to search for other minerals that commonly occur with diamonds. These include pyrope garnet, chrome diopside, ilmenite, and chromite.

Prior to the discovery of the Argyle Mine in northwestern Australia in 1979, it was thought that economic concentrations of diamonds could occur only in kimberlites, and furthermore, only in kimberlites intruding stable archons of Archean age. In the Argyle Mine, diamonds occur in lamproite, a rock related to, but mineralogically distinct from kimberlite, in a post-Archean tectonic mobile belt.

Lamproite is an ultra-potassic magnesian rock with primary constituents composed of variable amounts of phlogopite, clinpyroxene, amphibole, olivine, and sanidine (Bergman, 1987). In cross-section a lamproite has a champagne-glass shape, as opposed to the carrot shape of the classic kimberlite. Lamproites may also occur as dykes and sills. Diamond-bearing lamproites are known from craton margins and adjacent mobile zones that have experienced relatively young and persistent faulting. The western Australian lamproites show a strong structural control by major fracture zones.

The Argyle lamproite occurs within a cluster with several other diamondiferous lamproites intruding the Proterozoic mobile belt. The main diamond-bearing phase of the Argyle, as well as that of the diamondiferous Prairie Creek lamproite in Arkansas, is an olivine lamproite phase.

Diamond indicator-mineral types and populations in lamproites differ from those in kimberlites. The most abundant resistant indicator-mineral from a lamproite source is chromite. Other resistant indicatorminerals include zircon, tourmaline, pinkish magnesium-almandine (G-5 garnet), purple peridotitic garnet, picroilmenite, opaque rutile, orange eclogitic garnet, and diamond. Most grains are rounded and have frosted surfaces (Bergman, 1987). In addition spherical glass (coesite) and magnetic grains occur in Argyle area lamproites.

Although economically-diamondiferous kimberlites have not been found in areas underlain by rocks of post-Archean age, lamproite in this environment is demonstrably an economically-significant diamond host. The Argyle lamproite is the most productive diamond mine in the world in terms of volume (as opposed to value). The Prairie Creek lamproite in Arkansas, United States, is diamondiferous and has been mined historically, and the diamondiferous "kimberlites" of India have recently been reinterpreted to be of lamproitic composition.

5.1.2 The Grenville Diamond Setting

The Argyle lamproite in northwestern Australia is dated at 1.2 billion years (Ga) (Mid-Proterozoic) and intrudes rocks of Early Proterozoic ages within a Proterozoic mobile belt (Helmstaedt, 1993). This mobile belt is in many respects similar to the Grenville Province. Of additional relevance, the diamondiferous but sub-economic Prairie Creek lamproite in Arkansas, U.S.A., intrudes a Grenvillian basement, the southwestern continuation of Grenville Province rocks beneath younger cover rocks (Rivers, 1997).

The Properties are situated in the Central Gneiss Belt (CGB) of the Grenville Province in southwestern Quebec. The term Grenville Province is generally applied to the youngest part of the Canadian Shield, "cratonized" about one billion years ago, that extends southwestward from southern Labrador through Quebec into southern Ontario and New York State (Moore, 1986). The definition of the Grenville Province has been expanded over time from Logan's type locality north of the town of Grenville, Quebec, to its present extent, the boundaries of which were established in 1972.

The boundary of the Grenville with the older Superior Province craton to the northwest is the Grenville Front, or Grenville Tectonic Zone, a long, continuous zone of northwesterly-directed reverse faulting that separates the more highly-strained and metamorphosed rocks of the Grenville Province from the adjacent Archean-age Superior craton. Grenvillian rocks extend beneath Paleozoic cover to the southeast along the St. Lawrence lowlands, and to the southwest beneath southern Ontario and the Michigan Basin. It is now recognized that Grenvillian rocks extend beneath Paleozoic/Mesozoic cover southwestward as far as Texas.

5.1.3 Rock Types

The Central Gneiss Belt is a high-grade metamorphic terrain of upper-amphibolite to granulite facies that resulted from burial to depths of more than 10 kilometers. The major lithologies present over the entire area are quartzo-feldspathic, biotite/horneblende, and garnet gneiss (Katz, 1976). A thin layer of marble appears to underlie most of the length of the Coulonge River valley. Pyroxenite and amphibolite units occur locally. (Figures 6a, b)

The Central Gneiss Belt is interpreted to have formed along a long-lived ensialic arc (Dickin, 2000), and was subjected to pre-Grenvillian, MesoProterozoic orogeny, resulting in compressional folding and overthrusting about northwesterly axes.

All of the gneissic lithologies are cut by east-striking, Late Proterzoic diabase dykes that outcrop sporadically across the area.

5.1.4 Tectonic Setting

The Grenville Province has been the subject of a significant body of recent geological research, one result of which is the recognition that the Grenville is comprised of a series of structural terranes. The Properties are situated within the Allochthonous Polycyclic Belt (APB) (Dickin, 2000), which corresponds roughly to the older lithologic appellation used in this report, the Central Gneiss Belt (CGB). To the north and northwest, the APB has been thrust onto and against the Parautochthonous Belt (PB) along an irregular and poorly-defined thrust boundary termed the Allochthon Boundary Thrust (ABT) (Dickin, 2000).

The PB represents metamorphically upgraded and tectonically reworked equivalents of the adjacent Archean foreland to the northwest. (Figure 7)

The APB is comprised of several transported terranes of high-grade (upper amphibolite to granulite facies) orthogneiss and paragneiss intruded to a minor degree by gabbro, granite, anorthosite and pyroxenite that tectonically overlie the PB. The APB appears to have been exhumed from depths of at least 10 kilometers and shows evidence of having undergone major deformation prior to the Grenville Orogeny (Rivers et al, 1989). The APB is bounded to the southwest and south by the Allochthonous Monocyclic Belt (AMB) and is separated from it along the Monocyclic Belt Boundary Zone (MBBZ) (Dickin, 2000). The MBBZ lies about 40 kilometers to the west and 25 kilometers to the south of the Properties. The AMB corresponds roughly to the older, lithologic appellation, Central Metasedimentary Belt (CMB). The AMB is characterized by major northwest-directed ductile thrusting (Rivers et al, 1989).

The CGB region has undergone post-orogenic tectonic fracturing and differential uplift of individual blocks. (Figure 9, from Gouchtchine et al, 1993). The large block centered on Lynch Lake, and in which the majority of the Properties is situated, appears to be the stable "keystone" of the region. Surrounding blocks have moved up or down in relation to this central block.

5.1.5 Age Relationships and Crustal Thickness

Two areas of the CMB supracrustal terrane, 25 and 40 kilometers to the east and southeast of the Properties, were dated at 1.3 to 1.4 Ga (Rivers and Corrigan, 2000).

A recent isotopic age-dating study of the PB to the north of the APB immediately north of the Baskatong-Desert Lineament, concluded that the PB in this area is Paleo-Proterozoic to Archean in age (1.87 to 2.70 Ga) (Guo and Dickin, 1996). This includes the so-called Barilia Terrane (Dickin, 2000) which bounds the Baskatong-Desert Lineament to the north and includes the former Renzy Ni-Cu Mine some 40 kilometers to the northeast of the Properties.

The intervening terrane, including the Allochthonous Polycyclic Belt into which the Properties fall, has been collectively termed "Algonquia" (Dickin, 2000). This is the least well-defined of the southwestern Grenvillian terranes and Dickin (2000), although providing age determinations for surrounding terranes, does not provide an age specifically for the APB. However, Rivers (1997) shows Nd model ages of 2.09 to 1.72 Ga for the Algonquian Terrane. The APB may represent a long-lived ensialic arc active during the late PaleoProterozoic where crust was continually formed above a north-dipping subduction zone (Dickin, 2000).

Rivers (1997) infers, from seismic reflection and geological studies, an Archean-age lower crust beneath the entire Central Gneiss Belt. Crustal thickness (the seismically-determined vertical distance to the lithospere/upper mantle interface) across the Central Gneiss Belt is approximately 50 kilometers (Mereu et al, 1986). To the east across the CMB, it thins to about 40kilometers thickness. Average crustal thickness of cratons is 35 to 40 kilometers (Dawson, 1980).

Crustal thickness, while not a significant factor in diamond formation, may be a factor in diamond preservation. Diamonds ascending as xenocrysts from mantle depths of formation may face a lengthy delay at the crustal interface before being incorporated into kimberlitic magma capable of stoping its way to surface along crustal-scale fracture systems. Preservation of diamonds at this interface depends upon pressure maintenance (crustal thickness) combined with sufficiently cool temperatures and the correct geochemistry and redox conditions. An older, colder, thicker crust also is more brittle than younger, thinner crust allowing for the formation of crustal-scale extensional fractures, a key prerequisite for diamondiferous kimberlite/lamproite passage to surface.

5.1.6 Structure

One of the most important elements in the formation of kimberlitic and lamproitic diatremes is deep, crustal-penetrative structures. Kimberlites form during short explosive events. The kimberlite magma is cool and volatile-rich, and must rise from sites where adequate pressure, temperature and geochemical conditions to preserve diamonds prevail, at a rate sufficiently rapid to preserve diamonds under the particular geochemical conditions of that specific magma. Deep, penetrative, extensional structures, usually regional in extent, are required. The surface configuration of kimberlite and lamproite diatremes may be strongly influenced by local joint patterns in the country rock (Dawson, 1980).

Regional compilation of magnetic surveys in the Property area indicates a deep zone of magnetic rock extending in a north-south direction approximately following the line of 77̊W longitude, expressed by a wide, continuous zone of high magnetic susceptibility with irregular flanks. This feature extends southward from the Baskatong Reservoir through the central portion of the Property area, where it has a width of approximately 25 kilometers. This magnetic zone, suggestive of a deeply-buried mass of ultramafic composition, continues southward across the Ottawa River and beyond. (Figure 10 and Section 7.0)

The Varty Lake and Picton kimberlitic dykes occur further south along this trend in the Kingston-Belleville area. These intrusives are of Jurassic-age with both kimberlitic and lamprophyric affinities and their emplacement may have been controlled by late-Proterozoic basement faults reactivated during the Jurassic (Barnett et al, 1984). The structure that hosts the dykes appears to continue southward beneath Lake Ontario into the Finger Lakes area of New York State along the Clarendon-Linden Fault. The kimberlite/alnoite dykes at Ithaca, New York are further evidence of the deep-seated origins of this magnetic zone. These dykes are of early Cretaceous age (Dawson, 1980).

The north-trending magnetic feature coincides with an interpreted north-south fault in the area of the Properties. This fault is situated just east of the line of 77̊ W longitude and is very subtle. However, it was interpreted independently by Gouchtchine(1993) and by Charlton (1993). (Figure 8) North-trending extensional faults appear to be of importance in the localization of kimberlites in the Attawapiskat region of Ontario.

To the south of the property area, a regionally-prominent set of west-northwest-striking normal faults, related to the formation of the Ottawa Graben, are associated with late Proterozoic to Paleozoic tectonic activity that culminated in widespread post-Ordovician faulting and rifting (Katz, 1976). Intrusive activity along this regional structure is manifested by alkaline, ultramafic volcanism east from the Montreal area, along the Monteregian Hills, almost to the Maine border, and included intrusion of the alnoitic, diamondiferous dyke at Ile Bizard, Quebec. These ultramafics have Lower Cretaceous ages (Globensky, 1987). Katz (1976) describes a double aeromagnetic anomaly at the southeast edge of Ile des Allumettes as being similar to the anomalies of the Monteregian intrusives.

The Murtagh Creek Fault (Charlton, 1993) in the region of the Properties may represent the northern flank of the Ottawa Rift system. This fault strikes 105̊ to 110̊ and is traceable for over 150 kilometers. The Murtagh Creek Fault also coincides remarkably well with the track of the Great Meteor hotspot in this region (Crough, 1981), and therefore the fault may be an extensional feature associated with uplift caused by passage over the hotspot. The bulk of the Properties straddle the western 40 kilometers of the Murtagh Creek Fault and are centered upon the intersection of the north-trending magnetic feature, the coincident north-trending fault, and the Murtagh Creek Fault.

The area has experienced post-orogenic uplift that caused tilting and jointing of blocks as large as 30 kilometers, and as small as three kilometers across (Gouchtchine, 1993). Uplift may have occurred during early Cretaceous time and may have been caused by the Great Meteor hotspot over which this region drifted approximately 130 million years ago (Crough, 1981).

5.1.7 Quaternary Glaciation and Drainage

An understanding of the history of Quaternary glaciation and subsequent development of post-glacial local drainage is of primary importance in the assessment of the provenance, distribution, and frequency of diamond indicator-mi

In the CGB region there were three (3) major ice advances during the Quaternary. The last Laurentide ice sheet retreated from this area approximately 10,000 years ago. Although difficult to estimate accurately, ice thickness probably exceeded 2,000m in this region. The predominant most-recent ice advance direction was to the south-southwest. However, eskers indicate that the last ice retreated and melted in an average south-to-north direction.

Isostatic rebound in the CGB region is on the order of 50m. Local differential isostatic rebound has resulted in reversals of drainage direction, as exemplified by the drainage reversal from Bryson Lake (Katz, 1976 and Section 5.2.4, below).

The last glaciation deposited poorly-sorted boulder to clay-size tills in a random pattern over the CGB region. Melting and high-energy water flowage locally remobilized significant amounts of till into stream and riverbed, water-sorted boulder, gravel and sand deposits. Locally, there are expanses and significant thicknesses of sand outwash derived directly from melting ice. A peculiarity of the CGB region is the high predominance of sand-size particles over all other sizes; gravel and cobble-size material is almost nonexistent.

In the Slave Province, indicator-minerals commonly occur in glacially-dispersed trains that emanate from the source kimberlites. Because these trains narrow in the source direction, the source kimberlite can be located by following the indicator trains in the up-ice direction. However the success of this technique is critically dependant upon a uniform dispersal which, in turn, depends upon a simple and consistent history of glacial ice movement.

The Central Gneiss Belt region suffered more episodes of glaciation with much thicker ice sheets than did the Slave Province. This has resulted in a deeper erosion level and more-severe winnowing and dilution of indicator-minerals. The latter condition has been exacerbated by a moister climate, a much higher water-flow regime, and local reversals in drainage direction. These glacial and drainage conditions may have contributed to the paucity of indicator-minerals found to date in the region.

The relatively high precipitation in the CGB region (average of 130 centimeters/year) causes the high water-flow regime exemplified by the Coulonge and Black River systems. The voluminous spring melts constitute peak flow-levels and result in additional washing-out and downstream redistribution of indicator-minerals to degrees not seen in drier glaciated kimberlite terrains such as the Slave Province, West Greenland, and Yakutsk, Russia.

5.1.8 Summary

The Properties are grouped around the junction of a deep-seated, north-south magnetic feature, possibly signifying ultramafic rocks, and the northern edge of the Ottawa Graben represented by the Murtagh Creek Fault. Both are old crustal-scale structures that host alkaline ultramafic, including kimberlitic, intrusives along their respective lengths. The properties are underlain by a high-grade metamorphic terrane, the Allochthonous Polycyclic Belt or Central Gneiss Belt, that has an age of 1.72 to 2.09 billion years, and a lower crust of Archean age. Crustal thickness of the Central Gneiss Belt is estimated to be approximately 50 kilometers.

A key feature for diamond prospectivity may be the north-striking fault interpreted to cross the Properties, and to coincide with the north-trending regional magnetic high. The Great Meteor hotspot tracked directly beneath this part of the CGB during early Cretaceous time, and may have caused crustal uplift and possibly initiated or facilitated emplacement of kimberlites or lamproites.

The great thickness of Quaternary ice over the CGB region, coupled with relatively high annual precipitation, has resulted in a severe redistribution and possibly removal of diamond indicator-minerals in this region.