Summary:
The Timmins Talc-Magnesite deposit is a hydrothermally altered ultramafic rock composed, at its core, largely of talc and magnesite although, at its fringes, the content of calcium in the carbonate increases.
The deposit area is underlain by Archean-aged intrusive, volcanic and sedimentary rocks including large masses of altered ultramafic volcanic lithologies and at least one east-trending diabase dyke. Strike directions of units are generally east-west, with near vertical dips. The magnesite-talc-quartz rock unit is exposed on surface as large areas of outcrop rising 3 to 6 m above a sand plain floor.
Several occurrences of talc-magnesite are known to be present on the property, the largest of which is located to the south of the diabase dike and is referred to as the A Zone. This zone has been traced by surface trenching, mapping and drill hole information along a strike length of approximately 1,000 m, to depths of approximately 100 to 150 m and achieves widths of 200 m at surface. The information available to date suggests that the A Zone has a near vertical dip in an overall sense, although the north and south contacts can be seen to locally dip steeply to either the north or south. A second zone of magnesite mineralization is located to the north of the diabase dike, although its dimensions and extents are known only from a small number of drill holes that suggest a strike length on the order of 1,000 m, with widths measuring on the order of a few tens of metres. A third zone of mineralization is located in the southwestern portions of the claim holdings and is exposed in surface outcroppings, but the extents of this zone are not known in detail.
Mineralization
The following description of the mineralization is excerpted from Kretschmar and Kretschmar (1986) which describes the status of the knowledge of the mineralization found at the Timmins Talc-Magnesite deposit at the time.
The deposit consists of either a single large magnesite-talc altered dunitic komatiite or a series of altered flows. It is hosted by basaltic or andesitic lavas, serpentinized peridotitic komatiite and quartz-carbonate iron formation. It is about 1,800 m long, has a maximum width of 300 m and has been drilled to a depth of 120 m.
The very low CaO content in the magnesite-talc body makes the carbonate mineralization a potential source of refractory magnesia. However, iron substitution in the magnesite lattice means that the iron cannot be removed by standard physical methods. The iron, therefore, limits the grade of magnesia concentrate or dead-burned refractory product. Extensive metallurgical testing by Canadian Magnesite Mines over a period of years has demonstrated that the best grade of magnesite obtained by flotation concentration produces a 92-94 percent dead-burned MgO product with 4-6 percent Fe2O3.
The core magnesite zone is a massive, coarse grained, over-printed and re-crystallized magnesite and lesser talc unit showing no visible relic original textures. Within surface-stripped zones the exposures show a well developed set of quartz-carbonate extensional veins and stockworks, with subvertical to steep south dipping linker veins that strike easterly and are sigmoidally curved, moderately dipping tension ladder structures. Drilling indicates that the “high-grade” magnesite zones are wider than when exposed on surface, and carry much less veining than anticipated.
The transition zone has been logged as a talc-carbonate-chlorite zone. It is physically similar to the above described core magnesite zone, other than it tends to be darker in tone (medium grey) due to the presence of aphanitic to fine grained black chlorite and tends overall to be more bladed to foliated in texture. The zone may be richer in talc and has a strongly developed carbonate groundmass, but shows variable lesser amounts of magnesite in inverse proportion to developed ferro-dolomite.