Summary:
The Driftwood Creek and Brisco magnesite occurrences are classified as Sparry Magnesite deposits (E09) by the B.C. Ministry of Energy and Mines (Simandl and Hancock, 1998). This deposit type is characterized by stratabound and typically stratiform, lens-shaped zones of coarse-grained magnesite mainly occurring in carbonates but also observed in sandstones or other clastic sediments. Magnesite exhibits characteristic sparry texture.
Reports by Morris (1978), Rodgers (1989), and Simandl and Hancock (1992) provide the best available geologic information on the Driftwood Creek magnesite deposit. Klewchuk (2002) provides additional detail for the Eastern Magnesite area.
According to Simandl and Hancock (1992), magnesite and sparry carbonate form stratabound lenses and pockets within the “white marker beds” subdivision of the “middle dolomite” unit of the upper Mount Nelson Formation at the Driftwood Creek property. This middle unit is called unit Hmn1, with the lower part, Hmn1A, describing the buff to light grey dolomite horizon. The upper part, Hmn1B, is applied to the magnesite.
The magnesite is either white, pale grey, or beige, and weathers buff. The unit is characterized by coarse to sparry crystals, and locally contains light green interbeds less than 1 cm in thickness. The interbeds are either regular or disrupted by growth of sparry magnesite crystals within the coarsest magnesite-rich zones (Simandl and Hancock, 1992). Vestiges of hemispherical stromatolites are observed locally in finer-grained magnesite-bearing rocks. Chert, quartz veinlets, and dolomite are the most common impurities especially within the lower part of the deposit. Calcite, pyrite, and talc are typically present in trace amounts. The abundance and proportion of impurities change irregularly, both along strike and across bedding (Simandl and Hancock, 1992).
Magnesite weathers prominently, and the Driftwood Creek deposit is well exposed as an isolated ridge within relatively low valley bottom topography, at an elevation of 1,250 m (Klewchuk, 2010). Numerous cliff exposures are present, with some cliff walls greater than 15 m (50 ft) high.
Magnesite has been mapped over a strike length of 1,900 m and maximum width of about 220 m (Klewchuk, 2010). The magnesite occurs at surface in two discrete bodies; a larger “West Zone” and the smaller “East Zone”.
Texture of the magnesite is variable, ranging from fine- and medium-grained to very coarse-grained. Most of the deposit is of medium- and fine-grained texture, with irregular patches of more coarsegrained texture. Areas of coarse-grained magnesite appear to be irregularly developed within the area of exposed magnesite, and are not obviously related to any structure.
Thin quartz veins are irregularly distributed through the magnesite, in a near-ubiquitous manner, although the concentration of quartz veins does vary. There are areas with no apparent quartz, but these are not extensively developed. The more prominent quartz veins and quartz vein swarms tend to be oriented from N15°E to N60°E. Similar quartz veins are present in the host dolomite (seen mainly to the south of the Eastern Magnesite), indicating that these quartz veins are not related to development of the magnesite. It is possible that they are related to intrusives noted during drilling. These intrusives may have also introduced a second population of Fe2O3 that may be considered a potential impurity in the recovery of magnesite.
All the magnesite deposits in the Brisco and Driftwood Creek area are located within the upper half of the Mount Nelson Formation. Most are lenticular and seem to form chains, as illustrated by the Driftwood Creek deposits. All deposits are stratigraphically associated with red to purple dolomites, cherty dolomites, stromatolitic dolomites, dissolution breccias, and other rocks containing dolomite pseudomorphs after halite and lenticular gypsum crystals. Locally, stromatolitic textures are preserved, even within magnesite-bearing rocks. According to Simandl and Hancock (1992), most of the above features are indicative of the evaporitic depositional environment.