"Rock of the Month # 57, posted for March 2006" ---

Pulaskite is a variety of syenite. It is a nepheline-bearing alkali feldspar syenite with variable proportions of dark minerals such as sodic pyroxenes (e.g., aegirine) and amphiboles, fayalite (Fe-rich olivine) and biotite mica. This sample was collected in situ from a thick, upstanding dyke of pale syenite on the Crown Point property (Wilson et al., 1990), in the South Belt of the Rossland gold mining camp. The rock contains sparse white feldspar phenocrysts up to 15x5 mm in section and rounded masses which (?) may represent nuclei rich in nepheline within the white feldspathic mass.

Pulaskite is not limited to southern B.C.: a partial list of world occurrences includes localities in the late Proterozoic Gardar alkaline province of west Greenland; the Tertiary Volcanic District in east Greenland; the Monteregian alkaline district of Quebec; Essex county (Massachusetts, U.S.A.); Bolivia; Argentina; Scotland (the syenites of Sutherland); Portugal; Malawi; and several localities in India (in the states of Gujarat, Maharashtra and Andhra Pradesh).

The Rossland gold camp (Drysdale, 1915; Whittaker, 1949; Fyles, 1984) is in historic terms the second-largest gold-producing district of the province. The pulaskite and similar rocks are part of the Eocene-age Coryell alkaline suite of southern B.C. (Fyles et al., 1973; Stinson and Simony, 1994). They cut a variety of older metallic mineralization in the region (e.g., Church, 1977; see also last month's Rock of the Month for a discussion of local lamprophyres) and at best may be a locus for some remobilization of the pre-existing Au mineralizations (veins and skarns) in the camp. Locally, as at the Ymir quarry near Nelson, these Coryell syenitic rocks are excavated for building-stone purposes (White, 1987).

References

CHURCH,BN (1977) Geological investigations in the Greenwood area (82E/2E). In `Geological Fieldwork 1976', BC Ministry of Mines and Petroleum Resources Paper 77-1, 86pp., 7-10.

DRYSDALE,CW (1915) Geology and Ore Deposits of Rossland, British Columbia. GSC Mem. 77, 317pp. plus map folder.

FYLES,JT (1984) Geological Setting of the Rossland Mining Camp. BC MEMPR Bull. 74, 61pp. plus map folder.

FYLES,JT, HARAKAL,JE and WHITE,WH (1973) The age of sulfide mineralization at Rossland, British Columbia. Econ.Geol. 68, 23-33.

STINSON,P and SIMONY,PS (1994) The geology and structure of the Coryell batholith, southern British Columbia. In `Current Research: Cordillera and Pacific Margin', GSC Paper 1994-A, 243pp., 109-116.

WHITE,GV (1987) Dimension stone quarries in British Columbia. In `Geological Fieldwork 1986', BC MEMPR Paper 1987-1, 453pp., 309-342.

WHITTAKER,LH (editor) (1949) Rossland, the Golden City. Rossland Miner Ltd, 104pp.

WILSON,GC, RUCKLIDGE,JC and KILIUS,LR (1990) Sulfide gold content of skarn mineralization at Rossland, British Columbia. Econ.Geol. 85, 1252-1259.