Alkaline Rocks and Carbonatites of the World

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Blue Mountain

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Occurrence number: 
031-00-099
Country: 
Canada
Region: 
Ontario
Location: 
Longitude: -77.97, Latitude: 44.67

The Blue Mountain complex consists of a main mass 4x2.4 km from which extends a southwest-trending arm 6.4 km long and up to 0.4 km wide. It lies in the core of a northeast-southwest-trending syncline of Precambrian metasedimentary rocks including amphibolite, paragneiss and a limestone which lies adjacent to the alkaline complex at many places. Contacts are generally sharp and conformable but the Methuen granite lying to the southeast cuts across the foliated nepheline syenites of Blue Mountain. Payne (1968) suggests that the complex forms a sill, but structural interpretations differ depending on whether the writer favours an igneous or metasomatic origin; for relevant references see Payne (1968) and Duke and Edgar (1977). The complex consists essentially of foliated and folded nepheline syenite gneiss with lesser amounts of syenitic gneiss. A number of zones can be distinguished based on the proportions of biotite and hornblende, or characterized by the presence of muscovite, muscovite-magnetite or the absence or paucity of nepheline. There is some indication of a concentric arrangement with a central core of hornblende- nepheline syenite surrounded by a biotite zone which passes into a muscovite-bearing zone. A pink syenite is concentrated along the border and in the southwestern arm. All the nepheline syenites consist of about 50% albite, 20% microcline and 20-25% nepheline. Also present are biotite, muscovite, iron-rich hastingsite and riebeckite, aegirine-augite, andraditic garnet, magnetite, corundum, calcite, cancrinite and zircon. Sheets of more mafic rocks occur within the nepheline syenites and have been interpreted in a number of ways (Payne, 1968, p. 262), while nepheline-bearing pegmatites are common in some zones of the nepheline syenite. Rock analyses are to be found in Hewitt (1961) and Payne (1968) and mineral analyses in Duke and Edgar (1977). Melting experiments on nepheline syenite in the presence of H2O and CO2 are described by Millhollen (1971).

Economic: 
Blue Mountain is the West's biggest producer of nepheline syenite for the glass and ceramic industries. Two quarries are worked, the rock being commercially valuable because of the low proportion of mafics, averaging only 2% by volume. For details of history, production etc., see Allen and Charsley (1968, p. 67) and Hewitt (1960).
Age: 
A Rb-Sr whole rock isochron on nepheline syenites gave 1285+-41 Ma (Krogh and Hurley, 1968).
References: 
ALLEN, J.B. and CHARSLEY, T.J. 1968. Nepheline syenite and phonolite. Institute of Geological Sciences, Mineral Resources Division, Her Majesty's Stationery Office, London. 169 pp. DUKE, N.A. and EDGAR, A.D. 1977. Petrology of the Blue Mountain and Bigwood felsic alkaline complexes of the Grenville province of Ontario. Canadian Journal of Earth Sciences, 4: 515-38. HEWITT, D.F. 1961. Nepheline syenite deposits of southern Ontario. Annual Report, Ontario Department of Mines, 69(8): 1-194. KROGH, T.E. and HURLEY, P.M. 1968. Strontium isotope variation and whole-rock isochron studies, Grenville Province of Ontario. Journal of Geophysical Research, 73: 7107-25. MILLHOLLEN, G.L. 1971. Melting of nepheline syenite with H2O and H2O + CO2, and the effect of dilution of the aqueous phase on the beginning of melting. American Journal of Science, 270: 244-54. PAYNE, J.G. 1968. Geology and geochemistry of the Blue Mountain nepheline syenite. Canadian Journal of Earth Sciences, 5: 259-73
Fig. 56 Blue Mountain (after Payne 1968, Fig. 2).
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith