Alkaline Rocks and Carbonatites of the World

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Wolfe Belt

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Occurrence number: 
031-00-097
Country: 
Canada
Region: 
Ontario
Location: 
Longitude: -77.32, Latitude: 45.33

Situated mainly in Lyndoch Township, but extending eastwards into Griffith Township, the Wolfe Belt comprises a prominent east-west ridge of southward-dipping nepheline gneiss, nephelinized calc- silicate gneiss and metapyroxenite extending over some 6 km and with a maximum outcrop width of just over 300 m. It is conformable with the surrounding metasediments, principally limestones, dolomite and calc-silicate gneiss. There are later intrusive sills, dykes and pods of alkali syenite. The belt is essentially made of two units: on the northern side and extending its full length are banded, leucocratic feldspathic alkaline gneisses which are usually nepheline-bearing. These gneisses generally dip to the south or southeast beneath calc-silicate gneisses. There is some amphibolite, crystalline limestone and quartzite intercalated within the leucocratic alkaline gneisses. The leucocratic gneisses always contain microcline, often perthitic, and plagioclase of at least two generations including an older type (An23-35) and later corroding albite of An17-24. Nepheline is generally present and up to 40% but varying abruptly particularly across the strike. Amphibole, garnet, biotite, clinopyroxene and magnetite may be present in all combinations except that garnet and biotite do not occur together. The amphibole is a ferrohastingsite; garnets are grossular-andradite, the biotites are iron-rich varieties, and the occasional pyroxenes aegirine or aegirine-augite. Scapolite is found at a number of horizons, and carbonate, sphene, apatite, zircon, fluorite, sodalite, zeolites and secondary white mica and cancrinite may be present also. Amphibolites intercalated in the leucocratic gneisses have biotite, garnet and pyroxene facies and contain appreciable nepheline. The calc-silicate gneisses contain plagioclase (An29-35), calcic scapolite and hedenbergitic pyroxene, partly replaced by hastingsite, and grossular. Near contacts with leucocratic gneiss nepheline is usually present and then the garnet becomes andraditic, pyroxene richer in aegirine and hedenbergite, and idocrase becomes a major mineral constituent. At the eastern end of the ridge are intercalations of rocks consisting principally of clinopyroxene and hastingsite with a little scapolite and nepheline, while at the western end, on its southern side, are rocks comprising either sub-silicic titaniferous hastingsite or biotite, with scapolite, ilmenite, spinel and very abundant magnetite and apatite. Small pegmatitic bodies occur within the leucocratic gneisses and late intrusive alkaline syenites form sheets rarely exceeding 6-7 m in thickness and consisting essentially of approximately equal proportions of albite and microcline with a small and highly variable content of aegirine/aegirine-augite, ferrohastingsite, hornblende, biotite, magnetite and accessories. A general petrographic, structural and stratigraphic account of the Wolfe Belt will be found in Appleyard (1967), of textures and mineral parageneses in Appleyeard (1969), of amphiboles in Appleyard (1975) and of earlier work in Hewitt (1961, p. 97).

References: 
APPLEYARD, E.C. 1967. Nepheline gneisses of the Wolfe Belt, Lyndoch Township, Ontario. I. Structure, stratigraphy, and petrography. Canadian Journal of Earth Sciences, 4: 371-95. APPLEYARD, E.C. 1969. Nepheline gneisses of the Wolfe Belt, Lyndoch Township, Ontario. II. Textures and mineral parageneses. Canadian Journal of Earth Sciences, 6: 689-717. APPLEYARD, E.C. 1975. Silica-poor hastingsitic amphiboles from metasomatic alkaline gneisses at Wolfe, eastern Ontario. Canadian Mineralogist, 13: 342-51. HEWITT, D.F. 1961. Nepheline syenite deposits of southern Ontario. Annual Report, Ontario Department of Mines, 69(8): 1-194
Fig. 54 Wolfe Belt (after Appleyard, 1967, Fig. 3).
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith