Alkaline Rocks and Carbonatites of the World

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Kipawa Complex And Lac Tortue

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Occurrence number: 
031-00-102
Country: 
Canada
Region: 
Quebec
Location: 
Longitude: -78.5, Latitude: 46.8

A regionally metamorphosed complex of agpaitic nepheline-bearing rocks is poorly exposed along the eastern shore and hills beside Sheffield Lake. The dominant rocks are mafic gneisses composed of nepheline, sodic hedenbergite to aegirine-augite, arfvedsonite and katophorite, K-feldspar and eudialyte, which are intercalated with more leucocratic rocks in which nepheline, albite and K- feldspar predominate. Calcite and fluorite are ubiquitous accessories and locally assume major proportions. These rocks contain pods and lenses of pegmatite composed of exceptionally coarse eudialyte, feldspar, nepheline, agrellite, for which this is the type locality (Gittins et al., 1976), a wide variety of woehlerite group minerals, vlasovite (Gittins and Gasparrini, 1973), britholite, gittinsite ( also the type area, Ansell et al., 1980), and others. Alkali amphibolites also occur although their field relationships are not known, while non-agpaitic nepheline syenite occurs on islands at the south end of Sheffield Lake, but its relationship to the agpaitic rocks is also obscure. A chemical analysis of a eudialyte-rich rock together with REE data are given by Fryer and Edgar (1977).
Lyall (1959) has mapped a further mass of syenite on an island in Lac Tortue and along the eastern shore of that lake, but the degree of alkalinity of these rocks is not known.

Economic: 
The area was extensively drilled in the 1950's and late 1960's as part of a regional search for uranium. The complex is distinctly radioactive.
Age: 
K-Ar ages are typically Grenville but the complex is undoubtedly pre-Grenville (J.Gittins, personal communication, 1984).
References: 
ANSELL, H.G., ROBERTS, A.C., PLANT, A.G. and STURMAN, B.D. 1980. Gittinsite, a new calcium zirconium silicate from the Kipawa agpaitic syenite complex, Quebec. Canadian Mineralogist, 18: 201-3. EDGAR, A.D. and BLACKBURN, C.E. 1972. Eudialyte from the Kipawa Lake area, Temiscamingue Co., Quebec. Canadian Mineralogist, 11: 554-9. FRYER, B.J. and EDGAR, A.D. 1977. Significance of rare earth distributions in coexisting minerals of peralkaline undersaturated rocks. Contributions to Mineralogy and Petrology, 61: 35-48. J.Gittins, personal communication, 1984. GITTINS, J. and GASPARRINI, E.L. 1973. The occurrence of vlasovite in Canada. Canadian Mineralogist, 12: 211-4. GITTINS, J., BOWN, M.G. and STURMAN, D. 1976. Agrellite, a new rock-forming mineral in regionally metamorphosed agpaitic alkalic rocks. Canadian Mineralogist, 14: 120-6. LYALL, H.B. 1959. Preliminary report on McLachlin-Booth area Temiscamingue Electoral District. Preliminary Report, Quebec Department of Mines, 391: 1-13
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith