Alkaline Rocks and Carbonatites of the World

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St-Honore

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Occurrence number: 
031-00-147
Country: 
Canada
Region: 
Quebec
Location: 
Longitude: -71.07, Latitude: 48.55

Originally discovered from its aeromagnetic signature, the St- Honore intrusion covers 10 km2 but is blanketed by a thin layer of Trenton limestone which is locally overlain by black shales. The intrusion has been extensively drilled to evaluate the extent of Nb mineralization. The core of the complex is highly variable carbonatite which is surrounded by a ring of syenitic, nepheline syenitic and ijolitic rocks with, in the southeast, a triangular- shaped mass of cancrinite and melanite-nepheline syenite. There is some fenitization of the granitic and dioritic country rocks. The central carbonatite passes outwards from dolomitic and ankeritic rocks with up to 4.5% REE to ring dykes or cone sheets of Nb- and REE-poor dolomite. These are followed by Nb- rich dolomites and sovites with massive, red, altered dolomites in the south, which are succeeded by pyroxene sovites. To the north the outermost carbonatite is a partial ring dyke of phlogopite sovite. A conical form is defined by an inward-dipping foliation. Rare earths are concentrated in bastnaesite and minor monazite, while pyrochlore, pyrite, monticellite and sphene with a little sphalerite, chalcopyrite, pyrrhotine and baryte are present; apatite averages about 15%. Carbonatite dykes cut the country rocks. Analyses of a range of rocks are given by Vallee and Dubuc (1970, Table 4) and the evolution of the complex is discussed by Thivierge et al. (1983).

Economic: 
Two principal Nb-enriched zones were defined by drilling in 1970-3, ranging from 0.2-1.0% Nb2O5. Production from the south ore zone was started in 1976 by Niobec and ore reserves were established at 8 million tons grading at least 0.7% Nb2O5 (Gagnon and Gendron, 1981). Zones rich in rare earths have been defined in the central part of the complex, rare earth concentrations ranging from 0.1-1.7% (Gauthier, 1981).
Age: 
Seven K-Ar determinations on whole rocks, mica, mafic minerals and nepheline plus feldspar ranged between 629 and 656 Ma except for one whole rock determination on urtite which gave 496+- 17 Ma (Vallee and Dubuc, 1970, Table 3).
References: 
GAGNON, G. 1981. The St. Honore carbonatite complex and associated niobium deposits. In The St. Honore and Crevier niobium-tantalum deposits and related alkaline complexes, Lac St. Jean, Quebec. Excursion Guide-Book, Canadian Institute of Mining and Metallurgy: 4-15. GAGNON, G. and GENDRON, L.A. 1981. Geology and current development of the St-Honore niobium (columbium) deposits. In The St. Honore and Crevier niobium-tantalum deposits and related alkaline complexes, Lac St. Jean, Quebec. Canadian Institute of Mining and Metallurgy, Excursion Guide-book: 18. GAUTHIER, A. 1981. Geochemical, petrographic and mineralogical study of rare earth zones of the St. Honore carbonatite. In The St. Honore and Crevier niobium-tantalum deposits and related alkaline complexes, Lac St. Jean, Quebec. Canadian Institute of Mining and Metallurgy, Excursion Guide-book: 21. THIVIERGE, S., ROY, D.-W., CHOWN, E.H. and GAUTHIER, A. 1983. Evolution du complexe alcalin de St.-Honore (Quebec) apres sa mise en place. Mineralium Deposita, 18: 267-83. VALLEE, M. and DUBUC, F. 1970. The St-Honore carbonatite complex, Quebec. Transactions of the Canadian Institute of Mining and Metallurgy, 73: 346-56
Fig. 74 St-Honore (after Gagnon, 1981, Fig. 4).
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