THE ORIGIN OF RARE MINERALS IN THE KIPAWA SYENITE COMPLEX, WESTERN QUEBEC*
KENNETH L. CURRIE and OTTO VAN BREEMEN
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE8
* Geological Survey of Canada contribution number 57638.
The Kipawa Syenite Complex, in the Grenville Province of western Quebec, a concordant, folded sheet of mildly peralkaline kataphorite-aegirine
syenite less than 200 m thick, can be traced for more than 50 km in the Grenville Province of western Quebec. Several lenses of biotite-aegirine
nepheline syenite up to 200 long by 30 m thick occur within the complex. Along its lower margin, a region 1300 m long by 5 m thick consists
of diopside and magnesiorichterite-rich schist with large amounts of eudialyte, agrellite and other rare minerals. This skarn-like lens is fringed
on its upper side by alkali granite. The Kipawa Syenite Complex lies entirely within granitic gneiss derived from an Archean protolith and
emplaced at 1247 ± 47 Ma (Guo & Dickin 1994). The complex, emplaced about 1240 Ma ago, consists mainly of deformed alkaline igneous rocks
(plutonic, volcanic, or both) as shown by its geochemical signature. Marble-bearing sedimentary rocks were thrust-imbricated with the
complex during northwest-directed tectonic transport at amphibolite- facies (690 C, 9.5 kilobars) metamorphic conditions. Mechanical mixing
during this process, followed by alkali metasomatism and local anatectic melting, produced skarn-like rocks (contents of CaO and MgO of
12 and 10 wt.%) containing the rare minerals. U-Pb dating of zircon from the rare mineral occurrence shows that rare mineral formation
occurred at 994 ± 2 Ma. Alkalis, Zr, REE, Be and other elements were redistributed on scales ranging from meters to kilometers by a combination
of fluid flow and anatectic melting in the presence of F-rich brines.