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Location: 178 km W from Fort St John, British Columbia, Canada
15th Floor, 1040 West Georgia St.VancouverBritish Columbia, CanadaV6E 4H1
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In the Aley deposit, niobium occurs in pyrochlore that formed as early-stage mineral precipitates in primary magma. Alteration of the dolomite carbonatite by unknown factors created the Nb bearing alteration minerals fersmite and columbite. The changes are believed to have occurred largely in situ, and as such there has been less scope for transport or concentration of Nb by secondary processes. The type of deposit is considered to be that of magmatic segregation. The Aley Carbonatite complex intrudes Cambrian to Ordovician sedimentary rocks of the Kechika (limestone), Skoki (dolomite to volcaniclastics) and Road River Group formations (clastic sedimentary rocks). The intrusion is ovoid in plan view with a diameter of approximately 2 km and surrounded by a fenite aureole up to 500 m thick that has previously been mapped as “amphibolite” (Pride, Cominco Ltd., 1987) and “syenite” (Mäder, 1986). The intrusive contacts are parallel to bedding and lie at a uniform stratigraphic level near the base of the Kechika Formation. Three principal units within the carbonatite have been identified:1) a volumetrically dominant fersmite- and pyrite-bearing dolomite-apatite carbonatite unit that forms the core of the sill;2) a magnetite, pyrochlore, phlogopitebearing calcite-apatite carbonatite unit that forms the margins of the sill where it is in contact with the Kechika Formation; and3) a banded magnetite-apatite unit in the dolomite core.The niobium (Nb) minerals at Aley consist of pyrochlore, fersmite, and columbite. The alteration follows a general sequence whereby pyrochlore, and to a lesser degree, columbite, alter to fersmite. The chemistry of the alteration minerals appears to be inherited from the parent mineral. At Aley, no significant amount of tantalum (Ta) has been noted in the pyrochlore and the alteration minerals also do not contain it. Likewise, the reduction of solid solution capacity in the minerals reduces in the alteration sequence. The iron (Fe) content appears to increase in atomic proportion towards columbite.The two largest exploration targets are the Central and Saddle zones. The Central Zone occupies the core of the carbonatite complex and has a strike varying from 070° to 120° (predominantly 120) and dips 60° to 70° to the south. It is roughly ovoid in shape and extends some 1400 m E-W, up to 725 m N-S, and over a vertical range of 650 m. Mineralization is associated with bands and swirls of magnetite. The Saddle zone occupies the northern part of the carbonatite complex in proximity to the contact with the amhibolite annulus and has a strike of 070° to 090° dipping at 60° to 70° to the north. Mineralization is associated with alternating bands of pyritic calcite (varying in width from 5cm to 5m) with dolomitic or calcitic carbonatite.
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