The Aley Creek area is underlain by Cambrian to Devonian carbonate and clastic rocks of the Kechika Group, Skoki Formation and Road River Group. This miogeoclinal succession, deposited near the shelf/off-shelf boundary, was intruded by the Aley carbonatite complex (094B 027) prior to the main Late Jurassic-Early Cretaceous orogenic event. The complex consists of a rauhaugite (dolomitic carbonatite) core zone, 2 kilometres in diameter, surrounded by an older, outer ring of amphibolite. A contact aureole of recrystallized carbonate rocks surrounds the amphibolite margin. Rare-earth, carbonate-rich dykes occur throughout the complex but are most common in the outer alteration halo (contact aureole).
The dykes weather dark reddish-brown, are generally intruded parallel to bedding, and average 0.5 to 1.5 metres in thickness. Their primary component is dolomite. Accessory minerals include purple fluorite, pyrite, barite, quartz, bastnaesite and other rare earth carbonate minerals. Barium, strontium and total rare-earth elements may reach major element concentrations in the dykes. The dykes may represent residual, low-temperature liquids derived from a dolomite carbonatite-like parental melt.
Numerous minerals occurring in the carbonatite complex have been identified; refer to Geological Fieldwork 1986, Table 4-5-1, page 285 for a comprehensive list. Some minerals of interest, occurring in the dolomite carbonatite (core zone), include monazite, cheralite, thorianite, zirkelite and thorite.
Whole rock sampling of the barite-rich rare-earth element carbonatite dykes from the northwest ridge analyzed 0.721 per cent cerium, 0.358 per cent neodymium, 0.229 per cent lanthanum, 0.084 per cent thorium, 0.07 per cent strontium and 7.74 per cent barium (Fieldwork 1986).
See Aley (094B 027) for further details on the Aley carbonatite.