Experience: Ontario Department of Mines - I 968 Ontario Department of Mines - 196-9 Projex Ltd. - 1970 AMPHIBOLES AND PYROXENES FROM THE SYENTITIC ROCKS OF COLDWELL ALKALINE COMPLEX, THUNDER BAY, ONTARIO M. C. Lee Amphiboles and pyroxenes are separated from the rock specimens which are syenites and nepheline syenites from the Coldwell Alakaline Complex. The amphiboles and pyroxenes are determined by both optical and x-ray powder methods. The 2V angles, extinction angles and refractive indexes (a, 3, y ) are determined for these specimens. The pyroxenes are found to be soda augite, aegirine-augite and augite. Zoning is observed; there is an enrichment in aegirine content towards the rim of the crystals. The amphiboles determined by the optical studies are proved to be ferrohastingsite, hastingsite, and also some riebeckite. Zoning is also observed; the iron content increases from the center towards the rim of the crystals. Optical determination is a much better method than that of x-ray for these minerals. X-ray determination is a failure for the pyroxenes and amphiboles. It is due to the fact that the cell parameters of diposide is very similar to those of aegirine and augite. The same factor affects the x-ray determination of amphiboles; the cell parameters of riebeckite is very similar to those of ferrohastingste and arfverdsonite . The course of crystallization of these pyroxenes seems to be:- soda augite - aegirine-augite - Aegirine. According to Aoki (1954) as well as Yaki (1966), crystallization in the mentioned trend takes place under low temperature and high oxygen partial pressure conditions. When the crystallization trend is moving towards the aegirine-rich members, the temperature is decreasing gradually and the oxygen partial pressure is increasing simultaneously . From the analytical results; the sequence; - Ferrohastingsite - Arfvedsonite is suspected to be continuous. Formerly, both riebeckite and arfredsonite are suspected to be the final end product. The presence of riebeckite in some rock specimens of Coldwell Complex has shown that riebeckite is the final end member of the series. 41
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