FLUORITE AND CALCITE MELT INCLUSIONS IN APATITE FROM CARBONATITIC INTRUSIONS AT THE SCHICKLER OCCURRENCE AND DWYER MINE, ONTARIO, CANADA

Melt inclusions in apatite from the Schickler Occurence and Dwyer mine, two fluorite-bearing carbonatitic “vein dikes'' situated near the town of Wilberforce, Ontario, Canada, are examined in an effort to chemically characterize these unusual carbonatites. Centimetric fluorapatite crystals occur within a dissociated calcite and fluorite matrix at the Schickler Occurrence and Dwyer Mine and host inclusions preserving evidence of a complex magmatic history. Polished epoxy mounts of apatite were analyzed using scanning electron microscopy and X-ray energy dispersive spectroscopy (SEM-XEDS) in order to characterize the inclusions. These melt inclusions, interpreted to have crystallized from trapped melt (based on their external morphology, internal mineralogy, and texture), are present as rounded globules of calcite or fluorite within fluorapatite crystals. More rarely, these melt inclusions can also be found within crystals of augite. At both of these localities, most of the melt inclusions are monomineralic, however, more complex mineralogies also occur. Primary phases found within both calcite and fluorite-dominant melt inclusions include combinations of pyrite, thorite, uraninite, and quartz, whereas fluorite-dominant melt inclusions may additionally contain synchysite-Ce (all phases identified using SEM-XEDS). In addition to the melt inclusions, apatite from the Schickler Occurrence hosts a profusion of micromineral inclusions, predominantly found in altered portions of the crystals. Apatite from the Dwyer Mine hosts fewer micromineral inclusions. The textures and mineralogy exhibited by samples from the Schickler Occurrence and Dwyer Mine suggest that the carbonate-halide melt was heterogeneous and immiscible, resulting in separate fluorite and calcite melt inclusions. Secondary REE mineralization occurring in altered zones of apatite points toward a late stage REE-bearing hydrothermal fluid, possibly sourced from the carbonate-halide magma during cooling.