Vertical, W- and NW-trending, post-tectonic, Proterozoic dykes at Napoleon Bay, southeastern Baffin Island, Northwest Territories, contain mineral assemblages typical of lamproites: 1) phenocrysts of Fe-bearing leucite and sanidine, Ti-rich phlogopite, and high-Mg olivine and diopside, and 2) a groundmass of Ti-rich phlogopite, Fe-bearing sanidine and apatite. Except where preserved in chill zones, leucite has decomposed to a sanidine - kalsilite intergrowth or has been replaced completely by sanidine. Phlogopite grains are enriched in Fe (to annite and ferri-annite) on their margins, relative to cores. Late-stage titanian potassium magnesio-arfvedsonite appears in some dykes and is also progressively enriched in Fe (to titanian potassium arfvedsonite) toward the margins of grains. In a few crystals, aegirine and aegirine-augite (some grains Ti-rich) overgrow diopside. Rare and very late-stage, possibly magmatic development of minerals involves overgrowths of potassium magnesio-arfvedsonite on Fe-rich amphibole, and phlogopite and "ferriphlogopite" on Fe-rich mica. With the exception of aegirine and aegirine-augite, all ferromagnesian silicates are undersaturated in Si + IVA1, with average deficits in the tetrahedral position extending from 15.7% in annite and ferri-annite (grain margins) to 1.5% in magnesio-arfvedsonite (overgrowths). The vacancies in the tetrahedral position can be filled with Fe3+. Rare minerals in the Baffin dykes, that are characteristic of known occurrences of lamproite, are K, Ti-rich sodic-calcic amphiboles, shcherbakovite, Ti-rich chromite, and K-Ti-Fe oxide. However, some (ninor minerals in these dykes have not been described from lamproite [pectolite, lorenzenite, barytolamprophyllite, alcioancylite-(Ce), djerfisherite], and the late Na-Fe overprint seems extreme for lamproite. Evidence suggests differentiation with repeated, post-consolidation magmatic injections. Rocks that are possibly related include a porphyritic volcanic rock containing pseudoleucite (sanidine) - forsterite - diopside - titanian phlogopite, located ca. 20 km west of Napoleon Bay, not found in situ, small diatreme dykes and sills (cemented with K-rich, peraluminous glass), 8 km WSW, and coeval, mineralogically similar lamproite dykes at Sisimiut, southwest Greenland.
