A mica, pyroxene, ilmenite megacryst-bearing lamprophyre from Mt Woolooma, northeastern New South Wales.

A narrow lamprophyre dyke, dated at 85 m.y., intrudes early Carboniferous sediments at Mt Woolooma in E New South Wales. The lamprophyre contains megacrysts of titanbiotite (Mg_18-21, 7-8% TiO₂) and rare Ti-Al salite (Mg_67.72, 6-9% Al₂O₃), ilmenite (5% MgO), titanphlogopite (Mg₆₁, 9% TiO₂) and apatite. The host-rock consists of lamprophyric-textured titanphlogopite (Mg_62-70, 7-8% TiO₂), diopside-salite, olivine, kaersutite and Ti-magnetite in a K-feldspar-rich base. The rock resembles a minette (mica-lamprophyre), but its bulk composition is richer in SiO₂ and Al₂O₃ (53-54% SiO₂ anhydrous, approx 16% Al₂O₃), and poorer in MgO (3%), Ni and Cr (30 ppm) than many minettes elsewhere. This minette forms part of a diverse assemblage of alkaline igneous rocks from the Scone-Gloucester area. These include alkali olivine basalt, teschenite, biotite alnoite, kimberlite and leucite monchiquite, many of which carry mantle xenoliths/xenocrysts and/or megacrysts. (Authors' abstract)-C.N.