The area around Khtada Lake is dominantly underlain by grey biotite, plus or minus hornblende gneiss, amphibolite and minor sillimanite, plus or minus garnet gneiss of the Paleozoic (?) Central Gneiss Complex. The garnet-sillimanite-quartz-feldspar gneisses occur in a zone approximately 20 kilometres in length, extending from Kwin- itsa (refer to 104B 011) southeast through Khtada Lake to Big Falls Creek (Area 2, Figure 9, Open File 1988-26), apparently forming a continuous zone.

The garnet-sillimanite-biotite-quartz-feldspar gneisses outcrop along the north and south shores of Khtada Lake and on a ridge top 3 kilometres south of the south end of Khtada Lake. These gneisses host between 5 to 30 per cent garnet and 5 to 30 per cent sillimanite. The sillimanite occurs in densely felted layers ranging from 0.2 to 2.5 centimetres in thickness (Geological Survey of Canada, Memoir 394).