Fairly pure buff diatomite, 45 to 60 centimetres in thickness, occurs in a layer just below the surface soil and covers at least 0.4 hectares. The Prospect Lake deposit, of Recent age, is underlain by yellowish clays. The diatoms consist almost entirely of the small transparent cylindrical Melosiro Granulata which are well preserved. A thin layer of diatomite mixed with silt also occurs nearby to the north along Prospect valley.

A partial analysis of the deposit gave: 65.60 per cent SiO2, 14.43 per cent Al2O3, 1.87 per cent Fe2O3, 1.27 per cent MgO, 13.10 per cent H2O, and 1.70 per cent CO2 (CANMET Report 691, page 94). Another sample graded 75.92 per cent SiO2 (Geological Survey of Canada Memoir 36, page 138). About 180 tonnes are reported to have been taken out in 1921 (CANMET Report 691, page 53).