Talc mines located near Mount Fitton produce 60% to 80% of the South Australian production of talc, of which two thirds is high grade material (suitable for pharmaceutical or paint manufacture). Over 40 known deposits occurring within an area of 60 square km are hosted by Late Proterozoic Balcanoona Formation dolomite and dolomitic marble. Silica has been dissolved from older stratigraphic units and re-deposited on the dolomite by hydrothermal replacement, within the cores of minor folds, at the contact of the Balcanoona Formation and adjacent units, thereby producing tremolite, whereafter the subsequent removal of calcium has produced talc. Impurities found within the talc orebodies include remnant tremolite, recrystallised dolomite, blocks of host rock dolomite, and chlorite existing as chloritic schist near the ore body margins, and as zones of chloritic talc. Total recorded mine production from 1945 to 1986 is 274 000 tonnes. Talc has also been produced from the Mount Lofty Ranges (Lyndoch, Gumeracha and Truro) and Eyre Peninsula near Tumby Bay.