The Lawn Hill Platform Cover comprises a sequence of mildly deformed Proterozoic sediments and volcanics that crop out northwest of Mount Isa. Three subdivisions are recognised in the sequence: basal coarse clastics and acid and basic volcanics - the Bigie Formation and Fiery Creek Volcanics. They are overlain unconformably by fine to coarse fluvial and shallow marine clastics (the Surprise Creek Formation). The third, uppermost, and major subdivision of the platform cover, the McNamara Group, overlies the Surprise Creek Formation with minor unconformity. It consists of basal clastics, a thick sequence of carbonates, and an upper deep-water clastic sequence. The Lawn Hill Platform Cover is deformed into basins and domes, commonly intersected by major northeast and northwest-trending faults. Economic Cu, Pb and Zn sulphide deposits within the Lawn Hill Platform Cover are concentrated at two main stratigraphic horizons in the lower middle McNamara Group. The main deposits are associated with carbonaceous shales or laminated algal dolomite, suggesting that they may be formed by reduction of base metal rich solutions at an early diagenetic stage by the action of decaying algal material.