A number of small, fault-controlled, siliceous, copper deposits in the Precambrian of North-West Queensland contain most of their silica as tridymitic jasperoid. The tridymite has pseudomorphically replaced the dynamic metamorphic assemblages that resulted from earlier fault movements. It is proposed that seismic pumping (Sibson et al., 1975) forced copper and silica-charged hydrothermal solutions along major faults. At elevated pressures quartz-copper lodes were emplaced but in lower pressure zones on feather faults at the end of major fault zones or in small fault off-shoots tridymitic jasperoid deposits formed. As tridymite is unstable at quite low burial pressure the preservation of the tridymitic jasperoid desposits reveals the limited amplitude of uplift and erosion in north-west Queensland since the deposits formed in the middle Proterozoic.