Fluid inclusions to quartz overgrowths occurring within 6 selected samples of Patchawarra Formation drill cores obtained from 3 deep Cooper Basin wells, were investigated using closely controlled heating/cooling cycles to determine past temperatures of crystallization for secondary minerals, and by extension the ambient geochemical condition of migrating pore fluids. Evidence points to the overgrowths having developed from relatively low salinity pore water, mostly over a temperature range of 150-160 degrees Celcius, although some of the quartz overgrowth activity possibly commenced at lower temperatures.