Potassium-argon basalt dates and their significance in the Ilford-Mudgee-Gulgong region

Three different topographical environments occur in separate areas of the Ilford-Mudgee-Gulgong Region. Tertiary basalts varying in mode of occurrence were selected from each area for potassium-argon (K-Ar) dating. Results revealed flows of upper Eocene-lower Oligocene and middle Miocene ages, resting on two different erosion surfaces regarded as Eocene and upper Miocene, respectively. An intermediate and prominent erosion level forming undissected upland surfaces along the Main Divide, and extending across deeply dissected country to the west, is believed to be of lower Miocene age. The auriferous gravels of the Gulgong deep leads were probably deposited between late-lower and early-middle Miocene time and buried beneath middle Miocene basalt flows.