Continuing intensive exploration for economic sedimentary uranium deposits within buried Tertiary palaeochannel sediments in the Yarramba Homestead area, 50 km north-west of Cockburn, which had been invigorated by the recent discovery of strongly radioactive uraniferous fluvial sands in the vicinity of the Y8E and Y11 drillholes, that were put down near Yarramba Homestead during prior SML 417, has included further exploratory and close-spaced appraisal drilling (132 open rotary holes totalling 50,986 feet, plus an additional 176 feet 3 inches of core drilling in 4 holes), as well as the acquisition and interpretation of experimental gravity, ground magnetic, resistivity depth sounding and dipole-dipole IP surveys that were attempts to remotely map the distribution of palaeochannel sands. Four stepout open rotary drillholes put down 100 feet away from the Y8E discovery hole confirmed the local presence of highly radioactive zones in the subsurface, at depths comparable to the 301 feet and 320 feet depth intersections made originally, but again the mineralised zones did not exceed 1 foot in thickness. As drilling progressed, other thin radiometrically anomalous zones were also found in the Y8 area, attesting to the passage of uranium-bearing solutions through the Yarramba palaeochannel sands, which are up to 95 feet thick near the channel mid-point. In early November 1971 a second, more significant occurrence of uranium mineralisation was discovered in exploratory hole 580/1, drilled 4 miles west of Kalkaroo Dam. Immediately an appraisal hole, 580/1C1, was drilled alongside of it 15 feet away to allow coring of the find, with excellent core recovery being obtained over the mineralised depth interval 341 feet 9 inches to 388 feet 5 inches. XRF analyses of samples of this drill core gave grades of 0.195% U3O8 (almost 4 lbs/ton) from the depth interval 356 feet to 380 feet 9 inches, which included a section averaging 0.65% U3O8 (or 13 lbs/ton) between 362 feet 6 inches and 368 feet 4 inches depth. The uranium minerals appeared from laboratory examination to occur only as sub-micron sized grains within the sediment silt and clay fraction. An additional 27 holes drilled shortly afterwards in the area of this discovery showed that the mineralisation, which subcrops in a spotty, lenticular fashion, could be traced for a distance of at least 1100 feet along the eastern side of a northeast-southwest trending Tertiary stream channel. Further close-spaced drilling and coring carried out at the south-western end of the channel trend then revealed the existence of a probable meander loop re-entrant in the channel eastern bank, which exhibited a high degree of sandstone mineralisation that is spread now over three zones at 260, 320 and 360 feet depth levels. Future drilling will target other, hopefully larger re-entrants along the established Kalkaroo trend, in expectation of finding more such concentrated mineralisation. The presence of abundant pyrite in the basal Tertiary sediments deposited along the Kalkaroo palaeochannel eastern bank holds promise that an induced polarization technique may be successful for rapidly locating the position of this bank in nearby untested places. As for the other geophysical methods tried, it was seen that resistivity depth sounding is unable to directly locate the channel sands; however, these soundings, when combined with gravity and resistivity profiling results, did show an apparent correlation between the Precambrian bedrock topography and Tertiary sand deposition.