Base metal exploration activities undertaken by Thiess Brothers in the Yumali - Coomandook area investigated several coincident regional gravity and aeromagnetic anomalies arising from concealed Palaeozoic basement rocks. These anomalies are part of a major band of magnetic and gravity anomalies which rings the western margin of the Murray Basin in South Australia. An interpretation of the anomalies contained within the subject licence area suggests that they are caused by dense bodies with strongly magnetic layers separated by less magnetic layers. Following the conduct of 70 line km of ground magnetic and gravity surveys at 250 m station spacings, plus 38 line km of resistivity soundings at 25 m intervals along five traverses using an expanding Schlumberger array, to firm up basement drilling targets, 49 vertical rotary open holes totalling 4302 m of penetration were drilled. The results from 8 of these drillholes put down at the Ki Ki and Coomandook prospects in January 1980 showed that there the basement rocks consist of basic to intermediate intrusives and volcanics with trace amounts of pyrite and magnetite. Drillholes RH7 and RH8 encountered highly altered basic volcanic rocks which have only been metamorphosed to greenschist facies and so are thought to be younger than the Kanmantoo Group, and possibly equivalent to the Truro Volcanics. Importantly, a significant amount of brown coal was intersected in the Tertiary Knight Group, when drillhole RH6 encountered a 3.5 m thick seam of lignite at 50.5 m depth, which was equated to the Moorlands Lignite Member of this group. CSR took over as the sole licensee for EL 707 at the end of 1980, and commenced evaluating the extent of the coal discovery via two programmes of appraisal drillling performed in February and June 1981 (when it completed 34 open rotary, geophysically wireline logged holes totalling 2479.2 m). At this stage no drill cores were taken from the coal seams, but limited coring was eventually done during March 1982 to help to define the coal quality (28.17 m cored in two 100 mmm diameter diamond holes), while another two open rotary chip holes were put in to the east of the indicated deposit margin, for a total 346 m drilled, in order to improve the accuracy of the reserve estimation. The indicated brown coal reserves are 45 million tonnes in the Yarrawonga prospect, plus some other small inferred reserves to the east. The coal has high total moisture, averaging 55.2 %, and moderately low ash and high sulphur contents. It occurs at the top of the Renmark Beds, between 23 and 49 m below the surface, covers an area of about 16 square km, and has seams from 2 to 5.6 m thick. Shallow auger drilling of 31 holes for 57 m has shown that kopi and seed gypsum occurrences in the Cooke Plains Embayment are more widely distributed than previously reported, and that the thickness of gypsum in areas away from the gypsum dune system is less than 2 m. Reserves of gypsum in dunes not covered by mining leases total 150 000 tonnes of seed gypsum and 12 000 tonnes of kopi. Low grade seed gypsum can be upgraded for plaster feed stock. The kopi is suitable for agricultural use only.