The 1976-1978 drilling programme carried out in the Lock district was designed to establish the quantity, quality and extent of the known brown coal occurrence there. Exploration Licence (EL) 280, taken out by the Director-General, SA Department of Mines and Energy (SADME), in the name of the SA Minister of Mines, covered this programme. The licence was granted for one year on 24/1/1977, and at expiry was renewed for another twelve months on 23/1/1978. 104 open rotary mud appraisal drillholes totalling 7466 m of penetration, including 1420 m of core drilling, were completed 15 km west of Lock in three work phases. This drilling indicated the existence there of a low quality Jurassic coal deposit covering an area of approximately 9 km by 1.5 km, with a maximum width of 2.75 km. The average depth to the top of the coal is 52 m, and the coal seams vary from 0.2 m to 20 m thick. Phase I drilling, regional appraisal, included the three stratigraphic wells Colton 1, Tuckey 1 and Mucka-Cudla 1, plus a series of holes numbered P2 through P23 in the vicinity of the now-established coal deposit. The stratigraphic well locations were determined in advance of the programme, while the P-refix holes were located by the onsite geologist. Drilling funds were supplied by SADME. Phase II, involving drilling of holes P24 to P44 using four rigs, was initiated by SADME and jointly financed with ETSA. This phase defined the approximate limits of coal. Completion of this phase established the existence of approximately 100 Mt of inferred coal reserves, but since the bounding drillholes were spaced up to several km apart, yet more holes were required to better define the deposit and to determine the amount of mineable coal. Phase III was therefore designed to test more accurately the extent of the coal deposit, both horizontally and vertically, and to assess typical ash values, moisture, sodium and sulphur contents; to determine the number, extent and depths of any aquifers; to measure water content and productivity of each aquifer, and to assess the mechanical competence of the overburden, coal and underlying sediments. This phase was financed by ETSA and was supervised by SADME geologists, and the results indicated that about 200 million tonnes of coal are present which have a strip ratio of less than 10:1. Drillholes P45 to P104 were drilled in Phase 111; P45, P48 and P54 were cable-tool holes drilled for geotechnical and aquifer petrological information. Hole P71 (collared 15 m away from P45) and P104 (50 m away from P54) were drilled to allow monitoring of aquifer pump tests. In addition, several other drillholes lying either inside or outside of the coal deposit limits were completed as groundwater observation wells, using PVC pipe casing with a slotted section over the aquifer.