Report on geological investigations carried out on permit to enter no. 113/1 to 31 October 1964

Abstract

Investigation of the manganese deposits on Groote Eylandt indicated that the manganese is restricted to the lower part of the Cretaceous succession and it was considered desirable to examine those areas of Cretaceous sediments in the coastal belt between Darwin and Roper River. Aerial photographs of the area were purchased and they were examined in conjunction with maps of the area compiled by Bureau of Mineral Resources geologists, prior to the helicopter traversing which commenced on 4th May, 1964. Total flying time during the survey was 145 hours and the flight lines are shown on Plan No 1 attached, which also shows sample locations. Four geologists were used in relays and the barge 'Dolphin III' was chartered for use as a base. This Vessel was replaced by the Companies vessel 'Yampi Lass' on 4th of June 1964. The survey was completed at Roper River on 11th July, 1964, and the following mineral occurrences have been reported by the field party. Occurrences of lateritic material were noted on Elcho, Drysdale and Howard Islands, on Napier Peninsula and in the Peter John - Giddy River area. Samples from these occurrences were assayed which showed that the alumina contents are below that of a true bauxite. Sandy hematite beds no more than four feet in thickness were noted on Elcho and Howard Islands, these were assayed. Manganiferous material was encountered during the helicopter traverses and these locations are: Probable island where two beds of manganese five and seven feet thick are separated by 100 feet of silt stone and sandstone. A sample (CR.5294) from the five foot bed assayed 41.0 percent Mn, 7.52percent Fe and 12.5percent SiO2; Everett Island - Lake Evella there are small occurrences of manganiferous laterite along the Gwakura Formation from Everett Island to Lake Evelia; Two outcrops of manganiferous laterite occur three miles east of the mouth of the Peter John River; Caledon Bay - scattered outcrops of manganiferous laterite occur over an area approximately one mile square five miles west of the northern point of Caledon Bay; East Arnhem Land Coastal Area - small outcrops of manganiferoue laterite occur in the Cretaoeous sediments along the eastern coast of Arnhem Land. It was decided to carry out a more detailed investigation of the Giddy River area following the helicopter reconnaissance and on 25th July a land party with two geologists commenced operations from a base camp established three miles west of the river. Three land traverses were made from the camp, one to the Peter John River area, one to the lower reaches of the Gate River and a third to the area south of the Cato River headwaters, a total distance of 540 miles. This work was completed on 23rd August, 1964. A party consisting of two geologists, two field assistants, two miners, a cook and a plant operator landed at Caledon Bay from the barge Loellen-M on 21st September to commence testing of manganiferous occurrences by drilling and pitting. Drilling commenced on 29th September but unfortunately the drill become unserviceable after one days operation. Two pits have been sunk, No1 intersecting sandy manganese to ten feet then passing into manganiferous sandstone with the manganese content decreasing downwards to the pit bottom at 16 feet. Pit No2 was sunk on a ridge of manganiferous laterite and was completed at 14. feet in manganese stained sandstone. Neither pit gave any positive indication of good grade manganese. We do not yet have a plan showing the location of the drill hole or the two pits but the following references will be of assistance; Pit No1 - 4.6N, 355E and Pit No2 1450 feet from Pit No1 on a bearing of 262, Camp Site 4.7N, 10.7 W. The expenditure incurred on the work described above is GBP27,080 to September 30th, 1964.