1957 Geological report on Northern Hercules gold mine

Abstract

In preparing this Report it is the writer's intention to record all known facts and economic possibilities of the Hercules Mine prior to the flooding of the lower levels and subsequent inaccessibility of the workings. Mining and salvage activities by the Northern Hercules NL ceased at midnight the 28th December 1957. The mining assets were taken over by United Uranium at that date. Existing plant and machinery will be converted and used by the new Company to treat their Uranium ores from the South Alligator River district. It is not intended to criticize past actions and interpretations but to assess the economic value of the mine based on new data on band. The information obtained after detailed mapping and sampling of the latest development in the mine crystallizes the fact that the future of the mine would be marginal, even as a low grade proposition. The original grades and tonnages on which the Northern Hercules prospectus was based have not been realised by later mining operations and were too optimistic. Remapping and sampling of the latest exploratory driving and X cutting will indicate that; 1) Ore reserves above the 300' horizon are depleted. Most of the old stopes are inaccessible due to cave-ins, 2) Recalculating of ore reserves in the 200'/300' blocks will show that the mine able tonnages left are insignificant. The expected grades and tonnages of No 1 and No 2 ore shoots were not realised on the 4001 level, 4) No 4 ore shoot or the central lode cannot be considered as an additional source of ore, 5) Exploration by driving, X cutting and drilling on the 2001/3002/4001 horizons did not indicate the existence of additional mine able ore bodies, 6) The intensity of shearing is lessening on the 4001 level as well as at the faces of the 200'/300' levels, 7) The overall grade of the remaining ore will be below cutoff grade, 8) There is little hope that further diamond drilling or exploration either at depth or to the west of the known lodes would disclose sizable ore bodies to justify mining operations on the present scale. The Hercules Gold mine is situated 34 miles by road north-east of Pine Creek siding on the Darwin-Birdum railway and 157 miles by road south-east of Darwin. The road to the Hercules mine is moderately good for the first 15 miles after which with little expense it could be made trafficable for most of the year except for short periods after heavy storms. The crossings of the Evelyn and O'Neil creeks respectively 2 M and 3/4 miles west of the mine represent the biggest obstacles to all weather traffic to Pine Creek. After a close study of the recent development the following conclusions have been reached; 1) The ore reserves and values have been based on too optimistic calculations, 2) Ore reserves above the 3001 level were exhausted by June 1957, 3) Previous diamond drilling programmes did not indicate additional sources of ore at depth besides the known ore bodies, 4) The stopes were weak and restricted in output, 5) It has been proved that diamond drill intersections were inaccurate and the obtained grades did not coincide with later development and mining grades, 6) Possible parallel lodes belonging to the Hercules shear system will probably behave the same way as the worked lodes and are expected to be restricted in output. These facts indicate the futility of further exploration in the mine at present gold prices and high production costs. Exploration and development in the mine should be discontinued at present. The favorable fissures to the north of the mine should be carefully investigated by detailed mapping on the surface. The continuation of the Hercules shear system to the south of the mine should be re-mapped and the adjacent Rhyolite Dykes closely investigated. The object should be to locate substantial low grade ore bodies in these dykes.