Coronation Hill Joint Venture, Bench Widening report, September- December 1987

Abstract

During September to December, 1987, benches on 160m RL and 130m RL in the vicinity of the original Coronation Hill workings were to be widened to provide better access for drilling rigs. The exposures were to be mapped to gain information on the structural controls on precious metal mineralisation, and the excavation process was to be monitored to develop grade control methods. Geological mapping of the benches showed that the mineralisation occurrs as sub- vertical lodes, lensoidal in shape, associated with NNW and NNE trending fault zones. Various sampling procedures were investigated in the project, including rock chip sampling of bench floors, sampling of blast holes, and truck dump sampling. It was necessary to obtain special permission from Traditional Owners through the Aboriginal Sacred Sites Protection Authority to carry out the work. The operations were monitored by Jawoyn employees of BHP. Evaluation of the various sampling procedures showed that blast hole sampling was more representative of the mined volume than was chip sampling of benches. Tests of the repeatability of truck dump sampling indicated that sampling carried out was not an accurate method of grade control, and mined quantities and grades did not correlate well with estimates from blast hole sampling. Larger samples are recommended to solve this. Other recommendations are: further bench widening work is required for a better definition of structural controls on gold mineralisation; blast holes should be drilled at 60degrees to grid west in a staggered pattern to help avoid drilling parallel to vertical mineralised structures; every balast hole (1m by 1.25m grid) should be sampled in ore zones as defined from previous cuts; truck volumes and weights need to be measured until average weights per load and bulk density can be estimated more accurately; truck dump samples should be ~50kg, crushed on site to -3mm, and then split to 4kg before submission to a lab for further sample preparation.