New grade control programme at the Manhattan mine.

Grade control was formerly by panning assay of samples from 6m blastholes on 5m centres with the blasthole relocated by stadia survey after blasting. Holes assaying above the cut-off grade were flagged and mined as ore. Uneven distribution of gold made assay results unreliable, so an improved technique was introduced which, in some benches, has increased reserves by 50%. Blasthole drilling is now done on a 4m by 4m grid, with an assay sample every 3m. Holes are plotted on a level map together with their assays. The blasting technique used minimises disturbance to the rock enabling examination of its geological features. Mining is done in 3m lifts to minimise dilution; bench height is 6m. Although time-consuming and labour intensive, costs of improved grade control are offset by added tonnages discovered.
Grade control was formerly by panning assay of samples from 6m blastholes on 5m centres with the blasthole relocated by stadia survey after blasting. Holes assaying above the cut-off grade were flagged and mined as ore. Uneven distribution of gold made assay results unreliable, so an improved technique was introduced which, in some benches, has increased reserves by 50%. Blasthole drilling is now done on a 4m by 4m grid, with an assay sample every 3m. Holes are plotted on a level map together with their assays. The blasting technique used minimises disturbance to the rock enabling examination of its geological features. Mining is done in 3m lifts to minimise dilution; bench height is 6m. Although time-consuming and labour intensive, costs of improved grade control are offset by added tonnages discovered.