Sampling, grade control and ore reserve estimation at Renco gold mine, Zimbabwe: past, present and future

Abstract Modern gold mining activity at Renco Mine in southern Zimbabwe started in 1936. Since then a series of different companies have held the option to mine. The current owners, Rio Tinto Zimbabwe, took it over in 1973. Accurate grade control and ore reserve estimation has in the past been hampered by the complex geology. However, improved geological understanding since 1986 has led to changes in the sampling techniques, which in turn have brought about improvements in both grade and tonnage factors. For ore reserve evaluation, blocks of reef are defined by raises and reef drives. For each block the average grades and reef widths, calculated from the sampling of the peripheral developments, are used to estimate tonnages and grades. Since 1987, a geostatistical software package has been used to generate kriged plans of gold grade and reef thickness. It is now planned to incorporate the results of more recent geological research into this software package in the hope of further improving the accuracy of the orebody evaluation and production data.