This paper describes an investigation of the sampling problems which contributed to erroneous Concentrator production forecasts at the mining operation of Bougainville Copper Ltd (BCL) in the North Solomons province of Papua/New Guinea._x000D_
Reference figures provided by independently verified commercial shipment data demonstrated the existence of a bias in the calculated Concentrator production; the challenge was to identify systematic errors in each of the contributory measurements (feed tonnage and feed, tailings and concentrate grades)._x000D_
The uncertainty surrounding specific sampling and measurement errors precluded optimum metallurgical control and performance of the milling circuit, encouraged disputes about the difference between Mine versus Concentrator production estimates, and cast some doubt on efforts to follow political guidelines concerning a maximum feed tonnage or recovery oriented mill operating concept._x000D_
An evaluation of routine results as well as specifically targeted test work identified the sampling errors associated with measured individual parameters._x000D_
The emphasis in this report is on the procedure for quantitative error assessments._x000D_
The measured performance of a mineral dressing plant is subject to a systematic error balance which can be derived from the more familiar weight and metal balances such as the two- or three-product formula._x000D_
The resulting equations are generally valid, and they are applied to the measurements obtained at BCL's Concentrator to illustrate the method.