Downhole survey uncertainties observed at various De Beers operations prompted an investigation into their possible effect on deposit shape and volume. An accurately surveyed artificial borehole' was constructed and different downhole survey instruments tested. In this way an empirically determined error range of 0.1 per cent to ten per cent was derived for downhole survey data. These survey errors were applied to an orebody model at an existing mine. Visualising the sphere of uncertainty associated with a borehole trace using a general mining package (GMP) gives an indication of possible volume variance. The resulting orebody maximum and minimum volume scenarios for three different depths (200 m, 500 m and 800 m) are presented._x000D_
For certain instruments and borehole angles, the 3D positional error can be as high as 100 m at 1000 m down the hole. At depths below 200 m the resulting volume deviations can become significant for borehole survey errors exceeding 0.35 per cent. At 800 m depth the volume difference can approach 25 per cent._x000D_
These figures assume that the error is compounded._x000D_
The impact of these downhole survey errors is greatest for pipe-like orebodies such as porphyries and kimberlite pipes. Subhorizontal sill-like orebodies (and coal seams) will not be significantly affected by these errors._x000D_
The impact of this type of survey error needs to be stated (and quantified) and is significant in JORC classification._x000D_
FORMAL CITATION:Nordin, W, 2009. The effect of downhole survey uncertainty on modelled volume, in Proceedings Seventh International Mining Geology Conference 2009, pp 81-84 (The Australasian Institute of Mining and Metallurgy: Melbourne).