text: Block kriging is the most common geostatistical method used for interpolating metallurgical index parameters and it is often applied on a domain basis.   Classical geostatistics require that the estimation variable be additive, and there is currently some debate on the additive nature of the metallurgical index parameters measured by the above tests. The Bond ball mill work index test is thought to be additive because of its units of energy;  nevertheless, experimental blending results show a non-additive behavior.  The SPI(R) value is known not to be an additive parameter, however errors introduced by block kriging are not thought to be significant .  These issues, among others, are being investigated as part of the Amira P843 research program on Geometallurgical mapping and mine modelling.