Geostatistical comparison between blast and drill holes in a porphyry copper deposit
Serge Antoine Séguret MINES ParisTech, Center for Geosciences/Geostatistical team, 35 rue Saint Honoré, 7730 Fontainebleau, France. E-mail: [email protected]
Diamond drill-hole grades are known to be of better quality than those of blast holes; is this true? We present a formal study of a porphyry copper deposit in Chile where the variogram of 3-meter long drill hole samples is compared to 15-meter long blast hole ones and we show that the blast holes can be assumed to regularizing the point information deduced from the drill holes, except for a nugget effect specific to the blast samples. Complementary analyses based on migrated data show that the drill holes also have their own errors. After a brief description of the first steps in the blast sampling protocol, we show, by using extension variance concepts, that the blast error is not due to the arbitrary removal of material from the sampling cone produced by drilling.