Correct sampling practices are of vital importance to the mining industry; key decisions for the business are made on the basis of samples in all the value chain. Geology plays a relevant role in pre- and post-investment stages. Actually the understanding of natural variability is essential for geological modelling, geometallurgical modelling, mine planning, grade and process control. Improper sampling practices obstruct this objective introducing irrelevant variability components, which can cause monumental economic losses. A good approach to accomplish this understanding is the application of heterogeneity and Ingamells's tests, which are useful tools to quantify the variability of a certain well-delimited geological unit at different comminution scales. The application of heterogeneity test can help minimise Pierre Gy's fundamental sampling error and to study the impact of other sampling errors. Ingamell's test allows us to define the correct mass of sample for chemical analysis._x000D_
This paper presents the results of several heterogeneity and Ingamells's tests done in Chilean porphyry copper deposits that belong to CODELCO Chile (Chuquicamata, Mina Sur, Radomiro Tomic, El Salvador, Andina and Teniente), in different geological units (endogenous oxides, exotic oxides, supergene sulfides and hypogene sulfides) and for several elements (Cut, Cus, Mo and As). These tests, considering the natural variability, have helped us develop accurate sampling protocols to minimise the fundamental error to acceptable levels. A major contribution of these tests (more than 30) is the generation of secure sampling protocols using the highest sampling constant obtained in the tests, for new porphyry copper deposits that don't have information given by heterogeneity and Ingamells's tests.