The ATACAMA KOZAN mine is an underground copper mine which is located in the suburbs of Copiapó City,the III Region of the Republic of Chile. It commenced exploration activities in 1991, and production of high quality copper concentrate from 2003. Cu-grade and tonnage data, which should be estimated in each stage of mine development (exploration, F/S, development and operation), are most important factor for decision of mine development and for steady operation of mine. Here we report grade-tonnage estimation methods in the ATACAMA KOZAN mine, and the history and excellent result of improvement on the estimation method. Geological model of copper deposit in the ATACAMA KOZAN mine was modified from "Breccia type" at initial stage of exploration to "Manto type" at main stage of exploration, and finally it is considered to be "Manto-Breccia composite type" in proportion to accumulation of exploration data in the each stages of initial exploration to later exploration in production. Following to the modification of the deposit model, grade-tonnage estimation method was improved repeatedly from square inverse distance method in the period before the development of the mine to Kriging method using variogram model in the period after commencement of production. Furthermore, improvement of the estimation method was kept on even after adoption of Kriging method. While in the period of "Stage 1" Kriging method using variogram model was adopted, in the period of "Stage 2" we adapted "Variable variogram model" for grade-tonnage estimation, which can transform direction of variogram model to fit elongation of ore body. In order to eliminate such a bad influence that grade of "Manto type"body is evaluated excessively near high grade"Breccia type" body, we have invented newly "Composite method" in the period of "Stage 3", with which grade in each "Manto type" and "Breccia type" bodies are calculated independently at first, then the all calculated grade is composited together. Grade-tonnage model estimated with "Composite method" showed very good coincidence with the final grade-tonnage data just before exploitation. As a result of these efforts, a grade-tonnage estimation method was established, and this trustworthy method is contributing considerably to steady operation of the ATACAMA KOZAN mine.
