The Geological Strength Index (GSI) was introduced as an empirical tool to scale the intact rock properties, from samples to a jointed rock mass scale. Since his first conception, GSI was estimated in an empirical way, according to the proposed chart and according to a visual estimation of degree of fracturing and joint condition. Along the years, GSI has been modified for a better rock mass characterization, as for example including a massive rock mass category or presenting a special chart to characterize flysch sediments. Because many geotechnical users pointed out the necessity to quantify GSI, several Authors proposed different methodology to quantify it, based on joint spacing, rock block volume or RQD and joint condition. It is important to note that all the proposed methodologies are based on the characterization of a jointed rock mass, only recently, some Authors proposed a method to estimate GSI in weathered and hypogene rock mass. At present time, mine operations are facing the challenge to mine ore deposits at deeper conditions, with higher stress and to assess a rock mass characterized by cemented and sealed veins, that means a challenge regarding how to characterize a primary rock mass, formed by cemented joints, has occurred in many ore deposits in deeper condition. Los Sulfatos Ore Body, owned by Anglo American Sur, represents a porphyry copper deposit in hypogene environment and is characterized by a stockwork of cemented veins. The geotechnical assessment of the different Geotechnical Units, according to the traditional classification systems, shows a very uniform quality between them, so, arose the need of a better characterization of the primary rock mass. Because of that, the Authors developed a new method to quantify the GSI, based on the spacing of weaker cemented veins and on the weighted average hardness of the mineral infill. This methodology pointed out differences in terms of geotechnical quality better than the traditional classification systems.
