The Collahuasi Mine is located at 4,800 meters above sea level on the Andean Plateau in the Tarapaca Region of northern Chile. Commercial activity at the mine dates back to 1880 when its systems of high-grade copper and silver veins began to be exploited. These operations continued for fifty years until their interruption by the Great Depression. Work in the area resumed in 1978 when key components of the Rosario deposit were identified. Although the layout of many of the abandoned tunnels and stopes are relatively well documented by Collahuasi, confirmatory drilling showed that the information from historical records is neither exhaustive nor always complete (the result of lost or forgotten records). Because of the transit of heavy machinery, these conditions are a cause of concern for the continued safe conduct of today’s operations. In addition, these cavities must be taken into account when a mine block is designed for blasting/exploitation, since they may noticeably decrease the ore grade of the block.

Over the course of the past 3 years, Golder Associates and Collahuasi have worked closely together to developed a quick and reliable method for detecting potential underground voids/abandoned tunnels at the site. The method uses high resolution 3D electrical resistivity imaging (ERI), microgravity and GPR, in combination with systematic confirmatory drilling of anomalies to achieve a rate of success of nearly 70% in voids detect.

As a separate topic, if time allows, we will also look at the results of a non-conventional approach used at Collahuasi for blast damage characterization of the rock mass using borehole geophysical techniques.