George Greer, Pan American Silver Corp.; Martin G. Wafforn, Pan American Silver Corp
In early 2014, Pan American Silver Corp. commenced a project to construct a second shaft at its La Colorada underground mine located in the northern part of Zacatecas state in Mexico. The mine dates back to the 1920’s, and with favourable exploration results resulting in additional reserves below the current mining levels, an increase in mine production was justified. The existing shaft could not be expanded as it was already at maximum capacity, and mining had progressed well below the shaft depth. In addition it could not be used for the transport of personnel nor materials. This was the first new shaft development project undertaken by Pan American Silver in the history of the company. The new shaft was designed to extend to 618 meters below surface, with the option for a future extension to 1,000 meters. The existing mine workings allowed the use of a raise bore for the excavation of the shaft opening, utilizing directional drilling to control the pilot hole. The shaft was located between two separate vein systems and had to avoid extensive historic workings in the upper levels. A further challenge included poor ground conditions, particularly near the transition area between the dacite in the upper section of the shaft and the limestone structure below. This was an interesting project with many successes and numerous lessons learned. These include numerous raise bore pilot hole drilling challenges, the need to shotcrete the shaft pilot raise, the evolution of the sinking strategy, and a somewhat unique loading level design. The project was successfully completed in 2016, with the shaft operating at full mine production capacity within weeks.
