ABSTRACT:
The Porcupine gold mining camp, located in Timmins, Ontario has been in continuous production since 1910. Over that period, approximately 65 million ounces of gold have been produced by more than 50 mining operations. Past-producers include the Hollinger (19 M oz) and McIntyre (11 M oz) mines, as well as numerous smaller operations. Most of the underground stoping in the upper levels of the mines dates back to the early operating years of the mines. As a result, the upper-level stopes and their associated crown pillars were largely designed in accordance with the engineering standards and mining practices of the 1910''s to 1940''s. Evaluation of the long-term surface stability of crown pillars overlying underground mines is an important component of mine closure planning. Back-analysis is performed on observed stable and unstable crown pillars, using common empirical geometrical-based techniques to assess crown pillar stability. Using case examples, observations are made on the impact of other factors, such as mining method, historic mining practice and time on crown pillar stability.
1 INTRODUCTION
The Porcupine gold mining camp, located in Timmins, Ontario has been in continuous production since 1910. Over that period, approximately 65 million ounces of gold have been produced by more than fifty mining operations. Most of the underground stoping in the upper levels of these mines, typically less than 45m (150 feet) below surface, dates back to the early operating years of the mines. As a result, the upper-level stopes and their associated crown pillars were largely designed in accordance with the engineering standards and mining practices of the day. Mining operations in the Porcupine camp shared several common elements. Mining typically followed steeply dipping, linear trending narrow veins. Gold mineralization was hosted in quartz veining within a competent rockmass.
