Silica Control Practices in Sublevel Caving at Stobie Mine

Robert Assabgui, Colin McAnulty, Michelle Paquette, Simon Nickson,
Abstract Vale Inco’s Frood-Stobie Complex currently operates a sublevel cave mining area between 2100 level and 2600 Level. Mining at Stobie was initiated in 1885 through an open pit method and progressed underground in the early 1950’s. Underground mining at Stobie has utilized a variety of mining methods including blasthole, cut-and-fill, vertical retreat mining and sublevel caving. Sublevel caving was initially introduced in 1967 to recover ore remaining in the bottom of the Stobie Pit and below the Frood North Extension Pit at Frood Mine. Two main pillars (25 and 37 Pillar) were left to separate the North Extension Pit and the Stobie Pit from the initial Stobie sublevel cave. Mining of 25 Pillar was initiated on 1600 Level in 1995 as an additional sublevel cave mining area designed to augment the overall production rate. The 25 Pillar area has since joined with the main sublevel cave and proceeded downwards over the years to the current mining horizon on the 2400 Level.

One of the significant challenges encountered in the sublevel cave mining area is the control of dust particles in the production headings. Silica is a component of most rock and ore that can become airborne in dust created by crushing, drilling and hauling activities. Silica levels over established exposure limits were recorded in December 2001 on the 2100 and 2160 Levels after the commissioning of a new ore handling system that fed production ore to 9 Shaft. The sublevel cave mining method was believed to be contributing to the elevated levels of silica due to natural “milling” of ore and host rock in the cave. Drawpoint pulls that ran suddenly were noted to be closely associated with high levels of dust and associated silica.

In response to the situation, ore pass ventilation systems were immediately redesigned to place each pass under suction and various upgrades were implemented to manage water sprays and ventilations flows. Respiratory protection zones were created in certain areas on the 2100 and 2160 Levels in March 2002 in order to manage high silica levels in selective areas. The 2100 Level respiratory protection zone was lifted in March 2003 after several months of successful monitoring. The 2160 Level respiratory protection zone was lifted in June 2005 after the implementation of engineering controls and several months of successful monitoring. Subsequent strategies were developed to closely monitor silica levels after the respiratory protection zones were lifted. These strategies included daily monitoring of production areas for ventilation deficiencies, the move towards ore passes with a single dump point and the development of improved standards for drawpoint mucking. This paper will review the development of silica control practices that are part of the Stobie sublevel cave operation.
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