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Rock bursts in the deep metal mines of the Coeur d'Alene district present an ever increasing problem in the safe and economic mining of the district's silver, lead and zinc ores. Hecla Mining Company operates two mines in the district - the Star, a 1100-ton/day lead-zinc mine, and the Lucky Friday, a 750-ton/day silver-lead mine. Rock burst problems at both operations prompted Hecla management to make an all-out attempt to find a practical method of predicting and eventually controlling these bursts. Research by personnel from the Denver Research Center of the Bureau of Mines at ASARC¸'s Galena Mine indicated that a recognizable pattern of seismic activity preceded some bursts and this activity could be precisely monitored by present-day, off-the-shelf electronic devices. Using information gained by the Bureau and other sources, Hecla designed and installed a 24- channel seismic monitoring system in the Lucky Friday mine. Installation was completed in December 1973 and after a year of successful operation, it was decided that a similar system would be installed in the Star mine. This second installation was completed in June 1975. Both systems are now operating and providing continuous information on underground seismic activity. Each monitoring system consists of a network of geophones with attendant amplifiers that are connected by shielded cable through an interfacing device to a computer. The origin of each seismic event is determined by the computer and a three-dimensional location is printed out. This information is plotted daily and is used to pinpoint rock burst prone areas and chart their relative seismic activity. This paper will review the causes and effects of rock bursts in the Coeur d'Alene district, the equipment and operation of the micro-seismic system at the Star and Lucky Friday mines, and the results obtained to date.
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The Coeur d'Alene mining district lies in the "Panhandle" of northern Idaho. The Star and Lucky Friday mines are in the eastern end of the district, north of the Osburn Fault.
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The Osburn Fault is the predominant geological feature in the district. It is a steeply dipping, northwest trending structure with an apparent right lateral strike slip displacement of approximately 16 miles. Many parallel and sub-parallel fault systems traverse the district and most veins are closely associated with these subsidiary structures. Rock type in the district consists almost entirely of argillite and quartzite of the Precambrian Belt series. A few intrusive dikes of predominantly mafic composition are present in some mines and there is one area of Cretaceous quartz monzonite intrusion near the center of the district. The interbeded quartzites and argillites are intensely folded and, at most mines, beds are steeply dipping or even overturned. Veins are typically steeply dipping fissure fillings closely associated with major district faults. Vein widths vary considerably but most are under 12 feet in width. At most district mines, the dip length of a vein is its greatest dimension. Mining of these deep seated ore bodies has progressed to the point where seven of the district mines are now mining at depths greater than 4000 feet below surface and 1000 feet below sea level.
