A huge ore truck rumbles out of the main tunnel entrance to the Graymont (PA) Inc. Mine. Mining Customer Perspective SentriV oice Aids Mine Communications The Pleasant Gap Mine in north central Pennsylvania is an underground hard rock limestone mine. In June 1998, the current owners acquired the surface and underground operations under the new name, Graymont (PA) Inc. “The ore body we’re mining is called the Valentine,” explains Bill Granville, U

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