ROOF BOLTER OPERATOR WAS SPINNING A ROOF BOLT TO MIX THE RESIN. THE BOLT PLATE STRUCK OR RUBBED AGAINST THE STEEL MAT AND CAUSED HEAT OR SPARKS. THE BOLTER HELPER OBSERVED A YELLOWISH FLAME TH AT LASTED AN ESTIMATED 4 SECONDS. THE OPERATOR DID NOT SEE THE FLAME. WORK WAS STOPPED AND THE SCENE SECURED. MSHA WAS NOTIFIED. AN INVESTIGATION BEGAN WHEN MSHA INSPECTORS ARRIVED.