NSW Mine Safety said there were two other operators at the mine at the time of the incident who were unhurt.
"The power to the miner was tripped by the methanometer," it said.
"The scene was preserved immediately, however, it was later disturbed by mine workers."
NSW Mine Safety said when scene preservation was required the mine had to take all necessary steps to prevent people from disturbing the scene.
"This may include placing sentries," it said.
"Mines should have in place systems of work for mining in proximity of boreholes."
