Thirty-four charges of mixed 40-percent dynamite and black blasting powder had been placed in underground workings to break about 100,000 tons of iron ore from an ore bank in the Silver open pit.
The charges, averaging 425 pounds of 40-percent dynamite and 1,102 pounds of black blasting powder, were wired in series and connected to a point of the surface 1,000 feet from the ore bank where it was planned to explode them from a 110-volt circuit the following day.
Adequate protection was provided to prevent premature detonation from all sources other than lightning.
Forty-six men were in the underground workings, 41 were tamping the charges and generally cleaning up the workings, and 5 were seeking shelter from a storm when lightning struck the face of the ore bank and caused the premature detonation of an estimated 20 out of the 34 charges.
Twenty-eight men escaped from the upper levels without assistance, but the remaining 18 were killed.
Source: Historical Summary of Mine Disasters in the United States, Volume III
