At 11:30 p.m. the powder magazine on the 1,100-foot level of the Mexican mine exploded, killing 37 men and injuring 9.  The magazine, containing a day's supply of 20 to 30 boxes, was a chamber cut in the rock and closed in front by boards; it was 25 to 50 feet from the shaft and separated from it by a pillar.  Light was furnished by a 16-candlepower lamp a short distance inside the door.  There was no wiring over the stored powder.

The explosives had been thawed before delivery, therefore, no heat for thawing was introduced into the mine.

The explosion occurred just as the night shift workmen were waiting to go to the surface to eat.  The men on the 990-foot station reported two explosions.  The first extinguished their candles, but was of no great violence.  As the men relit their candles before proceeding to another shaft, a second explosion of greater violence knocked them over, seriously injuring one and slightly injuring three.  Men loading the skips only 45 feet below the 1,100-foot level, were uninjured, as were those on the 1,200-foot and 1,300-foot stations.

The posts on the 1,100-foot station were knocked out and, with the lagging and other timbers, formed a mass of debris that closed the shaft.  From the debris, 22 bodies were recovered; 5 injured also were rescued.  The doors across the skip compartments were closed, as ore was being hoisted from the level; one body was found on these doors.

The mancage compartment was open, and eight bodies were recovered from below in this compartment.  The light board shed used for a stable was entirely demolished; two bodies were found there; one of the two horses was killed, and the other was injured.  This stable was about 100 feet from the shaft, down the main drift.  Two bodies were found along the drift, and the fragments of at least one body were found in the magazine itself.

As is usually the case with an explosives accident, the cause could not be determined.  As is always frequently the case, no great damage was done to the mine.  A rescue party reached the scene within 35 minutes after the explosion, and the cage was in operation in about 11 hours.

The position of the magazine near the shaft, but beyond it, considered in reference to the main drift precluded the possibility of any man being cut off from escape in case of accident, and also aided in the rapid dissipation of the gas; no one was asphyxiated.

Source:
	Historical Summary of Mine Disasters in the United States - Volume III

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Miners Killed in Alaska When Magazine Blew Up
Alton Evening Telegraph, Illinois
March 4, 1910

Juneau, Alaska, March 3. -- Twenty-three miners were killed at midnight last night by the explosion of a powder magazine in the 1,100-foot level of the Mexican Mine, one of the group of Treadwell gold properties on Douglas Island.  Eight men were seriously injured, of whom it is feared four will die.

The last shots had been fired by the shift of men twenty minutes before the explosion took place, and the men had assembled at the landing of the skip and were arranging to enter it and go on top.

The magazine which contains 275 pounds of powder was thirty feet away from the place where the men were standing and every man was killed or injured.

Most of the miners were foreigners and only three had families on the island.

The man in charge of the magazine who had locked the door and was standing with the shift waiting to go up was among those killed.

Two horses in the mine were standing side by side.  One was killed by the shock and the other when found was munching oats, undisturbed.

The mine was little damaged.  The bodies were recovered.

Seven miners at work on the same level but at some distance from the magazine were not injured.