The water in the enclosed space was thrown out by steam siphons, and mining was commenced on October 5th. Everything worked successfully until October 26th, when 200 feet of breakwater was carried away by a heavy southeast gale. The coffer-dam also suffered considerable damage, and the pit excavated on the vein was completely filled with rock from the cribs. This breach was filled more substantially than at first by a double line of crib-work, having a base of twenty-six feet; the coffer-dam was repaired, the pit cleaned out, and mining resumed on November 18th, which was continued until November 26th, when the last shipment of ore was made for the season.
All through that season and the next the work was constantly interrupted by accidents. Whenever a severe storm arose the sea rolled in heavily and broke down portions of the dam, or crib-work, so that the mine would be flooded and the miners driven from their posts. But in spite of these delays, coupled with the small space in which the men could work, more than a million dollars worth of ore was taken out.
The mine is one of the richest ever opened in the country. The great deposit of ore occurs in a fissure vein having a bearing of N. 32° W., the dip or inclination being to the N. E. The vein is well defined at points, having good walls or clearages, but not uniform in width, opening out at points to 12 or 15 feet, and again closing up to a string of not more than six inches. The average width, however, might be put down from four to five feet. Still, aside from the vein proper, there are several strings or feeders, some of them at a distance of 30 feet, carrying rich packing ore.
The vein substance generally consists of calcareous spar and dolomitic spar, with quartz, in which are enclosed occasional masses of dioritic wall rock, slate, and plumbago. The contained minerals are galena, zinc, blende, iron pyrites, kupfer, nickel, cobalt ore, with small quantities of antimony, native silver, and silver glauce, or sulphuret of silver.
The deposit of silver is found at the intersection of the vein with an immense belt of diorite and plumbago. This diorite is an intrusive mass, cutting nearly perpendicularly through the original more or less horizontal formation of slates and sedimentary or silicious sandstone. The ore varies in value from $400 to $7,000 per ton, the general average being not far from $1,500 per ton. This is known as packing ore, for the reason that it is packed in barrels for shipment. In addition to it there is a broad vein of stamp rock, valued at from $45 to $50 per ton.
The vein, taking a northwesterly and southwesterly direction, crosses Silver Islet, where it was discovered. On its course north from the Islet the vein goes out of sight, being covered by the lake for about 3,000 feet, and then makes its appearance on Burnt Island; submerged again by water for a distance of 350 to 400 feet, it reaches the mainland, on which it can be traced for a long distance.
ISLE ROYALE.
Going south from Silver Islet, the vein passes under Lake Superior, and is said to cross Isle Royale, some twenty miles off. Tesels have been run out from the shafts, so that the miners work far under the lake, and during heavy storms they can distinctly hear the roar of the waters. But although the vein is placed below the lake, its position, so far, has not put it at a great disadvantage, compared with other mines producing silver.
CHARACTER OF THE MINE.
There are features about this mine which actually make it a favorite as regards cost of working. The two great causes which increase so rapidly the cost, and delay the progress of mining everywhere, are influx of water and the meeting with what is termed soft ground. This mine, so far, has been opened nearly 700 feet. The longest level opens up the vein about 730 feet, and yet by pumping some 155 gallons per minute, the mine is kept dry. Most of this water enters from above, and is therefore not expected to increase in proportion to the depth obtained in the future. Many mines, although situated on high and dry land, have to pump far more water than this. The rock here being less pervious to water than elsewhere, can only be accounted for by the fact that a longer time has elapsed since this region has undergone any serious volcanic disturbance. Some narrow belts of slaty shale lying next to the vein are identical, except in age, with the clay found next the true veins in other places.