Gentlemen: First the mines on the then frontier were always short of steel, explosives, labor, etc. They did no more work than was absolutely necessary for their labor to work, with no concern for safety or comfort.
Some mines look like a crack in the ground.
As a result they generally concentrated in simply sinking a shaft to the depth that they could still supply sufficient air to keep theirlabor alive, then stoped their way back up. Many times the vein continued strongly down, but today it will be covered with tons of dump or scrap rock which they used as a back fill..
They used fire to bring in cooler fresh air and also to actually mine with, as was earlier mentioned..
Not all were bonanza mines, but to excavate each one to find out, is a practical impossibility..
S T I L L -----There are many beauties out their, go get em..
DJUICI, get to cracking.
Don Jose de La Mancha