This is an old silver vein discovered in 1903, averaged 20 cm in width and yielded over 700 ounces of silver by 1932, for a 1986 $4,760,000.
This cut illustrates the confining conditions the miner's labored.
@taffy thanks for the insight into this photo I hadn't realized there was a number 7 but now that you pointed it out I can see it. Thanks For the comment.