Clues to a Spanish Mine

I was going through my files the other day and came across several things I have been holding on to in the hopes I might have the chance to work them myself. Unfortunately or fortunately, depending on how you look at it, I have so much stuff that I want to work myself that I will never have time to get it all done.

This description is said to have come from "an old Spanish document" and the story was originally published in 1950. This is the description and directions to a large Spanish mine. Pay close attention to the description of how deep the tunnels are.

“Follow straight ahead through the pass of Los Janos to the south about three leagues from the Guadalupe mine, which is one league from the big gate of the Tumacacori mission to the south, to another gateway or pass called The Gateway to Agua Hondo (Deep Water). To the south from this pass runs a creek that empties onto the desert near the old town of Santa Cruz.


The mine is to the east of the pass. Below the pass on the bank of the creek there are twelve arrastres and twelve patios. At the mine there is a tunnel 300 varas (835 feet) long that runs to the north. About 200 varas from the portal of this tunnel a crosscut is yellow and is one half-silver and one-fifth gold. Fifty varas from the mouth of the mine in a southerly direction will be found planchas de plata (slabs or balls of silver) weighing from 25 to 250 pounds each. In the rock above the tunnel is the name La Purisima Concepcion, cut with a chisel. The mouth of the tunnel is covered by a copper door and fastened with a large iron lock”
 
Hmmm, a copper door fastened with a large lock, this sounds familiar doesn't it?