The greatest challenge during the search for the lost Peralta Mines has been coming to grips with just how big the mining operations actually were. The cart ruts told of countless loads of ore going to First Water Canyon, but it didn’t completely “sink in”.
Over the past month, Cerro Negra has been pored over, trying to gain more understanding of the orebody and the mining that took place there. Dozens of rocks were gathered, cut, stared at with a loupe, outcrops were photographed, etc., and finally, while looking at Cerro Negra with Google earth, I realized the magnificence of what had taken place, and it took my breath away.
The “Great Mine” north of the Superstitions was described in the Phoenix Herald and Republican in 1893, and a portion of the article is in the opening post of the thread “Ancient Goldfield Mines” thread started by Dr. Glover. Joe Ribaudo discovered the article in the book “Arizona, the Last Frontier”, by Joseph Miller. Here is the excerpt (again):
“Over on the north side of this wonderful mountain so peculiar in shape, standing like the ruins of some great walled city with its tall spires and huge monuments, there has been discovered an ancient mining camp. Whether this mining was done by the Indians and Mexicans of the last century, or whether the operations date to years when de Vaca and Black Stephen started from the coast of Florida to find the gold fields toward the setting sun, may never be known. It is certain, however, that there are shafts and tunnels and drifts and stopes and the clearly-defined walls of a great mine. On the dumps are found tons of rock which without doubt came out of these workings.”
The description is of an underground mine, but how can you see the walls of an underground mine? It is surmised that the only thing it could be referring to is “subsidence” or the “cave zone”. The article said the prospectors found the mine in 1888, and they went on to find ore much richer in the Goldfield area. If this large cave zone was seen it 1888, it is certainly still able to be seen today, even if erosion has taken place.
It was described in a previous post that the only mining method available in the mid-1800’s and earlier for mining bulk ore was the top-slicing method. This was the precursor to block-caving and was used at Inspiration and Morenci, Arizona.
Well, let’s get to the good stuff. First, this is diagram of a typical VMS deposit. The Cerro Negra orebody is a little different in that it was formed under a layer of basalt, about 100 feet thick, but there is still abundant jasper, and jasperoid that vented through the basalt to the surface.
This is looking north towards the Cerro Negra ore body. Much of the center of the uppermost portion of of the deposit has been removed forming a deep trench; I’m guessing a thickness between 10 to 40 feet was mined. It appears that they focused on the richest supergene ore beneath the drainages. The orebody lies right up against the rhyolite.
This is what the rhyolite looks like. It resembles the “Imperial porphyry” of Rome
There is definite proof of subsidence and is on the ridge just north of Cerro Negra (the photo is looking south). This probably appeared long after 1848, after the timber posts and matt rotted and compressed. These are beds of silicified tuff that are tipped upwards; their edges are not eroded (Flatiron is in the background).
Even though a lot of mining took place here, they still barely scratched the surface.
One map depicts the mine very well, in typical Spanish style, and actually shows the cave zone. This appeared about 1895 (thanks Tom Kollenborn). It is the Hoddenplye Map. (Note the tiny hole through the top of the mountain)
The “breccia dike” labeled on the diagram is about 10 feet wide. It looks knobby, and pretty blah in the field, but below is a photo of what some of this rock looks like after it is cut; it is jasper and chlorite. There are large cobbles of jasperoid in the dike also.
The spot labeled “portal” in the map below had bees flying out from beneath large rocks there a couple of weeks ago during the worst of the drought. They were going for water. I dug down at the rock face there a while back and believe to have reached beneath the brow of the tunnel with my shovel; there was the mother lode of saguaro fruit there from pack rats, so there is a significant void.
I believe this was the portal indicated on the Ortiz Map below (thanks again Tom Kollenborn). If it is orientated the same as the diagram above, it can be seen that they had several tunnels into the caved zone, and they explored extensively along the rhyolite front. It is believed that some of these tunnels were used to assist in draining water after the exploration and delineation.
The first time the author ever stepped foot in the “cave zone” was about 12 years ago. It was late in the afternoon after the sun went down, and after seeing all the veinlets and alteration on the east side of the depression, my legs actually started shaking. I knew it was something good, but had no knowledge of VMS deposits, or even that the neck of the volcano was only about 200 feet away.
10 contiguous claims were held at the time, and felt it extremely important to put a claim on this ground, so unknowingly put the center of claim marker #11 right in the middle of the cave zone, creating a claim separate from the rest. That one claim, at the same bearing N20W as the other 10, covered almost the entire deposit and aligned perfectly with the cave zone it is now known.
From almost the time #11 was staked, I’ve believed that the satellite workings on the right side of the Burbridge map (thanks again Tom Kollenborn) were at Cerro Negra, but could not “see” the relationship and alignment.
t has always been my belief that this map with the title, “The Esteemed People of the Salt River District of the North” was a map of an exploration project. The original was dated by the U of A as truly being from the 18th century. Considering the Spanish drove a tunnel several miles long to drain the mines of Pachuca in the 18th century, this really was “light work” for them.
Where the crew of Mandozo Segundo Marzo drove their tunnels and sunk shafts in 1753 is likely where the cave zone is today. They simply blocked out the ore for others to follow, and it took almost 100 years to create the cave zone that remains today.
Below is a diagram of the old top-slicing mining method. If this is indeed a cave zone shown above, this is how they did it. This takes quite a bit of timber, and the Peralta’s did not have much nearby. This must have been the number one limitation regarding the amount of tons they could mine from underground.
Below is a photo of the cave zone next to the saddle area. In the background can be seen El Sombrero at the bearing of S65E. It appears like the rock over the stope is STILL subsiding even today on the sides of the cave zone as the decayed timber mat is crushed below.
low is a map showing most of the VMS deposits ever mined throughout the world. Where they are especially prevalent is in Japan and Spain/Portugal. The ones colored green are more apt to carry gold. This is from the USGS site @
https://mrdata.usgs.gov/vms/map-us.html. This is a great website.
Cerro Negra is a Kuroko style VMS deposit, rich in gold, and the “Kuroko” name was coined in Japan. The best diagram found of the Kuroko style VMS was found on this Japanese website:
Below is the same diagram that has been modified to show the situation of the deposit at Cerro Negra. A layer of basalt covers the deposit, and jasper, jasperoid, and some gossan has been ejected through the basalt. The ejected material can be found in large quantities today. Because of the abundant limestone cobbles that were beneath the basalt before the VMS was emplaced, jasperoid replaced the limestone, and some jasperoid cobbles have been ejected also.
This is what a cut piece of the jasperoid looks like: