Read on as Dr. Tim Marsh, President and CEO Bell Copper (TSXV:BCU), and I continue to unpack this unique exploration story where a copper porphyry in Arizona appears to have been cut in the middle and slid 8 kilometers to the east. The roots of the system are exposed at surface and show a pyrite shell measuring 3 kilometers by 5 kilometers, which is very encouraging for the size of the prize.
Peter Bell: One of the things you said the first time we talked, Tim, that really struck me was that the relief underneath the valleys can be similar to what's seen in the mountains above. It occurs to me that a good example of that relief is the trough that formed as the upper part of the system slid eastwards.
Tim Marsh: That’s right, Peter. There are many square miles of nothing but gravel, but if you could peel that gravel away and see the relief down in this basin then you would see that it is just as rugged as what you see sticking up by the mountains. There are a couple thousand feet of relief down there.
Peter Bell: I had thought that your comment was focused on the flat parts of the valleys further away from the mountains, but you are talking about what is more like the foothills here. Thanks for clarifying that for me. I am surprised to hear that there is that much gravel below these foothills with the washes, I would have thought the bedrock would be closer to surface there.
Tim Marsh: There is a bedrock horst that comes to surface in a little patch out to the north of us, but it is a tiny patch of about 300 acres. Still, it's quite important for supporting the slip vector I described to you before.
As you said at the start, Peter, the gravels are filling in a very deep trough between our Kabba property and the mountain. There are multiple bedrock ridges underneath all that gravel, which is associated with the stretching of the western part of North America.
Peter Bell: Are we talking a couple hundred meters of gravel in this trough?
Tim Marsh: The trough has more than 700 meters of gravel there.
Peter Bell: Really?
Tim Marsh: Yes, indeed Peter. That's where I first thought the target was located. I thought the slip on the fault was at a steep angle, so I started looking about a mile off of the range front after seeing the footwall exposure of a giant porphyry copper system.
The older timers in the 1950's, 60's, 70's and 80's saw that footwall, so they drilled down into the bedrock at the root of the porphyry system where you have a lot of quartz veins with spectacular alteration. There is a lot of molybdenite and a little bit of copper, but the copper shell was located above that when the system formed. Porphyries are generally shaped like a carrot and they were drilling into the bottom parts of the carrot. The bigger part of the carrot with better mineralization would have been above them, but it has been chopped off and slid out into the valley. Now, it’s hidden under this gravel.
Early on, we wanted to test the idea and find out what's underneath all this gravel so we ran some seismic reflection. Hard rock geologists rarely do seismic reflection, but oil geologists do it all the time.
Tim Marsh: Around the same time we got this seismic reflection data, we drilled some holes that really confirmed that the upper part of the porphyry really came down quite a bit as this thing stretched apart. That movement created a big trough that was subsequently filled with erosion from the mountains. When we drilled the gravels in that trough, we see what is called stratigraphic inversion. Whatever the layering was going up the side of the hill, you see the opposite in the gravels. The pieces on the top of the mountain are on the bottom of the trough. The whole sequence was inverted as it filled that basin.
Peter Bell: Right, you mentioned this before. You could literally see that in your holes?
Tim Marsh: Peter, we saw it in our first hole. K1 was drilled into this trough because I thought the upper part of the porphyry went down very steeply. We drilled the fault going through here in that K1 hole and it was dipping at a much shallower angle than we thought.
Once we got underneath the fault, the rock was too fresh and it was clear that the top of the carrot had moved a lot further at a much flatter angle than I ever would have guessed. My next hole was one mile step out from the first. And then we started seeing porphyry dykes – Laramide porphyry dykes that were 70 million years old with a little molybdenite and a little pyrite.
Peter Bell: And since then you've kept moving eastwards and northwards.
Tim Marsh: Generally, yes. The thing I didn't appreciate early on was the lateral slip. However, I know the system hasn't slid too far east because I can walk around and see some bedrock far off to the east that has a bit of alteration but not much.
Peter Bell: And you mentioned the stretching of the western part of North America -- that must have been a large-scale geological phenomenon. Was the slip fault that moved this porphyry related to the extension?
Tim Marsh: Yes, I believe so.
Peter Bell: Any sense of the sequencing for that mineralizing event versus the continental extension and the creation of that trough with the gravels?
Tim Marsh: The extension came around 40 million years after the mineralizing event.
There was a chain of volcanoes running from parts of Mexico up into Nevada with major stratovolcanoes every 40-50 miles. Like the whole chain of Mt. Baker, Mt. St. Helen's, Mt. Rainier, Mt. Hood up in the Pacific Northwest now, there was a similar chain located down in Arizona 70 million years ago. Underneath each one of these you have multiple pulses of magma. Some of them came up with a lot of juice but didn't make it to the surface. These ones that didn't erupt as volcanoes just stalled out and the juice was trapped in a small volume of rock. That’s where you end up with porphyry deposits. One day, people will drill Mt. Rainier and Mt. St. Helen's to look for yet another generation of porphyries.
Peter Bell: I can just imagine that a hundred years from now. People often say Arizona is all broken up and it sounds like the continental extension could be a reason for that. How about the upper part of the porphyry you’re looking for, is there reason to believe it's still intact?
Tim Marsh: What we see, so far, is that things are intact on a gross scale. We've got a hangingwall block and a footwall block. The hangingwall block, even in the places where it's extraordinary stretched, is internally coherent. We are not seeing little bits of a porphyry copper deposits appearing in several places. What we've defined as a good target for the copper shell is a big blob.
Peter Bell: And what’s the basis for that copper shell?
Tim Marsh: Good question, Peter. The basis for it is a zone in the footwall where quartz magnetite veins are abundant. Quartz magnetite veins are, in my mind, the deep equivalent of what would be chalcopyrite veins at shallower depths. The difference has to do with temperatures, mainly. Lower temperatures at shallower depths. There were a lot of magmatic hydrothermal fluids streaming up through the rock in this area that left behind quartz magnetite veins. This blob out here translates to roughly where that copper shell ought to be. That puts us in the ballpark, but you still have to do more to figure out where the copper shell is located.
It’s really quite important that I know where it isn't at a few points! If you get just outside of the copper shell in a few holes, then we see lead and zinc. Lots of galena, too.
Peter Bell: That's the typical zonation of a porphyry, right?
Tim Marsh: That's right.
Peter Bell: Okay. It’s one thing to refer to the zonation of a porphyry at a one level of the system horizontally, where you get the typical zonation from copper to gold and then lead-zinc, but this point you just made about the quartz magnetite veins being the deeper equivalent of the chalcopyrite veins is not something I’ve heard before. You’re talking about zonation horizontally and vertically, Tim. That’s new to me, thank you very much.
This document contains statements that are forward looking statements and are subject to various risks and uncertainties concerning the specific factors disclosed under the heading “Risk Factors” and elsewhere in the Company’s periodic filings with Canadian securities regulators. Such information contained herein represents managemefnt’s best judgment as of the date hereof based on information currently available. The Company does not assume the obligation to update any forward-looking statement.
The technical content of this release has been reviewed and approved by Timothy Marsh, PhD, PEng., the Company’s CEO, President, and Qualified Person. No mineral resource has yet been identified on the Kabba Project. There is no certainty that the present exploration effort will result in the identification of a mineral resource or that any mineral resource that might be discovered will prove to be economically recoverable.
Peter Bell has been compensated to prepare and distribute this promotional material.