Andesite, Breccia, Carbonate: The A, B, Cs of Geology in Yale’s Mexico
By Doug Hadfield, Resourcex.com
In a recent interview with the CEO of Yale Resources Ltd. (YLL-V), Ian Foreman, P.Geo., I was given a brush up on geology in Mexico. We covered everything from rhyolites in the Sierra Madres to skarns in Sonora, and I learned that there are a lot of plusses to a CEO who’s also a professional geoscientist.
Since I discuss geology with CEOs, CFOs and IROs (Investor Relations Officers) of Pubcos several times a week, I get a strong feeling when one doesn’t know what he or she is talking about. Sometimes, believe it or not, they even tell you:
“You know, I’m actually not a geologist, so I can’t tell you that.”
Right, then I’ll buy a million shares. Not.
Yale Resources has three distinct projects in Mexico: Urique is a joint venture with EXMIN Resources; Zacatecas is a joint venture with IMPACT Silver; the Carol project is owned exclusively by Yale.
Each of these projects is completely different from the other – the mineralization, the host rock, the age of the geological formations, and so on – but one thing is constant: Each has seen historic work done on it. As Foreman says, “The phrase “past producer” is a bit of a misnomer in Mexico. In Mexico, everything was a past producer. It’s a very prolific country.”
The first project Yale optioned in Mexico was the 290 square km Urique gold and silver project. Sandwiched between Goldcorp's two million ounce El Sauzal gold deposit to the south and Kimber Resources’ Monterde, with a reported 800,000 ounces gold and 45 million ounces silver to the north, Urique has been locally mined by the Spanish, but never using modern tools or technology.
“We’re on trend between significant deposits,” says Foreman. “And we know we’ve got mineralization, so we have all the smoke. Now all we need to do is find the fire. I think at the Cerro Colorado target we’ve got the burning embers. A couple of drill holes and we could blow that thing wide open.”
To understand why, Foreman argues you need to understand the geology of this area. Where Yale is operating here in the mineral rich Sierra Madres of northern Mexico, there are two “volcanic sequences” – an upper sequence and a lower sequence. Foreman, like many other experienced geologists working in the area, knew it was essential to be working in the lower sequence.
“In the upper sequence you’ve got mostly rhyolite; in the lower you’ve got mostly andesite,” he explains. “The rhyolite in the upper sequence is generally non-porous, and is a poor host for mineralization. On the other hand, the porous andesite in the lower sequence is reactive – fluids can permeate the rock, and with that action the chemistry of the rock is altered.”
Foreman retrieves a rock sample from the shelf behind him. It is the size of a cantaloupe and marked with a location and a gold-silver grade.
“This is a piece of rhyolite breccia from our Cerro Colorado target: 4.1 g/t gold and 33.8 g/t silver. It’s one of our drill targets at Urique – a breccia or broken rock that’s been re-healed,” he explains. The pink rhyolite tends to be poor host for disseminated deposits, but if you break the rock then fluids can penetrate it.
Another example of andesite: porous, good host
“It’s actually the epithermal fluids that went through here, you can even see the green material and that’s actually what is carrying all the grade, not the rock itself. Now you get to scenarios where you’re dealing with deposits like Mulatos where you’ve got the lower sequence rocks and the fluids come through and actually impregnate the rock and then they create these larger low grade systems.
”Urique actually straddles the contact between the lower sequence and the upper sequence in the Urique valley. Typically “contacts” in geology are very important to the formation of ore deposits. Sometimes that will be where the deposit stops, or potentially if the system’s strong enough to go through a bad host and turns into a good host, then all of a sudden all the minerals come out of the fluids or the chemistry changes or something along those lines.
“This is true for the entire Sierra Madres. Companies will talk about where they are in the upper or lower sequence of volcanic rocks. So, that’s why we’ve got more targets in the lower part of the valley, at the same elevation as El Sauzal.”
Zacatecas
At Zacatecas, Yale has an option to earn 80% in four properties in the immediate Zacatecas area. The Zacatecas silver district is known in the mining world for having produced over one billion ounces of silver in recorded history. To date, Yale has completed 1,800 meters of drilling on three of these concessions.
“What’s really unique about Zacatecas is, well, you wouldn’t want to walk around at night because you’d just fall into a hole. There are little shafts everywhere. On the Salvador-Zacatecas concessions I think there are 15 shafts.”
Beside these shafts, some of which date back to the 16th century, are piles of tailings commonly called “dumps”, where rock then considered too low-grade to process was disposed.
“You can tell from the dump material beside the shaft as to what they were finding. In some cases they went down to 20 meters, found nothing and stopped. But in each case the mineralized dumps all averaged between 200 and 300 grams per tonne silver,” Foreman told me. “And we get some really fantastic numbers. On the San Jose property we got one select sample that was 5,000 g/t silver.”
Foreman believes that by taking samples from the dumps, Yale will get an accurate picture of what lies in the earth below the dumps.
“One of the things difficult about drilling projects like this is that you’ve got 300 meters of vein, you’ve got one shaft, you know where the high grade mineralization probably was, probably an ore shoot. But when you drill a hole in it, you’re only sampling something that’s two and a half inches in diameter, and [the original miners] were sampling something that’s four or five feet in diameter. So they’re getting something that’s much more of a bulk sample, so in my mind’s eye, the results from the dump samples are almost more valuable than the drill samples.”
“We could drill a hole here and get 100 grams per tonne silver, but if you drill one meter over and you’ve got a 1,000 grams! It really is quite fickle sometimes. But you take what you get.”
Carol Property – the evolution of a skarn deposit
The Carol property, located in the state of Sonora in northern Mexico, is Yale’s first wholly owned property. According to Foreman, the mineralization at Carol appears to be a large copper-zinc skarn.
“A skarn is the alteration of a carbonate – typically limestone,” Foreman makes some sketches as he explains the evolution of a skarn. “So, you’ve got your limestone bed, sitting here. Then you intrude a porphyry into it.” (Fig. 1)
“The porphyry is the heat source, and all the fluids are running into the limestone around it. The fluid finds potentially favorable hosts, some will be more reactive, some will be less reactive, and some will be more favorable to alteration, and so on.” (Fig. 2)
“And maybe there’s a fault, which is more of a conduit to the fluids, and ultimately what you might find is that along the fault – there are a myriad number of options there – but you could have then a mineralized body, that is then associated with this porphyry at depth.” (Fig. 3)
“It doesn’t have to be vertical; it can be off to the side, as is the case at Carol.
“The important thing is that that process in itself changes the chemistry of the rock. But if that process brings mineralization with it, you can have gold skarns, copper-zinc skarns, gold-copper-silver skarns, a wide range of what’s coming through. And in the case at Carol, it’s copper and zinc.”
Carol is an early stage prospect that Foreman says he and his board of directors chose for two reasons. First, some early sample grades assayed as high as 1.3% copper and 16% zinc over four meters, which suggests a deposit with the correct economics for further development.
The other attractive thing about Carol is its proximity to Frontera Copper Ltd.’s (TSX: FCC) Piedras Verdes copper mine, which is a 191 million tonne copper porphyry grading 0.36% Cu. Piedras Verdes is less than 5 kilometers away – “spitting distance” says Foreman – and is the most likely source for the Carol skarn(s).
“It’s a huge deposit, a really large porphyry and we’re on the periphery of the porphyry – try to say that five times fast – and at Carol we’ve identified a body that appears to be just over a kilometre in length about 500 hundred meters in width. If that is all mineralized and has interesting grades, then it could turn into a significant project.”
To date, Yale has completed trenching, sampling and a mapping program on the property, with results expected sometime in June 2007.
“There are about 240 samples, of about 1.5 metres per sample. That’s sampling four hundred meters of trenches, which should really help as this is the kind of project that, with any kind of continued favourable results, we’ve got to get a drill onto.”
Writed by Doug Hadfield
By Doug Hadfield, Resourcex.com
In a recent interview with the CEO of Yale Resources Ltd. (YLL-V), Ian Foreman, P.Geo., I was given a brush up on geology in Mexico. We covered everything from rhyolites in the Sierra Madres to skarns in Sonora, and I learned that there are a lot of plusses to a CEO who’s also a professional geoscientist.
Since I discuss geology with CEOs, CFOs and IROs (Investor Relations Officers) of Pubcos several times a week, I get a strong feeling when one doesn’t know what he or she is talking about. Sometimes, believe it or not, they even tell you:
“You know, I’m actually not a geologist, so I can’t tell you that.”
Right, then I’ll buy a million shares. Not.
Yale Resources has three distinct projects in Mexico: Urique is a joint venture with EXMIN Resources; Zacatecas is a joint venture with IMPACT Silver; the Carol project is owned exclusively by Yale.
Each of these projects is completely different from the other – the mineralization, the host rock, the age of the geological formations, and so on – but one thing is constant: Each has seen historic work done on it. As Foreman says, “The phrase “past producer” is a bit of a misnomer in Mexico. In Mexico, everything was a past producer. It’s a very prolific country.”
The first project Yale optioned in Mexico was the 290 square km Urique gold and silver project. Sandwiched between Goldcorp's two million ounce El Sauzal gold deposit to the south and Kimber Resources’ Monterde, with a reported 800,000 ounces gold and 45 million ounces silver to the north, Urique has been locally mined by the Spanish, but never using modern tools or technology.
“We’re on trend between significant deposits,” says Foreman. “And we know we’ve got mineralization, so we have all the smoke. Now all we need to do is find the fire. I think at the Cerro Colorado target we’ve got the burning embers. A couple of drill holes and we could blow that thing wide open.”
To understand why, Foreman argues you need to understand the geology of this area. Where Yale is operating here in the mineral rich Sierra Madres of northern Mexico, there are two “volcanic sequences” – an upper sequence and a lower sequence. Foreman, like many other experienced geologists working in the area, knew it was essential to be working in the lower sequence.
“In the upper sequence you’ve got mostly rhyolite; in the lower you’ve got mostly andesite,” he explains. “The rhyolite in the upper sequence is generally non-porous, and is a poor host for mineralization. On the other hand, the porous andesite in the lower sequence is reactive – fluids can permeate the rock, and with that action the chemistry of the rock is altered.”
Foreman retrieves a rock sample from the shelf behind him. It is the size of a cantaloupe and marked with a location and a gold-silver grade.
“This is a piece of rhyolite breccia from our Cerro Colorado target: 4.1 g/t gold and 33.8 g/t silver. It’s one of our drill targets at Urique – a breccia or broken rock that’s been re-healed,” he explains. The pink rhyolite tends to be poor host for disseminated deposits, but if you break the rock then fluids can penetrate it.
Another example of andesite: porous, good host
“It’s actually the epithermal fluids that went through here, you can even see the green material and that’s actually what is carrying all the grade, not the rock itself. Now you get to scenarios where you’re dealing with deposits like Mulatos where you’ve got the lower sequence rocks and the fluids come through and actually impregnate the rock and then they create these larger low grade systems.
”Urique actually straddles the contact between the lower sequence and the upper sequence in the Urique valley. Typically “contacts” in geology are very important to the formation of ore deposits. Sometimes that will be where the deposit stops, or potentially if the system’s strong enough to go through a bad host and turns into a good host, then all of a sudden all the minerals come out of the fluids or the chemistry changes or something along those lines.
“This is true for the entire Sierra Madres. Companies will talk about where they are in the upper or lower sequence of volcanic rocks. So, that’s why we’ve got more targets in the lower part of the valley, at the same elevation as El Sauzal.”
Zacatecas
At Zacatecas, Yale has an option to earn 80% in four properties in the immediate Zacatecas area. The Zacatecas silver district is known in the mining world for having produced over one billion ounces of silver in recorded history. To date, Yale has completed 1,800 meters of drilling on three of these concessions.
“What’s really unique about Zacatecas is, well, you wouldn’t want to walk around at night because you’d just fall into a hole. There are little shafts everywhere. On the Salvador-Zacatecas concessions I think there are 15 shafts.”
Beside these shafts, some of which date back to the 16th century, are piles of tailings commonly called “dumps”, where rock then considered too low-grade to process was disposed.
“You can tell from the dump material beside the shaft as to what they were finding. In some cases they went down to 20 meters, found nothing and stopped. But in each case the mineralized dumps all averaged between 200 and 300 grams per tonne silver,” Foreman told me. “And we get some really fantastic numbers. On the San Jose property we got one select sample that was 5,000 g/t silver.”
Foreman believes that by taking samples from the dumps, Yale will get an accurate picture of what lies in the earth below the dumps.
“One of the things difficult about drilling projects like this is that you’ve got 300 meters of vein, you’ve got one shaft, you know where the high grade mineralization probably was, probably an ore shoot. But when you drill a hole in it, you’re only sampling something that’s two and a half inches in diameter, and [the original miners] were sampling something that’s four or five feet in diameter. So they’re getting something that’s much more of a bulk sample, so in my mind’s eye, the results from the dump samples are almost more valuable than the drill samples.”
“We could drill a hole here and get 100 grams per tonne silver, but if you drill one meter over and you’ve got a 1,000 grams! It really is quite fickle sometimes. But you take what you get.”
Carol Property – the evolution of a skarn deposit
The Carol property, located in the state of Sonora in northern Mexico, is Yale’s first wholly owned property. According to Foreman, the mineralization at Carol appears to be a large copper-zinc skarn.
“A skarn is the alteration of a carbonate – typically limestone,” Foreman makes some sketches as he explains the evolution of a skarn. “So, you’ve got your limestone bed, sitting here. Then you intrude a porphyry into it.” (Fig. 1)
“The porphyry is the heat source, and all the fluids are running into the limestone around it. The fluid finds potentially favorable hosts, some will be more reactive, some will be less reactive, and some will be more favorable to alteration, and so on.” (Fig. 2)
“And maybe there’s a fault, which is more of a conduit to the fluids, and ultimately what you might find is that along the fault – there are a myriad number of options there – but you could have then a mineralized body, that is then associated with this porphyry at depth.” (Fig. 3)
“It doesn’t have to be vertical; it can be off to the side, as is the case at Carol.
“The important thing is that that process in itself changes the chemistry of the rock. But if that process brings mineralization with it, you can have gold skarns, copper-zinc skarns, gold-copper-silver skarns, a wide range of what’s coming through. And in the case at Carol, it’s copper and zinc.”
Carol is an early stage prospect that Foreman says he and his board of directors chose for two reasons. First, some early sample grades assayed as high as 1.3% copper and 16% zinc over four meters, which suggests a deposit with the correct economics for further development.
The other attractive thing about Carol is its proximity to Frontera Copper Ltd.’s (TSX: FCC) Piedras Verdes copper mine, which is a 191 million tonne copper porphyry grading 0.36% Cu. Piedras Verdes is less than 5 kilometers away – “spitting distance” says Foreman – and is the most likely source for the Carol skarn(s).
“It’s a huge deposit, a really large porphyry and we’re on the periphery of the porphyry – try to say that five times fast – and at Carol we’ve identified a body that appears to be just over a kilometre in length about 500 hundred meters in width. If that is all mineralized and has interesting grades, then it could turn into a significant project.”
To date, Yale has completed trenching, sampling and a mapping program on the property, with results expected sometime in June 2007.
“There are about 240 samples, of about 1.5 metres per sample. That’s sampling four hundred meters of trenches, which should really help as this is the kind of project that, with any kind of continued favourable results, we’ve got to get a drill onto.”
Writed by Doug Hadfield
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