Finding Chuquicamata’s fabled ‘lost ore’

David Lowell, the famed octogenarian explorer credited with finding the Escondida copper deposit, among others, is now taking a crack at one of the world's greatest exploration mysteries: finding lost – or believed to be lost – Chuquicamata copper ore. Forgive the superlative. For the known Chuquicamata copper-molybdenum deposit and mine in Chile, now owned by Codelco, is ranked by many as the greatest – or certainly one of the greatest – copper ore bodies in the world.

Chuquicamata, Chuqui for short, is big and, for its size, very high grade. A mid-2000s estimate tallied 2 billion tonnes @ 1.54 percent copper as having been mined. These days, a grade a third that is considered pretty normal – good even – for a large porphyry deposit like this. So Chuqui is abnormal. And many billion tonnes of ore remain at the known Chuqui deposit. As the massive Chuqui open pit wanes, Codelco aims to continue mining in a giant block cave mine it estimates will cost about $4.2 billion to build. The pit is reaching its limits, about 900 metres deep, and four kilometres long and three kilometres wide.

The Chuqui mystery is this: a fault, called the West Fault, cuts through the Chuqui ore body and appears to have moved a chunk – how much is not clear – of Chuqui ore elsewhere, where or exactly how far is uncertain. But most guesses, those made in a so far fruitless search for lost Chuqui ore, have put it somewhere about 15 to 20 kilometres to the south on a property that is known as the Ricardo project.


Ricardo project as seen from the air with Chuquicamata deposit to the north and interpretation of West Fault in blue. (Source: Ramon Fam R., 2004, Rockwell report)


It's a roughly 16,000 hectare property on the edge of the Chilean town of Calama that has stymied many before Lowell, who spoke about his pursuit of lost Chuqui ore with Mineweb on Wednesday. Since the theory that such lost ore existed was developed in the 1970s, a slew of majors, among others, have puzzled over the quest, mapping, sampling and, more than anything else, drilling away at the Ricardo property through which the all-important West Fault traverses. All have come up empty handed. Superior Oil hit the ground between 1980 and 1982. Codelco was there in 1991 and 1992. Freeport came in the next two years and Inco, likewise, the next two after that. Among majors Rio Tinto made the last and still unsuccessful attempt at finding Chuqui ore at Ricardo in the mid 2000s. In all 72 drillholes have been drilled, multiple geophysical surveys have been conducted and a fair amount of brain power and cash has been expended on the mystery of the lost Chuqui ore. To no avail.

Lowell would not, however, be considered a geological crackpot, flogging an idiotic exploration idea. He exists on the opposite end of the scale. Something of a legend, a porphyry expert, and wildly successful explorationist. Over the years he has made many of the more important copper discoveries in Latin America, prime among them Escondida. Unlike this author, he is not prone to superlatives. He, of course, knows what he is up against – tough odds – but he is also unwilling to disregard Ricardo as a site for Chuqui's lost ore. At his most succinct, he called the endeavour, now the main thrust of his TSX-V listed company Lowell Copper (JDL), “high risk, high reward.” It's a company, he says, that will focus on Ricardo, for now, but that is also considering other opportunities born of the ongoing junior financing crisis.

Chuqui is abnormal, not just for its grade, but geological expression. As far as mineral deposits go, porphyry deposits aren't the greatest at concealing themselves. To find them is something like looking for a humpback whale in thick fog. Daunting though this may seem, in doing so you can rely on brutal halitosis and raspy breathing to guide you to the whale's general location. Porphyry deposits have their own stench and sound. They are often preceded by alteration halos, rock affected by the ore body undergoing mineralization, that give geologists clues about where to find them.

Lowell turns to the Red Mountain copper deposit in Arizona as an example. “The geo who found the deep porphyry deposit there, which has never been mined and may never be mined, told me it had a 100 to 1 ratio between recognizable hydrothermal alteration, in a big circle around it, as compared to the ore body.”

Then there's Chuqui. “We won't have that advantage here,” Lowell says. Chuqui, though a whale of a deposit, is relatively tough to spot beyond the actual ore. The alteration is limited, and the ore body – tabular – is oriented vertically. It's easier to miss than typical porphyries. Indeed, this is part of the reason Lowell, as others before him, believe exploration efforts to find Chuqui's lost ore at Ricardo have not yet been exhausted.

“There are several open targets in spite of the drilling that has been done,” Lowell says.

Indeed, the drilling at Ricardo has been spiteful, not just because Chuqui's lost ore (if it is to be found) by the very nature of it is going to be hard to find for lack of alteration. The Ricardo property is also laden by at times drill-defying cover, including gravel and conglomerate (imagine gravel in cement), that makes reaching bedrock targets frustrating. Only around two thirds the 72 drillholes at Ricardo reached bedrock. Others ended in cover that can be upwards of 500 metres deep or more. In easier areas it's deep in the 100 metre range. Lowell knows the numbers off the top of his head. Of the 72 drillholes, 46 hit bedrock. In a few, explorers hit weak indications of what may be porphyry alteration. None were led to elation. Yet, here again, allure lies in the challenging conditions. As Chuqui's stealth porphyry character increases the chance lost ore has been missed in past exploration attempts, the difficulty of drilling Ricardo suggests to Lowell, as others before him, that bonafide targets have gone untested.

Of course for those very same reasons the hunt is, as ever, going to be tough work. Lowell knows it. He sums it up this way: “We're looking for vertical tabular slabs of ore with no alteration halo on either side and it probably will be deep, which makes the holes more expensive.”

On strategy, Lowell keeps a tight lid. Does he and his team have new insight into the location of Chuqui's lost ore? That really is a question of the mechanics of the West Fault that appears to have cut ore from the Chuqui deposit to the north of the Ricardo property. And does he have an opinion on how much Chuqui ore may have been spirited away? These are questions he answers with: “We're getting into the confidential.”

That said, in the course of speaking with Mineweb, Lowell gave a general overview of the approach he and his Lowell Copper team are taking. Part of it is not to be encumbered by the past. “One of my strategies is not to worry too much about earlier analysis, especially geophysical surveys that have poor track records.” 

Indeed, this is one of the first things Lowell Copper has done at Ricardo. Lowell says the company has just completed a magnetic survey, which will primarily be used to try to better map the West Fault on the Ricardo property, the understanding of which, its movements, is so key to figuring out where Chuqui's lost ore might have gone. This will build on work Lowell did with a structural geologist about 20 years ago when they mapped over 50 kilometres of the West Fault.

“So it's not a new idea from my point of view,” he says, referring to the structural geology of the West Fault and hypotheses of where it may have moved Chuqui ore.

In being skeptical of past exploration pursuits, he notes that five majors had worked on Escondida before it was finally found. “The same thing could happen at Ricardo,” he says. “It's less certain at Ricardo, but it's certainly a possibility.”

Another part of the approach depends on a better understanding of Codelco's Chuqui ore body. Lowell says that in preparing to go underground, Codelco has done extensive drilling of the deposit, defining it over two vertical kilometres. The consultants working on the deposit “did a pretty comprehensive job of this,” he says, making advances in the geology of Chuqui. This, by extension, could help exploration efforts at Ricardo, for instance, by pinning down the various telltale signs there are to Chuqui ore – what little there may be.

“The thing we don't understand is where the pieces went,” Lowell says. “I think we have a better understanding than any other group. But still, it's not at all certain.”


This article appears courtesy of Mineweb. To read more international and finance mining news click here.

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