The mining newspaper for Alaska and Canada's North
The mining newspaper for Alaska and Canada's North
Australian explorer uses advanced modeling to pinpoint the high-grade lode source underlying surface mineralization at Tushtena
Australian Mineral Fields believes it is onto a world-class gold discovery in Interior Alaska. The Perth, Australia-based junior considers its innovative exploration techniques, used to uncover high-grade gold deposits in the Eastern Goldfields of Western Australia, uniquely suited for locating high-grade mineralization at the Tushtena gold project about 20 miles west of Tok.
The Western Australia-focused exploration company was not looking to expand its operations to the opposite side of the globe when the company's CEO, Marcus Willson, attended the 2008 AME/BC Minerals Exploration Roundup in Vancouver, B.C.
During a Jan. 7 interview, Willson told Mining News that while attending the 2008 Roundup, he was approached by David Rhys, an ex-associate who was familiar with Australia Mineral Fields' technologies and expertise. Rhys felt the Tushtena property would be a good fit for the Down Under explorer.
The mining exec said the company took a critical look at the project as well as Alaska's business climate before it signed an agreement in April to acquire the gold property.
"Logistically, from our point of view, we are an Australian-focused company. So (Tushtena) had to have true world-class potential in our opinion, before we were prepared to take the risk on the other side of the planet," Willson explained.
Technology to seek out deeper systems
Australian Mineral Fields uses advanced 3-D and 4-D (time) modeling, simulation and data analysis technologies to locate significant gold deposits that may not be found with conventional exploration techniques. The modeling incorporates data collected from litho-geochemistry and portable infrared mineral analyzers.
The Australian-based junior explains that litho-geochemistry uses the entire spectrum of elements contained in specific rock samples to define both the actual parent rock composition (providing a better understanding of the geology of the area) and the alteration of the rock. The alteration of the rock (evidence of the hydrothermal processes associated with the development of mineral deposits) typically covers a much larger area than the deposit itself, and varies depending on the proximity to mineralization.
PIMA technology uses short-wave infrared radiation and, according to Australian Mineral Fields, provides a rapid and cost-effective analysis of alteration minerals, including analysis of subtle variations in mineral crystallinity and composition.
The junior said its team developed this exploration technique to locate gold deposits in Western Australia, which has seen a geologically long period of deep weathering that has resulted in a greater than 90 percent cover across much of the most prospective rock layers.
This cover has paradoxically both allowed and prevented discovery. The cover, dominated by saprolitic regolith, allows for well-defined and understood lateral dispersion processes. Such dispersion, in turn, has made it relatively easy for drilling to identify very significant quantities of typically moderate to large tonnage resources that can be extracted with open-pit mining. The same cover, however, has effectively masked deeper mineralized systems.
Australian Mineral Fields believes a deeper, and potentially world-class, lode gold system lies under the altered bulk tonnage deposit found at the surface of the Tushtena property.
Down Under geologists scour Tushtena
To locate the deeper mineralized system the Australian Mineral Fields team completed a series of traverses across the entire Tushtena project, collecting litho-geochemical data and conducting PIMA hyperspectral analysis. The CEO reports that the hyperspectral analysis correlates well with the results they hoped to find in the original discovery zone.
"Previous work showed that Tushtena has abundant moderate- to high-level anomalism and numerous high-grade but narrow intersections in drilling. As such, the company, during last year's field season, concentrated on collecting samples across the property to better define the alteration system and provide a clear understanding and focus for the next round of exploration and drilling. This was amenable as the property has a reasonable degree of outcrop as well as some historic drilling from which to collect the appropriate data both at surface and at depth," Willson explained.
The company expected that the core had been previously sampled in entirety but found instead that the historical explorer had selectively sampled the core for its high-grade intersects. The Australian geologists recognized that significant portions of the unsampled core were strongly altered. This prompted the company to focus on analyzing the previously un-sampled core.
Willson said the company's Alaska team, in late August, began gathering the core and transporting it to Fairbanks to be assayed. To date the company has received results from three of the holes. The results gave the company stronger confidence in the historically reported results, and revealed a new intersection, suggesting the mineralization may be less constrained than previously thought.
"The data clearly shows that the area around the 'Discovery Zone' is where the prospective alteration gradient occurs. While this appears to be a circular argument, it provides, in the company's opinion, strong encouragement that the property can host an economically viable mineral system, which was not clear from the narrow, high-grade results previously intersected," Willson explained.
Australian targets underlying lode source
Willson told Mining News that Australian Mineral had planned to start a drill program in the fall of 2008, but due to the discovery of the unsampled core coupled with the lack of rig availability, the company has delayed the drill program until this spring.
The field work carried out at Tushtena in 2008 has produced a drill target for the upcoming season. According to Willson, the target, which lies to the southwest of the Discovery Zone and at depth, was identified very early on and much of the 2008 work was confirming whether the target or some variation thereof, would be valid.
He said near-surface targets of the historic drilling in the near-surface mineralization have the potential to develop into a low-grade bulk tonnage deposit, but his company is targeting the underlying lode source of the highly altered mineralization.
"Where the original drilling was focused on shallow high-grade narrow veins at surface, the data suggests that is likely not going to produce anything but potentially a bulk-tonnage low-grade system perhaps ala-Fort Knox. We are focusing on trying to intersect a lode-style system at depth, beneath (the low-grade system), basically where two structures intersect each other," Willson said.
Surgical strike in '09
He said the 3-D model being developed by the company, which is reasonably far advanced, indicates that the junior's main target is shallower than anticipated.
Australian Mineral plans to begin drilling on the property early in the 2009 season with a surgical test of the prospective targets located with last year's work. The junior also plans to continue to explore for additional targets on the property.
Willson told Mining News that the company will put together an exploration plan and budget once its 3-D model and interpretation of the data has been completed.
Over his more than 16 years of covering mining and mineral exploration, Shane has become renowned for his ability to report on the sector in a way that is technically sound enough to inform industry insiders while being easy to understand by a wider audience.
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