The mining newspaper for Alaska and Canada's North
The mining newspaper for Alaska and Canada's North
Heatherdale traces long trends of high-grade VMS mineralization in SE Alaska
Heatherdale Resources Ltd., a subsidiary of Hunter Dickinson Inc., (see Hunter Dickinson Inc.) is living up to its pledge to aggressively explore the Niblack copper-gold-silver-zinc project on Prince of Wales Island in Southeast Alaska. Some 23,000 meters of drilling completed by the junior over the past year traced nearly 1,000 meters of precious metal-rich volcanic massive sulfide mineralization under Lookout Mountain.
Heatherdale optioned Niblack from CBR Gold Corp. (see Niblack Mineral Development Inc.) in 2009 in hopes of earning a 51 percent interest in the project by spending US$15 million by mid-2012.
The junior completed its initial US$5 million exploration program in June, and is currently on track to complete the earn-in commitment around the beginning of 2011.
"Drilling with two drills, we continue to find more, and in typical Hunter Dickinson fashion, we are going to keep expending the money we need to develop the resources to move this project forward," Lena Brommeland, Heatherdale's executive general manager, told Mining News.
Once Heatherdale completes this initial commitment, it can increase its stake in the project to 60 percent by spending another US$10 million, and then to 70 percent by completing a positive bankable feasibility for the copper-gold-silver-zinc project.
"We fully intend to continue our investment at Niblack to move the project forward in a timely and efficient way," said former Heatherdale President and CEO Dave Copeland.
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Mine maker
hen Heatherdale took over exploration of Niblack, the Lookout zone had a previously defined indicated resource of 2.272 million metric tons grading 2.42 g/t gold, 34.66 g/t silver, 1.27 percent copper and 2.36 percent zinc. The deposit also had an inferred resource of 1.712 million metric tons grading 2.08 g/t gold, 32.56 g/t silver, 1.55 percent copper and 3.17 percent zinc. The estimate was based on a US$50 net smelter royalty cutoff.
What piqued Hunter Dickinson's interest in the project was high-grade mineralization struck by CBR Gold in an area to the southwest of the defined resource. Drilled late in 2008, holes U027 and U028 intercepted a previously unknown precious metal-rich zone with values nearly three times greater than the Niblack average.
Brommeland characterized the new discovery as a "mine maker."
"When you can peg into one of the high-grade zones in a deposit and establish substantial tons of that kind of grade, it really doesn't take that many tons in order to make an economic deposit," she said.
Precious metal-rich zone grows
Heatherdale began investigating the higher grade extension of Lookout by fan drilling the target from a 1,000-meter underground exploration drift completed in 2008.
As of mid-July the junior had received assay results from 10,670 meters of drilling. The results from these 23 holes, drilled from six underground drill stations, indicate that the precious metals-enriched system remains open in several directions.
U029, the first hole of Heatherdale's underground program, cut 18.7 meters with an average grade of 2.4 g/t gold, 48 g/t silver, 1.4 percent copper and 2.8 percent zinc. The best intersection of the first three holes was in U031, which cut 43.9 meters grading 3.01 g/t gold, 76 g/t silver, 2.25 percent copper and 8.66 percent zinc.
These precious metal-rich intercepts have continued throughout the exploration of this high-grade extension. U052 cut 9.7 meters averaging 1.49 percent copper, 3.78 percent zinc, 1.86 g/t gold and 85 g/t silver; and included 3.8 meter section grading 1.92 percent copper, 6.95 percent zinc, 3.25 g/t gold and 160 g/t silver.
"The findings validate our geological team's growing knowledge of the precious metals-enriched system we're seeking to delineate, and enhance our confidence that we will define a polymetallic VMS deposit with the grades, volume and other characteristics necessary to support an economically robust underground mining operation in future," Copeland said.
New geological model
A new resource estimate being completed by Heatherdale will not only outline the high-grade VMS mineralization the explorer has delineated with its aggressive underground drill program, but also will debut a new geological model for the Niblack project.
"I'm looking forward to being able to tell the world, when we do our new resource calculations, what we have here," Brommeland said. "We have been pretty much focused on understanding the geology so we can put together the model and then do a block model that is not only the grade-shell; it is a model that incorporates the geological environment," Brommeland explained.
The geology under Lookout Mountain is relatively simple compared to other VMS deposits. The mineralization has not been broken up by extensive localized faulting and folding.
"Historically Niblack was thought to be a very complex structurally modified deposit - a lot of folding, a lot of faulting," Brommeland explained. "We don't see a lot of offsetting, and we don't see a lot of complex folds. That has been a game-changer for the project. That is something we are definitely using to our advantage as we step out from known mineralization, and continue to expand the deposit."
This lack of complexity, coupled with the fact that both exhalative and replacement style mineralization exist, provide for large continuous sections of thick mineralization.
Exhalative deposits are formed when mineral-rich brine is "exhaled" into the ocean creating layers of sulfide ore. This process continues today in the form of black smokers on the ocean floor. When the brine is trapped in the ocean floor sediments, it is considered replacement-style mineralization.
"It's complicated in terms of being predictive of where those true exhalative sequences are, but once you are onto one of these replacement-style zones they can be rather large," Brommeland explained.
She said the company is encountering zones that are more than 150 meters thick with widths in excess of 20 meters and running several hundred meters long.
Connecting the zones
Heatherdale's drill program has connected the new precious metal-rich zone to the Lookout deposit, extending Lookout about 300 meters to the west. The drills at Niblack have the reach to continue to expand the deposit in this direction before the drift needs to be extended.
"At some point here we will definitely need to do underground development, and the timing of that is going to be dependent on when we achieve the maximum we think we can achieve from the underground stations," Brommeland explained.
The company has plenty of targets to investigate before it needs to expand the exploration drift, a nearly horizontal tunnel. The 1,000 meters of underground development was dug out to explore the mineralization to the east of the Lookout Zone and below the drift where rhyolite, an intrusive volcanic rock, winds its way through the mountain.
The Trio zone, which is located about 400 meters from the Lookout zone as the VMS mineralization plunges to the east, is one such target. An inferred resource at Trio of 493,000 metric tons grading 1.77 percent copper, 3.47 percent zinc, 2.06 g/t gold and 31.5 g/t silver is included in the previous estimate for Niblack.
The executive director said if drilling cuts mineralization in an untested gap of about 220 meters, some 900 meters of continuous mineralization from the zone west of Lookout through Trio will have been outlined.
From Trio the rhyolite continues along strike 800 meters to the Dama zone before it turns west on a limb that extends some 2,100 meters to the historical Niblack Mine.
A previous intersection at the Dama zone cut 19.2 meters grading 6.4 percent copper, 3.2 percent zinc, 1.37 g/t gold and 53 g/t silver. Because of the folding, it is anticipated that the mineralization will be particularly thick in this area.
The lack of geological complexity suggests that VMS mineralization could continue unbroken as it winds it way through these known zones from the historical Niblack mine to the newly discovered zone beyond Lookout.
"This system is amazing actually. All of our geoscientists that are on the project have seen a lot of these types of systems, and they are really impressed with this one," Brommeland said. "Their enthusiasm is really kind of contagious!"
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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