North of 60 Mining News - The mining newspaper for Alaska and Canada's North

Like an iceberg, it appears the 4.75 million metric tons of massive sulfide mineralization outlined so far at the Glacier Creek deposit near the top of Mt. Morlan at Constantine Metal Resources' Palmer project in Southeast Alaska may be just a glimpse of the precious metals enriched copper-zinc mineralization that lies below.

To find out, Dowa Metals & Mining Co. Ltd. has agreed to invest US$6.2-million on a 2014 exploration program that included at least 10,000 meters of drilling focused on a significant expansion of the Glacier Creek deposit as well as testing some of the other tantalizing volcanogenic massive sulfide prospects across the Palmer property.

"With the largest program to date at Palmer, there is tremendous potential in 2014 to expand the existing resource and discover new deposits," said Constantine President and CEO Garfield MacVeigh.

This program marks the second year of exploration funding by Dowa, which has the option to earn a 49 percent joint venture interest in Palmer by investing US$22 million over four years. The investment is part of the Tokyo-based smelting and mining company's strategy of securing copper and zinc concentrates by investing in mines and promising exploration projects.

Situated 33 miles (53 kilometers) from a Pacific Rim deep-sea port at Haines, a mine at Palmer would be well-situated to provide feedstock for Dowa's state-of-the-art Kosaka smelter in Japan.

In 2013 the smelting company invested roughly US$3 million on a program that allowed it to get a first-hand understanding of the geology and metallurgy of the VMS mineralization at Palmer.

Satisfied with what it learned during the inaugural program, Dowa has more than doubled its 2014 exploration budget for Palmer.

To meet its earn-in commitment, it is anticipated that Dowa will fund the 2015 and 2016 programs at similar levels as this year.

Tip of the iceberg

Since its formation in 2007, Constantine's exploration at Palmer has focused primarily on expanding Glacier Creek, a prospect that consists of five inter-related subzones of massive sulfide mineralization - RW East, RW West, and South Wall zones 1, 2 and 3.

The South Wall zones are parallel layers of nearly vertical VMS mineralization. At the upper extent of South Wall, a fault cuts and folds the three layers at which point they lay nearly flat. South Wall Zone 2 and Zone 3 are of the same age as two strata drilled at RW, the flat lying limb of mineralization found near the top of Mt. Morlan.

Based on 32 holes drilled through 2009, an inferred resource of 4.75 million metric tons averaging 1.84 percent copper, 4.57 percent zinc, 0.28 grams per metric ton gold and 29 g/t silver (using an NSR cut-off of US$50/t) was calculated for the RW and South Wall zones at Glacier Creek.

Constantine believes that, given the grades, increasing the tonnage of this resource to around 10 million metric tons would make Glacier Creek a compelling deposit to evaluate the economics of building a mine.

Given that the resource calculation does not include the results from seven holes that Constantine drilled into the Glacier Creek deposit in 2010 and a 10-hole program funded by Dowa in 2013, the partners have already made headway towards their target.

Seven of the holes drilled last year cut significant mineralization, two of which penetrated the flat-lying RW zone, the balance tapped the plunging zones at South Wall.

CMR13-44, a roughly 100-meter eastward step out from the nearest drill intersection at RW, cut a 3.36-meter zinc-rich intercept averaging 0.51 percent copper, 9.18 percent zinc, 0.92 percent lead, 46.2 g/t silver and 0.21 g/t gold.

Precious metal-rich oxide mineralization was intersected at the RW zone in hole CMR13-50, including 37.5 meters of 123.2 g/t silver and 0.62 g/t gold. The intersection includes a partially un-oxidized subinterval of 13.7 meters grading 0.51 percent copper, 4.97 percent zinc, 1.61 percent lead, 134.3 g/t silver and 0.71 g/t gold.

Another three holes of the 2013 program tapped South Wall zone 1:

Hole CMR13-43, which represents roughly a 35-meter down-dip step-out of South Wall Zone I, cut 25.23 meters grading 1.17 percent copper, 0.43 percent zinc, 8.5 g/t silver and 0.07 g/t gold;

CMR13-45, a 65 meter up-dip step-out at Zone I, cut 21.71 meters averaging 2.36 percent copper, 9.06 percent zinc, 0.13 percent lead, 28.8 g/t silver and 0.33 g/t gold; and

CMR13-49 intersected 24.7 meters near true width of 2.02 percent copper, 8.47 percent zinc, 31.7 g/t silver and 0.51 g/t gold.

Hole 49 was drilled roughly 30 meters up-dip of CMR10-40, a hole drilled in 2010 that cut 20.8 meters grading 1.03 percent copper and 5.01 percent zinc. Both these intersections are outside the limits of the resource estimate and are located 80 meters east of the nearest South Wall intersection in CMR08-11, which cut 36.3 meters grading 1.7 percent copper and 5.74 percent zinc.

At South Wall Zone 2, CMR13-46 cut 20.58 meters averaging 0.92 percent copper, 7.18 percent zinc, 0.25 percent lead, 45.3 g/t silver and 0.32 g/t gold approximately 50 meters west and 50 meters up dip of previous drilling.

Constantine said the intersection in hole 46 significantly expands an area of thick Zone 2 mineralization, and opens the potential to add additional tons between the base of Zone 1 and the currently defined top of Zone 2. The breadth of Zone 1, which has been traced over an area measuring roughly 200 meters by 450 meters, has largely been defined.

There is strong evidence, however, that zones 2 and 3 continue to plunge down the mountain.

CMR10-39, drilled 110 meters down plunge and to the west of any previous hole, cut 2.45 meters averaging 1.1 percent copper, 4.52 percent zinc, 0.13 g/t gold and 24.8 g/t silver.

While hole 39 was in and of itself a significant expansion of South Wall, a geophysical anomaly provided tantalizing evidence that this was at the edge of a ballooning area of VMS mineralization below.

Below the surface

A 400-square-meter conductive plate that trends downward and to the southwest of hole 49 was a tantalizing resource expansion target at Palmer in 2014. A similar, but much smaller conductive plate lies at the heart of the South Wall mineralization tapped near the top of Mt. Morlan. If the mineralization at and around the lower plate is analogous, then a larger portion of the deposits remains to be drilled.

Hole CMR14-54, the first hole to intercept the area were the lower conductive plate was identified, cut 22.1 meters grading 2.48 percent copper, 4.05 percent zinc, 24 g/t silver and 0.39 g/t gold. This intersection represents a major expansion of the South Wall zone to depth and provides the first evidence that a much larger portion of the deposit remains hidden.

MacVeigh said, "Hole CMR14-54 not only expands the footprint of the South Wall zones but opens up the opportunity for considerable further expansion and will be a focus for ongoing drilling. The thickness and high copper content associated with a large conductive target enhances the potential around this new area."

If the South Wall zonation found in the higher plate repeats below then thicker zones of copper-rich mineralization should be found as drilling nears the center of the conductive zone.

Constantine Vice President of Exploration Darwin Green told Mining News that the company will likely update the Glacier Creek resource with the results of the 2010, 2013 and 2014 drilling, following the completion of this year's program.

Intriguing targets

While two rigs traced South Wall, a third drill was originally designated to test some of the other intriguing exploration targets at Palmer.

The third rig tested targets beyond the resource but within the larger Glacier Creek prospect area before it too was aimed at expanding South Wall.

Mount Henry Clay, the source of enormous high-grade massive sulfide boulders that occur near the limits of a stranded glacier, is another outlying target waiting to be tested.

Twenty-six samples of various boulders collected by the U.S. Bureau of Mines at the toe of a small ice sheet near this prospect also known as MHC returned an average grade of 19.3 percent zinc, 1 percent copper, 0.4 percent lead, 38.2 g/t silver, 0.22 g/t gold and 20.6 percent barium. The source of these boulders, some of which measure up to six feet in diameter, has yet to be discovered.

Work completed by Constantine and Dowa in 2013, however, has provided a vector to a prospective source of these massive VMS stones trailing at the tail of the receding ice cap roughly two miles (3.2 kilometers) west of the Glacier Creek resource area.

Armed with GPS and chipping hammers, project geologists spent three days last fall locating and sampling more than 100 massive sulfide boulders strewn across the MHC prospect area.

Green said this exercise has outlined a narrow band of high-grade boulders that points to a small and "very compelling" target under the relatively thin ice sheet above.

CAP, a silver-rich target about 2.5 miles (four kilometers) south of Glacier Creek, is another prospect in queue for exploration drilling.

CAP01, drilled by Constantine in 2007, cut 23.2 meters of barite rich mineralization averaging 134 g/t silver. Constantine will apply what it has learned at Glacier Creek to target a larger zone of massive sulfide mineralization at this promising prospect.

In September, Constantine signed an upland mining lease on roughly 92,000 acres (37,200 hectares) of lands surrounding the Palmer property.

The company secured the property through a competitive lease process offered by the Alaska Mental Health Trust Authority, a state corporation within Alaska.

In addition to being prospective for VMS mineralization, the newly acquired Haines Block also covers areas upland of the Porcupine placer district, which is estimated to have produced 82,489 ounces of gold, adding to the intriguing targets on the expansive property.

MacVeigh said, "We are very pleased to have secured this large and prospective land package and look forward to exploring these properties for the mutual benefit of Constantine shareholders and Alaska Mental Health Trust beneficiaries."

Dowa the smelter

Beyond providing the funds needed to take Palmer to the next level, Dowa offers 130 years of experience in processing and refining complex VMS ore to the project.

The Japanese smelting and mining company has been improving its expertise in separating the various precious and base metals from VMS deposits since it began mining Kuroko ore in northern Japan during the 1880s.

Kuroko is a black-colored massive sulfide ore. Although Kuroko ore contained abundant precious metals such as gold and silver, they were difficult to smelt due to the ore's complex mineral composition.

As a result of technological improvements over the decades, Dowa overcame the metallurgical challenges of Kuroko ore. Today, Dowa's Kosaka Smelter is the largest zinc smelter in Japan and among the most technologically advanced smelters of complex ore in in the world.

This long history of refining massive sulfide ores makes Dowa ideally suited for understanding the best techniques for producing zinc and copper concentrates from the polymetallic mineralization at Palmer.

Working with metallurgists from Dowa, SGS Canada carried out locked cycle flotation tests on a composite of 212 assay sample rejects from past drilling at Palmer. These samples, which represent a blend of all major ore-types encountered during drilling of the South Wall resource area, had a head grade assay of 1.56 percent copper, 6.47 percent zinc, 28.5 grams per metric ton silver and 0.19 g/t gold.

The metallurgical testing yielded smeltable copper and zinc concentrates, with high metal recoveries produced at moderate grind sizes.

This relatively straightforward process returned copper recoveries of 89.6 percent to a concentrate containing 25.5 percent copper, and 84.9 percent of the zinc reported to a concentrate containing 59.1 percent zinc. Of particular importance to Dowa, which may very well want to refine potential future zinc concentrates from Palmer is the zinc concentrates produced from the locked cycle tests had low impurities and no potential penalty or problematic elements.

The concentrates produced during testing captured 89.7 percent of the silver and 75 percent of the gold in the samples; with 73.7 percent of the silver and 61.5 percent of the gold reporting to the copper concentrate.

"In addition to achieving high copper and zinc recoveries, particularly for an initial test program, we are also pleased with the precious metal recoveries. These favorable metallurgical results continue to remove project risk as the company advances Palmer," said MacVeigh.

No follow-up metallurgical testing is planned for 2014, which indicates that Dowa, as a likely smelter of concentrates from any future mine developed at Palmer, also is satisfied with the metallurgical results.

Author Bio

Shane Lasley, Publisher

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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