The mining newspaper for Alaska and Canada's North
The mining newspaper for Alaska and Canada's North
Alaska is rich in this oft overlooked technological metal Critical Minerals Alaska 2020 – Published October 29, 2020
Due to its use in the solders that make the innumerable connections in electronics, tin has been dubbed the metal that glues the technology revolution together.
A 2018 study by MIT found tin as the metal most likely to be positively impacted by new technologies.
A pair of 10th century BC bronze swords found in Switzerland. The first civilizations to master the ability to alloy tin and copper had a strategic and economic advantage over their counterparts.
Concentrates from gravity separation of placer samples collected from Ray River in Alaska returned up to 50% tin; 10% rare earths; and 0.01 to 1% tungsten, tantalum, and niobium.
Cans, cups, roofs, and foil hats are likely the first things that come to mind when thinking about tin – none of which conjure images of a metal that should be considered critical to a modern country like the United States. According to a study carried out by Massachusetts Institute of Technology, however, tin is the metal expected that be most impacted by new technologies.
Commissioned by Rio Tinto, the MIT study found that tin beat out more likely technology metals candidates such as lithium, cobalt, and graphite.
"Rio Tinto's Ventures group is looking for new areas to invest and tin is at the top of their list of metals likely to be positively impacted by new technology," the global miner informed colleagues at a 2018 battery metals conference in Australia.
With more than 100 known tin occurrences, Alaska tops the list of places in the U.S. to establish a domestic source of this critical technology metal.
"Today, Alaskan tin deposits are known to be widespread, occurring from the central Alaska Range north to the Brooks Range and across Interior Alaska ... Southwest Alaska and the Seward Peninsula," according to Mineral Deposits of Alaska, a 1997 publication that compiles the work of nearly 50 geologists.
And when it comes to critical minerals exploration in Alaska, tin could be considered the gateway metal.
In fact, more than a dozen of the 35 metals U.S. Geological Survey deemed critical to America – beryllium, bismuth, chromium, fluorspar, gallium, indium, manganese, niobium, platinum group metals, rare earth elements, scandium, strontium, tantalum, tungsten and vanadium – have been found associated with the placer and lode tin occurrences across the state.
Critical since 2300 BC
Tin's provenance as a critical metal can be traced back at least 5,500 years, when early human civilizations discovered that mixing a little tin with copper created bronze, an alloy that produced much more durable weapons and tools than those cast from copper alone.
The first civilizations to discover this cutting-edge metallurgical technology had a strategic and economic advantage over their counterparts. This edge was so powerful that we now consider the Bronze Age one of the most important epochs of human history, an era that spans roughly 2,000 years.
Not unlike our Bronze Age forebearers, we continue to almost exclusively use tin in alloys, mixtures that keep tin on the list of critical minerals.
In 2019, the United States consumed roughly 103.6 million pounds of tin for plating; solders; bronze, brass, and other alloys; bearing surfaces and other applications.
While these uses conjure images of high-tech, MIT researchers found that tin is the metal that is most impacted by new technologies such as autonomous and electric vehicles, advanced robotics, renewable energy, and advanced computer systems.
One of the main reasons these high-tech sectors are putting so much demand on tin is the metal's use in solders that make the innumerable connections in electronics and electrical products.
"Tin's extensive use in solders makes it the metal that glues the technology revolution together, and new applications, such as in emerging lithium-ion batteries, tend to grow as technology advances and diversifies," said Roskill, a world-leading metals consultant based in London.
Roskill expects emerging tech applications such as the rollout of a global 5G network, smart home devices, and advances in lithium-ion batteries to drive growing demand for tin.
"The use of tin in li-ion battery anodes is a sector that has shown some of the highest growth over the last decade, accounting for 0.4% of refined tin consumption in 2011 and growing to 3% in 2019," Roskill penned in a tin forecast report published in August.
Despite the many traditional and emerging uses for tin, none of this critical metal is mined in the U.S. Instead, roughly 77% of America's tin supply was imported from foreign countries –Indonesia (25%), Malaysia (24%), Peru (20%), and Bolivia (18%) are top tin suppliers. The balance of U.S. tin supply, roughly 22 million pounds, was the product of recycling.
"Tin has not been mined or smelted in the United States since 1993 and 1989, respectively," USGS penned in its Mineral Commodity Summaries 2020 publication.
This complete dependence on foreign sources for new supply, coupled with the alloying metal's importance to both manufacturing and defense, is the reason both the Pentagon and USGS consider tin critical to the United States.
The average paid for this tin during 2019 was around US$8.50/lb.
Based on the average Platts Metals Week New York dealer price for tin, the estimated value of refined tin imported into the U.S. last year was $703 million, and the estimated value of tin recovered from scrap domestically was $213 million," USGS wrote on the 2019 tin sector in the United States.
Placer dominates tin
Unlike most metals and minerals, where hardrock mining dominates large scale production, the majority of the world's supply of tin comes from placer mining of the mineral cassiterite from alluvial deposits that have eroded from the lode source.
"Placer deposits have traditionally been an important source of tin; in 2012, they accounted for about 70% of the world output of cassiterite concentrates," USGS penned in a 2018 report on critical minerals.
Tin-rich placer deposits are widespread across Alaska. There are a couple of aspects that make these deposits an intriguing source of tin – Mother Nature has completed the first stage of mineral processing, eroding cassiterite from the rocks and concentrating the tin mineral in deposits that can be mined with simple gravity recovery systems; and these rich sources of Alaska tin are almost always associated with an array of other metals critical to the United States.
One of the most intriguing places to explore for critical minerals-enriched placer tin deposits is a 200-mile-long area of Interior Alaska just north of the Yukon River that also happens to be prime hunting ground for rare earth elements.
Ray Mountains, which is about 40 miles north of the community of Tanana, is an area rich in placer tin, rare earths, and other critical minerals.
Ucore Rare Metals, who staked claims over much of the placer potential in this area about a decade ago, carried out preliminary work to test the viability of mining the critical minerals in the alluvial deposits at Ray Mountain.
Concentrates from gravity separation of placer samples collected in 2014 returned up to 50% tin; 10% rare earths; and 0.01 to 1% tungsten, tantalum, and niobium.
Ucore, which is focused on a mine at its Bokan Mountain rare earth deposit and associated REE separation plant in Southeast Alaska, has not carried out any recent work at Ray Mountain.
If the creeks give you cassiterite
The most widely known placer tin deposits in Interior Alaska are found along the Tofty tin belt, a 12-mile-long area of tin- and gold-bearing gravels in the Manley Hot Springs district, an area best known for the more than 600,000 ounces of placer gold mined there.
While it is unclear how much tin has been recovered from the streams of this mining district about 90 miles northwest of Fairbanks, gold miners were recovering placer cassiterite at the dawn of the 20th century.
"Gold mining in the district developed rapidly, and as the productive area in the vicinity of Tofty increased it was found that tin and gold were generally associated and that the richer concentrations of the two minerals were generally coincident," Henry Eakin wrote in a 1914 report, Tin Mining in Alaska.
This coincidence of tin and gold was oft a burden for early placer miners in the area. This is because the cassiterite, a relatively heavy mineral, would plug up sluice boxes and render them ineffective in recovering gold.
These miners, however, soon decided to try to cash in on the cassiterite piling up on their claims.
In 1911, about 1,200 lb of tin concentrates accumulated from cleaning out the sluice boxes were shipped to Singapore for processing.
"The ore was found to be of high quality, and the returns from the small shipment directed attention for the first time to the possible value of tin as a by-product," Eakin penned.
And in 1914, roughly 48 tons of cassiterite was shipped from the gold mines in the Hot Springs district.
Over the years since, various miners have recovered cassiterite as a by-product of gold mining.
A search for the lode source of the tin found in the stream did not turn up appreciable amounts of cassiterite but samples collected by the Alaska Division of Geological and Geophysical Surveys did find intriguing quantities of many other minerals deemed critical to the U.S.
Bismuth, chromium, gallium, manganese, niobium, rare earth elements, scandium, strontium, tantalum, and vanadium have been identified in samples collected from the Manley Hot Springs district.
Circle Hot Springs granites
Placer miners trying to recovery gold from Boulder Creek in the Circle Mining District ran into the same troubles as their colleagues in the Tofty Tin Belt about 200 miles to the west.
While there has been no systematic testing of the placer tin content, a miner attempting to recover the gold in a particularly tin-enriched portion of Boulder Creek estimated the gravel contained more than 2 lb of cassiterite per yard.
An investigation carried out by James Barker for the U.S. Bureau of Mines indicates that the lode source of this tin mineralization is very close.
"Cassiterite occurs as fresh unweathered crystals up to 3/8 of an inch long, some of which are attached to gangue rock," he wrote in a 1979 report. "Tin is particularly concentrated in the coarser size fractions. The gold is also quite fresh, occurring primarily as thin irregular flakes. The balance of the concentrate consists of rounded nuggets of hematite, magnetite, and scheelite."
Scheelite is a mineral of tungsten, which the USGS also considers critical.
One sample of fresh granite collected by Barker near Boulder Creek returned 20 parts per million tin and 22 ppm tungsten. The sample also contained gold and molybdenum.
Tin and tungsten have been found in many of the other creeks in the Circle Mining District – Bedrock, Deadwood, Independence and Half Dollar, to name a few.
The Lime Peak and Mount Prindle areas to the west of the Circle Hot Springs granitic intrusive feeding these creeks also has tin, tungsten, and rare earth mineralization.
Rediscover Tin City
When it comes to looking for rich sources of tin in Alaska, any mining company would be remiss if it overlooked a place called Tin City.
Located on the western tip of the Seward Peninsula, Tin City was established in 1904 by Nome Gold Rush miners who found rich deposits of cassiterite in Cape Creek about 90 miles northwest of Nome.
Placer mining of Cape Creek, which drains the mountain rising to the northwest of Tin City, produced an estimated 3.3 million pounds of tin, according to the USGS. The largest known chunk of cassiterite recovered during placer mining of Cape Creek weighed 142 lb.
While Tin City is more of a forgotten outpost than the metropolitan that its name suggests, the streams in the area still hold rich lodes of the critical metal for which the ghost town derived its name.
Other placer tin prospects found at this westernmost tip of the North American continent include Lost River and Potato Mountain.
Kougarok, located about 90 miles east of Tin City, is one of the most promising lode tin deposit on the Seward Peninsula.
Work in the 1980s estimated a portion of the tin-bearing granites there hosts some 6 million lb of tin in 240,000 tons of historical resource averaging 1.3% tin. Some of the cassiterite deposits at Kougarok also host considerable amounts of beryllium, tungsten, fluorspar, niobium, and tantalum, all on the USGS list of critical minerals.
Near highway lode
When it comes to hardrock sources of tin, one of the more promising areas discovered in the state near the Parks Highway about halfway between Fairbanks and Anchorage.
Coal Creek, a 2,400-acre property just west of the Parks Highway roughly halfway between Anchorage and Fairbanks, is one such property that has garnered some interest in recent years.
Discovered by Charles Hawley in 1972, Coal Creek was staked for its tin-silver potential by Houston Oil and Minerals in 1980. Over the ensuing five years, this exploration company carried out exploration programs that included 5,240 meters of drilling in 42 holes.
A preliminary resource calculated for Houston Oil and Minerals in 1982, estimated the drilled portion of the Coal Creek deposit contained roughly 4.8 million metric tons averaging 0.27% tin, according to data published by the U.S. Geological Survey.
While the resource does not meet the rigor of current reporting standards, sampling of core stored at the Alaska Geologic Materials Center in Anchorage and four holes drilled by Brett Resources in 2006 confirms the tin-silver potential of this easily accessible property.
Highlights from the drilling include: 9.4 meters averaging 0.41% tin, 18.21 grams per metric ton silver and 0.81% zinc; and 9.3 meters averaging 0.45% tin, 11.95 g/t silver and 0.29% zinc.
Tungsten and gold also have been identified at Coal Creek. Choice grab samples collected from the property in 1990 turned up 720 g/t tungsten, 65 g/t silver, 0.5 g/t gold and 4.86% zinc.
Like the other tin deposits in Alaska, Coal Creek has tin-bearing neighbors enriched with a suite of other critical minerals.
Ohio Creek, another Hawley discovery to the northwest, has yielded a wide variety of minerals and metals.
A study completed by the U.S. Bureau of Mines in the 1980s identified wodginite, a manganese-tin-niobium oxide; tungsten; gold; silver; palladium, a platinum group metal; and a suite of rare earths in the area.
As part of Alaska's Strategic and Critical Minerals Assessment project, the Alaska's DGGS re-analyzed rock samples from the earlier study. A report published by DGGS in 2014 confirmed the earlier findings.
Cornish Metals Inc. (formerly Strongbow Exploration) acquired Coal Creek and commissioned a technical report on the property in 2015 but has not followed up with any significant exploration there.
Tin-rich Kuskokwim Mountains
The Kuskokwim Mountains of Southwest Alaska is another place known for its tin potential and Cornish Metals also holds a cassiterite-bearing property there.
This property, Sleitat, was explored by Cominco (now Teck Resources) in the 1980s, which discovered two zones of tin mineralization.
One hole drilled by Cominco cut 3.1 meters of 12.55% tin and 197.5 g/t silver. The overall deposit evaluated by the nine holes drilled by the company was much lower grade.
Using the information from Cominco drilling and surface sampling, the Bureau of Mines estimated the area of known mineralization at Sleitat encompassed roughly 25.9 million metric tons averaging between 0.22 and 0.37% tin, 17 g/t silver and 0.04% tungsten.
In a 2015 technical report for Strongbow, Alaska Earth Sciences recommended airborne geophysical surveys that could help target future drilling at Sleitat.
Three other prospects in the Kuskokwim region of Southwest Alaska – Bismarck Creek, Win and Won – are also prospective for tin.
Chip-channel samples collected at Bismarck Creek, about 40 miles southwest of McGrath, returned up to 2.8% tin, 63 g/t silver, 590 g/t copper, more than 1% zinc and 0.03% antimony. Selected samples are also reported to run up to 0.01% indium, another USGS critical mineral.
Based on extensive surface sampling, it is estimated that the Bismarck Creek deposit contains 500,000 metric tons averaging 0.14% tin and 47.8 g/t silver.
Sampling at Win, located about 20 miles north of McGrath, yielded several high-grade samples of polymetallic mineralization. One 7.75-foot channel sample collected by the Bureau of Mines in 1992 returned 18.82 oz/t silver and 6.97% tin.
Other samples from Win ran as high as 94.63 oz/ton silver, 46.4% tin, 926 ppm bismuth, 0.36% copper, 0.17% niobium and 5% antimony.
Despite the high-grade metals found at Win, no drilling is reported for this prospect.
The tin-bearing veins at the Won prospect, however, have been drilled.
Two holes drilled by Anaconda Minerals Company cut up to 6.9% tin and 3.3 oz/ton silver, along with antimony, lead, arsenic, copper, and tungsten over unknown widths.
A 2004 USGS report, "Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera," said the Win and Won prospects "contain some of the most important tin-polymetallic resources in the Kuskokwim Mineral Belt and perhaps in all of Alaska."
Like the other tin-enriched regions of the state, a winning search for tin in Southwest Alaska will likely lead to the discovery of a suite of the minerals the USGS considers critical to America's security and economic well-being. This makes tin an ideal gateway metal for anyone exploring the Last Frontier's rich critical minerals potential.
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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