Though gold and silver tend to grab most of the glory whenever mining in the Yukon is discussed, there are other minerals that have been, and continue to be, of considerable economic importance to the Territory. One of the foremost of these is copper. This earthcache focuses on the Whitehorse Copper Belt, which extends for about 30 km, beginning about 5 km northwest of the city, and then sweeping in an arc that roughly follows the shape of the Yukon River and parallels the Alaska Highway.
The best way to learn more about the Whitehorse Copper Belt (which, for the sake of brevity, we shall abbreviate as WCB hereafter) is a visit to the Copperbelt Railway & Mining Museum, which is conveniently located just off the Alaska Highway, a few minutes drive from Whitehorse. This earthcache was placed with the permission of the operators of the museum, the Miles Canyon Historic Railway Society. The museum is open every day from 10AM to 5PM, from mid-May until Labour Day. Entrance to the museum, which also includes a 'Loki' ride around the 2 km mining track on the grounds, is well worth the modest admission price. However, if you are unable to come when the museum is open, you can still complete this earthcache. The answers you seek can be found by examining the outdoor exhibits along the trails that surround the museum.
Since there is a traditional cache located just outside the museum, the posted coordinates for this earthcache have been placed at the Alaska Highway turnoff to the museum in order to get some separation on the geocaching map. A reference point for the museum itself has also been provided.
We're putting this up front to make it easier to find; however, we strongly urge you to read the material that follows concerning the geology and history of the WCB. Send us your answers to the following questions via the email address or message link on our profile, mentioning the name of the cache in your message. You do not need to wait for a reply before logging a find. We're not concerned about absolute accuracy in your answers, just that you visited the site and made a reasonable attempt to obtain the required information. Posting photos with your log is encouraged, provided that they don't contain spoiler information.
1. What is epidote, and what role does it play in copper mining?
2. One type of rock is particularly abundant in the WCB. Name the type of rock and describe the two ways in which it was created here.
3. Name three important copper-bearing minerals that are found in the region, plus the percentage of copper by weight that they are capable of yielding.
4. How much copper in total (in pounds or kilos) was produced by the mines in the WCB?
5. There is a metal mining-related object located in front of the museum. Describe it and its contents.
Geology of the Whitehorse Copper Belt
The story of copper deposition in the Whitehorse area begins with volcanic activity that took place more than 200 million years ago. The mineral-rich lava and ash from the volcanoes became distributed through the area by erosion, and subsequently was covered by a shallow sea. When the sea receded, roughly 170 million years ago, it left behind sediment created from the remains of coral and other marine life, and this then became thick layers of limestone. These layers of sedimentary rock were up to 7 to 10 km thick in this region, which is part of the Whitehorse Trough that extends roughly from Atlin, BC up to a bit north of Carmacks.
The next reshaping of the area was due to plate tectonic movement, causing tilting and folding of the sedimentary rocks in the trough. About 110 million years ago, the grinding of the plates together created hot magma deep within the Earth's crust, which rose up and intruded into the sedimentary layers. The granitic magma reacted with the limestone (calcium carbonate), converting it to a silicate metamorphic rock known as skarn. More importantly, copper and other dissolved metals in the magma precipitated out, forming a number of minerals in association with the skarn that have the potential to be mined.
Mother Nature was not done yet, however. In more recent times (geologically speaking!), three major periods of glaciation occurred in this part of the Yukon. During the last such event, the McConnell glaciation, the Whitehorse area was covered by at least 1350 m of ice. The glaciers finished receding from the area about 13,500 years ago, leaving the mineralized skarn buried under a thick layer of glacial sediment. Fortunately, as glaciers recede, meltwater channels form to carry off the large volumes of water created by the melting ice. These fast-moving streams have tremendous erosive power, and in some cases they were able to cut through the glacial deposits and even some of the underlying bedrock. It was this meltwater action that exposed the skarn in the Whitehorse Copper Belt and drew attention to the rich copper-bearing minerals that lay within.
For an excellent example of a meltwater channel that cuts through the WCB, go to the lookout on Fish Lake Road (see reference waypoint below), where you can look south along the McIntyre Creek valley.
A Brief History of Mining in the Whitehorse Copper Belt
Copper deposits were first discovered in 1897 by prospectors who were on their way to the Dawson area, and the first claim was staked in July, 1898. Many more claims followed in the next few years, as the Klondike gold rush waned and interest in other mining ventures picked up. Getting the ore to smelters on Vancouver was difficult and costly, but the pace of mining in the WCB slowly picked up as roads and rail links were constructed. By far the most productive site was the Pueblo Mine, located in the north end of the Belt near the present Fish Lake Road. Though the ore here was rich, it was located in a zone with many fractures, and hence very dangerous to mine. The mine reached its peak of production in 1916, but in the following year, disaster struck. A collapse occurred, trapping and entombing six miners, resulting in the worst mining accident in Yukon history. This unfortunate event hastened the end of mining at Pueblo, and by 1920, all mining activity in the WCB had ceased. Aside from the accident, other factors contributed to the cessation of mining, most notably the postwar slump in copper prices.
After a hiatus of nearly fifty years, improvements in exploration and mining techniques heralded a revival of mining activity in the WCB, beginning in 1967. Construction of a mill in the area to concentrate the ore also served to lower the transportation costs and make mining more economically feasible. Both open-pit and underground mining were pursued, with much of the activity during this new era taking place in the south end of the Belt. Most of the mining operations were short-lived, however, with only the Little Chief Mine continuing past 1971. Mining at Little Chief continued until the ore became depleted in 1982.
Whether there will be another resurgence in copper mining in the WCB remains to be seen, but there are estimated reserves of 3,000,000 tonnes of copper ore (with a grade of about 0.95% copper) remaining in seven deposits. There is also considerable potential for new discoveries. For the time being, however, attention has shifted to other parts of the Yukon, particularly to the large deposits found in the central part of the Territory.
References and Resources
Copper, Yukon Geological Survey
Whitehorse Copper Belt, Yukon Geological Survey
Leyla Weston, Mining History and Geology of Whitehorse Copper Belt