by Erling Friis-Baastad
Many geologists call the diamond drill “the truth machine,” says territorial economic geologist Patrick Sack. “Until you have the rock in your hand, what you know about that rock is just conjecture.”
Core samples in hand, anyone considering investing in a piece of mining property, or mining-company stock, can get a more reasonable idea of their prospects. All mining is a gamble of sorts, so a selection of core samples helps companies determine how much overhead to assume before full-scale excavation begins.
A rock outcrop or anomalies in soil samples can call attention to a major deposit and give miners a place to begin their exploration, but a series of judiciously spaced core holes, and analysis of those cores, are needed to determine the extent and richness of a deposit.
“You can use other things to help you,” says Sack’s colleague Lee Pigage, head of mineral services for Yukon Geological Survey. But when it comes right down to it, not even advanced technology like ground-penetrating radar can get at the whole truth the way core samples can.
Territorial scientists and prospectors have been collecting core samples for decades and have amassed an impressive collection, along with other samples of rock plucked from much of the southern and mid-Yukon. These “truth” samples were stored at the H.S. Bostock Core Library on Takhini Road, but two years ago a new library – retaining the old name – was built on the Alaska Highway just north of the junction with Two Mile Hill.
Hugh Bostock, for whom the library is named, was a B.C. geologist who worked for the Geological Survey of Canada and moved into the territory in the 1930s. “He was at the forefront of the geological survey of the North,” says Johann Slam, core library manager. Among all the fascinating rocks and equipment at the library is Bostock’s original log book and one of his poems.
Slam continues to oversee moving and construction chores at the library. “We’re still bringing core over,” he says. Staff have been hauling over many tonnes of rock samples, some of which have already been fully studied. “I don’t want to pay to take them to the dump … a lot of money, energy and passion was put into gathering those rocks,” Slam says. He is now putting energy and passion into landscaping the library grounds, which includes building rock gardens, not surprisingly. “I figured, the theme of the geological survey is rocks, rather than flowers, let’s put the rocks there.”
Other rocks, those more likely to be studied again, get “palletized,” says Slam. They’re stored on pallets in heavy plastic wrap, which ensures a shelf life of at least 15 to 20 years. The core samples are arranged side by side in numbered cases, which are stored in rows of enclosed racks. A numbering system, similar to that used in book libraries, allows staff and clients to quickly locate the core samples they need to study.
The library building itself houses an array of fascinating equipment: state-of the art microscopes, specialized rock saws, grinding and polishing gear, and analytical instruments that measure gamma radiation, the rock’s magnetic strength, and an instrument that analyzes the chemical composition of the rock using X-rays. The equipment is available not only to Geological Survey of Yukon employees, corporations and other specialists, but also to members of the public.
“We have ‘just people’ clients who are interested in what’s inside one of their rocks that they’ve had as a doorstop for years,” says Pigage. “As long as you’re willing to go through a training session of 10 to 15 minutes, you’re welcome to use the equipment,” he adds.
What do clients look for in the rock samples, either those provided by the library or those they bring to the facility themselves? Texture, for one thing, says Pigage. This helps determine what sort of history the rock sample has gone through. “You cut a slab across so you get a fresh face,” he says. “Otherwise the surficial weathering hides a lot of internal things, and textures.”
A client might want to cut off a thin slice of rock for further analysis. Rock can be ground to a fine film and affixed to a small glass slide for use under a microscope. At a magnification of 50X or more, you can observe how the grains that make up the rock are arranged, “how they interlock or don’t interlock,” says Pigage.
The library’s portable X-ray florescence unit provides a special window on the past. “It bombards a sample with X-rays. Each element in that sample is going to emit radiation at a particular frequency. You can tell what elements are in it.” And this technology, like other library services, serves disciplines other than geology, Pigage adds. Take archeology, for instance. Obsidian, like gold, can have a different appearance or symmetry depending on where it was found. An obsidian tool can be matched to its source.
Another of the library’s roles is to support education. A special room houses a teaching collection of minerals, and hosts students from kindergarten up through graduate school. This outreach initiative is overseen by Sarah Laxton and teachers are encouraged to sign up their classes. Laxton can be reached at (867) 393-7187 or email@example.com.
The facility is both a community resource and an economic necessity. As Sack says, “The purpose of keeping an archive is, in the Yukon it costs somewhere around three or four hundred dollars a metre to extract a core.” When one considers that the library holds about 100 kilometres of core, being able to reference a sample repeatedly, close to home, rather than having to chopper crews into previously drilled property makes lots of sense.
For more information on the core library and its services go to: www.geology.gov.yk.ca/core_library.html
This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at