by Bruce Ryan

Newfoundland Department of Mines and Energy, Geological Survey Branch, 1993

The rocky landscape of Labrador conceals many treasures that are only recognizable to the trained or searching eye or those with a need to be filled. For instance, to most of us the flinty grey rock of northern Labrador that is known as Ramah chert is little different from any other rock. Yet, to the prehistoric inhabitants of Labrador in search of a superb stone from which to fashion the cutting tools they needed to make survival a little more probable in a hostile environment, the Ramah chert was an ideal material. In 1770 a Moravian missionary in Nain was given a piece of brightly coloured local rock, and became the first to appreciate the potential of “labradorite” as a decorative stone of wide appeal. The heavy red rocks of western Labrador were trodden over for generations before they were recognized as a world-class iron ore deposit by geologists in the late 1930’s. Now Labrador is being viewed as a potential source of other “rocks” — diamonds, the mainstay of the jewellery trade.

Diamonds have attracted humans for millennia. They are hard, brilliant, dazzling gems that adorn fingers and crowns, and evoke much emotion in their owners or would-be owners. They have been the cause of much grief inflicted on the hearts and pocketbooks of people and nations, as anyone who has read the story of the famous Koh-i-noor diamond will tell you. Many diamonds come from the ground as unattractive glassy knobs, but when crafted to perfection in the hands of the expert diamond cutter, they hold even the most indifferent person spellbound. All this from a mineral composed of the element carbon, the very same element that makes up the lead in your pencil and the graphite lubricant on your door hinges.

Diamonds form only under exceptional conditions of pressure and temperature deep under the surface, and they arrive at the surface through very fortuitous circumstances. Hence they are rare and are found only in certain parts of the Earth’s crust. In particular, the following facts are relevant to diamond discoveries. The regions of the Earth where diamonds occur, such as South Africa, are all crustal areas that are over two billion years old. The diamonds grew in these old crustal regions because these rocks remain relatively cool (900 – 1200EC) to great depths (150 – 200 km) below the surface in comparison to nearby regions. The diamonds are plucked from their deep crustal sites of formation and rapidly transported to the surface by special types of magma rising from the liquid mantle; these magmas give rise to small volcanic cones and to vertical carrot-shaped zones of rock known as pipes. The volcanic and pipe rocks are called kimberlite, after the diamond-rich district of Kimberly in south Africa where they were first described. One of the best ways to picture the process of diamond transport from 200 km up to the surface is to think of diamonds as the “passengers” who jump aboard the kimberlite “elevator” as it goes by.

How does Labrador fit into the picture of a diamond region? Firstly, it is made up of old crust, much of it older than two billion years. Secondly, although only a few kimberlitic rocks are known from Labrador, specifically in the region of Saglek Bay, other rocks are present that are indicative of probably kimberlite occurrences. The largest concentration of these can be found near Makkovik. So, even thought diamonds are not yet known in Labrador, this may be a reflection of the absence of the trained eye – you see what you look for! Perhaps in the not too distant future, Labrador may be able to claim the honour of having the province’s first real “jewel in the ground”!