Extraterrestrial diamonds – the long term future of gem production?
(Asteroids and comets bearing precious gemstones and precious metals are thought to be abundant)
It has long been speculated that celestial bodies may contain vast quantities of precious metals and precious gems. More recently in 2008 a meteorite named ‘Almahata Sitta’ fell to earth giving scientists significantly more evidence as to the scale of this possibility. Studies suggest that this meteorite, the first ever identified and tracked before it landed on earth, contained diamonds that were significantly larger than any discovered from previous impacts. What is even more intriguing is the fact that leading researchers from Hiroshima University believe these diamonds to have formed in a planet that developed in the early days of our solar system and no longer exists today. Received wisdom has it that diamonds in meteorites form when asteroids collide and the resultant shock of the impact is sufficient to crush carbon into tiny diamonds but the gems in Almahata Sitta are far too large to have been created in this way. Instead they most probably formed inside a ‘planetesimal,’ a heavenly body not large enough to constitute a planet but much larger than an asteroid.
(Asteroids striking the earth are thought to bring with them millions of tonnes of minerals)
This is not the only evidence of a meteorite bearing billions of carats of diamonds crashing into the earth. In 2012 Russian scientists revealed that a diamond field discovered in the early 1970s in the ‘Popigai Crater’ was formed by a meteorite impact that took place approximately 35 million years ago. They estimate the site contains trillions of carats of what have become known as ‘impact diamonds.’ These stones are however not suitable for jewellery but they do have some industrial uses. Another such example, ‘Sutter’s Mill’ meteorite, fell in California’s Gold Country in 2012 and also contained diamonds and other precious stones and metals. Intriguingly Peter Jenniskens of the ‘SETI’ (Search for Extra Terrestrial Intelligence) stated that “from what falls naturally to the ground, much does not survive the violent collision with the earth’s atmosphere,” opening up the tantalising possibility that much larger gems could be discovered within asteroids that are still in orbit.
(Popigai Crater, Siberia, Russia, is thought to contain trillions of carats of diamonds and gold)
It is clear that meteorite impacts not only have a profound effect on life on earth, they also alter the rocks in ways that can create valuable mining resources, according to Australian experts. Peter Haines, a respected sedimentologist with the Geological Survey of Western Australia, stated that “it is not widely appreciated that an estimated 25% of the world’s impact structures are associated in some way with economic or sub-economic mineral and petroleum resources. A better understanding and appreciation of impact as a geological process may accelerate the discovery of impact-related resources.” Haines presented his research on this phenomenon to the Australian Earth Sciences Convention in Perth in 2008. In addition to diamonds it is thought these resources include gold, platinum, nickel and petroleum. Whilst it has been recognised for some time that mineral deposits can owe their origin to meteorite or comet impacts, a new discovery technique involves identifying the impact site first and then looking for the mineral wealth around it, a method designed to speed up the whole process.
(Geological Survey of Western Australia are responsible for much of the recent research in this field)
There are already a good many substantial impact-related deposits that have been clearly identified around the world. A good example is the Vredefort crater in the Free State Province of South Africa, thought to be the biggest impact crater on the planet and an area that contains some of the world’s most prolific gold deposits. Another such site is the Sudbury Structure in Ontario, Canada, the world’s second largest impact crater and a vast reserve of nickel-platinum ore. It is thought that Western Australia contains a number of impact structures, many of which are found deep beneath other rocks, which may prove a productive future source of significant exploration. Haines asserts: “many geologists are not familiar with impact structures. They see impact structures as something of academic interest and of no great economic significance, but the case overseas clearly demonstrates that they can be of considerable economic importance.” In fact mineral resources can form instantly or sometime after the impact, resulting in many potential finds being dismissed in the immediate aftermath of an impact.
(The Sudbury Basin in Ontario, Canada, the world’s second largest impact crater)
A good example is the Popagai crater in Siberia, which was formed some 36 million years ago as a result of a meteorite strike that created impact diamonds from the carbon-rich rocks. It is also possible for minerals to form from melted crust, as was the case with the Sudbury Structure in Canada which resulted in a pool of molten magma containing the heavy minerals nickel and platinum in a sunken concentrated layer. Fracturing in rocks from the intense shock pressure of impact can also be conducive to hydrothermal (hot water induced) mineralisation, including precious stone and precious metal deposits. Buried impact structures, such as those in the Gulf of Mexico, have facilitated the discovery of oil and natural gas reserves. Rob Hough, one of the leading experts in this field and geochemist with CSIRO Exploration and Mining in Western Australia has studied this area in great depth. He believes that in Australia, one of the major impact areas of the world, no exploration is currently underway and he has referred to Haine’s research as a “nice piece of work,” as it pulls together a large amount of information on impact structure mineralisation in the context of Australia. Hough stated that “people have talked about looking for Sudbury analogues” but his efforts may well be hampered by the fact that Australia’s had a long history of erosion, which might have obscured some of the evidence of impact structures from the surface.