|Raw diamonds from Arkansas (photo from Glenn Worthington).|
Kimberlite pipes erupt as violent volcanoes - the magma, as it weathers, releases diamonds and tracer minerals such as chromian diopside, pyrope garnet, picroilmenite, chromite, etc. into streams where they can be panned and traced back to the source rock. While panning for these indicator minerals, sometimes other valuable minerals are found including diamond, gold, ruby, sapphire.
|Panning for diamonds at undisclosed location in Wyoming|
|Depressioin over Maxwell diamondiferous kimberlite, one|
of a few hundred untested diamond pipes in Colorado,
Wyoming and Montana.
Lamproites in the Leucite Hills,
Geophysical Surveys. Geophysical exploration has been successful in the search for hidden kimberlite and lamproite (Litinskii 1963a, b; Gerryts 1967; Burley and Greenwood 1972; Hausel and others, 1979, 1981; Patterson and MacFadyen 1984; Woodzick, 1980), particularly in districts where kimberlites have previously been discovered. Contrasting geophysical properties are often favorable for distinguishing kimberlite, lamproite and minette from country rock.
|Geonics EM31 worked very well over|
buried and exposed weathered
|Gem-quality diamonds recovered from Wyoming kimberlite in 1979. Largest stone is about 1 carat.|
Gregory and Tooms (1969) found that Mg, Ni, and Nb anomalies did not extend farther than 0.36 mile (0.6 km) from the Prairie Creek lamproite,
|Vegetation anomaly followed over kimberlite at Iron Mountain, Wyoming.|
The kimberlite underlies the thicker vegetation to the left and granite to the
right. We also noticed the presence of carbonate in the soil (left), with
periodic indicator minerals and also abundant diamondbacks (rattlers).
MINING & MILLING
Economic diamond deposits depend on the average price of stones, the amount of waste material removed, mining methods, company politics, socioeconomics of the area, and many other factors. For example, a diamond deposit may be mined at a comparatively lower cost in a third world country due to the availability of an inexpensive labor force, although constructing an infrastructure in such an area could offset some of these benefits. Whereas in the
, high labor and mining costs require higher-value ore for commercial operation, however, an infrastructure may already be available nearby. US
|Lost Lake volcanoclastic structure (circular depression with structural|
control and white carbonate-rich soil in center.
|Diamond Extraction mills were constructed in the Colorado Wyoming State|
Line district at the Sloan kimberlite and on the Kelsey Lake kimberlite
(above). Another portable mill was constructed on a trailer used at
Kelsey Lake and a fourth was built along the northern edge of Ft. Collins
by Cominco American. None of these were well designed and all rejected
many diamonds. This problem was documented at Kelsey Lake when a
company interested in purchasing the mine tested mill rejects. The first sample
processed yielded several diamonds (including a 6.2-ct stone).
This problem was serious as it basically resulted in questions as to what the
actual diamond grades of kimberlites were. How many
macrodiamonds were lost? Other gemstones (chrome diopside and pyrope
were all rejected at all four mills.
|14.2 carat diamond recovered at Kelsey Lake (Photo|
courtesy of Howard Coopersmith.
|620 carat diamond from African Craton.|
|Wyoming diamond with distinct trigons on its surface.|
|Arkansas diamonds (photo from Glenn Worthington).|
|Part of a day's diamond recovery from Argyle, Austraila in 1986|
|Diamond in matrix of Chinese kimberlite (GemHunter collection).|