|Raw diamonds from Arkansas (photo by Glenn Worthington). |
If you are interested in digging for diamonds, get a copy of
Glenn's book and video.
|The North America Craton. Dark gray areas are|
regions for highest potential for commercial
diamond deposits hosted by kimberlite pipes.
The light-gray area have lower potential.
|Panning for diamonds at undisclosed |
location in Wyoming
|Highwall of Kelsey Lake diamondiferous kimberlite breccia, State Line district, Colorado. Note|
the distinct, blue-gray color of kimberlite 'blue ground' intrusive rock, as opposed to the reddish
1.4 billion year old granitic rock. Photo by author.
To take advantage of the dispersion of kimberlitic indicator minerals, the size of samples are determined based on the environment. For example, where there is a general lack of active streams, much larger samples are taken compared to regions with active drainages. In areas with juvenile streams, samples are often panned on site to recover a few pounds of sample concentrates. Recovered indicator minerals are tested for chemistry using an electron microprobe to identify those that have higher probability of originating from the diamond stability field. The data are plotted on maps to facilitate evaluation.
|Depression over Maxwell diamondiferous kimberlite, |
one of a few hundred untested diamond pipes in
Colorado, Wyoming and Montana.
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 conductive kimberlite.|
|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 over the
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 at Kelsey Lake and a fourth was
built along the northern edge of Ft. Collins by Cominco
American. None 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 ore grades were. 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).|