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| State Line Kimberlite Province showing locations of (1) Radichal kimberlite & Mineral Indicator Anomalies, (2) the Iron Mountain kimberlite district, (3) Schaffer, Aultman, Ferris kimberlites, (4) Keslsey Lake Kimberlites (5) Nix kimberlites, (6) Sloan kimberlites, (7) Estes park kimberlites, (8) Boulder Kimberlite, (9) Boden diamond placer. In between these are several hundred cryptovolcanic structures with similarities to kimberlite pipes as well as more than 300 kimberlitic mineral anomalies. |
Research suggests that the Wyoming Craton encloses a world-class diamond province as well as major deposits of colored gemstones. The Wyoming Craton includes portions of Colorado, Nebraska, Kansas, Montana, Wyoming, Alberta & Saskatchewan, & encloses the two largest known kimberlite districts in the US & the largest lamproite & lamprophyre fields in North America. Diamonds have been reported in kimberlites and lamprophyres in this craton in Canada, Montana, Wyoming, Colorado and Kansas.
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Research suggests that the Wyoming Craton encloses a world-class diamond province as well as major deposits of colored gemstones. The Wyoming Craton includes portions of Colorado, Nebraska, Kansas, Montana, Wyoming, Alberta & Saskatchewan, & encloses the two largest known kimberlite districts in the US & the largest lamproite & lamprophyre fields in North America. Diamonds have been reported in kimberlites and lamprophyres in this craton in Canada, Montana, Wyoming, Colorado and Kansas.
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| Winkler Crater in Kansas with two trenches dug to sample the material. Originally classified as an impact crater until it was verified by Doug Brookins to be kimberlite. Tested by Cominco American in the 1980s the pipe may have yielded one microdiamond, but there is concern that the diamond may have been contaminate from the State Line district. |
Hundreds of kimberlites, lamproites and lamprophyres were identified over the past few decades. In addition the many known diamondiferous kimberlites & lamprophyres, in recent years, four significant iolite (water sapphire) deposits were found as well as deposits of ruby, sapphire, opal, kyanite gems, jade, chromian diopside (Cape Emerald), pyrope garnet (Cape Ruby), almandine garnet, spessartine garnet, peridot, gem-quality apatite, jasper, agate, onyx and other gems - all found since about 1975. Two of the iolite deposits are world class. This region has turned into an exploration geologists' and rockhounds' paradise.
Hundreds of cryptovolcanic structures were identified by the Wyoming Geological Survey and also by DiamonEx Ltd within this province. Many are quite large and some situated within known diamond districts and within large areas that remain unexplored. In addition to the the known kimberlite, lamproite and lamprophyre districts, more than a dozen new districts containing many cryptovolcanic structures were discovered. As incredible as it seems, a few lie adjacent to interstates and highways and have been missed by millions of travelers every year.
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| Sloan 5 kimberlite in Colorado - note the exploration pits and also a distinct structural lineament along the right edge of the open park. Most kimberlites found in the Colorado-Wyoming province do not support woody tree growth, and often have a distinct grassy anomaly. (Photo by the author) |
During the past 30 years, the two largest diamondiferous kimberlite districts in the US and the largest field of lamproites in North America were mapped in the Colorado-Wyoming region. Several hundred kimberlitic indicator mineral anomalies were also scattered all over Wyoming, parts of Colorado, Utah, Montana, Kansas and Alberta. Other researchers found similar anomalies.
The several hundred cryptovolcanic structures have characteristics that suggest most are kimberlite pipes. They are circular to elliptical in shape, structurally controlled, many are distinct depressions with distinct vegetation anomalies similar to kimberlites mapped in the past. Some of the depressions are so distinct that they have actually been mistaken as impact sites, such as the Winkler crater in Kansas, that was originally thought to be an impact site, and later discovered to be kimberlite, and a few depressions that were identified in the central Laramie Range and Medicine Bow Mountains. Field examination of many depressions show visible blue ground and carbonate-rich soil, with rounded boulders and cobbles –characteristics that are generally associated with kimberlite. In addition, samples from some sites yield the traditional kimberlitic indicator minerals.
Historically kimberlite pipes were described in 19th century South Africa as having ‘blue ground’, considerable calcium carbonate, and were thought to be old dry stream placers because they contained rounded cobbles and boulders (similar to the cryptovolcanic structures found in the Wyoming craton). The rounded boulders were instead due to country rock fragments that had been rounded and polished in the kimberlite magma as it erupted a few hundred million years ago.
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| Diamonds from Arkansas - photo from Glenn Worthington |
A few of these structures may represent some of the larger pipes in the world. The best explanation for most of these depressions is that they represent soft, circular deposits of rock that is dramatically different from the more resistant and harder basement granite and gneiss country rock they intrude. Kimberlite typically erupts in circular maar-like volcanoes and is a relatively soft rock. This is why so many kimberlites discovered in Canada as well as in the Wyoming craton form distinct open, treeless parks, with several being submerged under shallow ponds and lakes.
Such structures have been found in the Laramie, Medicine Bow, Front and Seminoe Mountains, the Green River Basin, Bighorn Basin, eastern Kansas, and Alberta. Several hundred were found as far south as Denver Colorado, to as far north as central Alberta, and as far west as Little America to as far east as eastern Kansas. In the vicinity of the Colorado-Wyoming border, Hausel mapped the State Line district with more than 40 diamondiferous kimberlites. Some of these form distinct circular depressions and have already be verified as diamond pipes.
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| Beautiful, gem-quality diamond with 'trigon' growth platelets on surface - one of many characteristics of diamond. Photo courtesy of Star Diamond Corporation from their Star-Orion project, Saskatchewan, Canada. |
Unfortunately, only a few of the anomalies and the known kimberlites, lamproites and lamprophyres have been tested for diamond. But nearly all that have been tested yielded some diamonds. The State Line district alone produced more than 130,000 diamonds during testing in past years. No one really knows what awaits discovery here as past diamond testing was inefficient.
For example, the four diamond mills constructed to test various diamond deposits in the State Line district had many significant flaws & evidence supports that they only recovered a small portion of the diamonds. Even so, gem diamonds >28 carats were recovered along with a octahedral diamond fragment from a larger diamond estimated at 80 to 90 carats. But much larger diamonds were very likely missed by the mills, and these deposits likely contain hundreds of thousands of carats! In Wyoming, kimberlites yielded 50% high-quality gem diamonds. In Colorado, about 30% with gem-quality.
Little effort to outline this resource has been done by the respective state geological surveys in recent years. Research expenditures on diamonds in Wyoming, Colorado, Montana & Kansas has been nearly non-existent compared to the tens of millions of dollars spent for Canadian research along with the hundreds of millions in exploration by companies. Canada now has some commercial diamond mines developed since 1998 an others in the planning stages. In fact, state and federal agencies in the US, which should be conducting research, have only hindered research.
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| Group of gem diamonds recovered by Cominco America, from Wyoming kimberlites in State Line district (photo by the author). |
Past work has shown that nearly 50% of the diamonds in this craton have been very high quality gemstones. But at the pace that various government agencies are investing to outline this resource (currently non-existent) is shameful and little will happen until a major diamond is accidentally found by a prospector or rock hound.
In Canada, it typically takes $1.5 million per discovery (whether diamondiferous or barren).
KIMBERLITE PIPES
Hundreds of kimberlite pipes occur in a large group of 12 districts within a major diamond province in Colorado and Wyoming. Some of the recently discovered districts enclosed as many as 50 known cryptovolcanic structures (along with potentially dozens of hidden kimberlites).
Aerial photo showing one of the larger cryptovolcanic structures in North America at Twin Lakes south of Interstate 80 west of Cheyenne. This field includes >50 structures (kimberlites?) outline by distinct vegetation anomalies, depressions in silicate-rich Proterozoic age granites & gneisses in cratonized belt. Most have considerable calcium-carbonate soil (white bull's eyes),
rounded boulders, are structurally-controlled and located between the State Line and Iron Mountain diamondiferous kimberlite districts.
The Wyoming Geological Survey and DiamonEx Ltd discovered these in the State Line district, the Red Feather Lakes district, the Boulder district, the Happy Jack district, Horse Creek district, Iron Mountain district, Middle Sybille Creek district, Indian Guide district, Harrison district, Twin Mountain district, Eagle Rock district, King Rock district, Strong Creek district, Grant Creek anomaly, Lone Pine field, Lost Lake field, Creedmore Lake field, Chicken Park field, BG field, Lake Owen district, and the Douglas Creek district. Very few of these are tested but provide evidence for one of the largest kimberlite provinces in the world. IN the past, the author mapped the two largest diamondiferous kimberlite districts n Mountain and State Line) in this region.
LAMPROITE AND LAMPROPHYRE
One of the largest lamproite fields in the world (Leucite Hills) and one of the largest lamprophyre fields in North America (Missouri Breaks) occurs in this region, and few of these have been tested even though a group of lamprophyres near Cedar Mountain Wyoming contain diamonds and several lamprophyres have produced diamond-stability minerals, and evidence suggests that one of the largest lamprophyre fields in the world is located in southwestern Wyoming near the Leucite Hills lamproite field.
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| Estimated erosion level of kimberlite pipes in the Iron Mountain district (Wyoming) and State Line district (Colorado-Wyoming), based on morphology of pipes and dikes, and kimberlite facies. This model suggests about 2,000 to 3,000 feet of the richest parts of the upper kimberlite pipes were eroded and likely dumped hundreds of thousands of diamonds in adjacent drainages. Yet, only a few drainages were ever tested for diamond at Fish Creek, George Creek, and Rabbit Creek, and all three drainages contained diamond including two diamonds of 5+ carats. |
Placer diamonds are likely to be found all over the region, but little exploration has occurred. In the state line district, the kimberlites are deeply eroded providing geological evidence for a very large placer diamond population to occur in the adjacent draininges. To date, only a few samples have been taken in these drainages, yet placer diamonds as large as 6.2 carats were recovered in the past.
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| Airborne input geophysical survey of northern part of State Line diamond district. Several distinct EM anomalies were detected and suggest possible kimberlite pipes as well as a group of weak magnetic anomalies of interest. |
