Tuesday, April 12, 2022

The GemHunter State


Since Idaho is known as the Gem State, shouldn't Wyoming be referred to as the Mineral & Rock State, Gemstone State, Rockhound State, GemHunter State, and/or Prospector State? After all, once we began to take a close look at the geology in Wyoming from 1977 to 2007, hundreds of gemstone discoveries, gold anomalies, mineral discoveries and unique rock discoveries were made, providing this once, homogeneous, Cowboy State and Jade State with a long list of minerals, rocks and gems that were mostly unknown prior to 1977. 

So what happened to change things? The answer is, someone decided to look. Yep, that's all it took. And over 30 years, literally hundreds of new discoveries were made statewide, many in the middle of nowhere (which is just about any place in Wyoming), others were found along dirt roads, state highways, and even along the Interstate system. It's amazing what one can find when they actually take a look. And after discovering potentially a king's ransom in gemstones, I was in demand all over the continent for talks. 

Industrial and gem-quality macro-diamonds collected from
Wyoming kimberlites along Highway 287 south of Laramie.
This larger diamonds were extracted from kimberlite a about
5 years after the first micro diamonds were found in the area.
Starting in the 1970s, diamonds were accidentally discovered in kimberlite (a very rare igneous rock on the earth's surface) in Wyoming, after rock samples from a kimberlite were collected in Wyoming by Dr. M.E. McCallum and Chuck Mabarak from CSU in the Colorado-Wyoming State Line district. These were tested by the US Geological Survey in Denver. 

The samples of garnet peridotite nodules (another rare rock type) were trapped in the kimberlite magma as it rose from the upper mantle of the earth. The peridotite, enclosed in kimberlite yielded several, tiny micro diamonds from sample concentrates. Not sure why it took so long to find these since a prospector in Colorado - Frank Yaussi, was actually recovering diamonds (and gold) from a creek in Colorado adjacent to a quarry of serpentinized rock on the Sloan Ranch (Frank Yaussi, personal communication). It turns out that the rock mined from the quarry later proved to be kimberlite by McCallum and Mabarak.

Later, mining companies, recovered many gem-quality (and some industrial) diamonds from a group of kimberlites extending 2.5 miles north into Wyoming and about 10 miles south into Colorado.  All within a short district of US Highway 287 running from Laramie to Ft. Collins. Hard to imagine that all of those kimberlite volcanoes, with the diamonds and many other gems and unique rocks, remained hidden and untouched for so long. Part of the reason was possibly due to the Great Diamond Hoax of 1872, where people including civil war generals and even a US Senator, lost investments on a diamond scam that occurred west of this area. 

Kimberlite specimens containing hidden diamonds along with
visible chromian diopside and pyrope-almandine garnet gem
megacrysts. Sloan Ranch kimberlite, Colorado. Kimberlite is
considered to be one of the rarest rock types on the earth's
Did we find all of the kimberlite volcanoes and diamonds? Nope! Barely touched the surface, so to speak. Based on research by the Wyoming Geological Survey, hundreds of kimberlitic indicator mineral anomalies were identified in the region indicating the presence of hidden, eroding, kimberlite pipes all over the place. Some research by the Wyoming Geological Survey and later by DiamonEx Ltd, found more than 300 cryptovolcanic structures with characteristics similar to kimberlite pipes - only one of these was ever drilled! And there have even been some geophysical anomalies detected that are interpreted as buried pipe-like structures sitting adjacent to known diamondiferous kimberlite pipes. So, yes, there is still a lot of possibilities. Then there is the extensive diamond indicator mineral anomaly (along with a couple of diamond-bearing lamprophyres) found in a region of the Greater Green River basin extending from Green River and Rock springs, south to the Utah-Wyoming border, and extending into the Uinta Mountains in Utah north of Skinwalker Ranch. These are described in a number of reports by Tom McCandless, Bill Nash, Dan Hausel and others. 

A 24,150-carat iolite rough gemstone from Grizzly Creek. This giant, is actually tiny, when compared
to some of the larger iolites sitting in outcrop that are estimated to weigh more than one million

Possibly, the greatest gemstone discovery in Wyoming occurred in 1995, and led to similar discoveries in 2004 and 2005. In 1995, the author went looking for the source of a rock collected by Wyoming Geological Survey Industrial Minerals Geologist, Ray Harris (RIP). Garnet was misidentified in the sample, but instead, these red gems had characteristic crystal habits of corundum. After getting the location of the sample site from Harris, the author examined the Palmer Canyon locality in the Laramie Mountains for ruby and sapphire. Sure enough, some high-quality specimens of ruby and sapphire (both varieties of corundum) were recovered from the vermiculite schist. And while searching the area for other outcrops of corundum, gem-quality kyanite, and also gem-quality iolite (cordierite, also referred to as water sapphire) was found including a large, 1,714-carat, fist-sized rough gemstone of the highest quality! Palmer Canyon was a poly-gem deposit. 

A 1,720-carat iolite gemstone rough collected at Palmer Canyon
This incredible discovery lead to the identification of several varieties of iolite gems, along with ruby, sapphire and kyanite. After developing some concepts for an exploration model for iolite, the author began searching for other localities and nearly a decade later, predicted to location of iolite at Grizzly Creek, and found evidence of a potential world class deposit in the Sherman Mountains area of the Laramie Range. The Grizzly Creek deposit contained giant iolite gemstones, some likely weighing millions of carats that still remain in situ, because they were not possible to recover from the outcrop because of size. 

Grizzly Creek outcrop containing 
hundreds of thousands of carats of iolite.
he discovery of ruby and sapphire at Palmer Canyon led the author to search other reported sites of vermiculite schist in Wyoming and six of these contained ruby and/or sapphire. Thus, geological models often provide a means to find similar deposits in similar geological environments!

In 1997, I decided to get out of the office again and go search for possible evidence of diamondiferous lamproite similar to what had been found at Argyle and Ellendale, Australia a decade earlier. One of these, the Argyle, had extremely rich grades for a diamond deposit. Well, Wyoming has one of the largest known fields of lamproites, so I figured I would go have a closer look at the rock types. In particular, I was searching for olivine (also referred to as peridot) because the Aussies had determined this was the identifying mineral in lamproites that separated diamond-bearing lamproites from barren lamproites. 

One of the first olivine grains faceted showing 
excellent transparency. Leucite Hills, Wyoming

After a little searching and some mapping in Wyoming's lamproite volcanic field near Rock Springs, known as the Leucite Hills, sure enough, not far from Black Butte lamproite, I came across two green anthills. Wow, I was excited, here were two anthills that had so many specimens of olivine, that they were green - I examined the olivine with my 10x hand lens, and whazzooo!!! They were mostly gem quality! This was amazing! Since the late 19th century, geologists visiting the field had reported some olivine, but never in concentrations like this, and also, not one had even mentioned these minerals were gem-quality. Talk about wearing blinders when going to the field. So, I collected the two anthills, these were later processed in our laboratory, and more than 1,300 carats of gem-quality peridot were recovered. Why, thank you ants! But, didn't find any diamonds, but at the same time, to find diamonds, typically large bulk samples must be taken with a bulldozer - not the kind of money that we had for research. But a couple of chromites  recovered from a couple of lamproites had favorable chemistry for diamonds. So, Wyoming just needs to get someone interested in digging diamonds near Rock Springs. 
A group of raw and faceted olivine (peridot) collected from anthills in the Leucite Hills, Wyoming
discovery by the author.

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