Thursday, September 19, 2013

Diamonds in lamproite in the Leucite Hills, Wyoming and Ellendale Field, Western Australia

Boars Tusk lamproite (wyomingite) forms a distinct and prominent volcanic neck with Table Mountain in background
The Leucite Hills north of Rock Springs consist of a group of lamproite flows, dikes, volcaniclastics, scoria, and volcanic necks that contain some of the more unusual minerals found on earth and moon for that matter. Unfortunately, most of these minerals are microscopic.

Ellendale diamond-bearing olivine lamproite exposed in
dozer cut.
Similar rocks were identified in the East Kimberley, as well as the Noonkanbah and Ellendale volcanic fields in the West Kimberley region of Western Australia. Even though some of these lamproites had been studied and researched in detail, it wasn't until exploration of East Kimberley for a source of placer diamonds reported by gold prospectors in the late 19th century in that region that a rich diamond deposit was found (in 1979) in an olivine lamproite that became known as the Argyle diamond mine. Since then, the Argyle has been a source of many relatively small diamonds including some of the more valuable fancy diamonds. Some Argyle pinks have now sold for more than US$1 million/carat (pre-Biden prices). One thing of note was that the Argyle lamproite was olivine-rich and much of the olivine had serpentinized producing a soft rock at the surface that eroded faster than much of the surrounding terrain, thus it  hidden under layers of sediment.

Regional map of diamond and lamproite fields in Australia
Later, fancy diamonds were found and mined at the Ellendale lamproite field. Just like the Argyle lamproite, only the olivine rich lamproites in this field in the West Kimberleys contain enough diamond to mine. Again, much of the surface olivine had serpentinized producing a softer rock. Even though there were several exposed leucite lamproites in this field that stood out as hills and knolls (similar to the Leucite Hills), the diamond-bearing lamproites were hidden under a thin layer of soil. So, could a similar diamond deposit occur in the Leucite Hills? It should be noted that diamonds had already been recovered for decades in olivine lamproite at Murfreesboro, Arkansas. So, it only makes sense to search for similar hidden olivine lamproites in the Leucite Hills of Wyoming and in the lamproite and lamprophyre fields of Montana. Are there hidden diamond-rich pipes in Wyoming and Montana? Diamonds were later reported from a kimberlite near the Yellow Water Butte area of Montana - an area I highly recommended for exploration to a couple of mining companies in the past,  and later diamonds were discovered at the location.

In 1985, I collected a group of hand samples from one lamproite in the Leucite Hills of Wyoming, and these were processed and examined for diamonds using a binocular microscope. The chances of finding diamonds in such a small sample was very unfavorable (even it they actually occurred in the rock) as large bulk samples measured in tonnes are necessary for diamond testing. I was surprised when we recovered an exceptional, transparent, micro-octahedron with triangular growth platelets on the octahedral surfaces. Wow! Did we have a diamond? Unfortunately, the crystal was so tiny, that I could not measure its hardness with our primitive tools and I could not measure any surface conductivity. So, we had a problem trying to figure out if we actually had recovered a diamond from this lamproite breccia.

Dan Hausel (left) and Karl Albert (right) in the outback of Australia (1986)
Luckily, our lab technician knew that the Department of Physics at the University of Wyoming (just a few yards from our building) had an x-ray precession diffractometer. So, we took our tiny crystal to the Physics Department and the mineral turned out to be a transparent spinel rather than a diamond. Bummer! Anyway, I wanted to check to see if there was any possibility of diamonds surviving the hot lavas in the Leucite Hills at the earth's surface. So, I took one of our diamonds and broke it with a hammer and places one of the diamond shards in the flame of a Bunsen burner and after a short time, it exploded. Upon examination of the remains, I found carbon (graphite) had replaced the diamond shard. But the Bunsen Burner flame was very high temperature, so I deduced that diamonds could possibly survive in a hot lamproite magma. So after those experiments, I was off to Australia to examine the lamproites in the Kimberley region of Australia in 1986.

The Leucite Hills were one of my favorite places to visit when I worked at the Wyoming Geological Survey. After the discovery of diamonds in lamproites in Australia in the 1980s, the State Geologist -Gary Glass, was able to wrangle some money out of the legislature to visit the diamond deposits in Australia. The Aussie discovery should have sparked much greater diamond interest in Wyoming - particularly since the Aussies opened diamond mines at the Argyle and Ellendale and produced some of the most valuable diamonds (and gemstones) in the world - pink diamonds - some which have sold for  many tens of thousands of times more valuable than an equivalent weight in gold!

Black Butte lamproite peaks over horizon as if to
say, sample
 me, sample me!
One of the methods used to predict possibilities for diamonds in a lamproite is to test the chemistry of specific minerals found in the rock and then compare the chemistry of these minerals to the chemistry of diamond inclusion minerals (minerals actually found inside of diamond). One particular mineral that is often used is chromite. 

After processing samples from Endlich Hill in the center of the Leucite Hills, we recovered chromite. The chromites where tested for geochemistry using the UW microprobe and a few yielded favorable geochemistry indicating that those particular lamproites began their uprise from the mantle at a depth where diamonds were formed. Thus, this suggested to us that the Leucite Hills represented a good target for diamonds. Later, some researchers from the University of Wyoming repeated my results.

Anthill with a couple of gem-quality pyrope
garnets from
 Butcherknife Draw
So, you would think the legislature would provide the Survey with a little extra cash to do some serious testing. However, this is where we ran into problems. First one has to convince the State Geologist to ask for money. Most state geologists are politicians (although I worked for two excellent State Geologists: Dr. Daniel Miller and Gary Glass), one not so good, and the fourth one made Obama and Hillary Clinton look honest. In Wyoming, they have to declare political affiliation. This is a serious problem when considering science: politicians like to influence science to fit their agenda by offering bribes, grants, and other unethical donations to influence scientists who lack standards - take for instance global warming. We all know how much we can trust politicians whether republican or democrat

Anyway, one has to be able to convince the state geologist to ask the legislature for special funds for various projects and then the State Geologist must ask the legislator for funds and then hope the governor doesn't cut out the funding. I had no political skills and thus, the project died with no funding.

Boars Tusk at sunset
Anyway, one can still visit the Leucite Hills and the Butcherknife Draw area to the southwest and search anthills for pyrope garnet, chromian diopside, peridot and even diamond. At least I hope that's true as the BLM seems to think public land is their land. The Leucite Hills was a beautiful place with some nifty wild horses and few people when I worked in the area.

Even though I didn't find any diamonds (I never got a chance to take any bulk samples needed to test for diamonds), I did find a few thousand gem-quality peridot gemstones. I found peridot in the Leucite Hills in 1997. I did this by searching the Leucite Hills for olivine because of the close connection of olivine in lamproites and diamond in lamproites in Australia. All peridot is, it is a gem-quality olivine. But olivine had been known in the Leucite Hills for more than a century and even described by various research geologists. But, using blinders, no one had ever looked at the quality of the olivine and when I found two anthills covered in the olivine, I took them back to the Wyoming Geological Survey to examine the material for diamonds - no diamonds, just a few thousand carats of peridot!

Boars Tusk volcanic neck lamproite breccia
Southwest of the Leucite Hills, many gem-quality pyrope garnets and chromian diopsides were found at Butcherknife Draw and at Cedar Mountain. By the way, diamonds were discovered in a group of lamprophyres at Cedar Mountain by a couple of different mining companies and diamonds were also discovered in kimberlites in the State Line district south of Laramie and also in the Iron Mountain kimberlites near Farthing in southeastern Wyoming. AND, diamonds were later found in a kimberlite in the Yellow Water Butte area in eastern Montana. So, are there more diamonds deposits to be found in this region of the US - yes, but it will take someone with money to find most of the deposits.

If you would like to read more about the gemstones in this region, have a look at And then you will want to read about my adventures at
And for now, I'm out looking for gold in Arizona and breaking rocks in the east valley of Phoenix. And if you like some of my stories, lies, adventures and other stuff, I have other blogs on the internet and books.

Anyway, I enjoyed my work at the Wyoming Geological Survey and loved to go to work every morning. I had dozens of leads and many more ideas on where to find more gemstones in Wyoming and the western US and I believe I would have found many more diamond, ruby and sapphire, iolite, and gold deposits in Wyoming by now, as I had many areas (based on favorable geology and geochemistry) where some more deposits should be found.

And did I know what I was doing? Well, heck yah (at least that's what I'm going to tell you). Actually, there were times I didn't know what I was doing, but I persevered, drank some beer with some prospectors, went out by myself with my tent and 44 magnum and continued to look until I made a discovery and then told everyone I knew exactly what I was doing.  Now that's exploration!

Mt Gytha, Noonkabob lamproite field, Western Australia. Note the large layered sandstone xenolith in the side of this lamproite volcano.
Some gemstones I found including light green peridot from the Leucite Hills, red
to purple red pyrope garnet from Butcherknife Draw, and emerald green chromian
diopside from Butcherknife Draw.
Mining small diamonds with small equipment in Australia

And if you can dig the olivine out of the lamproite, or take them
from an anthill covered with fierce ants, this is what one can do - produce a nice,
faceted, peridot gemstone. Can you imagine, these were examined
by geologists for more than 100 years, even described in professional papers
and books, yet nobody ever noticed they were mostly gemstones.
A few things I immediately noticed when I visited Australia is their rabbits hop higher and are much larger than Wyoming's - they also spoke a strange dialect of English - but after a few Aussie beers, it didn't matter. Here is the Argyle diamond mine as it appeared in 1986. It is much deeper now.
Olivine lamproite from Black Butte, Wyoming. Note the large olivine crystal in the sample - about 0.4 inch across.

Lamproite breccia, Wortmans dike, Leucite Hills
Lamproite scoria from Zirkel Mesa in the Leucite Hills.
A diamond in the rough - wild horses in the Leucite Hills. It is tragic, but the BLM has done its best to eradicate these horses. Even still, a few of them survive.
Leucite Hills from the south. One can never have enough volcanoes
Emmons Mesa, Leucite Hills

Kind of an ugly, uninteresting rock wouldn't you say? When this olivine lamproite was discovered at Argyle, Australia, it yielded some of the richest diamond ore on earth. I collected this particular sample from a zone that had an average grade of 6.8 carats per ton.
Badger's teeth lamproite breccia, Leucite Hills.

Pegmatitic lamproite from Walgidee Hills, Australia.

Diamond-bearing olivine lamproite from the Ellendale field, Australia
Chocolate diamonds from the Argyle lamproite, Australia. Are there similar
diamonds in a hidden lamproite pipe(s) in the Leucite Hills? We may never know.
Ellendale 9 diamondiferous olivine lamproite, Australia

Diamond Deposits by the GEmHunter
Great book about how to find Gemstones
Booklet about the Leucite Hills of Wyoming.  During 30 years of employment
at the Wyoming Geological Survey at the University of Wyoming, the GemHunter
published many more books, papers and maps than the entire geological survey combined,
discovered more mineral deposits than the entire university & geological survey and presented more
talks and field trips than the entire geological survey - yet, one State Geologist harassed
the GemHunter and more than a dozen other staff members until they resigned, ended
up on heart monitors, retired, transferred, or died.  Of a staff of only about 20 people, 3 people
died while being harassed by the director. The only investigation was by the Wyoming
Public Employees Association which reportedly delivered a 3-inch thick document of
complaints to the State Attorney and the Democrat Governor. It was said that both didn't even
bother looking at the complaints and tossed the document into the garbage in front of the WPEA
representative.  So, is the GemHunter mad about this - NO, of course not, at least he got away
with his life. So, why no investigations?

Typical leucite lamproite with considerable mica, Leucite Hills.

Gem peridots from the Leucite Hills, Wyoming

pyrope garnet faceted from gem material from Butcherknife Draw, Wyoming

Below - GemHunter (right) with Caleb King outside the DiamonEx Ltd USA office 
in Laramie where I searched for diamonds in the 1970s, 1980s and then
again in 2006-2008 with Caleb.

Hey, that good-looking guy is me mapping in the Leucite Hills in 1997. And I do get back to Wyoming
 periodically to consult on various diamond, gold and gemstone projects as well as to visit my beautiful daughter and fantastic son and grandkids.

Thursday, September 15, 2011

The Search for Diamonds In the Leucite Hills

Note that all the members on our field excursion to the outback
found the only two boab trees for hundreds of kilometers around
and at temperatures of 120 degrees F and above, shade was
at a premium.
I ended up looking for diamonds in the Leucite Hills: one indicator mineral for diamonds in lamproites is olivine. There is a correlation between the amount of olivine in lamproite and the possibility of finding diamonds that was recognized by Australian geologists several years ago.

When I visited the Ellendale lamproite field in Western Australia in 1986, some things were notable - first, it was hotter than Phoenix (but not by much). And the second was that there were a lot of leucite lamproites in the district that were similar to those in the Leucite Hills.

But then there were a couple of other interesting rocks in the Ellendale field that were not exposed at the surface. This was because these particular rocks had considerable olivine. The olivine serpentinized over geological time resulting in the breakdown of the rock. These olivine rich rocks were also diamond-bearing rocks that were buried under thin layers of soil in the outback.

These hidden lamproites were found under a few inches to a few feet of dirt because of the serpentinization process (serpentinization produces some magnetite that can be detected by magnetic geophysical surveys). Over the years, when I was at the Wyoming Geological Survey, I periodically had prospectors stop in my office with possible apple- and emerald-green jade specimens. They were curious as to why their jade was so soft. I would get out a magnet and show them that the samples contained pockets of magnetite (the rock was magnetic), and this was due to serpentinization that results in some iron separating from the magnesium silicates and reducing to magnetite. The remaining magnesium silicates are relatively soft.
Black Rock butte lamproite plug seen in the background.

But this magnetite is strong enough to result in a magnetic signature over a hidden lamproite pipe. And soon, an Australia company searched the Ellendale field and found hidden lamproites. The hidden lamproites all contained diamonds, unlike the lamproites exposed on the surface, and this was because of the correlation of the olivine, serpentinzation and diamonds.

So when I returned to the Leucite Hills, I started searching for olivine. This is how I made the discovery of more than 13,000 carats of peridot in just two anthills at Black Rock.

Then I started sampling some of the olivine leucite lamproites in the area as well as volcaniclastics for diamonds and indicator minerals. AND we recovered diamond-stability chromites from lamproites in the northeastern portion of the Leucite Hills. Diamond-stability minerals have the same chemistry as mineral inclusions found in diamonds - thus, it is thought that such minerals formed at depths in the earth where diamonds exist. Finding such indicator minerals suggests these rocks originated within a portion of the earth's mantle that has diamonds - so it is very likely one will find diamonds in the Leucite Hills (if only someone will seriously look).

But let's use Ellendale as an example. The real rich olivine lamproites in this area are also going to be serpentinized and the host rocks hidden. Where? If I were to search this area, I would start with aerial magnetic/conductivity surveys and start mapping out geophysical anomalies in the northeastern portion of the Leucite Hills. I would bet that there are hidden lamproites in this portion of the field and possibly further north under some of the dune fields.
Ellendale field with termite mound in foreground

So why doesn't somebody look? Good question. I tried to get the Director of the WGS to ask the legislature for funding for an airborne survey before I realized this guy was not in this position for the science. So, it never got done. Over the years while I sampled and mapped this region, I did recover one excellent, transparent micro-octohedron with surface trigons. Was it a diamond? Who knows?

Don't like me on Facebook or anyone else. These guys can't tell the difference between facts, opinion, and propaganda. Then there is Bill Gates, Fauci, Biden, and many others.

Thursday, February 12, 2009

Self-Guided Field Trip to the Leucite Hills & BUTCHERKNIFE DRAW, SW WYOMING in seach of Gemstones


The Leucite Hills, north of Rock Springs, Wyoming, are a great place to visit and examine the physical geology related to rare volcanic eruptions. The rare volcanics in this region are known as lamproites - ultrapotassic mafic volcanic rocks that are closely related to kimberlites. These are so rare that some of the volcanics were originally identified as 'Wyomingite', until it was discovered years later that similar rocks had been found in Western Australia and were also given local names in Australia. Thus in the 1980s, it was decided that all such lamproites would be named by their mineralogy - e.g., Wyomingite would be better known as a phlogopite lamproite.

This volcanic field has 22 flows, dikes, necks, plugs, cinder cones and pumice cones along the northern flank of the Rock Springs uplift. The flows are thought to range from 3.1 to 0.9 million years in age.

The volcanic rocks are lamproite. These are some of the rarest rocks on earth and classified as ultrapotassic to ultrabasic with 42.65-56.34% SiO2; 2.52-12.66% K2O; and 5.8-12.75% MgO. Individual flows are limited and typically 50 to 122 ft thick. They include vesicular lavas, scoria, intrusive breccias, lapilli tuffs, tuff breccias and agglomerates of diopside-leucite-phlogopite-lamproite, diopside-sanidine-phlogopite-lamproite, and diopside-madupitic lamproite. Vents are associated with most flows, although vents are not conspicuous at South Table Mountain, North Table Mountain, Black Rock or Hatcher Mesa. Either the vents were removed by erosion, or buried by lavas which is not uncommon for lamproite eruptions.

Microscopic studies show the rocks are unusual. They have diopside, phlogopite, titanian-potassium-richterite, leucite, sanidine, wadeite, priderite, and/or olivine, with minor apatite, perovskite, ilmenite, armalcolite and spinel. Typical 'kimberlitic' indicator minerals are rare although diamond-stability chromite was found in flows in the northeastern part of the field.

Some common xenoliths (foreign rock fragments) are found in lavas. Most are fragments from the underlying Green River Formation. Granitic xenoliths are common and some arkose, tuffaceous sandstone, argillite, siltstone, gabbro, and anorthosite are reported. Cognate xenoliths include lamproitic fragments of earlier flows. Phlogopite-chromite harzburgite, orthopyroxene amphibolite, clinopyroxene-rich pyroxenite, and mica-rich xenoliths are described.

Zirkel Mesa baked zone (red) where the overlying hot
lamproite lava baked the underlying mudstones and shales.
Cognate xenocrysts include olivine with reaction rims of phlogopite, chromite with similar reaction rims and green spinel. Sediment samples collected adjacent to Endlich Hill by the author yielded one pyrope garnet. Considerable amounts of gem peridot was collected around Black Rock by the author. For those hunting gemstones, pay attention to any flow that contains olivine and search the rocks and sieve nearby soils!

The field trip log begins at the BLM parking lot at the north end of Rock Springs along Highway 191.


mileage fromRock Springs (with Description) 0 miles -  BLM parking lot on Highway 191.
8 miles - Approximately 8 miles north of the BLM office, note the Tri-territory road #216. Turn east.

9 miles - Cross old railroad grade and turn north. This grade was a captive railroad spur of U.S. Steel Corp which used the spur to ship 5 million tons of taconite pellets/year from the Atlantic City iron mine near South Pass. The Geneva Steel blast furnaces near Provo Utah. The mine and spur were active from 1962 to 1983.

12 miles - Continue left at "Y" in road.

22 miles STOP 1.  Fifteen Mile Knoll is a low-lying hill north the road intersection. The hill is capped by pediment gravel with pebbles of quartzite, schist, sandstone, metagabbro, epidotite, jasper, and agate. North of Fifteen Mile Knoll is a prominent volcanic neck-Boars Tusk. Matthews Hill, another volcanic neck forms a low-lying hill to the right of Boars Tusk. Behind Boars Tusk on the horizon, are the snow caps of the Wind River Mountains. Directly behind Boars Tusk are dunes of the Kilpecker Dune field which lie on Wasatch Formation sediments. The Kilpecker dune field lies on a major active shear zone in sedimentary rock. The Nitch Gulch oil field can be seen NE of the dunes, and a little farther NE is Steamboat Mountain with a visible cinder cone on Green River Formation rock. Approximately due east is North and South Table Mountains: lamproites located on Fort Union Formation shale and sandstone. South of Table Mountain is Endlich and Hague Hills on Almond Formation (Cretaceous) sediments.

Endlich Hill is composed of olivine orendite and is a good target for diamond. The rocks have more than one population of olivine. In addition to xenocrysts and microphenocrysts, the lamproite has anhedral olivine mantled by phlogopite (out of equilibrium with the host magma) and represent upper mantle xenocrysts.

To our west, the promient white, Green River Formation supported cliffs of White Mountain are visible. Pilot Butte, the western-most lamproite in the volcanic field, can be seen rising above White Mountain. Madupitic lavas from Pilot Butte lack in chrome spinel and suggest this lava to be a poor target for diamond. Moving on, take the east fork of the Y prior to turning north at first trail to Boars Tusk.

25 miles - Matthews Hill is a remnant of a volcanic neck that forms a low, rounded knoll rising 40 feet above the surrounding terrane.

28 miles STOP 2. BOARS TUSK. Boars Tusk forms a prominent volcanic neck of wyomingite (phlogopite-leucite-lamproite) rising 300 feet above the valley floor. The neck is an agglomerate with abundant Green River and Wasatch Formation xenoliths & autobreccia fragments of lamproite. In addition some granitic xenoliths are found. Continue east towards Table Mountain.

37.5 miles Continue past the Westpine Canyon oil field turnoff on the right & pass Table Mountain on the south. Table Mountain consists of North Table Mountain, Middle Table Mountain, and South Table Mountain. North Table Mountain is a volcanic mesa capped by a single flow that exhibits well developed flow layering.

On the southern margin of North Table Mountain is a small volcanic plug known as Middle Table Mountain. South Table Mountain is the prominent mesa behind (southeast) North Table Mountain. Olivine phenocrysts in the rock led to this rock being named olivine orendite.
The lamproites at South Table Mountain are MgO-rich due to presence of phenocrystal and xenocrystal olivine.

48 miles Turn left onto County Road 83 to Steamboat Mountain.

51 miles STOP 3. STEAMBOAT MOUNTAIN Overlook of Leucite Hills. Looking south (L to R) are Black Rock, Spring Butte (in the distance is Black Butte), Zirkel Mesa with its five cinder cones, Hatcher Mesa (flat top butte in front of Emmons Mesa) and to the right is Deer Butte on the skyline (Aspen Mountain lies between Emmons & Deer Buttes on the skyline). Emmons mesa is made up of a cone and two flows.

Rocks from Streamboat Mesa are vesicular flows. Only sedimentary xenoliths have been found here. A glassey sample of wyomingite (lamproite) from this mesa yielded 12.66% K2O indicating this lava is one of the most potassic lavas in the world. Backtrack down the mountain and turn east (left) on Tri-territory Road.

56.5 miles - Intersection, turn east.

59 miles Turn on jeep trail to right towards Black Rock.

60 miles STOP 4. BLACK ROCK. Black Rock forms the easternmost extent of the Leucite Hills volcanic rocks. Black Rock to consist of a basal pyroclastic olivine orendite tuff overlain by a lava flow. The top 80 feet of the mesa consists of alternating layers of vesicular and nonvesicular lava. In all probability, the mesa represents an lava flow which obscures hidden vent facies lamproites.

Half of the >13,000 carats of facetable
olivine (peridot) recovered from two ant
hills by the author. Too small to cut?
Look at some of the faceted gems produced
from these stones.
Small nodules of dunite have been found at Black Rock. Olivine occurs in the rock. During a cursory search for evidence for diamonds in this area, the author recovered two anthills with 13,000 carats of olivine. Most was peridot and gem-quality. The ants were able to collect material up to 12 mm in length and soils between the anthills and Black Rock are rich in olivine. Some olivine up to 0.5 inch across was found in the rock at Black Rock. Much of the material is facetable. Backtrack on jeep trail.

61 miles - Turn west (left) on Tri-territory road and continue south past Spring Butte. The butte is a compound volcanic center with six cinder cones, at least six flows, and three dikes. The cones consist of welded clastic flows with ribbon and breadcrust bombs.

71 miles - Deadman Gulch. Turn right towards Hatcher Mesa. Caution, this is a jeep trail!

79 miles - STOP 5. HATCHER MESA. Hatcher mesa is an eroded remnant of a small ponded lava flow. The center of the mesa is depressed by 6 feet relative to the edges indicating the surface sagged and the lava flowed back into the vent. The vent is not conspicuous. The mesa contains the most abundant and diverse assemblage of xenoliths and xenocrysts in the Leucite Hills. Petrographically, these rocks consist of microscopic clinopyroxene, phlogopite, apatite, and iron-titanium oxide with uncommon grains of olivine, in a groundmass of leucite, clinopyroxene, potassium richterite, apatite, priderite, wadeite, and glass.

Olivine grains from Hatcher Mesa are comparable to olivines in lherzolite and harzburgite in kimberlite.

84 miles - Return back to the Superior Road. Turn south towards Zirkel Mesa.

94 miles - Turn north on jeep road leading to south flank of Zirkel Mesa.

96 miles - STOP 6. Zirkel MESA QUARRY. Highly vesicular pumaceous leucite lamproite is exposed in the quarry showing flow banding with common country rock xenoliths. Locally, the lava has a ropey appearence.

Zirkel Mesa is the largest of the exposures in the Leucite Hills. Flow thicknesses vary from less than 3 feet to as much as 50 feet.

Six cinder cones which rise more than 240 feet above the mesa surface. These coelesce into a single, volcanic-capped plateau. K-Ar dates from two micas yielded 1.25 million year old ages.

Group of faceted peridot from Black Rock anthills. Note the
color variations and clarity. Although small, much larger
material should be found in the soil as well as outcrop in this
area. The presence of olivine in these lamproites and
recovery of diamond-stability chromite suggests the liklihood
of hidden diamondiferous lamproites in this region.

It was estimated in 1912 that 197 million tons of potash were available in the Leucite Hills. Liberty Potash Company quarried wyomingite from Zirkel Mesa during the war and operated a plant in Green River to produce

KCl for fertilizer.

This is the end of the field trip - Have a nice day.

Recommended Reading
Carmichael, I.S.E., 1967, The mineralogy and petrology of the volcanic rocks from the Leucite Hills, Wyoming: Contributions to Mineralogy and Petrology 15, p. 24-66.
Coopersmith, H.G., Mitchell, R.H., and Hausel, W.D., 2003, Kimberlites and lamproites of Colorado and Wyoming, USA: Field Excursion Guidebook for the 8th International Kimberlite Conference, Geological Survey of Canada, 24 p.
Hausel, W.D., 2006, Geology & Geochemistry of the Leucite Hills Volcanic Field, Wyoming Geological Survey Report of Investigations 56, 71 p.
Hausel, W.D., 2009, Gems, Minerals and Rocks of Wyoming. A Guide for Rock Hounds, Prospectors & Collectors. Booksurge, 175 p.

Several gem-quality peridots (raw) found in the Leucite Hills of Wyoming.

Faceted peridot surrounded by raw peridot from the Leucite Hills of Wyoming. Olivine was known to occur in the Leucite
Hills for more than a century, but no one bothered to look to see if any of these material was gem-quality. Some well
known geologists and PhDs had looked at this, but missed the fact that nearly all of the olivine is gem-quality peridot.
All one has to do is open their eyes!
And if you would like to find some gemstones, I tell you
how I found dozens of gemstone deposits and even tell
you exactly where you can go (using GPS coordinates)
to find some gemstones and likely found some new gemstone
occurrences. All of this is in my recent book available at Amazon