Wyoming Garnets



Faceted pyrope garnet from raw material collected in
anthills at Butcherknife Draw, Wyoming

I remember walking into my first mineralogy class as an undergraduate at the University of Utah. The building was old; almost as old and dirty as some fossils in the museum on the other side of campus. But, when the mineral specimens were brought out – it brightened my image of the geology department. So much so, I spent six years studying geology, mineralogy, metamorphic and rare volcanic rocks prior to my sojourn to the  University of New Mexico in Albuquerque to continue a study of volcanic rocks and teach mineralogy. What would I do without rocks? What a wonderful gift these things are - some are pretty, and others are great for throwing. And not only that, we are related to rocks - yep, those same atoms found in me and you are also found in rocks and dirt, the only difference is that rocks a much of the time recluse and keep to theirselves until you get them together with a rock hound or geologist - and then they really start to talk!

Well-crystallized garnet in sericitized schist from Alaska

I've been particularly fascinated by well-crystallized beryl, pyrite, galena, calcite, diamond and garnet. How did God produce such perfect specimens? When well-crystallized, many garnets are beautiful, symmetrical, rhombic dodecahedral crystals that lead to pondering - how do they do that and how do they know where to place their crystal faces time and time again? The universe is amazing!

When transparent to translucent, some of these incredible garnet crystals can be manufactured (faceted) into beautiful gemstones. But centuries ago, since some garnets essentially had their own, natural facets (i.e., crystal faces), there was no need for additional lapidary work. Just mount the raw garnet in a necklace, crown, or ring as is!

If you look for garnet while rock hounding you’ll likely find them in schist or gneiss in the old mountain cores within the continental regions of Alaska, Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah and Wyoming. This is because many mica schists contain garnet in regions known as Cratons (which underlie much of these states). If you pan for gold, garnets will likely show up in the black sands; and if you attended a Wyoming Geological Survey field trip to Centennial Ridge, Douglas Creek, South Pass or the Sierra Madre in the past, you likely panned for gold and searched for garnet and diamond. On one trip to Centennial Ridge, a group of people visited the Middle Fork of the Little Laramie River to learn how to use a gold pan. No one found gold, instead we found dozens of pyrope garnets (a diamond indicator mineral). Wow, what could be better? Attend a free field trip and then take home some free gemstones. Don't you wish the government always worked like this instead of stealing everything from you?



Want a diamond mine? Attendees pan for gold at the Mother Lode placer on the Middle Fork of the Little Laramie River at Centennial Ridge. Instead of finding gold, all we could find were diamond indicator minerals (pyrope garnet), that suggest, somewhere upstream is a probable diamond deposit: pyrope transports only only 1.5 miles before complete disaggregation in rough terrain in the Rocky Mountains. To find a source of these garnets, all one has to do is to pan every few hundred feet upstream until they run out of pyrope (while keeping an eye out for diamonds). At that point, the source of the garnets would be somewhere upslope.

Then there were lectures on diamonds, These began with a discussions on Cratons: the very old continental core which is a great place to find metamorphic rocks. Rocks in the cores of most mountain ranges in Cratons, recrystallized over millions of years due to increases in pressure and temperature, to produce in metamorphic rock. Many metamorphic rocks have an abundance of mica. The more mica, the more likely you are to find garnet or some other porphyroblast (a large crystal in a metamorphic rock) of interest – such as ruby, sapphire, andalusite, staurolite, or iolite.

Just before I left the Wyoming Geological Survey, I was working on a project for exploration models to help prospectors and geologists find gemstones. It worked so well that Wyoming, once known as the ‘Jade State’, became known as the ‘Gemstone State’ in rock hound circles around the country. Now is is known to have the greatest variety of gemstones and semi-precious gems of any state in the US!

Garnet schist from Elmers Rock greenstone belt, 
 central Laramie Mountains. This aluminum-rich rock
and has common, iron-stained mica and nearly
20% almandine garnet as porphyroblasts.
A finger points to well-formed rhombic dodecahedral
garnet in the mist of dozens of garnets

I'm pretty sure, that my wife thinks I have rocks in my head. In some hardware and future stores, I just blare out, “Wow, look at this one, its filled with garnets – look at the transparency and color of these beauties – I wonder if these people know they are putting their coffee cups on gemstones? Wow, look at these tight and isoclinal folds: and a mini-fault to boot! Do you think the management would mind me taking a piece of their counter?”

Then there is the occasional anorthosite or syenite at Home Depot sometimes mislabeled as ‘Blue Granite’. Something that drives geologists crazy because it’s not granite! Anyway, these rock slabs are filled with gem-quality labradorite similar to material near the Game and Fish station in Sybille Canyon between Laramie and Wheatland. And in the road bed material along Albany County Road 12 - is amazing! Yes, labradorite and even some kimberlite. I always ponder if the rock cutters and polishers realized they could also be selling this stuff for gemstones?

But the same can be said of Wyoming. Billions of carats of labradorite gems and trillions of carats of the highest-quality water sapphire (iolite) should be promoted to industry to create jobs, assist chain gangs in sharpening sledge hammer techniques, and collect taxes from mining companies so Wyomingites can be free.

Gold from Douglas Creek, Wyoming. Note
the little reddish crystal sitting on the gold flake
in the pan (gold recovered by Paul Allred).
It’s another pyrope garnet that likely came
from another, hidden diamond deposit.

Some attractive garnets found in Wyoming were discovered in lamprophyres and kimberlites, and in alluvial debris shed from these rare volcanic rocks (notably stream gravels, anthills and the Bishop Conglomerate). The neat thing about these rocks is that you can sometimes find gem-quality garnet, chromian diopside, chromian enstatite and even diamond in them. Before we go any further, I’m sure you are wondering what in the heck a lamprophyre is. These are rare igneous rocks that geologists refer to as ‘ultrapotassic’ and ‘ultramafic’ igneous rocks that are often found as dikes and breccia pipes.  Many of you are likely familiar with kimberlite.

The terms ultrapotassic and ultramafic are geologists' jargon to impress the public that we probably know what we are talking about. They simply mean that a particularly magma had too much potassium and magnesium for the amount of silica such that when the hot magma cooled and crystallized, it produced potassium- and magnesium-rich minerals such as biotite, phlogopite, amphibole, pyroxene and olivine. After producing these minerals, no silica was left over to produce quartz (the most common mineral in the Earth’s continental crust).

Another important characteristic of lamprophyres is that some have diamonds –a few are very rich in diamonds. As a result, Dr. Ed Erlich and I highly emphasized this characteristic in a book on diamonds as we are convinced one day, commercial amounts of diamond will be found in some lamprophyres (Erlich and Hausel, 2002). When I investigated a group of lamprophyres in eastern Montana in the 1993 and 1994, I found indications of diamonds and highly recommended to the companies that they acquire the land – they ignored my recommendation. Years later, diamonds were found right where I said they would be discovered. What was that old saying? “You can lead a horse to water, but …”.

During the 1990s, a group of breccias were discovered along the southern edge of Cedar Mountain by Angola Diamond Company near the southwestern edge of the state (Hausel and others, 1999). These are thought to be lamprophyres and are responsible for some of the hundreds of thousands of pyropes, spessartine and almandine garnets, diopsides and enstatites in sediments, dirt, streams and anthills over a more than 250 square mile region in the Green River Basin. And as we had expected, diamonds were also recovered from these pipes by at least three different companies confirming this new diamond discovery (Hausel, 1998).

This ‘diamond indicator mineral anomaly’ is so widespread in southwestern Wyoming, northwestern Colorado and in the Uinta Mountains of northeastern Utah that the only way it can be explained is by the presence of a major lamprophyre and kimberlite field. In other words, there are likely dozens of hidden lamprophyres (and possibly kimberlites) in this region, some with diamonds and other gemstones. So why doesn’t the Wyoming do something? Well, why does the government spend $trillions more than it takes in to bankrupt itself? The answer is simple. The people we elect can talk non-stop without using their brains. In fact, most are dumber than a shoe!

Map showing location of the Cedar Mountain lamprophyres and Green River Basin
 kimberlitic indicator mineral anomaly (anthill garnets, chromian diopside, and even
a few diamonds) (from Hausel, 1998; Hausel and others, 1995). However, this map
 does not quite do justice to the extensive indicator mineral anomaly as it is much
larger than shown.

The anomaly is found covering a large portion of Butcher Knife Draw area northeast of Cedar Mountain. Kimberlitic indicator minerals (including pyrope garnet and chromian diopside) are also found in streams in the Uinta Mountains in Utah and even on top of Diamond Peak in northwestern Colorado (McCandless and others, 1999) at the site of the Great 1872 diamond hoax (Hausel and Stahl, 1995). I tried for years to get the State of Wyoming to invest in a project to find these and other diamond deposits in Wyoming, but could never get support – another of many examples of the State ignoring its mineral wealth. Wyoming could have major diamond, colored gemstone (not to mention gold, copper, rare earth, tungsten, and platinum group metal) industries that would produce hundreds of jobs and more tax money than a politician could collect in kickbacks at a brothel. Because such a project is what explorationists call “grass roots”, companies will not invest in these due to expenses that typically is incurred by government research agencies. It is just too expensive and too risky for mining companies. Government has to lead, something that it is not very good at.

Over the years, I led many public field trips to the Green River Basin to show the public the potential of the area and to teach them what to look for in this region, but the pipes are very difficult to identify and may require detailed exploration geophysics.



Me, the GemHunter showing off ants that love to
mine pyrope garnet, almandine garnet, spessartine
garnet, chromian diopside, chromian estatite
and occasionally a diamond or two.

The author shows field trip attendees what to look for and how to prospect for gem-quality garnet in the Green River Basin.

The ants in the Green River Basin are gemologists – they know where the good stuff is and they collect these beautiful stones to decorate their dwellings. Working together in pairs and larger groups, ants can recover sizable gemstones. Some gem-quality peridot found in the Leucite Hills to the north was as large as 20 millimeters across – not bad for a tiny ant. Anyway, these stones are facetable, and cutters in Sri Lanka and India specialize in cutting tiny stones, which is where I sent the stones only cost about $1 per stone to cut.

Faceted garnets collected from the anthills
in the Green River Basin.

If you would like to visit the Butcher Knife Draw, search Google Earth for “Butcher Knife Draw, Green River South, WY”. To find Cedar Mountain, search for “Cedar Mountain, Green River South, WY” and the lamprophyres were found along the southwestern edge of the hill near Lone Tree.

There are other places in Colorado, Montana and Wyoming with garnets. The kimberlites in the Colorado-Wyoming State Line district have some extraordinary diamonds as well as fabulous gem-quality pyrope garnets and chromian diopside that had been overlooked by nearly everyone. Why companies get so focused on one commodity and forget to look for others has always puzzled me. The Colorado-Wyoming kimberlites produced nearly 130,000 diamonds from very limited sampling: 30% more than has been recovered from the olivine lamproites at Murfreesboro, Arkansas, where diamonds have been recovered for decades, yet no gem-quality pyropes or chromian diopsides were produced. So are there commercial diamond pipes in the State Line district? You can bet on it and companies should not only recover diamonds, they should also consider the other gemstones which are much more common than diamonds.

Group of gemstones collected from Anthills in Green
River Basin by the author.

Another great location which has a large resource of diamonds is the Sloan kimberlites in Colorado. These contain some of the nicest garnet and diopside gemstones you will ever see! And nearby, there are dozens and dozens of crypto volcanic structures, some of which are likely undiscovered kimberlites. I found more than 300 of these and as incredible as it sounds, these all remain unexplored for diamonds and other gemstones - an anyone of them could contain a King's ransom in diamonds.

 

As far as garnets are concerned, there are several varieties found around the world that vary in color, specific gravity, chemistry, and index of refraction. The pure end-members include pyrope, almandine, spessartite, grossularite, andradite, and uvarovite with dozens of hybrids. Most garnets can be thought of as a mixture of two or more garnets.

Group of kimberlitic indicator
minerals collected from the
diamondiferous Sloan kimberlites
in Colorado. All of the pyrope
(purple to reddish purple), almandine
(red to reddish-brown and pink) and
spessartine (yellow-orange) garnets and
chromian diopside (green) are gem-quality.
The black minerals are chromite
and ilmenite.

Some of the better crystallized garnets in Wyoming are located in the Sierra Madre Mountains – but these are not really garnets – they are pseudomorphs of chlorite mica that have replaced the former garnet, atom by atom, and accepting the garnets former crystal habit or shape.

 

A rare garnet found in the Sierra Madre just outside of Encampment. Actually this is densely packed chlorite mica that replaced a former garnet but kept the former crystal habit of the original garnet (Hausel, 2009, 2014). It is actually termed a chlorite pseudomorph after almandine garnet.

 

Most varieties of garnet have been found in Wyoming. However, the extraordinary rare bright green varieties that have trade names such as demantoid (chromian andradite) and tsavorite (vanadian grossular) have not been found in the Cowboy State, but are instead found on other continents (Hausel and Sutherland, 2005).  It doesn’t mean that they will not found in Wyoming, it could simply be because nobody has looked for these gemstones in Wyoming. It’s amazing what can be found in the state when someone looks.

 

In the Colorado-Wyoming State Line district,  garnets were first found in kimberlites years ago. When I visited the Kelsey Lake diamond mine on the border, I was immediately impressed by the hundreds of gem-quality garnets dumped in the mine tailings. The company would not let me take any samples of the tailings (they were accidentally throwing away diamonds in the waste and were planning to reprocess this material).



Oldman Chlorite pseudomorph after garnet, Sierra Madre.



Faceted garnet from Butcherknife Draw, Wyoming

References

Erlich, E.I., and Hausel, W.D., 2002, Diamond Deposits - Origin, Exploration and History of Discovery. Society of SME. 374 p.

Hausel, W.D., 1998, Diamonds & Mantle Source Rocks in the Wyoming Craton with Discussions of Other US Occurrences. WSGS Report of Investigations 53, 93 p.

 Hausel, W.D., 2009, Gems, Minerals and Rocks of Wyoming. A Guide for Rock Hounds, Prospectors & Collectors. Booksurge, 175 p.

Hausel, W.D., Kucera, R.E., McCandless, T.E., and Gregory, R.W., 1999, Mantle-derived breccia pipes in the southern Green River Basin of Wyoming (USA): In J.J. Guerney et al (editors) Proceedings of the 7th International Kimberlite Conference, Capetown, South Africa. p. 348-352.

Hausel, W.D., and Stahl, Sandy, 1995, The great diamond hoax of 1872: Wyoming Geological Association Resources of Southwestern Wyoming Guidebook, p. 13-27.

Hausel, W.D., and Sutherland, W.M., 2000, Gemstones & Other Unique Minerals & Rocks of Wyoming - A Field Guide for Collectors: Wyoming Geological Survey Bulletin 71, 268 p.

Hausel, W.D., and Sutherland, W.M., 2006, World Gemstones: Geology, Mineralogy, Gemology & Exploration: WSGS Mineral Report MR06-1, 363 p.

Hausel, W.D., Sutherland, W.M., and Gregory, R.W., 1995, Lamproites, diamond indicator minerals, and related anomalies in the Green River Basin, Wyoming: Wyoming Geological Association Resources of Southwestern Wyoming Guidebook, p. 137-151.

McCandless, T.E., Nash, W.P., and Hausel, W.D., 1995, Mantle indicator minerals in ant mounds and conglomerates of the conglomerates of the southern Green River Basin, Wyoming: Wyoming Geological Association Resources of Southwestern Wyoming Guidebook, p. 153-163.



Pyrope garnet from Butcher Knife Draw



Spessartine garnet from Butcher Knife Draw

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