Saturday, March 15, 2014

Prospecting for Gem-Quality Garnet in the Cowboy State

Almandine garnet (about 1 inch in diameter) from the Teton
Range
Garnets occur in many Precambrian rocks in Wyoming and most are associated with mica schists. The garnets range from microscopic minerals to a few some that are fist sized. Yes, I found these interesting minerals in mica schists of Archean (more than 2.5 billion years in age) and Proterozoic age (600 million years to 2.5 billion years in age) in the cores of most of Wyoming's mountain ranges. But I also found them in a few 1.4 billion year old pegmatites (coarse-grained granites) in the Sherman Granite in the Laramie Mountains, and also found them in essentially every kimberlite I investigated. These kimberlite pipes also contain diamond, and most are thought to have erupted in the Cambrian and Early Devonian. 

Wyoming traffic jam (sketches by the GemHunter).
Many of the gem-quality garnets I collected in Wyoming, were found associated with diamond-bearing kimberlite pipes in the State Line district and Iron Mountain district in the Laramie Mountains and as detrital gems associated with stream sediments in the Miracle Mile area along the edge of the Seminoe Mountains district, and in sediments and anthills in the Green River Basin. These latter garnets are found in diamond-bearing lamprophres along the southern margin of Cedar Mountain, in the Bishop Conglomerate in the same region, and in anthills in the Butchknife Draw area near Cedar Mountain. I also recovered gem-quality garnets along with ruby and diamonds from the northern margin of Diamond Peak in Colorado - the site of the 1872 diamond hoax. This latter group of gemstones were actually 'salted' by scam artists.


A customer searching for gemstones in Wyoming

When I began mapping the Colorado-State Line district, I found several rounded and sheared pyrope-almandine megacrysts (giant crystals like this one sitting next to a .45 caliber cartridge. These ranged from several inches to about 2 inches across.





This is what the gem-quality pyrope garnets and their angry ants look like in the field.


Wow! All of these pyrope and chromian diopside gems were collected by Dick Kuchera from the group of lamprophyre diamond pipes on Cedar Mountain

Amazing how these ants in the basin pick up the gemstones - and my gosh, they
even cut them for you for a price.
 

Diamond indicator minerals associated with the Sloan kimberlite in Colorado. These two Sloan pipes have a considerable
 diamond resource associated with them, as well as all of these beautiful gemstones. Likely hundreds of millions of carats of
colored gemstones that companies always ignore.

Aren't these pretty? Garnets in schist from the Wrangell mine, Petersburg district, Alaska.
 


One of my favorite rocks - a kyanite eclogite I collected from the Aultman kimberlite in Wyoming. The nodule consists of chromian diopside, kyanite and garnet. I later found another of these that was about 5 times larger.
 
 

 


 
 

Monday, May 16, 2011

Wyoming Garnets


Faceted pyrope garnet from raw material collected in
anthills at Butcherknife Draw, Wyoming
I remember walking into my first mineralogy class at the University of Utah. The building was old; almost as old and dirty as some fossils in museum on the other side of the campus. But, when the mineral specimens were brought out – it really brightened my image of the geology department. So much so, that I spent six years studying geology, mineralogy, metamorphic and rare volcanic rocks before moving on the University of New Mexico to study more volcanic rocks and teach mineralogy.


Well-crystallized garnet in sericitized schist from Alaska

I was particularly fascinated by well-crystallized diamond, beryl, pyrite, galena, calcite and garnet. How did Mother Nature produce such perfect specimens? When well crystallized, many garnets produce beautiful and symmetrical rhombic dodecahedral crystals that are extraordinary(http://en.wikipedia.org/wiki/Rhombic_dodecahedron). 

When transparent to translucent, garnets produce beautiful gemstones (http://gem-garnet.blogspot.com). If you look for garnet while rock hounding and prospecting (http://planetnews-prospector.blogspot.com) you’ll likely find them in schist and gneiss in the old mountains of the continental regions such as in Colorado, Montana and Wyoming. This is because the vast majority of garnets are found 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 of your pan (http://searching-for-gold.blogspot.com); and if you attended one of my field trips to Centennial Ridge, Douglas Creek or South Pass, you likely had the opportunity to pan for gold and search for garnet and diamond. On one trip to Centennial Ridge, I took a group of people to the Middle Fork of the Little Laramie River to teach them some prospecting concepts. We did not find any gold in our pans, instead we found dozens of pyrope garnets (a diamond indicator mineral).


Want your own diamond mine? Attendees pan for gold at what was known as the Mother Lode prospect on the Middle Fork of the Little Laramie River at Centennial Ridge. Instead of finding gold, all we found were diamond indicator minerals (pyrope garnet). These suggest that somewhere upstream is a probable diamond deposit: pyrope transports only about 1.5 miles before completely disaggregating in the rough terrain of the Rocky Mountains. To find the source of these garnets, all one has to do is to pan every few hundred feet upstream until they run out of pyrope garnets (while keeping an eye out for diamonds). At that point, the source of the pyrope garnets would be somewhere up the hill. We found evidence for dozens of diamond deposits in the Medicine Bow Mountains and diamonds were found in Cortez Creek northwest of Douglas Creek, and recovered in drill core in the range during a search for gold by a mining company (http://diamondprospector.webs.com/exploration.htm).
For those who attended one of my talks in the past (http://danhauselauthor.pbworks.com/w/page/16733738/Award-Winning-Public-Speaker), particularly on diamonds (http://diamond1872.blogspot.com), I always began these with a discussion on Cratons: the very old continental core which is a great place to find metamorphic rocks. Rocks found in the cores of most mountain ranges in Cratons recrystallized over millions to billions of years due to intense pressures and temperatures resulting in metamorphic rocks. 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 (http://wyruby.blogspot.com), andalusite or iolite (http://iolite-wyoming.blogspot.com).

Just before I left the Wyoming Geological Survey, I was working on a project to develop exploration models to lead prospectors and geologists to gemstone deposits (http://gemhunter.webs.com/discoveries.htm). It worked so well that Wyoming was known as the ‘Jade State’ (http://dansjade.blogspot.com) prior to 1977, but with all of the new gemstone and mineral discoveries made over 3 decades, Wyoming became known as the ‘Gemstone State’ and now has the largest variety of gemstones and semi-precious gems (http://gemstonehunter.blogspot.com) of any state in the US (http://wygemstones.blogspot.com)!

Garnet schist from Elmers Rock greenstone belt
in the central Laramie Mountains of Wyoming
is aluminum-rich and has common iron-stained
mica and nearly 20% almandine garnet as porphyroblasts.
My finger points to a well-formed rhombic dodecahedral
garnet in the mist of dozens of garnets
My wife probably thinks I have rocks in my head from the comments I make when we arrive at hotels that have polished counters at the check in desk made out of gneiss. “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 signing into their rooms on gemstones? And look at these tight and isoclinals folds: here’s a mini-fault. 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 that is typically termed ‘Blue Granite’ that drives geologists crazy because it’s not granite. These are filled with gem-quality labradorite similar to the material collected near the Game and Fish station in Sybille Canyon of Wyoming and in the road bed material along Albany County Road 12. I always wonder if the rock cutters and polishers who mined these slabs realize they could also be making a profit selling discarded minerals as gemstones. Probably not.

But the same can be said of Wyoming. Billions of carats of labradorite gemstones and trillions of carats of the highest quality of iolite should not be so protected, but the government should promote its resources rather than being stingy.

Gold from Douglas Creek, Wyoming
(http://douglascreekgold.blogspot.com). 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 a nearby 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 a bunch of gem-quality garnet, chromian diopside, chromian enstatite and even diamond (http://diamondprospector.webs.com) associated with 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, but if you need information, visit my websites (http://diamondprospector.webs.com/kimberlite.htm)  (http://gemhunter.webs.com/diamonds.htm).

The terms ultrapotassic and ultramafic are jargon used by geologists to make the public think we 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) (see: http://en.wikipedia.org/wiki/Lamprophyre).

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 (http://www.cbsnews.com/stories/2004/10/19/tech/main650144.shtml). 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).


Drill core of breccia recovered from southeastern
edge of Cedar Mountain, Wyoming.

This ‘diamond indicator mineral anomaly’ is so widespread in southwestern Wyoming, northwestern Colorado and 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 several dozen or several hundred hidden lamprophyres (and possibly kimberlites) in this region, many with diamonds and other gemstones. So why doesn’t the government do something about it? Well, why does the government spend $trillions more than it takes in to bankrupt itself? The answer is simple. The people we elect are not nearly as smart as they sound.

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.


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 find many gem-quality stones.Working together in pairs, ants can recover sizable gemstones. Some of the gem-quality peridot (http://peridot1.blogspot.com) I found in the Leucite Hills (http://leucitehills.blogspot.com) to the north was as much as 20 millimeters across – not bad for a tiny ant. Anyway, these stones are mostly 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 comodity and forget to look for others has always puzzeled 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 (http://sloan-kimberlite.blogspot.com). These contain some of the nicest garnet and diopside gemstones you will ever see! And nearby, there are dozens and dozens of cryptovolcanic (http://discussionsondiamonds.blogspot.com) structures that are likely undiscovered kimberlites that remain unexplored for diamonds and other gemstones.
 
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). 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 (http://GemHunter.webs.com). 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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