Monday, December 23, 2013

Kimberlite and Lamproite - Host Rocks for Diamond

Chuck Norris's cousin, Vic, digs for hidden kimberlite under grassy vegetation
anomaly discovered by the Gem Hunter in the Iron Mountain kimberlite
district in Wyoming.
Kimberlite is very difficult to recognize. It is basically a potassic peridotite and comes in a variety of colors and textures. Most notable is green kimberlite due to abundant serpentinized olivine.

It typically erupts from a feeder dike complex at depth and rises to a pipe-like structure known as a diatreme and blows out at the surface like a canon under great pressure.


Hypabyssal facies kimberlites samples fro the Iron Mountain district, Wyoming. Note the large, rounded mineral grains - these are hematite -serpentine pseudomorphs after olivine. This type of kimberlite forms in dikes and at the 'blow' of the the kimberlite pipe.

Hypabyssal facies kimberlite, Masontown, Pennsylvania. This kimberlite dike is enclosed by black shale.
Almost looks like a basalt, but instead, this is a sample of Ison Creek kimberlite I collected in Kentucky. This is known as basaltic kimberlite.

Snap Lake hypabyssal facies kimberlite, Fort Smith, Canada.
 
 

Diamond-bearing diatreme facies kimberlite breccia from Lake Ellen, UP, Michigan.


You probably would never have guessed this to be kimberlite. This bleached, tuffaceous, crater facies kimberlite from the Iron Mountain district, Wyoming has some pyrope garnet and picroilmenite and looks more like scoria than kimberlite


IG3 Kimberlite from Iron Mountain. Another tuffaceous kimberlite.
 
The Ferris 2 kimberlite from Wyoming.
 

Large fractured chromian diopside (chrome diopside gemstone) megacryst in Sloan 2 kimberlite from Colorado. Gemstones like this are typically not recovered from diamond mines even though they are as beautiful as any emerald.
 

Kimberlite from the Victor pipe in Canada.

Saturday, October 26, 2013

How to Identify Diamonds in Nature

14.2 carat octahedral diamond from
Kelsey Lake, Colorado (photo
courtesy of Howard Coopersmith).
In addition to the type of diamond we see at weddings, other varieties of extremely hard natural carbon are known including carbonado (polycrystalline) and lonsdaleite (hexagonal). These are all forms of carbon, as is graphite. But carbonado and lonsdaleite are very rare combared to natural diamond (which in itself is very rare). For information on lonsdaleite and other natural forms of hard carbon, refer to Erlich and Hausel (2002). Only crystalline, isometric diamond (the kind of diamonds we buy from jewelry stores) will be considered.

In its simplest form, isometric diamond is an equal-dimensional mineral that may form six-sided crystals known to mineralogists as hexahedrons; but to prospectors, these are simply cubes. A more common habit (form) of diamond is the octahedron. To imagine what an octahedron looks like, try to visualize an Egyptian pyramid. Now imagine that pyramid surrounded by a crystal clear lake with its refection in the water. It would appear as if two pyramids were attached at the base: this would be an eight-sided octahedron.



Modified octahedron with many more faces.
Many octahedral crystals develop ridges on the octahedral faces resulting in crystals of trisoctahedral or hexoctahedral habit. Partial resorption of octahedral diamonds produce rounded dodecahedrons (12-sided crystals) with rhombic faces. Many dodecahedrons have ridges on the rhombic faces resulting in a 24-sided crystal known as a trishexahedron. Four-sided tetrahedral diamonds are sometimes encountered that are thought to be distorted octahedrons. Another relatively common form of diamond is a macle, or twinned diamond. Diamond macles appear as flattened triangular crystals. It should be obvious that diamonds have many crystal habits, so if you would like to know more about these, it is recommended to read Bauer (1968a) and Bruton (1978).



Most diamond surfaces will have growth trigons (equilateral triangles) and less commonly trigonal pits. And some will have hexagons (6-sided pits or raised areas. You are likely getting the idea that there are many complexities to understanding diamond crystal habits or shapes. But don’t despair. If the above information snowed you, just remember there is a simple instrument known as a diamond detector sometimes called a diamond detective that you can purchase on-line for a minimal price. It will tell you if you have a diamond or not by simply touching the crystal and pressing a button. Nothing could be simpler for a prospector, rock hound and even geologist and gemologist.
Magnified diamond surface showing several trigons.
Diamonds have distinct, brilliant, greasy luster that is likened to oiled glass. Often quartz is mistaken for diamond, but the dull luster of quartz is no match for the brilliant adamantine luster of diamond. Gem-quality diamonds can be translucent to transparent, colorless, green, yellow, brown, black and rarely blue or pink. Opaque and heavily included diamonds (bort) are used for industrial purposes and have little value.

Diamond is brittle, extremely hard (H=10 on the Moh’s scale), with a specific gravity of 3.5, and has perfect octahedral cleavage. Even though diamond is heavier than water, it is non-wettable (hydrophobic) and will float on water given the right circumstances. Some flotation devises have been designed to extract diamond using water’s surface tension. Being hydrophobic, diamonds are also grease attractive. This property is used to recover diamonds in many places around the world, where shaking tables are coated with grease to extract diamonds from concentrates run over grease tables with water. The grease, usually a mixture of Vaseline and paraffin in a 10:1 ratio, is coated on the shaking table surface.
 
Under ultraviolet light, many diamonds fluoresce pale blue, green yellow, and rarely red. This characteristic of diamond is used in many diamond mills, such as Sortex, which detects florescence from diamonds when they are x-rayed.

Since diamonds are extremely rare, it takes considerable effort and patience to find the gemstone. It has been estimated diamond occurs in concentrations of less than 1 part per million in commercial diamondiferous kimberlites. This means you have 999,999 parts of waste rock to run through to find that 1 part per million diamond only after you have searched and searched for the primary host rock. And not all kimberlites, lamproites and lamprophyres have diamond.

Sloan kimberlite, Colorado. This kimberlite contains diamonds as well as
other gemstones including Cape Ruby (pyrope garnet) and chromian diopside.
Years ago, it was common knowledge in the mining industry that only about 10% of kimberlites contained diamond (Lampietti and Sutherland, 1978; Hausel, 1998). This estimate was not quite correct as many other rocks at the time had been erroneously classified as kimberlite – and over the years, there has been a lot more kimberlites found (Hausel, 2008a). So the percentage of diamondiferous verses barren kimberlites is much higher than originally thought. But at the same time, the percentage of diamondiferous verses barren lamproites and lamprophyres is very low.

Iron Mountain kimberlite, Wyoming
The primary rocks that diamond is found in are known as peridotite and eclogite. These are rare mantle-derived rocks (nodules) that are actually sampled, or picked up by rare volcanic eruptions (i.e., kimberlite, lamproite and some lamprophyre). Thus the kimberlite, lamproite and lamprophyre magmas accidentally pick up these rare diamond-rich rocks at great depth and bring them to the earth’s surface in rare old volcanoes. Many of the diamond-rich nodules survive intact after being shot out of the earth’s mantle from depths of 90 to 120 miles, while others break up with their diamonds being diluted in the magma. As an example of how rich some primary host rocks are, one sample of eclogite from the Sloan kimberlite in Colorado contained an estimated 20% diamond! But kimberlite magma itself, was many times poorer in diamond than this eclogite.

No other mineral (other than gold) seems to elude correct identification by prospectors and rock hounds. This is because of a poor understanding of mineralogy and because most people tend to see things that don’t exist and let their imaginations run wild. After 30 years of working with the public and identifying samples for people almost on a daily basis, I only had two people who correctly identified diamond. Many hundreds thought they had diamond, but were seeing things that were just not there.

Iron Mountain vesicular? kimberlite, Wyoming. All of the
pores in this kimberlite may have been the result of either
abundant gas bubbles or alternatively, they could be the
impressions of minerals eroded out of the kimberlite, i.e.,
boxworks.
I have many stories about these prospectors and rock hounds that are both educational and interesting. One prospector called me from his truck at Jeffrey City and wanted to know what to do with all of the diamonds he had found. I was impressed: "How many did you find?" I asked.

"There are thousands all over the hill side!" He responded.

Being curious, I asked him, “How are you verifying these diamonds?"

"I just scratch the windshield on my truck, and they leave a nice scratch", he responded.

Being a wise ass, I asked, "Are you going to be able to see out your window well enough to drive home?"

Victor kimberlite, Canada.
He was right, diamonds will scratch windshields! Windshields are made of glass with a hardness of only 5.5 to 6 on the Moh's scale. This means many minerals will scratch windshields including pyrite, feldspar, corundum and of course quartz. One way windshield’s become pitted (scratched) during dust storms is due to all of the fine sand that is blown into the windshield.

Another prospector called and said he had been diamond hunting for years and never found any. After talking awhile he mentioned his method for diamond testing: "I simply put them on an anvil and hit them with a hammer!" He talked about all of the octahedral crystals he had picked up from streams and kimberlites in the Colorado-Wyoming State Line district (where several known diamond deposits occurred) but none were diamonds because they all failed his test!
 
 
 
A fairly inexpensive design for a grease table constructed by Jay Roberts at
the Wyoming Geological Survey. The light-bluish white coating is the grease
mixture. The problem with this material (particularly on a university campus)
was that we had to buy Vaseline by the case. We often received accusing
expressions from drug store employees assuming we were with a fraternity
planning for some weekend orgy.


A giant diamond from Africa - 620 carats in weight. This diamond was actually on display for a short time at Wiseman's
Jewelry in Laramie, where I was able to photograph the extraordinary stone.

I then explained to him about the difference between hardness and mechanical brittleness and that all diamonds will break when struck by a hammer. You could hear that sound of ... well, it sounded like muffled swearing in the background as he hung up.

In another case, I received a phone call from an individual who claimed to have found the largest diamond in the world just west of Cheyenne. According to an unnamed gemologist from Cheyenne, this crystal was pronounced to be diamond. But the gemologist suggested that before the prospector put it on and purchased a large mansion on the French Riviera, he should visit my office in Laramie for a second opinion.



I gave him directions to my office. It’s about an hour’s drive from Cheyenne, so I was surprised when he and his three family members were knocking on my office door about 30 minutes later. They were apparently anxious to cash in their millions.

The diamond discoverer introduced himself as ‘Jack’ and did not give a last name, and without further hesitation, opened a locked brief case chained to his wrist and showed me the ‘Star of Cheyenne’. It was fist size - about the same size as the famous Cullinan diamond. The Cullinan was by far the largest diamond ever found and weighed a whopping 3,006 carats and was recovered at the Premier Mine in South Africa. It was priceless and ended up in the Crown Jewels of England.



Kimberlite? Nope, some prospectors would call this kimberlite, but it is
actually a lamproite.
In the late 1970s, I had met Dr. Arnold Waters. Dr. Waters was at the time, the former Chief Geologist for DeBeers in South Africa and he told me that when the Cullinan was found, it had a distinct cleaved surface where part of the diamond had been broken in two during assent to the earth's surface in a kimberlite magma (volcano). He indicated the other half of the diamond could have been as large or larger, but was never found! Did it break off somewhere at great depth and still many miles deep in the earth? Did it make it to the surface and was missed by the sorters and ended up in the crusher where it made many little diamonds? It’s something to wonder about.
The ‘Star of Cheyenne’ was reluctantly handed to me. As soon as I saw it, I knew what it was, but decided to have a little fun. First I showed them how to test a mineral’s specific gravity by weighing the gem in water and then in air. I determined the crystal to have a specific gravity about 2.7 - too light for diamond (diamond's specific gravity at 3.5 is heavy enough it would show up with garnets and black sands in a gold pan). I also tested the hardness by taking a diamond chip and easily scratching a deep notch in the crystal. This resulted in an immediate protest by the family as they thought I was scratching their priceless diamond.

“Hold on!,” I exclaimed. “If this were a diamond, I wouldn’t be able to scratch it with a diamond chip, diamond has a Moh’s hardness of 10 and is the hardest known natural mineral, and it is very, very difficult to scratch a diamond with another diamond”. After I calmed them down and convinced them that they had an ordinary piece of rock crystal (transparent massive quartz), they left the office dejected and drove back to Cheyenne with visions of mansions and Porches fading. And I thought this was over.

The next day, I was contacted by one of our other geologists - Ray Harris (RIP) - who stopped in my office to tell me he had just received a call from a person in Cheyenne who had a probable diamond that he wanted to have verified. The person on the phone explained to him that they had already talked to me, but he and his gemologist decided that another opinion was necessary.

The diamond detective - yep, that's me when I was VP of US Exploration for DiamonEx Ltd, Australia. During exploration in Colorado, Montana, Kansas and Wyoming, we identified hundreds of cryptovolcanic structures that look almost like impact craters with the exception that these are structurally controlled - located on a fault or similar feature. Would you like more information from the Gem Hunter? Follow me on Facebook and link to my GemHunter website.
Ray went back to his office to await the family. I laughed to myself. Ray was a very good geologist, but he had a reputation as a klutz. He was famous for running into things, breaking things, and if anything could go wrong – leave it to Ray. One of my favorite stories about Ray took place at a staff meeting. Ray was holding a cup of coffee in his left hand. I notice this and decided to catch him off guard. So I quickly asked him for the time of day. Without hesitation, Ray rotated his wrist to look at his watch pouring his coffee into his lap. We all had a great time with Ray, but during his last year, he was bullied by his supervisor until he died. I will always miss Ray – he was a good friend.

Anyway, the Cheyenne family arrived with their gem. They talked about the gemologist’s opinions and their concern about my scratching the diamond. I don't know if Ray had ever seen a diamond in the rough before (few geologists had) and after examining the fist-size specimen with his hand lens, he decided to get a better look at the gemstone and carried it to his microscope in his adjacent lab with the family following him. Then it happened! He lost control of the sample and it crashed onto the floor shattering into dozens of pieces.

Ray told me the family turned white as ghosts. But Ray consoled them looking down at all of the pieces. “Well, guess it wasn’t diamond – it has conchoidal fracture”. The family scooped up the fragments of their precious quartz and went home, never to be seen again. When Ray told me about his event – I laughed, and pointed out to him that diamond (as well as quartz) has conchoidal fracture. Ray turned white. But don't worry - it was just a piece of quartz.
 
 

Friday, December 7, 2012

Kimberlite Pipes and Volcanoes


Would you like to see a kimberlite volcano erupt? Me too! Watch the following animation - but don't stand too close. These kimberlite eruptions are very explosive and at the point of eruption, likely have a gaseous emplacement temperature at the freezing point of water and velocities of Mach 3!!!

KIMBERLITE PIPE eruption.

Below are some photos of kimberlites, diamonds, books, etc.

High-wall with exposed diamond-bearing kimberlite breccia at the Kelsey Lake mine, Colorado. If you have Google Earth on your computer, search for 'Kelsey Lake, Colorado' to see the location of the blue ground to see this former diamond mine. Note the large angular rock fragments in the highwall - these indicate there was a tremendous amount of explosive energy during the eruption of this kimberlite pipe (photo by the author - Gem Hunter).

Diamond-bearing Schaffer kimberlite dike in Wyoming exposed in dozer trench in 1979 or 1980. Jay Roberts, geologist, stands in the trench for scale while I took this photo. The kimberlite is the gray-blue material. The reddish material in the foreground is sheared Proterozoic granite (Sherman granite facies).

Diamondiferous kimberlite from the Sloan 2 pipe in Colorado. Note the large, rounded pyrope garnet.  The Sloan kimberlites have identified diamond resources and remain mostly untouched. DiamonEx had acquired the Sloan property in 2007 under my direction, but the 2008 economic collapsed took its toll on world diamond prices, the company, and the world. The property was abandoned by DiamonEx, yet it likely still encloses hundreds of $millions in diamonds.

Kimberlite (Devonian) and Granite (1.4 billion years old) contact exposed by bull-dozer, Schaffer
kimberlite complex, Wyoming. Note how sharp the kimberlite contact is and there is no evidence that the granite was baked.

Maxwell diamondiferous kimberlite in Colorado - one of many kimberlite pipes and dikes in Colorado and Wyoming that still remains untested for commercial diamonds. Diamonds were recovered from a small sample from this pipe (C.D. Mabarak, personal communication).

Buried kimberlite dike in Wyoming - the kimberlite underlies the dirt in the right half of the photo where there appears to be thicker and slightly higher vegetation.

Diamonds in the US?  From Diamonds and Mantle Source Rocks in the Wyoming Craton - by W. Dan Hausel, 1998. The diamond-shaped figures represent reported diamonds. The triangles are kimberlite localities (open triangles are diamond-bearing kimberlites), squares are high-pressure volcanics similar to kimberlite, + are lamprophyres and lamproites, the + enclosed by a diamond is diamond-bearing lamproite, the white diamond is the location of the Great 1872 Diamond Hoax site, the dots represent kimberlitic indicator mineral anomalies of note.

Some of the high-quality gem diamonds from Kelsey Lake mine (photo courtesy of Howard Coopersmith).

Close-up of diamond surface with some of the distinct trigons etched in the surface.  Don't know how to identify diamonds? Its not all that difficult. If you do not have a background in mineralogy, all you need is the Diamond Detector - you can even make your own.

Popular book (129 pages) on diamonds in the US - you might be able to buy this at the Wyoming Geological Survey at the University of Wyoming - although that once productive agency has become as unproductive as most government agencies.




Book on rocks and minerals that also has brief information on diamonds and on kimberlite and lamproite. Available at  Amazon


Another popular book on gemstones (and diamonds) that the Wyoming Geological Survey forgot to reprint after the current edition was sold out. 
Gem kyanite from central Laramie Mountains (we found billions of carats of this gem - but it remains undeveloped). Some of this gem is found with iolite, ruby and sapphire in the central Laramie Mountains.





Free pamphlet on diamonds - this may still available in Wyoming.  If not, you can download a copy at the  GEM HUNTER website.
Rough diamond from Wyoming - wow, aren't these stone beautiful! Note how the gem has kind of a greasy luster. This is characteristic of diamond.




Exploration methods for kimberlite - this was one of the first diamond publications I published. I was excited about the publication and the work I did. For me, this was the perfect job with imperfect wages. But what the heck, you can't have everything.



Recent publication on geology of the Leucite Hills lamproites and possibilities of diamonds in the Leucite Hills lamproites in Wyoming (may or may not be available at the Wyoming Geological Survey).  I loved  working in this area. While conducting research on diamonds, we recovered diamond-stability chromites from some of the lamproites (this suggests the chromites formed under pressures and temperatures similar to that of diamond formation; thus there is a possibility for diamonds in this region).

Essentially all of the projects at the Wyoming Geological Survey were considerably underfunded and so was this one. Even though these rocks may contained diamonds, we were unable to test any material (other than a couple of rocks). Elsewhere in the world, there is a correlation between olivine and diamond content in some lamproites, so I was excited to find a couple of anthills with considerable olivine in the northeastern portion of the Leucite Hills. After looking at some olivine with a hand lens, it was apparent nearly all was gem-quality. So I took the two anthills in sample bags - and Robert Gregory processed the material (no diamonds were found), but we recovered 13,000 carats of gem-quality peridot from this sample!


Diamonds in the world - great book, but price is too high (don't blame me, I receive no royalties for this book and the publisher ignored our protests about the price - 374 pages.


Book  (42 pages) on a little known diamond-bearing kimberlite district in Wyoming. We didn't find any diamonds (found lots and lots of diamondbacks) - nor did we test any material for diamonds. However the geochemistry of all of the rocks showed that they all originated from the diamond-stability field and a couple of diamonds were reportedly found in the early 1980s by Cominco American.


Ruby from Granite Mountains, Wyoming. Specimen found by Eric Hausel.
Kimberlite 'diamond' Indicator minerals. These include pyrope garnet, spessartine garnet, pyrope-almandine garnet, emerald-green chromian diopside, picroilmenite (black metallic with white leucoxene crust) and two tiny black, octahedral chromites. Here is an example of how geologists miss gemstones. These were all recovered from the Sloan 2 kimberlite in Colorado when I was working for DiamonEx Ltd. Everyone working in this region for years focused only on the diamonds; yet these are all gemstones and can be faceted into beautiful colored gems while the chromites and picroilmenites could be fashioned into low-value gem cabochons.



Guide to finding gemsgold, diamonds and rocks in Wyoming. If you can't find it at the Wyoming Geological Survey, you can download a copy from the GemHunters website.

There are many gemstones in Wyoming. Most people would have laughed if you told them in 1975 that Wyoming had the greatest variety of gemstones in the US. In 1975, Wyoming had known jade deposits and some agates - but that was about all.

Over three decades, the more I looked, the more I found: dozens of overlooked gemstone deposits and evidence for hundreds more which included commercial gold deposits along with more than 100 gold anomalies.  It was my intention to continue this research along with educating the public to help YOU find gemstones, diamonds and gold using methods I found successful in finding a few hundred mineral deposits.

But morally and ethically, I could no longer work for the Geological Survey or the State of Wyoming, so I moved on. Since 2006, there have been no discoveries of new metal or gemstone deposits.

Follow us on Facebook and Gem Hunter and learn more about gemstones and gold.






Thursday, August 18, 2011

Colorado, Montana, Wyoming - a major diamond province remains overlooked

North American Craton with Wyoming Craton

Aerial photo over Twin Mountain Lake anomaly
A few of the Twin Mountain Lakes cryptovolcanic structures.
Note the white carbonate on the shoreline.


Hundreds of kimberlites, lamproites, lamprophyres, diamonds and cryptovolcanic structures have been identified  in the Wyoming Craton that lies under portions of Colorado, Kansas, Montana and Wyoming. Some of the larger targets were discovered in the Twin Mountains Lake district adjacent to I-80 between Cheyenne and Laramie by the author several years ago, and these remain unexplored. More than 50 cryptovolcanic depressions show structural control, carbonate-rich sediments (in an Archean crystalline terrain) and distinct depressions adjacent (east) of the State Line diamond district. These could potentially be kimberlites with untold amounts of diamonds.


Some Wyoming diamonds
To view these anomalies (some may represent some of the larger diamond pipes in North America) search Google Earth "Twin Mountains, Cheyenne West, WY 82059". I highly recommend that you also examine these on Virtual Earth in the Twin Mountains Lake - Twin Mountains area.