Diamonds (Ice) and their Host Rocks

Ever wonder why diamonds are called 'ice'?  They kind of look like ice, but this is not the reason. Diamonds are heat conductors, so if you ever have the opportunity to touch your lips with a large diamond, it will feel cool as the diamond conducts heat away from your lips.


Diamonds are the most valuable commodity on earth based on dollar value per weight. Some have sold for many times the value of an equivalent weight in gold - such as the Hancock Red diamond that weighed only 0.95 carat & sold for nearly US$1 million. To put this in perspective, one carat weighs only 0.2 gram, which is equivalent to 0.007 ounce. Thus this diamond was valued at >300,000 times an equal weight in gold! Several other pink to red diamonds have also been valued at nearly $1 million per carat.


Other priceless diamonds have been purchased by Royalty or donated to Royal treasuries. Most notable were those cut from the Cullinun rough, the largest diamond ever found that weighed 3,106 carats in the rough. The gems faceted from this fist-size rough diamond are now proudly displayed in the crown jewels of England. 


Diamonds are found with other gems; however few companies ever bother with the associated gems even though many are extraordinary stones in their own right and even out-shine ruby & emerald. These other gems are known as Cape Ruby (pyrope garnet) and Cape Emerald (chromian diopside and enstatite), but their lower value than the diamonds results in the diamond mining companies ignoring these gems. This is unfortunate as many are beautiful colored stones.


So, where do diamonds come from? Diamonds are found in several rock types, but the primary commercial host rocks are kimberlite and lamproite [2]. And there are also secondary hosts known as placers that contain diamonds - like those found along the west coast of Africa. Diamond being extremely hard results in most gem-quality diamonds surviving transport in rivers, streams and even along coastal shores. Many coastal diamonds in Namibia are thought to have been carried by the Orange River over distances of as much as 600 miles from their source area.


The principal host for diamonds are rocks formed in the earth's mantle that are known as eclogite and peridotite that are carried to the earth's surface in magmas known as kimberlite and lamproite. The kimberlite magma, when solidified, is known as the rock kimberilte that often has many mantle and crustal nodules including eclogites and peridotites and was named after Kimberley, South Africa where many of the original commercial diamond deposits were discovered in the 19th century. Kimberlite magma ascends from the earth’s upper mantle from depths of 90 to 120 miles and then explodes at the earth’s surface to form small maar-like volcanoes and dikes. At the surface, the pipes (maars) appear as depressions and several have been mistaken for impact craters in the past - such as the Winkler crater in Kansas. Some occur as circular to elongate depressions with vegetation anomalies controlled by fractures, have blue ground (montmorillonite clay) and are so carbonate rich that their soils react to dilute hydrochloric acid by fizzing as they release carbon-dioxide gas. Most pipes are <0.5 mile in diameter.

 

Several hundred cryptovolcanic structures discovered in northern Colorado and southeastern Wyoming discovered by the author in recent years likely include some kimberlites. Only a few dozen have been examined in the field, and only one was ever drilled - so it is possible that there is a major diamond province in this region.

 

When I mapped Iron Mountain ('fly to Farthing, WY, 82009' on Google Earth where you will be 4 miles south of the district), State Line (use Google Earth to fly to 'Tie Siding, WY' where you will be located 3 miles north of the State Line district. Search search due south of Tie Siding along the State Line to see an elongated scar immediately south of Fish Creek, this is the former Kelsey Lake diamond mine) and Sheep Rock districts, as well as the Leucite Hills volcanic field, it was apparent that there likely were some hidden kimberlites and lamproites in these areas. In fact, in the State Line district, surface and aerial geophysical surveys identified buried kimberlite. The other districts were never explored by geophysical surveys for diamond deposits. The type of geophysics that seemed to work well included INPUT airborne surveys and EM ground surveys.

 

Areas that remain unmapped include Indian Guide (fly to 'Indian Guide, East Albany, WY 82201' & you will be 3 miles due east of the Indian Guide cryptovolcanic structures and due west of the Iron Mountain diamond district), Twin Mountain, Happy Jack & others where there are many cryptovolcanic structures that could be kimberlites. One of these areas known as Twin Mountain Lakes has 50+ cryptovolcanic anomalies within view of I-80 west of Cheyenne! Some may prove to be the largest kimberlites in North America if they can ever be tested. If you examine these on Google Earth, you will see circular to elongate depressions, some with apparent, white soils (carbonate). These are located within the Proterozoic Colorado Province formed of basement rocks including amphiboles and granites that are poor sources for carbonate. So the carbonates in these depression were derived from some other rock type (kimberlite?).

 

In the Happy Jack area, I identified a distinct depression many years ago that I named the Bowling Pin anomaly. Later, we found several other depressions nearby that included rounded granitic boulders and carbonate rich soils typical of kimberlite. While working for DiamonEx Ltd, we wanted to drill these anomalies, but the BLM would not grant us access so these remain unknown anomalies. 


Lamproites were mapped in the Leucite Hills in SW Wyoming: a few of these yielded diamond-stability chromites and could contain uncommon diamond. In one area, more than 13,000 carats of gem-quality peridot was recovered from just two anthills adjacent to one of these lamproites - known as Black Butte. This is exciting in that there is a strong correlation in diamond content and olivine (peridot) content of lamproites. But in most areas in the world where commercial diamond-bearing lamproites were found - such as the Argyle mine and also the Ellendale mine in Western Australia, the diamond-rich lamproites were eroded and buried by a thin layer of soil while barren to diamond poor lamproites with little to no olivine stood out as distinct volcanic hills. So, in the Leucite Hills, there is a good possibility that some diamond-bearing lamproites lay under a few inches to a few feet of soil.

 

Some lamprophyres also have diamond, such as the lamprophyres found at Cedar Mountain Wyoming and a few minette lamprophyres scattered around the world.


Many of the kimberlite and the lamprophyres have been deeply eroded. Those in the State Line district spilled millions of diamonds into the surrounding streams, but no one has ever systematically looked for diamonds in the creeks! Even so, with a trivial effort of placer prospecting, several diamonds were found in Fish Creek on the Colorado-Wyoming border including a 6.2 carat gemstone! In Rabbit Creek, Colorado next to the Sloan kimberlites, only very recently has someone panned for diamonds - and recovered several diamonds including one flawless gem of 5-carats! This area was originally prospected for gold in the 1960s by Frank Yassai who recovered gold and diamonds in the creek, but no one paid attention. Additionally, many placer diamonds were found in George Creek Colorado in the 1980s. Overall, less than 1% of the streams in the district have been prospected for diamonds and these likely host thousands if not millions of diamonds!


Kimberlite is a ultrabasic, potassic igneous rock that erupts along fractures from 90 to 120 mi depths. They typically occur in very old cratons (basically ancient continental cores that consist of >1.5 billion year old granite, gneiss & schist). The kimberlite magma rises rapidly from the mantle with considerable water vapor & carbon dioxide in the magma. Some suggest gaseous emplacement velocities are on the order of Mach 3. The eruption is relatively cool: CO2 gas expands to cool the magma such that emplacement temperatures of 32 degrees Fahrenheit are not uncommon. 


Keep in mind: kimberlite will serpentinize because of water vapor reacting with the abundant olivine in the magma, this produces a soft rock (serpentinite) that erodes faster than surrounding country rock & usually results in depressions that support different vegetation than surrounding rocks. These depressions may contain shallow ponds, or they may just be outlined by distinct vegetation anomalies. In the State Line and Iron Mountain districts, I mapped many kimberlites based on the lack of trees in forested areas that also had high stands of bluegrass with carbonate-rich soil and scattered kimberlitic indicator minerals (rounded pyrope garnet, rounded spessartine garnet, rounded almandine garnet, large hand-sized sheared and rounded almandine megacryrsts, emerald-green chromian diopside, chromian enstatite, chromite, rounded picroilmenite coated with white leucoxene, large hand-sized picroilmenite megacrysts, diamonds, rounded cobbles and boulders of granite, amphibolite and mantle nodules of eclogite, peridotite, pyroxenite, dunite, etc. These anomalies were always structurally-controlled such that more than one anomaly was found along lineaments. Because of calcium carbonate in kimberlite, carbonate will leach into a pond staining the soil white. In the craton basement (i.e., mountain ranges of Colorado, Montana, Wyoming) carbonate sources are rare, so if you spot a structurally-controlled lake surrounded by white soil in old Precambrian rock (in the mountains), you might want to find out why.

 

Diamonds found in Colorado & Wyoming ranged from microdiamonds to 28.3 carats & included one chip from a 80- to 90-carat stone. Some believe there are no commercial deposits in this area, but all 4 mills constructed in the past were poorly designed and rejected many diamonds of all sizes. For example, the Kelsey Lake mill was designed to reject anything weighing >40 carats! It also rejected a very large number of diamonds under 40 carats such that when the waste tailings were later tested in 1997, the first sample yielded a 6-carat stone!

 

The grades of some kimberlites were high, the gem:industrial ratios were good & diamond values were reasonable. The biggest problem with the State Line district was companies with diamond expertise was in short supply. Another problem appeared to be an overall lack of large diamonds (except at Kelsey Lake). Large diamonds are very important for commercial operations because of high value. If you are a fan of Gold Rush you will remember when one group of prospectors traveled to Brazil to mine gold and instead thought they hit it big with diamonds. If they would have known something about diamonds, they would have packed up immediately. Rough gem diamonds sell for $50 to $450 per carat (and may only average about $150 and the diamonds picked up on Gold Rush appeared to be smaller than a carat, thus they would have been very low value. After diamonds are cut, they can increase in value typically 2 to 5 times the rough value. When mounted in jewelry, we often see another value increase. But large diamonds like the one in the photo below (Figure 1) of 620-carats bring high prices and some large rough diamonds may fetch many thousands of dollars and in some cases $millions. Because of this, a working diamond mine needs large diamonds to offset the costs of building a mine and mill. 

 

Diamond is relatively easy to recognize, but there are very few prospectors, geologists or jewelers with experience in recognizing uncut (rough) diamonds. One of the easiest methods is to use a relatively inexpensive device marketed as a 'Diamond Detector' or 'Diamond Detective'. This measures the unique surface conductivity of a diamond. It is so easy to use that its rumored that even some politicians can be taught to operate this push one-button instrument.  

 

Diamonds are the hardest minerals on earth - the only other minerals that have similar hardness include lonsdaleite and carborado, both considered diamond polymorphs. Thus diamond will scratch essentially anything. But don't fall for that old trick of scratching glass.

 

Glass has a moh's hardness of only about 5.5 while diamond is 10. There are a lot of minerals inbetween these two (including quartz, the commonest mineral on the earth's surface) that will also scratch glass. This is why I thought it humorous when I received a call from a diamond prospector who claimed to have found thousands of diamonds - his method of testing was scratching his truck's windshield. Poor guy, I hope he can still see out his window. Diamonds also appear greasy, attract grease (which is one reason grease tables are used to extract diamond), and they have distinct growth plates on the crystal surfaces.


Associated with diamonds are a host of rare mantle nodules & gemstones (See Figure 2 in Gallery below) known as Cape Ruby (pyrope garnet), Cape Emerald (chromian diopside & enstatite) that are always overlooked by mining companies. Yet these are very attractive, value-added gemstones. With marketing, these could capture parts of the colored gemstone market. For example, many Cape Emeralds are more beautiful than emerald.


What surprises me the most - Wyoming has one of the largest kimberlite-lamproite-diamond provinces in the world that extends south into Colorado. Montana has a separate province as does Kansas. A potential multi-billion dollar industry that the state's are ignoring.


References Cited

Coopersmith, H.G., Mitchell, R.H., and Hausel, W.D., 2003, Kimberlites and lamproites of Colorado and Wyoming, USA: Geological Survey of Canada, Ottawa, Ontario>

Hausel, W.D., 2014, A Guide to Gemstones, Gold, Minerals and Rocks: GemHunter Books, 368 p. 

Hausel, W.D., 2006, Geology and Geochemistry of the Leucite Hills volcanic field, WGS report of Investigations 

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

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

Hausel, W.D., McCallum, M.E., and Woodzick, T.L., 1979, Exploration for diamond-bearing kimberlite in Colorado and Wyoming: an evaluation of exploration techniques: Geological Survey of Wyoming Report of Investigations 19, 29 p.

Hausel, W.D., Glahn, P.R., and Woodzick, T.L., 1981, Geological and geophysical investigations of kimberlites in the Laramie Range of southeastern Wyoming: Geological Survey of Wyoming Preliminary Report 18, 13 p., 2 plates (scale 1:24,000).

Hausel, W.D., Gregory, R.W., Motten, R.H., and Sutherland, W.M., 2003, Geology of the Iron Mountain Kimberlite District & Nearby Kimberlitic Indicator Mineral Anomalies in Southeastern Wyoming: Wyoming State Geological Survey Report of Investigations 54, 42 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.

HOW TO FIND DIAMONDS

If you decide to prospect for diamonds, first learn to recognize diamond and then watch your pan to see if you trap any diamonds with your gold. Diamond has a specific gravity of 3.5, and will concentrate with black sands. So when you are panning and you see a clear to white crystal in your pan in the middle of those black sands that has very distinct greasy luster, get out your hand lens and diamond detector and test the crystal. Diamonds have unique surface conductivity, which is why they feel cool to the touch (ice), and can be detected by diamond detector tests. All you have to do is switch it on and then touch the suspected diamond and if it reads "diamond", be sure to send it to me as a gift. Otherwise, if it reads "simulate" it is something other than diamond. These are so easy to use that with effort you can even teach a few politicians how to use them. To aid in your expertise in diamond hunting, buy some uncut, rough, diamonds to have in your personal collection for comparison and to assist in your mineralogy education.


Many placer diamonds have been found in California and Colorado in the past, and other diamonds have been identified in many States across the nation. It is likely hundreds of rough diamonds were also discarded by gold prospectors not knowing what diamonds looked like and others likely are in private rock hound collections waiting for someone to discover the gemstone. 


To begin a search for diamonds, focus on kimberlites in cratons. Cratons are very old continental cores. In the past (2009), I published two articles for prospectors on how to use a Personal Computer to find cryptovolcanic structures. I recommend reading these articles as they will give you an advantage over other prospectors. First start searching areas where kiimberlites have already been reported because kimberlites often occur in clusters. As you begin your search, start identifying known kimberlites and pinning them on Google Earth to provide you with a visual reference. Now start looking for alignments (lineaments) of kimberlites as kimberlites also occur along deep-seated fractures. When you identify a fracture (lineament) with a kimberlite along the fracture - project that fracture out a few miles  and look for evidence of other kimberlites along trend. 


As an example, search for the Sloan 5 kimberlite in Colorado on Google Earth at the following coordinates: 40°52'6.17"N; 105°26'52.54"W. Here is a roughly elliptical open park free of trees that is about 0.12 miles across in a north-south direction and maybe 0.06 mile in the east-west direction. This park marks the kimberlite pipe. The fact that it is elongated in the north-south direction suggests this could be the location of its primary fracture. As you look in this area, you will likely see other lineaments and open parks, all worth exploring. 


Now lets look at the Indian Guide district in Wyoming west of Chugwater. I found these anomalies many years ago, but these remain unexplored and unsampled. Are they just ponds or are they kimberlites? Check the Indian Guide photo in the gallery above. This is a false-color infrared image over Indian Guide showing a group of depressions some which have small ponds (water shows up as black in this image). All of these are structurally controlled (note all of the lines (lineaments) that project through the various depressions). Note that a couple of ponds also have white rings (kind of like the bathtub rings we use to leave as kids for our mothers to clean up). On the ground, these react to weak (10%) hydrochloric acid. There is no known source for calcium carbonate in these Precambrian rocks that we know of, so these may be kimberlites.


If you were to visit these on the ground, you would want to look for rounded bounders and cobbles in the depressions (characteristic of kimberlite), and look for blue ground clays with considerable calcium carbonate as well as look for the kimberlitic indicator minerals and even diamonds. So how many kimberlites (or cryptovolcanic depressions) can you find in this one photo? At least 25. Keep in mind that when blue ground and yellow ground kimberlite was first discovered in the Kimberly region of South Africa, people though they were finding diamonds in an old paleoplacer because it contained many rounded boulders, cobbles and pebbles. However, instead of being rounded by stream action, these were rounded by magma polishing as the material was carried to the surface in the kimberlite magma. The kimberlite host rock was later identified as the early diamond prospectors dug deeper into the yellow ground, then blue ground and finally the kimberlite.


Next, learn to recognize the classical kimberlitic indicator minerals as these have been found in many places in Colorado, Montana and Wyoming. and even in places like Kansas, California and Michigan. You can search for kimberlitic indicator minerals by panning streams or in the questionable crypto volcanic depression. 


When you find kimberlitic indicator minerals in streams, it is assumed they originated from a short distance either upslope or upstream. For example, chromian diopside will only transport 0.25 to 0.5 miles from a source kimberlite. Pyrope garnet may transport 1 to 2 miles from the kimberlite and picroilmenite only 1.5 to 3 miles from the kimberlite. Several years ago, we conducted a stream sediment sample survey in southeastern Wyoming searching for the kimberlitic indicator minerals by panning various streams and we identified more than 300 anomalies. The source of most of those anomalies remains unknown.


Over years of looking for kimberlite and lamproite, I was amazed at how people overlook these rocks and many gemstones. On one field trip, I led a group of 50 geologists & prospectors to the Chicken Park kimberlites in Colorado. I told the group I would walk them over kimberlites and they were to watch and let me know when they saw kimberlite. I walked them over kimberlite a few times and not one person saw them until I took them back to show them what they had missed and the Chicken Park kimberlites are some of the more obvious kimberlites in the area. So you as a prospector have an opportunity to find a major diamond deposit. Here's how to find the obvious pipes:


Fly your Google Earth or Virtual Earth to the Kimberly Region of South Africa. Look for some diamond mines - now look in the areas surrounding the diamond mines (I found several probable kimberlites in this area). Do the same for the NW Territories of Canada (search the Ekati mine). The Ekati has about 120 kimberites in the area surrounding the mine, most are under shallow lakes.