Ever wonder why diamonds are called 'ice'? They kind of look like ice, but this is not the reason. Diamonds are heat conductors and if you ever have the opportunity to feel a large diamond pressed against your lips, you will notice the gemstone feels cool. This is because diamond is a good conductor and will conduct heat away from your lips, making it feel cool to the touch.
Diamonds are the most valuable commodity on earth based on dollar value per weight. Some diamonds have sold for many times the value of an equivalent weight in gold - such as the Hancock Red that weighed only 0.95 carat. The purplish-red diamond & sold for nearly US$1 million. To put this in perspective, one carat weighs 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 extraordinary gems faceted from this huge rough are now proudly displayed in the crown jewels of England.
Diamonds are found with other gems; however companies ever bother with these associated gems even though many are extraordary stones in their own right and out-shine ruby & emerald. These other gems are known as Cape Ruby (pyrope garnet) and Cape Emerald (chromian diopside and enstatite).
Diamonds are found in several rock types, but the primary commercial host rocks are kimberlite and lamproite .
Kimberlite erupts as a small maar-like volcanoes and dikes. At the surface, the pipes (maars) appear as depressions: several have been mistaken for impact craters. Many occur as circular to elongate depressions with vegetation anomalies. They are controlled by fractures, have blue ground (montmorillonite clay) and are so carbonate rich their soils react with dilute hydrochloric acid and fizz as they emit carbon-dioxide gas. Most kimberlites pipes are <0.5 mile in diameter.
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 F are not uncommon. This collection of unusual characteristics results in small, circular maar-like volcanoes (without cones) & dikes that are structurally controlled.
Keep in mind: kimberlite will serpentinize because of water vapor, this produces a soft rock that erodes faster than surrounding country rock & usually results in a depressions with different vegetation than surrounding rocks. These depressions may contain shallow ponds. They are structurally-controlled such that more than one anomaly is often found in a line. 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 salt in old Precambrian rock, you might want to find out why.
Photos (above) Faceted pyropes from Green River Basin, Wyoming.
HOW TO FIND DIAMONDS
Over the years of looking for kimberlite and lamproite, I was amazed at how people continue to overlook these rocks and gemstones. On one field trip, I led a group of 50 geologists & prospectors to the Chicken Park kimberlites. They were told we would walk over kimberlites and they were to watch for the kimberlites, as I would not tell them when we walked over the deposits. We walked over the kimberlites - not one person saw them until I took them back over the rocks to show them what they had missed (and these were considered relatively obvious kimberlites). There are literally hundreds of kimberlites in Colorado, Montana and Wyoming that remain unexplored! So you as a prospector have an opportunity to find a major diamond deposit. Here's how to find the obvious pipes:
Go to a good website such as Google Earth or Virtual Earth which has areal photography . A good place to start would be 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.
False-color infrared aerial photo over Indian Guide district, Laramie Range. Note the (white) haulage road, and the several, structurally controlled depressions, some filled with water (black).
Kimberlites can be recognized by looking for fractures (lineaments). Look at the above image (this is a false color IR image which means the colors are not natural). First, this is located in the craton (all of the rocks under the blue area are Precambrian and >1.5 billion years in age). This is known as the Indian Guide district in Wyoming west of Chugwater. I found this many years ago, but these remain unexplored and unsampled. Are they just ponds or are they kimberlites? Note all of the depressions - some form 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 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 will react to weak 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, as well as look for the kimberlitic indicator minerals. Also look for diamonds. So how many kimberlites (or cryptovolcanic depressions) can you find in this one photo? At least 25.
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.
- 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.
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Information Pamphlet 12 (Searching for Placer Diamonds)