DIAMONDS - A Hard Gemstone and Hard to Find.

Diamonds in the Rough

DIAMOND FACTS - Did you know: (1) Diamonds were initially found in India hundreds of years before the birth of Christ? (2) Diamonds are mentioned in Sanskrit manuscripts 320 to 296 BC, in Buddhist works as old as 400 BC, and mentioned in the Torah and is also mentioned in the Holy Bible at least six times, and appears in the Book of Book of Exodus possibly written about 500 to 600 BC. But the term used for diamond is adamant and could refer to ruby or some other hard gemstone. For instance, diamonds were initially termed adamas (invulnerable stone) which cause confusion in interpretation of ancient manuscripts, which also uses this term to describe other hard gems including corundum (ruby). (3) Diamonds were first found in rivers in India, where placer diamonds were considered of value because of hardness. Based on our current knowledge of the geology of India, most of these diamonds were likely derived from erosion of olivine lamproite and lesser kimberlite pipes. (4) Legendary diamonds such as the Koh-i-Noor (105.6 carats) and Hope (45.52 carats) were recovered from India. (5) The largest diamond ever recovered is the Cullinan diamond (3,106.75 carats) and recovered from the Premier mine ( 25°40'29"S; 28°30'50"E) in South Africa in 1905.

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

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 - 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 were purchased by Royalty or donated to Royal treasuries. Most notable are the diamonds cut from the Cullinun rough, the largest rough diamond ever found that weighed 3,106 carats. The gems faceted from the 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.

DIAMOND PROSPECTING HINTS When you decide to prospect for diamonds, learn to recognize diamond and then watch your gold pan to see if you trap any of these gems. Diamond has a specific gravity of 3.5, and will concentrate with black sands in a gold pan. So when you are panning and you see a transparent to white crystal (or even better - a pink or blue crystal) in your pan in the middle of the black sands with distinct greasy luster. Take it out and look it over closely with your hand lens (magnifying lens). It should look as if it has a thin coating of grease on the surface.

Now get out your diamond detector and test the crystal. Diamonds have unique surface conductivity, which is why they feel cool to the touch of your lips (ice), and can be detected by a diamond detector. All you have to do is switch on your diamond detector and touch the suspected diamond with the probe. If it reads "diamond", be sure to send it to me as a gift. If it reads "simulate" it is something other than diamond and don't bother sending it. Diamond detectors are so easy to operate that with some effort you can even teach a monkey and rarely a politician how to use them. To aid in your expertise in diamond hunting, buy a few very cheap, uncut, rough diamonds to have in your personal collection for comparison and to assist in your mineralogy education.

Without mineralogical training or a diamond tester, you probably will not be 100% positive as to you have. So take your crystal to a pawn shop and ask for $1 million - the pawn broker will most likely be able to tell you if you are crazy or if you have something of value. But also remember rough diamonds are not worth much unless you have a large one (10 or more carats). Remember those bozos on Gold Rush in South America when all they could find were diamonds - it took some time, but I suspect they finally caught on - small rough diamonds just don't have much value - if you have a good-quality rough gem diamond of about 1 carat - you may be able to get US$100 or $200 for it. If it is industrial diamond, you might be able to get enough to by one can of soup. Faceted diamonds attached to a gold necklace in a jewelry store do have value. And BIG gem-quality diamonds of a few hundred carats can be traded for a good field vehicle - such as a 4-wheel drive Porsche with monster tires.

Now examine photos of raw diamonds and check my sites on diamonds - I have a few of them scattered all over the internet. Now search the internet for photos of rough diamonds. Look at the crystal shape of the mineral in question - most diamonds look equal-dimensional (a few will not) and are isometric. Look for trigons on the crystal surface. 

Now this is very important! Don't let your imagination run wild. I've had hundreds of people report they see trigons (little triangles on the crystal surface) when there was nothing there. Not sure what they were smoking, but it should be easy to tell if you have triangles on a crystal surface or not. The crystal habit can also be helpful. Many rough diamonds occur as octahedrons - crystals that look like two pyramids attached at their base - 8-sided crystals. But again hold on - don't run out a buy a new car yet unless you plan to send it to me. There are many other minerals that form octahedrons, so this in not diagnostic. Another common crystal habit is a macle - looks kind of like a flattened triangle. Then there are cubes - those 6-sided crystals that look like dice. But then there are many modifications of these crystal habits.

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 kimberlites 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.

The Art of Finding Gold Deposits

The author (GemHunter) stands next to Big Mac in Arizona. Over the years, his 
field work & research contributed to discovery of nearly $90 billion in gold, dozens &
dozens of gemstone deposits, & a better understanding of the ancient Precambrian rocks
(greenstone belts) in Wyoming.

Some prospectors, rockhounds, geologists and others thought I could smell gold - this may be only partially true. Some gold deposits smell because of associated arsenic-sulfides (distinct garlic odor - should remind you of a good, Italian restaurant) such as arsenopyrite, realgar or orpiment. The associated iron-sulfides such as pyrite smell like politicians (rotten egg gas). In reality, I stumbled around much of the time as I tried to figure out the geology. Anyone watching me would have thought I had lost my mind - walking around in circles, breaking rocks, picking up pieces of rock to examine with a magnifying lens, licking rocks to clean surfaces, and jumping 30 feet in the air when startled by rattlesnakes. Along the way, I made mistakes in interpretations, but I persistent and continued to try to satisfy my insatiable desire to find what was on the other side of the hill.  

I was charged to summarize results in papers, books and public lectures: this required spending considerable time on the ground following outcrops, rock formations, veins, breccias, sulfide-pockets, etc. I loved every minute - even when I had to kick rattlesnakes off the rocks, fight hurricane-force winds in the Wyoming jet-stream, and then there were periodic threats from transplant ranchers from Pennsylvania. This transplant later became a Human pseudomorph, after he/she/it was arrested by Game and Fish for running English-style fox hunts harassing coyotes by feeding them out-of-season antelope meat. Last heard, the future White House Assistant Secretary of Mental Health scheduled a sex change operation - not something one would expect from a real, Wyoming, rancher. 

Anyway, report writing required me to put together thoughts on paper so Wyoming could promote its mineral resources. Sitting in my office and putting together these thoughts in the winter, helped me formulate new ideas on what to look for, and where to look. Even so, the job paid about half of what industry paid, but the research was a heck of a lot more interesting - it was the greatest job in the world.

After hunting gold, diamonds and colored gemstones for over three decades, I decided to share my secrets. In recent books at Amazon: (1) Finding Gemstones, (2) Gold, (3) Field Guide to Gemstones, Minerals and Rocks, (4) Gold in Arizona - a Prospector's Guide (bound and also (5) Kindle version), I described hundreds of mineral sites and provided legal descriptions and/or GPS coordinates to assist in finding gold, diamonds, colored gemstones and fresh air. I also provided information on what to look for in each deposit and how to identify gemstones and host rocks. Think of this as an education in prospecting. All one has to do is to get permission to visit some sites on private land, others on public land, you don't need anyone's permission. I did most of the ground work and even got rid of several rattlesnakes. 

Speaking of rattlesnakes (not my former boss, but the other kind of crawly reptile), did you know in the late spring when everything is green for a one or two days in Wyoming, rattlesnakes actually turn green, when everything dries out, they are brown. Just like politicians - when they get around your money, they turn green; whereas the rest of the time, they are brown, just like …. well you know.

What does gold look like?

People have a difficult time identifying gold in nature until they see it a few times in their pan, in quartz, or in rock. When I was at the University of Wyoming, many people visited my office with vials, Ball jars, shopping and sample bags filled with mica wanting to know if they had gold. It was rare for any of these people to have gold. Nearly all had mica.

Placer gold from the Gerald Stout placer on Rock
Creek, South Pass district, Wyoming.

Mica is mistaken for gold - in particular sericite, muscovite, phlogopite and paragonite mica fools many. With a specific gravity of only 2.76 to 3.0, mica should easily wash out of a gold pan with quartz. However, it takes effort to pan mica out of a gold pan. This is because mica exhibits a crystal habit of paper-thin slices of flakey, monoclinic (pseudohexagonal) crystals with perfect cleavage. Being essentially two dimensional, the mica acts like a blade while tumbling and slicing through water making it difficult to pan out. If you watch the mica as you pan, it will congregate on top of the black sands during panning, and also will tumble in the water. Gold is very heavy, and will sink to the bottom of a gold pan and not tumble.

Gold has a specific gravity of 15 to 19.3. In other words, if you compare an equal volume with water, gold is much heavier. Just imagine a 'shot class' from the Atlantic City Merchantile filled with 5-ounces of booze (sometimes you need that much just to keep from choking your democrat boss). Now down that shot and fill the glass with gold: it weighs 99 ounces, or more than 6 pounds! Gold is also malleable and can be easily scratched with a pocket knife; whereas, mica is brittle. Most of us never find chunks of gold large enough to scratch; but if you do find a piece large enough to stick with a pin, the gold will indent. If you apply pressure to mica with that pin point, it will break into smaller flakes.

Other minerals mistaken for gold include pyrite (fool's gold), pyrrhotite (a variety of fool’s gold), and chalcopyrite (copper-fool's gold). Pyrite is an iron-sulfide (FeS2). This means pyrite is formed of iron and sulfur. Even so, it may contain minor impurities such as gold in the crystal structure. Pyrite's crystal habits include brassy, disseminated, massive to crystalline cubes with striated faces, octahedrons, pyritohedrons (12-sided) as well as combinations of these habits. Unlike gold, pyrite is not malleable and will crush to a dark, greenish-grey powder by striking it with a rock hammer – whereas gold will flatten when struck. Pyrite will produce a streak of the same greenish-grey color. And, when you leave the brassy mineral outside in the rain for a a week or two, it will rust. Pyrite has a specific gravity of 5.0 (5 times heavier than an equal volume of water): although relatively high, the specific gravity is notably less than gold. 

Geologists and seasoned prospectors speak of heft. This is simply a relative measure of a mineral’s weight. For instance, a gold nugget has very high heft and pyrite has moderately high heft (Hausel and Hausel, 2011). To measure heft, just bounce a specimen in your hand and make a judgement as to whether the specimen has high, moderate or low heft.

Gold in black sands from Bobbie Thompson
placer, Douglas Creek, Medicine Bow 
Mountains, Wyoming.

If you find pyrite and throw it away because it’s not gold – you may be fooled again. Pyrite can enclose hidden gold within its crystal lattice. Gold-bearing pyrite rarely has visible gold unless it is completely oxidized and replaced by limonite boxworks. It is worthwhile to collect samples of pyrite for assay if you are in gold country (only use reputable assayers used by mining companies, as there are a lot of assayers who are good at scamming prospectors). In the old days, prospectors crushed pyrite to a very fine powder and panned the powder for native gold. Sometimes this worked, other times they missed very fine gold, particularly if the gold replaced individual iron atoms in the crystal lattice. Pyrite has no value except as mineral specimens or when it contains appreciable gold. Theoretically, pyrite can contain as much as 2,000 ppm (parts per million) gold. This is equivalent to a ton of pyrite containing 64 ounces of gold!

Some pyrite from Uzbekistan was reported to contain 37 to 232 ppm (1.18 to 7.42 opt) Ag along with 40 to 187 ppm (1.28 to 5.98 opt) Au. In Italy, Boyle (1987) described pyrite with 0.12 to 200 ppm (0.004 to 6.4 opt) Au. Pyrite from the Lost Muffler Prospect in the Rattlesnake Hills, Wyoming had as much as 10 to 20 ppm (0.32 to 0.64 opt) Au (Hausel, 1996). The pyrite occurred as cubes in a siliceous zone in metabasalt and metagabbro. The mineralized zone was traced over a distance of 4,800 feet.

The first specimen of pyrite I found was on a field trip to the Lark Mine in the Oquirrh Mountains along the western flank of the Salt Lake City valley. I was taking a mineralogy class as an undergraduate at the U of U. At one point, I looked at the mine back (roof) and saw a beautiful specimen of pyrite that had my name written all over it, so I dug it out. I’m not sure why, but excellent pyrite specimens are seldom mineralized in gold - I suspect it has something to do with temperatures and pressures of mineralization chemistry of the host rock and hydrothermal fluids.

Pyrite weathers to limonite (rust) over time. As an example, when I moved to Gilbert Arizona from Laramie, I filled part of an 18-wheeler full of rock and mineral specimens - yep, I'm a rock hoarder. My wife, bless her heart, decided to break me of that habit and 98% of my samples ended up making a rock garden in the back yard. Yesterday I looked at four massive pyrite specimens I placed in the garden a few months ago, and they were already turning to rust! One other sample received periodic sprinkles from the vegetable garden, was nothing but rust. It doesn't take long for such specimens to suffer. Last year, I also placed a massive specimen of galena (lead-sulfide) (PbS) in the sun and was shocked to see it was already being altered by the end of a month - it looked like the sun had burned this once, shiny, gray, metallic specimen.

When considerable pyrite is present in an outcrop, it will oxidize to rusty gossan with some porous boxworks. If the pyrite is gold-bearing the resulting limonite will be enriched in gold. Thus it always worthwhile to examine limonite in gossans with a 10x hand-lens and search for visible gold. If gold is not obvious, it still may be worthwhile to assay a few rocks. Pyrite is also found associated with chalcopyrite, sphalerite, galena, bornite, gold and/or arsenopyrite. Marcasite, a polymorph of pyrite, is described in sedimentary uranium deposits as finely disseminated grains. Marcasite rarely contains gold. 

Chalcopyrite is also mistaken for gold. It is a primary copper-iron-sulfide (CuFeS2) isreferred to as copper-pyrite. Chalcopyrite forms a metallic orange-bronze mineral that may have a metallic surface sheen that is bronze, violet, greenish to blue. It is mostly massive or disseminated and individual crystals are uncommon. Chalcopyrite has cleavage seen in some specimens. The mineral is brittle, has uneven fracture, and will yield a greenish black streak when scratched on white tile (streak plate). It occurs with other copper minerals such as chalcocite, malachite, and bornite as well as with pyrite. It has a hardness of 3.5 to 4 and specific gravity of 4.1 to 4.3. Some chalcopyrite will have anomalously high gold and silver. Gold in chalcopyrite likely substitutes for copper in the crystal lattice, since it is invisible in nearly all samples. Samples of chalcopyrite in gold-bearing areas have been found to have a trace to 22 ppm Au (0.7 opt), and a trace to 1300 ppm Ag (41.6 ppm Ag) (Boyle, 1979).

Types of Deposits

To a geologist, there are many types of gold deposits, such as hydrothermal, mesothermal, epithermal, replacement, etc. But to prospectors, there are two types: placer and lode. Placer deposits are essentially detrital deposits eroded and transported by water, such as the famous placers at Nome and Flat, Alaska, the Fortymile River in the Yukon, and Alder Gulch, Montana. Examples of lode deposits include the Mother Lode, California and the great Homestake mine in South Dakota.

But there is not always a clear distinction between lode and placer. For instance, the great Witwatersrand gold deposits in South Africa, the most productive deposits in the world, are known paleoplacers. Because they occur in brittle, consolidated rock (mined to depths greater than 13,000 feet), most prospectors would consider these lodes. However, geologists classify the great Rand deposits as fossil (paleo) placers, since the gold was deposited in streams and rivers more than 2.5 billion years ago and later these were compressed into hard, consolidated, brittle, rock ledges. Just like any placer, miners in the Rand search for evidence of ancient bed rock in contact with the conglomerates, ancient bench deposits, pockets in stream beds, meanders. These are just old fossilized river beds (without the water). One difference - when they were deposited, the earth’s atmosphere was not healthy to life because it had very little oxygen; thus minerals like pyrite did not oxidize (rust) and were transported in the ancient streams just like gold. So, miners now find both gold and pyrite nuggets in the Rand paleoplacers. 

Another not so clear distinction is eluvial gold. Eluvial deposits are essentially detrital, weathered in place material from nearby (or underlying) sources. Gold from eluvial deposits shows no evidence of stream transport and cobbles and boulders with the gold are angular. But since eluvial deposits are unconsolidated, many consider them as placers, even though they may directly overlie a lode, or just a short distance downslope from a lode. There are many examples of eluvial gold in Arizona. These have gold in angular quartz fragments that may also have some primary pyrite, chalcopyrite and/or galena. Arid environments are favorable for eluvial deposits due to lack of active streams. Where there is eluvial gold, there is a gold lode in the immediate area - something every prospector needs to keep in mind, especially when they prospect in the regions around Quartzsite, Arizona. Eluvial means that the material eroded in place from an underlying vein or source rock.

Placer deposits

Most placers are small and limited size and extent. Major mining companies ignore them because of small size. But such deposits are also comparatively less expensive to mine and require no chemicals to extract gold, and require little mining expertise. Even so, placer miners make mistakes that could be avoided, such as: (1) recognizing and recovering value-added precious metals, gemstones or strategic metals; (2) assuming the placer is equally mineralized throughout the gravel when in fact, placers are erratically mineralized requiring a search for pay streaks; (3) picking the wrong mill or concentrator for the deposit; or (4) using dowsers or fortune tellers. One classical example at Rock Creek in the South Pass greenstone belt of Wyoming, involved a placer miner who had found considerable gold in the stream alluvium adjacent to the creek. Instead of following the pay streak, he later mined the hillside adjacent to the creek because a dowser indicated the mother lode was on the hillside. So he spent all of his money digging worthless dirt and rock, when he had gold sitting just a few yards downslope.

If the placer has considerable aerial extent and depth, a miner should consider drilling or trenching to provide guide maps to minable paystreaks. After estimates of gold resources are determined, the miner should search for the most efficient method for gold extraction. 

Placers consist of detrital gold and other valuable minerals that were transported by water in creeks, rivers and even by wave action along the shores of lakes and the ocean. The wave action and water movement sorts minerals by specific gravity; thus when searching for valuable minerals in placer deposits, valuable minerals with high specific gravity are typically found with other heavy minerals. Black sands consist of dark opaque minerals with greater than average specific gravity and include magnetite, pyroxene, amphibole, ilmenite, garnet, sphene, chromite and monazite, as well as rare light-colored minerals of high specific gravity such as cassiterite and scheelite. Sometimes, diamonds, rubies, sapphires, benitoite and tourmaline are found in placers.

The opposite also occurs. Several years ago, after being provided grants by Union Pacific Resources to search for gold deposits in southern Wyoming, we found gold in many sand and gravel pits operated by the Wyoming Highway Department. We even found gold in an dry channel in the Laramie landfill. We recommended that companies in charge of these operations sample to determine if they had recoverable gold. The added value of the gold could have paid for (or partially paid for) the cost of sand and gravel operations. But we were ignored. So now, in addition to roads in Sybille Canyon area being paved by gemstones (spectrolite), it appears some of Wyoming's highways could be paved with gold.

If you take a trip to the Sweetwater River to the east of Atlantic City, Wyoming and sit down to pan at Wilson Bar, you will find heavy, nagging, white to brown ‘quartz’ that is very difficult to pan out. Examination of the ‘heavy quartz’ with shortwave ultraviolet light will show some of the material to fluoresce blue-white. Testing this so-called quartz for specific gravity will result in a SG=6, more than twice that of quartz. The so-called heavy quartz turns out to be a calcium-tungstate (CaWO4) known as scheelite, a tungsten ore found with some gold ore at the nearby Burr and Hidden Hand mines (Hausel, 1991). 

When found on public land, placers can sometimes be claimed under the 1872 mining law if the government hasn’t yet withdrawn public land from multiple use. Several years ago, the BLM withdrew a gold placer in Strawberry Creek in the Lewiston gold district of Wyoming in another effort to take public lands from the public. One prospector working in the area with primitive tools was evicted after he had recovered considerable gold in a very short time. 

Minerals of potential economic interest with relatively high specific gravity are periodically found in gold placers such as cassiterite, scheelite and a host of gemstones including ruby, sapphire, gem-garnet, diamond, platinum, and palladium. While prospecting for diamonds in the Laramie Mountains in southeastern Wyoming, several samples had trace amounts of ruby and sapphire in dry placers (Hausel, 2014). These were eroded from nearby, undiscovered, corundum (sapphire, ruby) schists. How do you tell if you have ruby or sapphire in your gold pan? Look at crystal habit. Usually, ruby and sapphire form hexagonal crystal prisms bounded by pinacoids (flat surfaces).

While prospecting for diamonds in the Sierra Nevada of California, benitoite was recovered near Poker Flat. A prospector from Saratoga, Wyoming, Paul Boden (RIP), found a couple of excellent gem-quality octahedral diamonds while searching for gold on Cortez Creek in the Medicine Bow Mountains, Wyoming. Another prospector, Frank Yassai (RIP), recovered many diamonds in Rabbit Creek, Colorado while prospecting for gold (Hausel, 2014). In this same region, another prospector panned a few dozen diamonds including one flawless gem-quality diamond of 5-carats in 2014. And at Fish Creek on the State Line, a diamond company searching for kimberlite in 1995 recovered several diamonds in the creek, including a 6.2 carat diamond.

During erosion, heavy minerals mix with light-colored, glassy, transparent to opaque minerals of low to average specific gravity such as quartz, apatite, feldspar, and mica. These and other minerals with high specific gravity are moved in streams. The sediment carrying capacity of a stream will diminish with decreasing water velocity and heavy minerals settle where declining water velocity occurs; such as areas marked by distinct increase in black sands. Heavy minerals tend to concentrate at the bottom of a stream, along the leading edge of stream meanders, behind obstructions (i.e., rocks, cracks in bedrock) in waterfalls, potholes, etc. Since many streams lack sufficient velocity to carry gold for any great distance, much gold (particularly where it is concentrated in pay streaks) will lie downstream from a lode. At the Rock Creek placer in the South Pass greenstone belt, gold was mined downstream from a group of gold-bearing shear zones (Hausel, 1985, 1991; Hausel and Love, 1992) that run from the hills west of Atlantic City, through Atlantic City and further downstream. But further upstream above the known gold lodes, Rock Creek has little gold. This is because the source of the gold sits in the hills immediately west of Atlantic City. One can trace gold downstream from those lodes all the way to the Sweetwater River.

Distances that heavy minerals can be transported are not known with accuracy. Some can be transported great distances. For example, diamond is 6- to 8-thousand times harder than any other mineral and is not overly heavy (specific gravity of 3.52 compared to 2.87 for quartz). Even so, there are cases where transport distances for diamond exceeded 600 miles. In southern Africa, diamonds are found in kimberlite pipes, in stream and river placers and in extremely rich beach placers along the west coast of the continent. Other gemstones are found with diamond, but only within a few miles of the source rock for the diamonds. These include pyrope garnet, chromian diopside and picroilmenite, but these only transport short distances until they completely disaggregate due to abrasion. In the Colorado-Wyoming region, studies show these transported downstream only about 0.25 to 1.5 miles before complete disaggregation.

Placer diamonds found in the Cortez Creek gold placer
Douglas Creek district, Wyoming, by Paul Boden.

Great transportation distances for gold are not possible because gold is too heavy and too soft (hardness of 2.5 to 3), so when in streams it is thought to have been derived from a nearby source. In some unusual cases, gold may be transported greater than normal distances dissolved in water. In Alaska, Dr. Paul Graff identified gold crystallized in nuggets downstream from nearby lode deposits. 

Flash flooding is important in producing paystreaks. Paystreaks, or lenses of gold-enriched gravel, are often found with an assortment of boulders, pebbles and cobbles with organic material (tree limbs, etc) providing evidence of a past flash flood. Pay streaks can be scattered over one or more intervals in a vertical column. It is important to remember, placers are never consistently mineralized and if you find good gold in one location, just a few feet away, the placer could be unmineralized.

Stream meanders are good to search for gold. Gold may concentrate on the inside of the initial curve of a meander as well as in the bank (point bar) on the upstream side of the meander. As an example, one of my favorite places to take students in geology and prospecting classes was the Bobbie Thompson campground area in the Douglas Creek gold district of Wyoming.

In the South Pass greenstone belt in western Wyoming, giant (Teritay age) paleoplacers surround the greenstone belt and are reported at McGraw Flats to the north and Oregon Buttes-Dickie Springs to the south. There are smaller ones in between. The southern paleoplacer was reported to have more than 28.5 million ounces of gold, yet most of this area is unexplored (Hausel and Love, 1992). Along the northern flank of the Seminoe Mountains greenstone belt, the Miracle Mile paleoplacer is totally unexplored even though the precious metal was found in the dry paleoplacer. This paleoplacer was discovered by Charlie and Donna Kortes and also contains many G10 pyrope (diamond-stability field) garnets that indicate somewhere in the region is a very-rich diamond deposit(s). So look for diamonds and gold when you dig in this dirt and pan it in the nearby North Platte River. Paleoplacers in the Medicine Bow and Sierra Madre Mountains in southern Wyoming also yielded gold and diamonds, along with uranium and thorium.

Lode deposits

One might think of lode deposits as veins or other consolidated rocks that contain anomalously high quantities of gold. Many occur as distinct quartz veins. These may form linear to tabular masses of quartz within fractured or altered country rock. One important characteristic of many productive veins is the presence of sulfides, such as pyrite (fool’s gold), or arsenopyrite (arsenic-pyrite).

When pyrite oxidizes, it produces sulfuric acid and rust, resulting in a gossan at the surface and a potential supergene zone (a mineral deposit, or enrichment, formed by descending fluids) a few tens of feet below the surface. Gossans are the oxidized sulfide-rich parts of veins and other mineral deposits that have distinct, rusty appearance. These offer excellent visual guides in a search for gold and other metal deposits. In any historic mining district, you will often find dozens, of old pits dug in rusty rock. Prospectors learn to recognize gossans as guides to ore.

Gossans are good places to search for high-grade gold. Gossans produced from the leaching of pyrite are typically rusty (reddish-brown) in appearance; gossans from arsenopyrite are typically greenish-yellow. Large gossans that cover several acres may be situated over massive sulfide deposits. These may contain gold and/or valuable base metals. One large gossan in the Hartville uplift, eastern Wyoming, is so distinct it is named “Gossan Hill”—and overlies a massive sulfide deposit. 

Some faults and breccias contain gold. Breccias are zones of broken rock with distinct angular rock clasts. When found, gold may occur in the matrix of the strongly limonite-stained gossan surrounding the rock fragments. Other faults, known as shears, may be mineralized. Shear zones consist of granulated rock. Many shears, particularly those in greenstone belts, are quite productive for gold. In some gold mining districts in the world, nearly every foot of exposed shear zone has been prospected.

Many veins have sporadic gold values with localized ore shoots enriched in gold. Some of these shoots may be enriched 100 to 1000 times the average value of the vein. The challenge given the prospector is how to recognize these shoots.

Ore shoots can be structurally or chemically controlled. Where pressures and/or temperatures dramatically drop during hydrothermal mineralizing events, structurally controlled ore shoots occur. Chemically controlled ore shoots occur where there was a chemical reaction between the mineralizing fluids and country rock. Any where an igneous rock (hot) comes in contact with a reactive rock (such as limestone) provides a great place to find gold, silver, and other minerals - such as the Tombstone district in Arizona.

When searching for structurally controlled ore shoots, look for places where you might expect pressures decreased in the geological past. Some structurally-controlled ore shoots occur in folds. Another type of structurally-controlled ore shoot is found in vein intersections. There are many other types of structurally-, and chemically-controlled ore shoots. For example, while prospecting in the Gold Hill district in the Medicine Bow Mountains of Wyoming, I noted gold was almost exclusively found in veins adjacent to amphibolite. In quartzite, the veins were unproductive.

Summary

The search for productive gold deposits requires good prospecting and geology skills, and luck. However, there are literally thousands if not millions of occurrences and deposits in the Western US including Alaska. The best way to begin prospecting is to get a book that describes gold mines and placers in mining districts near you. There are always deposits near old gold mines that have been overlooked. Look at geological maps to see what the trends of veins, faults or shear zones are and then find these on the ground and start walking along those trends - you will find more gold and vein occurrences along those trends than found in the past. I can't guarantee this for everyone, because there are always people who can't find their way out of a closet, such as one Colorado prospector I sent looking for iolite gemstones (Hausel, 2014).

Get hold of books in your area that describes where gold deposits are found. Pick out the exciting areas and look at the deposit described in a book and look around for what the old prospectors missed (they missed a lot!). Search for publications at your local geological survey. If you are in Wyoming, I published numerous books that are available on the Internet, the University of Wyoming bookstore and the Wyoming Geological Survey. In particular, get copies of Bulletin 68 and 70 and Report of Investigations 44. If in Arizona, there are hundreds of lode gold deposits that have been missed. Colorado and California have hundreds of possibilities, but personally, I would look in Arizona, Wyoming, Montana and Alaska. 

"Old mines never die, they are just forgotten". The United Verde mine property in Arizona was mined for copper, gold, silver and zinc for decades and then closed. Was it mined out? No - few mines are ever mined out. The economics prior to the 1960s made it uneconomic to mine. But at today's high gold prices (compare $1700+ per ounce to $35 per ounce) many old mines are likely economic. It is reported that past miners did not recover low-grade zinc and copper ore at the United Verde, and it likely still contains more than a million ounces of unmined gold. Examine aerial photos over the region, it is apparent there is a 10+ mile gossan that likely is underlain by several massive sulfide deposits that are unexplored. 

While you are looking for gold deposits, remember, there are probably just as many, that were missed by prospectors and geologists. I recently found a major field of cryptovolcanic structures that are likely diamondiferous kimberlites sitting right along Interstate-80 just west of the State Capitol of Wyoming. With a good arm, one could probably hit some of these with a rock while standing next to the interstate. These remain unexplored! 

Some of are so obvious, that it makes one wonder what everyone is doing. Take for instance the Cedar Ridge opal deposit. Possibly the largest opal and agate deposit in North America sitting right on the side of the main highway to Riverton, Wyoming and exposed in numerous road cuts in an oil and gas field and pipeline - but totally overlooked. Even after the announcement of this field in 2003, it still remains pretty much unexplored! This deposit has opals in road cuts that weigh more than 100,000 carats. The opal is mostly common opal, but I also found fire and precious opal and some spectacular 'Sweetwater' agate. It sat there, untouched, with just a few, brief, mentions of the presence of opalized rock in old USGS reports!

Then there is likely the two largest colored gemstone deposits on earth I found at Grizzly Creek and Raggedtop Mountain in the Laramie Range. How these can remain untouched is beyond understanding. At one, I found gem iolite as large as 24,000+ carats with pieces in outcrop that are the size of Smart Cars. And another deposit may host as much as 2.7 trillion carats based on past geological reports which missed the fact that these were gemstones. Just imagine how valuable these deposits are even if you mined them, cut the stones, sold them and only made $1 profit! The gem iolite, can be cut for $0.5/carat and sold for $15 to 150/carat. Nice profit! For those of you who wonder - I do not have claims on any of these, it was considered unethical when employed at the WGS.

The better areas to search for gold are historical mining districts. Many well-known giant mining companies of the past were notorious for overlooking significant ore deposits. Some of my old publications are listed on the Wyoming Geological Survey website, but they constantly change their site making access to information unreliable. So, contact the Wyoming Geological Survey and ask them for pdf copies.

GOLD FACTS:

(Historical Gold Prices)