Friday, January 2, 2015

Finding Gold - do I have carats, carrots, or karats?

When some think of gold, the word karat may come to mind. Or is it carrot or maybe carat? So did I just pan a vegetable of the stream? 
Schematic cross section through an ideal kimberlite
pipe showing carrot-shaped diamond pipe. Generally,

the vertical column from the blow to the maar is
about 5,000 feet. The blow is the enlargement at the
base of the pipe, and the maar is the volcanic orifice.


If you are a rabbit, possibly you panned a carrot - but then again, you wouldn't be reading this blog. Carrots are good sources for vitamin A and good for attracting rabbits. 

I tried my green thumb in Gilbert Arizona last summer and planted carrots only to discover few edible things grow in the Phoenix valley in the summer (other than prickly pear cactus - and its questionable if many of us would try to peel the skin off the cactus just to eat the slimy plant). All of my carrots deep fried in the ground as temperatures soared into triple digits for a month. 

I still have difficulty adapting to Arizona’s hot weather after living in Wyoming for   a few decades. But someone told me the other day that Arizona is like Wyoming, just in reverse. People just don’t go outside when temperatures hit -50oF in Wyoming (although I always skied to work when temperatures fell below -30) and they don’t go outside when temperatures rise above 110oF in Arizona. I never thought of it that way. But at least in Wyoming, my Nissan truck had a heater; in Arizona it doesn't have an air conditioner (didn't need AC in Wyoming). One day I'll have to break down and buy a truck with air conditioning.

The word carrot comes from the middle French carotte that refers to the favorite food of that old "wascal wabbit". It has nothing to do with the other two homonyms carat and karat; except that diamond exploration geologists like to use the shape of a carrot to describe what the cross-section of a diamond pipe (volcano) might look like, but this is as close to diamonds a carrot gets.
One of the more than 300 cryptovolcanic structures discovered in the Colorado-Montana-Wyoming kimberlite
 (diamond) province (Hausel, 2014). This depression is filled with water in the spring, but has an unexplained
 vegetation anomaly, enriched carbonate soils. The anomaly is circular and characteristic of many diamond
 pipes in the Colorado-Wyoming State Line region.


Diamond pipes are largely carrot-shaped because they erupt with large amounts of highly pressurized gas and shoot out of the earth's mantle like a shotgun blast producing a maar-like volcano. When the kimberlite magma breached the earth’s surface, the eruption was explosive with magma ejected with country rock boulders and highly pressurized gas (water vapor and carbon dioxide). Some researchers suggest gaseous emplacement velocities could have been as rapid as Mach 3. 


Distinct depression associated with a diamond pipe in Colorado.
The diamond pipe sits under an open, grass-covered park.
Many kimberlites lack tree growth and often give people an
impression of an impact crater. This cryptovolcanic structure
was trenched and diamonds along with kimberlite
were recovered at shallow depth. Also note the fault trace marked 

in red. As a prospector, you should always walk these traces out
as far as they go simply because more than one kimberlite often
erupted along the same fracture. This is how I discovered some 
kimberlites in this region that were missed by others.
So much carbon dioxide was present in these eruptions that the EPA would have issued a citation to Mother Nature for releasing these toxic(?) fumes. (In 2009, Obama’s EPA listed carbon dioxide as an air pollutant. Prior to 2009, carbon dioxide was just a simple gas or plant food used by all plants, algae and many forms of bacteria needed to produce organic compounds and release the oxygen we all breathe [you know its coming, Obama will likely tax us for using oxygen]. It's good our government is watching out for us, otherwise we would not have been aware that such an important gas required for life was a pollutant).

Kimberlite (diamond) pipes (unless deeply eroded) have circular expressions in plan. This expression often looks like an impact crater. To see some very impressive diamond pipes, I recommend searching the Internet for Ekati Airport, NWT to see Canada’s premier diamond mining operation. Now search for the Big Hole Kimberley, South Africa”. This is another diamond pipe that was operated years ago and looks like an impact crater. Search throughout the Kimberley city limits and you’ll find other diamond pipes. 


Now take a look at Russia. Search for “Mir Mine, Russia also known as Mirnyy Diamond Mine. This will take you to one of the more impressive circular pipes. While you are looking at these areas, remember kimberlites almost always occur in clusters and often line up on linear fractures. In these three areas, you may find other circular anomalies that have not been mined that are likely kimberlite pipes.


In addition to finding the circular to roughly circular depressions, one needs to look for other characteristics, such as a group of circular to elongated depressions lining up on some kind of lineament. For example, take a look at the Lost Lakes in the Red Feather Lakes region of northern Colorado. You will find a group of lakes and depressions that sit on a distinct linear fracture that trends about N30oE. And when you take a look at the lakes along the northeastern extent of this fracture - wow - the lake shores look like they are coated with salt or blue ground. Several years ago, I visited these anomalies, and the soils are very carbonate rich - if you drop some dilute HCl acid on the soil, it will fizz. The country rock in the region is mostly granites and amphibolites which do not have any known carbonate. Now these are excellent cryptovolcanic structures and possible kimberlites. 


Years ago, I also came across a cluster of depressions in the Indian Guide district of Albany County Wyoming. All of these are situated along N-S to northwesterly fractures immediately west of the Iron Mountain kimberlite district, where dozens of kimberlites (including a couple of diamonds) were found years ago (Hausel and others, 2003). I tried to get the State to provide me with a grant to drill these, but to no avail. The state was much more interested in providing another agency with money to see how high a rare and endangered jumping mouse could jump (it turns out this rare mouse was not so rare after all - just a normal field mouse that was startled). So these cryptovolcanic structures remain  unknown as to why they exist - but the fact they are sitting along the western trend of the Iron Mountain kimberlites strongly suggest Wyoming is losing its marbles, or should be say, carats.


Now take a look at the Twin Mountains Lakes area near Cheyenne. I identified more than 50 interesting structures (depressions and lakes) in this area that are situated in a distinct regional fold in the Proterozoic amphibolites that could be an extension of the State Line kimberlite district. Some appear to be very large - could these be kimberlites?  No one has ever drilled or sampled these and they look like good targets to me. 


Now take a look at the Kelsey Lake kimberlites in Colorado. These were mined for a short time and produced many high-quality gemstones including a 28.3-carat diamond along with a diamond fragment from a stone estimated to have been about 80 to 90 carats (Hausel, 1998, 2014). As you examine Kelsey Lake, keep in mind this was at one time a diamond mine (1996) and there are at least two reclaimed kimberlites and much of the diamond ore was never mined due to legal problems. Also note there is still fresh blue ground exposed in the reclaimed area. In this region, there are also several unmined kimberlites - I know, because I mapped them years ago. They are all located in my new book.


Now here is something you want to really think about! The Kelsey Lake kimberlites sit right on the edge of Fish Creek and a small tributary to the south of the pipes. These streams must be filled with diamonds! In southern Africa, it was noted diamonds from the Kimberley region were transported more than 600 miles in the Orange River to the coast of western Africa. Now imagine where could all of those diamonds that eroded from Kelsey Lake be. Personally, I would map out Fish Creek and follow it and associated drainages for at least a hundred or more miles down stream.

Gem-quality diamond indicator minerals from the Sloan kimberlites, Colorado
Diamond indicator minerals (chromian diopside to the left and pyrope garnet to the right) in Sloan kimberlite specimens.
When one diamond company was taking samples for kimberlite in this area, they recovered a group of diamonds including a 6.2 carat gemstone in Fish Creek near Kelsey Lake - and they were NOT even looking for placer diamonds. 

Recently, I was notified by a prospector who read my book on Finding Gemstones, that he panned out a cache of diamonds including one just under 5-carats in weight out of a stream I had identified that would be an important diamond placer. Remember, tiny diamonds are almost worthless (as the boys on Gold Rush discovered in South America). But large gemstone diamonds can be valuable. 


If you decide to search the area for diamonds, there is a lot of private property, but also remember a couple of other things: (1) Fish Creek is long, (2) gem-quality diamonds can survive stream transport of at least 600 miles, (3) kimberlites yield other gemstones known as diamond indicator minerals, and (4) the State Line kimberlites have been eroded off and on for the past 600 million years and the largest portion of the kimberlite pipes (the mouths) have been eroded and the diamonds carried downstream (see the schematic cross section through a kimberlite above). It has been estimated that 2000 to 3000 feet of vertical column of kimberlite pipe in this area has been eroded. So, what are you waiting for?



The Carat
The carat may not be enriched in vitamin A, but if large enough, some carats can by a lot of carrots and vitamin A. A carat is what is used to measure the weight of gemstones. One carat equals only 0.0066 troy ounces, or 0.2 grams (200 mg). If you have a troy ounce of gold, this is equal to 31.1 grams or 155 metric carats (152 troy carats). Periodically, jewelers speak in terms of points and there are 100 points in a carat and each point equals only 2 mg (milligrams).

A flawless, 1,720 carat iolite gemstone I found at
Palmer Canyon Wyoming with some sapphire, ruby, and kyanite
gemstones - now that's a lot of carats. 
Now, if you have one troy ounce of gold worth about $1800 and compare this to a rare, pink, Argyle pink diamond worth about $1,000,000 per carat (unfortunately, I don’t have any Argyle Pinks), you will get a good idea at the incredible value of some gemstones. A one-carat rare pink diamond could be worth about 150 times more than a equivalent weight in gold! Not bad for a little crystal.

So where do pink diamonds come from? The pink in diamonds is thought to be the result of shear stress on the diamond, and such gems are thought to form at depth in a subduction zone unlike other diamonds mined in most kimberlites. The great majority of pink diamonds have been mined along the northern coast of Australia at the Argyle mine. To see this mine on Google Earth, search for “Argyle Lake, Australia” and the mine is a short distance southwest of the lake. Very recently, the largest pink diamond ever found was recovered from the Argyle mine. Described by many news outlets as a giant diamond, this one is only 12.76 carats (probably around 12 to 14 millimeters across or a little more than a half inch). As a comparison, the largest diamond ever found was the Cullinun that weighed 3,106 carats). But because of its rarity and color, the Pink Jubilee diamond may sell for as much as $10 million. When cut and polished, it will of course be even smaller.
A group of very expensive Argyle fancy diamonds on display at the
Argyle mine in Australia. I asked, but they wouldn't let me have
any of these.

The Karat
Now let’s look at another word that sounds like the other two words - the karat. Karat also has little to do with rabbits and vitamin A unless you purchase a gold pendant in the shape of a rabbit. Karat refers to purity of precious metals in jewelry. 

When you recover gold in the nearby mountains, it could be nearly pure, yellow gold or could be not quite as pure brassy electrum. Natural electrum refers to a mixture of gold and silver (>20% silver) that is sometimes referred to as white gold.

Natural gold (or precious metals in general) is alloyed with other metals including silver, platinum, palladium, copper, nickel and other metals. It is seldom pure (99.9%) and must be purified to produce the golden metal with few alloys. The purer the gold, the more malleable, soft, heavy and noble (resistant to oxidation and corrosion) is the metal.
Gold from Rock Creek Wyoming mined a short distance downstream from several gold-bearing lodes. This gold is a little whiter (brassy) than gold from some other nearby localities and likely has some silver. Some gold in this area was tested and found to contain as much as 11% silver.

The Rock Creek placer mine was closed by a 1942 War Minerals Board order. This suggests that the World War II miners were recovering gold worth $34/ounce at a profit. Today, gold prices are 50 times higher. Thus this placer likely is still minable. To visit this placer on Google Earth, search for “Atlantic City, Wyoming”.  Atlantic City sits in the upper part of the Rock Creek placer and is the place I figured I would have retired and ending up working for the Prospecting and Mining Journal - but things didn't quite work out that way. Now instead of shoveling tons of snow, I'm basking in the sun.

There are many other placers in this region that contain minable gold. One may be Willow Creek that runs through South Pass City. Willow Creek has a relatively small volume of gravel, but its location (cutting across the Carissa lode, the principal gold-bearing lode in the district) guarantees it will have rich pay streaks. However, Willow Creek was closed to mining by the Wyoming Department of Environmental Quality due to the toxic levels of mercury (whether imagined or real). During my research of this region over a seven year period, I did not find any evidence of primary mercury in the district and the possibility of large quantities of mercury being dumped in the creek by 19th century miners is unrealistic. Mercury was a valuable commodity in the 19th century. If some mercury were actually lost in the creek in the 19th century, it would have been a very small, finite source and mining would only serve to clean the creek bed. 
Pure gold is designated as 24-karat by jewelers: 24-karat gold being the purest at 99.9% gold that is also referred to as 0.999 fine. Being essentially pure, 24-karat gold is soft and can be difficult to some jewelry applications where a wearer of the metal has an active life style. This is because the malleability of pure gold insures such jewelry will be easily scratched. Gold purity can be defined by the formula:

P(karat weight) = 24 x Mpg/Mt (mass of pure gold /total mass of the material).

It is defined that there are 24 units (24 karats). Thus if you could find jewelry of 1-karat purity, it’s would not be something to brag about. One-karat would mean such jewelry is made up of an alloy of 1 part gold and 23 parts alloy metal(s). The percentage of gold in 1-karat would be determined by dividing 1 by 24, which is equal to 0.0416666. Rounding off this number gives 0.042, which is the fineness. To get the percentage of gold in 1-karat simply multiply fineness by 100 to get 4.2% gold.

Yellow gold from Smith Gulch at South Pass, Wyoming.
Two prospectors recovered 20 ounces per week
while prospecting Smith Gulch in the 1980s using
a small backhoe and a trammel. And keep in mind, this was
a placer that supposedly had already been mined out.
 
Some jewelry is listed as 18-karat gold (18/24=0.750 fine). This consists of 75% gold. Another common mixture is 14-karat gold (14/24=0.583 fine) (58.3% gold); and 12-karat gold (12/24=0.500 fine) (50% gold).

12 karat gold = 12/24 = 0.500 (fine)

0.500 x 100 = 50%

Metals often alloyed with gold include nickel, copper, palladium, manganese, silver, zinc, aluminum, iron, gallium, indium, ruthenium, platinum, palladium and rhodium. By using various alloys, gold can be hardened or it can change color.

Using nickel and silver will give gold a subtle white appearance to yield white gold. The nickel provides not only white color, but gives the noble metal strength. However, some people are allergic to nickel. In this case, palladium, platinum, or rhodium can be used to substitute for nickel in white gold. Platinum-group metals are inert just like gold and will not produce allergic reactions (but they cost a lot more than nickel).

Rose and pink gold is formed by using copper as an alloy. The more copper, the deeper the pink color. The use of copper was popular in Russia in the past and this became known as Russian gold, which is now archaic, but the term still persists in the literature. Rose gold is 18-karat gold with 25% copper. Red gold is 12-karat gold (50%) with about 50% copper.

By adding zinc, one can produce less malleable and harder gold. Cadmium can be used to produce green gold. Other varieties include black, purple or blue gold. Purple or amethyst gold is a mixture of gold and aluminum that is 18-karat and brittle. Blue gold is produced by adding indium or gallium to 12- or 14-karat gold. By adding certain metals to gold, the gold can become more and more brittle, more corrosive, and may even discolor in contact with skin.

So karat is not a vegetable, but instead a measure of purity. If we were to weigh gold, the precious metal is weighed in ounces or measured in grams. But, then there is an ounce, and there is an ounce.

When is an ounce an ounce?
Weighing precious metals has caused considerable confusion. This is because there are two different ounces and few people indicate which ounce they are dealing with and not everyone uses the proper ounce for weighing precious metals. Most have the impression there are 16 ounces in a pound. Well, this is true when you are weighing something besides precious metals. The avoirdupois ounce we see on our bathroom scales when we weigh ourselves in the morning is the unit used to weigh objects in most English speaking countries. It comes from the Old French aver de peis which is interpreted to mean weight of goods. So how much your goods weigh in the morning is a result of how much indulgence you had during the previous night.

A 24 ounce gold nugget from Rock Creek Wyoming. 
The weight of precious metals is reported in troy ounces. The troy ounce was part of the Roman monetary system and many assume it refers to the city of Troy of the ancient Roman Empire. But it is instead named after the city of Troyes, France. The troy ounce is different from the avoirdupois ounce and equal to 20 pennyweights (another weight measurement used by prospectors). There are only 12 troy ounces in a troy pound and it takes 1.09714 avoirdupois ounces to equal a troy ounce. A troy ounce also has 31.1 grams while the avoirdupois ounce has 28.35 grams. There is a great website that does all of these conversions for you: 

The fire assay furnace at the Vulture mine, Arizona. Yes the assay house needs a little cleaning.
Gold has been prized since earliest times. Intricately sculptured objects and jewelry have been found in tombs in Iraq and Egypt where Jason and the Argonauts searched for the Golden Fleece. In Biblical times, placer miners used sheep fleece to capture gold in primitive sluices; thus this was the prize sought by Biblical Jason. Gold’s rarity is one reason why the metal became a symbol of wealth and power. The rareness of gold is due to it being formed during supernovae explosions when enough energy and pressure are possible to fuse atoms together to form gold. Without exploring stars (and likely the big bang) we would be without gold.

References:
Boyle, R. W., 1987, Gold – History and Genesis of Deposits: Van Nostrand Reinhold Company, 676 p.
Erlich, E.I. and Hausel, W.D., 2002, DiamondDeposits – Origin, Exploration and History of Discovery: Society of SME, 374 p.
Hausel, W. D. and Hausel, E.J., 2011, Gold –Field Guide for Prospectors and Geologists (Wyoming and Adjacent Areas): CreateSpace, 365 p.
Hausel, W. D. and Sutherland, W.M., 2000, Gemstones and Other Unique Minerals and Rocks of Wyoming – A Field Guide forCollectors: Wyoming State Geological Survey Bulletin 71, 268 p.



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