Showing posts with label gold. Show all posts
Showing posts with label gold. Show all posts

Saturday, July 23, 2016

Gold Prospecting


Note visible gold (distinct yellow) surrounded by pyrite (brassy to silver 
metallic material). Core from the Copper King gold-copper mine, Wyoming.
My latest book 'Gold in Arizona' is now available. It is amazing how many gold deposits there are in Arizona, many sitting idle and many possible extensions of known gold deposits that have been overlooked. Every time I research gold deposits, I am so impressed by how many possibilities there are out there - hundreds and hundreds! My suggestion for those who are new at prospecting (or even been around for many years) is to start looking in known gold mining districts. Those old miners went for the obvious deposits and left a lot of good stuff. Just follow veins and gossans along trend and look for extensions.

Looking to find gold? You've come to the right place. After finding many gold anomalies over the years, mapping gold districts and gold mines, found I was able to identify some gold deposits including a major gold district that was described by one newspaper as having commercial gold mineralization, and also finding a world-class gold deposit with 6 other geologists, I decided to share my experience with prospectors! This latter deposit, known as the Donlin Creek gold deposit in Alaska, is one of the 10 largest gold deposits ever found in all of human history! We were even awarded recognition by the largest gold prospecting and mining association in the world - the Canadian PDAC for our discovery in 1988!

Remember those guys on Gold Rush? Yes, they were finding a lot of gold - a hundred ounces, a thousand ounces, a couple of tiny diamonds. We found more than 40 million ounces of gold, and also a couple of diamond deposits and even some world-class gemstone deposits - but - unlike the Gold Rush guys, I didn't get to keep any of my diamonds or gold - because of who I worked for. Yes, unlike the Fauci CDC gang, I worked for that part of government which thought it was unethical and a conflict of interest to take out patents and rake in $Billions after being paid by tax payers. And there is a good reason for this - imagine, getting all that money after you spread a virus around the world! But am I angry - heck no - I knew what I was getting into. Besides, I received a priceless education and if I had all those $billions, what would I do? Well, I would buy a 4-wheel drive truck with air conditioning, a nice AR-15 rifle, a small cabin in the mountains, and then I would give the rest to charity.

Gold in Arizona - A book about gold deposits in Arizona and where to find them.
Anyway, after hunting gold for more than 30 years, finding the yellow metal for mining companies and the State of Wyoming, I've decided to let you know about gold and other valuable treasures so, I've put together ideas on where to find gold. I published books on gold, diamonds, gemstones that will take you right to the source using GPS coordinates. Over the years I published hundreds of papers along with the books and currently, I'm working on another book on Gold in Arizona where there are a lot of very interesting gold deposits - so please watch for my new book on Arizona when it comes out on Amazon in 2017.

Rock foliation in the Archean age Miners Delight formation metagreywacke
along Rock Creek in the South Pass greenstone belt, provide excellent
natural riffles to trap gold where they crosscut the Rock Creek placer.
One of the state's I did a lot of work in was Wyoming. Wyoming is a strange anomaly. It should be filled with gold based on its geology - it has a continental core known as a craton with some greenstone belts and the craton has been partially destroyed by a very, active igneous system known as the Yellowstone Caldera. This region should be dripping in gold. Greenstone belts are well known in places like Canada and Australia for all of the gold they produce - so why not Wyoming? And the Absaroka volcanics surrounding the Yellowstone caldera contains all kinds of volcanic rocks that should also have gold - where has it gone? There are some scattered gold deposits in the greenstone belts in Wyoming, some large paleoplacer gold deposits, and a few porphyry copper deposits and gold deposits in the Absaroka Mountains, but little gold has ever been reported in Yellowstone. I would bet that Yellowstone is filled with gold, but it is illegal to prospect for gold in that region. Wyoming should have a lot of gold but it historically produced 50 to 200 times less gold than all of its surrounding neighbors (except Nebraska), yet it has more favorable geology for gold. This suggests there are still some major gold deposits that are hidden in Wyoming.

Take for instance the Copper King, the Carissa, the Wolf, Rattlesnake Hills, Seminoe Mountains, Ferris-Haggarty, Puzzler Hill, Kurtz-Chatterton, Mineral Hill, Black Buttes, Bear Lodge Mountains, Dickie Springs-Oregon Buttes and the copper porphyries in the Absaroka mountains. These areas all contain some gold and likely hide a few million+ ounce gold deposits. But why would Wyoming try to keep these deposits from you and me? I have some ideas, but I will let you come to your own conclusions. Other places I have been looking for gold include Alaska, Arizona, Australia, California, Colorado, Idaho, Montana, South Dakota. 

Gold in milky quartz vein material made as inlay in this match
box apparently owned by the Lost Dutchman. 
Some prospectors look for gold and find nothing, others find a little gold or other treasure: maybe ruby, sapphire, gem garnet, diamond, platinum, chromian diopside, palladium or some other valuable metal or mineral. I found all of these in Wyoming; and while prospecting for diamonds in California my gold pan touched some gold, chromian diopside, sapphire and a beautiful sapphire look alike known as benitoite. Diamonds were also found in gold placers in California by others (Hausel, 1998). Others catch a incurable case of 'gold fever' or 'diamond fever' such that they will give up everything - their homes, jobs and common sense just to search for gold. Some are so taken by the fever that they are exposed to scams and con-men who take whatever worldly possessions are left. 

If you want to get rich - learn a little about gold prospecting, geology from a good prospector or field geologist, and learn something about contracts and marketing. Personally, I found $billions in mineral deposits, but unfortunately, didn't learn anything about contracts or marketing - so yes, I never made anything more than wages and all of the minerals I could carry in my back pack. But I had a great time in the wilds.

There are many types of gold deposits to a geologist - hydrothermal, mesothermal, epithermal, replacement, etc., but to prospectors, there are only two types: placer and lode (Hausel, 2001, 2010). Famous placer deposits include Nome and Flat, Alaska, and Alder Gulch, Montana. Examples of lode deposits include the Mother Lode, California and the great Homestake mine in South Dakota.

There is not always a clear distinction between lode and placer gold deposits. For instance, the great Witwatersrand gold deposits in South Africa, the most productive in the world, are classified geologically as paleoplacers. Because they occur in brittle, consolidated rock (mined to depths of greater than 13,000 feet), most prospectors would consider these to be lode deposits. 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 now the rocks deposited by the former rivers and streams are preserved as hard, consolidated rock ledges.


Eluvial gold typically sits on top of a vein or lode. Eluvial deposits are restricted in size but may be enriched in gold. A
lode may not be exposed at the surface, but if you are finding gold-bearing quartz in alluvium, a vein is likely hidden 
under the alluvial (eluvial) cover. Such deposits are common in Arizona, though few of the eluvial-alluvial deposits have
been explored in detail in a search for the underlying lodes. In Wyoming, there are likely some giant gold deposits under
eluvium and alluvium near South Pass. 

Another not so clear distinction may arise with eluvial deposits. Eluvial deposits are essentially composed of detrital material weathered in place from a nearby (often underlying) source. Gold from an eluvial deposit would show little or no evidence of transportation. Since eluvial deposits are unconsolidated, some prospectors would consider them placers, even though they may directly overlie a lode. There are many examples of eluvial gold in Arizona. The arid environment is favorable for eluvial deposits due to the lack of active streams and - where there is eluvial gold, there is lode gold in the immediate area - something every prospector needs to keep in mind. Eluvial means that the material essentially eroded in place or from a nearby source area. In Arizona, there are many placer, alluvial and eluvial gold occurrences in streams, conglomerates and fanglomerates.

Paleoplacer gold, uranium and diamond deposit from the Snowy Range in
the Medicine Bow Mountains, Wyoming. Note the rock is very hard and
massive, yet it contains many rounded pebbles deposited in streams more
than 2 billion years ago. Uranium, thorium, gold and even diamonds have
been recovered from these rocks in Wyoming. 
Placer deposits
Placers consist of detrital gold and other valuable minerals transported in streams or by wave action to be concentrated with other heavy minerals known as black sands. If you have ever panned for gold, you are familiar with black sands. Black sands consist of dark opaque minerals with greater than average specific gravity, which may include magnetite, pyroxene, amphibole, ilmenite, garnet, sphene, chromite and monazite, as well as some rare light-colored minerals with relatively high specific gravity such as cassiterite and scheelite. If you ever panned near Wilson Bar or Wilson Gulch at South Pass, Wyoming, you may have found all of this heavy, nagging, white to brown quartz that was impossible to pan out. Well, it probably wasn't quartz. With a shortwave ultraviolet light, this heavy quartz likely will fluoresce blue-white simply because it was not quartz, but instead is scheelite, a tungsten ore found in some of the gold ore at the Burr and Hidden Hand mines (Hausel, 2009). When found,on public land, placers can often be claimed under the 1872 mining law. But if you want the lode under the placer, you better look at filing a lode claim too.

Take a close look at this sample. It was one of many found by 
field trip attendees on my past field trips to South Pass. 
Everything you see that is gold colored in the rock is gold.
This was found at the Carissa mine. 
Other minerals of potential economic interest with relatively high specific gravity may occur 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 with trace amounts of ruby and sapphire were recovered along with heavy minerals (Hausel and others, 1988; Hausel, 1998). These were eroded from nearby, undiscovered, corundum (sapphire, ruby) mica schists and gneisses. How do you tell if you have ruby or sapphire in your gold pan? Look at crystal habit. The habit is the common form of the crystal. Ruby and sapphire form hexagonal crystals that are bounded by two pinacoids (basically flat surfaces).

While prospecting for diamonds in the Sierra Nevada of California, I found sapphires and benitoite near Poker Flat. And one prospector (Paul Boden) found a couple of excellent gem-quality octahedral diamonds while searching for gold on Cortez Creek in the Medicine Bow Mountains, Wyoming, and another prospector (Frank Yassai) found several diamonds in Rabbit Creek, Colorado while prospecting for gold.
Another sample collected on my field trips for the public. 
Visible gold is seen in every vug in the piece of quartz found
at the Carissa mine at South Pass. So what did the State do?
This likely multi-billion dollar gold deposit was purchased by
the State of Wyoming, withdrawn, and placed within the 
South Pass City historic site where the state now collects 
nothing for all of that gold. 

During erosion of bedrock, these heavy minerals mix with abundant light-colored, glassy, transparent to opaque minerals with low to average specific gravity such as quartz, apatite, feldspar, and mica. Along with these, minerals with high specific gravity are slowly moved in streams with moderate to high water velocity. The sediment carrying capacity of a stream diminishes with decreased velocity. The heavy minerals concentrate by settling out where diminished velocity occurs; such areas are marked by a 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) and at waterfalls. Since many streams lack sufficient velocity to carry gold for any great distance, much of the gold in these streams (particularly where it is concentrated in pay streaks) is probably transported during flash flooding events or during heavy spring runoff.

The distances heavy minerals can be transported are not known with any accuracy. Some minerals can be transported great distances. For example, because diamond is 6000 to 8000 times harder than any other mineral and is not very heavy (specific gravity of 3.52 compared to 2.87 for quartz), there are cases where transport distances for diamonds has 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.

Such great transportation distances for gold are not possible. Gold is too heavy (specific gravity of 15 to 19.3), so when found 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 while in solution. In Alaska, geologist Paul Graff identified gold that had crystallized in nuggets downstream from nearby lode deposits. Maximum transportation distances for gold in solution is unknown.


The color change (upper arrows) more than 1 foot above the gold pan (circled) mark the site of a pay streak in Smith Gulch discovered by prospectors Hank Hudspeth and Buddy Presgrove. This streak was produced during a flash flooding or unusually high spring runoff. A second pay streak was found at the base of the open cut near the standing water (lower arrow). Even though this placer was located in a dry drainage when mined, it was immediately down slope from several lode deposits that provided a favorable site for gold concentration. At this point, the prospectors had not yet reached bedrock, where there is likely another pay streak. 

Flash flooding events appear to be important in forming pay streaks of gold and diamonds. Pay streaks, or lenses of gold-enriched gravel, are often found in zones of coarser-grained pebbles and cobbles. The pay streaks may be scattered over one or more intervals in a vertical column of gravel.

Schematic showing development of meander. Where the stream starts to meander, water velocity decreases & minerals with higher specific gravity concentrate (stippled areas). Through time, the meander may mature, leaving deposits on the inside banks as the stream migrates. Material in the stream as well as the adjacent bank material (which may be high and dry after episodes of flooding and high water) will contain heavy minerals & possibly gold and diamond. 















Where meanders occur in streams, gold may concentrate on the inside of the initial curve in the channel, as well as in the bank (point bar) on the upstream part of the inner meander where gold was deposited in the past. As an example, one of my favorite places to take students in the past in my prospecting courses was near Bobbie Thompson adjacent to a historical gold placer in Douglas Creek, Wyoming. Here the bank gravel sits away from the active stream, but contains enough gold to keep the interest of the students.

Gold Road Lode vein in northwestern
Arizona
In addition to modern placers, some regions contain paleoplacers. Places like Wyoming and the Witwatersrand of South Africa are famous for paleoplacers scattered over large regions. In the Witwatersrand, the paleoplacers are so important, that they have produced about 50% of all of the gold mined in human history. Today, they have the deepest mines on earth. In Wyoming, most paleoplacers have either not been prospected, or only have been cursory examined at best, even though it is a safe bet that economic gold deposits occurs in some of these. Paleoplacers are simply fossil placers that were deposited by streams or by wave action along prehistoric seas in the geologic past. In most cases, these may not lie anywhere near an active stream or sea today; thus, mining would either require transporting water to the paleoplacer, or transporting material from the paleoplacer to water.




Wayne Sutherland, WSGS geologist, examines paleoplacer at Dickie Springs to the south of South Pass. Note all of the rounded boulders and cobbles typically found in active streams and rivers. 











Where the paleoplacer consists of relatively unconsolidated gravel, it can be mined in a manner similar to a sand and gravel operation. If the operation is located near a road, the sand and gravel by-product can be used in road construction. Conversely, gold can be extracted as a by-product of sand and gravel operations. For example, gold was found in several sand and gravel operations and placers adjacent to Interstate 80 in southern Wyoming (Hausel and others, 1993). Where paleoplacers are extremely old and well consolidated, such as in the Witwatersrand, the gold is typically mined underground.
Gold recovered the dry paleoplacer near
Dickie Springs. The gold suggests a 
hidden lode somewhere between this site,
and the exposed South Pass greenstone belt 
to the north. Foster Howland with Hecla Mining
 explored this area & identified a good target - 
a sulfide-bearing iron formation at depth that
could contains gold. The project was 
terminated before the work was completed. 

In the South Pass greenstone belt in western Wyoming, giant paleoplacers surround the region at McGraw Flats to the north and Oregon Buttes-Dickie Springs to the south. And there are smaller ones in between. The southern paleoplacer was reported by Love and others (1978) of the US Geological Survey to contain more than 28.5 million ounces of gold, yet most of this area is unexplored. Along the northern flank of the Seminoe Mountains greenstone belt, the Miracle Mile paleoplacer is unexplored even though myself and field assistants recovered gold from the dry paleoplacers nearly everywhere we sampled. This paleoplacer was discovered by prospectors Charlie and Donna Kortes, also contains dozens of G10 pyrope garnets that indicate somewhere in this region is a very rich diamond deposit or deposits. Keep your eyes out for diamonds when looking in any placer or paleoplacer! Paleoplacers in the Medicine Bow and Sierra Madre Mountains in southern Wyoming yielded some gold and diamonds, but are rich in uranium and thorium.

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

Classic lode. This auriferous quartz vein in metatonalite at the Mary Ellen
mine at South Pass was offset along a small, reverse fault. Lodes are considered
in situ deposits in hard rock
When pyrite oxidizes, it produces sulfuric acid and rust (a massive sulfide deposit of pyrite will smell like rotten eggs, and a massive arsenopyrite deposit will smell like garlic, and both can have considerable gold and silver), 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 a distinct, rusty appearance. These gossans offer excellent visual guides in the search for gold and other mineral deposits. In any historic mining district, you will often find dozens, if not hundreds, of old prospect pits dug into the rusty rocks. Prospectors learned to recognize gossans as guides to ore deposits.

Gossan at Red Mountain in the San Juan Mountains, 
southern Colorado. Note all of the red to light 
yellow-colored rock found nearly everywhere in the photo. 
These are gossans that contain significant amounts 
of gold and silver. 
Gossans are good places to search for high-grade gold in lodes. The recognition of gossans in the field can be very helpful to the prospector. For example, gossans produced from the leaching of pyrite are typically very rusty (reddish-brown) in appearance; gossans produced from arsenopyrite are typically greenish-yellow. Gossans are so important that an entire book was written on their different characteristics (Blanchard, 1968).

Large gossans that cover several acres may be situated over giant sulfide-enriched veins or massive sulfide deposits. These may contain gold and/or valuable base metals (copper, zinc, lead, etc). One very large gossan in the Hartville uplift in eastern Wyoming is so distinct that I ended up naming it “Gossan Hill”—it overlies a massive sulfide deposit. One of the better places to look for specimen-grade gold samples is within gossans containing boxworks. Boxworks is a distinct vuggy and rusty rock.



This specimen of boxworks exhibits pore spaces formed where sulfide minerals were removed by oxidation. The sulfides
 were oxidized by oxygen-rich water near the surface, leached out, and removed. Gold, which often is found in pyrite, is
mostly inert, and may remain in place within the boxwork pits, while some of the iron from the pyrite stains the rock and
the walls of the pits. Much of the sulfur was likely mobilized by groundwater cane carried down dip. At Bradley Peak in
the Seminoe Mountains, I found nearly a
dozen of these samples and started a gold rush in 1981. Even this area 
remains essentially unexplored to this day!

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

A breccia (angular fragments) cemented by quartz - a good place to check for gold. Such breccias are formed in faults or by the release of gas under pressure which produces a breccia pipe. Note the difference between the breccia with angular rock fragments (left) and the Tertiary-age (about 30 million years old) paleoplacer with rounded pebbles (below left) and the stretched pebble conglomerate (very old paleoplacer nearly 2 billion years old) (below right) All three can contain gold. 



















Consolidated conglomerate 


Ore shoots
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 dropped during hydrothermal mineralizing events, structurally controlled ore shoots occur. Chemically controlled ore shoots may 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) is a great place to find gold and other minerals.

Paleoplacer with stretched pebbles from the Medicine Bow Mountains, WY
These ancient stream deposits were later deformed under great pressure
that flattened and stretched the pebbles in the rock. Such rock sometimes
contain gold, uranium and even diamonds - basically any type of heavy
mineral that would have been carried in rivers more than 2.5 billion years
ago before the earth had any appreciable oxygen.
When searching for structurally controlled ore shoots, it is necessary to look for places where one would expect the pressure to have decreased along vein systems. Some structurally controlled ore shoots are found in folds. Many fold closures in gold-bearing veins will be enriched in gold. Another type of structurally controlled ore shoot includes vein intersections. Some intersections of gold-bearing veins have been dramatically enriched in gold.




The Carissa mine at South Pass. The shear zone in the background is rich in gold [average grade reported at 0.3 opt Au, much higher than the ore currently recovered from mines in Nevada (0.02 to 0.15 opt Au) (opt Au= ounces per ton of gold)]. Although not visible to the untrained eye, this giant gold-bearing structure lies in a large fold in the shear. The ore zone is 970 feet long, nearly 1,000 feet wide and continues to a minimum depth of 930 feet (and likely a few thousand feet deep). The property was withdrawn by the State of Wyoming even though it very likely hosts a few million ounces of gold worth a few $billion. 

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. The same veins in quartzite were unproductive. Additional information on ore shoots can be found in various books on economic geology and ore deposits (see Earll and others, 1976; Evans, 1980; and Peters, 1978).

What does gold look like?
Most people have a difficult time identifying gold at first. Gold is very heavy! It is 15 to 19 times heavier than water, it is malleable (it will easily scratch with a pocket knife), and has a distinct gold color that does not tarnish. Most people mistaken mica, pyrite (fool's gold), or chalcopyrite (copper-fool's gold) for real gold. These latter minerals are brittle and will crush to a fine greenish black powder. But don't be fooled. Some pyrite (fool's gold) may contain up to 30 parts per million gold hidden in the crystal structure (about an ounce per ton). To test for this gold, you will either have to assay, or powder the pyrite and pan it for gold. And chalcopyrite may have as much as 20 parts per million gold hidden in its crystal structure. 


Large specimen of mica (muscovite) shows a mirror-like surface, bronze-color, and will break into tiny pieces by a pocket knife unlike gold. Tiny mica flakes will easily move around in a gold pan while panning. As you pan, if the gold material stays flat on the surface of your pan and is difficult to move, it may be gold. However, if it moves easily, rotates or spins in the water, it is not gold. Mica is hard to pan out of a gold pan simply because it is essentially 2-dimensional and will cut through the water like a knife. 


Gold in the pan is angular, heavy and a brightly yellow-gold color. It does not have mirror-like surfaces and will stay put in the pan. Pyrite will crush to a greenish black powder and the same with chalcopyrite (photo of gold from Dickie Springs, Wyoming courtesy of Dr. J.D. Love). 

Conclusions
The search for productive gold deposits requires a good background in prospecting and economic geology as well as some luck. However, there are literally hundreds of occurrence and deposits in nearly every state in the West including Alaska. The best way to begin prospecting is to get a book that describes the gold mines and placers and visit these as I have found there are always many deposits near old gold mines that have been overlooked. This is how I found more than a hundred gold deposits and anomalies. An understanding of geology also helps: I found an entirely new gold district (Rattlesnake Hills in the early 1980s) that was missed by everyone else, simply because of the geology. It had very favorable geology and is currently being explored and drilled by several companies even though I discovered this district nearly 30 years ago! I was also on the discovery team of the giant Donlin Creek gold deposit in Alaska. Part of our discovery team (Rob Retherford, Bruce Hikock, Toni Hinderman) had recognized that some place gold at Donlin Creek was like corn flakes, very angular. Paul Graff visited the area with Mark Bronson and Richard Garnett and WestGold decided to explore this region. I was hired to map the deposit - it was a major discovery that includes more than $42 billion in gold! Yet this discovery occurred all the way back in 1988 and the gold deposit, considered one of the largest in the world, still is not being mined (but is under exploration).

So, get hold of books in your area that describe 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 (usually they have a few good publications). 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 likely hundreds of lode gold deposits that have been missed because of so many eluvial placers with no reported gold source (the gold came from somewhere!). Colorado and California have hundreds of possibilities, but personally, I would look in Arizona, Wyoming, Montana and Alaska. For additional information on gold, gold in Nevada, New Mexico, Utah, Idaho, Washington, Oregon and South Dakota, watch for other blogs and keep track of my GOLD and Consulting websites as I will periodically update these. Myself and my son (Eric) who is also a geologist, are currently writing a couple of books on gold and we will tell you exactly where to look.



"Old mines never die, they are just forgotten". And enormous gossan exposed at the United Verde mine in Arizona. This property was mined for copper, gold, silver and zinc over many decades and then it was closed. Was it mined out? No - few mines are ever mined out. It is just that 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 of these old mines are likely economic. It is reported that the former miners did not recover the low-grade zinc and copper ore that likely contains more than a million ounces of gold. Additionally, after examining the aerial photos over this region, it is apparent that there is a 10+ mile gossan that likely is underlain by several massive sulfide deposits that remain unexplored. Remember, old mining districts often contain many opportunities. 

Fisher dredge on Rock Creek, South Pass, Wyoming showing unmined ground
While you are looking for gold deposits, remember, there are probably just as many if not more gemstone and diamond deposits that have been missed by prospectors and geologists. I recently found a major field of cryptovolcanic structures that are likely diamondiferous kimberlites sitting right along Interstate 80 west of the State Capitol of Wyoming. With a good arm, one could probably hit some of these with a rock next to the interstate. These remain unexplored and were just discovered a couple of years ago! 

Some of these are so obvious, that it makes one wonder what everyone has been doing. Take for instance the Cedar Ridge opal deposit. Probably the largest opal deposit in North America was 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 in a pipeline - but totally overlooked. Even after the announcement of this major field in 2003, it still remains pretty much unexplored! This deposit contains opals in road cuts that weigh more than 100,000 carats and has common, fire and precious opal and some spectacular 'Sweetwater' agates. How anyone could have overlooked this, is beyond comprehension. But it sat there for several million years, untouched, other than 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 that I found at Grizzly Creek and Raggedtop Mountain in the Laramie Range. How these can remain essentially untouched is beyond my understanding. At one deposit, I found gem iolite as large as 24,000+ carats with pieces in the outcrop that likely weigh hundreds of thousands (if not millions) of carats. The other deposit may host as much as 2.7 trillion carats based on past geological reports (that 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 primary gemstone, iolite, can be cut for $0.5/carat and is 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 I was employed at the WGS (Although, today I am a consultant).

Stacked pay gravel on Rock Creek placer, South Pass.
Note the distinct clay and silt false bedrock layer. The
gold occurs in the gravels above and below the false
bedrock. The clay and silt represent a very dry period. 
There are many placer and lode deposits to be found, although the discovery of entirely new mining districts is rare. In all my years as an exploration geologist, I have only been able to find one new gold district. However, I have found many gold deposits within known districts and you should be able to do the same armed with a little knowledge.

Some of the better areas to search for gold are historical mining districts. In my experience, it is rare that any ore deposit has been completely mined out. Many historical and modern mines still contain workable mineral deposits as well as nearby deposits that have been overlooked. Many well-known giant mining companies of the past were notorious for overlooking significant ore deposits and ignoring others. For example, AMAX explored a large porphyry copper-silver-gold-lead-zinc deposit in the Absaroka Mountains southeast of Yellowstone. They focused on the prophyry and ignored nearby vein deposits that assayed >100 opt silver! Thus, one could potentially make a living just following up on the exploration projects of many of these past giants [as well as some projects of present giants]. 

Pyrite (fool's gold). Note the brassy color (not gold colored). 
Pyrite is brittle and the upper photo shows crystalline (cubic) 
pyrite. Upper specimen from the Lost Muffler gold prospect, 
Rattlesnake Hills and lower specimen from the Pickwick 
vein, Kirwin district, Wyoming. But don't throw them away: 
pyrite can contain a few hundred parts per million to potentially
2,000 ppm (64 ounces per ton) hidden in its crystal structure! 






Some References 
Blanchard, R., 1968, Interpretation of leached outcrops: Nevada Bureau of Mines Bulletin 66, 196 p. 
Earll, F.N., and others, 1976, Handbook for small mining enterprises: Montana Bureau of Mines and Geology Bulletin 99, 218 p. 
Evans, A.M., 1980, An introduction to ore geology: Elsevier, Amsterdam, The Netherlands, 231 p. 
Hausel, W.D., 1989, The Geology of Wyoming's Precious Metal Lode and Placer Deposits: Wyoming Geological Survey Bulletin 68, 248 p. 
Hausel, W.D., 1991, Economic Geology of the South Pass Granite-Greenstone Belt, Wind River Mountains, Western Wyoming.Geological Survey of Wyoming Report of Investigations 44, 129 p. 
Hausel, W.D., 1997, Copper, lead, zinc, molybdenum, and associated metal deposits of Wyoming: Wyoming State Geological Survey Bulletin 70, 229 p. 
Hausel, W.D., 1998, Diamonds and mantle source rocks in the Wyoming Craton, with a discussion of other U.S. occurrences: Wyoming State Geological Survey Report of Investigations 53, 93 p. 
Hausel, W.D., 2001, Placer and lode gold deposits: International California Mining Journal, v. 71, no. 2, p. 7-34. 
Hausel, W.D., 2009, Gems, Minerals and Rocks of Wyoming. A Guide for Rock Hounds, Prospectors & Collectors. Booksurge, 175 p. 
Hausel, W.D., 2010, How to find gold: Lost Treasure Magazine, July, p. 56-60. 
Hausel, W.D., Marlatt, G.G., Nielsen, E.L., and Gregory, R.W., 1993, Study of metals and precious stones in southern Wyoming: Wyoming State Geological Survey Mineral Report MR 93-1, 54 p. 
Hausel, W.D., Sutherland, W.M., and Gregory, E.B., 1988, Stream-sediment sample results in search of kimberlite intrusives in southeastern Wyoming: Wyoming State Geological Survey Open File Report 88-11, 11 p. (5 plates) (revised 1993). 
Hausel, W.D., and Sutherland, W.M., 2000, Gemstones and other unique minerals and rocks of Wyoming—A field guide for collectors: Wyoming State Geological Survey Bulletin 71, 268 p. 
Peters, W.C., 1978, Exploration and mining geology: John Wiley and Sons, New York, 696 p. 



Specimen of chalcopyrite in quartz (with green malachite and silver-colored specularite) from the Kurtz-Chatterton mine (a great, unexplored, gold prospect) from the Sierra Madre, Wyoming. The chalcopyrite is the brassy-orange material in the specimen. Some chalcopyrite can contain as much as 20 ppm Au (a considerable amount of gold equal to about 0.7 ounces per ton) hidden in the crystal structure along with some silver. 



Just hit a rock and you will smell garlic? No, it was not that Italian prospector standing up wind from you - it was most likely the smell of arsenic from the arsenopyrite that you just hit with your rock hammer. Arsenic-pyrite, or arsenopyrite, often is found around many gold or silver deposits and can hold up to 1,000 ppm gold (32 ounces per ton) hidden in its crystal structure. Whenever I find arsenopyrite, I have it assayed. Sometimes the mineral will assay high in silver, such as at South Pass. At Donlin Creek, Alaska, both arsenopyrite and stibnite yield high gold assays. Thus, arsenopyrite is a good guide to precious metals. The rock above contains considerable prismatic, silver gray metallic arsenopyrite with scorodite (reddish brown to yellow oxidized arsenopyrite). 


Cuprite (earthy red), malachite (green) and tenorite (black) from the Sunday Morning prospect, Seminoe Mountains, Wyoming. These minerals can all contain some silver and gold in their crystal structure. Malachite will emit CO2 bubbles just like soda pop when sprayed with dilute (10%) hydrochloric acid. Spray cuprite and tenorite with dilute hydrochloric acid and rub a well used rock hammer in the wet mineral and it will replace the worn parts of your hammer with native copper. 


Gold from Rock Creek at South Pass. 


Green malachite, a copper carbonate, often contains anomalous 
silver and gold detectable in assays 


Azurite (blue), tenorite (black) and cuprite (red) -
classical copper minerals. Don't make
the mistake many prospectors do - collect
these pretty minerals without having some assayed.
Copper minerals often contain gold hidden in the
mineral or replacing some copper atoms in the crystal
lattice. They also contain silver more often than not.



Not all assayers are created equal. Do some research and check on an assayer before using them. 

Friday, January 2, 2015

Finding Carats, Carrots, and Karats | Searching for Gold and Diamonds


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, a piece of gold, or a diamond from that 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 were hoping to pan 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 much of my life. 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 one in Wyoming). One day I'll have to break down and buy a new truck with AC.

Carrot comes from the 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 (kimberlite 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.



HEY, there are many OLDER posts - be sure you look at them