Prospecting for Gold, Diamonds & Colored Gemstones
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Gold, Gold Gold
After hunting gold for >30 years, finding the yellow metal for several companies and the State of Wyoming, I've decided to let the public know about gold and other valuable treasures. So, I've put together some ideas for prospectors on where to find gold and other valuable minerals.
Wyoming is a fairly good place to look: it's the least populated state in the US; it is underlain by geology similar to southwestern Australia where the Superpit Gold Mine is located in a greenstone belt in the Kalgoorlie area; yet Wyoming produced 50 to 200 times less gold than surrounding states even though it has more favorable geology for gold! This suggests there are major gold deposits that have been overlooked in Wyoming.
Take for instance the Copper King, the Carissa, the Wolf, Rattlesnake Hills, the Seminoe Mountains, the great Ferris-Haggarty mine, the recently discovered Puzzler Hill anomaly, Kurtz-Chatterton, Mineral Hill, Black Buttes, Bear Lodge Mountains, Dickie Springs-Oregon Buttes and copper porphyries in the Absaroka mountains and volcanogenic massive sulfide deposits in the Sierra Madre mountains. These areas all contain significant gold and likely hide some million+ ounce gold deposits.
When Spring arrives in Alaska, Arizona, the golden state, the Colorado Rocky Mountains, Idaho, the ranching state of Montana, Oregon, South Dakota, Utah, Washington and Wyoming, prospectors comb the hills in a search for the yellow metal - GOLD!
In Arizona, you will want to prospect anytime other than summer when temperatures compete with the surface of the sun. Even so, Arizona has many attractive gold deposits: it is amazing more gold mines are not operating. But if you prospect Arizona, take your firearms! With thousands of illegals crossing the border every month, and a lack of concern by the Justice Department, this can make it a dangerous place to prospect, particularly south of Phoenix. We found some gold companies and prospectors refuse to explore in southern Arizona because of this. It is such a problem that the US government closed and provided warnings to US citizens to stay out of this region. Imagine, a region the size of Connecticut surrendered to the Mexican drug cartel. This area likely has good gold and copper - there have been nearly 500 mineralized breccia pipes reported in this region. Such pipes are often found above major copper porphyry deposits.
Some prospectors look for gold and find nothing, others find gold or other treasure: maybe ruby, sapphire, gem garnet, diamond, platinum, chromian diopside, palladium or some other valuable metal or mineral. I found all in Wyoming; and while prospecting for diamonds in California my gold pan touched gold, chromian diopside, sapphire and a beautiful sapphire look-alike known as benitoite. Diamonds were also reported in gold placers in California (Hausel, 1998).
Some prospectors catch a incurable case of 'gold fever' or 'diamond fever' such that they will give up everything including common sense just to search for gold. Some are so taken by the fever that they are easily 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 about contracts and marketing. Personally, I found $billions in mineral deposits, but unfortunately, I didn't learn anything about contracts or marketing - so yes, even after finding more than 40 million ounces of gold (nearly US$70 billion), an entire gold district and hundreds of gemstone deposits, I never made anything more than wages. But I had a great time in the wilds.
There are many types of gold deposits: 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 are 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.
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, and the more I research this region, the more I'm convinced there are dozens and dozens of dry placers for the most part remain untouched. These would be cheap to mine and prospect using either a metal detector and hauling water to process the placer in a sluice or trommel. The arid of Arizona 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. In one extraordinary case, but following tiny, rough, cornflake gold, a group of geologists found one of the largest gold deposits in North America in 1988.
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.
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 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. 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. Another prospector (Frank Yassai) found several diamonds in Rabbit Creek, Colorado while prospecting for 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.
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.
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.
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.
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.
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.
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).
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 these gossans as guides to ore deposits.
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.
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.
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.
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.
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.
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.
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).
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]. Now if you get out in the field and forget your rock hammer - you may have a problem. This is of course if you have not kept up on your karate lessons. In Arizona, we try to keep up with our martial arts classes.
Some References Cited
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.