How to Find and Identify Gold
How to Find and Identify Gold
"By gold, all good faith has been banished; by gold, our rights are abused; the law itself is influenced by gold, and soon there will be an end of every modest restraint."
- Sextus Propertius
Thank you, thank you thank you! Dr. Daniel N. Miller, Jr (RIP) and Gary B. Glass hired me as the 'Minerals Geologist' for the Wyoming Geological Survey in 1977 - I had no experience, so they were taking a big chance on me. One thing I did have was dreams and ambition - which they apparently recognized when they saw me jumping up and down and running around the office after they told me what was required of the person who they would hire for the job. "Yes, yes, yes" I screamed each time they mentioned the duties.
I was hired and placed in charge of mapping mining districts, diamond deposits, ancient rocks in mountain cores, searching for new mineral deposits, and assisting prospectors in a quest for mineral deposits. When on annual leave and after I left the Geological Survey, I worked as an independent consultant for mining companies.
Some prospectors thought I could smell gold - this is only partially true, because some deposits actually smell because of associated arsenic sulfides (which have a distinct garlic odor) such as arsenopyrite, realgar or orpiment and iron sulfides such as pyrite (which smell like politicians or rotten egg gas). But in reality, I stumbled around much of the time as I tried to figure out the geology. Anyone watching me in the field would have thought I had lost my mind - walking around in circles, breaking rocks, picking up pieces of rock to look at with a magnifying lens, jumping 30 feet in the air when startled by rattlesnakes, etc. Along the way, I made some mistakes in interpretations, but I was persistent and continued to try to satisfy my insatiable desire to find what was on the other side of the hill.
I was also charged with summarizing my results in papers, books and public lectures - this required I spend considerable time on the ground following outcrops, rock formations, veins, breccias, sulfide-pockets, etc. And I loved every minute - even when I had to kick rattlesnakes off outcrops, fight hurricane force winds of the Wyoming jet-stream, and periodically threatened by transplanted ranchers from back east. One transplant from Pennsylvania was arrested by the Game and Fish for running an English-style fox hunt designed to harass coyotes and kill antelope out of season. Last heard, this future politician had scheduled a sex change operation - not something one would expect from a real rancher. My report writing required I put together my thoughts on paper so the State could promote its mineral resources to companies, prospectors and rock hounds. Sitting in my office and putting together these thoughts each winter helped me formulate new ideas on what to look for and where to look during the next field season.
After hunting gold, diamonds and colored gemstones for more than three decades, I decided to let prospectors in on my secrets. In my recent books available at Amazon, (1) Finding Gemstones, (2) Gold and (3) Field Guide to Gemstones, Minerals and Rocks, I described hundreds of mineral sites and provided legal descriptions and/or GPS coordinates to assist you in finding gold, diamonds, colored gemstones and fresh air. I also provided information on what to look for in each deposit and how to identify the gemstones and host rocks. Think of this as an education in prospecting. All one has to do is to get permission to visit some sites. I did most of the ground work for you and even got rid of several of several rattlesnakes.
Speaking of rattlesnakes (not my former boss, but the other kind of crawly reptile), did you know in the late spring when everything is green for a few days in Wyoming, rattlesnakes actually turn green while much of the field season, they are brown. Just like politicians - when they get around your money, they turn green, whereas the rest of the time, they are brown, just like …. well you know.
What does gold look like?
Most people have a difficult time identifying gold in nature until they’ve seen it a few times in their pan, in a quartz or in rock. When I was at the University of Wyoming, many people visited my office with vials, Ball jars, shopping and sample bags filled with mica wanting to know if they had was (Figure 1, see gallery at right). It was rare for any of these people to have any gold. Nearly all had jars full of mica.
Mica is commonly mistaken for gold - in particular sericite, muscovite, phlogopite and paragonite mica fools many. With a specific gravity of only 2.76 to 3.0, mica should easily wash out of a gold pan with quartz. However, it takes effort to pan mica out of a gold pan. This is because mica commonly exhibits a crystal habit of paper-thin slices of flakey, monoclinic (pseudohexagonal) crystals with perfect cleavage. Being essentially two dimensional, the mica will act like a blade while tumbling and slicing through water making it difficult to pan out. If you closely watch the mica as you pan, it will tend to congregate on top of the black sands during panning. Gold being very heavy, will sink to the bottom of a gold pan and not tumble.
Gold has a specific gravity of 15 to 19.3. In other words, if you compare an equal volume of gold with water, gold is 15 to 19 times heavier. Gold is malleable and can easily be scratched with a pocket knife, whereas mica is brittle. Most of us never find chunks of gold large enough to scratch with a knife; but if you do find a piece large enough to stick with a pin, the gold will indent. If you apply pressure to mica with a pin point, it will break into smaller flakes.
Other minerals mistaken for gold include pyrite (fool's gold), pyrrhotite (a variety of fool’s gold), and chalcopyrite (copper-fool's gold). Pyrite (Figure 2) is an iron-sulfide of the general formula of FeS2. This means pyrite is formed of iron and sulfur, but may contain minor impurities such as gold. Pyrite occurs as brassy, disseminated, massive to crystalline specimens that form cubes with striated faces, octahedrons, pyritohedrons (12-sided) as well as combinations of these crystal habits. Unlike gold, pyrite is not malleable and will crush to a dark, greenish-grey powder by striking it with a rock hammer – whereas gold will flatten when struck. Pyrite will produce a streak with the same color. Additionally, if you leave the brassy mineral outside in the rain for a few weeks, it will rust.
You can also be fooled because some of these brassy sulfide minerals will contain gold hidden within the crystal structure. Pyrite will fool some prospectors into thinking they have gold – hence the term ‘fool’s gold’. But with a little experience, one should never be fooled twice by this mineral. Gold is very heavy, malleable, and has distinct, warm, golden-yellow metallic color. The specific gravity of pure native gold is 19.3. Pyrite has a specific gravity of 5.0 (5 times heavier than an equal volume of water): although relatively high, the specific gravity of pyrite is notably less than gold.
Geologists and seasoned prospectors speak of heft. This is simply a relative measure of a mineral’s weight. For instance, a gold nugget has very high heft and pyrite has moderate heft (Hausel and Hausel, 2011). To measure heft, just bounce a specimen in your hand and make a relative judgement as to whether the specimen has high, moderate or low heft.
If you find pyrite and throw it away because it’s not gold – you may have been fooled again. Pyrite can enclose hidden gold within its crystal lattice. Gold bearing pyrite rarely has visible gold unless it is completely oxidized and replaced by limonite boxworks (Figure 4). It is worthwhile to collect samples of pyrite and have them assayed if you are in gold country. In the old days, prospectors crushed pyrite to a very fine powder and panned the powder for native gold. Sometimes this worked, other times they missed very fine gold, particularly if the gold replaced individual iron atoms in the crystal lattice. Pyrite is of no value except as mineral specimens or when it contains appreciable gold and silver. Theoretically, pyrite can contain as much as 2,000 ppm (parts per million) gold. This is equivalent to a ton of pyrite with 64 ounces of gold, hidden within the mineral!
Some pyrite from Uzbekistan was reported to contain 37 to 232 ppm (1.18 to 7.42 opt) Ag along with 40 to 187 ppm (1.28 to 5.98 opt) Au. In Italy, Boyle (1987) described pyrite with 0.12 to 200 ppm (0.004 to 6.4 opt) Au. Pyrite from the Lost Muffler Prospect in the Rattlesnake Hills, Wyoming was found to have 10 to 20 ppm (0.32 to 0.64 opt) Au (Hausel, 1996). The pyrite was found as cubes (as large as 0.2 inch) in a siliceous zone in metabasalt and metagabbro. The mineralized zone was traced over a distance of 4,800 feet.
The first specimen of pyrite I ever found was on a field trip to the Lark Mine in the Oquirrh Mountains along the western flank of the Salt Lake City valley. I was taking a mineralogy class as an undergraduate at the U of U. At one point, I looked at the mine rib (wall) and saw a beautiful hand specimen of pyrite cubes that had my name written all over it, so I dug it out (Figure 5). I’m not sure why, but excellent pyrite specimens like the one I collected in the mine seldom are mineralized in gold - I suspect it has something to do with temperatures and pressures of mineralization and likely the chemistry of both the host rock and the hydrothermal fluids that allowed for the unimpeded growth of the pyrite crystals.
Pyrite will weather to limonite over time. As an example, when I moved to Gilbert Arizona from Laramie, I filled part of an 18-wheeler full of rock and mineral specimens - yep, I had a hoarder's infliction for rocks. My wife, bless her heart, decided to break me of that habit and 98% of my samples ended up making a rock garden in the back yard. Yesterday I looked at four massive pyrite specimens in the garden, and they were already turning to rust - these were all placed in the garden just last year! One other sample that received periodic sprinkles of water from the vegetable garden is now nothing but rust. It doesn't take long for such specimens to suffer. Last year, I also placed a massive specimen of galena in the sun. I was shocked to see it was already being replaced by the end of a month - it looked like the sun had burned this once, shiny, metallic specimen.
If considerable pyrite is present in an outcrop, it often oxidizes to a distinct gossan with scattered porous boxworks (Figure 6). If the pyrite is gold-bearing the resulting limonite will be enriched in gold. Thus it always worthwhile to examine limonite in gossans with a 10x hand-lens to look for visible gold. If no gold is obvious, it still may be worthwhile to assay a few samples. Pyrite is also found associated with chalcopyrite, sphalerite, galena, bornite, gold and/or arsenopyrite. Marcasite, a polymorph of pyrite, has been reported in sedimentary uranium deposits as finely disseminated grains. Marcasite rarely contains gold.
Chalcopyrite is also periodically mistaken for gold. It is a primary copper ore with a formula of CuFeS2 that is sometimes referred to as copper-pyrite. Chalcopyrite forms a metallic orange-bronze mineral that occurs as compact masses that sometimes has a distinct metallic surface sheen that is bronze, violet, greenish to blue. It is mostly massive or disseminated and individual crystals are uncommon. Chalcopyrite has cleavage seen in some specimens. The mineral is brittle, has uneven fracture, and will yield a greenish black streak when scratched on a white tile. It occurs with other copper minerals such as chalcocite, malachite, and bornite as well as with pyrite. It has a hardness of 3.5 to 4 and specific gravity of 4.1 to 4.3.
Some chalcopyrite has been reported to have anomalously high gold and silver. Gold in chalcopyrite likely substitutes for copper in the crystal lattice since it is invisible in nearly all samples examined. Some samples of chalcopyrite in gold-bearing areas yielded a trace to 22 ppm Au (0.7 opt) and a trace to 1300 ppm Ag (41.6 ppm Ag) (Boyle, 1979).
Types of Gold Deposits
To a geologist, there are many types of gold deposits, such as hydrothermal, mesothermal, epithermal, replacement, etc. But to prospectors, there are only two types: placer and lode. Placer deposits are essentially detrital deposits eroded and transported by water, such as the famous placers at Nome and Flat, Alaska, the Fortymile River in the Yukon, and Alder Gulch, Montana. Examples of lode deposits include the Mother Lode, California and the great Homestake mine in South Dakota.
But there is not always a clear distinction between lode and placer. For instance, the great Witwatersrand gold deposits in South Africa, the most productive deposits in the world, are known as paleoplacers. Because they occur in brittle, consolidated rock (mined to depths greater than 13,000 feet), most prospectors would consider these lodes. However, geologists classify the great Rand deposits as fossil (paleo) placers, since the gold was deposited in streams and rivers more than 2.5 billion years ago and now these river rocks are hard, consolidated, brittle, rock ledges. But, just like any placer, miners in the Rand search for evidence of ancient bed rock in contact with the conglomerates, ancient bench deposits, pockets in the stream beds, meanders, etc. These are just old fossilized river beds. But one difference is when they were deposited, the earth’s atmosphere was not healthy to live in because it had very little oxygen; thus minerals like pyrite did not oxidize (rust) and were transported in the ancient streams just like gold. So, miners now find both gold and pyrite nuggets in the Rand paleoplacers.
Another not so clear distinction is eluvial deposits. Eluvial deposits are essentially detrital material weathered in place from a nearby (often underlying) source. Gold from eluvial deposits show no evidence of stream transport and cobbles and boulders carrying the gold are angular. But since eluvial deposits are unconsolidated, many consider them to be placers, even though they directly overlie a lode, or just a short distance downslope from a lode. There are many examples of eluvial gold in Arizona. These have gold in angular quartz fragments that may also have some primary pyrite, chalcopyrite and/or galena. Arid environments are favorable for eluvial deposits due to lack of active streams. Where there is eluvial gold, there is a gold lode in the immediate area - something every prospector needs to keep in mind, especially when they prospect in the regions like those around Quartzite, Arizona. Eluvial means that the material eroded in place from an underlying vein or source rock. In Arizona, there are many placer, alluvial and eluvial gold occurrences in streams, conglomerates and fanglomerates.
Most prospectors are familiar with placers. Most placers are small and of limited size and extent. Major mining companies ignore them because of their small size. But such deposits are also comparatively less expensive to mine and require no chemicals to extract gold, and also require little mining expertise. Even so, placer miners make many mistakes that could be avoided, such as: (1) recognizing and recovering value-added precious metals, gemstones or strategic metals, (2) assuming the placer is equally mineralized throughout the gravel when in fact placers are erratically mineralized requiring prospectors to search for pay streaks, (3) picking the wrong mill or concentrator for the deposit, or (4) using dowsers or fortune tellers. One classical example at Rock Creek in the South Pass greenstone belt of Wyoming involved a placer miner who had already found considerable gold in the stream alluvium adjacent to the creek. Instead of following the pay streak, he later spent all of his money digging on the side of the hill adjacent to the creek because a dowser indicated the mother lode was on the hillside. So he spent all of his money digging worthless dirt and rock on the hillside.
If the placer has considerable aerial extent and depth, the miner should consider drilling or trenching to provide guide maps to minable horizons. After estimates of gold resources are determined, the miner should search for the most efficient method for gold extraction.
Placers consist of detrital gold and other valuable minerals that were transported by water in creeks, rivers and even by wave action along the shores of lakes and seas. The wave action and water movement sorts minerals by specific gravity; thus when searching for valuable minerals in placer deposits, those valuable minerals with high specific gravity are typically found with other heavy minerals known as black sands. Black sands consist of dark opaque minerals with greater than average specific gravity that include magnetite, pyroxene, amphibole, ilmenite, garnet, sphene, chromite and monazite, as well as rare light-colored minerals of high specific gravity such as cassiterite and scheelite. Rarely, diamonds, rubies, sapphires, benitoite and tourmaline are found in placers. Even so, these are almost always overlooked by gold prospectors.
The opposite also occurs. Several years ago, after being provided grants by Union Pacific Resources to search for gold deposits in southern Wyoming, we found gold anomalies in many sand and gravel pits operated by the Wyoming Highway Department. We even found gold in an dry channel in the Laramie landfill. We recommended that the agencies in charge of these operations sample their deposits in detail to determine if they had recoverable gold. The added value of the gold could have paid for, or partially paid for, the cost of the sand and gravel operations. But our suggestions were ignored. So now in addition to roads in Sybille Canyon area being paved by gemstones (spectrolite), it appears some of Wyoming's highways are paved with gold.
If you take a trip to the Sweetwater River to the east of Atlantic City, Wyoming and sit down to pan at Wilson Bar and Wilson Gulch in South Pass, you will find some heavy, nagging, white to brown ‘quartz’ that is difficult to pan out. Examination of the ‘heavy quartz’ with shortwave ultraviolet light will show much of the material to fluoresce blue-white. Testing the so-called quartz for specific gravity will result in a SG of 6, more than twice that of quartz. The so-called heavy quartz turned out to be a calcium tungstate known as scheelite, a tungsten ore found with some of the gold ore at the nearby Burr and Hidden Hand mines (Hausel, 1991).
When found on public land, placers can sometimes be claimed under the 1872 mining law if the government hasn’t yet withdrawn our public lands from multiple use. Several years ago, the BLM withdrew a gold placer in Strawberry Creek in the Lewiston gold district of Wyoming in another effort to take public lands from miners. One prospector working in the area with very primitive tools was evicted after he had recovered considerable gold in a very short time.
Minerals of potential economic interest with relatively high specific gravity are periodically found in gold placers such as cassiterite, scheelite and a host of gemstones including ruby, sapphire, gem-garnet, diamond, platinum, and palladium. While prospecting for diamonds in the Laramie Mountains in southeastern Wyoming, several samples with trace amounts of ruby and sapphire were recovered in dry placers (Hausel, 2014). These were eroded from nearby, undiscovered, corundum (sapphire, ruby) schists. How do you tell if you have ruby or sapphire in your gold pan? Look at crystal habit. The habit is the common form of the crystal and ruby and sapphire form hexagonal crystals bounded by two pinacoids (flat surfaces).
While prospecting for diamonds in the Sierra Nevada of California, sapphires and benitoite were recovered near Poker Flat. A prospector from Saratoga, Wyoming, Paul Boden (RIP), found a couple of excellent gem-quality octahedral diamonds while searching for gold on Cortez Creek in the Medicine Bow Mountains, Wyoming. Another prospector, Frank Yassai (RIP), recovered many diamonds in Rabbit Creek, Colorado while prospecting for gold (Hausel, 2014). In this same region, another prospector panned out a few dozen diamonds including one flawless gem-quality diamond of about 5-carats in 2014. And in the Fish Creek drainage on the State Line, a diamond company searching for kimberlite in 1995 recovered several diamonds in the creek including one of 6.2 carats.
During erosion, heavy minerals mix with light-colored, glassy, transparent to opaque minerals of low to average specific gravity such as quartz, apatite, feldspar, and mica. These and other minerals with high specific gravity are moved in streams. The sediment carrying capacity of a stream will diminish with decreasing water velocity and heavy minerals settle where declining water velocity occurs; such as areas marked by distinct increase in black sands. Heavy minerals tend to concentrate at the bottom of a stream, along the leading edge of stream meanders, behind obstructions (i.e., rocks, cracks in bedrock) in waterfalls, potholes, etc. Since many streams lack sufficient velocity to carry gold for any great distance, much gold (particularly where it is concentrated in pay streaks) will lie downstream from a lode. At the Rock Creek placer in the South Pass greenstone belt, gold was mined downstream from a group of gold-bearing shear zones (Hausel, 1985, 1991; Hausel and Love, 1992) that run from the hills west of Atlantic City, through Atlantic City and further downstream. But further upstream above the known gold lodes, Rock Creek has little gold. This is because the source of the gold sits in the hills immediately west of Atlantic City and gold will be downstream from those lodes. One can trace gold downstream from those lodes all the way to the Sweetwater River.
Distances that heavy minerals can be transported are not known with any accuracy. Some minerals can be transported great distances. For example, diamond is 6- to 8-thousand times harder than any other mineral and it is not overly heavy (specific gravity of 3.52 compared to 2.87 for quartz). Even so, there are cases where transport distances for diamond 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. Other gemstones are found with diamond, but only within a few miles of the source rock for the diamonds. These include pyrope garnet, chromian diopside and picroilmenite, but these minerals only transport short distances until they completely disaggregate due to abrasion. In the Colorado-Wyoming region, studies showed these minerals transported downstream only about 0.25 to 1.5 miles before complete disaggregation.
Great transportation distances for gold are not possible because gold is too heavy and too soft (hardness of 2.5 to 3), so when found in streams it is thought to have been derived from a nearby source. In some unusual cases, gold may have been transported greater than normal distances while dissolved in the water. In Alaska, Dr. Paul Graff identified gold that had crystallized as nuggets downstream from nearby lode deposits (Figure 14). Maximum transportation distances for gold in solution is unknown, but it can also result in regeneration of a placer deposit!
Flash flooding is important in producing paystreaks. Paystreaks, or lenses of gold-enriched gravel, are often found with an assortment of boulders, pebbles and cobbles with organic material (tree limbs, etc) that provide evidence of a past flash flood. Pay streaks can be scattered over one or more intervals in a vertical column. It is important to remember, placers are never consistently mineralized and if you find good gold in one location, just a few feet away, the placer gravel could be unmineralized.
Stream eanders are good places to search for gold. Gold may concentrate on the inside of the initial curve of a meander as well as in the bank (point bar) on the upstream side of the meander. As an example, one of my favorite places to take students in the past in prospecting classes at UW was the Bobbie Thompson campground area in the Douglas Creek gold district of Wyoming.
In the South Pass greenstone belt in western Wyoming, giant (Teritay age) paleoplacers surround the greenstone belt and are reported at McGraw Flats to the north and Oregon Buttes-Dickie Springs to the south. There are smaller ones in between. The southern paleoplacer was reported to contain more than 28.5 million ounces of gold, yet most of this area is unexplored (Hausel and Love, 1992). Along the northern flank of the Seminoe Mountains greenstone belt, the Miracle Mile paleoplacer is unexplored even though gold has been found in the dry paleoplacer. This paleoplacer was discovered by prospectors Charlie and Donna Kortes and it also contains many G10 pyrope (diamond-stability field) garnets that indicate somewhere in this region is a very rich diamond deposit or deposits. So look for diamonds and gold when you dig in this dry dirt and pan it in the nearby North Platte River. Paleoplacers in the Medicine Bow and Sierra Madre Mountains in southern Wyoming also yielded gold and diamonds, along with uranium and thorium.
One might think of lode deposits as veins or other consolidated rocks that contain anomalously high quantities of 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, resulting in a gossan at the surface and a potential supergene zone (a mineral deposit, or enrichment, formed by descending fluids) a few tens of feet below the surface. Gossans are the oxidized sulfide-rich parts of veins and other mineral deposits that have distinct, rusty appearance. These gossans offer excellent visual guides in a search for gold and other metal deposits. In any historic mining district, you will often find dozens, if not hundreds, of old prospect pits dug into the rusty rocks. Prospectors learn to recognize these gossans as guides to ore deposits.
Gossans are good places to search for high-grade gold in lodes. Gossans produced from the leaching of pyrite are typically very rusty (reddish-brown) in appearance; gossans from arsenopyrite are typically greenish-yellow. Large gossans that cover several acres may be situated over massive sulfide deposits. These may contain gold and/or valuable base metals. One 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.
Some faults and breccias may contain gold. Breccias are zones of broken rock with distinct angular rock clasts. When found, gold may occur in the matrix of the strongly limonite-stained gossan surrounding the rock fragments. Other faults, known as shears, may 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.
The search for productive gold deposits requires a good background in prospecting and economic geology and some luck. However, there are literally thousands if not millions of occurrences and deposits in the Western US including Alaska. Learn to identify gold. The best way to begin prospecting is to get a book that describes the gold mines and placers of a mining district near you. There are always many deposits near old gold mines that have been overlooked. Look at any geological maps to see what the trends of the veins, faults or shear zones are and then find these on the ground and start walking along those trends - you will find more gold and vein occurrences along those trends than was found in the past - this is almost guaranteed. I can't guarantee this for everyone, because there is always one or two people who couldn't find their way out of a closet, such as one guy I sent looking for iolite (Hausel, 2014).
This is how I found more than a hundred gold deposits and anomalies. An understanding of geology helps. 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.
"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.
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 porphyry and ignored nearby vein deposits that assayed greater than 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].
A note for you - some of my old publications are periodically listed on the Wyoming Geological Survey website, but they constantly change their site making access to information very unreliable. So, contact the Wyoming Geological Survey and ask them for pdf copies.