The amount of black sand and other heavy minerals, found associated with placer gold, varies a lot: there is not a simple direct correlation. There are places that are loaded with black sand but have no gold. Conversely, there are also places that have good quantities of gold but very little black sand.
Flour gold or flood plain gold is defined as ultra-fine gold found in low micron size fractions, often smaller than 74 microns or 200 mesh.
You might have heard the term “flood plain gold” and are wondering what it really means. A very simple definition is “fine-sized gold flakes carried or redistributed by flood waters and deposited on gravel bars as the flood waters recede.” When this “redistribution” occurs, it is usually after heavy winter storms that churned up rivers enough to turn part of the bedload over and move the river bar gravels from one place to another. Within these gravels is fine gold that was previously deposited there. When waterways flow way up and above their normal banks, they generally drop the heavier gold in the front of the bar, and as pressure decreases, the finer gold starts dropping into the mixed gravel. Over time, some of this finer gold will work its way down to bedrock, but generally it stays on the move.
Never throw away your black sand concentrates. It takes extremely good panning techniques to capture fine or flour gold in a pan, and a high energy sluice will generally wash the micron gold out with the tailings, maybe even easier than washing out the fine black sand. If you suspect you have micron gold, the first step is to look for it with a good 20X or 30X magnifier, looking for discrete, small particles.
Fine Gold Recovery Equipment
Fine gold recovery equipment is specifically designed to reduce the amount of raw gold bearing material to a manageable amount for further processing and/or aid directly in the separation of finer grains of gold from heavy black sand.
Gold is one of the first minerals used by prehistoric cultures. The Latin name for this mineral was "aurum" and Jöns Jakob Berzelius used Au to represent the element when he established the current system of chemical symbols. The Old English word "gold" first appeared in written form about 725 and may further have been derived from "gehl" or "jehl". May be derived from Anglo-Saxon "gold" = yellow. (Known to alchemists as Sol.)
A native element and precious metal, gold has long been prized for its beauty, resistance to chemical attack and workability. As it is found as a native element, has a relatively low melting point (1063 degrees Celsius) and is malleable, it has been used by mankind for thousands of years.
Gold is used as a standard for international currency and is also widely used in jewelry, electronics (where its superb properties as a conductor help offset its tremendous cost), dentistry and in photographic processes.
Gold occurs in significant amounts in three main types of deposits: hydrothermal quartz veins and related deposits in metamorphic and igneous rocks; in volcanic-exhalative sulphide deposits; and in consolidated to unconsolidated placer deposits. It may also occur in contact metamorphic or hypothermal deposits (eg. Skarns), or epithermal deposits such as volcanic fumaroles. It is most commonly found as disseminated grains in quartz veins with pyrite and other sulphides, or as rounded grains, flakes or nuggets in placer deposits in recent to ancient stream and river deposits. Gold is often panned from such deposits by taking advantage of its high density to wash away the lighter sediments from a pan or sluice.
Nuggets are almost exclusively hypogene in origin, forming mostly in veins, but can be somewhat modified in form and chemistry by weathering, erosion, and transport (Hough et al., 2007).
Gold:
Gold is one of the densest of all the chemical elements.
It also the most malleable metal.
One ounce of gold can be drawn into a wire about thirty miles long.
Gold is chemically related to copper and silver
It is highly resistant to chemical change and cannot be dissolved in common acids
Gold does dissolve in aqua regia and cyanides.
If the current volume of fiat dollars was converted to gold it would exceed $50,000 per oz.
Details:
AU—the chemical symbol for gold
Gold’ atomic number is 79 and its atomic weight is 196.967
Gold melts at 1064.43 Centigrade
Gravity for Gold is 19.3, meaning gold weighs 19.3 times more than an equal amount volume of water.
Tinsel Strength 11.9
Hardness (Brinell)=25
Occurrence of gold in Earth’s crust= .005 parts per million
Standard Bar Sizes
400 troy ounces (12.5 kilos)
32.15 troy ounces (1 kilo)
100 troy ounces (3.11 kilos)
*Wide varieties of bar sizes are traded on the market, but are not deliverable to an exchange as the bars above.
Fineness and Karat Weight
Percent Gold
European System
Karat System
100%
1000 fine
24 karat
91.7%
917 fine
22 karat
75.0%
750 fine
18 karat
58.5%
585 fine
14 karat
41.6%
416 fine
10 karat
Of the 92 natural elements in the earth’s crust, Gold ranks 58th in rarity.
Every state in the U.S. has some gold deposits.
When gold is legal tender, governments try to regulate or manipulate its value, and that’s always difficult… when Roosevelt raised gold from $20.67 to $35 in 1934, it immediately devalued the dollar by 40%.
But from 1786 to 1933, the U.S. government only allowed the price of gold to rise from $17.92 to $20.67. A 15% increase in the official price of gold in 141 years. In the same span, U.S. GDP grew about 28,000%.
Among the worst debasers of gold coins were Henry VIII, Diocletian and Nero. Debasement is a hidden tax. Henry added base metals to coins. Nero reduced silver content and made the gold coins smaller.
In 1542, Francisco Pizarro took more gold from the Inca in a week than European miners produced in a year. The conquistadors brought so much gold from the New World to Europe that they increased supply by 500% and started the first gold-induced inflation. Other inflations caused by sudden gold supplies happened during the U.S. and Australian gold rushes in the 19th century.
When used in trade, gold coins wear out in about 18 years.
It is believed that most of the gold coins used in trade between the U.S. and the West Indies before the U.S. Revolution were 15-20% “light.” Crooks and traders put coins in a coarse bag and shook them to create gold dust—called sweating the coins. They traded the coins at full value and made money on the dust.
For years, banks sent gold coins to England from the U.S. and back again to maintain trade balances. In each trip, $178 in value from every $1 million in gold shipped, rubbed off during transport, according to an 1894 book on banking practices.
An ounce of gold can be stretched into a wire 80 kms (50 miles) long.
Gold is not only precious, but pure gold is also very, very soft. So soft, in fact, that a single gram can be beaten into a sheet of one square meter! If you ever get some pure gold to play with (you wish, eh?), remember the following sciensational fact:
Absolutely pure gold is so soft that it can be moulded with the hands
Seventy-five percent of all gold in circulation has been extracted since 1910.
A medical study in France during the early twentieth century suggests that gold is an effective treatment for rheumatoid arthritis.
Gold is so pliable that it can be made into sewing thread. An ounce of gold can be stretched over 50 miles.
Gold is edible.
The largest gold nugget ever found is the “Welcome Stranger” discovered by John Deason and Richard Oates in Australia on February 5, 1869. The nugget is 10 by 25 inches and yielded 2,248 ounces of pure gold. It was found just two inches below the ground surface.
Gold is chemically inert, which also explains why it never rusts and does not cause skin irritation. If gold jewelry irritates the skin, it is likely that the gold was mixed with some other metal.
One cubic foot of gold weighs half a ton. The world’s largest gold bar weighs 200 kg (440 lb).
The Incas thought gold represented the glory of their sun god and referred to the precious metal as “tears of the Sun.” Because gold was not yet used for money, the Inca’s love of gold was purely aesthetic and religious.
Around 1200 B.C., the Egyptians used unshorn sheepskin to mine for gold dust from the sands of the Black Sea. This practice is most likely the inspiration for the “Golden Fleece.”
There are more than 400 references to gold in the Bible, including specific instructions from God to cover furniture in the tabernacle with “pure gold.” Gold is also mentioned as one of the gifts of the Magi.
The Greeks thought that gold was a dense combination of water and sunlight.
During the fourteenth century, drinking molten gold and crushed emeralds was used as a treatment for the bubonic plaque.
In 1511, King Ferdinand of Spain coined the immortal phrase: “Get gold, humanely if possible—but at all hazards, get gold.”
Both Greeks and Jews begin to practice alchemy in 300 B.C. The search to turn base metals into gold would reach its pinnacle in the late Middle Ages and Renaissance.
The San Francisco 49ers are named after the 1849 Gold Rush miners.
Gold and copper were the first metals to be discovered by humans around 5000 B.C. and are the only two non-white-colored metals.
The world’s largest stockpile of gold can be found five stories underground inside the Federal Reserve Bank of New York’s vault and it holds 25% of the world’s gold reserve (540,000 gold bars). While it contains more gold than Fort Knox, most of it belongs to foreign governments.
The “troy ounce” of gold comes from the French town of Troyes, which first created a system of weights in the Middle Ages used for precious metals and gems. One troy ounce is 480 grains. A grain is exactly 64.79892 mg.
Gold is higly reflective: Since this metal completely reflects infrared rays, it is used widely for radiation reflection and is a good conductor of thermal energy.
So how do they sample rocks for gold and silver? Gold, silver and platinum are categorized as precious metals. This means they are highly valuable with a high demand. This translates into a high monetary value for relatively small amount of the metal (Gold/Platinum ~ $1500/ounce, Silver ~$25/ounce). In addition to the high monetary value, nature only supplies precious metals in small amounts (usually) which results in some difficulty in sampling at all stages.
Of particular problem to precious metals is called the nugget effect. This is where the tiny amount of precious metal may be rich in one part of a rock, and completely absence in another – it is never evenly distributed, Nature doesn’t like making things easy. Overcoming the nugget effect typically means larger sample sizes or targetted samples based on indicator minerals. Tiny gold in a core sample - nugget effect - Indicator minerals are a mineral associated with the precious metal but much more common in the rocks.
Typical indicator minerals are referred to as sulfides and include Pyrite (FeS2), arsenopyrite (FeAsS), Pyrrhotite (Fe1-xS), Chalcopyrite (CuFeS2) amongst others. These are minerals which are of no to little economic value in small quantities however the do indicate the potential presence of a more valuable precious metal. A very useful property any iron sulfides (contain iron (Fe)) is that they rust, leaving a nice rusty stain to see. All samples are then assayed for the precious metal.
The sample is pulverized into a powder, mixed to distribute any precious metal evenly, then divided down to a small manageable size for assaying. A 1 kg sample will end up with only a 30g or 50g sample size. Without proper mixing, the nugget effect can be greatly enhanced leading to either very negative results to over reporting of the precious metal content. various techniques are used for assaying specific minerals, I wont go into that here.
The end result is a report on the amount of precious metal in your sample of rock from which you can extrapolate potential value to proceed or move your exploration elsewhere.
Stage one sampling
Stage one sampling occurs at the outcrop level, these are bedrock (not boulders) exposures accessible with no to minimal excavation. A quick way to see if a rock isn’t just a large boulder is to place your foot on it and hit it (not your foot) with a hammer. If it vibrates its likely a boulder, if not likely outcrop. Looking for a nice rusty rock, with the proper indicator mineral, hammer off a chunk a little larger than your fist. Do the same thing in another section of the rock, rinse repeat.
The more samples you take, the more representative it is. The more samples will also narrow down where the precious metal is depending on the amount, nature and ratios of indicator minerals which result in a positive gold showing when assayed. Molybdenum / pyrite rich hand sample
Stage two sampling - 2 bladed saw cutting channel sample
Stage two sampling, in theory, provides a more reliable indication of precious metal value.
Channel sampling uses a rock saw to cut two deep cuts forming a channel approximately 2 inches apart and 4-5 inches deep. The channel is cut perpendicular to any structure (across the vein) if present. using chisels and hammers, the channel rock between the two cuts is then removed/broken from the rock. Length of samples are determined by rock type, mineralization and localized constraints to precious metal mineralization. Since these samples tend to be larger, and are cut from solid rock, the resulting sample tends to be “fresh” allowing for an easier indicator metal determination and lessen potential contamination from other rocks above them.
Stage three sampling
The most widely reported form of rock sampling comes from drill core. A diamond drill is use to produce a drill core of varying size. This cylindrical peice of rock from deeper in a deposit tends to be untouched by surface action and uncontaminated from materials above. Drill core is usually drilled at an angle through the deposit so length of a mineralized “zone” in core does not correspond to the actual width of the deposit. Core is examined for indicator minerals, mineralized zones, geological structures and whatever else can be learned from raw untouched rock. For sampling, the core is split, cut with a rock saw, in half – half stays with the core for future reference (43-101 compliance rules dictate this must happen). The other half is bagged and sent toan assay lab for processing like the other samples. Drill core - samples where core halved
