Nuggets - Native Gold
Gold Ore in Quartz
Gold was likely the first of the metals to be recognized and exploited by primitive humanoids, though actual mining for gold was probably antedated by the mining for flint. Because of its color, gold is easily seen on river bottoms. It’s high density and its resistance to tarnishing – along with its comparative scarcity – make it desirable for ornamentation. It was a natural progression to the use of the metal for coinage, in which endurance of the metal is key.
Gold mining reaches back to the Egyptian period; there are numerous references in the Bible. Pictorial rock carvings depict ‘gold washing’ as early as 4000 BCE, and even subsurface mining was known to be carried on. Because no heat is necessary to separate the gold from its ore (which is often quartz, as pictured), it could be obtained by simple means. Deposits near surface require little digging or handling of material. The first gold mines were probably placer deposits where the gold was concentrated in the gravel or in the bed of a stream. It would be natural to scoop up the sand below the surface to look for yellow particles, while water could be used to ‘wash’ away remaining unwanted material.
Ore was likely broken with stone hammers and subsequently ground in mortars to free the gold from the waste stone, which was then recovered by washing. Hides and skins have been used to catch fine particles. It is likely the famous legend of the Golden Fleece was a reference to the practice of sheepskins for saving gold dust in placer operations.
Lode mining, as opposed to ‘panning,’ follows typically quartz veins through other rock. Gold, however it is obtained, often occurs in significantly sized pieces called ‘nuggets.’ Huge nuggets up to 100 pounds have been found. A substantial amount of gold also occurs as a by-product of copper and other base-metal mining, as small veins can occur in mines where another metal provides the greater return. Compared with other metals, gold represents a extraordinarily small proportion of the rock in which it is found, as low as 0.03 oz. per ton. Gold that exists in proportions of less than 1:300,000 are generally not considered practical for mining – unless other metals are also present.
The time honoured gold pan has held its primary use with miners since time immemorial, and is used for hand-working rich placer ground. In form, it is a shallow pan of copper or iron, from 15-18 inches in diameter, about two and a half inches deep, with sloping sides. It will hold about 20 pounds of gravel and, when used with experience, has a capacity of about one half to one full cubic yard of panning per ten hour period – or approximately one ton of material. If the gold were in the proportion stated above, the yield would be about 23 c.p. per day of hard labor.
In tropical counties, the
batea is used by the natives instead of a gold pan. This resembles a shallow wooden bowl, cut out of hard wood, and is wider and deeper than the metal pan. A skilful native can do remarkable work with it, saving even the finest particles of gold. It is believed the wooden surface is superior to metal for recovering fine gold.
A ‘rocker’ is commonly used in hand placering to increase capacity. This is a simple contrivance consisting of a box in which to dump gravel, a screen for sifting out the coarse material, and an apron, set on a slope and covered with a canvas to catch the finer concentrate. The overall machine is created to be rocked, hence the name. Water is fed into the gravel, and the box is rocked back and forth, the fine gravel being caught by the canvas below. This concentrate is later panned to remove the gold. Two workers with a rocker can handle about 3 to 5 cubic yards of gravel in a ten hour period. The system requires from 100 to 800 gallons of water for it to be practical.
In ancient times gold was much sought after, but there were no large scale movements of population into areas in which large discoveries had been made. Trade was often by barter; gold, though valuable, was only one of several mediums used. The Spanish and Portuguese discoveries of gold in the New World have produced some emigration movements, the most significant being gold mines in the highlands of Columbia, but the difficulty of the journey and the obscurity of these locales has reduced the number drifting to those mines to little better than a steady trickle. Hoarded gold by the Incas and Aztecs, found and distributed a century and a half ago, cause serious repercussions on European markets ... but since the effects have stabilized. Piracy upon the Atlantic has sent many a ship loaded with South American gold to the bottom of the ocean.
Gold is one of the heaviest of the metals and the most malleable and ductile. It is impervious to every acid known except aqua regia, in which it reduces the metal to a yellow deposit used for gilding glass and porcelain. Gold alloys with mercury, copper, silver and platinum. Alloys show various colors, with copper giving red or yellow; nickel and zinc, white; silver, green; and iron, blue. The tinge in gold can give a clue to the purity of the metal.
Because the pure metal is too soft and too easily worn away to be used as a pure metal for coinage or for most jewellery, gold is typically alloyed with other materials, measured in parts per 24 of gold. Thus, ‘18K’ gold is alloyed as 18 parts of the alloying material per 24 parts gold.
Gold leaf, in which the metal is pounded to a remarkable thinness, is used for making window signs, illuminating manuscripts and occasionally architectural decoration. Its beauty and resistance to weathering makes it highly prized.