Metals Native Elements,
Gold Groups and Ismetric

Gold
Composition. Gold, commonly alloyed will small amounts of silver and at times with traces of copper and iron. Ordinarily, native gold contains varying amounts of alloyed silver up to 16 per cent. California gold contains between 10 and 15 per cent of silver. The greater part of native gold is about 90 per cent “fine” or contains 10 per cent of other metals. Gold containing unusually high percentages of silver (25 to 40 per cent) is known as electrum.

Crystallization. Isometric. Crystals are commonly octahedral in habit, showing also at times the faces of the dodecahedron,  cube, etc (see Fig 213, 214 and 215) Often in arborescent crystal groups with crystals irregularly distorted and passing into filiform, reticulated and dendritic shapes.

Structure. Usually in irregular plates, scales or masses. Seldom definitely crystallized.

Physical Properties. H. = 2.5-3.  G. = 15.6 – 19.3 (becomes greater as the percentages of the other metals present decrease). Very malleable and ductile. Color various shades of yellow, depending upon purity, becoming paler increase in the percentage of silver present.

Test. Easily fusible at 2.5-3, Insoluble in ordinary acids but soluble in a mixture of hydrochloric and nitric acids. To be distinguished form certain yellow sulphides (particularly pyrite and chalcopyrite) and from yellow flakes of altered micas by its malleability, its insolubility and its great weight.

Occurrence. Although gold is a rare element, it is to be found widely distributed in nature, occurring small amounts. Its presence as a primary constituent of igneous rocks, more particularly of commonly in quartz veins. It occurs in detrital sands and gravels in what are known as placer deposits. It present in small amounts in sea water. Is it important to note that gold occurs almost wholly as the native metal, the only class of compounds which it forms in nature being the tellurides.

The chief source of gold is the gold – quartz veins. It occurs in these veins usually as very small specks scattered uniformly throughout the quartz gangue. The contents of these veins are in general considered to have been deposited from ascending mineral-bearing solutions. That gold is capable of solution and subsequent precipitation bye means of underground waters has been repeatedly demonstrated. In the majority of veins the gold is so finely divided and uniformly distributed that its presence in the ore cannot be detected with the eye. It is interesting to note that with the value of gold at $ 20.67 a troy ounce, ore which contains one per cent of gold weight would be worth $ 6028 to the ton, while an ore containing only 0.01 per cent of gold would still be a rich ore, having a value of $ 60 per ton. Ores are mined at a profit sometimes which contain only 0,001 per cent of gold and yield but $ 6 to the ton. So it might be quite impossible to detect the presence of gold in a valuable ore by any ordinary tests. A definite estimation of the amount of gold present by means of a careful assay is the only way usually to determine the value of an ore. But occasionally, under favorable conditions, the gold may collect in larger amounts, in nests and pockets in the veins, occurring usually as irregular plates and masses between the crystals of quartz . In the quartz veins the fold is frequently associated with sulphides, particularly with pyrite. It is thought that the gold does not exist in any chemical combination with the quartz.  The upper portions of the gold-quartz vins as a rule have been enriched in their values. The gold present in this upper zone was in part deposited contemporaneously with the formation of the vein, but frequently the fretted part has been transported, either in solution or bye mechanical settling, from that upper portion of the vein which has been graylag eroded away. And so the told in this part of the vein repents the concentration in a small space of the original gold content of much greeted length of vein. Bye the oxidation of the gold-bearing supplied originally deposited in this portion of the vein the gold. Embedded in them has been set free, rendering the gold easy of extraction. Ores that contain the gold free from intimate association with syhlphides are known as “freemilling” because their gold content can be recovered by amalgamation with the mercury of the plates over which the finely crushed or runs from the stamp mill. Where are present in any quantity all of the fools cannot be recovered b y amalgamation and a chemical process, either the cyanide or chlorination process, must be used, either alone or in addition to the amalgamation.

In addition to occurring with quartz and pyrite, gold has been found associated with chalcopyrite, sphalerite, galena, stibnite, cinnabar, arsenopyrite, limonite, calcite, etc.