Characteristics of natural gold in the wild
Form Characteristics
Natural gold often presents tree-like, granular, scaly or blocky and other irregular forms, and rare regular crystals. Its crystals are generally small, and the aggregate forms are diverse, occasionally seen as irregular large blocks weighing dozens of kilograms, such as “dog head gold”.
Color and Luster
Natural gold has a typical golden yellow color, bright and bright, streak is also golden yellow. With the increase of silver content, the color gradually becomes light yellow. The surface of natural gold presents a strong metallic luster, reflected significantly under light, and the color is warm and moist.
Hardness and Ductility
The Mohs hardness of natural gold is 2.5-3, relatively low, and can be left with a slight mark on the surface with a fingernail. Natural gold has excellent ductility, and 1 gram of gold can be drawn into a gold wire up to 2 km long, and can be rolled into a gold leaf only 100,000th of a millimeter thick.
Density
Natural gold has a large density, the specific gravity of pure gold is 19.3, and it feels heavy. Compared with ordinary rocks of the same volume, natural gold is obviously heavier.
Chemical Properties
The chemical properties of natural gold are stable. It does not oxidize when heated in air, and is insoluble in other acids except aqua regia. It is not easy to be corroded and weathered in the field environment.
Distinguishing from similar minerals
Distinguishing from Pyrite:
Pyrite has a color that leans towards light brass, slightly lighter and brighter than natural gold, with spots or streaks often visible on its surface. In terms of hardness, pyrite is harder than natural gold; when scratched with a small knife, pyrite leaves little mark, whereas natural gold, being softer, can be easily scratched. Additionally, pyrite is brittle and breaks easily when struck with a hammer, while natural gold can be flattened by striking.
Distinguishing from Chalcopyrite
Chalcopyrite has a copper-yellow color with a distinct copper hue, differing from the golden yellow of natural gold. The streak of chalcopyrite is greenish-black, while that of natural gold is golden yellow. Chalcopyrite is also harder than natural gold and less malleable, making it prone to breaking or cracking when struck.
Distinguishing from Gold Mica
Although the color of gold mica is similar to that of natural gold, it has a flake structure, is soft and thin, and will float or suspend in water. Gold mica is less hard, and can be easily scraped off with a fingernail, while natural gold will not.
Methods of finding natural gold
Natural gold minerals are basically impossible to identify directly in the field because few of them can be seen with the naked eye. Therefore, gold is usually found by indirect methods.
1. Pay attention to silicification zones, quartz veins, and secondary quartzite. This is because gold mineralization is closely related to silicification; one could say “no silicon, no gold.” Of course, not all siliceous bodies contain gold, but those that do often appear smoky gray with good water color. This is due to the presence of varying amounts of sulfides in gold-bearing siliceous bodies, which, being extremely fine, give the quartz a smoky gray hue. In particular, tabular quartz veins (which may contain multiple black bands, such as a mixture of carbonaceous and fine-grained sulfides) tend to have better gold content. Even in clear gold-type quartz veins with low sulfide content, when gold deposits occur, they are often accompanied by sulfides like antimony pyrophosphate, bismuth pyrophosphate, chalcopyrite, calomel, and fish-egg-like lead-zinc ores.
2. Pay attention to fault zones, especially ductile shear zones. Gold mineralization is invariably associated with faults; one could say “no structure, no gold.” Particular attention should be given to ultramylonitic, mullite, micro-sand-like quartzite, and talc-magnesite schist, which often contain gold-rich ore bodies. Large to medium-sized fault zones themselves are often poor in gold content, while secondary fault zones on their flanks are frequently the sites of gold ore bodies.
3. Pay attention to the determination of gold content in iron caps, reddish-brown and brown-yellow residual slope deposits and carbonate dissolution gully deposits. They can not only become iron cap type and red soil type gold deposits themselves, but also indicate the search for primary gold deposits.
4. Pay attention to gold exploration in areas with antimony, mercury, and arsenic mines (especially realgar and orpiment). For antimony mines, they can either coexist with gold to form antimony-gold deposits or be separated but not far apart, hence the saying “if not in it, then not in its traces.” Gold can also be found around some lead-zinc mines, such as the periphery of Qingchengzi lead-zinc mine; the lower part of copper deposits. The alteration zone of copper-nickel sulfide deposits is also a good place for gold exploration.
5. In addition to silicification, the alteration related to gold mineralization also includes iron dolomite petrification, iron calcite petrification, chromium dolomite petrification, pyrite serpentine metamorphism, ice long metamorphism, fine pyrite petrification, arsenic, antimony, mercury, bismuth, thallium petrification and other low temperature alteration combinations.
6. Pay attention to the fracture zones and tectonic alteration zones in basic rocks, ultrabasic rocks, lamprophyre, alkaline rocks, slightly alkaline granitic rocks, carbon-silica mud rocks and impure carbonate rocks.
7. The most important method of gold finding is to carry out the work of heavy sand in rivers, secondary haze in gullies and various geochemical methods to find gold by means of gold.
8. Find gold according to the indicator elements, such as mercury, antimony, bismuth, arsenic, thallium, selenium, lead, zinc, copper and silver.
9. Use geophysical exploration methods to find out the distribution of fault structures and sulfide to indirectly find gold deposits.
