Identifying Gold Ore: What to Look for - HobbyLark - Games and Hobbies
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Identifying Gold Ore: What to Look for

John has prospected for gold in Arizona 10 years. His experience taught him to deal with the terrain, heat, and gold fever. He makes tools.

Native gold found in pure form. This nugget was found in Australia. Gold nugget from Australia (public display, Field Museum of Natural History, Chicago, Illinois, USA) A mineral is a naturally-occurring, solid, inorganic, crystalline substance.

Native gold found in pure form. This nugget was found in Australia. Gold nugget from Australia (public display, Field Museum of Natural History, Chicago, Illinois, USA) A mineral is a naturally-occurring, solid, inorganic, crystalline substance.

The real voyage of discovery consists, not in seeking new landscapes, but in having new eyes. - Marcel Proust

This article is written with an eye to further increasing the knowledge of the amateur prospector. A discussion follows about native gold and a few compounds of gold ore that are found on Earth. A greater appreciation of the rarity of the metal compared to other metals found in compounds should give prospectors an insight into just how special gold is.

What Is a Native Metal?

A native metal is a metal that can be found in its elemental form - and
the list of these is extensive. However, gold distinguishes itself because it resists oxidation.

When some metals are in contact with oxygen their color can change. Some elemental metals do not change color when exposed to air. Gold is the premier metal that does not oxidize.

For instance, anyone searching for sunken Spanish galleon gold may have to scrape off debris that has gathered on its surface (etching), but once that is performed, the surface of the gold is golden. One does not have to apply chemicals or harsh abrasives to see the gold.

Oxidation Can Be a Bummer

Oxidation is a process that often eliminates metals from consideration for parts manufacture in technology. The oxidized coat can decrease conductivity and increase decay. This makes gold not only a precious metal for jewelry, but also a requirement in the construction of tech hardware.

It's All I Have Ever Seen

In free elemental form, gold often is found as nuggets or grains, in alluvial deposits, in rocks, and in veins. It occurs with the native element silver (electrum) and is also naturally alloyed with copper and palladium. Gold nuggets are usually 70 to 95 percent gold. And of course, those of us who are placer prospectors are very interested in this.

Iron Stains

The compounds of gold discussed below are often brown, iron-stained rock or massive white quartz, and usually contain only minute traces of gold. My personal experience leads me to believe that the form most often found in Arizona is that of iron-stained rock. It can be observed frequently while searching for the yellow, or simply on a hike.

Calaverite

Calaverite Locality: Cripple Creek, Cripple Creek District, Teller County, Colorado, USA (Locality at mindat.org) Size: 6 x 5 x 3.5 cm. Calaverite is a very rare crystallized gold telluride species, found in good crystals over 1mm in few locations.

Calaverite Locality: Cripple Creek, Cripple Creek District, Teller County, Colorado, USA (Locality at mindat.org) Size: 6 x 5 x 3.5 cm. Calaverite is a very rare crystallized gold telluride species, found in good crystals over 1mm in few locations.

May Look Like Silver, But Contains Gold

Calaverite is a mineral with a metallic luster, and its color may range from a silvery white to a brassy yellow. Closely related to the gold-silver telluride mineral sylvanite, a mineral containing significantly more silver. A telluride is a compound of two elements, one of which is the element tellurium. An interesting aside is that tellurium is a metaloid, meaning it contains characteristics of metals and nonmetals.

Calaverite and sylvanite are major telluride ores of gold, although such ores are minor sources of gold in general. As a major gold mineral found in Western Australia, calaverite played a major role in the 1890s gold rushes in that area. It is also found in the mother lode belt, Calaveras County, California, and in Colorado.

Those of us who may be quick to draw conclusions (like me on occasion) might deduce that Telluride, Colorado was named thusly for the discovery of tellurides. But strange as it may seem, tellurides were never found there, however, gold, silver, zinc, lead, and copper were.

A Relative of Calverite

Sylvanite has a gold to silver ratio varying from three to one up to one to one. It is a metallic mineral with a color that ranges from a steely gray to almost white. It is closely related to calaverite, which is more purely gold telluride with three percent silver. Sylvanite is found in Transylvania, a region in central Romania. Its name is partially derived from this area.

It is also found and mined in Australia in the East Kalgoorlie district. In Canada it is found in the Kirkland Lake Gold District, Ontario and the Rouyn District, Quebec. In the United States it occurs in California and in Colorado where it was mined as part of the Cripple Creek ore deposit.

Sylvanite

The Cripple Creek Gold District of central Colorado, USA is famous for its unusual gold and silver mineralization. Precious metal mineralization occurs in the Cripple Creek Diatreme, the root zone of a deeply eroded volcano dating to  Early Oligocene

The Cripple Creek Gold District of central Colorado, USA is famous for its unusual gold and silver mineralization. Precious metal mineralization occurs in the Cripple Creek Diatreme, the root zone of a deeply eroded volcano dating to Early Oligocene

Sulfides

Sulfides are compounds of sulfur bound with many metals. Sulfides occur in ores (other rock mineralization) with the main sulfide being gold sulfide. These concentrated ore deposits are considered low grade because of the economic costs associated with processing, but they can be separated economically when prices for these metals rise on the open market. In addition, gold can sometimes be found bound with pyrite (iron sulfide) in pyrite ores, but again, the cost to separate the precious metal is usually prohibitive.

This is a piece of pyrite ore. I found this in a flat desert area near no waterway or rock formations. When I crushed it there was gold inside. Gold is where you find it!

This is a piece of pyrite ore. I found this in a flat desert area near no waterway or rock formations. When I crushed it there was gold inside. Gold is where you find it!

Iron-Stained Ore

Azurite-malachite on gossan (Morenci Mine, Arizona, USA) The red area is iron oxide.

Azurite-malachite on gossan (Morenci Mine, Arizona, USA) The red area is iron oxide.

Krennerite

This rare gold silver telluride forms in some of the finest crystals in the world in the Cripple Creek Mining District. Fine crystals of Krennerite on matrix are virtually impossible to obtain as the mines around Cripple Creek have long been played.

This rare gold silver telluride forms in some of the finest crystals in the world in the Cripple Creek Mining District. Fine crystals of Krennerite on matrix are virtually impossible to obtain as the mines around Cripple Creek have long been played.

Krennerite

Whereas calaverite and sylvanite have similar crystalline structures, krennerite is different. It has perpendicular axes that are unequal in length with the base of the crystal forming a rhombus. The bases of the calaverite and sylvanite crystals are parallelograms.

Krennerite occurs less frequently than calaverite and sylvanite which are considered primary ores of gold. It is also a gold telluride. Krennerite is, however, found in the same areas of the United States.

Conclusion

There is an old saying among gold prospectors that "gold is where you find it." The saying is an implicit acknowledgement that given all the rules for finding gold, there are times when those rules are broken and gold appears in an unlikely and strange place. The rules are created to minimize frustration and maximize the probability of finding color.

For those of us who wander the desert in the pursuit of gold, knowing what gold ores look like might prove helpful.

Sources

Vaughan, J.P. (July 2004). The Process Mineralogy of Gold:The Classification of Ore Types. Retrieved from https://link.springer.com/article/10.1007/s11837-004-00928#:~:text=The%20principal%20gold%20minerals%20that,and%20pyrite%2C%20is%20also%20important.

Bacher, Diane. (January 9, 2018). How to Extract Precious Metals from Sulfides. Retrieved from https://sciencing.com/how-7462326-extract-precious-metals-sulfides.html.

Kubach, Charles. (n.d.) Recovery of Gold in Pyritic Sulfide Ores. Retrieved from http://mine-engineer.com/mining/minproc/gold-in-pyrite.htm

Staff. (July 23, 2017). An Introduction to Native Metals. Retrieved from https://www.irocks.com/an-introduction-to-native-metals.

Barbara Shreiber. (n.d.).Gold: Properties, Occurrences, and Uses. Retrieved from https://www.britannica.com/science/gold-chemical-element/Properties-occurrences-and-uses.

Galbraith, F.W. (1940). Tellurides. Retrieved from http://www.minsocam.org/msa/collectors_corner/arc/idtellurides.htm.

Chen, T.T., Cabri, L.J., Dutrizach, J. E. .(December 2002). Characterizing gold in Refractory Sulfide Gold Ores and Residues. Retrieved from https://link.springer.com/article/10.1007/BF02709181#:~:text=Gold%20is%20present%20in%20refractory,converted%20to%20the%20metallic%20form.

King, H.M. (2020). What is Pyrite? Retrieved from https://geology.com/minerals/pyrite.shtml.

Staff. (August 16, 2019). Sylvanite. Retrieved from https://en.wikipedia.org/wiki/Sylvanite

Fortey, R. (2004). Calaverite. Retrieved from https://en.wikipedia.org/wiki/Calaverite.

Staff. (May 13, 2014). Identification of the Commoner Tellurides. Retrieved from http://www.minsocam.org/msa/collectors_corner/arc/idtellurides.htm.

Guilbert, J.M. and Park, C.F. (June 3, 2020). Gossan. Retrieved from https://en.wikipedia.org/wiki/Gossan.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 John R Wilsdon

Comments

johnabrahamuniv on August 02, 2020:

Looks very interesting :)