Nevada is home to many mines that produce gold from a variety of different types of gold deposits. One of the more interesting types of gold deposits is known as the Carlin deposits. These Carlin-type gold deposits consist of very small, microscopic gold that is found in arsenopyrite or pyrite. This particular type of gold deposit is named after the Carlin Mine where it was first discovered in Carlin, Nevada.
The Geology of Carlin-Type Gold Deposits
These types of gold deposits are a combination of gold, mercury, thallium, antimony and barium. Essentially, the enrichment process is created uses what is known as hydrothermal circulation that may reach temperatures of up to 300 degrees Celsius or higher.
There rocks underneath the minerals are dissolved at these temperatures and form small carbonates which remain in the mixture. While the source of the heat remains up for debate, all the materials found in the deposit are either dissolved or transformed into other materials and unusual alterations occur such as clay minerals forming when feldspar and water are combined. Because there are no base metals sulfides present, the even distribution of the arsenopyrite and pyrite in the rock formations make this type of formation stand out from deposits of sulfide.
Mining of Carlin-Type Gold Deposits
The Carlin mine is home to some of the largest hydrothermal gold deposits that have ever been found, however, because the gold itself is often microscopic it makes them very difficult to find under normal conditions. The early gold miners that explored this region during the mid-1800ís had no idea that they were even there, and and the mining technology at the time would have limited their ability to extract the gold from the rock regardless.
By the 1960s, the Carlin Mine exported this type of gold on a large basis and the results were a search for similar types of geologic formations around the world. Macedonia and China have deposits of this particular type as well as many other mines in the state of Nevada, most notably in the Great Basin region, particularly around Elko and Battle Mountain.
The Carlin Unconformity & History of Carlin
A collision of tectonic crustal block and the North American Plate occurred around 350 million years ago, and this collision created the temperatures and pressure which produced the geologic forces that made Carlin-type gold possible. There were several hot springs along this particular zone which affected the entire Great Basin area. The hot springs were able to bring gold and silver up to the surface where they dissolved outwards into the fissures and rocks along the basin area.
Although microscopic in nature, the Carlin Gold is one of the richest gold mining districts in the world with deposits stretching more than 40 miles in length and 5 miles in width running from southeast to northwest through the town of Carlin, Nevada. Although larger size deposits of gold were found in the area starting in the 1870s, very little was actually take out over the next 90 years until the discovery of the microscopic Carlin-type gold. Since then, roughly $85 billion of gold has been removed from the mining areas with these deposits present.
Also Read: Gold Prospecting in Nevada
And: Rare Gems and Minerals in Nevada
For the average prospector, these gold deposits are unworkable. Standard prospecting methods like panning, sluicing, metal detecting, and drywashing will not capture the gold. It is just too small, and locked up within the rock. It is the large mining companies that have really taken interest in this area in recent decades.
Although it is difficult for the average gold prospectors to capture this gold, this part of northern Nevada also has an abundance of gold occurrences that are more typical deposits that you would expect to find throughout the West. Using a metal detector or drywasher is a great way to find these larger pieces of gold, which are often eolian type deposits found near the surface of the ground. These are the types of gold occurrences that most prospectors should focus their attention on in this area. Leave the Carlin-type deposits to the large mining companies.