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The Milling Techniques of the Gold Rush

The Argo Mill was completed in the early 1900s, soon after the 10-year Argo Tunnel operation was completed. In its time, the state-of-the-art milling techniques of the Argo processed over $100 million worth of gold ore!

The prices per ounce ranged from $18 to $35, meaning the mill operations were hard at work each and every day. Various techniques were used to extract gold and other minerals, requiring different machines to process the ore diversity. Below, we explore the Argo’s machinery and how it aided its prosperity during the Colorado Gold Rush.

Exploring Milling Techniques – Amalgamation Table

Amalgamation requires mercury to extract minerals from the rock. To get the gold by itself, the mixture of mercury and gold is heated until the mercury vaporizes, allowing for nearly pure gold to be left behind.

This process had been used for centuries before the Colorado Gold Rush, and is still widely used in small-scaling mining worldwide. Efforts to eradicate this practice are in effect, as the high levels of toxic exposure affect both miners and the environment negatively.

Flotation Cells

Flotation cells are used in a variety of industries to this day. It is an effective concentration method used to separate finely ground materials. In a mixture of chemicals, water, oil and air, the metallic products would float to the frothy top, allowing any gold to be extracted.

The origins of this process were developed in the early 1900s in Australia, and have been refined for commercial use. Introducing flotation technology to the mining industry allowed the supply of low-grade ores to flourish, setting up the industry to prosper globally.

Concentrating Tables

Concentrating tables utilized simple technology to separate gold ore from other minerals of the Rocky Mountains. The Argo Mill employed seven concentration tables, which vibrated the powered ore to separate heavy and light materials.

Also known as gold shaking tables, Arthur Redman Wilfley created the original patented design in 1896 in the U.S. Other variations of this table were created, but the purpose remained the same—it served as the last stop in the milling techniques of The Argo to recover valuable gold that may have been missed during the other concentration methods.

Cyanide Leaching Tank

This gold processing method allows for maximum recovery for many forms of gold ores. The cyanide dissolves the gold, which is then extracted from the solution by absorption via carbon or resin granules. Essentially, the cyanide turns the finely ground gold into a liquid form, allowing it to separate from other materials.

This process dates back to 1783, but wasn’t introduced to the gold mining industry until 1887.

Ore-Crushing & Grinding

None of these processes would have been possible without the machines helping turn the large mined rocks into processable sizes. This was done through the arrastra, the ball mill and the tube mill. Furthermore, stamps weighing over 1,000 lbs were used to pulverize these materials.

Most of these machines, especially the stamp mill, produced a deafening noise, affecting the miners manning the equipment forever. It was so loud, they called it Thunder in the Valley.

Want More?

The Argo Mill’s three-decade reign is owed to the stellar milling techniques that processed gold ore from the many mining towns near Idaho Springs. They implemented the most recent technologies to yield the highest percentage of precious metals.

If you’re fascinated by the history of the Colorado Gold Rush, we can guarantee you’ll enjoy a tour of The Argo Mill & Tunnel. Experiencing the size of Idaho Springs’ mining operations and viewing the milling techniques firsthand will allow you to put yourself in the shoes of a miner in the late 19th century.

Book your tour today!