Column No. 49

Mining Technology Transfer from the Far West

Bob Ring, Al Ring, Tallia Pfrimmer Cahoon

With the Gadsden Purchase in 1853, southern Arizona became part of the United States. But American mining development did not get off to an immediate or particularly energetic start. The combination of hostile Apaches, poor transportation, climatic extremes, and little available capital, held back the development of mining. Additionally, there simply were not that many people in Arizona in the 1850s. In fact, a full decade after the Gadsden Purchase, only 4,573 non-Indians claimed residency. By 1870 the population had grown to 9,658.

There was little capital available for south-central Arizona mining development because of the fabulous California gold rush, starting in 1849, and other huge mining strikes in Nevada (Comstock Lode) and Colorado (Leadville) that followed over the next 30 years. These huge strikes demanded the attention of U.S miners and financiers.

The tremendous mining booms in the Far Western states completely overshadowed early mining efforts in the southwest. But, these successful operations produced new technology and mining processes that miners applied later in Arizona, though on a much smaller scale.

The simplest and most direct technique to obtain placer gold from old streambeds was “panning for gold.” In this “placer mining,” a miner scooped up stream sediments in his hand-held pan, shaking the pan to expose the grains of gold. In California, miners developed wooden rockers, also called cradles, that they shoveled dirt and gravel into, and then moved back and forth as water was poured through it. Gold particles settled to the bottom and caught behind pieces of wood nailed crosswise to the flow.

In larger operations, miners increased the length of the rocker to as much as thirty feet and added screens to filter out the gold. Such a “long tom” rocker required 6-8 men to operate.

Of course lode mining was more complicated than placer mining. First you had to find the vein or ore body, then remove the overburden (or approach the vein through underground shafts and tunnels), break out the pieces of richer ore, crush the ore to the size of coarse sand, and finally apply chemicals to separate and recover the precious metal from the crushed ore.

In the Far West, the mechanical drill soon replaced the miner’s pick, shovel, and hammer and the application of dynamite made the process of breaking out chunks of ore much more efficient.

The process to crush the ore evolved from the simple arrastra to complex milling machines.

Arrastras, developed and long used by the Spanish in Mexico and the southwestern U.S., were circular pits dug in the ground, with the floor lined with flat stones. Miners set a heavy upright pole in the center of the pit and attached horizontal crossbars. Then they tied huge rocks to the spoke-like crossbars and used burros or mules to drag the rocks over chunks of ore placed in the pit to grind them into small pieces. Arrastras were the ore crushing solution of choice in isolated, small-scale mining operations. Unskilled labor was adequate and the process required little capital.

The improvement in California gold mining of the stamp mill to pulverize large quantities of ore, offered a much more productive (albeit more costly) alternative to arrastras to crush the ore to fine particles.

A stamp was nothing more than a heavy pestle (think mortar and pestle). A bin fed ore to a mortar containing several stamps and water. Steam power controlled the crushing action of the stamps. The crushed ore-pulp passed through a strainer, then into a trough below, and finally flowed into settling pans. By the 1870s larger stamp mills contained tens of stamps and could process tens of tons of ore each day. Stamp mills were heavy, bulky pieces of equipment and required major transportation support to bring the component parts “into the field.” Stamp mills also required higher order skills for their setup, operation and maintenance and required significant capital investment.

Amalgamation was the most common early process for recovery of precious metals. Miners added mercury to the ore-water mixture to “amalgamate” (alloy) with the gold or silver. Then they retorted or boiled away the mercury to recover the precious metal. In this crude recovery process, sometimes less than half of the gold or silver was recovered.

The ultimate recovery process (sometimes approaching 100% recovery) was smelting, which involves converting the ore into a fluid by means of heat and chemicals, and then separating the metallic from the earthy ingredients by means of their specific gravity. Some larger mining operations in the Far West, especially in Nevada, built their own smelters “on-site” to process their own ore. But local smelters were typically not efficient because the nearby mine(s) often did not produce enough ore to keep a custom smelter in continuous operation. Also, high costs for labor, supplies, transportation, and the only fuel available, charcoal, were a problem.

Eventually, what evolved were a few specialized, large smelters that serviced an entire region.

By the late 1850s, some of this mining technology and processes developed in the Far West were ready to be applied in southern Arizona.

(Sources: Rodman Wilson Paul, Mining Frontiers of the Far West, 1848-1880, 2001; Marshall Trimble, Arizona Cavalcade of History, 1989)

Wooden Rocker

Wooden rockers like this one helped miners settle out gold particles
from streambed gravel. (Photo from History of Mining in Arizona, 1987)

Stamp Mill

Stamp mills such as this 15-stamp assembly could crush several tons of ore per day. (Reproduction from the Dr. J. A. Munk Collection, Southwest Museum, Los Angeles, California)

 Next Time: The Beginning of American Mining in Southern Arizona

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