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Column No. 49
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)
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Next Time: The Beginning of American Mining in Southern Arizona
