Mining in the Western US
Written by David Brown P.E., Vice President of Engineering
The first exposure that many of us had to mining was through Western movies or television shows. Some of us remember scenes of the twenty mule teams hauling Borax out of Death Valley; or the cranky old prospector wandering the desert mountains of the west, with his trusty mule or burro, looking for and then following geological formations, hoping to find the mother lode gold seam. Or in the mid nineteenth century adventurous young men making their way to the streams and rivers of California or Alaska hoping to pan or sluice the gold that lined them.
True stories, or close to it. More often than not, though, finding precious metals or minerals was always much more difficult and scientific than that. Early prospectors were geologists and civil engineers, many were well educated. Miners were often experienced immigrants, from Eastern Europe, Western Europe, Wales or Ireland. Descendants of these early miners still live in the Western US mining towns.
As placer and free gold was panned out, chemists, engineers along with geologists were needed to develop new processes for preparing ore and extracting metals and minerals. Early chemical extraction processes were crude and inefficient and often left significant residual materials.
An acquaintance worked as a mining engineer at Homestake Gold Mine in the Black Hills of South Dakota starting in the early 1930’s. He had a degree from South Dakota School of Mines in chemical engineering and was an expert on extractive processes used in separating precious metals from ore. He bought a mine property that had been worked in the 1930’s and 1940’s. It was complete with processing equipment, a bunk house and a chow hall. It was an underground mine in very poor (you might say dangerous) condition. The metals that were mined were gold and silver. He had inspected the mine and found that the gold seams had been mined out and there was very little high grade gold or silver ore left to be mined. That, combined with the dangerous conditions of the mine shafts, convince him to change directions and use current technology with his extensive experience to make the mine worthwhile. One of the tests he performed was to assay the waste dump materials (tailings) from the original mining activities. He found that gold content was good and his approach, therefore, was to re-process the tailings using technology that was current in the 1980’s.
He retired from Homestake, bought a small used crusher, a ball mill and a couple small process tanks and spent his remaining years making a very decent living reworking his gold mine tailings dump. In his spare time he operated a floating placer vacuum barge that would suck up mud and sand from cracks and seams in river bottoms and separate out placer gold. He hoped to be able to access places that could not be reached by miners who panned and sluiced these rivers. His design is still being used today.
Most mined products are commodities and value is determined by demands that fluctuate. This has created a history of boom and bust that is more dramatic than most other hard commodity markets. As a result, mining has evolved drastically over the years, although the roots remain the same as in the early days. Processes and equipment are largely more efficient versions of earlier ones.
In the early days of mining in the Western US, environmental and safety considerations were not high priorities. Mining was considered a very risky occupation and significant damage was done to rivers and mine sites with toxic residual materials.
The mining industry has become more sensitive to environmental considerations. Processing facilities that have been in service for years are upgrading their systems to have less effects on air and ground water. New mines are designed with latest technology and equipment to minimize environmental impacts. Most operating mines have detailed renovation plans to restore the mine sites to original conditions.
Mines and processing facilities have adopted rigorous safety policies and procedures and safety features are designed into them. Safety is a high priority for all mines. MSHA is the regulatory entity for mine safety and OSHA is the regulatory entity for most processing facilities, and most mines and processing facilities strive to exceed regulatory requirements. Process Safety Management (PSM) is widely adopted as the methodology for safety programs at most processing facilities. One of the elements of this method is Process Hazard Analysis (PHA), which is a rigorous and systematic way of evaluating process safety. PHAs are performed at least every five years on every process system.
Much of the prospecting for new mines and mine expansions is now done by satellites and aerial photogrammetry to determine potential mining sites. The extent and quality of ore is determined on-site with seismic and sonic testing. Verification is performed with boring samples that are lab tested and quantified. Large quantities of data are collected and used to create three dimensional ore body and quality boundary limit models, then, in the case of underground mines, to prepare three dimensional mine shaft alignment drawings and mining plans, and in the case of open pit or combination mines, to prepare mining plans and mine haul road alignments.
Processing facilities are designed and controlled by sophisticated use of data specific to the ore and metals or minerals being extracted. The physical design of these facilities is largely done with three dimensional modelling of the entire processing facility, including material handling, processing, equipment and piping, structures and foundations, site leveling and drainage and electrical equipment. Most control systems are computerized and are fed continuous data from instrumentation on equipment and piping that measure every aspect of the process systems. Process systems can be computer simulated remotely and verified prior to integration and commissioning. This can prove out the process designs and minimized process field problems.
Metals and minerals mining in the Western US has come a long way and still has a long way to go. Mines and Process facilities are becoming more and more efficient, safer and environmentally friendly.
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