History & Geology
Understanding and Prospecting Benches
September 2011 by Jim Halloran
The most obvious benches are usually near the valley floor, but they can be thousands of feet above the valley floor. Since benches were made by streams, they can contain placer deposits.
Las Médulas—The Gem of the Roman Gold Mines
This mine was a real wonder of engineering, and the water supply and drifts had to be carefully managed to keep it in operation. In fact, it didn’t close due to lack of gold, but instead closed with the fall of the Roman Empire.
Gold in the San Francisco District Oatman, Mohave County, Arizona
I suspect detailed geological mapping and prospecting would lead to discovery of one or more overlooked gold deposits in the district even though it has been heavily prospected in the past.
Ask The Experts
Q: Is there a correlation between fault zones and mineralization of economic metals?
Northwestern Alaska Mineral Resources
Gold and jade are actually only minor mineral resources for the Northwestern Alaska region as a whole. Modern prospecting has focused more on base metal than precious metal resources.
Critical Minerals: Titanium—Part II
There are both hard rock and beach sand types of titanium deposits, but the hard rock deposits need to be at least 10 percent titanium while the beach sands often are economic with only two or three percent titanium.
The Heavy Minerals in Your Concentrates
The fact that mineral deposits can contribute specific types of heavy minerals is why the analysis of the heavy mineral concentrates in the streams of an area can be an important prospecting technique for finding undiscovered mineral deposits.
The Ups and Downs of Geologic Faults
Faults are fractures, breaks and broken zones in the Earth’s crust where one side of the break has moved relative to the other, and they come in many different varieties.
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