History & Geology
ICMJ Visits Colfax, California
February 2023
All About Chalcopyrite
…there are loads of different copper minerals, but a large number of them form first in the ground as chalcopyrite and then through the effects of weathering are changed into other minerals like malachite, cuprite and chrysocolla.
Residual Placers: An Often Overlooked Gold Source
Because the forces of erosion and gravity tend to carry lighter materials like quartz away more easily, the heavy minerals like gold or silver will tend to be concentrated in the general area around the vein outcrop. These concentrations are what make residual placers so attractive.
Calcite and Limestone
The other distinguishing feature of calcite has to do with its chemistry. Geologists sometimes take a small bottle of dilute hydrochloric acid out into the field with them because calcite reacts with acids to make a bubbly foam.
The Potholes—California’s Oldest Known Mining District
Every time we prospected here we found gold, sometimes some really coarse flakes, but no large nuggets (yet).
What Are Those Rocks In My Pan?
The placer mineral identification key is designed to answer this question. It attempts to recognize all the minerals in your gold pan concentrates.
Green Valley Gold District, Payson, Arizona
Most gold-bearing quartz veins found in the district were fracture fillings in faults enclosed by crushed quartz zones along their margins. Since the host rocks were often extensively weathered, portions of the veins stood out as positive, resistant outcrops. The gold-bearing veins ranged from a few inches wide to the vein at the Gowan mine that was as much as 12 feet wide. Testing Ores for Free Gold
I get a number of questions from people about testing and treating hard rock ores. The simplest way, but also an expensive one, is to just have an assay test done by an independent assay firm. As an alternative...
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Lost and Undiscovered Gold Mines of the East: Why Research is Key!
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The Bawl Mill
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