History & Geology
For approximately 30 years, the mines produced good ore, some so rich it was simply sent straight to bagging, bypassing milling and loaded directly on the rail cars.
I regularly get inquiries along the line of: “Hey, I found this rock, and I think it might be gold ore. How can I tell?” Prospectors are always on the lookout for gold-bearing rocks that may be the source of any nearby placer gold.
Geology is a science of general tendencies with frequent exceptions, not one of hard and fast rules that are always true and never vary. For almost every well-accepted rule of gold deposits, I can point you to a number of important exceptions.
The majority of the gold produced in Goldfield has come from ores that are close enough to the surface to be oxidized by the air. This oxidized ore is normally a soft, shattered, earthy material usually stained yellow to brown by oxides of iron.
An example of some of this extraordinary ore was a lot of about four tons from the Florence mine during the last days of a lease that averaged over 300 ounces of gold per ton.
The big interest to prospectors thinking about the effect of erosion is not what might happen long into the future, but what they might find in the rivers later this summer when the water levels go down.
Epithermal deposits form in the ground at shallow depths. They are popular with prospectors because can yield very rich deposits and they are widespread in the Western US.
…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.
When prospecting for lithium, after confirming for macro attributes through research and field work, including examination of surface geology, the main tool is an accurate lithium assay.
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 holes were overloaded with explosives, but I didn’t know it. I was just a green mining engineer fresh out of school and told to watch as the experienced miners set the charge.
It also happens sometimes that glaciers will bury valuable placer deposits. This occurs when the glacier goes over the top of an existing placer deposit.
The process of recognizing ores all starts with being able to recognize some basic minerals and knowing what hard rock ore looks like in the districts where you prospect.
Climbing up the debris, I pointed my flashlight up a shaft ascending straight up as far as my light would shine. It was the stope of the pay shoot leading to the old tunnel above!