History & Geology
Exploring Iron Oxide Copper Gold Deposits
The excitement over IOCG deposits began with the discovery of a monster deposit at Olympic Dam in Australia in 1976. The discovery was accidental as the operator was searching for strata-bound copper deposits.
Conrey Dredge No. 4
The large buckets were favorable for the type of ground worked. The gravel was tenacious and compact, due to the existence of irregular pockets of clay.
Kennecott Copper Mine, Kennecott, Alaska
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.
How to Recognize Hard Rock Gold Ores
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.
The Rochester Mining District of Nevada
Only the richest ores could be worked and shipped off for processing at a profit. As a result, early mining in the southern part of the Humboldt Range was short-lived. In the 1880s, placers were discovered in Spring Valley and American Valley on the east side of the range...
Simple Rules of Gold Geology: Comparing Epithermal and Mesothermal Deposits
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 Goldfield Mining District, Nevada—Part II
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.
Critical Minerals: Tungsten
Because tungsten minerals are heavy, exploration can be done using stream sediment samples. Prospectors looking for gold have found scheelite or wolframite in their placer concentrates, and in some cases this has led them to make important tungsten finds.
The Goldfield Mining District, Nevada—Part I
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.
Weathering, Erosion and Placers
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.
Diary of a Diamond Prospector
I couldn’t wait to get started. With no field budget, an assay budget of $100/year, a 1975-Ford Bronco that was a road hazard, a gas card, a topo map and full support of the director, I headed to the State Line district near Tie Siding along US Highway 287 to begin mapping kimberlite.
Epithermal Gold and Silver Deposits
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.
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.
The Goldfield Mining District -- Then and Now
In 1983, some of the ore yielded more than 2,500 ounces of gold within 30 feet of the surface. The shoot pinched to a narrow vein.
Nevada's Lithium Boom
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.
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.
Gangue Minerals - What Do They Tell Us?
There are a large number of different kinds of gangue minerals, and each of them has its own tale to contribute to the story of the chemistry and geology of a deposit.
Prospector's Guide to Rock Breaking and Blasting
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.
Glaciers and Placer Gold Deposits
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 Seven Troughs Mining District
The favorable geology of the northeastern and central parts of the Seven Troughs Range are the parts most interesting to prospectors. They are underlain by a thick sequence of Tertiary volcanic rocks, mostly rhyolites and andesites.