Main U.S. Gold Deposit Types (Conclusion)
(Schematic of a Noranda-type gold deposit.)
Here is my final installment on the main types of U.S. gold deposits. By the way, for those of you in other countries, these deposit types may not have the same names but probably share the same (or similar) characteristics as those in your homeland:
Gold Panning Kits
Noranda: These types of deposits are frequently associated with copper. Both the gold and the copper will typically be found in granitic and tonalite porphyries (zones of igneous rock) containing magnetite, chalcopyrite, and bornite. Small gold placers are often associated with Noranda-type deposits.
Picacho: I believe these sorts of deposits received their name from gold-bearing areas (Picacho Mountains, Picacho District) in extreme southeastern California and southwestern Arizona. The well-known "Potholes" gold district near Winterhaven, California and Yuma, Arizona is a Picacho-type deposit. Gold placers in these deposits can be quite extensive and are usually associated with a multi-colored breccia while the vein materials are associated with chalcopyrites. Other minerals that are typically present in Picacho deposits are barite and fluorite.
(Typical terrain associated with Picacho-type deposits.)
Sado: Andesite and rhyolite form the typical country rock host for Sado-type gold deposits which are epithermal in origin and contain significant indications of chalcopyrite. The state of Nevada has a number of good examples of Sado deposits. Gold placers are not usually associated with Sados but their vein material can be quite rich in free-milling vein gold as well as silver as a secondary precious metal. (Japan actually has some significant Sado deposits...this is, in fact, where the name came from.)
(Japanese coins made from Sado-type deposit gold.)
Tedi: These deposits are composed of ancient lava flows and tuffs overlain by chemically altered rocks of hydrothermal origin known as propilitics. Copper and gold in substantial quantities can be found in Tedi-type deposits and associated minerals include pyrites, molybdenite, magnetite, and chalcopyrite. Tedis may include gold placers of minor quantity and quality.
That's it on this topic. Best of luck to you all.
If you liked this post, you may want to read: "Best States for Placer Gold in the U.S.A."
(c) Jim Rocha (J.R.) 2011
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