Gold Occurrences in Utah

Mountains like this in Utah are where you can find gold.
Photo by Scott Catron

Most gold deposits found in Utah are in the mountains around Salt Lake City, and placer gold is found in the streams draining the Brigand district. Gold is also produced as a byproduct of the copper mining business at Bingham Canyon. Today most of the gold that has been mined in Utah was found during the Great Depression of the 1930s.  Please are gold is still found in the rivers and dry washes that are coming down the mountains in the area around Salt Lake City.

It has been recently discovered that there is gold present in skarn deposits in the Western part of the state that has a potential for gold. So far gold is been found in 146 of the skarn deposits in Utah that continues across the border into southwestern Montana. Skarn's are a variety of calc-silicate rock that occurs when limestone is intruded by igneous rocks. These rocks consist primarily of calcium bearing silicate such as diopside, wollastonite that are formed by the metamorphism impure limestone or dolomite. Typically the calc- silicate minerals have a greenish hue.

According to the Utah geological survey many of the skarn deposits are considered to be economic. Many of these skarn deposits also contain other or under rules such as sheelite one of the ores for tungsten. They also contain copper rowers such as chalcopyrite and the bornite.

Another source of gold in Utah is as a byproduct of the copper ores from Bingham Canyon, and Gold Hill. These copper deposits are found in porphyry that can also contain molybdenum and Gold.

Gold can sometimes be found as detrital gold in sedimentary rocks especially in the sedimentary rock conglomerate where it is found as fossilized placer deposits.  Conglomerate is nothing more complicated then a gravel deposit that has been turned to stone.  The largest gold producing area in the world, the Witwatersrand in South Africa is conglomerate.  This one area has in just over a century produced 40% of the gold that has ever been mined.  Gold is also produced from conglomerate in the Abitibi gold belt in Ontario and Quebec from conglomerate at Timmins Ontario.

Gold is often found associated with marble especially where it has come into contact with intrusive magma.  Often these deposits occurred during the Mesozoic era when dinosaurs roamed the Earth.

A crystal of bixbite on a matrix of rhyolite
Photo by Rob Lavinsky

Gold is not the only mineral those found in Utah that has great worth. The state gemstone of Utah is topaz that is found in topaz rich rhyolite as well as another mineral called “bixbite” that is reckoned to be more than 1000 times as valuable as gold.  According to the Utah geological survey bixbite is even more valuable than diamonds. If the stone was cut and polished it is worth far more than $2000 per carat.

Gold Producing Metallogenic Provinces and Epochs (MPE)

There are many metallogenic provinces and epochs (MPE) that can be traced through the formations of various rocks including those particular places and times when gold was deposited. There are at least eight of these episodes that can be found in the Appalachian Mountains of southern Québec. These MPE's can range all the way from the Grenville orogeny that occurred around 1.2 million years ago, and can be traced to different types of orogenies and mineralization to the end of the Permian era. 

A map of selected worldwide ore deposits of metals.
By KVDP

The different MPE's can be directly related to specific orogeny like the Grenvillian or any other orogenic event that has happened in the history of the world. An MPE can be found anywhere on the face of the earth. That means you had better know the geological history of the area where you are prospecting, and remember that some orogenic events left more gold behind them than others.

MPE's are usually associated with a suture zone where one tectonic plate has collided with another. In the case of an oceanic plate colliding with the continental plate the oceanic plate is subducted beneath the continental plate, and about 20 km inside account metal plate there should be a line of granitic intrusions.

The subduction zone acts as a giant heat engine melting the material that has been dragged downward by subduction causing it to become heated to the point the material is melted.  The subducted material is also saturated with water that lowers the melting point of the material, and supplies the water that at depths of kilometers beneath the surface of the earth becomes super heated water that is capable of dissolving many minerals that when they reach the right environment through the action of the superheated hydrothermal fluid are deposited as ore.

A subduction zone.
By A.J. Stern

Searching around in the area that has been intruded one is apt to find gold in the aura of contact metamorphism that is associated with the granitic intrusions. In this case gold is often associated with scheelite, an ore of tungsten in the form of tungsten carbonate. This occurrence is often found where the granite has intruded through an older layer of carbonate rocks such as limestone or dolomite where it forms a skarn..

On the oceanic side of the subduction zone are found many metal sulfide deposits where this whole deposits are usually found in small amounts, but there can also be some really huge deposits of sulfide that are formed this way. These are the result of sulfide deposits that are laid down by black smokers found on spreading centers located on the bottom of the ocean. These deposits are laid down very much like plums in a pudding at the scattered across the bottom of the ocean.

A black smoker at a spreading center at the bottom of the ocean. NOAA

As these deposits are carried away from the spreading center by the action of more magma being injected they cover the ocean bottom with spots where they are eventually subducted beneath a continental plate where they are often reactivated to form secondary mineral deposits sometimes in quantities large enough to form ore deposits.

MPE's are where ore deposits are typically found, and in many cases are considered to be the primary source of mineralization, and they eventually break down to form detrital mineral deposits.