Gold in Wyoming
Gold, the intrinsically valuable "royal metal," derives its value from the combination of its rarity and beauty along with its softness (2.5 to 3 on the mohs hardness scale), malleability, ductility, ease of alloying with other metals such as copper and silver, and its high resistance to corrosion and tarnish. Various estimates place the average gold content of the earth’s crust around 3.1 parts per billion (ppb), or roughly 0.0001 ounce/ton. Although disseminated gold is widely distributed, concentrations greater than 0.5 ppm, or 0.5 g/tonne, are near minimum for economic recovery in a modern low-grade, large-tonnage gold mine. Higher grades are always desirable and are usually necessary to initiate mining prior to recovery of the lowest grade material.
Gold has a specific gravity of 19.3 – much heavier than the specific gravity of quartz (2.65), a common host rock for gold. Other host rocks may be heavier than quartz, but even the heaviest, such as banded iron formation, have specific gravities less than half that of gold. The great difference in weight between gold and its host rocks allows it to concentrate in placer deposits from which it can easily be recovered. Since earliest times, gold has been used for both objects of art and for coinage.
Gold and other metals have been mined from primary deposits in Precambrian rocks exposed in the cores of Wyoming’s mountain uplifts and in some Tertiary volcanic and intrusive rocks. Gold has also been mined from placer deposits concentrated by weathering and erosion of those primary occurrences.
History
Around 1842, travelers along the old emigrant trail (part of the Oregon Trail) first reported placer gold near the Sweetwater River in the area now known as the Lewiston district, near the southern tip of the Wind River Range (see Principal Metal District Map). Indian hostilities prevented serious prospecting until the 1860s. Wyoming’s first gold rush sprang from the 1867 discovery of bedrock-hosted gold west of the Lewiston district in what became the famous Carissa lode.
In 1869, the settlements of South Pass, Atlantic City, and Miners Delight boasted a combined population of more than 2,500. Gold production from the Carissa totaled between 50,000 and 180,000 ounces before 1911. Total production from Wyoming is unknown because no records were kept, and few estimates were made before about 1900.
Mining districts were organized in several locations across Wyoming during the late 1860s and 1870s. The South Pass-Atlantic City district was first and foremost. Other districts discovered during that era of relatively high gold prices included Lewiston (about 12 miles southeast of the South Pass-Atlantic City district); Centennial Ridge, Douglas Creek, Gold Hill, Keystone, and New Rambler (all in the Medicine Bow Mountains); Seminoe Mountains; Copper Mountain in the Owl Creek Mountains; and Mineral Hill in the Black Hills. Recent gold exploration activity in Wyoming has emphasized both historic mining districts as well as newer discoveries.
Wyoming gold districts are included within the principal metal districts and mineralized areas (see Principal Metal District Map) but may represent more detailed subdivisions. These gold districts are discussed under headings of some of Wyoming’s mountain ranges, including Wind River Range, Medicine Bow Mountains and Sierra Madre, Absaroka Mountains, Laramie Mountains, Rattlesnake Hills, and the Bear Lodge Mountains (see separate tabs on this page).
The dramatic rise of gold prices beginning in 2005 led to renewed interest in Wyoming gold. Individual prospectors, recreationists, and a few major companies have recently explored historic gold districts and potential new deposits.
Precious Metal Purity
Fineness refers to the purity of precious metal contained in an alloy as parts per thousand. A purity of 99.9% precious metal is 999 fine, which may be written in decimal form as .999 fine. A precious metal containing 10 percent other metals is said to be 900 fine or to have a fineness of 900.
Purity of a gold (or platinum) alloy may also be stated in karats. One karat is 1/24 part by weight of the total mass; pure gold (999 fine to 1000 fine) is 24-karat gold. 18-karat gold is an alloy of 75% gold or 750 fine. The spelling "carats" is used outside of the United States and Canada and should not be confused with the carat weight used for gemstones. A karat designation of purity is accompanied by the abbreviation K (or ct).
Old mines are often a good place to begin prospecting. Information on most of Wyoming’s gold and precious metals deposits can be found in the following recommended publications by the Wyoming State Geological Survey:
Additional references relating to gold and other metals in Wyoming are found on the References Page.