Diamonds have moderate specific gravity (3.5) and tend to concentrate with black sands in creek and riverbeds. A prospector should be able to pan for diamonds as one would pan for gold, and Wyoming and Colorado provide excellent hunting grounds for placer diamonds. When found in streams, diamonds may have been liberated from nearby kimberlite, lamproite, or related lamprophyric pipe or dike, or may have come from diamond pipes hundreds of miles away. Because of the extreme hardness of diamond, some diamonds are thought to be able to resist stream abrasion over great distances. With the nations only commercially active Diamond mine just a short distance from the Poudre River, this might be a great place to start your adventure. Using only a gold pan, a prospector recently panned a diamond from the Poudre River (Vic Norris, personal communication, 2002). When planning your Poudre Canyon Adventure you might want to begin by booking your cabin at Archer’s Poudre River Resortto be used as base camp while you pan the local rivers for Placer Diamonds.
In order to search for placer (stream-deposited) diamonds, a prospector needs to become familiar with natural diamond. Diamonds are isometric and have high symmetry. In their simplest form, they occur as a cube (Figure 1). One of the more common habits for diamond is an octahedron (8-sided diamond formed by two-pyramids attached at a common base). Many diamonds have crystal habits that are a modified octahedron and may include such varieties known to a mineralogist as hexoctohedral, rhombic dodecahedron, trisoctahedron, and others.
When identifying a raw diamond, it is important to look at the luster as well as the individual crystal faces under a microscope. Crystal faces are frequently rounded and may have distinct tiny triangles known as trigons. These are triangular depressions (or growth platelets) found on the octahedral crystal faces (Figure 1b). Cubic diamonds may show similar depressions with pyramidal morphology that appear as rotated squares or parallelograms. Twin diamond crystals often occur as a flatten triangular shaped diamond known as a macle.
The Kelsey Lake Mine is North America’s only commercially active Diamond Mine.
The Kelsey Lake mine, located almost on the Colorado-Wyoming line, just 25 miles south of Laramie, Wyoming. This makes it a short distance from Archer’s Poudre River Resort. The mine includes eight kimberlite pipes, the two largest have a combined area of about 20 acres. The mine was first opened by Redaurum, a Canadian company. It has changed ownership several times.
The Kelsey Lake mine was operated from 1996 to 1998 and produced North America's largest-known cut diamond--a pale yellow 16.86-carat faceted stone that was cut from a well-formed 28.18-carat crystal found in 1997. The largest diamond ever found in Colorado was a 28.3-carat gem found in 1996, pictured here. The diamond was unearthed 43 miles northwest of Fort Collins at the Kelsey Lake Mine. This diamond was also the fifth largest found in the United States. It was sized down into a 5.9-carat gem that sold for $87,000.
Mining has been inactive since 1998, but it is anticipated to be bought out of bankruptcy in 2000 by a Detroit Businessman, with improvements having been made to the plant's crushing and recovery circuits. Other large diamonds found at Kelsey Lake include a 14.2-carat colorless octahedron and stones of 16.29, 11.85, 10.48, and 9.40 carats.
In recent years a limited number of faceted diamonds as well as uncut crystal specimens from both the Sloan and Kelsey Lake mines have appeared on the market from mineral dealers and jewelers, sizes range up to about 1 carat. The Sloan kimberlites are a group of two large and four small pipes and dikes, located about 25 miles northwest of Fort Collins, near Prairie Divide. The two largest, the Sloan Nos. 1 and 2 pipes, have a combined area of about 18 acres. Discovered in 1964, they were first seriously prospected for diamonds in the early 1980s.