I love searching for diamonds. My first chance to explore for diamonds deposits occurred in 1977 when I was hired by Dr. Dan Miller of the WGS to appraise the newly discovered district south of Laramie. I ended up mapping the State Line district, found 9 diamond-bearing kimberlites my first 2 years & later mapped the Iron Mountain & Sheep Rock districts and the Leucite Hills lamproite field and explored for diamonds for some US companies, an Australian company and some Canadian companies. In fact, I was promoted to US Exploration Manager and later VP of DiamonEx USA for DiamondEx Ltd (see GEMHUNTER).
I found lamprophryes in Montana & Wyoming & identified several hundred cryptovolcanic structures within & surrounding the State Line that are likely diamond deposits (these remain unexplored). A few of these include Indian Guide, Twin Mountain, Happy Jack & others. I expanded my research & found similar cyptovolcanic structures in Canada & even in the Kimberley region of South Africa. I found a major district of 50+ anomalies sitting along the interstate in the US!
Photos – Above, gem diamonds from Kelsey Lake, Colorado, vegetation anomaly over kimberlite at Iron Mountain, and exposed blue ground in highwall at Kelsey Lake. Below, 14.2 ct flawless octahedron from Kelsey Lake, aerial photo over the Ekati diamond mine in Canada (one of 5 major mines developed in Canada since 1998), carbonate-stained soil over cryptovolcanic structure, and view of one of the Lost Lakes cryptovolcanic structures.
Commercial deposits occur in placers, kimberlite and/or lamproite & I’ll bet other commercial deposits will be found in lamprophryre in the future. The diamond deposits south of Laramie were in kimberlite & placers. The kimberlites are deeply eroded & spilled millions of diamonds into the surrounding streams, but no one has ever systematically looked for diamond in the creeks (even so, diamonds were accidentally recovered in Rabbit Creek and hundreds were recovered in George Creek, and several including a 6.2 carat diamond were recovered in Fish Creek, but the rest of the streams are UNPROSPECTED!
Kimberlite is a ultrabasic, potassic igneous rock that erupts along fractures from 90 to 120 mi depths. They typically occur in very old cratons & cratonized rocks (basically ancient continental cores that consist of >1.5 billion year old granite, gneiss & schist). The magma, under pressure rises rapidly from the mantle because of the great depth & because of considerable water vapor & carbon dioxide under pressure. Some suggest gaseous emplacement velocities of kimberlite are on the order of Mach 3. The eruption is relatively cool: CO2 gas expands cooling the magma such that emplacement temperatures of 32 degree F are not uncommon. This collection of unusual characteristics results in small, circular maar-like volcanoes (without cones) & dikes that are structurally controlled.
Gem diamond with excellent characteristic trigons on surface
Things to keep in mind: kimberlite will serpentinize because of water vapor, this produces a relatively soft rock that erodes faster than surrounding country rocks & usually results in a depression with different vegetation than the surrounding rocks. These depressions may contain shallow ponds. They are structurally-controlled such that >one anomaly is often found in a line. Because of calcium carbonate in kimberlite, carbonate will leach out into the pond staining the soil white. Keep in mind that salts are not all that uncommon in basins where lots of young sedimentary rocks occur with considerable carbonate. But in the craton basement (i.e., mountain ranges of Wyoming) there is no known source for carbonate, so if you spot a structurally-controlled lake surrounded by salt in old Precambrian rock, you might want to find out why? And if you find one, typically, with effort, you will find others along the same structure.
Diamonds found in Colorado & Wyoming ranged from microdiamonds to 28.3 cts & included one chip from a 80- to 90-ct stone. Some believe there are no commerical deposits in this area, but all mills were so poorly designed they rejected all diamonds of any size. For example, the Kelsey Lake mill rejected anything weighing >40 cts! It also rejected most diamonds under 40 cts such that when the tailings were tested in 1997, the first sample yielded a 6.2-ct stone! The grades of several kimberlites were high, the gem:industrial ratios were good & diamond values were reasonable. The biggest problem with the State Line district was good diamond companies with diamond expertise were in short supply.