Wyoming prospective for diamonds, says geologist

Although much of the state is underlain by an Archean craton favorable for diamond mineralization, only about a half dozen companies are exploring Wyoming for the gem stones.

W.D. Hausel, senior economic geologist with the Wyoming Geological Survey, says about 100 kimberlites, together with one of the largest lamproite fields in the world, have been identified in a geological region that extends from Wyoming, south into Colorado and north into Montana.

Southern Wyoming is viewed as “especially attractive” for diamond exploration, says Hausel. Over the past 12 years, the Geological Survey has identified about 300 heavy mineral anomalies from more than 1,600 stream sediment samples collected in the Laramie, Medicine Bow and Seminoe Mountains of southeastern Wyoming.

The anomalous samples include pyrope garnet, chromian diopside, and/or picroilmenite. Several of the samples also contain gold. Similar “kimberlitic” heavy mineral anomalies have been identified also in the Green River Basin of southwestern Wyoming, as well as along the western flank of the Sierra Madre Range.

In addition to the mineral anomalies, more than 12,000 diamonds, ranging from microdiamonds to 14.2 carats, have been recovered from several kimberlites in the Colorado-Wyoming State Line district.

Other diamonds have been found in a modern placer, and in a Proterozoic quartz-pebble conglomerate in the Medicine Bow Mountains. Diamonds also have been recovered from a coal bed parting in the Powder River Basin of northeastern Wyoming. There are also unverified reports of diamonds from other regions in Wyoming and Colorado.

The Wyoming Geological Survey has several reports available on the state’s diamond resources and potential. For information, contact W.D. Hausel at (307) 766-2286.