EXAMINATION OF DIAMOND STABILITY PHASE MANTLE INDICATOR MINERALS FROM LEUCITE HILLS, SWEETWATER COUNTY, WYOMING & CRATER OF DIAMONDS STATE PARK, PIKE COUNTY, ARKANSAS LAMPROITES

Lamproites are a highly unique ultrapotassic continental igneous rock. Lamproites are also one of the only primary deposits of diamonds other than kimberlites. Volumetrically the Leucite Hills located in Sweetwater County, Wyoming is the largest lamproite field yet to be discovered. Despite this aspect diamonds have yet to be discovered at this location; nonetheless it is a conducive locality for the occurrence of diamonds. The Crater of Diamonds lamproite field is a known diamond bearing location, found 2.5 miles southeast of Murfreesboro, Arkansas. It is the only diamond rich lamproite open for public collecting. These two locales differ in age and near surface volume with the Leucite Hills lamproite field being ̴ 3.0-0.89Ma and containing ̴ 30km³ of material. The Crater of Diamonds lamproite field is ̴ 106Ma and contains ̴ 0.5km³ of material. Both are in geologic settings 100-200km from the margins of Precambrian cratons. The purpose of this research is to better understand why no diamonds have been discovered in the Leucite Hills. They will be compared to the Crater of Diamonds lamproites through the examination of diamond stability phase mantle indicator minerals collected from the two locations.

In June of 2015 geology students from the University of West Georgia conducted an experiential learning fieldtrip to the Leucite Hills and collected lamproite material from ant hills at the bases of the various buttes and mesas that are capped by the igneous rock. The samples were sieved and separated to analyze any mantle indicator minerals that are present. Indicator minerals are pyrope, pyrope-almandine, chrome diopside, chrome spinel, chrome enstatite, and chromite. The sampled areas of focus from the Leucite Hills are Black Rock, North Table Mountain, and South Table Mountain. Detrital lamproite material collected by prior geology students from the University of West Georgia from the Crater of Diamonds lamproite field were also examined. Data collection including XRD analysis for accurately identifying the indicator mineral suite for the Leucite Hills and with Crater of Diamonds lamproite material. SEM-EDS point analysis will be performed to obtain semi-quantified chemical data of the indicator minerals to determine any similarities and differences in compositions to further understand North American lamproites.