MINERALOGICAL AND GEOCHEMICAL STUDY OF HEAVY INDICATOR MINERALS AT THE CRATER OF DIAMONDS STATE PARK, ARKANSAS

The Crater of Diamonds State Park in Murfreesboro, Arkansas is a lamproite. When searching for diamonds at the park, or any other place in the world, it is helpful to look for key indicator minerals. These minerals are formed in similar conditions as diamonds so they are found in close proximity to them. Due to their higher density, similar to diamonds, they are not washed away as easily as the lighter minerals and are often found in the lower portions of the field where the rain-wash has deposited. In the park there are three major indicator minerals. These are chromite spinel, chrome diopside, and pyrope garnet (Cox). The purpose of this study was to determine the chemical makeup of the minerals from the diamond mine to better understand other potential lamproite.

The project is to study the mineralogy and geochemistry of the indicator minerals in the lamproite and the texture of the lamproite. The samples of weathered lamproite are used to concentrate the heavy minerals. Samples were collected in October of 2012 and September of 2013. Large blocks and one boulder of the lamproite were also collected. The blocks were trimmed in the field so that the least weathered samples were collected. These samples were cut to 4.5 mm x 2.5mm x 2mm blocks. These blocks show the complex texture of the Crater of Diamonds lamproite. The rock appears to have a complex texture that surrounds a center spot that’s different from the rest of the rock. The rock has a fine grained matrix with fragments of sedimentary materials. We see alteration zones around larger fractures where vein filling has occurred. These unique zones were captured in samples for further observation and testing. Thin sections were produced. Additionally, the lamproite soil was washed and screened at the mine. From this concentrated wash heavy minerals were separated using a lithium metatungstate. With a density of 2.85 it separates out all the lighter minerals and only allows the denser ones to sink. These heavy minerals are where the indicator minerals are found.