A STUDY OF HEAVY MINERALS FROM GRATER OF DIAMONDS STATE PARK, MURFREESBORO, ARKANSAS

Crater of Diamonds State Park is located in Murfreesboro, Arkansas within Pike County. It is the only diamond bearing area that can easily be accessed by the general public. The first diamonds were discovered by a local farmer in the year 1906. The Crater of the Diamond is located on a 96 million year old volcanic pipe. This pipe is a lamproite magma found within the sedimentary rocks of the West Gulf Coastal Plains. Lamproites are even less common than kimberlites. One of the first large lamproite mines is the Argyle diamond mine in Western Australia. Kimberlites and lamproites have similar shapes except that lamproites will have a broader surface area, allowing for easier access. Diamond rich pipes always cut through cratons and the Crater of the Diamonds lamproite is found on the southern end of the North American Craton (Laurentia). This project is to study the heavy minerals in the lamproite.

Samples of weathered lamproite are used to concentrate the heavy minerals. Samples were collected in October of 2012 after a heavy rain storm, in muddy conditions. They were collected and sieved in water to remove most of the clays using methods demonstrated by the park geologist. Samples worked with are a somewhat concentrated heavy fraction from the mine since many of the light clays had been removed before leaving the sample site. Once the samples were brought back to the lab they were cleaned further by hand sieving in water to remove mud. The next step was to separate the samples by size in sieves and to put them in a shaker to ensure proper sorting. The final step in cleaning the samples was in kerosene. This breaks apart the bonds in any remaining clays stuck to the samples. After giving a final wash to the samples were dried and processed through a lithium metatungstate fluid with a density of approximately 2.85. Samples are picked through by hand under a microscope for identification and observation. The heavy minerals from one size fraction represent 0.002%.