Dispersion patterns of kimberlite indicator minerals, West Greenland

Twenty seven 50 kg stream sediment samples and two 300 kg stream sediment samples were collected from two streams in the Sarfartoq area, West Greenland. The numerous kimberlite dykes known to outcrop along the two streams carry kimberlite indicator minerals such as pyrope, chromediopside, picroilmenite and chromespinel. Diamonds were not found, but kimberlite indicator minerals such as pyrope, picroilmenite, chromediopside and chromespinel were found in the fine fraction of the stream sediments. The dispersion pattern of the indicator minerals in the streams show that kimberlites can be traced by stream sediment sampling, and that even a few indicator minerals indicate kimberlites upstream.

Two bulk samples of kimberlite dykes were investigated. One 610 kg sample from Sarfartôq and one 195.8 kg sample from Maniitsoq. No diamonds were found in any of the samples. The Sarfartoq dyke proved to be highly micaceous and very low in indicator minerals which were all fine grained. One pyrope from the Sarfartôq sample was of class 3 according to Dawson & Stephens (1975) classification. The Maniitsoq dyke was a low micaceous kimberlite with an abundance of indicator minerals in grains up to 1 cm. Most pyropes from this dyke were of classes 9, 11 and 12 according to Dawson & Stephens (1975) classification.

Pressure-temperature estimates on pyrope-clinopyroxene equilibrium, general mineralogy and chemical composition indicate that the Maniitsoq kimberlite holds a better potential of being diamondiferous than the Sarfartôq kimberlite.