Glacial dispersion study of kimberlitic material in Quaternary till from the Lahtojoki pipe, eastern Finland
Marja Lehtonen, Jukka S. Marmo · International Kimberlite Conference Extended Abstracts: 2003 · 2019
In 2001-2002 the Geological Survey of Finland (GTK) carried out sampling of Quaternary till around the Lahtojoki kimberlite (Pipe 7) in eastern Finland.The objective was to study the mineralogical and geochemical signatures of the kimberlite in the surrounding basal till.Pipe 7 belongs to the Kaavi cluster of the Neoproterozoic Eastern Finland Kimberlite Province situated at the edge of the Karelian Craton.It has mineralogy typical of Group I kimberlite.The 2-ha pipe is located in a swamp and covered by thick glacial overburden.The 2 x 2.5 km sampling area was situated down-ice from Pipe 7, samples being taken by an excavator and a drill rig.The concentration of indicator grains (0.25-1.0 mm) was based on a GTK modified 3"Knelson Concentrator.Chemical analysis of the till fine fraction (< 0.063 mm) was performed using XRF and ICP-MS instruments.The indicator grains form a relatively well-defined fan in the basal till that can be followed at least 2 km down-ice from the pipe.The maximum concentration of indicators is found at 1.2 km distance.Another small kimberlitic body was discovered by drilling 300 m down-ice from the pipe.The indicator population in till corresponds to that of the pipe in grain size, mineralogy and texture.All till samples turned out to be uniform in their chemical composition; no obvious correlation was found between fine fraction geochemistry and indicator content.