Kansas Geological Survey, Open-file Report 2012-17

The Geology, Petrology, and Elemental Composition of Kimberlites from Riley and Marshall Counties, Kansas, USA

by
Robert L. Cullers¹, Pieter Berendsen², and Andrzej Barczuk²
1: Kansas State University
2: Kansas Geological Survey

KGS Open File Report 2012-17
Written in 2006

Abstract

Thirteen kimberlites in Riley and Marshall counties, Kansas, have been discovered at the surface or in the subsurface by drilling into magnetic anomalies. These kimberlites are contaminated by varied amounts of mostly crustal xenoliths (mostly shales and limestones). The Swede Creek, Randolph #1, Randolph #2, Leonardville, Bala, and parts of the Antioch kimberlites contain the fewest xenoliths and, thus, have contamination indices (CI's) close to 1 (CI or contamination index = (SiO₂+Al₂O₃+Na₂O)/ (MgO+K₂O) as weight percent).

These least contaminated kimberlites are undersaturated in SiO₂ and contain low Na₂O/ K₂O ratios, Al₂O₃, K₂O, and Rb, and high LOI and TiO₂. These results confirm that these samples are kimberlites (Type I kimberlites) rather than orangites (Type II kimberlites). These kimberlites, like other kimberlites, also contain relatively high Cr, Ba, Sr, La, Ce, and (La/Lu)cn ratios compared to many other mantle-derived rocks. Plots of data relative to primitive mantle show anonymously low K and Rb concentrations relative to adjacent elements. These results are consistent with standard interpretations that type I kimberlites could be derived by small degrees of melting of a garnet-carbonate-phlogopite-peridotite or by larger degrees of melting of a varied mix of complex, carbonate-bearing veins and lherzolite-harzburgite.

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Kansas Geological Survey
Updated Oct. 4, 2012
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