Ore-textural and geochemical features of Bohnerz and Rasenerz concretions in Gutland (Luxembourg)

Abstract

Rasenerz and Bohnerz concretions from Gutland have been studied geochemically and by reflected light microscopy. The greater part of either type can be characterized by a single microscopic feature: more than 50% of the Rasenerz samples has an oolitic texture which is considered indicative of the Minette Formation; about 65% of the Bohnerz samples displays festoon development that is regarded as a sign of supergene origin. Festoons that occur in ooid-lacking Rasenerz (27%) suggest that Rasenerz also derives in part from destructed iron-bearing crusts. Common population statistics of individual trace element abundances fails to discriminate between the two types, but a statistical interpretation of 13 normalized concentrations enables their distinction. When clustered on textural grounds into oolitic Rasenerz, festoon-bearing Rasenerz, and festoonbearing Bohnerz categories, only the Na values of the first and the second category are significantly different. Especially on the basis of the rare earth chemistry, the festoon-bearing Rasenerz and Bohnerz concretions are thought to derive from different surface crusts.