Origin of Iron Ore Nuggets (“Bohnerze”) through Weathering of Basalt as Documented by Pebbles from the Herbstlabyrinth, Breitscheid-Germany

Povzetek

Namen te študije je bila raziskava izvora kep železa, ki so bile najdene v Herbstlabyrinthu pri Breitscheidu, severni Hessen/Nemčija. Vsega skupaj je bilo zbranih deset prodnikov. Petrografsko prodnike lahko razdelimo v tri skupine: precej svež bazalt, opazno ali popolnoma preperel bazalt (vsebuje železova zrna) in temen peščenjak. Železova zrna izvirajo iz procesa preperevanja (oksidacija in hidratacija) bazaltnih prodnikov. Geokemična študija je pokazala, da so izvorni prodniki bazalta alkalnega tipa in da pripadajo Na-seriji. Magma, iz katere so nastali, je bila nerazvita in je izvirala iz peridotitnega plašča.

This study was conducted to investigate the origin of the iron nuggets that have been found in the Herbstlabyrinth at Breitscheid, northern Hessen/Germany. A total of ten pebbles were collected. Petrographically, the pebbles can be divided into three groups: rather fresh basalts, markedly or totally altered basalt (including the iron nuggets) and a dark sandstone. The iron nuggets originate through a progressing alteration (oxidation and hydration) of the basaltic pebbles. The geochemical study shows that the original fresh basaltic pebbles are of alkali type and belong to the Na-series. The magma that gave rise to them was primitive and originated in peridotite mantle source.