Hydrothermal high field strength element enrichment in the Bukk Mts. (NE Hungary)

This study demonstrates the possibility of high field strength element (HFSE) enrichment in a geological setting which differs from the known models, as no contacted alkaline magmatic rock body, or other potential source is known. Metasomatised rock bodies were discovered recently in fault blocks of two major fault zones of the Bukk Mts. The existence of this rock alteration implies long-range transport of mobilized HFSE in a carbonatedominated lithological environment. Enriched elements are Zr, Nb, Ta, Th, U, Y, and rare earth elements except Eu which is depleted together with Ti and P. Host rocks are beds or layers of metavolcanics and metasediments dominated by silicate minerals, embedded in non-anomalous carbonate formations. These rocks are also enriched in potassium hosted by phengite or K-feldspars. The most abundant HFSE-carrier minerals are zircon, monazite-(Ce) and niobian Ti-oxides, but these are invisible due to their micrometric or submicrometric grain size. The metasomatic mineral assemblage overprints the texture formed during the Late Cretaceous regional metamorphism.