The physical-chemical regime of a sulfide-bearing semi-graphite mineral assemblage in metabasic rocks (SE Germany)

A multidisciplinary study of the missing link between impsonite and graphite

authored by

Harald G. Dill, J. Kus, S. Goldmann, I. Suárez-Ruiz, T. Neumann, S. Kaufhold

Abstract

Along the western edge of the Bohemian Massif, SE Germany, graphitic carbon occurs in metabasic rocks plus calcsilicates, metabiolites, and paragneisses (graphite I), in pegmatites (graphite II) and in mineralized structure zones (semigraphite and impsonite) The current studies unveiled these graphitic carbon compounds are strikingly different with regard to their age and temperature of formation: Graphite I (≥324 Ma, 570 to 625 °C), graphite II (317 ± 3 Ma, >400 °C), semi-graphite (305 ± Ma, 225 to 400 °C), impsonite (<298 ± 4 Ma, 100 to 363 °C). Semi-graphite takes a special position among these graphitic carbon compounds because it links the different carbon modifications with regard to its age of formation, its structural position and its S- and C isotopes that point to a mantle and crustal influence on its formation in contrast to graphite (graphite I: crustal, graphite II: mantle) and impsonite (mantle). Semi-graphite precipitated in a fault zone which evolved from a zone of strong felsic mobilization in metabasic rocks spawning K–Na feldspar-quartz pegmatoids/aploids. During conversion of a pre-existing zone of felsic mobilization into a brittle shearzone not only carbonaceous matter but also Ni-, Pb-, Cu-, Zn-, As-, Fe-, Hg- and Mo sulfides were concentrated. The semi-graphite-bearing mineralized zone is located near rare element pegmatites hosting graphite flakes. The C-bearing systems are useful pathfinders to locate structurebound mineral deposits hosting U or base metals in the Variscan orogen. The structurebound metalliferous semi-graphite mineralization in metabasic rocks can be taken as a reference type of dual-source hydrocarbon immigration into fault zones, syn- to postkinematically relative to the fault movement. The model can be applied to host rocks undergoing retrograde medium- to very-low-grade stage dynamo-metamorphic conditions. To elucidate the complex history of the various types of graphite and metamorphosed bitumen a multidisciplinary approach has been taken involving petrographic and geological field mapping combined with drill core examination, petrographic and ore microscopy supplemented by electron microprobe, X-ray diffraction and scanning electron microscopy with EDX, micro-Raman spectroscopy in addition to classical coal petrographic studies, and inorganic geochemistry of major and minor elements and isotope (carbon and sulfur) chemical analysis followed up by a statistical treatment of the various chemical datasets.

Organisation(s)

Institute of Mineralogy

External Organisation(s)

Federal Institute for Geosciences and Natural Resources (BGR)
Spanish National Research Council (CSIC)
Technische Universität Berlin

Type

Article

Journal

International Journal of Coal Geology

Volume

214

ISSN

0166-5162

Publication date

01.10.2019

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Fuel Technology, Geology, Economic Geology, Stratigraphy

Sustainable Development Goals

SDG 10 - Reduced Inequalities

Electronic version(s)

https://doi.org/10.1016/j.coal.2019.103262 (Access: Closed)