Hydrothermal flake graphite mineralisation in Paleoproterozoic rocks of south-east Greenland

Nanna Rosing-Schow, Leon Bagas, Jochen Kolb, Tonči Balić-Žunić, Christoph Korte, Marco L. Fiorentini

Publikation: Bidrag til tidsskriftArtikelForskningpeer review

10 Citationer (Scopus)

Abstrakt

Flake graphite mineralisation is hosted in the Kuummiut Terrane of the Paleoproterozoic Nagssugtoqidian Orogen, south-east Greenland. Eclogite-facies peak-metamorphic assemblages record temperatures of 640–830 °C and pressures of 22–25 kbar, and are retrogressed in the high-pressure amphibolite-facies during ca. 1870–1820 Ma. Graphite occurs as lenses along cleavage planes in breccia and as garnet-quartz-graphite veins in various metamorphic host rocks in the Tasiilaq area at Auppaluttoq, Kangikajik, and Nuuk-Ilinnera. Graphite contents reach >30 vol% in 0.2–4 × 20 m wide semi-massive mineralisation (Auppaluttoq, Kangikajik). Supergene alteration formed 1- to 2-m-thick and up to a 2.5 × 2.5 km wide loose limonitic gravel containing graphite flakes in places. The flake size ranges from 1 to 6 mm in diameter with an average of ~3 mm. Liberation efficiency is at minimum 60%. Hydrothermal fluids at ~600 °C, transporting carbon as CO 2 and CH 4, formed the mineralisation commonly hosted by shear zones, which acted as pathways for the mineralising fluids. The hydrothermal alteration assemblage is quartz-biotite-grunerite-edenite-pargasite-K-feldspar-titanite. The δ 13C values of graphite, varying from −30 to −18‰ PDB, indicate that the carbon was derived from organic matter most likely from metasedimentary sources. Devolatilisation of marble may have contributed a minor amount of carbon by fluid mixing. Precipitation of graphite involved retrograde hydration reactions, depleting the fluid in H 2O and causing graphite saturation. Although the high-grade mineralisation is small, it represents an excellent example of hydrothermal mineralisation in an eclogite-facies terrane during retrograde exhumation.

OriginalsprogEngelsk
Sider (fra-til)769-789
Antal sider21
TidsskriftMineralium Deposita
Vol/bind52
Udgave nummer5
DOI
StatusUdgivet - 1 jun. 2017

Programområde

  • Programområde 4: Mineralske råstoffer

Fingeraftryk

Dyk ned i forskningsemnerne om 'Hydrothermal flake graphite mineralisation in Paleoproterozoic rocks of south-east Greenland'. Sammen danner de et unikt fingeraftryk.

Citationsformater