TY - JOUR
T1 - Hydrothermal flake graphite mineralisation in Paleoproterozoic rocks of south-east Greenland
AU - Rosing-Schow, Nanna
AU - Bagas, Leon
AU - Kolb, Jochen
AU - Balic Zunic, Tonci
AU - Korte, Cristoph
AU - Fiorentini, Marco
PY - 2017/6/1
Y1 - 2017/6/1
N2 - 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-quartzgraphite 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 × 20mwide semimassive 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 to6mm in diameter with an average of ~3 mm. Liberation efficiency is at minimum 60%. Hydrothermal fluids at ~600 °C, transporting carbon as CO2 and CH4, formed the mineralisation commonly hosted by shear zones, which acted as pathways for the mineralising fluids. The hydrothermal alteration assemblage is quartz-biotite-gruneriteedenite-pargasite-K-feldspar-titanite. The δ13C 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 H2O 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.
AB - 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-quartzgraphite 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 × 20mwide semimassive 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 to6mm in diameter with an average of ~3 mm. Liberation efficiency is at minimum 60%. Hydrothermal fluids at ~600 °C, transporting carbon as CO2 and CH4, formed the mineralisation commonly hosted by shear zones, which acted as pathways for the mineralising fluids. The hydrothermal alteration assemblage is quartz-biotite-gruneriteedenite-pargasite-K-feldspar-titanite. The δ13C 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 H2O 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.
U2 - 10.1007/s00126-016-0701-9
DO - 10.1007/s00126-016-0701-9
M3 - Journal article
SN - 0026-4598
VL - 52
SP - 769
EP - 789
JO - Mineralium Deposita
JF - Mineralium Deposita
IS - 5
ER -