This MSc project on stratabound tungsten mineralisation in the Ivisaartoq Greenstone Belt (IGB) has been done in cooperation with the Geological Society of Denmark and Greenland (GEUS). The Mesoarchaean IGB (3075 Ma) in southern West Greenland is part of the Kapisilik Terrane situated between the Isukasia and Faeringhaven Terranes. The IGB is composed of mafic to ultramafic metavolcanics with minor gabbros, diorites, metasediments and pegmatites. It is divided into a lower and an upper amphibolite unit separated by the magnetite-rich Magnetic Marker horizon; scheelite-bearing calc-silicate rocks occur associated with the latter. Two types of calc-silicate rocks are distinguished. Type I formed by alteration of pillow basalts which preserve pre-metamorphic zoning. This type is predominantly composed of epidote, clinopyroxene, plagioclase, quartz, calcite, and scapolite. It is interpreted to have formed prior to upper amphibolite facies regional metamorphism. Type II calc-silicate rocks formed synkinematically between the two main deformation events in the IGB during regional low-P metamorphism. Type II rocks are rich in calcic garnet coexisting with clinopyroxene, epidote, quartz, calcite, titanite, and scheelite and they have higher tungsten contents. Whereas Type I rocks do not show systematic chemical changes during alteration Type II calc-silicate alteration is characterised by systematic enrichment of Ca, depletion of LIL elements and considerable variation in and mobility of HFS elements and REE. Comparison of altered rocks with their unaltered protoliths indicates that tungsten is enriched together with lithophile elements (e.g., Be, Nb) indicating a pegmatitic / granitic elemental affinity. P-T conditions of metapelites containing garnet + biotite + sillimanite + muscovite + quartz range from 550 - 650°C and 5.0 - 5.7 kbar, respectively. Tungsten mineralisation is restricted to Type II calc silicates and can be traced for several kilometres along strike; hence, it is clearly strata-bound. However, field relationships and the results of chemical investigations do not support a syngenetic-exhalative origin of tungsten mineralisation.
|Translated title of the contribution
|Schichtgebundene Wolframvererzungen im Ivisaartoq Greenstone Belt, SW Grönland
|27 Jun 2008
|Published - 2008
Bibliographical noteembargoed until null
- stratabound tungsten mineralisation Ivisaartoq Greenstone Belt Calc-silicate rocks hydrothermal alteration West Greenland