Mineral occurrences in central East Greenland (70°N-75°N) and their relation to the Caledonian orogeny- A Sr-Nd-Pb isotopic study of scheelite

The Caledonian orogen of North-East Greenland hosts numerous mineral occurrences related to (1) pre-Caledonian crystalline complexes (Pb-Zn skarn type); (2) Neoproterozoic basins (strata-bound copper); (3) Caledonian granites (vein-type gold, silver, tungsten, arsenic, and antimony); and (4) late Caledonian extensional structures (vein base metal ± silver). Sr, Pb, and Sm-Nd isotope analyses of scheelite (CaWO ₄ ) indicate a heterogeneous, probably local, source for tungsten, and Sr iso topic data support a genetic link to Caledonian magmatic activity. Pb isotopes indicate mixing of Pb derived from late waning-stage fluids from the granites and from interaction with wall rocks. Sm-Nd isotopic data for the investigated scheelites indicate that a portion of the rare earth elements was derived from fluids that had interacted with both Archean-Paleoproterozoic crystalline basement and Mesoproterozoic-Neoproterozoic sedimentary rocks. Mineral occurrences associated with fault zones and late Caledonian veins all show a genetic relationship with Caledonian granite emplacement. Sm-Nd isotopic data from scheelite define an errorchron with a slope corresponding to 382 ± 39 Ma (mean square of weighted deviates [MSWD] = 2.6) and an initial ¹⁴³ Nd/ ¹⁴⁴ Nd value of 0.511642 ± 0.000049. This indicates emplacement during the latest stages or even subsequent to emplacement of most Caledonian granites around 425 Ma. The initial Nd isotopic ratio defined by the scheelite Sm-Nd isotopic correlation line is identical within error to the values of S-type granitoids. The multi-isotope studies indicate that tungsten may have been deposited from fluids associated with Caledonian granites, which provided heat sources for local hydrothermal circulation cells. Forced into faults, thrusts, and fractures, the fluids were trapped by dominantly Ca-rich sediments.