Geology and Ore 39, 2025

Tungsten and tin occurrences in East Greenland

The East Greenland Caledonides host an array of tungsten (W) and tin (Sn) mineral occurrences, representing three different deposit types: skarn, greisen, and quartz-scheelite veins. Tungsten is found in scheelite and tin in cassiterite. The observed deposit types correspond to distinct geological processes driven by magmatic and metamorphic fluids during the Greenlandic Caledonides orogenic evolution. U-Pb dating, carried out at GEUS, of scheelite and cassiterite has led to the identification of three significant mineralisation pulses at ~425 Ma, ~400 Ma, and ~370 Ma. These correspond to the emplacement of S-type granites during thrusting, emplacement of A-type granites during the onset of syn-orogenic extension, and migration of metamorphic fluids released during late-orogenic extension, respectively. The first two pulses, related to magmatic fluids, formed skarn and greisen occurrences, and the latest event triggered the formation of quartz-scheelite veins. Trace element geochemistry on scheelite and cassiterite allows for the differentiation of the three studied deposit types. The geochemical fingerprinting provides a novel tool for identifying and differentiating cassiterite and scheelite deposit types, optimising early-stage exploration strategies in less-accessible terrain. Detailed analysis of mineral assemblages, geochemistry, U-Pb dating and structural controls have enhanced the understanding of the East Greenland mineral occurrences.

Introduction

Exploration efforts by Nordisk Mineselskab (Nordmin) during field campaigns in the 1960s to 1980s targeted scheelite occurrences, guided by stream sediment sampling. These field campaigns identified scheelite-rich skarns typically in Krummedal metasedimentary rocks, Sn-W-bearing greisen mainly formed in the lower part of the Eleonore Bay Supergroup (EBS), and structurally controlled quartz-scheelite veins often seen in the upper EBS, but also in other rock types. Nordmin’s initial focus revolved around high-grade W occurrences in skarns, greisen, pegmatites, and especially in quartz-scheelite veins. In Margeries Dal, a resource was delineated, with 82 000 tons with a diluted concentration of 2.3 wt% W, with concentrations up to 24 wt% in drill cores half metre intervals. Subsequent work by GEUS highlighted the potential of cassiterite-bearing systems and their association with greisenised granite. From the 1990s-2000s further limited exploration for W or Sn in the East Greenland Caledonides was mainly performed by NunaOil-NunaMinerals A/S, as well as more recently by SRK Exploration and Greenfield Exploration Ltd. Within the scope of the European Union co-financed EIT-Raw Materials project MinExTarget and the Tin&Tungsten project financed by the Greenlandic Government and GEUS, samples of these occurrences have been studied in detail and the results of these investigations are summarised herein.

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