Lead isotope studies on mineral showings and ore deposits in East Greenland

Abstract

Lead isotope studies indicate an age of 680 ± 65 Ma for syn-diagenetic stratiform copper mineralisation in the Upper Proterozoic Eleonore Bay Supergroup (EBS) sediments. Metals in EBS-hosted veins were remobilised from local host rocks, or derived from underlying Middle Proterozoic gneisses. Tungsten-arsenic skarns associated with Caledonian granites intruded into the EBS incorporated lead mobilised from the basement gneisses mixed with Caledonian granite lead. Isotopic compositions of trace lead in sparse sulphide occurrences in North-East Greenland point to Late Archaean – Early Proterozoic sources, comparable to the local basement gneisses. Base metal mineralisation in Upper Palaeozoic – Mesozoic rocks in central East Greenland shows a limited range. in lead isotope compositions, suggesting that a large, homogeneous crustal reservoir supplied the metals, or that metals from different sources were effectively mixed. Mineralisation in Tertiary igneous rocks in the Kangerdlugssuaq area of southern East Greenland shows lead isotope evidence for contamination by material from lower crustal Archaean sources.