Abstract
• We compare Pb-Zn mineralization at Black Angel and Qaarsukassak, West Greenland. • S-isotopes and Pb-isotopes address S and Pb sources to mineralizing systems. • A Re-Os isotopes demonstrate Paleoproterozoic-aged sulfide mineralization. • Black Angel, Qaarsukassak represent MVT and SEDEX mineralization, respectively. Sediment-hosted Pb-Zn mineralization occurs in the Mârmorilik and Qaarsukassak formations of the Paleoproterozoic Karrat Group in arctic West Greenland. The timing and model of mineralization of the historical Pb-Zn Black Angel Mine in the Mârmorilik Formation and how it might be related to Pb-Zn mineralization in the nearby Qaarsukassak Formation is enigmatic. This study aims to understand the origin of the Pb-Zn mineralization in both formations by petrographic analysis, pyrite- and ore-sulfide sulfur isotope analysis, Pb-Pb isotope analysis, and Re-Os isotope analysis of pyrite associated with the mineralization. Sulfur isotope results from secondary ion mass spectrometry show a range of δ 34 S values between 0‰ and +6.9‰ on sulfide minerals (pyrite, sphalerite, galena, pyrrhotite); isotopic fractionations and geothermometry suggest contributions from both bacterial sulfate reduction and abiotic thermochemical sulfate reduction processes. Isotopic analysis (Pb-Pb) of galena from ore zones hosted by the Mârmorilik Formation shows a relatively homogenous Pb isotope signature that is consistent with local basement as a likely source for the metals. Results from Re-Os analysis of pyrite indicate that the Mârmorilik and Qaarsukassak mineralizing events are Paleoproterozoic. Ore textures and mineralogy, as well as S and Pb isotope data, associated with the carbonate-hosted Mârmorilik Formation are most consistent with a Mississippi Valley-type (MVT) deposit model, whereas characteristics of the dominantly siliciclastic-hosted Qaarsukassak mineralization textures are most consistent with a sedimentary exhalative (SEDEX) mineralization model. The Mârmorilik (Black Angel) mineralization represents the oldest documented MVT deposit outside of the Neoarchean–Paleoproterozoic Transvaal basin in South Africa.
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