Origin of sediment-hosted Pb-Zn mineralization in the Paleoproterozoic Mârmorilik and Qaarsukassak formations, Karrat Group, West Greenland

https://doi.org/10.1016/j.oregeorev.2021.104164Get rights and content

Highlights

  • 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.

Abstract

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 δ34S 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.

Introduction

The Mârmorilik Formation of the Paleoproterozoic Karrat Group, West Greenland, hosts one of the largest Precambrian Pb-Zn mines in the world, the Black Angel Mine, which produced 11.2 Mt of Pb-Zn-Ag ore from 1973 to 1990 (Fig. 1; Thomassen, 2003). After production ceased, exploration north of the Black Angel Mine resulted in the discovery of Pb-Zn mineralization in the Kangerluarsuk Fjord area, roughly 40 km north of the Black Angel Mine, by RTZ Mining (Fig. 1; Coppard et al., 1992). This Pb-Zn mineralization, known as the Discovery zone, is hosted within a thin (<50 m) sequence of quartzite, pelite, and marble of the Karrat Group (Coppard et al., 1992). Originally correlated with the Mârmorilik Formation, this stratigraphic unit was later mapped and described in detail and defined as the Qaarsukassak Formation (Guarnieri et al., 2016). These two formations were deposited directly on crystalline basement rocks and might have similar depositional timing; however, they are separated by a basement topographic high and are not observed in stratigraphic contact. The relationship between the two formations with respect to their mineralization and stratigraphy is unclear even though they are relatively proximal. Their interpretation is further complicated because the host rocks are poly-deformed and metamorphosed at least to greenschist facies, which led to various degrees of ore remobilization and destruction of some primary ore textures (Pedersen, 1980, Pedersen, 1981). Thus, there has been no clear link between the genesis of the Black Angel deposits and the Discovery zone, and a mineralization model, or models, for the sediment-hosted Pb-Zn mineralization in the Mârmorilik and Qaarsukassak formations has been enigmatic. Sedimentary exhalative (SEDEX), Mississippi Valley-type (MVT) and Kipushi-type deposit models have been suggested for the Black Angel Mine (Pedersen, 1980, Thomassen, 2003, Rosa et al., 2017, Horn et al., 2019), whereas the Qaarsukassak mineralization has not been studied.

A contributing factor in the uncertainty of origin for the sediment-hosted Pb-Zn ores of the Karrat Group has been controversy in the literature in what constitutes the two major subdivisions of these deposits, MVT and SEDEX. The characterization of these two broad subtypes is further complicated by the occurrence, and presence in the literature, of Irish-type and Broken Hill-type deposits. Studies of sediment-hosted Pb-Zn ore deposits have resulted in many attempts at classification (e.g., descriptive: either deposit morphology or host-rock type, or genetic: syngenetic versus epigenetic). No single classification scheme exists that allows for unequivocal subdivision of all sediment-host Pb-Zn deposits. In this paper we use the broad classification scheme presented by Leach et al. (2005) for SEDEX and MVT, as well as characteristics of the Kipushi Zn-Cu-Pb deposit, which are summarized in Table 1, to classify the Pb-Zn ores of the Mârmorilik and Qaarsukassak formations.

Here, we combine petrographic, stable and radiogenic isotope geochemistry, and field data to identify the mineral deposit characteristics of the Pb-Zn mineralization in the Mârmorilik and Qaarsukassak formations in order to create mineral deposit models for these mineral occurrences. Accordingly this study presents: (1) petrographic analysis of seven different Black Angel orebodies at Maarmorilik as well as the mineralization from Qaarsukassak Formation at Kangerluarsuk Fjord to determine a paragenetic sequence; (2) sulfur and Pb-Pb isotopic analyses of sulfide minerals to determine their respective sources; (3) Re-Os geochronology of pyrite associated with the ore to determine the timing of the mineralization; and (4) ore deposit models for the Pb-Zn mineralization.

Section snippets

Geology of the Karrat Group

The Karrat Group is part of the Rinkian fold belt of West Greenland, which is part of the larger Trans-Hudson orogen (St-Onge et al., 2009). The Karrat Group is a siliciclastic-carbonate-volcanic succession and has been subdivided into the lower Karrat Group, the Qeqetarssuaq Formation, and the upper Karrat Group, which includes the Mârmorilik, Qaarsukassak, Kangilleq, and Nûkavsak formations (Rosa et al., 2018). The tectonic setting of the Karrat Group is not well agreed upon, and has been

Samples

A combination of outcrop samples collected in the field in addition to archived samples were utilized to characterize the mineralization for this study. Field work took place in the summer of 2016. Outcrop samples were collected in the context of geologic mapping, which outlined the extent of the surface mineralization within the Qaarsukassak Formation (Fig. S1, S2 supplementary material). Outcrop samples were also collected in the Maarmorilik area, including the South Lakes zone (Figs. 2B, 3, 4

Petrography

Petrography was completed on a total of 13 samples from ore zones hosted in the Mârmorilik Formation around the Black Angel mine and from the Discovery zone of the Qaarsukassak Formation. Archive samples from ore zones of the Black Angel mine used in this study are from banded, massive, and porphyroclastic ore zones and show various degrees of deformation ranging from annealed pyrite grains and durchbewegung textures in the most deformed ores to undeformed, angular pyrite grains with original

Ore textures: Implications for ore-forming processes

The sulfide mineral assemblage for the Black Angel ores is dominated by pyrite, sphalerite and galena, with dolomite and calcite as the dominant gangue minerals. Angular pyrite fragments with preserved botryoidal texture, within non-porphyroclastic Black Angel ores, represent a primary pyrite phase (Py-1). Broken fragments of botryoidal pyrite indicate the precipitation of primary botryoidal pyrite and subsequent brecciation of this early pyrite. Sphalerite occurs as matrix to the botryoidal

Conclusion

Detailed mapping, petrography, and the development of paragenetic sequences of ore sulfide minerals, in combination with radiogenic and stable isotope analysis has resulted in new insights into the sediment-hosted Pb-Zn mineralization of the Karrat Group in West Greenland. The ore deposit models presented indicate the mineralization in the Mârmorilik Formation (including the Black Angel mine) and the less-well studied Qaarsukassak Formation are genetically unrelated, which is not unexpected as

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This study stems from a M.Sc. thesis completed at the University of Saskatchewan in collaboration with the Karrat Zinc Project, led by the Geological Survey of Denmark and Greenland (GEUS) and the Ministry of Mineral Resources (MMR). This research was supported by GEUS, MMR, the Natural Sciences and Engineering Research Council of Canada (NSERC Discovery Grant (RGPIN-2016-04501) to Partin), and a Mineralogical Association of Canada student research grant (to Magee).

References (92)

  • M. Sanborn-Barrie et al.

    The Laurentia-West Greenland connection at 1.9 Ga: new insights from the Rinkian fold belt

    Gondwana Res.

    (2017)
  • D. Selby et al.

    Re–Os elemental and isotopic systematics in crude oils

    Geochim. Cosmochim. Acta

    (2007)
  • J. Stacey et al.

    Approximation of terrestrial lead isotope evolution by a two-stage model

    Earth Planet. Sci. Lett.

    (1975)
  • H. Stein et al.

    Subgrain-scale decoupling of Re and 187Os and assessment of laser ablation ICP-MS spot dating in molybdenite

    Geochim. Cosmochim. Acta

    (2003)
  • H.J. Stein

    Dating and Tracing the History of Ore Formation

  • P.N. Taylor et al.

    Dating the metamorphism of Precambrian marbles: Examples from Proterozoic mobile belts in Greenland

    Chem. Geol. Isot. Geosci. Sect.

    (1990)
  • K. Thrane

    The oldest part of the Rae craton identified in western Greenland

    Precambrian Res.

    (2021)
  • F.M. Vokes

    A review of the metamorphism of sulphide deposits

    Earth-Sci. Rev.

    (1969)
  • P.B. Barton et al.

    Chalcopyrite disease in sphalerite; pathology and epidemiology

    Am. Mineral.

    (1987)
  • Barton, P.B., Skinner, B.J., 1979. Sulfide mineral stabilities, in: Geochemistry of Hydrothermal Ore Deposits. Holt,...
  • Bortnikov, N.S., Genkin, A.D., Dobrovol’skaya, M.G., Muravitskaya, G.N., Filimonova, A.A., 1991. The nature of...
  • D.E. Canfield

    Biogeochemistry of Sulfur Isotopes

    Rev. Mineral. Geochem.

    (2001)
  • D.E. Canfield et al.

    Animal evolution, bioturbation, and the sulfate concentration of the oceans

    Proc. Natl. Acad. Sci.

    (2009)
  • D.E. Canfield et al.

    Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies

    Nature

    (1996)
  • A.J. Carmichael

    The tectonics and mineralization of the Black Angel Pb–Zn deposits, central west Greenland

    (1988)
  • J.N. Connelly et al.

    Rapid determination of Pb isotopes to define Precambrian allochthonous domains: an example from West Greenland

    Geology

    (2005)
  • J. Coppard et al.

    Karrat exclusive exploration licence: 1992 year-end report

    (1992)
  • D.E. Crowe et al.

    Characterization and use of isotopically homogeneous standards for in situ laser microprobe analysis of 34S/32 S ratios

    Am. Mineral.

    (1996)
  • A. Cugerone et al.

    Behavior of critical metals in metamorphosed Pb-Zn ore deposits: example from the Pyrenean Axial Zone

    Miner. Deposita

    (2021)
  • J.A. De Roo et al.

    Sulfide remobilization and sulfide breccias in the Heath Steele and Brunswick deposits, Bathurst mining camp

    New Brunswick. Econ. Geol.

    (2003)
  • B. Dubé et al.

    The LaRonde Penna World-Class Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi, Québec: Mineralogy and Geochemistry of Alteration and Implications for Genesis and Exploration*

    Econ. Geol.

    (2007)
  • Duckworth, R.C., Rickard, D., 1993. Sulphide mylonites from the Renström VMS deposit, Northern Sweden. Mineral....
  • Eglington, B.M., Harmer, R.E., 1999. Geodate For Windows Version 1: Isotope Regression and Modelling Software. Council...
  • C.S. Eldridge et al.

    Hydrothermal inoculation and incubation of the chalcopyrite disease in sphalerite

    Econ. Geol.

    (1988)
  • M. Fakhraee et al.

    Proterozoic seawater sulfate scarcity and the evolution of ocean–atmosphere chemistry

    Nat. Geosci.

    (2019)
  • J. Farquhar et al.

    Connections between sulfur cycle evolution, sulfur isotopes, sediments, and base metal sulfide deposits

    Econ. Geol.

    (2010)
  • L. Fontbote et al.

    Genesis of the mississippi valley-type Zn-Pb deposit of San Vicente, central Peru; geologic and isotopic (Sr, O, C, S, Pb) evidence

    Econ. Geol.

    (1990)
  • Gannicott, R.A., 1980. Report on the surface diamond drilling project carried out on the Greenex utilization concession...
  • A.A. Garde

    The Lower Proterozoic Marmorilik Formation, east of Mârmorilik

    (1978)
  • A.A. Garde et al.

    A buried Palaeoproterozoic spreading ridge in the northern Nagssugtoqidian orogen, West Greenland

    Geol. Soc. Lond. Spec. Publ.

    (2010)
  • W.D. Goodfellow et al.

    Sedimentary exhalative (SEDEX) deposits. Miner. Depos. Can. Synth. Major Depos. Types Dist. Metallog. Evol. Geol. Prov. Explor. Methods Geol

    Assoc. Can. Miner. Depos. Div. Spec. Publ.

    (2007)
  • B. Govindarao et al.

    Sulfide partial melting and chalcopyrite disease: An experimental study

    Am. Mineral.

    (2018)
  • J. Grocott et al.

    Basin evolution and destruction in an Early Proterozoic continental margin: the Rinkian fold–thrust belt of central West Greenland

    J. Geol. Soc.

    (2017)
  • Grocott, J., Pulvertaft, T.C.R., 1990. The Early Proterozoic Rinkian belt of central West Greenland, in: Lewry, J.F.,...
  • P. Guarnieri et al.

    Palaeovalleys at the basal unconformity of the Palaeoproterozoic Karrat Group, West Greenland

    Geol. Surv. Den. Greenl. Bull.

    (2016)
  • Gummer, P.K., Rainbird, R.H., Plint, H.E., 1996. The Esker Lake prospect: Stratabound Pb-Zn-Cu-Ag in emergent inner...
  • 1

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