Coupling mineralogy, textures, stable and radiogenic isotopes in identifying ore-forming processes in Irish-type carbonate-hosted Zn–Pb deposits

Yesares, L., Drummond, D. A., Hollis, S. P., Doran, A. L., Menuge, J. F., Boyce, A. J. , Blakeman, R. J. and Ashton, J. H. (2019) Coupling mineralogy, textures, stable and radiogenic isotopes in identifying ore-forming processes in Irish-type carbonate-hosted Zn–Pb deposits. Minerals, 9(6), 335. (doi: 10.3390/min9060335)

Abstract

Irish-type deposits comprise carbonate-hosted sphalerite- and galena-rich lenses concentrated near normal faults. We present new data from the Tara Deep resource and overlying mineralization, at Navan, and the Island Pod deposit and associated Main zone orebodies, at Lisheen. Tara Deep mineralization predominantly replaces Tournasian micrites and subordinate Visean sedimentary breccias. The mineralization is mainly composed of sphalerite, galena, marcasite and pyrite. A range of Cu- and Sb-bearing minerals occur as minor phases. At Tara Deep, paragenetically early sulfides exhibit negative δ34S values, with later phases displaying positive δ34S values, indicating both bacterial sulfate reduction (BSR) and hydrothermal sulfur sources, respectively. However, maximum δ34S values are heavier (25‰) than in the Main Navan orebody (17‰). These mineralogical and isotopic features suggest that Tara Deep represents near-feeder mineralization relative to the Navan Main orebody. The subeconomic mineralization hosted in the overlying Thin Bedded Unit (TBU) comprises sphalerite replacing framboidal pyrite, both exhibiting negative δ34S values (−37.4 to −8.3‰). These features indicate a BSR source of sulfur for TBU mineralization, which may represent seafloor exhalation of mineralizing fluids that formed the Tara Deep orebody. The Island Pod orebody, at Lisheen, shows a mineralogical paragenetic sequence and δ34S values broadly similar to other Lisheen orebodies. However, the lack of minor Cu, Ni, and Sb minerals suggests a setting more distal to hydrothermal metal feeder zones than the other Lisheen orebodies. Pb isotope data indicate a very homogeneous Lower Palaeozoic Pb source for all Navan orebodies. Lower Palaeozoic metal sources are also inferred for Lisheen, but with variations both within and between orebodies. Carbon and oxygen isotopic variations at Navan and Lisheen appear to result from fluid-carbonate rock buffering. The emerging spectrum of mineralogical and isotopic variations define proximal to distal characteristics of Irish-type systems and will assist in developing geochemical vectoring tools for exploration.

• Item Type: Articles
• Additional Information: This paper has emanated from research that is supported in part by a research grant from Science Foundation Ireland (SFI), under grant number 13/RC/2092 and co-funded under the European Regional Development Fund. This research was in part funded by the Geological Survey Ireland/DCCAE Postdoctoral Fellowship Programme, No. 2016-PD-00. In addition, AJB is part-funded by NERC support of the National Environmental Isotope Facility (NEIF) at SUERC. DD’s PhD is funded by Boliden Tara Mine.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian and Drummond, Drew

Creator Roles

Drummond, D. A.: Methodology, Validation, Formal analysis, Writing – review and editing
Boyce, A. J.: Validation, Writing – review and editing, Project administration, Funding acquisition

• Authors: Yesares, L., Drummond, D. A., Hollis, S. P., Doran, A. L., Menuge, J. F., Boyce, A. J., Blakeman, R. J., and Ashton, J. H.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Minerals
• Publisher: MDPI
• ISSN: 2075-163X
• ISSN (Online): 2075-163X
• Published Online: 29 May 2019
• Copyright Holders: Copyright © 2019 The Authors
• First Published: First published in Minerals 9(6): 335
• Publisher Policy: Reproduced under a Creative Commons License