Now showing 1 - 8 of 8
  • Publication
    Preliminary paragenetic studies of the high grade Island Pod Zn-Pb orebody, Lisheen
    (The Institute of Geologists of Ireland, 2017-03-05) ; ; ;
    Irish-type deposits are a series of Zn-Pb orebodies which formed from the carbonate replacement of Lower Carboniferous limestone, triggered primarily by fluid mixing. This project aims to use isotopic (Zn-Cu-S and clumped O-C) techniques to identify geochemical halos and increase our understanding of hydrothermal fluid processes in these deposits.
  • Publication
    Constraining fluid mixing processes at the Irish-type Lisheen and Navan Zn-Pb orebodies: preliminary evidence from clumped C-O isotopes
    Our research has applied the clumped O-C isotope technique to the Irish Zn-Pb ore field. Preliminary clumped C-O data will be presented from the Lisheen Zn-Pb orebody (22.3 Mt mined at 11.7% Zn and 2.0% Pb) [4] along with fluid inclusion data . Samples were analysed from all main carbonate generations across the deposit , including: regional dolomite (D 1), dark grey to black pre-ore hydrother mal dolomite (D 2 ; also known as black-matrix breccia), medium-to-coarse-grained ore-stage white ferroan dolomite (D 3 ; white-matrix breccia) , late veins of ferroan dolomite (D4) and white calcite (C4), post-ore crosscutting pink saddle dolomite (D 5), and post-ore white blocky calcite (C 6). We will discuss existing metallogenetic models for the Lisheen deposit and the potential for clumped C-O analysis to constrain fluid flow pathways and mixing processes, and as a tool for mineral exploration .
  • Publication
    Clumped C-O isotope temperature constraints for carbonate precipitation associated with Irish-type Zn-Pb orebodies
    Ireland hosts the greatest concentration of discovered zinc per square kilometre on Earth, with production from 5 carbonate-hosted deposits, including the giant Navan deposit. Clumped C-O isotope analyses of carbonates offer a powerful new technique to directly deliver accurate fluid temperatures and precise calculations of fluid O isotope compositions, offering a significant opportunity to refine the evolving genetic models, and develop new vectoring tools for exploration. We present the first clumped C-O isotope results for parageneticallyconstrained carbonate generations from a number of Irishtype Zn-Pb deposits. Preliminary analysis of hanging-wall white matrix breccias from Lisheen show non-systematic temperature variation (~100 to 170°C), with fluid d18OV-SMOW increasing with temperature. Significant variations in temperature at the thin section scale may be indicative of fluid mixing and/or multiple phases of WMB dolomite brecciation. Post-ore pink dolomite at Lisheen, and crosscutting calcite veins formed at significantly lower temperatures (67 to 42°C). Temperatures of 61 to 110°C were obtained for sphalerite-bearing calcite veins in the hanging-wall of the Randalstown Fault near Navan. These veins contain coarse sphalerite interpreted to have been remobilised from the nearby Navan orebody by a single, cool fluid (Marks, 2015). Clumped C-O data will also be presented for samples from Galmoy, Kilbricken and Castlegard ("Pallas Green"), from which existing fluid inclusion constraints are available.
  • Publication
    Enhancing current understanding of Irish Zn-Pb mineralization: a closer look at the Island Pod orebody, Lisheen deposit
    (Society for Geology Applied to Mineral Deposits, 2017-08-23) ; ; ; ;
    Irish-type deposits are a series of Zn-Pb orebodies, formed from the carbonate replacement of Lower Carboniferous limestone, triggered primarily by fluid mixing. Current understanding of the complex fluid flow and mixing dynamics associated with mineralization is limited. By applying clumped O-C isotope analysis to these deposits, these processes can be constrained. Preliminary paragenetic studies of the Island Pod orebody (0.4 Mt @ 20% Zn & 1.6% Pb) have yielded textural evidence for early fluid mixing of sulphide-rich fluids, in a quiescent, far-from equilibrium environment, resulting in the rapid precipitation of dendritic galena and intergrowths of dolomite and sphalerite. Initial clumped O-C analysis has revealed temperatures of 100-170°C for hanging-wall white matrix breccias that accompanied ore formation. This technique will be used to constrain temperature variations across the orebody, thus yielding information on how the fluid evolved as precipitation continued. A more detailed paragenetic study is underway and will form the foundation of future clumped O-C isotope and Zn-Cu-S isotope analysis.
  • Publication
    Clumped C-O isotope temperature constraints for carbonate precipitation associated with the Irish-type Lisheen and Navan Zn-Pb orebodies
    Mineral C-O isotope values are controlled by crystallization temperature and the isotopic composition of the fluid.
  • Publication
    A comparison between clumped C-O and fluid inclusion temperatures for carbonates associated with Irish-type Zn-Pb orebodies
    (Institut de Physique du Globe de Paris, 2017-08-12) ; ; ; ;
    Ireland hosts the greatest concentration of discovered zinc per square kilometre on Earth, with past and current production from five Irish-type carbonate-hosted deposits, including the giant Navan deposit. Clumped C-O isotope analysis of carbonate phases offers a powerful new technique to deliver accurate fluid temperatures and fluid O isotope compositions, refining evolving genetic models and developing new tools for exploration.
  • Publication
    3-D Modeling of the Lisheen and Silvermines Deposits, County Tipperary, Ireland: Insights into Structural Controls on the Formation of Irish Zn-Pb Deposits
    (Society of Economic Geologists, 2019-02-01) ; ; ; ;
    Faults are important structures in the formation of many mineral deposits, often acting as conduits for ore-forming fluids and sometimes providing, or generating, the bounding structures to associated mineralizing sites. Using 3-D analysis and modeling of the Lisheen and Silvermines deposits within the Irish ore field, we investigate the geometry of normal fault systems and their implications on the origin and nature of associated deposits. These Irish-type deposits are carbonate hosted and developed within the hanging walls of normal faults arising from an Early Carboniferous episode of north-south rifting, with relatively limited amounts of later deformation. Structural analysis of high-quality mine datasets indicates that fault segmentation is ubiquitous with left-stepping segments arising from north-south stretching developed above generally ENE-NE-trending fault arrays, which are subparallel to older Caledonian penetrative fabrics and structure within underlying Silurian and Ordovician rocks. Fault segments occur on different scales and have a profound impact on structural evolution, with larger scale segments and intervening relay ramps defining distinct orebodies within deposits and smaller scale segments and relays potentially providing paths for upfault fluid flow. The difference in behavior is attributed to the integrity of associated relay ramps where intact ramps represent orebody-bounding structures, and smaller breached ramps provide enhanced associated hydraulic properties and act as vertical conduits. Hanging-wall deformation along the rheological boundary between host-rock limestones and underlying shales has an important control on the localization of earlier dolomitization and/or brecciation and later mineralization adjacent to this contact, and on the migration pathways for basinal brines and mineralizing fluids.
      463Scopus© Citations 15
  • Publication
    Controls on Metal Distributions at the Lisheen and Silvermines Deposits: Insights into Fluid Flow Pathways in Irish-Type Zn-Pb Deposits
    The world-class Irish Zn-Pb(-Ag) deposits occur within one of the world’s major metallogenic provinces. While it has been well documented that these orebodies are structurally controlled, exactly how fluids migrated from source to trap is still poorly understood. Using 3-D modeling techniques, the current study investigates metal distribution patterns at the Silvermines and Lisheen deposits to gain insights into fluid pathways and structural controls on mineralization. Distinct points along segmented normal faults are identified as the feeders to individual orebodies, allowing hot, hydrothermal, metal-bearing fluids to enter host rocks and form orebodies. These points are characterized by highly localized and elevated Ag, Cu, Co, Ni, and As concentrations as well as low Zn/Pb ratios, which increase away from the feeders. Metal distributions are initially controlled by major and minor normal faults and subsequently affected by later oblique-slip dextral and strike-slip faults. High-tonnage areas without typical feeder signals are interpreted to be structural trap sites, which are distal to fault-controlled feeder points. This study highlights both the importance of a well-connected plumbing system for metal-bearing fluids to reach their basinal traps and the control that an evolving structural framework has on spatial distribution of metals.
      368Scopus© Citations 12