Now showing 1 - 3 of 3
  • Publication
    Regional variations of Tournaisian and Viséan lithostratigraphy and their links to basin and structural evolution in Ireland
    (University College Dublin. School of Earth Sciences, 2023)
    This work details the lithological and unit thickness variability across a large portion of the Tournaisian and Viséan of Ireland, using 476 stratigraphically representative boreholes. A particular focus was put on how lithological changes link with their depositional environment and with the evolving rift structural framework. The deposition of carbonates during the Tournaisian in Ireland is characterised by a south to north diachroneity, reflecting a northward transgression, initially on a generally south-dipping overall ramp geometry. The transgression was accompanied by a northward stepping of facies belts in several sub- Waulsortian units across the study area. Compiled micropalaeontological information suggests that early extensional faulting initiated in the early Ivorian, represented by clear syn-sedimentary thickening of the Moathill Fm across faults in the Central Midlands province. Conversely, such relationships are not shown for the underlying units such as the Meath Fm. The character of the Waulsortian Limestone Fm changes dramatically in terms of facies and thickness across the study area. In south-eastern areas, the Waulsortian forms laterally continuous “sheet-reef” growth forms which substantially thicken towards the central Iapetus suture zone. However, towards the north its development becomes less consistent and is evidently more often localized to the immediate proximity of faults and in most northerly areas, the Waulsortian is commonly absent. Some of the reasons for this dramatic change in character are discussed. The Waulsortian Limestone Fm records the transition from a general ramp geometry to an increasingly fault-controlled basin architecture. The Lower Viséan to Arundian is marked by a major change in facies deposition. Continued syn-rift extension localized on fewer but faster moving faults, temporally associated with a complex facies mosaic comprising areas of interfingering coeval deep basinal and shallower water shelf deposition. This was interpreted to coincide with eustatic sea level changes which strongly influenced the sedimentary environment. Using newly compiled biostratigraphical data, and lithological correlations, regional shallowing and (sudden) deepening trends can be recognized which correlate with well documented examples in laterally equivalent basins in Belgium, Wales and Germany.
      33
  • 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.
      511Scopus© Citations 20
  • 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.
      688Scopus© Citations 27