Browsing by Author "Corcoran, Loretta"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    The carbonate-hosted Gortdrum Cu-Ag(?Sb-Hg) deposit, SW Ireland: C-O-Sr-Nd isotopes and whole-rock geochemical signatures
    (2023) Cordeiro, Pedro; dos Santos, Anderson Matias; Steed, Geoffrey; Silva, Andressa de Araujo; Meere, Patrick; Corcoran, Loretta; Simonetti, Antonio; Unitt, Richard
    The Gortdrum Cu-Ag(+/- Sb-Hg) deposit, consisted of a fault-controlled orebody (3.8 Mt @ 1.19 % Cu and 25.1 g/t Ag) formed at the base of the Irish Midlands basin, in Lower Carboniferous rocks laterally time equivalent to Navan Group rocks hosting the giant Navan Zn-Pb deposit, and form the base of the Irish Midlands basin. The ore body is hosted on the hanging-wall of the Gortdrum Fault either along strata or within a wedge of brecciated carbonate rocks. Vertical zonation based on predominant host rock, ore textures, sulfide assemblages, and whole -rock geochemistry allowed the detailing of three ore types: a) the lower ore, representing Cu sulfides hosted within basal carbonated siliciclastic rocks; b) the upper ore, representing Cu, Cu-Sb, and Hg sulfides hosted within upper calcareous rocks and; c) the vein-associated ore, dominantly hosted in the more competent upper carbonate rocks. The origin of the deposit is unambiguously related to the development of the Gortdrum Fault and its associated permeability, which allowed basement/basin-derived fluids to react with carbonates and induce copper-silver mineralization. The mineralogy, ore shoot geometry, and geochemical association of Gortdrum are shared with classic Zn-Pb Irish-type deposits such as Navan, Lisheen, Silvermines, and Tynagh (sub-seafloor replacement). In these Irish-type deposits, copper-silver mineralization is associated with the late stage of Zn-Pb mineralization and shares a common geochemical footprint with Gortdrum of anomalous Ag, As, Sb and Hg. Additionally, the C-O and Sr-Nd isotope range of Gortdrum and Navan samples overlap, indicating that mineralization processes in both deposits were ineffective in modifying the original host-rock signature. These similarities suggest that Gortdrum could represent a variation of Irish-type mineralization where late-stage Cu-Ag-Sb-bearing fluids succeeded in forming a deposit. Hypothetical early-stage Zn-Pb fluids a) never existed; b) deposited disseminated sulfides in country-rocks, c) formed an undiscovered resource or, d) deposited ore concentrations that were eroded off.
  • No Thumbnail Available
    Item
    The Carbonate-Hosted Tullacondra Cu-Ag Deposit, Mallow, Ireland
    (2021) Silva, Andressa A.; Cordeiro, Pedro; Johnson, Sean C.; Lagoeiro, Leonardo E.; Corcoran, Loretta; Simonetti, Antonio; Meere, Patrick A.; Unitt, Richard; Colaco, Laisa Stingelin; Santos, Anderson M.
    The Tullacondra Cu-Ag deposit is located on the southern margin of the Lower Carboniferous Irish Midlands orefield and contains historical reserves of approximately 4.2 Mt at 0.7% Cu and 27.5 ppm Ag. The deposit is hosted within the hanging wall of a feeder fault, the EW-trending Tullacondra Fault, where sulfides and sulfosalts containing elevated Cu, Ag, As, and Sb deposited, whereas Zn and Pb are nearly absent. The deposition of Cu sulfides in Tullacondra took place along bedding and bedding-parallel dissolution seams, suggesting an epigenetic mineralization that formed: (a) the Transition Series-hosted mineralized zone containing elevated Cu associated with Ag, As, and Sb; (b) the Lower Limestone Shale-hosted mineralized zone, Cu-dominated and depleted in other metals, and (c) a near-vertical mineralized zone associated with fractures related to the Tullacondra Fault. Some similarities are shared with Irish-type Zn-Pb deposits, such as structural and stratigraphic controls, and elevated Cu, Ag, As, and Sb within feeder-fault proximal zones (such as in Lisheen and Silvermines). Whether Tullacondra mineralization was part of the Irish-type system or not, our deposit geometry evaluation, whole-rock geochemistry, paragenetic sequence, and texture relationships indicate that Cu-Ag deposition involved the reaction of metal-bearing fluids with carbonate rocks.