Establishing a geochemical baseline for the Lower Carboniferous stratigraphy of the Rathdowney Trend, Irish Zn-Pb orefield

Turner, Oakley; Hollis, Steven P.; Güven, John; McClenaghan, Seán

doi:10.1016/j.gexplo.2018.11.003

Cited by 4 publications

(8 citation statements)

References 13 publications

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“…The mineralogical and geochemical data are consistent with the interpretation that the Tullacondra mineralized zones are hosted in rocks deposited during a marine transgression [55]. Host rocks show high contents of SiO2 at the base of the sequence, consistent with siliciclastic-dominant sediments, which decrease up sequence along with an increase in the CaO abundance due to the progressive dominance of limestones and marls (Figure 9).…”

Section: Host Rocks and Post-depositional Eventssupporting

confidence: 83%

“…Our geochemical data suggest that phyllosilicates control the abundance of Al 2 O 3 in Tullacondra rocks, although feldspars occur within siliciclastic rocks, and Al 2 O 3 contents show a strong positive correlation with both K 2 O and TiO 2 (Figure 10). These significant correlations are also observed in other barren or Zn-Pb mineralized Irish Lower Carboniferous rocks [55,56]. They suggest that K-Ti-bearing phyllosilicates are common throughout the Irish Midlands and Munster basin.…”

Section: Host Rocks and Post-depositional Eventssupporting

confidence: 55%

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The Carbonate-Hosted Tullacondra Cu-Ag Deposit, Mallow, Ireland

et al. 2021

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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.

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Section: Host Rocks and Post-depositional Eventssupporting

confidence: 83%

Section: Host Rocks and Post-depositional Eventssupporting

confidence: 55%

The Carbonate-Hosted Tullacondra Cu-Ag Deposit, Mallow, Ireland

et al. 2021

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“…The stratigraphy above the Waulsortian Formation is shown in Figure 5 (based on Doyle, 2022). Recently, a baseline geochemical was established for stratigraphy of the Rathdowney Trend, which derived a heuristic methodology for chemical classification of units, which is of particular use in units in these upper parts of the stratigraphy (Turner et al, 2019). The Lower Visean Crosspatrick Formation has variable thicknesses from 150 to 220m.…”

Section: Supra Waulsortian Stratigraphymentioning

confidence: 99%

“…The ore exhibits a wide range of textures including complete and partial replacement of black matrix breccia, delicate replacement of host rock lithologies, multiphase sulphide breccias, and cavity-filling with both colloform and laminated, precipitated sulphides. Descriptions below are based on observations underground and in core, as well as building on detailed petrography by various authors (Shearley et al, 1996;Redmond, 1997;Hitzman et al, 1998Hitzman et al, , 2002Eyre, 1998;Everett et al, 1999;Fusciardi et al, 2003;Wilkinson et al, 2003;Wilkinson et al, 2005;Barrie et al, 2007;Boni et al, 2007;Wilkinson et al, 2011;Riegler & McClenaghan, 2017;Röhner, 2017;Turner, 2019;Yesares et al, 2019 andDoran et al, 2022)…”

Section: Sulphide Mineralizationmentioning

confidence: 99%

“…Pyrite and to a lesser extent marcasite comprise the vast majority of iron sulphides and represent the earliest sulphides to follow initial black matrix breccia development (e.g., Hitzman et al, 2002;Wilkinson et al, 2005;Turner, 2019;Doran et al, 2022). Rare pyrrhotite is also present but only proximal to feeder zones where sulphide content was likely higher and is considered to be paragenetically late.…”

Section: Iron Sulphidesmentioning

confidence: 99%

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The Rathdowney Trend, Ireland: Geological evolution and controls on Zn-Pb mineralization

Guven,

Torremans,

Johnson

et al. 2023

Irish-Type Zn-Pb Deposits Around the World

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The Rathdowney Trend in south-central Ireland, is a NE-SW trend of fault-controlled Zn-Pb deposits that includes the Galmoy and Lisheen orebodies. The deposits are broadly stratabound and flat-lying occurring at or near the base of the Waulsortian Limestone Formation - a 200m thick massive biomicrite that is regionally dolomitised. The ore is largely developed by replacement of a dark, hydrothermal dolomite and dolomitic breccia - the black matrix breccia that is intimately associated with the mineralization event. Faulting exerts a major control on the ore thickness and distribution. The largest structures provided conduits for hot, metal-bearing fluids from basement to enter the Waulsortian at discrete feeder zones. Metal distribution patterns indicate that fluids progressed northwards from these feeder zones, facilitated by a network of small-displacement, low-angle extensional structures developed at the base Waulsortian contact with the underlying Ballysteen Formation. Significant dissolution of carbonate by hydrothermal fluids was important in developing conduits and promoting fluid flow. Fluid inclusion and isotope studies indicate that mineralization resulted from the mixing of hot, metal-bearing fluids with colder, saline fluids bearing sulphur derived from the bacteriogenic reduction of Carboniferous seawater sulphate. Mineralization developed during growth of the fault systems associated with basin development. Hydrothermal activity initiated shortly after rifting commenced during mid to late-Waulsortian sedimentation.

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Irish-type Zn-Pb deposits - What are they and can we find more?

Ashton,

Andrew,

Hitzman

2023

Irish-Type Zn-Pb Deposits Around the World

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Seven carbonate hosted Zn-Pb (+/-Ag, Ba) or Cu deposits have been mined in Lower Carboniferous limestones in Ireland since 1960 - representing a resource base of ca. 22 Mt of metal (Tynagh, Gortdrum, Magcobar, Silvermines, Navan, Galmoy and Lisheen). The orebodies are amenable to modern mining and metallurgical processes and exploration for further deposits continues. Several significant prospects remain unexploited with numerous smaller prospects and mineralized localities attesting to the metal endowment of the country (Pallas Green, Stonepark, Ballinalack, Kilbricken and Keel). These deposits share sufficient characteristics to be termed Irish-type Base Metal Deposits and define a metallogenic province of worldwide significance known as the Central Irish Ore-field. Early discoveries resulted from shallow soil geochemistry, Induced Polarization surveys, and follow-up of legacy mining or mineralized outcrops. More expensive, deeper penetration methods including deep drilling, airborne geophysics and seismic methods have been utilized extensively in more recent years - but thus far with variable success. Large amounts of ground remain unexplored at depth, but further discovery is extremely challenging. Following over 60 years of discovery and mining this contribution summarizes our knowledge of Irish-type deposits and their exploration with a view to generating new ideas for future discovery. The Tynagh, Silvermines, Lisheen and Galmoy deposits, all hosted in the Waulsortian Limestone, occur in a distinct area in the SW of the Orefield. Silvermines, Lisheen and Galmoy are remarkably similar, comprising several, tabular, stratabound, lenses containing locally massive and high-grade sphalerite-galena with substantial pyrite +/- barite. These deposits are hosted in the first clean limestone above basement in Lower Carboniferous limestones and dolomites and exhibit fine grained, replacive sulphides with significant breccia and crosscutting mineralization. Structurally all these deposits abut major syn-sedimentary faults usually trending NE or ENE. The Navan deposit occurs on the NE side of the Orefield and is hosted in stratigraphically lower, Pale Bed limestones, that are roughly age equivalent to the Waulsortian Limestone in the SW of the Orefield. Navan is much larger and more complex than the deposits in the SW Orefield but shares several of their key characteristics. A review of the characteristics of Irish-type deposits and exploration results suggests some important areas for future exploration and research. For example, most observers relate the location of Irish-type deposits to the regional distribution of host rocks and structures of a certain age. It is suggested that the spatial location of these deposits is more fundamentally controlled by deep structural heterogeneities related to the collisional zone between basement rock terranes termed the Iapetus Suture. Understanding the timing of fault development is likely key to further discovery at depth as the mineralizing feeder structures are located on faults that did not necessarily extend through post-Waulsortian aged strata. Several promising fields for research and development to help enable further discovery are discussed.

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Establishing a geochemical baseline for the Lower Carboniferous stratigraphy of the Rathdowney Trend, Irish Zn-Pb orefield

Cited by 4 publications

References 13 publications

The Carbonate-Hosted Tullacondra Cu-Ag Deposit, Mallow, Ireland

The Carbonate-Hosted Tullacondra Cu-Ag Deposit, Mallow, Ireland

The Rathdowney Trend, Ireland: Geological evolution and controls on Zn-Pb mineralization

Irish-type Zn-Pb deposits - What are they and can we find more?

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