Title: Hydrothermal fluid flow in Irish Zn-Pb deposits: a Zn-Cu-S isotope and clumped isotope approach
Researchers: Aileen Doran, Dr Julian Menuge
Project Background and Rationale
Irish-type Zn-Pb deposits are a type of structurally controlled, stratabound sulphide mineralization. Within the southern Irish orefield, mineralization is typically hosted in the marine Waulsortian Limestone Formation. Sulphide precipitation was initiated when metal-bearing hydrothermal fluids (up to 200 ˚C) mixed with cooler (<100 ˚C) hypersaline brines, carrying bacteriogenically reduced sulphur of seawater origin (Fallick et al., 2001; Wilkinson et al., 2005). Orebodies are typically found in the hanging-wall of normal faults, which acted as fluid conduits, allowing the two source fluids to mix. Five significant Zn-Pb discoveries have been mined to date in Ireland: Tynagh, Silvermines, Galmoy, Lisheen and Navan.
The Lisheen deposit, which closed in 2015, produced 23 Mt of ore at 13.3 % Zn and 2.3 % Pb. The Island Pod is a small satellite body in the north of the Lisheen deposit, which hosted some of the best quality ore at Lisheen and exhibits a weaker structural control than elsewhere in the deposit.
This research aims to use Lisheen and other Irish-type deposits as testing grounds for new isotopic vectoring techniques, to identify possible geochemical halos and enhance our current understanding of fluid flow processes responsible for metal deposition. Since Lisheen was operational as a mine for over 15 years, there is a wealth of deposit information available. Clumped O-C and Zn-Cu-S isotopic analyses will be carried out at Lisheen to test their value as new exploration methods. Once these techniques have been tested at Lisheen, they’ll be applied to similar deposits in Ireland (e.g. Harberton Bridge, Galmoy). Sphalerite Zn-Cu-S isotopic analysis will be used to detect geochemical haloes and potential buried copper mineralization. Clumped O-C isotope analysis of hydrothermal carbonates adjacent to and from within areas of Zn-Pb mineralization will be used to track fluid flow and mixing.