Abstract -
The Lisheen Zn-Pb mine, Co. Tipperary, Ireland is a Lower Carboniferous carbonate-hosted massive sulphide
deposit. It was discovered by Chevron Mineral Corporation of Ireland in 1991 by soil geochemistry and
geophysics and has been in production since September 1999 as a joint venture between Anglo American plc
and Ivernia West Inc. Waulsortian dolostone (regional dolomite) and hydrothermal alteration breccia (Black
Matrix Breccia) host the majority of the mineralization, which occurs at or close to the base of the Waulsortian
Formation. The Argillaceous Bioclastic Limestone (ABL - Ballysteen Formation) is the geological footwall to
the mineralization. Minor mineralization is hosted by the Lisduff Oolite Member of the ABL where it occurs in
the footwall of major, north-dipping, ENE trending fault zones (~200m throw). These structures are part of a
group of early faults, which occur in a ramp-relay system resulting from ~N-S extension. Post-mineralization
compression (possibly Variscan-related) in the same direction created folding and, in the south of the mine,
thrusting. N-S to NNW-SSE trending strike-slip faults exhibit the latest movement although these may be
reactivated early faults. Mineralization is generally massive pyrite-(marcasite)-sphalerite-galena that occurs in
stratiform lenses with subordinate vein and disseminated sulphides. Minor Cu and Ni mineralization occurs,
especially in the Lisduff Oolite and towards the south in the Waulsortian host rock. Mineralogical evidence
suggests that initial massive pyrite-marcasite mineralization was followed and partially replaced by the main
ore-stage Zn-Pb mineralization. The Cu and Ni mineralization occurred during the early ore-stage. A twosource
fluid-mixing model fits the limited fluid inclusion, isotopic and mineralogical evidence to date: (1) a deepsourced,
relatively high temperature, reducing fluid; mixed with, (2) a low temperature, seawater-sourced,
sulphur-bearing fluid. Metal distribution investigations illustrate increased Zn, Pb, Fe, Ni and Ag content and
massive sulphide thickness not only adjacent to the southern normal faults but further north also, evidence that
the major faults were not the only mineralization centres. NW mineral trends are also evident. The earliest age
of mineralization at Lisheen is mid-Crosspatrick Formation time (Chadian).
In: Europe's Major Base Metal Deposits. Special Publication of the Irish Association for Economic Geology, 455-282. 2004.