Searching for the “next big thing”: Examining the potential for new feeder zone mineralisation in the western Navan area, County Meath, Ireland

Convery, Michael (2017) Searching for the “next big thing”: Examining the potential for new feeder zone mineralisation in the western Navan area, County Meath, Ireland. MRes thesis, University of Glasgow.

Full text available as:
[thumbnail of 2017ConveryMRes.pdf] PDF
Download (34MB)
Printed Thesis Information:


This study focuses on the Navan Deposit, County Meath, Ireland – a carbonate-hosted Zn-Pb
sulphide deposit originally comprising 110Mt @ 8% Zn and 2% Pb, prior to depletion by mining.
Navan belongs to the “Irish-type” deposit group – Zn-Pb deposits hosted in the Irish Ore Field that
have characteristics of both MVT and SEDEX-style deposits, though cannot be easily be
categorised as either. The Irish-types formed from mixing of two fluids – a metalliferous
hydrothermal fluid, and a bacteriogenic-sulphide enriched brine. The hydrothermal fluid from
Irish-types in the southern Irish Midlands yield a respective hydrothermal fluid homogenisation
temperature and salinity range of 170-280oC and 12-18 wt.% NaCl. The Navan hydrothermal fluid
was notably lower temperature at 100-140oC and had a salinity of 5-10 wt.% NaCl. Mixing of this
moderate temperature fluid with a high salinity bacteriogenic-sulphur enriched brine (70-100oC,
20-25 wt.% NaCl) allowed high-grade Zn-Pb ore to precipitate along a shallow, extending sea basin
at approximately 345 Ma (Lower Carboniferous).

Navan ore has an average Zn/Pb ratio of 4, though low-grade, low Zn/Pb below 3 is observed in
the hangingwall of the Randalstown Fault 200 metres west of the mine site – an end-Variscan
reverse fault of at least several hundred metres throw and one kilometre dextral displacement.
Low Zn/Pb has been previously noted in Navan and other Irish-type deposits as an indication of a
nearby “feeder zone” – early-forming normal faults that allowed hydrothermal fluid upwelling.
Hydrothermal fluids then mixed with downwelling bacteriogenic sulphide-enriched brines on, or
close to the seafloor to produce high-grade Zn-Pb sulphide ore. Low Zn/Pb in western Navan,
therefore, is of particular interest and may point to a new, unidentified feeder. In addition, Cpy-
Qtz(-barite) veining has been identified in drillcore for the first time in the Navan area
approximately 850 metres west of the Randalstown Fault, coinciding with the low Zn/Pb area.
Notable chalcopyrite has been identified close to feeder-zone faults in other Irish-type deposits,
though is absent at Navan – until this discovery.

Mineralised samples were selected along four drillhole transects – The “A1 Transect” was
selected trending southeast along the hangingwall of the Randalstown Fault, while the “A2
Transect” trends southeast along the Randalstown Fault footwall. The “B and C Transects” trend
perpendicular and parallel to the Main Orebody, respectively. Sulphides from the Main Orebody
and western Navan share a similar paragenesis, suggesting that both may have derived from the
same hydrothermal fluid event. Sulphur isotope analysis constrains a δ34S range of -1.5 to 12.5‰
for Zn-Pb sulphides west of the Randalstown Fault. This range coincides with previous studies that
have constrained the δ34S range for the hydrothermal fluid (-4 to 16‰) that supplied Zn-Pb to the
Navan Main Orebody and is interpreted to represent hydrothermal fluid that migrated westward
during early normal faulting. Fluid inclusion analyses constrain a mineralisation temperature and
salinity range of 87-136.5oC, and 6.8-22.7 wt.% NaCl, respectively. This is broadly coincident with
the hydrothermal fluid temperature and salinity range. Higher fluid salinity is interpreted to
reflect mixing with limited downwelling seawater and/or in-situ pore water.

Cpy-Qtz(-barite) veining in western Navan is hosted in a 10.5 metre thick stratal dolomite and
formed from a separate mineralising fluid to the Navan Deposit. δ34S analysis of three
chalcopyrites yield a range of 0.8-3.3‰, results consistent with a hydrothermal fluid origin. Fluid
inclusion analysis of two-phase quartz-hosted inclusions yield a temperature range of 191-223oC,
while monophase inclusions constrained a salinity range of 10.2-22.8 wt.% NaCl. The assemblage
is both distinct from Navan and closer to higher temperature systems in the southern Irish
Midlands – an observation supported by a mineralisation temperature range that is closer to the
southern Irish-type deposit systems. The mineralising fluids were both higher temperature and
more saline than the Navan hydrothermal fluid, potentially pointing to the feeder zone of a new,
unidentified system.

Item Type: Thesis (MRes)
Qualification Level: Masters
Keywords: Mining, exploration geology, Irish-type, Mississippi Valley-Type, sedimentary-exhalative.
Subjects: Q Science > QE Geology
Colleges/Schools: College of Science and Engineering > Scottish Universities Environmental Research Centre
Supervisor's Name: Boyce, Professor A.J., Newton, Dr. J., Ashton, Dr. J. and Blakeman, Dr. R.
Date of Award: 2017
Depositing User: Mr Michael Thomas Convery
Unique ID: glathesis:2017-7900
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 23 Mar 2017 12:10
Last Modified: 25 Apr 2017 13:46

Actions (login required)

View Item View Item


Downloads per month over past year