H. Lewis et al., CHARACTERIZATION OF FLUID-FLOW SYSTEMS FOR IRISH LEAD-ZINC DEPOSITS -CONTRIBUTIONS FROM MASS-BALANCE, Transactions - Institution of Mining and Metallurgy. Section B. Applied earth science, 104, 1995, pp. 145-155
Citations number
34
Categorie Soggetti
Mining & Mineral Processing","Geosciences, Interdisciplinary",Mineralogy
The lead-zinc sulphide deposits of central Ireland are hosted primaril
y in Lower Carboniferous strata of the Midland Basin. The ores are tho
ught to be approximately contemporaneous with their sedimentary hosts,
but the mode of their formation is a subject of dispute. The minerali
zation is variously regarded as having either a predominantly sediment
ary-exhalative or a predominantly Mississippi Valley type of genesis.
The ores are hydrothermal, so the interpretation of mineral genesis is
strongly linked to the interpretation of the fluid-how system that ge
nerated the deposits. A range of fluid-flow systems was investigated b
y calculating, via a mass-balance approach: whether a candidate system
can provide sufficient metals to create the known deposits; and how m
any pore volumes of fluid are needed to do this. Most of the systems t
hat have been suggested for the deposits were found to be capable of p
roducing adequate metals, but, in examples based on typical flow-syste
m sizes, tens to several thousands of fluid pore volumes are required
to deliver the metals to the sites of deposition. This requirement eli
minates those proposed fluid-flow systems which are incapable of produ
cing sufficient pore volumes. The only tested fluid-flow systems to su
rvive both the metal-balance and fluid-balance tests are deep convecti
on and (Midland and Munster) basinal flow driven by the Variscan oroge
ny. When the driving mechanisms for fluid-flow and crustal heat distri
butions are also considered the viability of tectonically driven flow
in the Irish Midlands becomes questionable, leaving crustal-scale conv
ection as the most likely transport system for the hydrothermal fluids
.