Peer-Reviewed Journal Details
Mandatory Fields
OReilly, C,Feely, M,Holdstock, MP,OKeefe, WG
1997
January
Transactions Of The Institution Of Mining And Metallurgy Section B-Applied Earth Science
Fluid inclusion study of the unexposed Kentstown Granite, Co Meath, Ireland
Published
()
Optional Fields
ORE DEPOSITION STABLE ISOTOPE MINERALIZATION EVOLUTION EQUATION SYSTEMS
106
31
37
The presence of the Kentstown Granite, of inferred late Caledonian age, at a depth of 662.5 m in Co. Meath, Ireland, has recently been confirmed by a Tara Mines, Ltd., mineral exploration borehole. The borehole was collared in basinal Brigantian shales and passed downwards into a thick sequence of Visean shallow-water carbonates that form the Milverton Group and which unconformably overlie sediments of the Courceyan Meath and Liscartan Formations. A ca 11 m thick section of interbedded elastic and carbonate sediments unconformably overlies the granite. A petrographic and microthermometric study of fluid inclusions in the Kentstown Granite, crosscutting quartz (V-1) and calcite+quartz (V-2) veins in the granite and calcite+quartz (V-2) veins in the overlying sediments was performed on samples taken from the borehole.Aqueous-carbonic fluids (type 1 and type 2), found only in granite quartz, were the earliest fluids to have circulated through the granite. The estimated trapping conditions for these earliest fluids are ca 300-330 degrees C and ca 1.6 kbar. Later low-salinity (<9 equiv. wt% NaCL) fluids of moderate (ca 150-250 degrees C) temperature of homogenization (T-H) and Of probable meteoric origin occur as secondary inclusions in granite quartz and as primary and secondary inclusions in V-1 vein quartz (type 3). Moderate-salinity (ca 10-15 equiv. wt% NaCl), moderate-T-H (ca 110-200 degrees C) fluids (type 4) that were trapped as secondary inclusions in granite and in V-1 vein quartz are of uncertain origin. Low-T-H (ca 50-150 degrees C), high-salinity (ca 20-27 equiv. wt% NaCl) CaCl2-rich brines (type 5) occur as primary inclusions in V-2 vein calcite and quartz and also as secondary inclusions in V-1 vein quartz and in granite quartz. Comparisons of the type 1, type 2 and type 3 fluid inclusion populations recorded in the present study with those from other Irish Caledonian granites strongly suggest a similar fluid evolutionary history. Furthermore, the low-temperature CaCl2-rich brines (type 5) of this study, which must be syn- to post-lower Carboniferous in age, have correlatives both in Irish Caledonian granites and in the Lower Carboniferous base-metal deposits of the Irish midlands.
Grant Details
Publication Themes