Petrography of metalimestones and metadolostones from the Argyll and Southern Highland groups, Dalradian, Northern Ireland

Thirteen samples of metacarbonate rocks from the Argyll and Southern Highland Groups
within the Dalradian of the Sperrin Mountains, central Northern Ireland, have been studied
by optical petrography and cathodoluminescence (CL) imaging. Three of the metacarbonate
samples are metadolostones and the remaining ten are calcitic metalimestones. Mineral
assemblages are dominated by calcite or dolomite, but subordinate quartz, feldspar and white
mica are ubiquitous. Graphite appears common in some samples as dusty inclusions. Grain
boundaries are only moderately well equilibrated texturally and the CL imaging reveals
considerable chemical heterogeneity on the grain-scale. Mineral assemblages and CL images
indicate that infiltration of metamorphic fluid was very unlikely to have been significant in
most samples and it is probable that many samples have retained pre-metamorphic (postdiagenetic)
geochemical signatures, particularly of strontium and stable isotopes. Of the
thirteen samples, six calcitic metalimestones have best potential for further work on their
major oxide, trace element and isotope geochemistry. Geochemical data resulting from
analysis of these samples could have significant potential for geochemical correlation of
lithostratigraphical units and aiding interpretation of the geological structure. This, in turn,
would aid mineral exploration and other geological programmes of work in Northern Ireland.
In addition, the data elucidate further the significant changes which occurred in marine
87Sr/86Sr and δ13C during the late Neoproterozoic.