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.