Regional geochemical comparisons from the Lower Palaeozoic, Southern Uplands–Down-Longford terrane in Northern Ireland and Scotland

Abstract

SynopsisNewly-acquired regional geochemical data for the Down-Armagh (Northern Ireland) sector of the Southern Uplands -Down-Longford terrane are assessed by comparison with the equivalent dataset for southern Scotland. Despite the much thicker glacigenic cover to the Down-Armagh bedrock, the principal geochemical lineaments identified in the Southern Uplands are still apparent. Patterns of element distribution emphasise the continuity of structure and stratigraphy between the two regions, with Cr, Zr, Sr, Rb, Ba and Ca (as CaO) proving particularly instructive. Much of the Down-Armagh outcrop consists of Llandovery strata from the Gala and Hawick Groups, so it is this part of the terrane that is most closely considered. Though continuity is clear, there is a suggestion of additional structural imbrication in Down-Armagh, whilst variability in the defining element ratios suggests along-strike compositional changes in the turbidite sandstones. These changes may be controlled by lithostratigrapical variation in sedimentary provenance, or may be influenced by the dominant palaeocurrent flow towards the south west, which has resulted in a broadly more distal and mature Llandovery turbidite lithofacies in Down-Armagh than in the Southern Uplands.

The significance of copper concentrations in natural gold alloy for reconnaissance exploration and understanding gold-depositing hydrothermal systems

“…They also mention the contrasting absence of such haloes around the Criffel and Newry plutons, and the Mournes granite, which intrude mainly Hawick Group strata. Breward et al (2011) were unable to categorically ascribe these features to original geochemical differences in the greywackes or to the intrusion process of the granite.…”

“…A possibility then is that copper has been introduced from a concealed magmatic source. Breward et al (2011) mention the prominent haloes of Pb-Zn-As and lesser Cu enrichment in stream sediments (and therefore bedrock) around the Loch Doon and Cairnsmore of Fleet plutons which intrude Gala Group strata (Fig. 1).…”

The Tellus geochemical surveys, results and applications

“…Much of the bedrock of the north of Ireland is overlain and obscured by glacial deposits and peat, but the geochemistry of soils and sediments has nevertheless been shown to be representative of bedrock. Breward et al (2011) compared the stream sediment geochemistry for the Tellus survey with that for sediments overlying equivalent Lower Palaeozoic bedrock in southern Scotland. Despite the much thicker cover overlying the bedrock in the Down-Armagh area of Northern Ireland, the principal geochemical lineaments identified in Scotland are still apparent, with patterns of the distribution of several elements demonstrating the continuity of structure and stratigraphy between the two regions.…”

The Southern Uplands Terrane in Scotland – a notional controversy revisited

“…Stone et al (1999 identified two element assemblages as being of particular value in tracking geologicallycontrolled changes in sediment composition: the basic-ultrabasic elements (Cr-Ni-Mg-VTi), and the feldspar association (Rb-Sr-K-Ba), both of which had potential as lithostratigraphical mapping surrogates. Breward et al (2011) were able to extend the element distribution patterns seen in the Southern Uplands westward into the DownLongford inlier, Ireland, utilising similar geochemical data acquired there as part of the TELLUS project. However, the direct spatial associations between the patterns of element distribution in stream sediment and changes in the underlying bedrock outcrop do not necessarily mean that the two media have the same compositions.…”