The loss in uniaxial compressive strength between UCS dry and UCS sat for 35 British sandstone types is discussed. The difference between UCS dry and UCS sat for the clay-rich Cretaceous Greensand was 78% while for the Siliceous Sandstone the strength decreased by only 8%. Over the whole range of sandstones, however, the view that the weaker varieties are more sensitive to moisture content is not supported. The degree of sensitivity to moisture content is controlled primarily by the proportions of quartz and clay minerals present and to a lesser extent by the rock microfabric. Research indicates that the development of pore pressure during loading is negligible especially in pure sandstones and hence does not play a significant role in moisture related strength reduction. The work has demonstrated a large variation in sensitivity to moisture content throughout the range of sandstones studied and has shown that an increase in moisture content of as little as 1 0.000000rom the dry state can have a marked effect on both strength and deformability. A classification scheme for moisture content sensitivity is proposed.

19Detrital-zircon analysis of sandstones interbedded with ca 464

Zircon (ZrSiO 4 ) is the most commonly used mineral in U-Pb geochronology. Although it has proven to be a robust chronometer, it can suffer from Pb-loss or elevated common Pb, both of which impede precision and accuracy of age determinations. Chemical abrasion of zircon involves thermal annealing followed by relatively low temperature partial dissolution in HF acid. It was specifically developed to minimize or eliminate the effects of Pb-loss prior to analysis using Thermal Ionization Mass Spectrometry (TIMS). Here we test the application of chemical abrasion to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) by analyzing zircons from both untreated and chemically abraded samples. Rates of ablation for high alpha-dose non-treated zircons are up to 25% faster than chemically abraded equivalents. Ablation of 91500 zircon reference material demonstrates a ca. 3% greater down-hole fractionation of 206 Pb/ 238 U for non-treated zircons. These disparities necessitate using chemical abrasion for both primary reference material and unknowns to avoid applying an incorrect laser induced fractionation correction. All treated samples display a marked increase in the degree of concordance and/or lowering of common Pb, thereby illustrating the effectiveness of chemical abrasion to LA-ICP-MS U-Pb zircon geochronology. OPEN ACCESSMinerals 2014, 4 504

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The Upper Ordovician Avoca volcanic rocks host a Kuroko-type massive sulphide deposit in southeast Co. Wicklow, Ireland. Immobile element geochemistry of lavas shows a bimodal subdivision into acid and basic groups. Basalts have characteristics of magmas from both subduction zone and enriched mantle sources, and are interpreted as products of the rifting of a volcanic arc. Rhyolites are highly enriched in HFS-elements and were originally peralkaline. Constant incompatible element ratios throughout the compositional spectrum indicate a fractional crystallization relationship between the basic and acid end members. The basaltic magmas evolved by crystallization of an assemblage in which plagioclase feldspar was an important component, producing large negative Eu anomalies. The transition to peralkalinity is marked by LREE depletion and no further increase in the Eu anomaly, which may represent the interval of minor phase precipitation and fO 2 variation seen in other peralkaline series. A group of acid pyroclastic Avoca volcanic rocks are subalkaline and are probably unrelated to the main evolutionary series. The Avoca volcanic rocks were erupted in an extensional tectonic setting within a continental margin volcanic arc, similar to the contemporaneous Welsh marginal basin.