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Munster
Summary Down-hole magnetometric resistivity (MMR) measurements have been conducted in Tobermalug prospect in County Limerick, Ireland. The survey was used as an alternative to down-hole electromagnetic to delineate subhorizontal zinc/lead mineralization lenses that are poorly conductive. Two survey areas were investigated, DHMMR1 and DHMMR2. Interpretation is based on the regularized least-squares inversion of MMR data, in which MMR modeling is performed by resolving electrostatic and magnetostatic equations using finite volume method. Inversion of synthetic data of two conductive horizontal discs model shows that conductive structures are well positioned but their extensions is biased to current electrodes orientation. Inversion allowed localizing a few conductive elongated targets. At DHMMR1, the conductivity is weaker and seems to be associated to disseminated mineralization. DHMMR2 contains a higher conductivity and more elongated target. It seems to be associated to semi-massive sulphides. Introduction Ireland was one of leading European producer of zinc and lead. During the last fifty years, zinc and lead concentrates have been extracted from the Irish Midlands Orefield that covers a surface area greater than 35000km2 (Blaney, 2011). It is one of the world’s major zinc provinces with five major producing mines with large size and high grade ore. In 1999, Minco Ireland signed a joint venture agreement with Noranda (now Glencore) for the exploration of Pallas Green block located between Limerick city and Tipperary town in the centre south of Ireland. The zinc/lead mineralisation at Pallas Green ranges from disseminated and stringer-fracture fill textures to massive (Blaney, 2011). It consists of multiple, subhorizontal, stratiform lenses between 0.5 m to >18 m thick and comprises sphalerite, galena, pyrite and minor marcasite within a Carboniferous limestone. Disseminated and sphalerite rich ores are generally poor targets for electrical resistivity and electromagnetic methods (Denith and Mudge, 2014). In contrast, the MMR technique is more appropriate because it can respond to highly conductive and to weakly conductive targets in a conductive host. For example, it was successfully used in Australian environments for poorly conducting metal sulphide targets, such as sphalerite rich bodies (Asten, 1988; Bishop et al., 1997) and nickel sulphide mineralisation (Bishop et al., 2000).
ABSTRACT Competitive interactions amongst sessile organisms and their mediation by grazing Echinus esculentus in the infralittoral and circalittoral communities on Whirlpool Cliff, Lough Hyne, County Cork, Ireland were investigated using SCUBA Lough Hyne is a sheltered sea lough, the sublittoral cliffs of which support a diverse assemblage of encrusting sessile organisms. Space on the subtidal cliffs, particularly Whirlpool Cliff, is limited, with percentage cover often reaching 100 percent or greater and leading to competition for space amongst settled organisms. The sheltered nature of the Lough minimises physical disturbance, hence the major factors responsible in structuring the subtidal communities are biological interactions. Previous studies have suggested both the importance of interference competition amongst settled organisms and grazing by Echinus esculentus in influencing species abundance and distribution on Whirlpool Cliff. The study aimed to investigate suggestions that factors such as thickness and size are important determinants of competitive ability amongst sessile, encrusting organisms and that the results of such competitive interactions are mediated by the dominant grazers in the community The in situstudy allowed detailed observations to be made over all successional stages in the communities and a number of dissections to be carried out A total of 426 encounters were observed in the infralittoral and 489 in the circalittoral communities, involving 28 and 32 species respectively Of these, 308 (72%) in the infralittoral zone and 273 (56%) in the circalittoral zone, were overgrowth interactions and the remainder were stand-offs Stand-offs were found to be an important space retaining strategy, especially amongst colonial ascidians and sponges. The Corallimorphanan, Corynactis viridis accounted for the majotity of interactions in both communities C viridis and colonial ascidians were the competitively dominant groups (Figure 1 and 2) The encrusting algae Lithothamnion sp and Hildenbrandia rubra had the lowest competitive abilities in both communities Generally, solitary organisms had a lower competitive ability than colonial forms The competitive hierarchy of the main encrusting groups in both communities followed the pattern Colonial ascidians =Corynactis viridis = Sponges > Barnacles and Serpulids > Algae The ability of Corynactis viridis to monopolise space on the cliff was attributed to the anemones ability to resist overgrowth via its powerful nematocysts. It is suggested that the anemone is able to acquire space via rapid asexual proliferahon once space is made available. During an eight day photographic study of 98 individuals, none moved by pedal locomotion as has been suggested recently in studies carried out on Whirlpool Cliff There was no significant correlation between species competitive ability (expressed as a ratio of number of wins to losses or no of wins to the total number of wins in the community) and the mean marginal thickness in the infralittoral community (w/l rs = 0 297; w/wtot rs = 0.036,6 d f., p<0.05) and a significantly negative correlation in the circalittoral community (w/l rs = -0 793; w/wtot rs = -0.782,9 d.f., p<0.05
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- Research Report > New Finding (0.99)
- Research Report > Experimental Study (0.99)
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