Reconnaissance stream sediment surveys, carried out both by IGS and by\ud Noranda Exploration (UK) Limited, detected zinc anomalies in the Afon\ud Dulyn. It seemed probable either that they reflected a hidden extension\ud of the Llanrwst lead-zinc mining field, or that they were concentrations\ud related in the first instance to hydrous oxide precipitates produced by\ud changes in the secondary environment. To test which of these possibilities\ud was the most likely, a more detailed drainage survey of the Afon Dulyn\ud and Llyn Eigiau areas was carried out. Stream sediment , panned concentrate\ud and stream water samples were collected from each of 28 sites and analysed\ud for a range of elements which included copper, lead and zinc in all three\ud sample types, and iron, manganese and barium in sediments and concentrates.\ud Readings were taken of the pH in stream water and soil at many points in\ud the area. In addition , ground magnetic traverses were surveyed in the\ud Foe1 Fras and Drosgl areas where there are known to be positive aeromagnetic\ud anomalies.\ud The analytical results were examined in some detail by various statistical\ud methods, from which it was concluded that most of the high zinc in stream\ud sediment results were related to hydrous oxide precipitates. The distribution\ud of elements in a few samples showed some indications of mineralisation, but\ud mineralogical examination of the panned concentrates from these sites found\ud no mineral phases which could be related directly to mineralisation or\ud contamination, zinc occurring mainly in iron oxide coatings. It is thus\ud apparent that a source of zinc exists in the general area, perhaps on the\ud wide interfluves, but it is not known whether this source is dispersed or\ud concentrated (i.e. mineralisation)
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