The results of a reconnaissance geochemical drainage Introduction\ud survey across an area of 850 km2 in the Cheviot Hills are\ud reported. At each of the 708 sample sites, the - 0.15 mm\ud fraction of the stream sediment, a panned heavy mineral\ud concentrate derived from the - 2 mm fraction of the\ud stream sediment and a water sample were collected. Be,\ud B, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Zr, MO, Sn, Ba,\ud Ph and Lo1 were determined in stream sediment samples;\ud Ti, Mn, Fe, Ni, Cu, Zn, As, Sr, Zr, MO, Sn, Sb, Ba, Ce,\ud Pb, Bi and U in panned concentrate samples and Cu, Zn\ud and Pb in water samples.\ud The survey area is composed largely of andesitic\ud volcanic rocks of Lower Devonian age. Underlying _\ud Silurian greywackes and shales and overlying Devonian\ud and Carboniferous sedimentary rocks and basaltic lavas\ud are exposed around the periphery of the volcanic complex.\ud The Cheviot granite crops out on the eastern margin\ud of the area.\ud Anomalous concentrations of metals recorded in the\ud drainage samples are, in general, related to (i) known\ud mineral occurrences, (ii) hydrous oxide precipitation and\ud scavenging processes, (iii) the relatively _ widespread\ud occurrence of baryte, (iv) contamination, (v) tourmalinisation\ud and other hydrothermal activity and (vi) high\ud background levels in unmineralised rocks. At several\ud localities, however, the source of an anomaly is uncertain\ud and some of these may reflect hitherto unknbwn mineralisation.\ud Anomaly groupings and regional variation patterns\ud in the data are influenced by major structures such\ud as the Gyle-Harthope fracture zone.\ud Follow-up investigations into a wide range of metal\ud anomalies in the the Kingsseat area involved more detailed\ud drainage sampling, geological mapping at 1: 10 000\ud scale and petrographic, mineralogical and lithogeochemical\ud studies. Rocks, previously mapped as extrusive\ud mica felsites, are reinterpreted as a high level intrusion\ud complex, named the Cock Law Complex, which contains\ud live distinct types of porphyry. Many of the intrusive and\ud extrusive rocks are highly altered and seven alteration\ud assemblages are identified, arising from sericitisation,\ud kaolinisation, silicification, tourmalinisation, haematisation\ud and carbonate alterations. All except haematisation\ud are related to Lower Devonian igneous activity. Metal\ud enrichments were recorded in many of the analysed rocks.\ud The greatest enrichments, for the widest range of\ud elements, occur in samples taken from a gossanous structure,\ud where the mineralisation has features in common\ud with the epithermal precious-metal style of mineralisation\ud associated with sub-aerial volcanism
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