Field investigation, petrographic studies and lithogeochemical sampling have defined an area of hydrothermal alteration and mineralization associated with a subvolcanic centre of late Caledonian age at Lagalochan near Kilmelford, Argyllshire, Scotland. The igneous rocks of an area of 2.5 km2 comprise a large body of porphyrite, flow-banded dacitic rocks, pyroclastic rocks and several bodies of hydrothermal breccia. The close relationship between pyroclastic masses, dacites and discordant breccia bodies within and peripheral to the porphyrite is indicative of a subvolcanic level of emplacement near a volcanic vent. This subvolcanic zone evidently channelled mineralizing fluids leading to widespread alteration of the rocks and introduction of anomalously high concentrations of silver, copper, molybdenum, zinc, lead, arsenic and gold.

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