Forty-seven new K-Ar analyses are reported from 15 mines in the Lake District. Analyses of clay mineral concentrates from vein gouges and altered wallrock support a hypothesis of at least 3 distinct isotopic events. Caledonian ages (388 Ma) are reported from the Coniston Copper deposits, while the extensive mineralization in and around the Vale of Newlands indicates a metasomatic event occurring at around 360 Ma. The ages of the sporadic mineral localities to the E of the area (i.e. Greenside, Threlkeld, etc.) are grouped around 325 Ma while those of the Caldbeck Fell deposits are close to 230 Ma. An epidosic model may be advanced for the Carrock Fell Tungsten deposits with a range from 197 to 282 Ma. The geochronological significance of these and other previously published results is considered.

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Episodic hydrothermal mineralization has previously been recognized in the northern section of the Pennine orefield. Igneous rocks from the southern section (the Derbyshire orefield) have yielded isotopic ages, some of which are thought to represent ages of hydrothermal metasomatism (deuteric or subsequent). In order to ascertain whether epicyclic hydrothermal events gave rise to the Derbyshire mineral deposits, samples of highly altered doleritic lava and pumice tuff were collected adjacent to areas of mineralization. Clay-mineral concentrates from 34 samples were dated by the potassium-argon method. The conclusions drawn from these analyses support a hypothesis of repeated hydrothermal alteration of the clay minerals, reflecting at least two episodes of mineralization, one about 270 m.y., the other about 235 m.y. The geochronological significance of these and other results is considered.

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