Chronology of granite magmatism and associated mineralization, SW England

A Rb/Sr study of Hercynian magmatism in Devon and Cornwall has established that the major granites were emplaced at approx 290- 280 m.y. and that the inferred sequence of intrusion shows no geographical pattern. High initial (super 87) Sr/ (super 86) Sr ratios (0.710-0.716) are compatible with 'S-type' and peraluminous mineralogical characteristics of the granites. REE distributions are consistent with those for normal leucogranites, in that they have a high LREE/HREE ratio and negative Eu anomaly; the REE profiles for Bodmin and Carnmenellis granites, however, contrast markedly with those for Land's End and Dartmoor, implying differences both in the chemistry of their source regions and in conditions of crystallization. The Meldon aplite yielded an isochron age of 279 + or - 2 m.y., confirming it to be a late-stage magmatic differentiate of the Dartmoor granite (280 + or - 1 m.y.). An independent fluid-inclusion Rb/Sr age for the South Crofty Sn-W deposit (269 + or - 4 m.y.) has shown that in the Camborne-Redruth area the main stage of polymetallic mineralization is significantly younger than the Carnmenellis host granite. There is little evidence for an older Westphalian event and in the European Hercynian context the granites show greatest affinity with the younger Sn-W granites of Portugal.