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Elvan and ongonite magmas with associated rare metal mineralization
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
V. Antipin, C. Halls, R. Seltmann
The granite cupolas of the Cornubian batholith, located in the SW peninsula of the UK, have a distinctive belt of porphyry dykes trending WSW-ENE along the main intrusive axis. The dykes cross the five major plutons of the batholith and the Devonian and Carboniferous country rocks. These porphyry dykes of granitic composition have been given the name elvan, a term deriving from the Cornish language. Typical elvans are quartz-porphyries with total alkalis similar to those of associated granites, but with values of K2O ≫ Na2O (Hall 1973). The elvans and granites were formed during closely related intervals of time between 269-282 Ma and 268-290 Ma (Darbyshire & Shepherd 1994). Granites and elvans both have peraluminous compositions with SiO2 = 70-75%, K2O+Na2O = 7.0-8.5% and low contents of CaO, MgO and K/Na>1. Elvans also have relatively high contents of Rb, Cs, Ba and Sn (Table 1), which are similar to those of the granites in the Cornubian batholith. New analyses of the total contents and distribution patterns of REE in elvans are very similar to those of the associated Cornubian granites as given by Darbyshire & Shepherd (1987). Elvans from Praa Sands and Wherry Rocks have high REE contents of 186 and 169 ppm respectively, and also have La/Yb ratios of 21.8 and 17.3. These values are close to those characteristic for the granites of the Lands End pluton which has total REE=208 ppm and La/Yb=26.6.
Luzonite and associated Cu-excess tennantite from the Levant Sn–Cu deposit, Cornwall, England: Evidence for a high sulphidation hydrothermal event
Published in Applied Earth Science, 2021
Benjamin A. Grguric, Malcolm P. Roberts, Mark D. Raven, Kendal Martyn
The Cornubian Batholith in south-west England is host to numerous tin and base metal deposits (Jackson et al. 1989; Willis-Richards and Jackson 1989) which have been worked since antiquity. The Levant Mine (SW 368 346) is located on cliffs near Boscaswell in west Cornwall (Figure 1), and was worked discontinuously between 1793 and 1930 (Jackson 1976). The mine is host to the classic, spatially-zoned Cu–Sn mineralisation, well-described from Cornwall (Dewey 1925; Hosking 1963), which led to the early workings being directed at exploitation of copper, later followed by tin. In this paper, we report on the overprinted paragenesis of early Sn–As and later Cu–As–S mineralisation in specimens from the Levant Mine dumps which includes luzonite (Cu3AsS4) and Cu-excess tennantite. The mineral chemistry of the luzonite and associated tennantite are characterised, and the implications for a high-sulphidation episode in the long-lived hydrothermal paragenesis of the Levant vein systems are investigated.