Genetic constraints from paleomagnetic dating for the Aliva zinc–lead deposit, Picos de Europa Unit, northern Spain

Abstract

Aliva has been the most productive Zn–Pb mine in the Picos de Europa Mississippi Valley-type (MVT) district of Spain’s Cantabrian Zone. The mineralisation is hosted in a Variscan thrust sheet by strata of the Late Carboniferous (~309 ± 3 Ma) Picos de Europa limestone–shale formation. Paleomagnetic and rock magnetic analyses of 194 specimens from 23 sites show that the sphalerite–galena–dolomite ore carries a stable characteristic remanent magnetisation (ChRM) in magnetite–titanomagnetite with minor pyrrhotite. Uncorrected for bedding tilt, the ChRM’s direction is declination (D) = 347.2°, inclination (I) = 61.8° (N = 20 sites, k = 75.4, α95 = 4.3°). A negative paleomagnetic fold test shows that the MVT mineralisation is in one or more carbonate olistoliths of the Picos de Europa Formation in shales of the overlying Late Carboniferous Lebena Formation and that the ChRM entirely postdates Variscan orogenic deformation. No plausible tilt correction of the ChRM’s paleopole supports a previously proposed late Variscan (Permian–Triassic) age for the genesis of the MVT mineralisation at Aliva. The paleopole does support an age of 112 ± 8 Ma for the hydrothermal dolomitisation and MVT mineralisation event with a subsequent increase in bedding tilt by ~10° NNE during the Oligocene–Miocene Pyrenean (Alpine) Orogeny. The 112 ± 8 Ma Aptian–Albian age ties ore genesis to the 35° ± 2 counterclockwise rotation of the Iberian peninsula relative to stable Europe and strongly favours an origin in the rift’s flank associated with rift hydrothermal activity.