Hornblende–biotite– (?)pyroxene dacite from Cerro Morrón de Mateo, Sierra de Gata, SE Spain has two types of zircon grains, a major, younger group with a weighted average ion microprobe U–Pb zircon age of 11.69 ± 0.15(2σ) Ma and a minor, older one of 13.58 ± 0.31(2σ) Ma. The younger crystals have mostly euhedral habit and zoning, and vary in size from c. 50 to 650 μm; a few show signs of late stage resorbtion in the form of glass filled embayments. The older crystals have anhedral zoning and irregular, corroded outlines. Considering its eruption age of 10.70 ± 0.15(2σ) Ma (40Ar/39Ar biotite plateau ages), these two zircon generations suggest a gestation period of at least 1 (–3) Ma for the Morrón de Mateo magma. Like zircon, quartz, plagioclase, biotite and hornblende, major phenocryst phases, also show variable resorbtion effects. That suggests that the erupted dacitic magma body consisted of several batches with somewhat different history, which were brought together some time before extrusion.