www.guildsomm.com keeps detailed records for all AOPs, sourced directly from the INAO and lists the following for Gigondas:
"Encépagement: Min. 90% combined Grenache (min. 50%), Syrah, and Mourvèdre (min. 15% Syrah and Mourvèdre); plus Bourboulenc, Brun Argentè, Cinsault, Clairette, Clairette Rosé, Counoise, Grenache Blanc and Gris, Marsanne, Muscardin, Piquepoul Blanc and Noir, Roussanne, Terret Noir, Ugni Blanc, Viognier
Min. 50% Grenache is mandatory from 2014 harvest forward
Min. 15% Syrah and Mourvèdre is mandatory from 2014 harvest forward"