Quorum requirements for a referendum to be valid

Law 25.432 onReferendum (2001-05-23) [Ley 25.432 Consulta popular vinculante y novinculante]

ARTICULO 4? — Toda consulta popular vinculante ser? v?lida y eficaz cuando haya emitido su voto no menos del 35% de los ciudadanos inscriptos en el padr?n electoral nacional.

http://infoleg.mecon.gov.ar/infolegInternet/anexos/65000-69999/67518/norma.htm

35% of registered voters

For binding optional referenda —where voting ismandatory— to be valid such percentage is required, while not-binding referendahave no requirements of this kind.