What was found
During climb out from LGA, @ approximately 1000 ft., crew noted that a ring of sparks were coming from the RH engine. With engine indications normal crew reduced power-sparks continued. In flight emergency was declared-air return to LGA. Aircraft landing was uneventful. Upon taxi to gate, maintenance concluded that sparks were coming from prop blade(s). Upon closer examination, maintenance noted a heating element on one blade had burn marks. Suspect de-ice boot was arcing. R&R prop. Op's check good. Aircraft returned to service.