MADRID, June 26 (Reuters) - Authorities in Mallorca are investigating a coronavirus outbreak involving more than 600 students celebrating the end of term in the Spanish island, just as it prepares for British tourists to return following the easing of travel curbs. Students visiting from the mainland went to a music concert at a bullring in the capital, Palma, as well as parties on boats and in hotels, and officials said on Saturday they wanted to find out if venues had adhered to virus-control measures. The outbreak comes as the Balearic Islands gear up for an expected influx of tourists after the British government put the islands on its "green travel list" from June 30. That means holidaymakers will not have to quarantine on return from the islands, long a popular destination for sun-seeking Britons. read more All of the students who tested positive for coronavirus were Spanish and had travelled from different parts of the country to celebrate the end of university qualification examinations. At least 1,000 students have had to go into isolation, the Balearic Islands" health authorities said, and some of the teenagers showed mild symptoms of COVID-19. Spaniards were allowed to stop wearing face masks outdoors on Saturday after more than a year as coronavirus cases fell, but they must continue to wear them inside or when social distancing is impossible. read more