Coarsely chop 1/2 cup of the blueberries and place in a medium bowl. Add 1 cup whole blueberries to the bowl. Using a sharp knife, remove peel and white pith from 2 oranges. Cut sections from oranges. Coarsely chop orange sections and transfer, with any juices, to the bowl with the blueberries. Stir in red onion, vinegar, mint and salt.