In a small saucepan, combine the sugar with 3 cups of water. Bring to a boil over high heat, reduce the heat, and simmer for 5 minutes. Add the mint, remove the pan from the heat, cover, and let the liquid steep for 1 hour. Strain the liquid into a bowl. In a large pitcher, combine the mint syrup, lemon juice, orange juice, and ginger ale. Stir until well blended. Serve over crushed ice.