Pour boiling water on the mint leaves. Add grated lemon rind, lemon juice and orange juice. Stir in sugar. Steep until cool.
Decant syrup into a tightly capped bottle. Refrigerate until chilled.
To serve, pour syrup into a glass to fill it 1/4 or 1/3 full; then add ice water, club soda or ginger ale. Add ice. Garnish with lemon wheels and whole mint sprigs. The syrup will keep in the refrigerator for 2 weeks. Makes about 4 cups.