To Prep: Pour rum into a punchbowl and add sprigs of rosemary. Give it a quick stir, making sure to fully immerse the rosemary. Let the mixture sit until it is ready to serve. Remove the spigs of rosemary from the bowl and discard them. Next, add the lime juice to the rosemary-infused rum and chill in the refrigerator until you're ready to serve.
To Serve: Add rosemary ice block and ginger ale to your rum punch mixture and you're ready to go! Serve over ice in a punch glass. Garnish with a small piece of rosemary sprig.
Rosemary Ice Blocks: Fill a couple of round plastic containers with water and a couple rosemary sprigs and put it in the freezer. When serving your punch, float the ice blocks in the punch bowl.