Mystic Blackberry Cocktail

1 (.75-oz.) pkg. fresh mint sprigs12 (1/4” thick) cucumber slices2 (6-oz.) pkgs. fresh blackberries¾ c. fresh lime juice8-12 t. superfine or powdered sugar1 c. plus 2 T. gin1 c. cold club sodaCrushed iceGarnishes: cucumber slices, fresh blackberries, lime wedges and…