Cut 4 limes into small pieces; place in a pitcher and add 1/2 cup superfine sugar. With a large wooden spoon, muddle the limes until juicy. Stir in 1 cup cachaca. Spread gold coarse sugar on a plate. Moisten the rims of 6 to 8 glasses with a lime wedge, then dip in the gold sugar; fill the glasses with ice. Pour in the cocktail and top with lemon-lime seltzer.