Preheat an oven to 350 degrees F (175 degrees C). Grease and flour 2 3x7-inch loaf pans. Whisk together the all-purpose flour, whole wheat flour, salt, and baking powder in a mixing bowl; set aside.
Beat the eggs, sugar, sucanat, grapeseed oil, half-and-half cream, rum extract, vanilla extract, lime zest, and spearmint with an electric mixer in a large bowl until smooth. Stir in the flour mixture until just moistened, then stir in the blueberries, and pour into the prepared loaf pans. Sprinkle the tops evenly with the turbinado sugar.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 30 minutes. Cool in the pans for 10 minutes before removing to cool completely on a wire rack.