Melt the butter in a skillet over medium heat. Add the onion and ginger and cook until tender, about 3 to 4 minutes. Add the cherries and cook 1 to 2 minutes more. Add the brown sugar, vinegar, spices and salt and cook, stirring occasionally, until the mixture begins to thicken slightly, about 3 minutes. Remove chutney from the heat, and then stir in the mint. Set each round of Brie on a sided plate. Divide, top and mound each Brie with some of the cherry chutney. Garnish with mint sprigs and serve.