Combine the marmalade and sugar in a small saucepan. Mix well, place over low heat and cook, stirring, until the sugar dissolves.
Cut the peel from the oranges, cut into slices and then quarter each slice, removing the white center pith from each. Put into a medium bowl.
Pour the sugar/marmalade mixture and Champagne or grape juice over the sliced oranges. Refrigerate for 8 hours.
Sprinkle with almonds before serving and add a sprig of mint.