Preheat oven to 180 degrees C. Grease a cast iron skillet.
In a medium bowl, mix together the flour, baking soda and sugar. Toss the raisins with the flour mixture until coated. Make a well in the centre and add the egg, buttermilk and melted margarine. Stir until all of the dry ingredients are absorbed. Turn the dough out on to a floured surface and knead for a few quick turns, just to even out the dough. Handle the dough as little as possible. Pat into a flat circle, and place into the prepared pan.
Bake the bread for 40 to 45 minutes, or until the edges are golden.