SIMPLE SYRUP: Mix the sugar and water in the sauce pan and bring to a boil. The sugar should dissolve completely. Transfer ¼ cup of the hot syrup to a heat proof bowl and allow the remaining syrup to cool in the saucepan. (Makes about 12 ounces and will keep for up to 1 month in the refrigerator. I have some in the refrigerator all the time for cocktails.)
Add the sliced ginger root to the hot ¼ cup of syrup, allow it to steep for 10 to 15 minutes, then remove the ginger slices. Let the syrup cool to room temperature, then chill.
Add the rice vinegar to the syrup and stir well. Toss the mango chunks and blueberries together in the serving bowl, then drizzle the ginger vinaigrette over the fruit. Gently toss again and put in the refrigerator to chill for about 30 minutes. Serve.