To your blender, add the frozen mango, tequila, grand marnier, lime juice, simple syrup and ice.
Blender and blend the mixture on high for 30 seconds.
If you find the margarita is too thick add a tablespoon more tequila or water to the blender.
Blend once more on high for 15-30 seconds, or until the mixture is free of lumps.
Run a lime wedge along the edge of your margarita glass to wet the rim and act as a glue.
Pour the Tajín onto a salad plate and dip the rims of your margarita goblets into the Tajín to coat it thoroughly.
Pour 1 ounce of chamoy into each margarita glass and swirl your glass to spread the chamoy throughout the glass.
Pour your frozen mango margarita into the prepared glass and garnish with a mile wedge.