Preheat oven to 325 degrees F.
In a coffee grinder, pulse spices until well combined and slightly coarse; add sea salt. Rub prime rib thoroughly with spices, coating entirely.
Pour oil over roast. Gently rub in. Sear prime rib in a heavy saute pan on all three sides; about 2 to 3 minutes each side. Place pan in oven. Cook for 1 1/2 hours until you reach an internal temperature of 135 degrees F.
Remove from oven and place on hot grill for an additional 15 minutes to grab grill flavor and caramelize the surface of the meat. Remove from grill and let rest for 10 minutes before slicing. Serve with the Horseradish Sauce.
In a medium sized bowl, mix together all ingredients and serve with Prime Rib. Place in refrigerator until ready to serve.