Blend all spices to powder in grinder or mill. Transfer spice rub to small bowl.
Heat oil in heavy large pot over medium-high heat. Add bones; saut&é until brown, about 10 minutes. Add celery, onion, garlic, ginger and bay leaves. Reduce heat to medium; saut&é until celery is tender, about 5 minutes. Mix in tomatoes and 2 tablespoons spice rub; stir 2 minutes. Add broth, wine and mint. Bring to boil. Reduce heat to medium-low; cover and simmer 1§ hours. Strain into medium saucepan, pressing hard on solids in sieve. Spoon fat off top of broth; reserve fat for use with lamb. Boil broth until reduced to 1§ cups, about 25 minutes. Season sauce to taste with salt and pepper; set aside.
Brush each lamb rack with some of reserved lamb fat. Sprinkle each rack with salt and pepper; rub each with 1 tablespoon spice rub. Place on rimmed baking sheet. Let stand at room temperature 2 hours. (Sauce and lamb can be prepared 1 day ahead. Cover separately; chill. Bring lamb to room temperature before continuing.) Preheat oven to 400°F Heat large skillet over high heat. Sear 1 lamb rack on all sides until brown, about 8 minutes. Return to baking sheet. Repeat with remaining lamb racks. Roast lamb until thermometer inserted into center registers 125°F for rare, about 25 minutes.
Rewarm sauce. Cut lamb between bones into chops. Divide lamb among 6 plates. Spoon sauce over lamb.