Preheat the oven to 375 degrees F.
In a 7- or 8-quart enameled cast-iron Dutch oven, heat the oil over medium-high heat. Season the swordfish with salt, add it to the pan, and brown it, about 2 minutes per side. Add the onion, garlic, fennel, chili and carrot; lower the heat to medium, and cook to sweat the vegetables, about 2 minutes. Add the chorizo and continue to sweat. Pour in the sherry and bring to a simmer, scraping the bottom of the pot. Add the saffron, stock, tomatoes and clams and bring to a simmer.
Cover the pot and place it in the oven for 5 minutes, or until the clams open. (Discard any clams that do not open.) Remove from the oven, add the olives, parsley and basil and serve.