For the past decade, the mining industry has argued that the ocean floor is an essential frontier for precious metals needed in the batteries used in cell phones and laptops. As companies eye the best patches of ocean to search for the precious sulfides and nodules, widely dubbed “truffles of the ocean,” the waters near the Saya de Malha Bank—a submerged plateau the size of Switzerland in the Indian Ocean between Mauritius and Seychelles—have emerged as an attractive target.