Guarello Island is an island in Madre de Dios Archipelago in Magallanes Region, Chile. Guarello Island is in a limestone area that also includes Madre de Dios Island. The island has the World's southernmost limestone mine. The island has reserves for 100 years, and 600,000 tons of limestone with a millesimal fineness of 96% of Calcium carbonate are extracted each year. Half of the production is used in the steel mills of Huachipato which also owns the mines.