user: Question: What's the lowest ranking source of copper, Copper ore, concentrated and leached?
Columns: ['Rank', 'Mine', 'County', 'Operator', 'Source of copper', '2012 Cu Production (lbs)']
Types: ['real', 'text', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'Morenci', 'Greenlee', 'Freeport-McMoRan', 'Copper-molybdenum ore, concentrated and leached', 632.0]
SQL:

assistant: SELECT MIN("Rank") FROM "Table" WHERE "Source of copper" = 'Copper ore, concentrated and leached';