This section is from the book "An Elementary Outline Of Mechanical Processes", by G. W. Danforth. Also available from Amazon: An elementary outline of mechanical processes.
The greater part of the world's supply of copper is produced by smelting the sulphide ores. A very extensive source of supply of native copper is the Lake Superior deposit. Only a small supply of copper comes from oxides, carbonates and low-grade ores.
The sulphides and other ores, including those containing as little as 5 or 6% of copper, are smelted; native copper is melted down to separate it from rock and other earthy substances it holds; and very low-grade ores are leached by the wet process.