The large-scale mining of copper had its origins in the late 1800's, primarily in the American West. Small mines existed around the country, particularly in the Upper Peninsula of Michigan and in Arizona, but they were able to extract copper only from high-grade ores. The development of efficient flotation processes ¹ around the turn of the century opened up the exploitation in Arizona, Montana, and Utah of large porphyry ore deposits in which the copper-bearing minerals are widely dispersed throughout the host rock. Open-pit mining techniques were developed for these low-grade porphyry deposits and the United States quickly became the world's largest producer of copper.
The US brass mill industry has a longer history, beginning in the early days of the Republic. The industry was heavily concentrated in the Naugatuck Valley in Connecticut over a 40 mile stretch from Torrington through the center of the industry-Waterbury-south to Ansonia and Derby. The early mills made such objects as brass buttons and copper vessels, and later pins and clock brass, and developed melting and rolling techniques. Only since World War II has the brass mill industry been dispersed widely throughout the eastern half of the United States, and little of it remains in Connecticut.
The electrical wire mill industry started in 1877, when a Connecticut brass mill man named Thomas Doolittle developed hard-drawn copper wire strong enough to be strung overhead. Prior to that time, iron wire had been used in the telegraph system. The telephone system was commercialized quickly after its discovery in 1876 and both it and the growing electric power grid began to consume large quantities of copper wire. While these events were transpiring in the USA, similar developments in copper production and in the consumption of copper mill and foundry products were occurring also in the rest of the industrialized world. Annual growth rates over these periods have ranged from a high of 5.8% at the dawning of the electrical and telecommunication ages (late 1800's-early 1900's) to a low level of 1.3% in the period since the mid 1970's. Over this time period, annual world consumption has grown by about a factor of 30. In fact, despite copper's 10,000-year history of continuous use (and re-use), about three-quarters of all copper ever consumed has been produced in the period since World War II.