The success of Crane Iron and the many other iron companies that sprang up in the Lehigh Valley led to a major mining boom in Lehigh County, with no less than 261 mines of varying size being opened. Some were worked by independent operators and the ore sold on the open market, others leased by iron companies, and some owned outright by the companies. In 1875, Crane Iron leased eleven limonite mines in Lehigh County, owned three outright and one jointly with Thomas Iron, and leased a hematite mine at Zionsville.