The intrusion of the granite into the surrounding sedimentary rocks gave rise to extensive metamorphism and mineralisation, and this led to Cornwall being one of the most important mining areas in Europe until the early 20th century. It is thought tin was mined here as early as the Bronze Age, and copper, lead, zinc and silver have all been mined in Cornwall. Alteration of the granite also gave rise to extensive deposits of China Clay, especially in the area to the north of St Austell, and the extraction of this remains an important industry.