“An essential link between Yahweh and copper is suggested in the book of Zechariah, where the dwelling of the God of Israel is symbolized by two mountains of copper (Zech. 6.1-6).

In his prophecies, Ezekiel describes a divine being as 'a man was there, whose appearance shone like copper' (Ezek. 40.3), and in another part of this book, Yahweh is even explicitly mentioned as being a smelter (Ezek. 22.20).

A similar association is encountered in the book of Zechariah (Zech. 13.9). It is interesting to notice that these visions are not simple popular metaphors. Both Ezekiel and Zechariah described processes of metal purification (fractionation through melting for Ezekiel and cupellation for Zechariah), suggesting that the authors of these two books had a deep knowledge not only of Yahwistic traditions, but also of metallurgy. (p. 394)

from 'Yahweh, the Canaanite God of Metallurgy?', JSOT 33.4 (2009): 387-404”