The real reason copper is down...is not trade wars, Chinese recession, or global economic collapse. The Escondida expansion has increased production by 300kt/ann, and just ramped up in the first half of 2018. This is 1.5% of global consumption, in a very tight market. It is natural to have a bit of a pullback as inventories build and the pressure is lifted from consumers. Where is the next copper mine going to come from? My guess is RIO and BHP will think twice about sinking the next 5 billion into the hidden mountain, now putting out a head grade of 0.5%, unless prices are significantly above 2.75/lb.
https://www.jltspecialty.com/our-insights/thought-leadership/mining/copper-an-outlook-on-global-supply-and-demand