You have a couple of good posts that aver that copper is regarded as the belwether to the economy. If copper is in demand, then stuff must be being built. In the same way that DJ Transports are regarded as a “health indicator”. If stuff is being sold, it is being shipped.
Now as to the underlying cause or causes: One is certainly the deteriorating demand from China. As it turns out, some Chinese speculators developed huge stockpiles of copper when it was in demand. Well, they can’t just let it sit there; they have to borrow against it, to use it as collateral for loans. To lever up, as they say. At minimum, to help pay for the warehouse rent. But with the price of copper plummeting, those loans become undercollateralized and lenders demand a “top off”. The copper hoarders then sell copper, but they are selling it into a declining market. Which exacerbates the decline. In many cases, the Chinese copper holders have (fraudulently) taken out *multiple loans* against their copper. So some of it is super-leveraged. They are in effect getting a margin call.
This is one of a few core differences between most commodities and stocks. While it is true that a stock can go to zero and some think or believe that commodities cannot because they are representations of real things, trends...uplegs and downlegs in commodities can go on much, much longer than *anyone* can believe. Much longer. And then even longer. Who on earth thought oil would go from $110 to $40? That’s really a giant move on any kind of basis, especially for such a vital commod.
It is also happening with USDollar, relentlessly strong and causing serious disruption in the rest of the world. Yaaaay! Oil got cheaper! People trying to call a turn in copper or oil or the USD are getting cornholed, over and over. One reason is the incredible turmoil roiling currency markets. Volatility in forex is causing all manner of distortions in the stock market and various commod markets. Just saying. Not decrying it.
However, Maxine Waters told me via private email that these oil price changes were the fault of evil speculators. Just passing that on.
By the way, I don’t know if they are still doing it, Goldman Sachs had several giant metals warehouses that they established in crumbling Detroit warehouses they probably got for free in various BKs and foreclosures. (Base metals, copper, zinc, nickel, not especially gold/silver although they are certainly involved in those markets) They worked to manipulate the domestic market by withholding stocks and delaying deliveries. Their market-cornering practices engendered a lot of complaints and I think they were quietly told to back off.