Copper exchange traded funds have seen a much weaker bounce than U.S. stocks in October, which raises some questions about the rally in risky assets.

Copper prices and the S&P 500 have shown a tight correlation in recent years, and many technical analysts use the red metal to keep their finger on the pulse of the global economy.

“This is a big negative divergence on copper and it may be that copper will accelerate to the upside soon, but while this negative divergence persists copper is arguing for lower prices,” the Channels and Patterns blog writes Thursday.

The iPath Dow Jones- UBS Copper Sub-Index Total Return ETN (NYSEArca: JJC) has traded lower this week and was down about 2% in early trading Thursday. [Copper and Silver ETFs Hit By Economy, Position Limits]