Base metals tumbled to multi-week lows on Friday, drawing minimal support from a turn-around in pummelled stock markets as traders focused on slowing economies and the end of a major strike in Chile. Benchmark September copper futures on the COMEX exchange in New York finished the session 11.85 cents lower at $4.1170 per lb, a 2.80 percent decline. It earlier fell as low as $4.0795 per lb, a level last seen on June 28.