Copper prices were on the rise Wednesday as traders worried that a strike at a major producer would threaten supplies of the metal.

Benchmark contracts for copper were tacking on 4 cents at $3.75 a pound in recent action on the Comex division of the New York Mercantile Exchange.

The

PowerShares DB Base Metals

(DBB) - Get Report

exchange-traded fund, which tracks the value of copper and other industrial metals, was ahead by 1.3%.

Workers at a

Southern Copper

( PCU) facility in Peru are staying off the job for a second day and the action is raising concerns that an already tight market for the metal will get worse, explains William Adams, an analyst at

BaseMetals.com

in London.

Shares of Southern Copper were recently edging lower by 0.2%.

In precious metals, silver prices were up a penny at $13.46 an ounce, while gold prices were off 40 cents at $735.90 an ounce.

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Among agricultural products, cocoa prices were shedding 2.6% at $1,867 a ton, while coffee prices were rising 1% at $1.36 a pound.

As for the commodities-producing stocks, Bear Stearns upped its rating on shares of smelter

Kaiser Aluminum

(KALU) - Get Report

to outperform from peer perform, helping lift the shares almost 7%.

RBC Capital Markets raised

Kinross Gold

(KGC) - Get Report

to an outperform rating from sector perform, sending the shares higher by 1%.

Piper Jaffray took coffee seller

Green Mountain Coffee Roasters

(GMCR)

to outperform from market perform, a move that boosted the stock more than 7%.