The declining grade of copper ore, a simultaneous increase in costs and political problems are other major problems facing Freeport.

FORBES: Freeport McMoran's Earnings: China Recovery, Energy Foray In Focus

Newmont attributed the lower production to the processing of lower grade ore from stockpiles as it prepared for a new phase of mining at the vast open pit in the mountains of Sumbawa.

FORBES: Newmont Mining's Rocky Year And The Way Forward

Newmont has attributed the lower production to the processing of lower grade ore from stockpiles as it prepares for a new phase of mining at the vast open pit in the mountains of Sumbawa.

FORBES: Newmont's Revised Production Forecast In Indonesia May Cause Labor Troubles

This is expected to be driven mainly by cost savings in Indonesia where higher grade ore and economies of scale will bring down costs by nearly 50%.

FORBES: Freeport Banks Future On Better Copper Production And Energy Exploration

However, it is important that investors do take serious note of how steep the decline in ore grade has been.

FORBES: Silvercorp Back in Focus

Copper-market analysts believe that Zaire's high-grade ore could help create a world surplus of copper by the end of the decade, and bring prices down heavily.

ECONOMIST: Zaire

They too want to reopen some of their closed mines to look for low-grade ore, and plan to expand production through joint ventures with international players.

BBC: Golden opportunity for old Indian mines

The current phase of production at the Ekati Diamond Mine includes ore sourced primarily from the lower grade, but high carat value, Fox open pit supplemented by underground production from the lower portion of the Koala kimberlite pipe and from the Koala North pipe.

FORBES: Harry Winston to Purchase Ekati Diamond Mine For $500 Million