Miner Keith Emerald uses a pneumatic drill to drill holes that will be packed with explosives to blast into the sold rock wall at the Sutter Gold Mining Co.'s mines near Sutter Creek, Calif.

Matt Collins, chief operating officer of the Sutter Gold Mining Co., left, watches as, from left, Allen Smith, Brain Herfel, Ted Chapman and Wayne Murphy calibrate the water flow of a gravity table at the company's newly constructed mill near Sutter Creek, Calif. The gravity table uses technology similar to those used by gold rush-era miners who used pans to separate gold from surrounding materials.

Sutter Gold Mining Co. mill superintendent Paul Skinner removes a crucible of glowing molten gold that will be poured into a mold.

One of the nine rescued Peruvian miners kisses his wife after being rescued from the Cabeza de Negro copper mine on April 11.

Rescued miner Javier Tapia receives medical attention after being rescued from the Cabeza de Negro mine on April 11.

Rescued miner Jacinto Pariona, the first to be rescued, walks outside the mine Cabeza de Negro where he was trapped since April 5, in Ica.

Clothing used by miners dry on a rock wall outside the entrance of the Cabeza de Negro gold-and-copper mine where nine miners were trapped in Yauca del Rosario, Peru.

Chinese rescuers carry out one of the rescued miners from the Qianqiu colliery in Yima, central China's Henan province on Nov. 5. Forty-five miners trapped underground after a rock blast in a Chinese coal mine were brought to the surface in a rare successful rescue.

A Bolivian mine worker throws sticks of dynamite during a protest rally in La Paz.

Bolivian mine workers cover their ears from the noise from dynamite explosions during a protest rally in La Paz.

An ice cream cart is seen during a protest rally in La Paz.

A miner hurls a stone at a riot police van during a protest called by Bolivia's Workers Central (COB) in demand of a salary rise superior to the 10 percent announced by the government of Bolivian President Evo Morales for the Armed Forces,

A miner gestures as he waits for the retrieving of the corpses of four of his colleagues which remain inside the shafts at "La Preciosa" in Corregimiento San Roque, Sardinata's municipality, department of Norte de Santander, Colombia on January 27, 2011. Twenty-one miners were killed when "La Preciosa" coal mine exploded on Wendsday in Corregimiento San Roque, Sardinata municipality. Dozens of rescuers scrambled Thursday to locate four miners missing and feared dead after the bodies of 17 others were recovered from the coal mine in northeastern Colombia. Six other miners survived with serious injuries after an explosion ripped through La Preciosa coal mine early Wednesday.

A police officer walks his search and rescue dog outside "La Preciosa" in Corregimiento San Roque, Sardinata's municipality, department of Norte de Santander, Colombia on January 27, 2011

People look over the wall of the morgue as relatives claim the bodies of workers who died from a mine explosion in Sardinata, northeastern Colombia, Thursday, Jan. 27, 2011.

Relatives carry the coffin of a miner who died in a mine explosion from the morgue in Sardinata, northeastern Colombia, Thursday Jan. 27, 2011. Twenty-one miners were killed when an explosion, likely caused by a methane gas buildup, rocked La Precisoa underground coal mine early Wednesday. A similar blast killed 32 miners at the mine four years ago.

Relatives of miner Abel Ortega mourn over his coffin at their home in Sardinata, northeastern Colombia, Thursday, Jan. 27, 2011. Ortega was among 21 miners killed when an explosion, likely caused by a methane gas buildup, rocked La Preciosa underground coal mine early Wednesday. A similar blast killed 32 miners at the mine four years ago.