DRC has 3.1 million tons out of the 4.8 million tons of cobalt reserves in the copperbelt. Political unrest and obsolete equipment caused a precipitous drop in gold production. In the early 1990s, many large mines closed. Kipushi Mine, a copper, zinc and germanium mine near Lubumbashi shut down in 1993, although feasibility studies indicated potential for producing up to 200,000 tons of copper a year prompting the possibility that it might be reopened. Some mines were shut down even earlier, such as a manganese mine in Kisenge closed in the 1970s after the Angolan Civil War shutdown the Benguela railroad used to export ore. Coal production at the Luena Mine in Shaba Province has been curtailed by ethnic conflicts. Coltan, a mix of columbite and tantalite is common in eastern DRC, which yields tantalum when refined. With soaring demand for tantalum capacitors in cellphones, computers and other electronics, prices of the metal increased rapidly. Artisanal mining, often associated with rebels involved in the Kivu conflict has arisen to meet international demand. DRC also has large diamond deposits, mainly extracted through artisanal mining of alluvium near Mbuji-Mayi in Kasai Province, although many of these reserves are becoming depleted. One third of the DRC's diamonds are smuggled out of the country every year.