we got a tip about a mine in a place called nyabibwe, the very first in eastern congo to be certified as conflict free. we stopped within sight of it but weren't able to get close. until last year nyabibwe was part of a project piloted by companies like philips, intel, and motorola that was held up as proof minerals could be traced from mine to export. but a source told us that untagged minerals had been brough there illegally, mixed in with the tagged minerals, and passed off as conflict-free. to find out more, we headed to a remote mining village called numbi - a 6 hour drive even deeper into the mountains. >> we're just arriving in numbi. it's one of the largest mines in the area and the most recent one to be certified. >> it's been four years since u.n. forces and the congolese army cleared this area of armed groups, but it's only recently been designated "conflict free". in numbi, we met ombeni chikala, a supervisor at a local tin mine. for 15 years, he's made his living as a miner starting as a digger and working his way up. >> on the day we visited ombeni's mine site, agents lo