harder than it sounds
From Reuters' Katrina Manson:
"Suffering caused us to know how to do this work -- there was nothing else I could find to do," said mother-of-eight Marie as she crouched in a cramped mud hut near a mining village emptying a plastic bag of red and green stones, among them emeralds and tourmalines worth $3,500 (2,242 pounds).
...Tracking bulky bags is hard enough, let alone much more valuable and portable gold, which is easily moved unseen.
A U.N. panel of experts is due to recommend Congo's mineral customers take greater responsibility for the chain of sale, in line with guidelines under development from the Organisation for Economic Co-operation and Development, but it may not be enough.
"It is currently impossible to trace all gold exports effectively," Nicholas Garrett, director of RCS, told Reuters. "The state is weak and underpaid state services are often implicated in gold smuggling along porous borders."