As the yellowish mud swirls away in the waters of Thailand's Sai Buri river, Sunisa Srisuwanno lifts her wooden pan with a cluster of gleaming specks caught in the centre. "That's 100 baht," she said, pointing to grains worth about $3.30 after little more than 15 minutes work with her gold panning partner, Boonsom Aeamprasert.