South Korea’s government-run Korea Development Institute (KDI) has said mineral trades between North Korea and China remain a “cash cow” for Pyongyang despite tough sanctions, in a report released on Tuesday.

Trade flows of mineral resources accounted for 53.6% of the North’s total trade volume to China in the first half of 2016, KDI reported, based on statistics from the Korea International Trade Association (KITA).

Nam Jin-wook, a senior research associate at the Department of North Korean Economy at KDI, categorized the bilateral mineral trades into four different types, based on the proportion of the North’s total revenue from exports in general