Since the early 1960s, Chinese geologists have conducted extensive exploration for diamonds. One of their most important discoveries to date is the Changma kimberlite district in Shandong Province, which encompasses two pipes and eight dikes. The most active mine currently, the Victory No. 1, produces approximately 6,000 ct of diamonds annually, 20% of which are gem quality. The ore is processed locally and the rough stones are given a preliminary sort before they are sent to special factories for cutting. Large, good-quality stones have been recovered at Changma; the largest to date weighs more than 119 ct.