The Bureau of Mines identified and evaluated major sources of quartz dust during overburden drilling at a surface coal mine. The relative contribution of each source to the total dust hazard was estimated, using personal gravimetric and instantaneous dust-sampling devices. No attempt was made to determine actual dust generation rates. The major sources of dust at the drill rig during dry drilling operations were the collector dump, drill shroud leakage, and drill stem seal leakage. These sources contributed 90 pct of the respirable dust and 89 pct of the respirable quartz dust generated during drilling. The collector dump cycle (21.6 pct of total drilling time) accounted for 38 pct of the respirable dust and 41 pct of the respirable quartz dust, with peak dust concentrations reaching 68 mg/m3. Shroud and drill stem leakage contributed 28 and 24 pct of the respirable dust and 32 and 16 pct of the respirable quartz dust, respectively. A dragline and second drill rig contributed the remaining 10 pct of dust and 11 pct of quartz dust. Gravimetric dust samples collected inside the drill cab and outside, near the cab door, averaged 1.65 and 1.43 Mg/m3, respectively, with 6 pct respirable quartz.