Abstract: To address the problems of complex and variable lithology and difficult blasting fragmenta⁃ tion control at the Mirador Open-pit Copper Mine in Ecuador，field tests on delay time optimization were carried out for four typical rock masses based on rock mass blastability classification，and reasonable delay time parameters for different lithological zones were determined. The results show that according to the RMR classification system，granodiorite has a blastability grade of Class II，granodiorite porphyry and quartz sandstone are Class III，and breccia is Class IV. Granodiorite exhibits a weak response to delay ad⁃ justment，and shortening the inter hole delay time of granodiorite porphyry leads to a poorer fragmentation effect; therefore，the conventional scheme of 42 ms + 65 ms is recommended for both rock types. After adopting the“dual hole simultaneous initiation”scheme for quartz sandstone，the shape of large boulders changes from“pie type”to regular square，and the fragmentation uniformity is significantly improved. For breccia，using 25 ms + 42 ms combined with 600 ms in hole detonators completely eliminates boulders larger than 500 mm，and the fragment size is mainly concentrated in the range of 150~500 mm. The delay parameters determined by the tests can effectively improve the blasting fragmentation effect in different lith⁃ ological zones，providing a theoretical basis and engineering guidance for refined blasting design in mines with complex lithology.

Key words: open-pit mine, bench blasting, blastability classification, delay time