*This is an abstract only. No full paper is available for this abstract.* Reverse circulation is used widely in open cut mines for ore delineation and grade control in various deposit types. It has also been employed for underground grade control at Sunrise Dam mine (Clark and Carswell, 2014), to improve sampling quality and support in a high-nugget gold deposit. The Mount Isa copper deposit is a massive sediment-hosted orebody (Davis, 2004; Perkins, 1997), which is nearing life-of-mine (LOM) around 2023. Subsequently a paradigm shift is required in Mount Isa copper operations' (MICO) approach to ore delineation and mitigating grade risk within the LOM window as copper grades decline and ore occurrence becomes increasingly disseminated towards the halo of the orebodies.Underground reverse circulation (RC) drilling is being trialled at MICO to assist in the de-risking of the production profile. The potential application of RC in grade-control means that the diamond drill fleet can decide to target specific high-value poorly delineated areas of mineralisation near the mine to extend LOM. MICO has previously not had the resources to investigate these potential ore sources. There are several other subsequent advantages of RC, including using it to delineate the 500 Orebody, which is within a highly leached and weathered zone in which diamond core recovery is poor.The trial program consisted of 4800 m in total, which twinned pre-existing diamond drill holes across the underground environment; the aim of which was to compare samples from RC and diamond results in order to test sampling methodology and drilling practices. The early stages of the trial have been a steep learning curve; operationally, the most significant of these was the limited information available on the change management process of implementing reverse circulation in an established underground mine.Technical staff at MICO raised concerns around workflow, site availability and preparation, dust suppression, hole deviation, reactive ground drilling and sampling practices and quality assurance / quality control. This poster outlines the learnings from implementing reverse circulation drilling at MICO.CITATION:Taylor, D and Ila'Ava, P, 2017. Underground reverse circulation drilling trial at Mount Isa copper operation, in Proceedings Tenth International Mining Geology Conference 2017, pp 459-460 (The Australasian Institute of Mining and Metallurgy: Melbourne).