An integrated classification framework for open pit–underground mining transitions and interactions

Open pit-to-underground (OP–UG) transitions extend mine life, but create coupled systems requiring coordinated surface and underground decisions. The literature remains fragmented, with inconsistent and uneven reporting that limits cross-case comparison. This study presents a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-guided systematic literature review of OP-UG mining configurations published from 1990 to 2025. It synthesises classification schemes, strategic and tactical decision variables, key performance indicators (KPIs), interface-related risks and controls from documented real-world cases. An integrated framework classifies OP-UG scenarios through three dimensions: temporal configuration (sequential, transitional/handover or simultaneous), interaction geometry (vertical, lateral or hybrid), and mining domain or method. Cross-case synthesis identifies recurring decision drivers and major evidence gaps, including limited post-implementation KPI reporting, scarce documentation of operational triggers, and insufficient long-term subsidence and crown-pillar data. Evidence for the reverse underground-to-open-pit configurations remains limited, highlighting a priority for future research.