Abstract Reactive‐surface exposure during basalt carbonation is controlled by the entry and retention of fracture‐transported CO2 solute within adjacent pores, yet these pore‐scale processes remain poorly constrained under reservoir temperature and pressure. Here, real‐basalt microfluidic experiments were conducted at 30°C–60°C and 5–15 MPa. Fluorescence‐based concentration reconstruction and multi‐rate mass transfer model parameters were used to quantify and interpret CO2 solute transport and retention. Results indicate that slow CO2 concentration‐front propagation under low temperature‐pressure conditions favored solute entry into micropores with short characteristic lengths. Increasing temperature and pressure enhanced preferential fracture‐parallel solute transport, causing an unsteady fracture‐wall concentration boundary and promoting solute back‐transfer from micropores, whereas stable retention was mainly maintained in macropores. A favorable thermodynamic window existed before solute retention in micropores was fully suppressed, allowing substantial fracture‐pore solute accumulation. These findings reveal how reservoir temperature‐pressure conditions and fracture‐pore structure jointly control storage‐relevant mineralization potential in basaltic CO2 storage.