Mine waste remains a persistent challenge for the minerals industry, posing significant environmental concerns if not properly managed. The 1996 Marcopper mining disaster in Marinduque, Philippines, left a legacy of mine tailings that continue to threaten local ecosystems and communities. This study investigates the valorization and stabilization of Marcopper river sediments contaminated with mine tailings using a combined geopolymerization and cement hydration approach. Hybrid mortar samples were prepared with 7.5%, 15%, 22.5%, and 30% mine tailings by weight, incorporating potassium hydroxide (KOH) at 1M and 3M concentrations as alkaline activators, along with ordinary Portland cement (OPC). The mechanical properties of the hybrid geopolymer-cement mortars were evaluated through unconfined compressive strength tests, while their crystalline structure, phase composition, surface morphology, and chemical bonding characteristics were also analyzed. Static leaching tests were conducted to assess the mobility of heavy metals within the geopolymer matrix. Compressive strengths ranged from 24.22 MPa to 53.99 MPa, satisfying ASTM C150 requirements. In addition, leaching results confirmed effective heavy metal encapsulation and immobilization, demonstrating the potential of this method for mitigating environmental risks associated with mine tailings.