The Gaofeng mining area in the Dachang ore field, Guangxi, is an important tin-polymetallic ore concentration area in China. However, the age, genesis, and mineralization potential of its deep magmatic activity remain unclear. This paper focuses on the concealed granite porphyry in the deep part of the Gaofeng mining area and conducts monazite U-Pb dating and trace element analysis. Combined with whole-rock geochemical data, it systematically discusses its petrogenesis and mineralization indicators. LA-ICP-MS monazite dating yields a weighted average age of 85.86-86.38 Ma, accurately defining for the first time a Late Cretaceous magmatic event later than the Tongkeng mining area granite porphyry (~91 Ma), revealing that the Dachang ore field has at least four periods of magmatic activity. Geochemical analysis indicates that this granite porphyry belongs to highly differentiated, peraluminous crustal A-type granite, formed in a post-collision extensional environment. The monazite in the rock mass exhibits a high Th/U ratio and strong Eu negative anomaly, consistent with the whole-rock geochemical characteristics, collectively indicating strong plagioclase fractional crystallization. Although this dike intrusion occurred later than the main mineralization period (~92 Ma) and is not a direct ore-forming parent rock, its significantly high Sn content (average 48 ×10-6) suggests that it originated from a deep parent magma chamber that underwent tin pre-enrichment. Therefore, this period of magmatic activity is a direct manifestation of deep tin enrichment events, implying the potential presence of related concealed tin ore bodies in the deep part of the Gaofeng mining area. This study further refines the regional metallogenic model and provides key evidence for guiding deep prospecting.