Located in the Sangjiang metallogenic belt, Laochang is one of the important noble metal and nonferrous metal ore-forming belts of southwestern China, whose geotectonic location is very unique with rich ore resources and lots of metal deposits. Laochang is one of the areas with significant breakthrough for new discovery of great thick porphyry molybdenum ore bodies in the depth since 2008. Geochemical characteristics of the concealed granite porphyry in the Laochang ore deposit were studied in this paper. Tectonic setting and genetic mechanism of the granite porphyry were investigated by using various discrimination diagrams. Petrologic research indicates that granite porphyry of this area is light gray and grayish white in color and has porphyritic texture and massive structure. Phenocrysts are mainly composed of orthoclase, quartz, plagioclase and biotite, whereas the matrixes are composed of equiaxial fine-grained orthoclase and quartz. It is concluded that chemical compositions of the concealed granite porphyry in Laochang are characterized by the similarity to China's granite porphyry in average SiO₂ (68.09%～73.48%), alkali enrichment (Na₂O+K₂O=7.73%～8.51%), K enrichment (K₂O/Na₂O=1.85～25.8), LREE enrichment, HREE depletion, (La/Yb)_N varying from 12.01 to 24.85, weak negative Eu anomaly (δEu varying from 0.79 to 0.99), and smoothly right-declined REE distribution pattern. Thus, the granite porphyry belongs to acid, aluminum medium-saturated, High-K calc-alkalic series of magmatic rock. A comprehensive study of geochemical characteristics by using discrimination diagrams and zircon features of concealed granite porphyry in Laochang indicates that the granite body was mainly derived from crust source mixed with minor mantle materials and formed at the main collision stage of the Cenozoic collisional oregeny of the Tibetan Plateau under the regional compressional environment. Zircon SHRIMP U-Pb dating of the Laochang granite porphyry yielded 44.6±1.1 Ma. The chronologic age shows that the granite porphyry was formed in Eocene. The petrogenesis and mineralization of the Laochang granite porphyry took place during the main collisional stage of the Cenozoic intracontinental collision orogeny, and this is consistent well with metallogenic peak period of porphyry type deposits in the Sangjiang region. Based on the results from Sr-Yb classification of granite-porphyry diagram, R₁-R₂ discriminating tectonic setting of granite-porphyry diagram and regional tectonic development, it is suggested that the Laochang granite porphyry was formed in the collisional setting. The magma, which was derived from partial melting of deep mantle initiated by collision, experienced upwelling through the core part of early developed rift, and became a major driving force for structural, magmatic and thermal events. The input of mantle material into the crust induced partial melting of the lower crust to form a potassium-rich ore-bearing magma with mixed sources of the crust and the mantle.