## 6 Discussion
### Exploration for the Sanjiang Tethyan Orogenic Belt  
The Triassic porphyry Cu-(Mo-Au) deposits and Middle Eocene to Early Oligocene porphyry Cu-(Mo-Au) deposits are developed in a magmatic arc within the Garze-Litang suture and the Jinshajiang-Laohuoshan suture zone, with a high \(\epsilon\)Hf(t) region (Figures 3 and 4). Ore-bearing porphyry magmas forming the juvenile lower crust in the Sanjiang Tethyan orogenic belt were derived from asthenospheric mantle wedge metasomatized by theupwelling of the asthenosphere in post-subduction and post-collision settings [17]. The underplating of these magmas at the bottom of the crust inevitably led to the enrichment of the juvenile lower crust in Cu(-Mo-Au) contents (Figure 5) [16]. These results suggest that the juvenile crust plays a major controlling role in the formation of porphyry Cu(-Mo-Au) deposits. Late Triassic I-type granites and related porphyry Cu-Mo deposits (e.g., Xuejiping (No. 10), Pulang (No. 11)) occur in the southern part of the Yidun Arc (Figure 3 and Table 1). The porphyry Cu mineralization in the southern part of the Yidun Arc region most likely originated from the enriched mantle wedge metasomatized by subduction-derived fluids and sediments [55; 174]. The subduction-derived fluids and sediments not only provided the volatile components (H\({}_{2}\)O and Cl) but also controlled the high oxygen fugacity (\(\mathrm{f_{O2}}\)), which makes calc-alkaline magmas favorable for porphyry Cu mineralization [55; 174]. A small area of high \(\varepsilon\)Hf(t) anomaly is distributed in the Yidun Island Arc, mainly located at the southern margin of the Yidun Arc. The area reveals medium acidic volcanic rocks of the Upper Triassic Tumgou Formation interspersed with shallow metamorphic sandy mudstone and carbonate rock stratigraphy [45; 55]. In general, it is an NW-trending compound anticline structure that developed NW-trending faults [55; 175]. The medium acidic (porphyritic) rocks are widely distributed in groups, which can be divided into three rock belts from east to west: the Late Triassic island arc porphyry belt in the eastern north, the Early Triassic genus ophiolitic melange belt in the middle, and the Early and Middle Triassic porphyry belts in the southwest [53]. This area is located in the North-South positive magnetic anomaly zone, and both sides are gentle negative magnetic field areas. Regional chemical prospecting has identified several \"high, large, and complete\" anomalies with high intensity, large lining, large scale, good concentration zoning, and obvious concentration centers, such as Cu, Mo, Pb, Zn, Ag, and Au [53]. The remote sensing image shows a dense intersection of northwest and northeast linear tectonics, forming a fine rhombic network of fracture blocks, with magma rings and hydrothermal rings developed in complex combinations of overlapping, concentric, and offset superposition [53; 175]. Important porphyry Cu(-Mo-Au) deposits such as Pulang (No. 11) ultra-large porphyry, Xuejiping (No. 10), and Hongshan (No. 9) have been evaluated in this area [45; 55; 171; 176], and its periphery, Pushang and Songnuo, have a similar metallogenic background and mineralization characteristics as Pulang. It is a favorable area for finding porphyry Cu(-Mo-Au)  
Figure 5: Model of composite metallogenic systems. deposits, and the prospecting prospect is good [53], which is consistent with the area with a high abnormal value of Hf in this paper. Middle Eocene to Early Oligocene potassic-ultrapotassic intrusive rocks and related porphyry Cu-Mo-Au deposits dominantly extend along the Jinshajiang-Ailaoshan tectonic belt [30; 33]. The potassic-ultrapotassic intrusive rocks are derived from the partial melting of a thickened, potassic, mafic lower crust with minor input from an older igneous felsic component. Partial melts of K-rich mafic lower crust produced high-K calc-alkaline granitic intrusions and porphyry Cu-Mo deposits [94].