The Yanshanian Granites and Associated Mo-Polymetallic Mineralization in the Xiangcheng-Luoji Area of the Sanjiang-Yangtze Conjunction Zone in Southwest China

The Xiangcheng‐Luoji area is located in the conjunction of the southern part of the “Sanjiang” mineralization belt and the west margin of Yangtze craton. The geological studies were carried out to know the Indosinian large porphyry Cu polymetallic deposits. Recent studies revealed that the area existed in the superposition of Late Yanshanian acidic intrusive rock belt and developed Mo‐Cu polymetallic mineralization where promising exploration results have been achieved. Through the systematic study of geochronology, formation age of the Renlin Mo‐minieralization monzogranite is 81.7±1.1 Ma. Re‐Os dating results concentrate on 82.34±1.2–88.27±1.23 Ma for the model ages of molbdenite of Tongchanggou Mo deposits, average age is 85 ± 2 Ma where seven data points constitute a good isochron which shows that they were the same period products of mineralization. Geochemical features shown that the rocks have a high content of SiO₂ (66.59–77.36wt%), alkaline‐rich (K₂O=2.68–6.08wt%; Na₂O=0.50–4.91wt%; K₂O/Na₂O ratios are 0.71–5.56, where average ratio of 1.89) and have aluminum‐rich features (Al₂O₃10.38–15.15wt%) with σ values less than 3.3. Which indicate that they belong to the high‐K calc‐alkali to shoshonite series. Geochemistry of Yanshanian intrusions shows that rocks are enrich in LREE with obvious negative δEu anomalies, enrichment of trace elements like, LILE elements (Rb, Th, Ba) with a relative loss of Ba, and loss of high field strength elements (Nb, Ta, P, Ti) and HREE elements. The granite genetic classification diagram shows that the granites belong to A‐type granite and formatted in syn‐collision tectonic environment. Meanwhile, the Yanshanian granites also inherited the characteristics of island arc environment which formed in the process of crustal melting caused by upwelling of asthenospheric substances in the extensional tectonic background. The process of partial melting existed substances from the deep (lower crust or upper mantle) which have been added. In the Xiangcheng‐Luoji area, monzogranite and granodiorite porphyry bodies are widely developed Mo polymetallic mineralization, the deep porphyry mineralization have great potential for geological prospecting.