# Genesis and Magmatic Evolution of the Gejiu Complex in Southeastern Yunnan, China
## 4 Results
### Geochemistry
#### 4.2.3 Rare Earth Element (REE) Geochemistry  
The rare earth element geochemistry of the samples is presented in Table 3. The granites exhibited a wide range of total rare earth element (EREE) contents, but there were systematic differences among different rock groups (Figure 6a). Porphyritic granites from the Longchahe and Jiasha areas showed the highest \(\Sigma\)REE values (average = 609.52 ppm) and weak negative Eu anomalies (8 Eu = 0.50-0.75, average = 0.63). Their steep (La/Yb)\({}_{n}\) ratios (33.84-73.51) indicate pronounced fractionation between light (LREEs) and heavy rare earth elements (HEREs),  
Figure 5: Spider diagram of trace elements for (**a**) granite, (**b**) gabbro, (**c**) diorite and monzonite, and (**d**) syenite. suggesting prolonged magmatic evolution dominated by garnet and zircon fractionation [23]. In contrast, alkali feldspar granites from the Falang and Shenxianshui areas exhibited lower \(\Sigma\)REE (average = 249.90 ppm) and moderate Eu anomalies (\(\delta\)Eu = 0.38-0.53, average = 0.45). Their moderately high (La/Yb)\({}_{\text{n}}\) ratios (16.86-40.57) imply continued magmatic differentiation, where plagioclase fractionation altered Eu partitioning between minerals and melt, intensifying the Eu depletion. Equigranular biotite granites from the Laochang and Gaosong areas displayed the lowest \(\Sigma\)REE value (average = 140.07 ppm) and the most pronounced Eu anomalies (\(\delta\)Eu = 0.02-0.1, average = 0.055). Their flat (La/Yb)\({}_{\text{n}}\) ratios (0.69-4.36) reflect limited LREE-HREE fractionation, likely resulting from the late-stage crystallization of plagioclase and K-feldspar, combined with fluid-mediated HREE mobilization during hydrothermal activity. The systematic transition from right-sloping REE patterns (Figure 6a) in porphyritic granites to flattened trends in equigranular types highlights a co-genetic magmatic differentiation sequence. Progressive plagioclase fractionation reduced \(\delta\)Eu values, while residual melts accumulated LREEs, ultimately generating distinct REE signatures across the granite suite. These variations underscore the interplay between mineral-melt partitioning, fluid interactions, and magmatic evolution in shaping REE distribution. The rare earth element (REE) characteristics of gabbros, diorites, monzonites, and syenites are summarized below. All three rock types had high total REE contents (gabbros: \(\Sigma\)REE = 204.00-924.48 ppm, average 625.51 ppm; diorites and monzonites: \(\Sigma\)REE = 69.55-1008.76 ppm, average 610.16 ppm; syenites: \(\Sigma\)REE = 229.32-811.8 ppm, average 552.24 ppm). Strong fractionation between LREEs  
Figure 6: Chondrite-normalized REE patterns [36] for (**a**) granite, (**b**) gabbro, (**c**) diorite and monzonite, and (**d**) syenite. and HREEs was observed in all three rock types (gabbros: (La/Yb)N = 10.87-56.42, average 40.56; intermediate rocks: (La/Yb)N = 4.91-128.84, average 56.24; spernites: (La/Yb)N = 49.85-75.74, average 62.41). Eu anomalies were weakly negative (gabbros: \(\delta\)Eu = 0.60-0.82, average 0.74; intermediate rocks: \(\delta\)Eu = 0.64-1.04, average 0.83; spernites: \(\delta\)Eu = 0.55-0.66, average 0.59). The chondrite-normalized REE distribution patterns of all three rock types displayed right-sloping trends with pronounced LREE enrichment and concavity in intermediate-to-heavy REEs, indicating significant amphibole differentiation (Figure 6b-d). Gabbros exhibited the most pronounced enrichment in total rare earth elements (\(\Sigma\)REE) and light rare earth elements (LREEs), a feature that is likely linked to delayed saturation of rare earth element (REE)-bearing mineral phases (e.g., apatite, zircon) within the gabbroic system, which prolonged the enrichment of REEs in the residual melt and resulted in elevated total REE concentrations (\(\Sigma\)REE).