Geochemical Characteristics and Geological Significance of the Monzonitic Porphyry in the Laojinshan Section of the Daping Gold Deposit, Yuanyang, Yunnan Province

云南元阳大坪金矿石哀牢山成矿带重要组成部分之一，大坪金矿老金山矿段岩浆活动较为复杂，矿区内出露的二长斑岩与金矿体的关系密切，其岩石学、地球化学特征对老金山矿段深部找矿有重要指示意义。本文选取二长斑岩进行岩石学、地球化学研究。研究表明岩体中SiO2含量为65.23%~72.61%；岩体呈现高钾钙碱性特征(K2O/Na2O = 0.83~1.82，全碱8.22%~10.27%)，富集大离子亲石元素(K, Rb, Sr, Ba)并亏损高场强元素(Nb、Ta、Ti)，轻稀土显著富集(LREE/HREE = 3.7~11.0)，且具轻微Eu负异常(δEu = 0.58~0.81)。该岩体形成于喜马拉雅期印度–欧亚板块碰撞后的陆内伸展构造背景，属典型的后碰撞高钾钙碱性花岗岩。岩浆来源于壳–幔混合作用与成矿流体源区相同，二长斑岩与金矿在时空分布和成因上密切相关。The Daping Gold Deposit in Yuanyang, Yunnan Province, is an important component of the Ailaoshan metallogenic belt. The magmatic activity in the Laojinshan section of the Daping Gold Deposit is relatively complex, and the exposed monzonitic porphyry in the mining area is closely related to the gold ore bodies. The petrological and geochemical characteristics of the porphyry provide significant indications for deep prospecting in the Laojinshan section. This study focuses on the petrology and geochemistry of the monzonitic porphyry. Research shows that the SiO2 content of the rock ranges from 65.23% to 72.61%. The rock exhibits high-potassium calc-alkaline characteristics (K2O/Na2O = 0.83~1.82, total alkali content = 8.22%~10.27%), with enrichment in large-ion lithophile elements (K, Rb, Sr, Ba) and depletion in high-field-strength elements (Nb, Ta, Ti). The light rare earth elements are significantly enriched (LREE/HREE = 3.7~11.0), and there is a slight negative Eu anomaly (δEu = 0.58~0.81). The rock formed in a post-collisional intracontinental extensional tectonic setting following the collision of the Indian and Eurasian plates during the Himalayan period, and it is a typical post-collisional high-potassium calc-alkaline granite. The magma originated from crust-mantle mixing, sharing the same source region as the ore-forming fluids. The monzonitic porphyry is closely related to the gold deposit in terms of spatial-temporal distribution and genesis.