龙首山芨岭地区中粗粒花岗岩地质特征及其地质意义

Geological Characteristics and Significance of Middle-coarse Grain Granites in Jiling Area of Longshoushan

为了探讨芨岭地区的肉红色中粗粒花岗岩与铀成矿的关系,通对龙首山芨岭地区的肉红色中粗粒花岗岩进行锆石U-Pb同位素测年,测得其侵位于426.4±2.0 Ma,形成时代为晚奥陶世。岩石地球化学数据分析表明,主量元素中SiO_(2)、Al_(2)O_(3)、Na_(2)O和CaO含量偏高,Fe_(2)O_(3)和K_(2)O含量较低;微量元素中富集大离子亲石元素,亏损高场强元素;稀土元素配分曲线呈右倾型,轻、重稀土元素分馏较为明显,岩石为准铝质、碱性I型花岗岩。通过构造环境研究表明早古生代祁连山-龙首山造山作用进入非造山板内活动阶段。结合勘查成果查明,中粗粒花岗岩亦为芨岭地区含矿岩性之一,其与中粗粒似斑状花岗岩、闪长岩的侵入界线是成矿有利部位之一。

Zircon U-Pb isotopic dating of the middle-coarse-grained flesh-red granites in Jiling area ofLongshoushan showed that the granites were emplaced at 426.4±2.0Ma and formed in the Late Ordovician.Geochemical data analysis show that the granite are relatively high in the contents of SiO_(2),Al_(2)O_(3),Na_(2)O andCa O,relatively low in the contents of Fe_(2)O_(3)and K_(2)O,enriched in large ion lithophile elements and depletedin high field strength elements.The middle-coarse-grain granites bears a right-leaning REE pattern,andobvious fractionation of l REE and HREE,and falls into the quasi-aluminum and alkaline I-type.The study oftectonic environment indicated that the Early Paleozoic Qilian Mountain-Longshoushan orogeny entered thestage of non-orogenic plate activity.Combined with the exploration results,the middle-coarse-grain granitewas believed one of the ore-bearing rocks in Jiling area,and the intrusive boundary of the middle-coarse-grain porphyritic granite and diorite is the favorable for the ore-formation.