皖南休宁县里东坑似斑状花岗闪长岩成岩成矿特征分析

Rock-forming and ore-forming characteristics of the Lidongkeng porphyritic granodiorite in Xiuning County, south Anhui Province

通过野外考察、岩石地球化学、锆石u—Pb测年和Re—Os同位素测试等手段．对里东坑似斑状花岗闪长岩及钼矿床的成因类型、成岩机制以及与壳幔作用的关系进行了分析讨论。测试结果显示：赋矿似斑状花岗闪长岩的LA—ICP—MS锆石u—Pb年龄为（153．01±0．90）Ma（MSWD=1．14），辉钼矿Re—Os模式年龄为（144．9±1．9）Ma（MSWD=2．0），成岩与成矿均发生于燕山早期。主微量元素分析结果显示：岩石富si和K，贫Mg、Ca、P等元素，具有高Rb、低Yb＋Ta的特征，稀土元素具有轻微负Eu异常，轻稀土富集；辉钼矿样品Re含量主要介于24．17～27．92μg·g^-1。说明赋矿似斑状花岗闪长岩具有I型花岗岩的特征．并经历了壳幔混合作用。判断里东坑似斑状花岗闪长岩为碰撞花岗岩类，形成于挤压背景．具备良好的成矿条件。

The Lidongkeng molybdenum deposit is located in Xiuning County, south Anhui Province. Accompanied by detailed geological description, this paper presents new ages and bulk-rock geochemistry for the Lidongkeng deposit. The LA-MC-ICP-MS zircon U-Pb age of 153.01 ± 0.90 Ma （MSWD = 1.14） for the ore-bearing porphyritic granodiorite and the Re-Os model age of 144.9±1.9 Ma （MSWD =2.0） for the molybdenite suggest that both of the ore body and the porphyry occurred during the Early Yanshanian period. According to the analyses of elements, the rock is rich in Si and K but poor in Mg, Ca and P and is characterized by high Rb and low Yb ＋Ta values, suggesting a collision environment. The porphyry is geochemically characterized by slight negative Eu anomaly. The porphyry shows I-type granite affinity. The molybdenite samples have Re content from 24.17 to 27.92/μg.g^-1, which implies that the molybdenum in the Lidongkeng deposit might have been derived from the crust with partial mixture of mantle materials.