新疆西天山莱历斯高尔-3571斑岩铜钼矿田地质地球化学和成矿年代

摘要

新疆西天山斑岩型矿床面临找矿攻坚,重要铜钼矿化研究十分必要.近年在毗邻莱历斯高尔钼矿新发现3571铜矿,构成重要铜钼矿田.研究认为,莱历斯高尔-3571铜钼矿田形成于准噶尔洋壳向南俯冲在哈萨克斯坦-伊犁板块东北缘形成的早石炭世陆缘弧环境中.矿田内强烈角岩化的志留系粉砂泥岩中侵入了花岗闪长斑岩小岩体群,伴随陆缘弧构造-岩浆-热液过程发生了铜钼矿化.铜钼硫化物矿体呈脉状、板状和透镜状产在花岗闪长斑岩体顶部或边部、接触带和附近围岩中.从岩体到围岩,热液蚀变具有从钾硅酸盐化到绢云母化、再到青磐岩化的分带性,铜钼硫化物矿化显示从浸染状、细脉浸染状、细脉网脉状等矿石构造变化.矿石中金属矿物主要为辉钼矿、黄铜矿、磁黄铁矿、斑铜矿、黄铁矿等,斑岩型铜钼矿化特征明显.花岗闪长斑岩高硅、低镁、富铝、富碱、高钾,Rb、Ba、Th等大离子元素富集和Ta、Hf、Zr、Sm、Sr、Y、Yb等高场强元素亏损,微量元素洋中脊花岗岩标准化分布曲线与陆缘弧花岗岩分布型式相似;岩体的平均∑REE为133.84×10-6, ISr为0.707 9～0.710 3,εNd(t)为-0.61～-3.71,明显低于地壳重熔S型花岗岩,初始岩浆属壳幔混源或下地壳源.铜钼硫化物矿石δ34SV-CDT＝2.7‰～4.3‰,206Pb/204Pb＝18.099 7～18.258 8,207Pb/204Pb＝15.605 2～15.624 2,208Pb/204Pb＝38.124 5～38.307 8,成矿金属元素来自上地幔和下地壳,与陆缘弧岩浆直接有关;成矿晚阶段流体δ18OH2O V-SMOW＝-1.33‰～5.46‰,δDH2O V-SMOW＝-81‰～-101‰,属岩浆水混合了大气降水.LA-ICP-MS U-Pb法测得莱历斯高尔钼矿化花岗闪长斑岩形成于(346±1.2) Ma,3571铜矿化花岗闪长斑岩形成于(350±0.65) Ma,成岩成矿时代为早石炭世.新疆西天山莱历斯高尔-3571斑岩型铜钼矿与阿希浅成低温热液型金矿同属西天山海西期陆缘弧构造-岩浆-热液铜钼金成矿系列,具有实际找矿指导意义.%It faces much difficulty to find the porphyry copper deposit in western Tianshan, Xinjiang, and it is essential to research on the Cu-Mo mineralization. The 3571 Cu deposit was recently found next to the Lailisigao'er Mo deposit, and they constitute the Lailisigao'er-3571 Cu-Mo ore-field. It is suggested that the Cu-Mo ore-field occurred in the Early Carboniferous continental margin arc which was formed by the Junggar oceanic crust subduction under the Kazakhstan-Yili Plate. The Siluric silt-mud hornstones were intruded by several small granodiorite porphyry bodies in the ore-field, and Cu-Mo mineralization may have happened during the structure movement, magma activity and hydrothermal processes on the continental margin arc setting.The Cu-Mo sulfide ore-body in shape of veins, tabular and lens occurred in the top or edge parts of the granodiorite porphyry, contact belts and the wall-rock nearby. The hydrothermal alterations changed from K-silication to sericitization, and then propylitization, and the mineralization shows the change in the structure of ores from dissemination to vein-dissemination, and then veins. The major ore minerals include molybdenite,chalcopyrite, pyrrhotine, bornite, and pyrite The mineralization is characterized by a porphyry Cu-Mo type.The granodiorite porphyry is rich in Si, Al, K, Na, Rb, Ba, Th, and poor in Mg, Ta, Hf, Zr, Sm, Sr, Y,and Yb, and the trace element character is similar to that of continental margin granites. The average ∑REE of the porphyry is 133. 84× 10-6 and lower than that of S-type granites. Isr is from 0. 7079 to 0. 7103, εNd (t) is from-0. 61 to -3. 71, and the magma was from the mantle-crust mixing or the lower crust. The ore δ34Sv·CDT is from 2. 7‰ to 4. 3‰, 206Pb/204 Pb from 18. 0997 to 18. 2588, 207Pb/204 Pb from 15. 6052 to 15. 6242, 208Pb/204Pb from 38. 1245 to 38. 3078, and the metal was from the upper mantle and lower crust directely related to the continental margin arc magma. The δ18 OH2Ov-SMOW of the late stage ore-forming fluid is from -1.33‰ to 5. 46‰, δDH2ov-SOW from -81‰ to -101‰, and the water in the ore-forming fluid is mainly the magma water with meteoric water mixed. The porphyry was dated as 346 ± 1. 2 Ma in the Lailisigao'er Mo ore-district and 350±0. 65 Ma in the 3571 Cu ore-district by LA-ICP-MS U-Ph method. The Cu-Mo mineralization occurred in the Early Carboniferous Period. The Lailisigao'er-3571 Cu-Mo ore-field should have been in the same metallogenic series with the Axi Au ore-field, and this is very important for the exploration in western Tianshan, Xinjiang.