内蒙古西拉木伦成矿带库里吐钼(铜)矿区二长花岗岩地球化学、构造环境及含矿性分析

Geochemistries,tectonic setting and mineralization potentiality of the ore-bearing monzogranite in the Kulitu molybdenum(copper)deposit of Xar moron metallogetic belt,Inner Mongolia.

西拉木伦成矿带库里吐钼(铜)矿大地构造位于华北板块北缘造山带中段。通过对矿区含矿岩体的主量、微量元素及同位素组成进行测试和研究,表明矿区含矿岩石主要为二长花岗岩,其SiO_2含量为70.60%～72.95%,Na_2O和K_2O的含量分别为3.98%～4.40%和4.57%～5.49%,里特曼指数σ介于2.9～3.1之间,均小于3.3,指示其属钙碱性岩石系列;微量元素测试结果表明,二长花岗岩重稀土元素(HREE)分馏轻微[(Gd/Yb)_N=1.05～1.86],轻稀土元素有一定分馏[(La/Sm)_N =4.27～6.41],轻重稀土元素之间分馏较强[(La/Yb)_N=8.03～19.27],具有较明显的Eu负异常(δEu=0.65～0.77);在原始地幔标准化的微量元素蛛网图解上,都显示出Nb、Ta、Ti、P、Ba等元素亏损,Rb、Th、U、K等元素富集的特征;同位素测试结果表明,岩石初始^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb和^(208)Pb/^(204)Pb组成变化范围分别为18.3281～18.9980、15.5902～15.6644和37.7778～38.4129;(^(87)Sr/^(86)Sr)_i及ε_(Nd)(t)变化范围分别为O.706113～0.706783和-0.90～+2.04。通过研究该区含矿岩石地球化学特征结合区域构造背景,本文初步认为该区二长花岗质岩浆来源于新生陆壳,形成于中朝板块和西伯利亚板块间的后碰撞阶段;同时本文还对含矿二长花岗岩含矿性进行了初步分析,为矿床研究和进一步找矿预测工作提供依据。

Kulitu molybdenum （copper） deposit, belonged to Xar moron metallogetic belt, was located along the northern marginal orogen of Northern China Block. Based on the study of the ore-bearing rock, it shows that the host rock is mainly monzogranite. Geochemical results indicate that the SiO2 （wt. % ） are in 70.60% - 72.95%, Na2O and K2O range from 3.98% to 4.40% and 4.57% to 5.49%, respectively. The Rittmann index （σ） of monzogranite vary from 2.9 to 3. 1, which means the calc-alkaline characteristic. The trace elements analysis demonstrate intense fractionation between LREE and HREE [ （La/Yb）M = 8.03 - 19.27] with insignificant HREE fractionation [ （Gd/Yb） N = 1.05 - 1.86 ] and negative Eu （ δEu = 0.65 - 0.77 ） anomalies. The primitive mantle-normalized spidergrams are characterized by Nb, Ta, Ti, P, Ba depletion and Rb, Th, U, K enrichment. Sr-Nd-Pb isotopic compositions of monzogranite show that the initial Sr values change from 0. 706113 to 0.706783, εNd （t） values are in -0.90 ～ ＋ 2.04 and the initial ratios of ^206Pb/^204Pb, ^207Pb/^204Pb and ^208Pb/^204Pb vary from 18. 3281 to 18. 9980, 15. 5902 to15. 6644 and 37. 7778 to 38. 4129, respectively. The geochemical results indicate that the monzogranite was crust-derived and might form during the postcollision stage between Sino-Korean Block and Siberian Block. Moreover, mineralization potentiality of monzogranite has also been analyzed to offer a theoretic basis for the study and forecasting work of the mineral resources.