西藏弄如日金矿床花岗斑岩年代学与岩石成因  

Geochronology and petrogenesis of ore-hosting granitic porphyry in the Nongruri gold deposit,Tibet

作　　者：钟婉婷[1,2] 多吉 李明礼 黄勇[2] 黄瀚霄[2] 李光明[2] 张林奎[2] 董随亮[2] ZHONG WanTing;DU0 Ji;LI MingLi;HUANG Yong;HUANG HanXiao;LI GuangMing;ZHANG LinKui;DONG SuiLiang(College of Earth Science, Chengdu University of Technology, Chengdu 610059 , China;Chengdu Center, China Geological Survey, Chengdu 610081 , China;Tibet Bureau of Geology and Mineral Exploration and Development, Lhasa 850000, China;Central Laboratory , Tibet Bureau of Geology and Mineral Exploration and Development, Lhasa 850000, China)

机构地区：[1]成都理工大学地球科学学院,成都610059 [2]中国地质调查局成都地质调查中心,成都610081 [3]西藏地质矿产勘查开发局,拉萨850000 [4]西藏地质矿产勘查开发局中心实验室,拉萨850000

出　　处：《岩石学报》2019年第3期913-933,共21页Acta Petrologica Sinica

基　　金：国家重点研发计划(2016YFC0600308;2018YFC0604103);国土资源大调查项目(DD20160346;DD20160015);国土资源部公益性行业科研专项(201211035);西藏自治区重大科技项目(XZ201801-GB-02);西藏自治区重大科技专项(2015XZ01G50);西藏自治区矿产资源勘查专项([2018]09号)联合资助

摘　　要：弄如日矿区发育中新世浅成花岗闪长斑岩和二长花岗斑岩两类岩体,本文对这两类花岗斑岩体进行了LA-ICPMS锆石U-Pb定年和系统的岩体地质、岩石学和元素地球化学研究。结果显示,花岗闪长斑岩和二长花岗斑岩近于同期侵入,前者为未分异或弱分异花岗岩,后者为高分异花岗岩。花岗闪长斑岩和二长花岗斑岩的侵位年龄测试结果表明,前者形成时代为20. 3±0. 8Ma,后者形成于20. 20±0. 41Ma～20. 51±0. 52Ma。花岗闪长斑岩具有低硅、低钾、低碱、高铝的特点,SiO_2介于63. 37%～66. 78%之间,Al2O3变化于15. 14%～16. 04%,Na_2O+K_2O=4. 46%～5. 33%,A/CNK=1. 13～1. 26,稀土总量高,重稀土和Y含量低,具有埃达克质岩石的地球化学特点,主体为Ⅰ型花岗岩。二长花岗斑岩具有高硅、高钾、高碱、低铝、稀土总量低的特点,SiO_2=70. 46%～77. 17%,Al_2O_3=12. 22%～15. 06%,Na_2O+K_2O=7. 14%～7. 98%,A/CNK=1. 03～1. 21,稀土总量低,为Ⅰ型花岗岩。两种岩石稀土元素分配典线呈右倾型,均富集大离子亲石元素(Rb、Ba等),亏损高场强元素(Nb、Ta、Zr);此外,花岗闪长斑岩轻重稀土分馏明显,而二长花岗斑岩中稀土和重稀土分馏不明显。花岗闪长斑岩形成于弄如日矿区加厚下地壳中变基性岩的部分熔融,变基性岩很可能是榴辉岩(可能含有角闪石),部分熔融后的残留物以石榴石为主,含金红石。二长花岗斑岩可能是由花岗闪长斑岩浆通过分离结晶衍生而来,分离结晶的矿物包括斜长石、黑云母、钾长石、钛铁矿、榍石、磷灰石等。综合研究表明,弄如日金矿成矿时代略晚于花岗闪长斑岩侵位,成矿与花岗闪长斑岩及其分异的二长花岗斑岩关系密切。花岗闪长斑岩及二长花岗斑岩的侵位时代及成因研究,对揭示弄如日金矿矿床成因有重要意义,也为区域寻找该类矿床指明了方向。In Nongruri mineral district, there occurred Miocene hypabyssal granodiorite-porphyry and monzogranite porphyry intrusions. Base on the study of LA-ICPMS zircon U-Pb dating, field geological features, petrography and geochemical characteristics, we found these two kinds of intrusions may be formed in a simultaneous magmatic activity. The granodiorite porphyry is undifferentiated or weakly differentiated, while the monzogranite porphyry is strongly differentiated. The crystallization ages of the granodiorite and monzogranite porphyry intrusions are ca. 20.3Ma and ca. 20.2~20.5Ma, respectively. The granodiorite porphyry is characterized by relatively low silicon (SiO2=63.37%~66.78%), potassium, alkali (Na2O+K2O=4.46%~5.33%) and aluminum (Al2O3=15.14%~16.04%) contents, with a high ∑REE and HREE abundances and low Y contents. Thus, this kind of intrusions has an adakitic and I-type affinity. Similar to some I-type granites, monzogranite porphyry has high silicon (SiO2=70.46%~77.17%), potassium, alkali (Na2O+K2O=7.14%~7.98%) and aluminum (Al2O=12.22%~15.06%) contents, with a relatively low Y and ∑REE abundances. Both of them are rich in large ion lithophile elements (Rb, Ba, etc.) and depleted in high field strength elements (Nb, Ta and Zr), with high La/Yb ratios. The granodiorite porphyry show obviously fractionated REE patterns, while the REE patterns of monzogranite porphyry is different from those of them. The granodiorite porphyry is formed by the melting of the metal-mafic rocks with garnets and a small amount of rutiles in the residue from thicken lower crust, and these metal-mafic rocks might be eclogites and probably with some hornblende components. The monzogranite porphyry may be generated by fractional crystallization of the magma of the granodiorite porphyry, and mineral assemblages formed during this process include plagioclase, biotite, K-feldspar, ilmenite, sphene and apatite. Besides, metallogenic epoch of the gold in this region is latter than the emplacement time of granodiorite porphyry, and t

关 键 词：花岗闪长斑岩 二长花岗斑岩 锆石U-PB定年 岩石成因 弄如日金矿 西藏 

分 类 号：P588.13[天文地球—岩石学] P597.3[天文地球—地质学]