摘要
西藏北姆朗矿区斑岩体具备斑岩型铜矿成矿有利地质条件,结合作者主持本地区野外矿产勘查工作的新认识和新发现,展开该地区成岩成矿地质背景及成因等问题研究。本文对北姆朗矿区内与成矿密切相关的斑岩体开展了详细的岩相学和岩石地球化学研究,结果表明:矿区斑岩体主要由中新世形成的斑状黑云母二长花岗岩、中细粒黑云母二长花岗岩和二长花岗斑岩组成。地球化学组成上,这套岩石具高硅(均值依次为68.60%→66.62%→70.30%)、高钾(均值依次为4.08%→3.83%→4.22%)、富碱(均值依次为8.16%→7.73%→8.32%)、贫MgO(均值依次为1.00%→1.62%→0.82%)、准铝质—过铝质,高钾钙碱性—钾玄岩系列I型花岗岩地化特征;δEu缺乏显著负异常(均值依次为0.85→0.80→0.80);微量元素表现出富集大离子亲石元素(Rb、Th、U、K、Sr、Hf)和亏损高场强元素(Nb、Ta、P、Ti)的特征,仅二长花岗斑岩相对亏损Sr;同时,具有高Sr、低Yb、低Y、高Sr/Y比,具有典型埃达克岩的特征。综合分析表明,岩石形成于印度与欧亚大陆碰撞后的伸展构造背景,岩浆源区可能为镁铁质的新生加厚下地壳部分熔融岩浆与深俯冲而进入拉萨地块之下的印度古老地壳组分经混合作用的产物。同时,北姆朗矿区找矿勘查的重要目标地质体是二长花岗斑岩和中细粒黑云母二长花岗岩,这一认识对北姆朗矿区及外围找矿提供了重要勘查启示。
The porphyry pluton has favorable geological conditions for porphyry copper mineralization in Beimulang ore district,in Tibet.Therefore,combined with the author’s new understanding and new discoveries in the field works,it is of great geological significances to study the geological backgrounds and genesis of diagenesis and mineralization in this area.In this paper,the author has carried out a detailed research of petrography and petrogeochemical,for porphyry pluton closely related to mineralizatin in Beimulang ore dirsrict,the results show that the porphyry pluton is mainly composed of porphyry biotite monzogranite,medium fine grained biotite monzogranite and monzogranite porphyry,namely the formation age of Miocene.Chemically,analyses show that these rocks have a characteristics of high SiO2(the average value in turn is 68.60%→66.62%→70.30%),high K2 O(the average value in turn is 4.08%→3.83%→4.22%),rich K2 O+Na2 O(the average value in turn is 8.16%→7.73%→8.32%),depleted MgO(the average value in turn is 1.00%→1.62%→0.82%),metaluminum-peraluminous,Geochemical characteristics of I-type granites of high-K calcalkaline and shoshonite.and show indistinct Eu negative anomalies(the average value in turn is 0.85→0.80→0.80).Enriched in such as Rb、Th、U、K、Sr、Hf and depleted in such as Nb、Ta、P、Ti,Only relatively depleted in Sr for monzonitic granite porphyry.Specifically,they show typical adakitic signatures:high Sr,low Yb and Y,contents with high Sr/Y ratios,and is characterized with properties of the adakitic rocks.However,intergrated petrology and elemental compositions indicate that the magma sources may have produced by mixing between magmas from partial melting of the thickened mafic juvenile crust and components from the subducted ancient Indian continental crust that they have formed in post-collisional extension setting of India-Asia contional collision orogenic belt.At the same time,the important target geological bodies of prospecting and exploration are monzonitic granite porphyry and medium fine grained biotite monzonitic granite,which provides important exploration enlightenment for the prospecting in Beimulang Ore District and its periphery.
作者
赵亚云
刘远超
次琼
刘晓峰
龚福志
李军
ZHAO Ya-yun;LIU Yuan-chao;CI Qiong;LIU Xiao-feng;GONG Fu-zhi;LI Jun(NO.2 Geological Team,Tibet Bureau of Geology and Mineral Exploration and Development,Lhasa 850003,China)
出处
《甘肃地质》
2021年第4期38-55,共18页
Gansu Geology
基金
中国地质调查局整装勘查区项目(DD20190159-1,DD20190159-2020-13)
西藏自治区专项资金项目(201904,ZXZJ2020005,54000021210200001048)联合资助。
关键词
西藏
北姆朗
斑岩体
地球化学
含矿性分析
Tibet
Beimulang
porphyry pluton
geochemistry
analysis of ore-bearing potential
