摘要
湘中地区的锑(金)成矿多与脉岩相伴生,对其成因及对矿床成矿作用的贡献至今仍不清楚。本文通过对板溪石英斑岩脉的研究表明,全岩KAr年龄为200Ma±,至少比板溪锑矿成矿晚200Ma,因此脉岩与成矿不存在成因联系。板溪脉岩显示过铝质特征,其A/CNK为1.08～2.61,A/NK为1.08～2.71,K2O为0.9%～3.66%,K2O+Na2O为4.28%～7.5%,大多数样品的K2O/Na2O小于1。稀土元素以相对富集LREE,LREE分馏不明显、HREE分馏明显,配分曲线右倾为特点,其(La/Yb)n为14.47～28.11,(Gd/Yb)n为9.8～14.3,并且具强负Eu异常,δEu为0.05～0.14,这表明岩石在成岩演化过程中,经历了强的分异结晶作用。在原始地幔标准化蛛网图上,脉体相对富集LILE,并具Ti和P负异常。(87Sr/86Sr)i变化范围较大,为0.6653～0.7149,其中B3样品的(87Sr/86Sr)i为0.7149,与来自地壳上部的花岗岩的87Sr/86Sr初始比值相当。在构造环境判别图中,样品显示岛弧/同碰撞花岗岩的特点。结合前人的研究成果,笔者推测板溪脉岩为地壳上部岩石部分熔融的产物,并经历了混染和高度的分异演化。其动力来源为200Ma左右,地壳叠置加厚作用后幔源岩浆的底侵作用。
Felsic or mafic dikes mostly intruded into antimony-gold ore districts in central Hunan, and there are still no clear ideas concerning the relations between these dikes and the ore deposits. The authors revealed that the intrusion of Banxi quartz porphyry dikes took place at 200 Ma ±（K-At）, at least 200 Ma younger than Banxi antimony mineralization. Therefore there are no relations between the dikes and the formation of the ore deposit. Banxi dikes are peraluminous rocks, their A/CNK = 1.08～2.61, A/NK = 1.08～ 2.71, K2O= 0.9 %～3.66 %, K2O ＋ Na2O = 4.28 %～7.5 %, and K2O/Na2O〈 1 in mat samples. They are relatively enriched in LREE, with flat LREE and stepwise HREE patterns, （La/Yb） n = 14.47～ 28.11, （Gd/Yb） n = 9.8 ～ 14.3, and negative Eu anomalies are obvious. All these data imply that the rocks must have experienced strong fractional crystallization. In the primitive mantle normalized spider diagram, they are relatively enriched in LILE, with negative Ti and P anomalies. （^87 Sr/^86 Sr） i = 0. 6653～0. 7149, and the reliable （^87Sr/^86Sr）i Of B-3 sample is 0. 7149, corresponding to 87Sr,/86Sr ratios of granite in the upper crust. In the plots of tectonic discrimination, they are projected in IAG/VAG/Syn-COLG regions. In combination with the conclusions reached by other papers, the authors hold that the Banxi dikes were derived from the upper crust and were predominantly attributed to basaltic underplating at about 200 Ma ±during the thermal-stress relaxation after the ending of the tectonically thickening event.
出处
《地球学报》
EI
CAS
CSCD
北大核心
2005年第6期525-534,共10页
Acta Geoscientica Sinica
基金
国家自然科学基金项目(编号:40472053)
中国科学院创新项目(编号:KZCZ2102)联合资助。
