北京怀柔地区白云岩蚀变过程中的元素含量两端元混合模型  

Bimodal Mixing Model on the Dolomite Alteration Geochemistry in the Yangshudixia Gold Deposit in Huairou,Beijing

作　　者：姚宁 龚庆杰[1] 王旭阳 晁岳德 彭程 吴媛 刘宁强[1] YAO Ning;GONG Qingjie;WANG Xuyang;CHAO Yuede;PENG Cheng;WU Yuan;LIU Ningqiang(School of Earth Sciences and Resources,China University of Geosciences,Beijing100083,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《现代地质》2020年第5期945-956,共12页Geoscience

基　　金：中央高校基本科研业务费专项(2652017221)。

摘　　要：蚀变岩是研究热液成矿作用的重要对象。北京怀柔杨树底下金矿区白云岩蚀变特征清晰,选择矿区一条白云岩蚀变剖面开展元素地球化学特征研究。在蚀变剖面两端采集白云岩样品2件,剖面中部采集不同蚀变程度的蚀变岩样品2件,针对剖面中的石英脉采集样品2件,分析6件样品的11项主量元素(或氧化物)和39项微量元素的含量。测试结果表明位于剖面两端的2件白云岩样品具有相似的化学组成,2件邻近的石英脉样品的元素含量也相一致,而2件不同蚀变程度的蚀变岩的化学组成存在显著差异。基于两端元混合模型,首先确定白云岩和石英脉两个端元的化学组成,进而依据11项主量成分分别采用正比例函数法和坪台法计算两端元的混合比例。结果显示正比例函数法计算结果受元素含量单位影响显著,即具有拟合结果受最大值控制的技术缺陷,而坪台法采用元素比值的中位值克服了正比例函数法的技术缺陷。基于坪台法计算的端元混合比例,分别计算2件蚀变岩样品中39项微量元素的理论含量值,结果表明在可靠的测试数据基础上微量元素的理论计算值与实测值在实验误差范围内相一致,说明两端元混合模型可以很好地刻画杨树底下金矿区白云岩蚀变产物的地球化学特征。研究结果这为揭示该区白云岩蚀变的形成机制提供了地球化学依据。Altered rocks are important objects in the study of hydrothermal mineralization.The alteration belt is clear at the Yangshudixia gold deposit in the Huairou district of Beijing(China).A lateral surficial alteration profile on dolomite was selected to investigate the alteration geochemistry.Two dolomite samples were collected from each end of the profile,2 altered samples with different alteration intensity were collected from the quartz vein in the profile,and 2 samples were collected from the quartz vein.Eleven major element oxides and 39 trace elements were analyzed on the 6 samples.The results indicate that the 2 dolomite and the 2 quartz vein samples have similar geochemical contents,while those of the 2 altered rocks are clearly different.Using the bimodal mixing model,two end-members of dolomite and quartz vein were first determined geochemically.Subsequently,the proportional function method and the plateau method were adopted to calculate the mixing ratios of the 2 altered samples based on the 11 major components.The calculation results show the technical defect of the proportional function method,in which the fitting results are much affected by the maximum value and the feasibility of the plateau method,and the median values were used to overcome the defect.According to the mixing ratios of the 2 altered samples calculated on 11 major components with the plateau method,the contents of other 39 trace elements were calculated on the bimodal mixing model for the 2 altered samples.Within the error of 03 log interval,the calculated values are similar to the analytical results.This indicates that the bimodal mixing model can well be used to explain the geochemical components of the altered dolomite at Yangshudixia.Our findings can help to reveal the formation mechanism of the dolomite alteration zone in the area.

关 键 词：杨树底下 北京怀柔 金矿床 石英脉 正比例函数法 坪台法 

分 类 号：P595[天文地球—地球化学] P618.51[天文地球—地质学]