Characteristics and indications of rare earth elements in dolomite of the Cambrian Loushanguan Group,SE Sichuan Basin

Jiang Wenjian; Hou Mingcai; Xing Fengcun; Xu Shenglin; Ling Liangbiao

doi:10.11743/ogg20160403

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Characteristics and indications of rare earth elements in dolomite of the Cambrian Loushanguan Group,SE Sichuan Basin
Vol. 37, Issue 4, Pages: 473-482(2016)
Online First：08 August 2016，

Published：2016
DOI： 10.11743/ogg20160403
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DOI：

Jiang Wenjian, Hou Mingcai, Xing Fengcun, et al. Characteristics and indications of rare earth elements in dolomite of the Cambrian Loushanguan Group,SE Sichuan Basin[J]. 2016, 37(4): 473-482. DOI： 10.11743/ogg20160403.

摘要

通过对四川盆地东南部（简称川东南）寒武系娄山关群两剖面（京竹和中坝剖面）的白云岩样品进行岩石学和稀土元素特征研究，主要有微晶白云岩、颗粒白云岩、晶粒白云岩和鞍形白云石4种类型。稀土元素特征分析结果表明：①4种类型的白云岩（石）均具有较低的稀土元素含量（平均含量为15.69×10

-6

）和较高的Y/Ho比值（平均值为50），且与铁锰含量相关性很弱，反映了研究区白云岩受陆源碎屑物和铁锰氧化物的污染较小。②不同类型白云岩（石）其稀土元素总含量有一定差别，泥微晶白云岩具有高的稀土元素含量（平均值为21.06×10

-6

），主要与其含有丰富的藻类有关；颗粒白云岩（平均值13.66×10

-6

）与晶粒白云岩（平均值13.02×10

-6

）具有相近的稀土元素含量；鞍形白云石具有较高的稀土元素含量（平均值为16.28×10

-6

），可能与热液参与有关。③4种类型白云岩（石）均具有与灰岩相似的稀土配分模式，（Nd/Yb）

平均值为1.52，相对轻稀土富集和重稀土亏损，负δEu和负δCe异常（平均值分别为0.79和0.36），显著Y正异常和La正异常，这些特征表明其白云岩化流体主要为海源性流体，成岩系统较封闭，成岩环境为还原环境，成岩温度较低。

Abstract

Petrologic study and REE (rare earth element) characterization of dolomite samples from Jingzhu and Zhongba outcrops of the Cambrian Loushanguan Group in SE Sichuan Basin identified four types of dolomite:micritic dolomite

grain dolomite

crystalline dolomite and baroque dolomite.The analysis results of the REE characteristics show that all the 4 types have low REE content (avg.15.69ppm) and relatively high Y/Ho ratios (avg.50).The very poor correlation of REE content with Fe and Mn contents suggests a limited effect of terrigenous clastics and iron and manganese oxyhydroxide on the dolomite in the study area.Different types of dolomite vary in their total REE content readings.The micritic dolomite is rich in algae and has the highest content of REE (avg.21.06ppm).The grain dolomite (avg.13.66ppm) and crystalline dolomite (avg.13.02ppm) have similar REE content.The baroque dolomite has relatively high REE content (avg.16.28ppm)

indicating possible involvement of hydrothermal fluids.It also shows that all types of dolomite shares similar REE patterns with limestone.The average value of (Nd/Yb)

in dolomite samples is 1.52

indicating they are relatively rich in LREE and depleted in HREE.All the samples show negative Eu and Ce anomalies (avg.0.79 and 0.36

respectively).Significant positive Y anomalies and positive La anomalies were also observed.All these facts indicate that the dolomite was formed by fluids of marine origin in a relatively closed diagenetic system of relatively reducing environment and low temperature.