贵州罗甸玉岩石化学特征及成因意义

以XRF、ICP-MS及常规化学分析方法为主要研究手段,对贵州罗甸玉的岩石化学特征进行研究,玉石常量化学特征表明,罗甸玉中透闪石的形成经历了Mg相对饱和及不饱和两个阶段,Mg相饱和的成矿阶段形成了白色罗甸玉中接近理想透闪石晶体化学组成的透闪石,其晶体化学通式为A0.01B2.00C5.34T8O22(OH)2;而在Mg不饱和阶段,则形成了青色系列罗甸玉中具有高Ca低Mg特点的透闪石,相应的晶体化学通式A0.01B2.35C4.13T8O22(OH)2。微量元素研究表明,罗甸玉中的白色与青色系列,由不同微量元素组合所表征的三个主因子有所差异,同时,罗甸玉中青色主要由其化学组成中微量的V,Cr引起;罗甸玉的稀土元素配分具有δCe和δEu异常的特点,稀土配分模式与围岩辉绿岩及灰岩均较为一致。在罗甸玉岩石化学特征研究的基础上,认为罗甸玉的形成是罗甸玉为岩床状辉绿岩顺层侵入时带来气液流体,与灰岩围岩发生长期的交代蚀变所形成的,灰岩提供成矿所需的Ca,Mg,而气液流体则主要提供了Si,为一种新类型的软玉矿体。

PETROCHEMICAL CHARACTERISTICS AND GENESIC SIGNIFICANCE OF LUODIAN JADE FROM GUIZHOU

Petrochemical characteristics of Luodian Jade from Guizhou Province were studied by using XRF,ICP-MS and conventional chemical analysis.Tremolite in Luodian Jade experienced two stages of relative saturated and unsaturated in Mg.Tremolite formed in Mg saturated phase is mainly white jade series,close to the standard crystal chemical composition with general formula of A0.01B2.00C5.34T8O22(OH)2,whereas,relatively green jade series may appear in Mg unsaturated stage and is rich in Ca and poor in Mg with general formula of A0.01B2.35C4.13T8O22(OH)2.Analysis of trace elements shows that the formation of white jade series and green jade series is affected by different trace element associations,especially,Cr-V,Co-Ni and Mn-Sr.It is indicated that Cr and V ions in chemical composition are responsible for the green color of Luodian Jade.Moreover,REE analysis of Luodian Jade revealed abnormal characteristics in δCe and δEu,and chondrite-normalized REE distribution pattern is similar to that of the surrounding rock of diabase and limestone.On the basis of petro-chemical characteristic study of Luodian Jade,it is considered that Luodian Jade is a new type of nephrite jade formed in a long term contact metasomatism between the limestone and gas-liquid fluid brought by diabase intrusion.In the process of metallogenic metasomatism,the limestone provides Ca and Mg,and the gas-liquid fluid s mainly provides Si for Luodian Jade.