滇西福贡亚五夺透闪玉矿物学特征及成因

在滇西福贡亚五夺地区普遍发育有规模不等的透闪石玉矿(化)体,呈不规则大脉状产于片麻岩、片岩的大理岩夹层与糜棱岩化花岗岩的接触部位。本文在系统调查矿床(体)地质的基础上,采用化学分析、粉晶X衍射及能谱分析等方法,研究了区内透辉石玉的宝石学、矿物学特征,进而对其成因进行探讨。透闪石玉矿石折射率1.60,硬度5.6,密度2.9g/cm~3±,达到玉石品质的指标要求,可作为一种新类型的软玉矿床开发;其主要矿物组成(体积分数)为透闪石(45%)、透辉石(40%),并含方解石(5%)、石英(5%),以及少量的长石、石榴石、磷灰石、榍石、独居石等;透闪石的SiO_2、CaO、MgO含量(质量分数)分别54.54%、22.32%、18.62%,并有少量的Fe_2O_3、Na_2O、Al_2O_3,其晶胞参数a0、b0、c0及β分别为0.978×10~(-10) m、1.785×10~(-10) m、5.284×10~(-10) m及104.45°。结合矿床地质特征以及矿石与围岩稀土元素示踪分析,该透闪石玉矿床仍属变质热液型矿床,但其是在区域性同岩浆同变形时期的拉张阶段,变质流体混合岩浆残余热液沿裂隙充填而成的,应是一种新的矿床成因类型。其成矿时期与碧罗雪山—崇山变形带喜马拉雅中晚期大规模的走滑剪切作用相关大体时限为22~15Ma。本区域具有同等地质背景和成矿条件的地段范围巨大,具有很大的找矿前景。

The gemological characteristics and genesis of the Yawuduo tremolite nephrite deposits in Fugong county, western Yunnan province, China

In Yawuduo area,Fugong county,western Yunnan province occur widely different sized irregular nephrite dykes at,contact zone between mylonitized granite and marble intercalations of gneiss and schist.The results of microscopic observation,X-ray diffraction spectra and energy dispersion spectra and chemical analysis of the nephrite samples show that the refractive index is 1.60,hardness 5.6,and density about 2.9 g/cm3.The data meet requirements of jade and they can be served as one new type of the jade to exploit.The mineral volumetric measurement of the Yawuduo nephrite is tremolite (45％),diopside (40％),and calcite (5％),quartz (5％),and minor feldspar,garnet,apatite,sphene,monazite,etc.Percentage (mass fraction) of SiO2,CaO and MgO in tremolite is 54.54％,22.32％ and 18.62％ reapectively.Fe203,Na2O and Al2O3 are in minor amount.Crystal cell parameters,a0、b0、c0 and β of tremolite are 0.978× 10 10 m、1.785× 10-10 m、5.284× 10-10 m 及 104.45° respectively.The geological characteristics of the deposit and tracing analysis of REE of the wall rock reveal that the nephrite deposit is still a metamorphic hydrothermal deposit.However,it is formed by fissure filling of mixture of metamorphic fluid and residual magmatic fluid during regional synmagma,syndeformation-tensile extension thus should be a new genetic type of nephrite deposit.The mineralization is related to large-scale strikeslip shearing of Biluoxueshan-Chongshan shear zone and timely limited by Late Himalayan orogeny,about 22～15 Ma.The same geological setting and mineralization condition as the deposit is in huge area and is of great potential for prospecting.