墨西哥Sonora(索诺拉州)锌绿松石的矿物学及谱学特征

锌绿松石少见产出，在现有研究和报道中也甚少提及。墨西哥索诺拉州是美洲绿松石的一个重要产地，所产绿松石于近期活跃在市场上。采用常规宝石学测试、X射线荧光能谱测试、X射线粉晶衍射分析、傅里叶变换红外光谱测试、紫外-可见光光谱测试等方法，对该产地绿松石的化学成分、物相组成、系列光谱学特征等方面进行系统的分析，并初步探讨其矿床成因。结果表明，墨西哥绿松石的颜色以淡蓝色和青白色为主，外观上以大量肉眼可见、分布在基体和围岩中自形程度极高的黄铁矿团块以及围岩中少见的呈放射状生长的镁电气石等特征显著区别于其他产地的绿松石。其化学成分以质量分数大于1的ZnO/CuO比定义为含铜锌绿松石，属于绿松石-锌绿松石类质同像系列接近锌绿松石的端员矿物，且由于与铜矿床共生，墨西哥绿松石中(CuO+ZnO)的含量偏高。XRD测试结果表明，墨西哥绿松石的主矿物相为锌绿松石，与EDXRF的测试结果相吻合，其常见的矿物组合为锌绿松石+石英+钾长石+镁电气石，这一组合方式在前人研究中并不常见。红外光谱特征由结构中的羟基、水合离子及磷酸根基团的振动特征共同决定，其中羟基的振动峰主要出现在3 400~3 700 cm-1范围，水合离子的振动峰位于3 000~3 300 cm-1，磷酸根基团引起的振动峰则出现于1 000~1 200和400~650 cm-1的指纹区。该地区所有样品中均显示其他产地绿松石少见的3 732 cm-1处的红外吸收峰，从某种意义上具有一定的产地指示作用，同时选择对红外光谱中的3 500~3 600 cm-1范围与氢键最强的结构水相关的区域进行积分处理，其积分面积能够辅助判断样品中水的含量。紫外-可见光光谱显示，在256和430 nm处分别有由O2--Fe3+和Fe3+引起的谱峰，位于670 nm处与Cu2+电子禁戒跃迁相关的谱带被以852 nm为中心的由Fe2+电子跃迁形成的宽缓谱带所包络，最终显示为以800 nm为中心的由Cu-Fe离子联合作用而形成的谱带。从伴生矿物组合、矿物结构构造、地质特征等方面综合推测，墨西哥锌绿松石是与该区斑岩型铜矿床伴生的非金属矿种，其成因属于典型的中酸性火山岩热液蚀变型。

Mineralogical and Spectral Characteristics of Faustite from Sonora,Mexico

Faustite is rare and rarely mentioned in existing research and reporting. Mexico is an important producer of American turquoise, and Mexican turquoiseis active in the market recently. In this paper, the authors studiedthe chemical composition, phase composition, and a series of spectrum of turquoise samples from Mexico by conventional gemmological tests, X-ray fluorescence spectroscopy, X-ray powder diffraction, fourier transform infrared spectroscopy and UV-Vis spectroscopy, andpreliminarily discussed the deposit genesis. The results indicated that the main colors of Mexican turquoise are light blue and bluish white, and the features of pyrite with high degree of idiomorphic in matrix and surrounding rock and rare radial growth of dravite in surrounding rock were obviously different from turquoise in other origins. Mexican turquoise was recognized as Cu-bearing faustite due to the ratio of zinc oxide to copper oxide was greater than 1, which belongs to turquoise-faustite isomorphism series close to the end member mineral of faustite. And because of paragenesis with copper deposit, the content of CuO and ZnO in Mexican turquoise is much higher. The results of XRD experiment showed that the main mineral phase of Mexican turquoise is faustite, which is in agreement with the testing results of EDXRF testing, and the common mineral assemblage was faustite, quartz, orthoclase and dravite. The infrared spectrum was determined by the vibrationof hydroxyl (located at 3 400~3 700 cm-1), hydrated ion (located at 3 000~3 300 cm-1) and phosphate group (located at 1 000~1 200 and 400~650 cm-1 in fingerprint region) in the structure. And all the samples from Mexico showed the infrared absorption peak at 3 732 cm-1 while rarely seen in other origins, which has the function of indicatingthe originin a sense. Meanwhile, the integral computation within a range of 3 500~3 600 cm-1which related to constitution water with strongest hydrogen bonding can be used to determine the water content in the samples. Besides, the UV-Vis spectrumshowed that there were two peaks caused by O2--Fe3+ and Fe3+ at 256 and 430 nm, respectively. The band associated with the forbidden transition of Cu2+ at 670 nm was enveloped by the band formed by the electronic transition of Fe2+ at the center of 852 nm, finally, it was shown with the band centered on 800 nm which was caused by the combined action of Cu-Fe ions. Inferred from associated mineral combination, mineral structure and geological characteristics, Mexican turquoise is a nonmetallic mineral associated with porphyry copper deposit and belongs to the typical hydrothermal alteration genesis of intermediate-acid volcanic rocks.