新疆天湖东绿松石的矿物学和地球化学特征

Mineralogy and Geochemistry of Turquoise from Tianhu East, Xinjiang, China

  • 摘要: 中国是世界绿松石的主要产地之一,拥有丰富的绿松石资源,主要分布于湖北、安徽、陕西、河南和新疆等地。根据赋矿类型可分为沉积变质岩和岩浆岩1。其中,鄂豫陕和新疆矿区绿松石均属于沉积变质岩类型1,安徽的马鞍山和铜陵矿区绿松石属于岩浆岩类型2。天湖东绿松石矿床位于中国新疆维吾尔自治区哈密市东南180 km处。该矿床最早被开采的时间可以追溯到公元前1279-379年,属于古代采矿遗址3。2015年左右,天湖东绿松石矿被重新开采,产出的绿松石在中国市场上短暂销售过一段时间。出于对该古矿遗址保护的考虑,这里的开采活动后来被禁止了。长期以来,沉积变质岩类型的绿松石一直是我国绿松石市场上的主要来源,如产自湖北竹山、郧西、郧县、以及陕西白河等地的绿松石均属于此种类型,其成因与黑色岩系密切相关4-6。关于该类型绿松石的成矿机制,一直有不同的观点6-8。本研究以新疆哈密天湖东绿松石为例,结合野外地质特征和地质资料,对其进行了系统性的宝石学、矿物学和地球化学研究,重点研究了该地区绿松石的产地特征,并阐明其成矿过程。天湖东绿松石常呈蓝色和蓝绿色细脉出现在寒武纪坡城山组石英岩的裂隙和剪切带中。该矿点绿松石的地球化学特征以高Li、V、Cr、Sr、Ga以及低Ba为显著特征。通过拉曼光谱和电子探针显微分析,发现该矿点绿松石中典型的杂质矿物有石英、磷灰石、硫磷铝锶石、针铁矿、赤铁矿、黄钾铁钒、三水胆矾、白云母、石膏等。同时本研究首次在中国绿松石中发现了氯铜矿,该矿物可作为该产地的标志性矿物,可与中国其他产地绿松石区分,具有重要的产地鉴别意义。根据岩石学、矿物学和地球化学特征,以及伴生矿物的结晶顺序,本文提出天湖东绿松石矿属于表生风化淋滤成因。黑色岩系是绿松石成矿的主要物质来源,为绿松石的形成提供了所需的Al、P和Cu元素,而石英岩为其沉积成矿提供了空间。

     

    Abstract: China is one of the main producing areas of turquoise in the world, boasting significant deposits mainly located in regions such as Hubei Province, Anhui Province, Shaanxi Province, Henan Province, and Xinjiang. Turquoise deposits in China can be categorized into two types: sedimentary metamorphic rock and magmatic rock1. The turquoises from Hubei Province, Henan Province, and Xinjiang are of the sedimentary metamorphic rock variety, whereas the specimens from Maanshan and Tongling in Anhui Province are extracted from magmatic rock1. The turquoise deposit from Tianhu East is located 180 km southeast of Hami (also known as Kumul) in Xinjiang, China. This deposit had been mined since as early as 1 279-379 BCE3. The turquoise mine from Tianhu East was re-exploited around 2015, and some of the production emerged briefly on the Chinese market. The mining was subsequently prohibited because of the location's protected status as an archaeological site. For a long time, turquoise sourced from sedimentary metamorphic rocks has dominated the Chinese market. Regions such as Zhushan, Yunxi, Yunxian in Hubei, and Baihe in Shaanxi are known for producing this type of turquoise, which is closely associated with black rock series4-6. The metallogenic mechanism of this variety of turquoise has been subject to various interpretations6-8. The geology of turquoise deposit from Tianhu East as well as updated reports and field exploration systematically summarized in this study. The turquoises usually occur as blue and bluish green veins in the fissures and shear zones of quartzite in the Cambrian Pochengshan Formation. It is characterized by high lithium, vanadium, chromium, strontium, and gallium concentrations and low barium contents. Multiple associated minerals (e.g., quartz, apatite, goethite, hematite, jarosite, bonattite, muscovite, atacamite, svanbergite, and gypsum) were identified using Raman spectroscopy and electron probe microanalysis. This study contains the first report of atacamite in Chinese turquoise, a mineral that could serve as a distinctive marker for this specific origin. Petrography, mineralogy, and geochemistry of the bedrock as well as the crystallization sequences of the associated minerals are highlighted. Based on the results, the authors propose a supergene weathering origin and elemental derivation for turquoise from Tianhu East. Black shale is likely the main original source of the aluminum, phosphorus, and copper necessary for formation, while quartzite provides enough space for precipitation.

     

/

返回文章
返回