云南来利山锡矿矿物学研究及氢氧同位素特征

Mineralogical research and H-O isotopic characteristics of the Lailishan tin deposit in Yunnan Province

在详细的野外调研及岩相学研究基础上,通过X射线粉晶衍射和红外光谱等测试手段,研究云南来利山锡矿不同成矿阶段石英和锡石的晶胞参数及红外光谱特征,解译石英和锡石的成因信息。研究表明,来利山锡矿热液成矿期可分为4个成矿阶段,即云母-黄铁矿-黄玉-粒状锡石阶段(Ⅰ)、云母-石英-黄铁矿-柱状锡石阶段(Ⅱ)、石英-黄铁矿-放射状锡石阶段(Ⅲ)和萤石-石英-黄铁矿-球粒状锡石阶段(Ⅳ)。从第Ⅰ阶段到第Ⅳ阶段,石英晶胞参数中a0、c0、V0和c0/a0均有减小的趋势,石英轴变化率比值为0.773 07~3.496 88;石英红外光谱各吸收峰的吸光度有增大的趋势。推测第Ⅰ、Ⅱ阶段石英所含杂质以Al3+、Fe3+等置换杂质为主,第Ⅲ阶段较为复杂,可能存在置换杂质和填隙杂质两种类型,第Ⅳ阶段所含杂质以Na+、K+等填隙杂质为主。锡石晶胞参数中a0、c0和V0随着成矿阶段的演化先减小后增大,其中第Ⅱ阶段a0、c0和V0值最小。这与不同成矿阶段锡石中杂质元素总量的变化规律一致,反映了锡石的晶胞参数变化主要受混入晶格元素的影响,而温度对锡石晶胞参数的影响较小。锡石红外光谱特征在不同成矿阶段的基本相似,属于变形谱,反映了锡石-硫化物热液矿床的谱形特征。此外,石英氢氧同位素组成显示成矿流体为岩浆水与大气降水混合物,推测初始成矿热液主要来自岩浆,随着热液演化,大气水沿构造裂隙混入到热液中,使热液的氢氧同位素组成向大气水一侧偏移。

In this paper, the authors conducted a study of the features of cell parameters and infrared spectroscopy of quartz and cassiterite at different ore-forming stages in the Lailishan tin deposit of Yunnan Province by using X-ray powder diffraction and infra-red spectroscopy and on the basis of detailed field investigation and petrographic research, so as to interpret the genetic information of quartz and cassiterite. The results show that the hydrothermal mineralization period of the tin deposit can be divided into four stages, i. e., mica-pyrite-topaz-granular cassiterite stage（ Ⅰ）, mica-quartz-pyrite-columnar cassiterite stage（ Ⅱ）, quartz-pyrite-radial cassiterite stage（ Ⅲ） and fluorite-quartz-pyrite-sphaerolitic cassiterite stage（ Ⅳ）. From stageⅠ to Ⅳ, the values of a0, c0, V0 and the c0/a0 ratios of the cell parameters in quartz show a decreasing trend. Axis ratio of the rate of change in quartz is from 0. 773 07 to 3. 496 88; the absorbance of each absorption peak of the infrared spectroscopy in quartz tends to increase. The authors infer that quartz mainly has substitutionimpurities such as Al3 ＋and Fe3 ＋at stage Ⅰ and Ⅱ, has substitution impurities and interstitial impurities at stageⅢ, which is complicated, and has interstitial impurities such as Na^＋, K^＋at stage Ⅳ. The values of a0, c0 and V0decrease firstly and then increase in cassiterite with the evolution of the ore-forming stage, and are smallest at stage Ⅱ, which is consistent with the changes of the total amount of impurity elements in cassiterite at different ore-forming stages. These phenomena suggest that changes of cell parameters in cassiterite are mainly affected by mixed impurity elements in lattice rather than temperature. The characteristic infrared spectra of cassiterite at different ore-forming stages are similar and belong to the deformation spectra, implying the characteristics of cassiterite-sulfide hydrothermal deposits. Moreover,the composition of hydrogen and oxygen isotopes in quartz shows that the ore-forming fluid is a mixture of magmatic and meteoric water, and the initial ore-forming fluid is derived from magma. With the evolution of hydrothermal solution, meteoric water enters hydrothermal solution along the tectonic fissures, which makes the isotopic composition of hydrogen and oxygen shift to atmospheric water.