CHARACTERISTICS OF GARNET IN SHIZHUYUAN SKARN DEPOSIT, HUNAN PROVINCE
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摘要: 通过野外与显微镜观察和电子探针分析, 对柿竹园多金属矿床矽卡岩中石榴石的特征进行了研究.根据石榴石的产出状态、矿物的共生组合, 矽卡岩可分为4个带: 磁铁矿-辉石-石榴石带、辉石-石榴石带、符山石-石榴石带、矽卡岩化大理岩带.从成分上的变化, 探讨了石榴石在各矽卡岩带中的特征.柿竹园矿床矽卡岩中的石榴石可分为早、晚两期, 早期形成的石榴石颜色为暗棕色, 并且在垂直和水平方向上有明显的变化规律.从磁铁矿-辉石-石榴石带到矽卡岩化大理石带, 随着石榴石中Fe2O3含量的减少, Al2O3含量的增加, 由钙铁榴石向钙铝榴石变化; 石榴石晶体具有从核部向边缘由均质性向非均质性变化的规律.早期石榴石形成于较氧化的条件下, 温度为520~620℃, 压力为1000×105Pa, 由富含Si, Al, Fe, Cl, F组分的热液和泥盆纪佘田桥组灰岩反应交代形成.当温度降至450~ 540℃, pH, Eh值降低时, 晚期石榴石形成的同时使白钨矿沉淀.晚期石榴石颜色比早期形成的石榴石浅, 为红色.结晶颗粒较大, 并且, 普遍可以观察到石榴石环带结构.Abstract: In the Shizhuyuan polymetallic skarn deposit in Hunan Province, China, the research for garnet is made by means of the field survey, the microscopic observation and EPMA. This skarn is classified into four zonal distributions in terms of the occurrence of the garnet and the mineral assemblages: magnetite-yroxene-arnet zone, pyroxene-arnet zone, vesuvianite-arnet zone and skarnized marble zone. The features of the garnet in various skarnized zones are discussed with changes of chemical composition and mode of occurrence. The garnet is divided into two stages: early and late stages. During the early stage, the color of the garnet is dark brown, and shows a distinctive zonal pattern with various chemical compositions. In addition, the magnetite-yroxene-arnet zone to skarnized marble zone has transformed from andradite to grossular as the content of Fe2O3 decreases and that of Al2O3 increases. The garnet crystal is characterized by the pattern of compositional changes from core to rim. During the early stage, the garnet occurred in the relatively oxidizing environment at the temperature ranging between 520 and 620 ℃ and at the pressure of 1 000×105 Pa. In addition, this garnet resulted from the metasomatic reaction between the thermal liquids of Si, Al, Fe, Cl, F components and the Devonian limestone of the Shetianqiao Formation. When the temperature falls to 450-540 ℃ and the pH and Eh values decrease in the late stage, the garnet occured with sheelite. The color of the garnet crystal in the late stage is red, and is lighter than that of the early stage. Furthermore, the crystal grain size is larger, and the zonal structure can be universally observed in the late stage.
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Key words:
- skarn /
- garnet /
- zonal structure /
- Shizhuyuan deposit
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图 1 湖南省郴州柿竹园矿床
1.第四纪; 2.石英脉; 3.煌斑岩; 4.石英斑岩; 5.细粒黑云母花岗岩; 6.中粗粒黑云母花岗岩; 7.细粒斑状黑云母花岗岩; 8.上泥盆统碳酸盐岩; 9.中泥盆统碳酸盐岩; 10.震旦系变质岩; 11.矽卡岩; 12.断层
Fig. 1. Geological map of the Shizhuyuan deposits in Chen-zhou, Hunan Province
图 2 柿竹园矿床490 m水平中段坑道及采样位置
1.中粗粒黑云母花岗岩(2期); 2.细粒黑云母花岗岩(3期); 3.花岗斑岩(4期); 4.石英脉; 5.巷道; 6.采空区; 7.断层; 8.矽卡岩的分带界线; 9.采样位置及编号
Fig. 2. Underground geological map and sampling site of 490 m level in the Shizhuyuan deposits
图 3 石榴石脉的产出照片(a) 和不同矿物的电子显微照片(b)
Fig. 3. Photograph of occurrence of garnet vein (a) and SEM photograph of cassiterite, fluorite, pyrite and garnet (b)
图 4 辉石-石榴石带中石榴石环带显微照片
a.单偏光, 比例尺100μm; b.背散射电子像
Fig. 4. Micrographs of zonal garnet in pyroxene-garnet zone
图 5 柿竹园矿床中各矽卡岩带的石榴石成分
●磁铁矿-辉石-石榴石带中的石榴石组成; ■辉石-石榴石带中的石榴石组成; ▲符山石-石榴石带中的石榴石组成; ◆矽卡岩化大理岩带中的石榴石组成
Fig. 5. Compositions of garnets in different skarnized zones from the Shizhuyuan deposits
图 6 辉石-石榴石带中环带状石榴石的成分变化
Fig. 6. Composition profiles of zonal garnet in the pyroxene-gar-net zone along the traverse from core to rim
x (Al) =n (Al) /n (Fe3++Al+Ti+Cr), x (Fe3+) =n (Fe3+) /n (Fe3++Al+Ti+Cr), x (Mn) =n (Mn) /n (Ca, Mn, Mg), x (Ca) =n (Ca) /n (Ca, Mn, Mg)
表 1 柿竹园矿床磁铁矿-辉石-石榴石带的石榴石电子探针分析
Table 1. Electron microprobe analysis of garnet in magnetite-pyroxene-garnet zone of the Shizhuyuan deposits
表 2 柿竹园矿床辉石-石榴石带的石榴石电子探针分析
Table 2. Electron microprobe analysis of garnet in pyroxene-garnet zone of the Shizhuyuan deposits
表 3 柿竹园矿床符山石-石榴石带的石榴石电子探针分析
Table 3. Electron microprobe analysis of vesuvianite_garnet zone in the Shizhuyuan deposits
表 4 柿竹园矽卡岩化大理岩带的石榴石电子探针分析
Table 4. Electron microprobe analysis of garnet in skarnized marble zone of the Shizhuyuan deposits
表 5 柿竹园矿床辉石-石榴石带的环带石榴石电子探针分析
Table 5. Electron microprobe analysis of zonal garnet from pyroxene-garnet zone in the Shizhuyuan deposits
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