Garnet and scheelite as indicators of multi-stage tungsten mineralization in the Huangshaping deposit, southern Hunan province, China
Garnet and scheelite as indicators of multi-stage tungsten mineralization in the Huangshaping deposit, southern Hunan province, China
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DOI：
10.1016/j.oregeorev.2018.01.029
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发表时间：
2018-03
影响因子：
3.3
通讯作者：
Teng Ding;Teng Ding;D. Ma;Jian-Jun Lu;Rongqing Zhang;Rongqing Zhang
中科院分区：
文献类型：
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作者：
Teng Ding;Teng Ding;D. Ma;Jian-Jun Lu;Rongqing Zhang;Rongqing Zhang
湖南黄沙坪钨钼铅锌存款矿床是在矽卡岩和硫化物-碳酸盐蚀变岩中产出的多世代石榴石和白钨矿。利用激光原位烧蚀-电感耦合等离子体质谱分析获得的石榴石和白钨矿的光学特性和稀土元素的REEN谱图，区分不同世代的石榴石和白钨矿。这些数据显示石榴石REEN模式与主要元素分带的明确对应关系，HREE（例如，Gd-Lu）被整体耗尽。黄沙坪存款中的粗粒石榴石具有极端的HREE亏损和显著的LREE（例如，La-Eu）富集，特别是Ce、Pr和Nd。这表明这些石榴石中的稀土元素是耦合置换的结果：[Ca 2 +]VIII− 1[REE 3 +]VIII+1和[Fe 2 +]IV+1[Al 3 +]IV− 1。中粒石榴石的REEN模式显示出明显的轻稀土富集和亏损的重稀土元素，具有较高的Sn含量。这表明这些石榴石中稀土元素的取代形式为[Ca 2 +]VIII−1[REE 3 +]VIII+1[Sn 4 +]IV−1[Al 3 +]IV+1。中粒石榴子石中Sn含量高，表明成矿流体具有氧化性，这与Eu的显著正异常相一致。然而，石榴石边缘的驼峰形REEN图案表明被[Ca 2 +]VIII−2[Na+]VIII+1[REE 3 +]VIII+1取代，其中Nd-Tb优先并入石榴石晶格中，而不是其他稀土元素。1a组白钨矿在阴极发光图像中具有黑色核心，REEN图案显示LREE极度富集和HREE极度亏损。1b组白钨矿的核心具有精细的振荡环带，富集轻稀土元素，亏损重稀土元素，类似于2a组白钨矿的REEN模式，其以明亮的CL围绕1a组和1b组白钨矿的边缘出现。稀土元素在这三种白钨矿中的取代机制是：[Ca 2 +]VIII−3[ ]VIII+1[REE 3 +]VIII+2，其中[ ]是Ca位空位。热液中稀土元素形态的影响主导了这些类型白钨矿的稀土配分模式。然而，对于白钨矿的2b族亮边，稀土元素以[Ca 2 +]VIII−2[Na+]VIII+1[REE 3 +]VIII+1的形式结合，类似于石榴石边。白钨矿的Mo含量和δEu值从1a组到2b组逐渐降低，表明成矿流体的氧逸度在时间上逐渐降低，而Y/Ho比值和Mo含量从1a组和1b组到2a组和2b组逐渐降低，其比值分别与斑岩型夕卡岩型W（Mo）和石英脉型Au-W矿床相似。研究还表明，该存款中的白钨矿均为岩浆流体。黄沙坪存款，中粒石榴石与1a组白钨矿沉淀演化岩浆流体在俯冲变质作用，这表明他们的互补Y/Ho比值。副年轻的白钨矿，特别是组-2b，可能形成于稀释的岩浆流体，经历了大规模的热液循环。1b、2a族白钨矿的特征反映了黄沙坪多金属存款钨矿化过程中的过渡环境和流体混合作用。
The Huangshaping W–Mo–Pb–Zn deposit in southern Hunan province, south China, contains multiple generations of garnet and scheelite in skarn and sulfide–carbonate altered rocks. Optical characteristics and chondrite-normalized rare earth element (REEN) patterns obtained by in situ laser ablation–inductively coupled plasma–mass spectrometry analysis were used to distinguish different generations of garnet and scheelite. These data show a clear correspondence of garnet REENpatterns to major element zonation, with HREEs (e.g., Gd–Lu) being depleted overall. Coarse-grained garnets in the Huangshaping deposit have extreme HREE depletions and significant LREE (e.g., La–Eu) enrichment, particularly for Ce, Pr, and Nd. This indicates that REEs in these garnets are the result of coupled substitutions: [Ca2+]VIII− 1[REE3+]VIII+1and [Fe2+]IV+1[Al3+]IV− 1. Medium-grained garnets have REENpatterns showing significant LREE enrichment and depleted HREEs, with high Sn contents. This suggests that substitution of REEs in these garnets occurs as [Ca2+]VIII−1[REE3+]VIII+1[Sn4+]IV−1[Al3+]IV+1. The fact that medium-grained garnets have high Sn contents indicates mineralizing fluids were oxidizing, which is consistent with significant positive Eu anomalies. However, hump-shaped REENpatterns for garnet rims suggest substitution by: [Ca2+]VIII−2[Na+]VIII+1[REE3+]VIII+1, where Nd–Tb are preferentially incorporated into the garnet lattice over other REEs.Group-1a scheelite has black cores in cathodoluminescence images, and REENpatterns showing extreme LREE enrichment and HREE depletion. Group-1b scheelite has cores with fine oscillatory zoning and enriched LREEs with depleted HREEs, similar to the REENpatterns of Group-2a scheelite that occur as rims with bright CL surrounding both Group-1a and 1b scheelite. The substitution mechanism for REEs in these three types of scheelite is: [Ca2+]VIII−3[ ]VIII+1[REE3+]VIII+2, with [ ] being a Ca site vacancy. The influence of REE speciation in the hydrothermal fluid dominates the REENpatterns of these types of scheelite. However, for Group-2b bright rims of scheelite, REEs are incorporated as: [Ca2+]VIII−2[Na+]VIII+1[REE3+]VIII+1, similar to the garnet rims. Finally, scheelite Mo contents and δEu values that decrease from Group-1a to 2b support a temporal decrease in oxygen fugacity of the mineralizing fluids.Ratios of Y/Ho and Mo contents that decrease from Group-1a and 1b to Group-2a and 2b scheelites are similar to those in porphyry-related skarn W (Mo) and quartz vein Au–W deposits, respectively. Our studies also suggest that all these scheelites in this deposit formed from magmatic fluids. At the Huangshaping deposit, medium-grained garnets associated with Group-1a scheelite precipitated from evolved magmatic fluids during prograde metamorphism, as indicated by their complementary Y/Ho ratios. Paragentically younger scheelite, particularly Group-2b, may have formed from dilute magmatic fluids that underwent large-scale hydrothermal circulation. The characteristics of Group-1b and 2a scheelite likely reflect a transitional environment and fluid mixing during tungsten mineralization in the polymetallic Huangshaping deposit.