The carbonate-hosted Pb–Zn deposits in the Sanjiang metallogenic belt on the Tibetan Plateau are typical of MVT Pb–Zn deposits that form in thrust-fold belts. The Jiamoshan Pb–Zn deposit is located in the Changdu a...The carbonate-hosted Pb–Zn deposits in the Sanjiang metallogenic belt on the Tibetan Plateau are typical of MVT Pb–Zn deposits that form in thrust-fold belts. The Jiamoshan Pb–Zn deposit is located in the Changdu area in the middle part of the Sanjiang belt, and it represents a new style of MVT deposit that was controlled by karst structures in a thrust–fold system. Such a karst-controlled MVT Pb–Zn deposit in thrust settings has not previously been described in detail, and we therefore mapped the geology of the deposit and undertook a detailed study of its genesis. The karst structures that host the Jiamoshan deposit were formed in Triassic limestones along secondary reverse faults, and the orebodies have irregular tubular shapes. The main sulfide minerals are galena, sphalerite, and pyrite that occur in massive and lamellar form. The ore-forming fluids belonged to a Mg2+–Na+–K+–SO2-4–Cl-–F-–NO-3–H2 O system at low temperatures(120–130°C) but with high salinities(19–22% NaCl eq.). We have recognized basinal brine as the source of the ore-forming fluids on the basis of their H–O isotopic compositions(-145‰ to-93‰ for δDV-SMOW and-2.22‰ to 13.00‰ for δ18 Ofluid), the ratios of Cl/Br(14–1196) and Na/Br(16–586) in the hydrothermal fluids, and the C–O isotopic compositions of calcite(-5.0‰ to 3.7‰ for δ13 CV-PDB and 15.1‰ to 22.3‰ for δ18 OV-SMOW). These fluids may have been derived from evaporated seawater trapped in marine strata at depth or from Paleogene–Neogene basins on the surface. The δ34 S values are low in the galena(-3.2‰ to 0.6‰) but high in the barite(27.1‰), indicating that the reduced sulfur came from gypsum in the regional Cenozoic basins and from sulfates in trapped paleo-seawater by bacterial sulfate reduction. The Pb isotopic compositions of the galena samples(18.3270–18.3482 for 206 Pb/204 Pb, 15.6345–15.6390 for 207 Pb/204 Pb, and 38.5503–38.5582 for 208 Pb/204 Pb) are similar to those of the regional Triassic volcanic-arc rocks that formed during the closure of the Paleo-Tethys, indicating these arc rocks were the source of the metals in the deposit. Taking into account our new observations and data, as well as regional Pb–Zn metallogenic processes, we present here a new model for MVT deposits controlled by karst structures in thrust–fold systems.展开更多
陶土矿是制作紫砂工艺品的原料。目前,行业内用来判别陶土矿质量的常规方法主要是主量元素含量、矿物组成与可塑性、烧失量、收缩率和吸水率等性能的分析与测试。常规分析测试方法虽然对判别陶土矿质量有较好的效果,但是对于粉砂质泥岩...陶土矿是制作紫砂工艺品的原料。目前,行业内用来判别陶土矿质量的常规方法主要是主量元素含量、矿物组成与可塑性、烧失量、收缩率和吸水率等性能的分析与测试。常规分析测试方法虽然对判别陶土矿质量有较好的效果,但是对于粉砂质泥岩和泥质粉砂岩这两类对陶土矿质量影响较大的岩石,在化学成分上却难以区分。笔者在开展宜兴陶土矿资源调查时,采用综合矿物分析系统(Tescan Integrated Mineral Ana-lyzer,TIMA)对从岩心中选取的矿料和当地优质矿料的矿物成分、含量及其粒度分布等进行了测试分析和对比,研究发现:优质陶土矿中黏土矿物的含量占比在30%以上,矿物的粒度区间极窄,基本为泥级;石英的粒度区间较宽,基本为泥级、粉级和细砂级,且不同粒级的石英分布较均匀,石英含量趋势线平稳或向粗粒级方向收缩。因此,认为矿物的成分、含量及其粒度分布是影响陶土矿质量的重要因素。通过TIMA测试不仅可以弥补利用化学成分难以判别矿与非矿的不足,还可以有效地判别矿石质量与产品质量之间的内在关系。展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2016YFC0600306)the National Natural Science Foundation of China(Grant Nos 41773042,41922022,41773043,41772088,91962105 and 41702082)+1 种基金the independent research project from Key Laboratory of DeepEarth Dynamics of the Ministry of Natural Resources(Grant No.J1901-6)the IGCP-662 program。
文摘The carbonate-hosted Pb–Zn deposits in the Sanjiang metallogenic belt on the Tibetan Plateau are typical of MVT Pb–Zn deposits that form in thrust-fold belts. The Jiamoshan Pb–Zn deposit is located in the Changdu area in the middle part of the Sanjiang belt, and it represents a new style of MVT deposit that was controlled by karst structures in a thrust–fold system. Such a karst-controlled MVT Pb–Zn deposit in thrust settings has not previously been described in detail, and we therefore mapped the geology of the deposit and undertook a detailed study of its genesis. The karst structures that host the Jiamoshan deposit were formed in Triassic limestones along secondary reverse faults, and the orebodies have irregular tubular shapes. The main sulfide minerals are galena, sphalerite, and pyrite that occur in massive and lamellar form. The ore-forming fluids belonged to a Mg2+–Na+–K+–SO2-4–Cl-–F-–NO-3–H2 O system at low temperatures(120–130°C) but with high salinities(19–22% NaCl eq.). We have recognized basinal brine as the source of the ore-forming fluids on the basis of their H–O isotopic compositions(-145‰ to-93‰ for δDV-SMOW and-2.22‰ to 13.00‰ for δ18 Ofluid), the ratios of Cl/Br(14–1196) and Na/Br(16–586) in the hydrothermal fluids, and the C–O isotopic compositions of calcite(-5.0‰ to 3.7‰ for δ13 CV-PDB and 15.1‰ to 22.3‰ for δ18 OV-SMOW). These fluids may have been derived from evaporated seawater trapped in marine strata at depth or from Paleogene–Neogene basins on the surface. The δ34 S values are low in the galena(-3.2‰ to 0.6‰) but high in the barite(27.1‰), indicating that the reduced sulfur came from gypsum in the regional Cenozoic basins and from sulfates in trapped paleo-seawater by bacterial sulfate reduction. The Pb isotopic compositions of the galena samples(18.3270–18.3482 for 206 Pb/204 Pb, 15.6345–15.6390 for 207 Pb/204 Pb, and 38.5503–38.5582 for 208 Pb/204 Pb) are similar to those of the regional Triassic volcanic-arc rocks that formed during the closure of the Paleo-Tethys, indicating these arc rocks were the source of the metals in the deposit. Taking into account our new observations and data, as well as regional Pb–Zn metallogenic processes, we present here a new model for MVT deposits controlled by karst structures in thrust–fold systems.
文摘陶土矿是制作紫砂工艺品的原料。目前,行业内用来判别陶土矿质量的常规方法主要是主量元素含量、矿物组成与可塑性、烧失量、收缩率和吸水率等性能的分析与测试。常规分析测试方法虽然对判别陶土矿质量有较好的效果,但是对于粉砂质泥岩和泥质粉砂岩这两类对陶土矿质量影响较大的岩石,在化学成分上却难以区分。笔者在开展宜兴陶土矿资源调查时,采用综合矿物分析系统(Tescan Integrated Mineral Ana-lyzer,TIMA)对从岩心中选取的矿料和当地优质矿料的矿物成分、含量及其粒度分布等进行了测试分析和对比,研究发现:优质陶土矿中黏土矿物的含量占比在30%以上,矿物的粒度区间极窄,基本为泥级;石英的粒度区间较宽,基本为泥级、粉级和细砂级,且不同粒级的石英分布较均匀,石英含量趋势线平稳或向粗粒级方向收缩。因此,认为矿物的成分、含量及其粒度分布是影响陶土矿质量的重要因素。通过TIMA测试不仅可以弥补利用化学成分难以判别矿与非矿的不足,还可以有效地判别矿石质量与产品质量之间的内在关系。
