| 祝新友,王京彬,王艳丽,程细音.宁乡式铁矿成因新解——后生热液成因的地质与地球化学证据[J].矿产勘查,2015,6(1):7-16 |
| 宁乡式铁矿成因新解——后生热液成因的地质与地球化学证据 |
| Study on genesis of Ningxiang type (Clinton type) iron deposit, Hunan |
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| DOI： |
| 中文关键词: 宁乡式 铁矿 鲕状赤铁矿 盆地卤水 矿床成因 湖南 |
| 英文关键词: Ningxiang type iron deposit, oolitic hematite, basin brine, genesis, Hunan |
| 基金项目:国家科技支撑课题 (编号:2011BAB04B08)、国土资源部公益性行业科研专项(编号:201411024)和全国危机矿山接替资源找矿项目(编号:20089927)共同资助。 |
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| 中文摘要: |
| 宁乡式铁矿床广泛分布于华南及四川盆地等地区,矿体呈层状产于浅海相细碎屑岩—碳酸盐岩中,局部形态复杂,常见穿切关系及以鲕状赤铁矿为胶结物的角砾状矿石,围岩蚀变弱。矿床及矿石未遭受明显的后期热变质影响。矿石矿物为鲕状赤铁矿,大部分矿床中还共生有磁铁矿、菱铁矿,少量黄铁矿,脉石矿物主要是白云石、方解石。石英砂粒表面遭受溶蚀而不平。矿石中常见完整的化石与鲕粒共存,部分化石被镜铁矿、磁铁矿交代,细粒白云石作为胶结物。矿石碳酸盐的δ13C为-2.8‰~-4‰,δ18O为18.7‰~20.7‰,87Sr/86Sr为0.7132~0.7176,不同于正常沉积的海相碳酸盐岩,而与密西西比河谷型(MVT)铅锌矿床相似,且自近矿围岩→赤铁矿矿石→磁铁矿矿石→菱铁矿矿石,δ13C、δ18O降低,86Sr/87Sr升高。地质地球化学特征均显示,宁乡式铁矿可能并非简单的浅海相正常沉积矿床,而更可能是后生的,成矿作用可能与盆地卤水作用有关,沿特定层位交代成矿。 |
| 英文摘要: |
| The Ningxiang type iron deposits are widely distributed in the South China and Sichuan Province. The iron orebodies occurred in the marine fine clastic - carbonate rocks in lamellar form but complicated shape locally. It is common to see the intersected orebodies and brecciated ore cemented by the oolitic hematite. The wall rock alteration is weak, the orebodies and iron deposit have not suffered significant thermal metamorphism. The main ore mineral is oolitic hematite and associated with magnetite and siderite and minor pyrite within most deposits. Gangue minerals mainly are dolomite and calcite. The surface of quartz grain is not smooth because of hydrothermal dissolving. The fossil commonly coexists with oolitic hematite in the ore. And some fossils are replaced by specularite and magnetite. The δ13C value in the ore is -2.8‰ ~ -4‰, δ18O in the ore is 18.7‰ ~ 20.7‰, and the ratio of 87Sr/86Sr in the ore is 0.7132 ~ 0.7176, which are very different from those values of marine carbonates and similar to those of Mississippi valley type lead-zinc deposits. From the wall rock nearby the orebody to the oolitic hematite ore to magnetite ore and to siderite ore, there is a trend of decreasing δ13C and δ18O value but increasing trend of 87Sr/86Sr ratio. The geological and geochemical characteristics of the iron deposits indicate that the Ningxiang type iron deposit may not be formed in the simple marine sedimentary basin in the shallow sea, probably the deposit is epigenetic mineralization, which may be related to the basin brine, and the orebodies are formed along a particular layer by the replacement mineralization process. |
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