| 凡口铅锌矿床海底热泉喷溢成矿的物理化学环境 |
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| 引用本文：.1998.The physical and chemical environment of the Fankou lead-zinc deposit formed by submarine hot-springs[J].Mineral Deposits,17(3):240~246 |
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| 基金项目:地矿部“中国若干超大型矿床成矿背景和找矿预测”和国家攀登预选项目（95-预-39） |
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| 中文摘要:凡口铅锌矿是发育下碳酸盐岩建造中的海底喷溢沉积矿床，以“一大二富三集中”的特点和典型的地质地球化学特征吸引着中外矿床地质工作者。叠层状矿体发育于同沉积断裂的旁侧，矿层与灰岩呈沉积接触关系。矿石具沉积碎屑组构，黄铁矿、闪锌矿具外生特征。稀土元素组成和硫同位素组成反映矿床与同生作用有关。铅同位素组成具有壳源和下地壳来源铅的特征。矿区主要矿层经历海底热泉喷溢沉积成岩的演化。 |
| 中文关键词:海底热泉，元素分布，稀土组成，同位素，包裹体，凡口铅锌矿床 |
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| The physical and chemical environment of the Fankou lead-zinc deposit formed by submarine hot-springs |
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| Abstract:The Fankou lead-zinc deposit, a very important stratabound deposit in northern Guangdong, is a sedimentary-accumulative deposit of ore-bearing hot spring. The host rock is Upper Middle Devonian and Lower Carboniferous limestone. The ore-bearing hot water circulated at the deep level was exhaled along contemporaneous faults onto the sea floor, followed by the precipitation of metallic sulfides to form orebodies on both sides of the contemporaneous faults. The mineralization and the precipitation of carbonate are developed simultaneously, and there is no intersection between the bedding orebodies and the veinlike orebodies. Some water worn structures are observed on both the top surface and the floor of the orebodies, and collapse structures are found within the orebodies. Due to the influence of the ore-bearing acidic hot spring, S, Pb, Zn, Fe2+ and SiO2 contents of limestone in the apicalplate of the orebodies increase evidently, while Cao content decreases. Semrrounded pyrite gravels are observed in the limestone of the apical plate. Mineral composition is simple, and the granularity of the metallic sulfides are very fine, with 80% of them smaller than 0.1~ 0.2 mm. Metallic minerals are mainly pyrite, sphalerite and galena, whereas gangue minerals include quartz, calcite, clay, dolomiteetc. Many pyrite and sphalerite grains unde rwent precipitation-stirring or removal- resedim entation. EREE values of ores are lower than those of limestone, and EREE values of pyrite from ores are lower than those of sphalerite. δ34S of sulfides from ores are 15‰~25‰, showing a marine sulfate origin. Lead isotopic constituents of ores are of simple crustal origin with μ9.90~ 9.39 and monostage model age of 310×l06 a, which is equivalent to the period of the Paleozoic sedimentary basin. The authors hold that the acidic ore-beaaring hot spring water erupted along the contemporaneous fault prevented CaCO3 in the sea water around it from crystallo-precipitation, leading to the formation of a"V" -shaped trough. This "V" -shaped trough not only caused the high-density ore-forming solution to stay in it for a long time but also prevented the crystalloprecipitated sulfides on the sea floor from large-scale sea current washing. Therefore, this "V" -shaped trough is indispensable for the form ation of such massive sulfide deposits as the Fankou lead-zinc deposit. |
| keywords:submarine hot-spring, distribution of elements, REE composition, isotopic composition, fluid inclusion |
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