| 论罗河铁矿床地质特征及矿床成因 |
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| 引用本文：.1984.A Brief Discussion On Geological Characteristics Of The Luohe Iron Deposit In Anhui Province[J].Mineral Deposits,3(4):9~19 |
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| A Brief Discussion On Geological Characteristics Of The Luohe Iron Deposit In Anhui Province |
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| Abstract:The Luohe iron deposit, a polycomponent magnetite deposit buried at a depth of more than 400 m, lies in volcanic rocks of the Lujiang-Zongyang area in Anhui Province. These volcanic rocks are a suite of Mesozoic eruptive rocks of continental facies characterized by well-defined bedding, basically correlatable eruptive cycles and remarkable variations in lithological characters and thickness along the strike. On the basis of the regional geology, four eruptive cycles may be distinguished, i.e., the Longmenyuan cycle, the Zhuanqiao cycle, the Shuangmiao cycle and the Fushan cycle. Isotopic ages of rocks of various cycles are from 162.3 m.y. to 108 m.y. According to the regional correlation, the sediments underlying and overlying the Zhuanqiao cycle are tentatively assigned to the Upper Jurassic and Lower Cretaceous respectively. With the volcanic eruption, the corresponling hypabyssal intrusive rocks were developed which were obviously closely related to the eruptive lava in time, space and composition, suggesting that they were derived from the same source. Petrochemical characteristics indicate that volcanic rocks in this area are a suite of approximately SiO2- saturated, slightly alkaline intermediate rocks with σ=3.3-14. The increase in alkalinity from bottom to top both in Long-menyuan and in Zhuanqiao cycle implies that during this period chemical evolution process intimately related to mineralization of this area took place in magmatic chamber. The Luohe iron deposit, for example, was produced in high-alkaline phase of the Zhuanqiao cycle. The Luohe iron deposit has three sorts of genetically related orebodies, they are in upward succession magn6tite orebody, pyrite orebody and anhydrite orebody. Ores mostly take the shape of vein or stockwork while orebodies occur in stratoid or lenticular forms. Orebodies dip gently; their projections in plan look like three concentric circles gradually getting smaller upward, thus assuming the form of a truncated cone in three dimensions. Mineralization is accompanied by extensive wall rock alterations with apparent vertical zoning, they are in downward order of hydromicazation→argillization→silicification→anydritization→pyritization→ anbydrite-pyroxeni-zation→pyroxene-K feldspathization. Temperature determinations show that formation temperatures for both alterations and mineralization decrease in upward direction, varing in the range of 5000-200℃. An investigation into the ore-controlling structure reveals the existence of a domed fracture system developed progressively in upward direction. The sulfur isotopic study and lead isotopic study of iron ore support the derivation of iron mainly from the mantle and partly from the overlying sediments-probably the Triassic anhydrite bed. This also accounts for the source of calcium. The ore-controlling structure, temperature distribution, isotopic data and thermodynamic calculations all imply the probable presence of a domed intrusive body beneath the alteration zone of the Luohe iron deposit. |
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