Effect of Sulfate Evaporate Salt Layer over the Formation of Skarn-Type Iron Ores
详细信息
- 责任者：Li Yanhe (Key Laboratory of Metallogeny and Mineral Assessment ; MLR ; Institute of Mineral Resource ; CAGS ; Beijing 100037 ; China) ; Xie Guiqing
- 刊名：Acta Geologica Sinica
- 出版年：2013
- 卷期：87(9)
- 关键词：铁矿 ; iron ores ; 膏盐层 ; gypsum and salt succession ; 河北 ; Hebei Province ; 湖北 ; Hubei Province
- 页码：p.1324-1334
- 图表：6 illus., 1 table, 50 refs.
- 分类号：1001
- issnNo：ISSN0001-5717
- isbnNo：CN11-1951/P
摘要
The skarn type iron deposit is one of the most important types of rich iron deposits,accounting for about 60% of total rich iron ore reserves in China.The ore-controlling mechanism of sulfate evaporate salt layers is unclear,however,the relationship between layers and skarn iron deposits have been attracting widespread attention of geoscientists recently.In this paper,the effect of sulfate evaporate salt layers on the skarn type iron mineralization has been discussed,through the case studies of Daye type and Handan type deposits which are the important iron types in China.The sulfate evaporate salt layers are rich in carbonates,gypsum and halite,and they can provide a large number of agents of mineralization for the sodium alteration,scapolitization,skarn alteration,and the Fe2+ transport as the complex（e.g.Na-Fe-Cl）,like Na+,Cl-,CO32+ and so on.On the other hand,the sulfate evaporate salt layer is the most important oxidation barrier in the depth crust,which could oxidize the Fe2+ into Fe3+ in the silicate magma and hydrothermal solution and enrich the iron to be the iron deposit.It is a key factor of the ore-forming of the skarn type iron deposit.In Daye district,the salt layers belong to the Jialingjiang Group in the lower part of Middle Triassic,and in Handan-Xingtai district,the salt layers belong to the Majiagou Group and Fengfeng Group in Middle Ordovician.The high δ34 S values of sulfide in both districts indicate that most of sulfur of the skarn iron deposit is derived from sulfates in the salt layers,and the proportion is approximately 80%.The reduction temperature is more than 500℃.The temperature of the sulfide precipitation was lower and the time of the precipitation was relatively later than reduction.The higher the δ34 S value of sulfate or the reduced temperature is,the higher the δ34 S value of sulfide will be.Otherwise the more the proportion of the original magma sulfur is,the lower the δ34 S value of sulfide is.While the magma is assimilating salt layers,SO42- oxidize Fe2+ into Fe3+ in the silicate melt,which prevent Fe2+ to enter the lattice silicate minerals,with forming Fe3O4 or Fe2O3 to enter melt.The immiscibility occurs between iron oxide and silicate melt in magma chamber,by the effects of P,NaCl,water,and so on,forming the iron ore magma which eventually precipitated in a favorable tectonic area as the magma type iron deposit.In skarn iron deposits,ore magma filling type and hydrothermal-metasomatic type ore bodies coexist,with a certain zonation or gradual transition in space.The ore magma filling type ore bodies are usually located deeply near the intrusive rocks related mineralization,while the hydrothermal-metasomatic ore bodies are located in front of ore fluid migration.In addition,SO42- itself is reduced into S2-,while it is oxidizing the Fe2+,and S2- combine with Fe2+ to form pyrite which is located in top or side of iron deposits.
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