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Geochemical Characteristics of the Huoqiu BIF Ore Deposit in Anhui Province and Their Metallogenic Significance: Taking the Bantaizi and Zhouyoufang Deposits as Examples
详细信息   
摘要
As a large BIF iron ore field,the Huoqiu iron ore filed in Anhui Province is located in the North China craton. Twenty eight samples from both Bantaizi and Zhouyoufang deposits within Huoqiu banded iron formations ( BIFs) ore field were analyzed for major and trace element compositions. The results have demonstrated that the protolithes of Bantaizi gneiss and amphibolite belong to a series of subalkaline rocks,which have the volcanic arc rock characteristics of large ion lithophile elements ( LILE) enrichment and high field strength elements ( HFSE) depletion. The Bantaizi amphibolites have the low K 2 O concentrations with low Ti / V ( Ti / V = 22. 7 ～ 25. 9 with an average of 24. 5) ,which is consistent with those of island arc tholeiite. Back-arc basin basalts are similar in chemical compositions to island arc tholeiite. The formation of BIFs frequently require tectonically stable half deep-deep basin,back- arc basin can provide the stable depositional environment for generation of the BIFs rhythm strip. Therefore,BIFs occurrences illustrate the Bantaizi amphibolites are formed in back-arc basin,which imply the tectonic environment of the Huoqiu iron ore filed. The bulk compositions of Bantaizi deposit have slightly Eu positive anomalies with ( Eu / Eu * ) SN = 1. 57 ～ 1. 82,which is consistent with Superior-type BIFs ( Abbre. S-type) . However,the Zhouyoufang deposit mainly occurred as pseudomorph specularite with significantly Eu positive anomalies ( ( Eu / Eu * ) SN = 1. 93 ～ 3. 41) ,which is resemble with Algoma-type BIFs ( Abbre. A-type) . The degree of Eu positive anomalies reflects the distance between BIFs deposition position and submarine exhalative hydrothermal vent. Therefore,the depositional environment of the Huoqiu BIFs was medium away from submarine exhalative hydrothermal vent,thus we suggest that the formation type of Huoqiu BIFs iron ore filed should belong to the transition from A-Type to S-Type. The good linear correlations between Al 2 O 3 and TiO 2 are present in amphibolites,gneiss and enclave iron deposit,demonstrating that some of the material provenances of iron ores are sourced from erosion of the back-arc basin basalt. The Y / Ho ratios range from 31. 05 to 56. 67 with the average of 46. 65, demonstrating the Huoqiu iron ore field inherited the mixtures between hydrothermal and sea water and the later contribute more. Compared with average Phanerozoic limestones,marbles in the Zhouyoufang deposit contain 28. 49% ～ 29. 10% CaO,20. 25% ～ 21. 22% MgO and minor SiO 2 ( 2. 45% ～6. 10%) ,relatively depleted in LILE and HFSE. In contrast,compared with Post Archean Australia Shales ( PAAS) ,the Zhouyoufang deposit displayed lower total REE,with considerably Eu positive anomalies,no Ce anomalies,Y / Ho ratios range from 35. 00 to 56. 67 with an average of 48. 81. These features demonstrate that the marble and iron ores hosted within are formed in an anoxic marine environment,the oxygen in sea water can oxidize Fe 2 + to Fe 3 + and lead to precipitation into Fe( OH) 3 ,but can not oxidize Ce 3 + to Ce 4 + .

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