Geochemical Features And Protolith Restoration Of Liubagou-Hadamengou Magnetite-quartzite Deposit

Precambrian banded iron formation, widely distributed in the Early Precambrian volcanic - sedimentary rocks around the world, not only is an important part of the early geological body, but also reflects the geological features and crustal evolution characteristics in this area to some exten. Therefore, there is a great theoretical significance for studying this banded iron formation.The iron ore in the Precambrian banded iron formation plays a decisive role in the iron ore resources around the world. Occurred at the southern Ural Mountains- Daqing anticlinorium of Inner Mongolia platform uprise in the north margin of North China platform,the magnetite-quartzite formation of Liubagou-Hadamengou magnetite-quartzite deposit is one part of the northern,metallogenic belt of North China platform and belongs to the (volcano)sedimentary-metamorphic iron formation. On the basis of analyzing the ore-forming geological conditions, the protolith restoration of metamorphic wall-rocks has been carried out, the tectonic setting of the formation of the meta-volcanic rocks was analyzed and the genesis of magnetite-quartzite formation has been discussed in this paper by the method of making the analysis of geochemical features about ores and host rocks.The Liubagou-Hadamengou magnetite-quartzite deposit occurs at the biotite hornblende plagiogneiss of the Wulashan group of Archean. The trends of orebodies , controlled by the fault, stretch along east-west approximately with banded structure. The wall rock alterations developed widely, types of which are also diverse.After analyzing the major elements of these rocks, it is found that the w(SiO₂) of gneiss series changed greatly, with the range of 45.15% 72.12%; amphibolite series are dominated by low silica and alkali, which belong to unsaturated SiO₂; leptynite / leptite series have main characteristics of high silicon and alkali; magnetite-quartzite series are major in silicon and iron, in which Fe³⁺/FeT is varied from 0.47 to 0.62 and is rich in ferric iron. All of these features show that the rocks from this mining area are formed in the oxidizing environment. According to the analysis of trace elements and REE, there are obvious fractionations of LREE and HREE in the wall rocks there, showing a rightwardheeling pattern in the REE distribution diagram. Magnetite-quartzite has an relatively low REE content, andΣREE changed in the range of 34.86⁷5.67 with LREE enrichment and HREE loss, which also showed an rightwardheeling pattern in the REE distribution diagram. All trace elements have relatively low content, showing the losses of Ba, Nb, Sr, Hf and Ti in trace element spider diagrams. The protolith restoration on wall-rocks shows that gneiss series are dominated by basic volcanic rocks anda small amount of neutral-acidic volcanic rocks and argillaceous rocks, that amphibolite series mainly are basalt- basaltic andesite, that leptite series are acidic volcanic rocks, and that leptynite series belong to ferrous pelite. Through amphibotite, gneiss, leptite to granulite, the protolith of them has the trends of basalt/basaltic andesite, mediate to acid volcanic rock to sedimentary rock. Based on the analysis, the setting of the formation is mainly back-arc basin nearby the active continent margin.In addition, after analyzing, it is known that Eu of magnetite-quartzite from the Liubagou mining area has an obvious negative anomaly, while Ce shows an significant or strong positive anomaly, possibly indicating that there is a close relationship between mineralization and low-temperature hydrothermal activity with relative oxidation.