| The Erguxishan Fe polymetallic deposit is located in eastern Songnen Massif, middle of Yichun-Yanshou fold belt, NS-trending Xulaojiugou-Ergu anticline, Beiguan-Ping’an fault. The exposed strata in the mining area is Cambrian Xilin Group Qianshan Fromation, which is composed of dolomite marble, dolomitic crystallization limestone, crystallization limestone, banding marble, dolomitic marble, crystallization limestone with carbonaceous slate. The intrusive rock well developed in the mining area account for 80%, which is composed of granodiorite, biotite granite, syenogranite and porphyraceous granite occurred as dyke, stock and batholith. According to field work, processing and anylizing of data, combing with collect and analyse data, we conduct research on ore-associated rock and skarn from petrography, geochemistry, and obtain following conclusions:1. The Erguxishan Fe polymetallic deposit occurred contact zone between granodiorite and Qianshan Fromation Mg-rich carbonatite. The skarn is characteristic of zoning in space with width of 5~20 m. Calcareous skarn is developed close to rock body, and magnesium skarn is developed keep away from rock body. The geochemistry of trace elements for skarn and mineralized skran indicate the genesis of skarn is magmatogene with positive anomaly of Eu.2. The granodiorite in Erguxishan mining area intrude into Qianshan Formation rich-Mg carbonatite, and wall-rock alteration and mineralization is well developed in SN-trending contact tectonic fault zone, including skarnization, epidotization, ochre and petrochemicals, silicide, albitization, phlogopite, serpentine, carbonatization, chloritization, and sericitization, greisenization. Epidotization, ochre and petrochemicals, silicide is closely associated with mineralization, and Fe polymetallic occurred within it. According to material composition of orebody, paragenetic association of minerals, ore-fabric characteristics, we divided the ore-forming stage into five stages: early period of no mineralized sakrn stage, late period of magnetite skarn stage, oxide stage, early period of sulfide stage and late period of sulfide stage.3. The intrusive rock in the mining area is characteristics of rich in Si and Me, poor in Fe, and belong to high-K calcalkaline and quasi-aluminous rock. The major elements variation range for two samples of skarn rock is large. The content of Fe2O3 T and Ca O for mineralized sample(EGXS19) is clearly increase keep away from marbl. While content of Mg O is not changed, conent of Si O2 and Al2O3 is clearly reduced.4. The intrusive rock is characteristics of rich in LREE, poor in HREE, no abnormality of Ce, negative anomaly of Eu, relative poor in HFSE(Ba, Sr, P) and LILE(Nb, Ti). The REE content of marble is characteristics of rich in LREE, weaker negative anomaly of Ce and clear negative anomaly of Eu, rich in LILE(Ba, Sr), poor in LILE(K, Rb) and HFSE(Th, K, Nd, Ti). The two samples of skarn is characteristics of clear positive anomaly of Eu and HFSE(Nb, Zr, Hf, P).5. Combine with results of regional diagenetic age and isotopic dating, the ore-forming age for Erguxishan Fe polymetallic deposit is later period of Early Jurassic. The ore-forming rock is characteristic of I type granite, and forming environment is that subuction of Pacific Plate in Jurassic result in extension within study area, and lead to delamination of thickened lithosphere. The hypomagma intrude into lower crust, and heated lower crust lead to melt and happened assimilation-contamination with lower crust materials. The mixed magma ascend and formed rock associated with mineralization.6. The skarn in the mining area is genesis of magma. The ore-forming process of Erguxishan Fe polymetallic deposit is as follow: The subuction of Pacific Plate in Jurassic result in extension within study area, and lead to delamination of thickened lithosphere. The hypomagma intrude into lower crust, and heated lower crust lead to melt and happened assimilation-contamination with lower crust materials, and formed curst-mantle mixed magma in the high level magma chamber. The curst-mantle mixed magma ascend along tectonic weakness belt in the mining area, which lead to separation of rich-Fe magma and granodioritic magma. The granodioritic magma relative displacement in the vertical direction and ascend to superficial position of crust, and consolidate diagenesis with weak mineralization. Meanwhile, the rich-Fe magma happened assimilation-contamination with Qianshan Formation marble. Ca in the strata mixed into rich-Fe magma and form skarn magma. The addition of Ca is convenient to unload of Fe, and formed magmatic type dense blocky magnetite orebody and granet malacolite skarn type orebody. |
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