Metallogenic And Geological Characteristics Of Iron Ore Deposits In Wolong, Benxi

Anshan-Benxi, a region in Liaoning province, has the most widely dispersed iron ore in China, and Benxi, most of all, has extensively occurring iron deposits of varying sizes. Wolong is located in the southeast of the Anshan-Benxi metallogenic belt and forms part of the Anshan-Benxi iron belt. In Wolong, iron-bearing metamorphic sequences occur in the upper Archean Anshan Gr. The paper analyzed primarily the host rock and lithogeochemical conditions of Wolong iron deposits in order to determine local prospecting ranges and ore indicators. The thesis is aimed at determining the genesis of iron ore deposits in Wolong area to provide the basis for ore prospecting.In Wolong, iron ore occurs in stratiform or stratoid layers in the Cigou Fm. of the Archean Anshan Gr.(Arcg). Distributed mostly as relicts of varying sizes in late Archean metamorphic plutonic intrusions, iron ore occurs primarily in the form of amphibolite, biotite granulite, chlorite schist and magnetite quartzite, with occasional occurrence of various schist types containing special metamorphic minerals. Because local iron ore is basically low-grade magnetite ore, the major minerals include magnetite and the minor minerals include martite and pyrite(occurring in very rare amounts). Gangue includes primarily quartz, feldspar, biotite and amphibole and secondarily chlorite, actinolite, tremolite and muscovite.The major iron-bearing exposed strata belong primarily to Arcg, a widely distributed and highly mineralized formation in the area of interest. Arcg is the major iron-bearing formation in the Anshan Gr. and the major ore indicator of Anshan iron deposits. It is a sedimentary metamorphic iron deposit, or “Anshan iron deposit”. The paper tried to investigate the host rock and metallogenic conditions in Wolong iron ore deposits on the basis of the formations, ore body features, ore features and lab analysis findings of Huanxiling Iron Mine, Sanjiazi Iron Mine and adjacent mining areas.Both Arcg and Ardyg underwent regional dynamothermal metamorphism in the late Archean metamorphic stage. A typical metamorphic rock assemblage comprises phyllite, granulite, amphibolite, magnetite quartzite, etc. The metamorphisms temperature is 410-760 ?,the pressure is 2-10 Kb(strong-pressure rock deformation), and themetamorphic series isamedium-to-lowpressure, high amphibolite and low greenschist series. The metamorphic grade is an amphibolite togreenschist facies. The protolith is constructed of intermediate to basic, volcanic to sedimentary siliceousferrilite.The total amount of rare earths in the plagioclase amphibolite of Cigou Fm is slightly low, ?REE(65.10~88.90)×10-6, with an average of 74.30×10-6; the ratio of light and heavy rare earth is 1.77~2.99, with an average of 2.09, a right-slow-inclination type with the feature of the slight gathering of light rare earth. Based on the relevant data of major elements, trace elements and rare earth elements, as well as TAS, AFM and tectonic discrimination plot, the protolith of plagioclase amphibolite is considered as island arc tholeiite.The total amount of rare earth in iron ore is 3.48~21.07, which is low. Rare earth curve is generally right inclined, La_N/Yb_N=1.40~7.04. Light rare earth is right inclined, La_N/Sm_N=1.85~13.72, with a slight fractionation. Heavy rare earth is flat, almost with no fractionation. Eu shows positive anomaly. ?Eu values are between 1.36 and 4.33, showing significant positive Eu anomaly. The Y/Ho value is high, ranging from 29.38 to 76.67, which is similar to the Y/Ho value of modern seawater, suggesting the contribution of seawater in the mineralization process. The Ce/Ce* value is between 0.71 and 0.94, which is generally greater than 0.80, and the negative anomaly of Ce is not obvious.The paper revealed the laws of metallogenesis in Wolong iron deposits by studying their metallogenic characteristics, local metallotectonics, metallogenic geology, protolith types and ore composition. On the whole, the paper studied Wolong iron ore deposits to summarize local metallogenenic/geological settings and laws of metallogenesis.