A Study On Metallogenic Environment And Genetic Of The Longshoushan Group Metamorphic Iron Ore In The Jinchuan Area

The Jingchuan Longshoushan rock group is located in the Longshou mountain uplift beltof the southwestern margin in Alashan Block of the North China Plate, known for itsword-class giant Ni-Cu sulphide deposits.In order to take a further exploration of Jingchuandeposits’ deep extension as well as how the major fault F1spread in this region, the JSDCdeep drilling position is located in the mining area of the second Jingchuan mine.In the JCSD drilling process, there are4section magnetite layers founded through corecatalog and statistics, which are all1000meters below the surface, the cumulative thicknessis more than260meters. The magnetite phenomenon of such grade has never been found inthe limits of this area before, its mineral composition、mode of occurrence、metallogenicenvironment and mineralization are not clear. Through this surface sampling、regionalgeological profile survey and drilling core detailed catalog in the area, caring out the researchof the petrology、geochemistry、 mineralogy characteristics, compared with the DongdashanIron Mine, get the initial understanding about magnetite mineralization environment、mineralization age、deposit genesis in this area, achieve the following results:1、 The metamorphic rocks of the Longshoushan rock group include plagioclaseamphibolites、mixed granite、the marble rock、schist and gneiss; Metamorphism based mainlyon regional metamorphism, According to the typical mineral assemblage of mainlydetermined lithology of the rock group have reached amphibolite facies.2、The original rocks of the Baijiazuizi formation composed by the two types ofsedimentary rocks and volcanic rocks, metasedimentary rocks include mudstone、greywacke、and sandstone, it belong to the continental margin sea environment, metavolcanic rocksinclude basalt、trachyte、rough dacite，the basalt’s tectonic environment belongs to thecontinental margin arc environment, the total construction area described as continentalmargin sea-continental margin arc environment.3、According the zircon U-Pb isotopic dating of rocks to get the original diagenetic ageabout2.02~2.18Ga, the regional metamorphism age is1.85~1.93Ga; The magnetitedeposits by the regional metamorphism and migmatization enrichment, its metallogenic ageslightly later than the metamorphic rock diagenetic age.4、The magnetite type in this area belongs to the sedimentary-metamorphic, the formingmaterials are from sedimentary rocks and volcanic rocks, late regional metamorphism and migmatization is the main mineralization. The metamorphic restructure iron-bearingconstruction of the original rock, eventually formed the banded magnetite; Comparison withthe Dongdashan Iron Mine, the two deposits have similar geological setting and geochemicalcharacteristics, they have the same genetic type. Average content of magnetite in the areaaround6%,20samples were analyzed the change of the content of TFe in3.17%~23.17%, theaverage content of TFe is11.49%, it belong to the ultra-poor magnetite.