| The Huogeqi ore field is a typical wholescale copper polymetallic deposit of Neoproterozoic SEDEX in the north side of langshan orogenic belts in the western area along the northern edge on the north China Craton(NCC),which consist of three deposits,the No.1 mainly includes Cu occupied the most part in Huogeqi,the No..2 and No.3 deposit mainly include Fe associated with copper and lead,they show Cu-Pb,Zn-Fe mineralization horizontal zoning from the No.1 deposit to the No..3 deposit of NEE-striking.The iron ores from No.3 deposit is studied by this paper,which present a structure of syncline and returning drape looking like a tongue with some unknown plastic faults,occurring only in diopside amphibolite of the second rock formation in Langshan group,and has a apparent edge with the roof and floor surrounding rock.According to the age(from 984Ma to 1024Ma)of galena from the same stratum in No.1 deposit and petrogeochemistry imply that it originates from Mesoproterozoic mudstone and limestone.So it controlled by strata,times,and rock obviously.Among the No.3 deposit,the types of iron ore are distributed into magnetite and phyrrotite-magnetite,and have the mineral arisen sequence of magnetit-phyrrotite-pyrite-chalcopyrite-galena and diopside-tremolite-actinolite,in which has a connection between magnetite and diopside-tremolite and the typical characteristics of sedimentation,metamorphism,shearing.The magnetite is composed of fine and coarse grain,which mainly contain fragmented and minor metasomatic morphology.And can be found some magnetite looking like metasomatism occurred in crevice and cleavage and mineral inclusion in calcite of the palimpsest cuttings.And discover some blastoporphyric garnets without breaking the microstratification of rocks in growing,and contains a set of conjugate schistositys.The garnets have two periods:the early phase which is close colorless form from high-grade amphibolite-facies,the later which is shallow rosy,radial,ring-shaped and clean form from the low amphibo-lite grade,and also can be found the later thick veins and latest supergene phenomena.The REE model of magnetite is characterized by enrichment in light REE which are no significant differences,positive Eu and Ce anomaly and high abundance of Ge?Co?Cr?Ni?Cu?Pb?Zn.It also can be found features of Eu and Ce anomaly in diopside amphibolites,igneous rock and stratum,and the REE and model of magnetite is very similar to the model of diopside amphibolites,igneous rock.combine the study of trace element characteristics about the roof and floor wall rocks,the existence of siderite,the analyses of sulfur and lead isotope,and the study of mafic igneous rocks show that the magnetite come from the metamorphism of siderite and ferrous carbonatite,and on the primitive ore-forming materials,the strata take up the main part,little may originate from Archeozoic crystalline basement,part from Mesoproterozoic igneous rocks which also provide high heat resulting in circulation of seawater and thermal metamorphism of rocks.The existence of joints in Neoproterozoic amphibolites and Caledonian homblendite,mylonitization in wall rock,and conjugated joint in garnet,all these show that the intense shear structure in hercynian period.To sum up,it experienced 4 stages:Neoproterozoic syngenetic sedimentation with part of the formation of magnetite,regional metamorphism in late Neoproterozoic with integral part of the formation of magnetite in low amphibolite facies,magmatic thermal contact metamorphism in hercynian period which have multistage effects(the early recrystallization of magnetite,then the development of crevices,the terminal generation of thick veins),the development of hypergenesis.So the genetic type of the No.3 ore deposit is a submarine hydroth-ermal sedimentation(with thermal metamorphism)-regional metamorphism-magmatism restruction superposed deposit. |
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