| The Middle-Lower Yangtze River Valley Metallogenic Belt is an important copper(iron),gold and polymetallic metallogenic belt in China,which is represented by porphyry-skarn type copper-gold deposit and porphyrite type iron deposit.The porphyrite type and skarn type iron deposit in the Metallogenic belt are mainly produced in Luzong Basin,Fanchang Basin and Ningwu Basin,and many researches have been done on magnetite in iron ore deposits,but the study of hematite in the deposit is relatively weak.The iron ore deposits with hematite as the main ore mineral in the Metallogenic belt,including Dabaozhuang iron deposit,Panshiling iron deposit,Daling iron deposit,Gushan iron deposit and Taochong iron ore deposit,are good targets for studying different genetic types of hematite.On the basis of previous studies on the genesis of the deposits,carrying out the detailed microscopic structure observation of hematite,and the mineralogical characteristics of different genetic types of hematite were determined by means of oxygen isotope test and diffuse reflectance analysis.On this basis,LA-ICP-MS in situ analysis of different genetic hematite is carried out to explore the characteristics of trace element composition of different genetic hematite,and to try to analyze the differences of trace elements and their controlling factors.The main conclusions of this paper are as follows.(1)Hematite is the volcanic sedimentary origin in Panshiling deposit,and hematite in Dabaozhuang deposit is the result of sedimentary-hydrothermal superposition reconstruction in the Middle-Lower Yangtze River Valley Metallogenic Belt.The genesis of hematite from the Daling deposit as a magmatic hydrothermal origin.An obvious metasomatic structure of hematite in the Gushan deposit,which indicates that the magnetite was oxidized to hematite by the late hydrothermal process.Hematite and specular hematite from Taochong are non-magmatic hydrothermal genesis.The crystalline forms,symbiotic minerals and diffuse reflectance spectra of different genetic hematite are distinctly different.(2)Hematite,which is closely related to the genesis of magmatic rocks,such as volcanic sedimentary genesis,sedimentary-hydrothermal superposition reconstructed genesis and magmatic hydrothermal origin,the oxygen isotopic values of them are similar,ranging from 0.5~3.4‰,and the hematite of non-magmatic hydrothermarl origin is-0.7~2.3‰,which is obviously different from the former three.The total amount of REE of hematite,which is closely related to the genesis of magmatic rocks,is very similar to the right-dip type of the distribution pattern and the characteristic value,while the total amount of REE of hematite of non-magmatic hydrothermal origin is obviously two orders of magnitude lower,only 2.88~4.51 ppm.The above geochemical characteristics indicate that it is difficult to invert the formation process of most hematite by the oxygen isotope values and the REE characteristics of hematite and it is not of obvious of significance for the genesis of hematite but it can clearly distinguish the non-magmatic hydrothermal hematite.(3)The V-Ti?Mg-Mn-Al?Co-Ni and As-Sb elements in hematite of different genetic types have regular variation characteristics and are characteristic trace elements of hematite,which reflects the different conditions of formation temperature,oxygen fugacity and metasomatic source rock of different genetic hematite.The contents of these characteristic elements are controlled by the above-mentioned conditions,so it is feasible to determine the genesis of hematite and even invert their formation environment by the characteristics of some elements in hematite.(4)Based on the statistical method of IOGAS software,the genetic discriminant diagrams of As-Sb?As+Sb-Ti+V and Mg/Al-Ti in hematite are established.These diagrams can be used to distinguish between different genetic hematite,and volcanic sedimentary hematite has high Ti,low Mg/Al ratio;the sedimentary-hydrothermal superposition reconstructed hematite is characterized by low Ti,high Mg/Al ratio,the magmatic hydrothermal hematite Ti is between the former two and low Mg/Al ratio;hematite with metasomatic origin of magnetite has higher Mg/Al and As/Sb,and hematite of non-magmatic hydrothermal origin has the lowest content of Ti and the lowest value of Mg/Al. |
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