| Magnetite has always been the main type mineral in diagenesis and mineralization,and it occurs in all kinds of rocks and ores in nature.At the same time,due to its special lattice characteristics,the protoplasmic homomorphism is generally developed,which affects the components of the trace elements.With the rapid replacement of high-precision detection techniques,researchers can well restrict the key issues such as genetic types,metallogenic mechanisms and complex metallogenic environments?such as temperature,oxygen fugacity and melt/fluid composition?in ore deposits by using magnetite geochemical characteristics.This article through to the Laos warned magma type iron ore deposit,Zhongdian Hongniu-Hongshan skarn type copper deposits in the two different mineralization type magnetite as the research object,and according to the metallogenic system in the aspects such as petrology,ore deposits,geochemical study,summarize the magnetite ore deposit geological characteristics and genetic types of the ore deposits,metallogenic environment and the influence of the metallogenic mechanism,and on the basis of research on magnetite,comparative analysis of the similarities and differences between type of magma and hydrothermal magnetite and significance to the study of ore deposit instructions.The Pa Lay Thong iron deposit in Laos is the most typical large iron deposit in the south vientian-khorat Mesozoic basin.It is divided into two ore sections,the west ore section is the pea-shaped and block-shaped magnetite rich ore body,the east ore section is mainly the bacce-shaped poor hematite ore body,and the west ore section is mainly the Cenozoic iron-rich basalt.In this paper,the detailed field geological survey and microstructure analysis of the pea-shaped and blocked-magnetite in the west ore section were carried out.Analysis of relatively fresh magnetite electron probe?EPMA?and laser densification inductively coupled plasma mass spectrometry?LA-ICP-MS?shows that Ti O2-Al2O3-Mg O triangular map of magnetite in the Pa Lay Thong iron deposit falls into the ultrabassion-basic-neutral magmatic region.Trace elements were enriched with V,Ti,Cr,Co,Ni and Ga,and incompatible elements such as deficit Sr,Ba and Mg.The content of elements Co and Ni is high,and the higher Ni/Co ratio can reflect the origin and the deep source material.Ti content is high and Ni/Cr ratio?1,which falls into the range of hydrothermal magnetite in the Ti-Ni/Cr figure.Ga-Sn diagram shows that magnetite belongs to porphyry hydrothermal origin.The genetic discriminant map of?Ca+Al+Mn?-?Ti+V?or Ni/?Cr+Mn?-?Ti+V?shows the characteristics of both Kiruna type and porphyry type deposits.V content indicates that magnetite is formed in a low oxidation environment.The discriminant diagram of?Al+Mn?-?Ti+V?formation temperature shows that the formation temperature of magnetite is within the range of300°-500°c.It is believed that the ore-forming materials in the Pa Lay Thong iron deposit are mainly derived from the iron-rich fluid formed by magmatic evolution,and the magnetite has the characteristics of hydrothermal origin due to the metasomatism of magmatic hydrothermal fluid in the later period.It is of great significance to study the genesis of Pa Lay Thong iron ore to summarize the regional metallogenic rule and guide the prospecting and prediction of the same type ore deposits.The Hongniu-Hongshan copper deposit in Yunnan is a typical skarn deposit in the Zhongdian arc region of northwest Yunnan.The ore bodies are mostly stratiform,stratiform and vein-like in the position of the contact top and bottom surface between the marble intercalated top and the keratinized sandstone,and the closer they are to the carbonate rock,the stronger the surrounding rock alteration is.Papers in collecting a large number of relevant field geological data and on the basis of predecessors'research summary,has carried on the detailed petrology,mineralogy,ore deposit and geochemical research,selected the main mining areas are closely associated with mineralization in granite porphyry,skarn magnetite in the microscopic observation of microstructure,and select representative magnetite by electron microprobe?EPMA?and laser ablation inductively coupled plasma mass spectrometry?LA-ICP-MS?test in situ composition analysis.The test results show that the magnetite in granite-porphyry is characterized by high Ti,V,Ga,Cr,Ni and low Mg,Al,Ba,Sr,Mn,with typical genetic characteristics.In some samples,there are two stages of magnetite,and the elements show a trend of evolution from magmatic magnetite in the first stage to hydrothermal magnetite in the second stage.In the genetic discriminant diagram of Ti O2-Al2O3-Mg O and Ti O2-Al2O3-Mg O+Mn O,the primary magnetite fall is mainly of magmatic origin,while the secondary magnetite shows contact metasomatism origin,and the two phases of magnetite show a transitional trend.The genetic discriminant charts of Al+Mn-Ti+V and Ga-Sn indicate that both the primary and secondary magnetite have the characteristics of porphyry deposits.V was enriched in both phases of magnetite,indicating that the oxygen fugacity ratio in the forming environment of magnetite was low,and the difference in oxygen fugacity in the forming environment of magnetite in the two phases was not significant.?Al+Mn?-?Ti+V?formation temperature discrimination diagram shows that the temperature range of the formation environment of the primary magnetite is greater than 500?,and the temperature range of the secondary magnetite formation environment is 300-500?.The magnetite in skarn is a typical hydrothermal metasomatism with high Mg and Mn values,and its average contents are 1992×10-6 and 3668×10-6,respectively.The metallogenic temperature is close to 200-300?,and the content of Ga element is also decreasing.The degenerating and metamorphic stage of magnetite was between skarn stage and metal sulfide precipitation?metallogenic stage?,and the oxygen fugacity was between-30 and-32,which was significantly lower than that of skarn stage,indicating that the ore-forming fluid in magnetite formation had been transitive from oxidization to reduction;The change of REDOX conditions may be the main reason for the massive precipitation of metal sulfide during the metallogenic period.Comprehensive the above two different magnetite typomorphic characteristics of ore deposit formation,and with the world within the scope of the trace elements in different geological environment generated in the magnetite comprehensive study found that the change of the trace elements in magnetite range wide,special elements such as Mg,Al,Ti,V,Co,Ni,zinc,Cr,Mn,Ga and Sn in various genetic types of magnetite can reach levels,and these elements in the form of magnetite and magma hydrothermal magnetite is slightly different,Mn,Ni,Cr,Ti,V and Ni/Cr,V/Ti ratio can be used to trace magnetite genetic types,Ti can indicate temperature,V and Cr can indicate oxygen fugidity,etc.At the same time,it is also found that the changes between trace elements in either magma or hydrothermal magnetite can effectively trace the study of ore deposit mineralization process. |
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