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Geological And Geochemical Characteristics And Genesis Of Longqiao Iron Deposit In Luzong Basin, Anhui, China

Posted on:2010-08-27Degree:MasterType:Thesis
Country:ChinaCandidate:C DuanFull Text:PDF
GTID:2120360275478108Subject:Mineralogy, petrology, ore deposits
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The Luzong Mesozoic volcanic basin is located in the Lower Yangtze fault Belt, north margin of the Yangtze Block. It extends from the Tan-Lu fault zone to the east. There are abundant of metal and non-metallic mineral resources in it. Longqiao iron deposit is one of the important large deposits in this basin. It is controversial on the genesis of this deposit. Different genesis leads to different prospecting criteria. The study of geological–geochemical characteristics and genesis of Longqiao iron deposit is very valuable.This author of this paper takes ore and altered wall rocks of Longqiao iron deposit as the main research object under careful detail field study. The geological and geochemical characteristics, the age of the iron mineralization, the mineralization process of Longqiao iron deposit have been investigated through petrography, X-ray, electron probe analysis and 40Ar-39Ar isotopic dating.Lamellar ores are included by massive ores and present in the upper parts of ore bodies. It consists of siderite and magnetite. Some siderites are decomposed into magnetites, left residual texture, some siderites are replaced by magnetite. Lamellar iron ores display characteristics of both hydrothermal and sedimentary genesis.The process of mineralization can be divided into sedimentary stage and hydrothermal stage. Based on the electron probe analysis and typomorphic research on siderite and magnetite, the results show that the siderite in the lamellar ores is from sedimentary process, the magnetite in the lamellar and massive ores is metamorphic origin from sedimentary, but the magnetite in the altered wall rocks belong to magma.Andradite and phlogopite are the two major gangue minerals in Longqiao deposit, they intergrowth with magnetite. Calculation based on the garnet– biotite geothermometer, the ore-forming temperature of the hydrothermal minneralization stage is about 350℃.The characteristics of lead, hydrogen, oxygen, and sulfur isotopes of ore minerals and gangue minerals suggest that the ore– forming fluid and a portion of metals are from the magma. The isotopic age of hydrothermal mineralization of Longqiao iron deposit is 130.5±1.1Ma, through 40Ar-39Ar isotope dating. The 40Ar-39Ar plateau features indicate that the sample has not been affected by any new heat event since the formation of the Phlogopite.Geochronology and isotope geochemistry of syenite under the iron ore bodies show that the hydrothermal mineralization and the magmatism are closely related.According to the above geological and geochemical studies on the Longqiao iron deposit, a metallogenic model has been set up. This deposit is a sedimentary– hydrothermal reworked deposit, which is different to porphyrite iron deposits of Ningwu basin and can not be put into the category of IOCG type deposit. It provides an effective tool for iron deposits exploration in the study area.
Keywords/Search Tags:Luzong basin, Longqiao iron deposit, Magnetite, Siderite, Phlogopite, 40Ar-39Ar age, Mineralization process
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