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Characteristics And Genesis Of The Hemushan Iron Deposit, Maanshan, Anhui Province

Posted on:2016-12-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:G LuoFull Text:PDF
GTID:1220330461995856Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
The Hemushan iron deposit in the famous Ningwu porphyrite iron ore district is unique in background and ore type. The orebodies of this deposit are mainly hosted in contact zone between diorite pluton and Triassic marble of the Ningwu volcanic basin. Based on the previous studies, a detailed study has been carried on this deposit, with focuses on the discrimination of characteristics of the diorite, iron orebodies, and metallogenic fluid, division of ore type, alteration, and metallogenic period, and establishment of a model for the formation of the Hemushan iron deposit.Field investigation and microscopic observation indicate the occurrence of brecciated, disseminated, and vein ores in the Hemushan iron deposit. The wall-rock and magnetite breccias occur in the brecciated ore, and the magnetite has subhedral-anhedral texture. The disseminated ore is mainly composed of actinolite, phlogopite, apatite, and magnetite. These minerals are small in size and metasomatic in texture. The vein ore mainly consists of phlogopite, apatite and magnetite. They are characterized by coarse grain and euhedral- subhedral texture. Sometimes, intergrowth vein of magnetite with apatite can be observed. According to the mineral assemblages and mutual interpenetration relationships, the ore-forming process could be divided into early metallogenic period(albite-diopside stage), middle metallogenic period(magnetite and hematite stages), and late metallogenic period(quartz-pyrite and carbonate stages). The magnetite stage in the middle metallogenic period could be further divided into disseminated and vein magnetite sub-stages.Geological section survey and petrographic observation show the existence of the outer zone of hornfelsization and marbleization in the periphery strata(the Zhouchongcun and Huangmaqing Formations) of the ore bodies, the dark zone of actinolite- phlogopite- apatite- magnetite alteration in the contact zone, and the inner light zone of albitization in the pluton. More phlogopite occurs near stratum and more actinolite near pluton in the dark alteration zone. Laser Raman microprobe analysis and microthermometry of fluid inclusions show that ore-forming fluids could be approximated as an unsaturated Na Cl-H2 O system. From the magnetite stage to the carbonate stage, the ore-forming fluids varied from a magmatic hydrothermal solution with higher pressure(20 to 70 MPa), higher temperature(averagely 414℃), and higher salinity(averagely 25.01 wt. % Na Cl equiv.) to a mixing hydrothermal solution of magmatic water with meteoric water with low pressure(1-10 MPa), low temperature(averagely 168℃), and low salinity(averagely 6.18 wt. % Na Cl equiv.). Water-rock interaction and fluid boiling in the magnetite stage may be the significant mechanism for the formation of magnetite.Based on the data in this paper, the Hemushan diorite belongs to a quasi-aluminous type of magmatic rock with mixing source of crust with mantle. Iron as a type of ore-forming material was mainly derived from dioritic magma, while sulfur partially from the magma and partially from strata. Integrated study indicates that the Hemushan iron deposit is a magnetite-apatite deposit with an origin of moderate-high temperature magmatic hydrothermal replacing and filling. The brecciated magnetite was formed by hydrothermal cryptoexplosion, the disseminated magnetite by hydrothermal metasomatism, and the vein magnetite by hydrothermal filling.
Keywords/Search Tags:Porphyrite iron deposit, ore deposit geology, mineralogy, ore deposit geochemistry, ore deposit genesis, Hemushan in Anhui province
PDF Full Text Request
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