| Pingchuan iron ore deposits located on Pingchuan region,the easten of Yanyuan, the westen of Jinhe-Qinghe deep faule for the westen of Yalongjiang fault, and its tectonic position located on the western Yangtze quasi platform,between the eastern edge of the Yanyuan-Lijiang platform margin depression zone and the westen edge of the middle part of Kangdian axis,which constituted the famous Panxi Iron ore concentration area in our country, with V-Ti magnetite deposits widely distributed in Panxi region. Pingchuan iron ore deposits is a typical continental subvolcanic-rock type iron deposit in western China,which has been mined over 50 years since put into operation in 1958,becoming a crisis mines for Proved resource depletion.It's a typical crisis mines with high-level exploration and low-level research, for it's main understanding focus on the 80s in the last century,leading to a seriously lagging on scientific research.The author has been researched metallogenic regularity for Pingchuan iron ore deposits, starting with analysing mineralization spatio-temporal structure, based on field geological investigation in the system,according to the research condition, With some key geological problems during exploration.The paper has been divided dre-type, clarified the relationship between diagenetic evolution series and mineralization, determined the temporal-structure of metallogenic evolution, analysed the spatial-structure of mineralization, discussed ore deposits genesis and established a deposit model on the basis of previous work, through researching geological-geochemical characteristics and mineralization spatio-temporal structure.The main ideas and results obtained are as follows:(1) The ore types has been divided into subvolcanic hydrothermal-type,volcanic eruptions (overflow) sedimentary ore-type and magmatic shaped,according to ore-forming methods and ore-bearing rocks;(2) The basic-ultrabasic rocks with a low calcium, aluminum, magnesium-rich features,are transitional rock series between sodium-rich continental tholeiites and continental alkali basalt,which are products of continental rift environment,and Dashanshu gabbro with a evolution toward to poor calcium,high-level, iron-rich of bearing V-Ti magnetite Taihe gabbro, probablely indicated a transition of ore-type. The basic-ultrabasic rocks has a higher level of basic tend with diagenetic evolution,Huangcaoping gabbro,Dapingzi Norite-gabbro and Nantiangou lherzolite represented three basical rock units with gradually increased basic-level, and lherzolite may represent the composition of source mantle rocks. A variety of different basic-levels basic-ultrabasic rocks are product of homologous but different phases of mantle-derived magma,which constituted a complete series of diagenetic evolution. Geology-geochemistry characteristics show that Diagenesis and mineralization are different forms of the same geological processes, and basic-ultrabasic rocks and ore deposits are product of homologous but different phases by Magmatic differentiation of Comagmatic, having a very good geological-geochemical Correspondence;(3) Kuangshanliangzi ore deposit has a correspondence compositional-type of magnetite with igneous carbonatite,and also owns a similar characteristic with difference with hydrothermal magnetite,displaying a characteristic of hydrothermal mineralization on the genesis of discrimination diagram, probably having a deep-epithermal characteristic. Pyrite is metallic mineral that most closely with the magnetite,it's Co,Ni content and Co/Ni ratios indicates that mineralization is related to volcanism,and its ore-forming fluids connects with deep-source mafic, ultramafic rocks. Magnetite oxygen isotope composition indicates that ore-forming fluid with deep magma sources. The features suggest that magnetite may be subvolcanic hydrothermal magnetite with ore-forming fluid coming from deep magma;(4)Obtained a zircon U-Pb age of 255.9±1.2 Ma for Huangcaoping gabbro,which represents the time of intrusion of Huangcaoping gabbro and eruption of Emeishan basalt, and the geological age of 266.5±2.4 Ma coming from captured zircon may represented the incubation time of magmatism. Near-ore diabase and picrite obtained 248Ma reference diagenetic age, which may be matched with mineralization-age. 65Ma metamorphic age of metamorphic zircon and 58.2±5.3Ma apatite fission track age represents the time of Himalayan intracontinental orogenic fold;(5)The metallogenic evolution of the reaserch region is closely related to the Hercynian-Indosinian tectono-thermal event and Himalayan intracontinental orogenic fold of Panxi area. Pingchuan iron ore deposits, V-Ti magnetite deposits and Cu-Ni deposits are product of different metallogenic series with internal relations of Hercynian-Indosinian tectono-thermal event in the same deep geological process of Panxi area. Pingchuan iron ore deposits has gone through a macro-structure of metallogenic evolution formed by magmatic differentiation phase, volcanic eruptions (overflow) formations phase, hydrothermal phase, and subsequent transformation phase.The hydrothermal phase is the main metallogenic phase of Pingchuan iron ore deposits,and its microstructure of metallogenic evolution formed by Apatite-magnetite phase, fine-grained carbonate-magnetite phase, siderite-magnetite phase and carbonate-sulfide stage. Magmatic shaped type-volcanic eruptions (overflow) sedimentary type- volcanic hydrothermal type Constituted a complete metallogenic evolution series by multi- phases and multi-stages metallogenic evolution;(6) The spatial distribution of deposits are joint controlled by tectonic and magmatic activity. Pingchuan iron ore deposits displays a characteristic that composite structure graded controlled the deposit, derived broken branch fault of regional Jinhe-Qinghe fault and Dabanshan-Guanfanggou anticlinorium joint controlled the overall spatial distribution toward to NE of the deposit, Kuangshanliangzi fault and Xipangou fault subjected the spatial location of iron ore, Kuangshanliangzi caldera structure became the most important direct ore-controlling structure and ore-bearing space.There is a exclusive features between basic-ultrabasic rocks and mineralization type,that is,volcanic eruptions (overflow) sedimentary type, sub-volcanic hydrothermal type and magmatic shaped type has a good spatial correspondence with Volcanic rock, subvolcanic rock and intrusive rock. Orebody output styles are divided into Kuangshanliangzi sub-style,Lanzhichang sub-style and Dashanshu sub-style,according to difference of ore-forming methods, mineralization types and orebody location spaces, collectively referred to as Pingchuan type.Subvolcanic hydrothermal type mineralization with a space zoning,that is,there is a inside and outside zonation between Kuangshanliangzi slurry filling type magnetite and Daopingzi high-temperature gas-liquid contact with filling-metasomatic magnetite at the macro,and significant hydrothermal alteration zoning for Daopingzi and ore structural types zoning for Kuangshanliangzi at the micro.Orebodies of Kuangshanliangzi mianly occurred in the caldera structure,cotrolling by faults of the caldera, interlayer fracture zone and rock fracture zone, with a obvious filling metallogenic features, having a mutation contact relationship with ore-bearing rock,the bigger orebodies are mainly occurred in the collapse space of contact zone, while the smaller orebodies always filled in interlayer fracture zone structure and rock fracture system.Orebodies have no selectivity for ore-bearing rock, however, orebodies location in space are usually close with near-ore diabase, or occurred in contact zone between diabase and stratum,or located in inner fracture zone structure space of diabase,the top and the recess of diabase are always favorable ore-bearing space.Daopingzi contact with filling-metasomatic type orebodies are mianly occurred in tectonic contact zone between rock and stratum, contacting with ore-bearing rock with mutant contact relationship.Volcanic eruptions (overflow) type mineralization is mainly affected by Kuangshanliangzi caldera fracture and Lanzhichang fault, forming Kuqiaodi and Lanzhichang with the difference of ore-forming material migration distance from the crater structure.Orebodies are mianly occurred near the contact zone between dense massive basalt and basaltic breccia,always having a Fault contact relationship with roof and floor ore-bearing rock,there are many secondary orebodies nearly parallel arrangement on the both sides of mian orebody,and having a growth and decline relationship between the distance from the crater structure and the proportion of the total iron content of magnetite from north to south,and also having a positive correlation between the depth fFrom the surface to depth and the proportion of the total iron content of magnetite.Shaped mineralized magmatic gabbro occur in the construction, and showed a gradual transition between rock; Magmatic shaped type mineralization are occurred in gabbro,having a gradual transition relationship with ore-bearing rock.Pingchuan iron ore deposits is a volcanic eruptions (overflow) deposition-penetration iron deposit related to Hercynian-Indosinian continental volcanism-subvolcanic magmatic activity,having a "three floors" metallogenic model,that is,volcanic eruptions (overflow) sedimentary type-hydrothermal type-magmatic shaped type metallogenic evolution series is Corresponding with volcanic rockâ†'subvolcanic rockâ†'intrusive rock diagenetic evolution series in the spatial. Pingchuan iron ore deposits can be compared with ore deposits occurred in dark rock construction at home and abroad. |
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