Geological And Geochemical Characteristics And Metallogenic Mechanism Of Ree Deposits,Northwestern Guizhou

Combining with the research project of 113 geological team,Bureau of Geology and mineral resources of Guizhou Province,this thesis selected REE deposits in Weining area of the Northwest Guizhou as the research object to carry out scientific research work.The author attempted to reveal the mechanism of REE elements geochemistry of mineralization by probing geological and geochemical characteristics of the REE deposits,as well as investigating the source,transport,poly-geochemical processes.And based on the result,the metallogenic model was established which provide new scientific basis for rare earth ore prospecting and geological prospecting.Based on the geological survey,the regional geology background was discussed by using research methods of Geology and tectonics.And the Late Permian Lithofacies Palaeogeography and its relationship with REE ores was researched by means of sedimentology,stratigraphy,petrology and mineral deposits research methods.On this basis,the geochemical characteristics of REE deposit were investigated by using the method of ore deposit geochemistry and mineralogy.The applications of mineral petrology,major element geochemistry,geochemistry of trace elements,REE geochemistry research method and experimental geochemistry were put into the studies of material source rocks,forms of REE in rocks and minerals,REE transport and deposition enriched geochemical processes.And a metallogenic model of REE deposits was set up in this area.Through the above research,the main conclusions are drawn as follows:1.In the late stage of Early Permian and early stage of Late Permian,the strong tectonic movement occurred in southwestern Yangtze Plate,bringing about the regional crust-mantle ultrabasic magma activity and a massive eruption.Overflow magma formed basic-ultrabasic rocks,huge Emeishan basalt with wide coverage and large thickness.The ejected lava formed large scale of volcanic clastic tuff,thus constituted our large igneous province.2.Major and trace elements analysis of rocks in containing minerals strata and rock-minerals microscopic identification results show that diagenetic materials were from Emeishan basalt and volcanic clastic tuff.This shows that Emeishan basalt and volcanic tuff are the mother-rock for formation materials.The content of REE in ores and rocks were analyzed.The results show that,the Emeishan basalt and volcanic tuff are rich in REE,up to 223.85×10^-6,with an average of 201.98×10^-6.REE compositions of ores are consistent with that of Emeishan basalt and volcanic tuff.This proves that REEs of ores are originated from the Emeishan basalt and volcanic tuff,which has the same material source as ore bearing strata.Owing to its wide coverage and large thickness,Emeishan basalt provided a large number of weathering products under the strong weathering conditions which became an eroding source area.These weathered materials can provide sufficient material sources for the later rock and ore forming.3.REE form analysis in ores and rocks by scanning electron microscope and electron probe analysis shows that independent REE does not exist in rocks and ores.Rocks and ores leaching test results show that REE in rocks and ores have higher leaching rate in several kinds of dilute reagent leaching.This shows that,the REE are in ionic form rather than mineral state in rocks and ores,adsorbed on the surface of kaolinite clay minerals.4.The results of transportation forms of REE show that Emeishan basalt rocks would generally broke into fragments when suffered a strong weathering.These fragments decomposed and altered into kaolinite clay material under surface water effect.At the same time,the existing REE given in the form of ions adsorbed on the surface of kaolinite clay minerals,and transported with the kaolinite clay minerals to the volcanic sedimentary depression,forming rocks and containing rare earth formation.In the REE-bearing strata,REE still were adsorbed on the surface of kaolinite clay minerals in the form of ions in the rock.In short,the REE migrates,precipitates and concentrates in the form of ions.5.During diagenetic process,the syngenetic fluid existed in clay minerals kaolinite had discharged under the upper static pressure,diffusing,forming the seepage,and became syngenetic fluid.In diffusing and seeping process of the syngenetic fluid,part REE in the original sediments of the kaolinite clay were likely to be brought out and entered the syngenetic fluid to form REE containing fluid.The REE containing fluid diffused and circulated under the driving of internal geological force.When this kind of REE containing fluid diffused and circled into the ore bearing strata,frequently led to mineralization,made REE activate and re-enrich in ore-bearing strata rocks,thus formed REE deposits of sedimentary-reconstituted type.Main results and innovations are as followes:1.As for source of ore-forming materials,volcanic tuff is an important source of rare earth elements except for Emeishan basalt.Volcanic clastic rock is an important contribution not neglected to the formation of rare earth deposits in this area.2.For the first time researched and determined the existent form of REE in rock and ore by using methods of rock identification,scanning electron microscope,electron probe and leaching test.The author suggests that REEs exist mainly in form of ions adsorbed on the surface of kaolinite clay in rocks and minerals,thus enrich and mineralize in form of ions adsorbed by clays.This cognition is of great significance:the existent form of REE in rocks and ores in this area is not yet clear before.The government of Guizhou Province,Bureau of Geology and Mineral Resources of Guizhou and 113 geological team feel urgently to know the existent form of REE.If the REEs are found exist in mineral form,the cost is too high for development and utilization.If REEs are in the form of adsorbed ions,the cost is relatively low to develop and utilize.If is the latter,the REE ores in the region are in enormous reserves,which is of great industrial value for development and utilization.3.The migration form of rare earth elements was determined by this paper.The author suggests that REEs exist mainly in form of ions adsorbed on the surface of kaolinite clay moved and transported by surface water,thus enrich and mineralize in form of ions adsorbed by clays.4.It is considered that REE deposit in this area was of sedimentary-reconstituted type.This paper argues that the REE deposit formation in this area was of syngenetic sedimentation.Under the influence of epigenetic groundwater containing REE,the activation and re-enrichment occurred in ore-bearing strata rocks.5.A metallogenic model of sedimentary-reconstituted type is set up by this paper,which not only has important scientific significance,but also has important guiding significance for ore prospecting in practice.