Precambrian Copper-iron-gold-uranium Polymetallic Deposits And Their Regional Metallogeny In Southwestern Margin Of Yangtze Block

There are a large number of copper-iron deposits, which are characterized by largescale and associated with polymetallic mineralization, in the precambrian stratigraphicunits in southwestern Yangtze Block. Research on Lala, Dahongshan deposits have animportant theoretical significance and practical value, for their large scale-typical oredeposits and associated with Au-Ag-Co-Mo-REE-U polymetallic mineralization. Theselection of this doctoral dissertation are based on the research project(12120113095500) and the cooperative item from CNNC and CNG managed by theauthor’s supervisor.Based on research of the typical deposits, such as the Lala in Huili, Dahongshan inXinping, Yinachang in Wuding, Chehe in Yuanjiang, etc., with systematically samplingon rock, mineral and single mineral samples, this doctoral dissertation has researchedthe continental geodynamics, the age of magmatic rocks and metallogenic epoch, thecoupling relationship between polymetallic elements, the source of ore-forming fluidand the coupling relationship between magma evolution and polymetallicmineralization by the latest metallogenic theory and the modern analysis technology.With systematically study on the fluid inclusions, the stable and rare gas isotopes andthe geochemistry of the trace and rare earth elements, the source of the ore-formingfluid and the mineralization are identified on basis of the study on the geological featureof these deposit. The relationship between the marine volcanism, the magmatism, thelate hydrothermal superimposition and polymetallic mineralization has be discussed.The mineralization mechanism and the metallogenic regularities of the IOCG depositsin this area have be revealed. The metallogenic model of these deposits and theirregional metallogeny mainly about the metallogenetic space-time evolution insouthwestern margin of Yangtze Block are established, and the metallogenic series isoutlined eventually.The doctoral dessertation achieves the following main results and understanding:(1)The regional geological background, formation, structure, magmatic rocks and regional geological evolution in the study area are summarized. Through the systematicresearch of the petrology, geochemistry and chronology, the author propose that theA-type granite in Lala mining area formed in1657±15Ma of the anorogenic extensionenvironment——the intraplate rift setting, which may be related to thinning ofcrust-lithosphere and the upwelling of asthenosphere mantle. The geochemistry ofgabbro-diabase indicates that it is derived from the enriched mantle with the mixing ofcontinental crust lithosphere. The A-type granite in this area form after the invasion,upwelling and strong crystallization differentiation of the basaltic magma, suggestingthat there exist "bimodal type" intrusive rocks in this area represented bygabbro-diabase dyke swarms and A-type granite porphyry.(2)The combination characteristics of polymetallic elements and assemblage ofminerals are studied. And on this basis, the polymetallic combination rules ofCu-Fe-Au-Mo-Co-U and speciation of ore-forming elements of Lala deposit arestudied by electron probe and microelement analysis in this paper. The ore-formingprocess of Lala deposit are divided into three metallogenic periods: volcanicsedimentary and magmatic hydrothermal period, hydrothermal fluid mineralizationperiod, supergene oxidation period. The polymetallic combination rules ofCu-Fe-Au-Mo-Co-U are divided into: Fe①-P(1), Fe②-Co-Cu①(2), Mo-Au-Cu②-U(3).(3)Compared with the typical IOCG deposits, there are many similar aspects. TheLala and Dahongshan copper-iron polymetallic deposits are both not only big scale,important meaning, but are two typical IOCG deposits in the study area. From thestandard features, such as Fe-Cu polymetallic mineralization, the combination ofAu-U-REE and so on, and the relationship between the mineralization and magmaticrocks, magnetite, fault, fold, breccia, fluoritization, and the occurrence of ore bodies, itcan be concluded that some deposits in this area, such as Lala, Dahongshan andYinachang, have obvious characteristics of Iron Oxide-Copper-Gold deposits (IOCG).(4)Data from sulfur isotope of ore minerals, element geochemistry of magnetiteshow that deposit possess the characteristic of IOCG deposits. element geochemicalcharacteristics of magnetite indicate that ore-forming materials with multi-sources, areof the sedimentary source-reformation, and are formed by the late hydrothermalmetasomatic superposition. Element features of pyrite indicate that the metallogeniccharacteristics of the volcanic eruption-depositional and the later hydrothermalsuperimposition. Both the deep and shallow fluid contribute to the mineralization. Andthe deposit are formed by the early volcanic eruption-depositional stage and the latermetasomatic hydrothermal superposition. (5)Study results of the rare gas isotope of chalcopyrite inclusions indicate thatore-forming fluid are different from the metallogenic characteristics of the generalhydrothermal sedimentary deposits. The carbon and oxygen isotope of calcite indicatethat these deposits are associated with the magmatic fluid, metamorphic fluid of deepsource, which are similar to the features of the typical IOCG deposit relatively.According to the sulfur isotope of metal sulfide, carbon and oxygen isotope of calcite,rare gas isotope of chalcopyrite inclusions, the research results show that ore-formingfluid of the Lala and Dahongshan deposits are mixed sources of surface water and deepsource of magmatic water-mantle fluid. The rare earth elements of sulfide, calcitemineral are studied, a further clue the mantle fluid is of great significance formetallogenic. The participation of mantle fluid in the process of mineralization are thesignificant conditions for the (ultra-) large copper-iron-gold-uranium polymetallicdeposit in this area.(6)The age of Lala deposit, Dahongshan deposit, Chahe deposit are measured byRe-Os isochron age of chalcopyrite, which are1085±27Ma,1083±45Ma,1082±46Ma, respectively. These three metallogenic epoch data have high consistency,which indicates that mineralization of these deposits may belong to the same geologicalevents in the late Mesoproterozoic, forming the metallogenic series of polymetalliccombinations, such as copper-iron-gold-uranium, etc. A preliminary age of iron ofDahongshan deposit is determined by Re-Os isochron age of magnetite for1325±170Ma (MSWD=40). This may represent the age of the hydrothermal genesis magnetite,and the magnetite, apatite, et al. may enrich at this stage. The uranium metallogenic ageof the824±15Ma, is identified by the electron microprobe dating method on uraninitein Lala deposit. The uranium metallogeny are later than iron-copper-molybdenum-goldpolymetallic mineralization, which is a Neoproterozoic metallogenic event.(7)The metallogenic model of the typical ore deposit are established. By variousmineralization superimposition, the formation of the typical ore deposit are after theformation of the original source bed and the later complex superposition. From theview of regional evolution characteristics, Paleoproterozoic is the pre-enrichment ofLala Fe-Cu polymetallic deposit. In several superimposed mineralization events,1.4~1.2Ga and1.1~1.0Ga are two necessary and important metallogenic epoch forcopper polymetallic mineralization. The~0.8Ga is identified as the age of uranium bythe electron microprobe dating method on uraninite in Lala deposit. Thus, the metalcombination of iron-copper-gold-uranium-molybdenum-cobalt-rare earth are formedby the multiple superimposed mineralization, which are the significant conditions for Lala and Dahongshan copper-iron polymetallic deposits.(8)The response of the mineralization and the major geological events is studied.Columbia supercontinent breakup, the Grenville orogenic event, the breakup andreconstruction of Rodinia in the study area are summarized and studied. Theoreforming process can be divided into pre-enrichment, two other mineralization, andseveral small mineralization. The formation of iron and copper is related to the breakupof Columbia supercontinent, while Cu polymetallic deposits are controlled by theGrenville orogenic event, the reconstruction of Rodinia. Paleoproterozoic is thepre-enrichment of Fe-Cu polymetallic deposits. The hosting rock of ore deposit and thesource bed form by the marine volcanic eruption-depositional cycle at the end of thePaleoproterozoic. The main IOCG deposits in the research area, such as the Lala andDahongshan deposits, formed in1.1~1.0Ga after several Mesoproterozoicsuperimposed mineralization events.