| As one of the significant achievements from recent ore-prospecting actions within Baoshan-Zhenkang Block, Luziyuan super-large Lead-Zinc-Iron polymetallic mineral deposit in West Yunnan is a typical representative when studying a series of similar hydrothermal Pb-Zn deposits in the Block. That can be attributed to the deposit’s large scale, ore bodies’ long trending (over 3 km) and dipping (over 2 km), many mineralization (Fe, Cu, Zn, Pb, Ag) and associated elements (W, Sn, Cd, Co, Mn), apparent zoned features of mineralization elements (upper Zn-Pb-Ag, middle Zn-Pb-Fe-Cu and lower Fe-Cu) and intensive wall-rock alteration. Most ore bodies in the deposit occur along the bedding as stratiform-like or veined within the interlayered cleftiness or fractured crushed zone of the marbles in the Shahechang Formation, Upper Cambrian; while ore-bearing wall-rock is predominated by stratiform manganese skarns. Ore minerals are dominated by metal sulfides including Sphalerite, Galena, Magnetite, Chalcopyrite and Bornite; and Calcite, Quartz and a few Skarn characteristic minerals, such as Actinolite, Rhodonite, Chlorite, Epidote, Garnet, Diopside and so on, are primary gangue minerals. Whether the geological, geophysical, geochemical exploration and remote sensing interpretation or the previously researched results infer that there may be a hidden magmatite body in the deep, while the direct assertive evidence correlated genetically with the magmatic body hasn’t yet been found up to now. What’s more, it lacks of a systematic isotopic tracing study and a precise mineralogenetic epoch determination on this deposit, thus ore genesis has been paid much attention and remained debatable greatly.Based on across-the-aboard analyzing and summarize the many studied fruits of the deposit by the fore scholars and further field geological investigation research works as well as detailed indoor microscope observations, a systematic united tracing concerning multiple (C-D-O-S-Pb-Sr) isotope of single mineral separates in ores and Sm-Nd isotope dating of calcite are carried out in this Master’s thesis by means of application of isotopic geochemical tracing and dating methods. Combining these microcosmic measurement data with macroscopical geologic characteristics of the deposit and the previous researched consequences, the metallogentic materials provenances and hydrothermal fluids sources and their evolution features are synthetically discussed; and the ore-forming dynamic settings are analyzed; and then the ore deposit genesis type is determined eventually. The new conclusions achieved are as follows:(1)Multiple Isotopic Tracing:①C-O isotope compositions of calcite are-1.4～ +1.2‰,+10.3～+13.6‰, respectively. They reflect that the C was mainly sourced from the deep magmatic hydrothermal solutions, probably blended with partial groundwaters and meteoric waters. ②H-O isotope compositions range respectively from -76.6 to -56.3‰ and -15.3 to -12.0‰ for quartz and between -81.7 and -68.8‰, +5.4 and +6.1‰ for rhodonite, separately. This indicates that the early metallogenic fluids were primarily magmatic in origin, and characterized by the addition of several meteoric waters later. ③ S isotopic compositions of sphalerite, galena, chalcopyrite and bornite vary from +8.9 to +12.0‰, which shows that the S stemmed principally from the deeply mantle-derived magmas, maybe affected by the thermo-chemical effect of the seawater sulfate.④ Pb isotope ratios for sphalerite and galena alter within the ranges of 18.243～18.314,15.725-15.816 and 38.460～38.759 for 206Pb/204Pb, 207pb/204Pb and 208Pb/204Pb severally, implying that the Pb source was crust-mantle mixed-type subduction zone lead related to magmatism. ⑤ The initial 87Sr/86Sr ratios of sphalerite, quartz, calcite and rhodonite display a variation from 0.713502 to 0.720102, suggesting that the Sr originated chiefly from the continental crust, which is perhaps contaminated by or added in a few mantle materials. It also implicates that the metallogenesis is in close correlationship with magmatic activity. In summary, C-D-O-S-Pb-Sr isotope tracing results demonstate that the magmatic hydrothermal solution is the cardinal source of the metallogenic fluid, that the chemical constituents in the ore-forming fluids are of multiple derivations, and that the metallogenetic metals are dominated by crust-derived materials, maybe added in small amounts of mantle-sourced materials.(2)Isotope Dating:Calcites yield a Sm-Nd isotopic isochron age of 130±15Ma, further proofing that Late Yanshanian period is ore-forming time of this deposit. In consideration of this age corresponding roughly to Early Cretaceous epoch when the main Meso-Tethys ocean represented by Bangong Lake-Nujiang River is closed, it is thought that probably under the influence of the subduction of the ocean basin and as a response to continent-continent collision orogenesis after it is shut, the metallogenesis occurred within the dynamic background of decompression and stretching of the thickened crust, which is a significant ore-forming process type in the Sanjiang Tethyan composite orogenic metallogenic system.(3)Ore Genesis:It is comprehensively revealed that the researched deposit is considered to be a stratabound-distal Skarn-type Pb-Zn-Fe polymetallic deposit. Meanwhile, a greater concealed intermediate-acid intrusive magmatic rock body is inferred to be present in the deep or surrounding. |
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