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OBJECTIVES The Xiuwacu Mo-W deposit is a typical hydrothermal quartz vein deposit in the Yidun island arc Cu-Mo metallogenic belt, northwest Yunnan. Numerous studies have been conducted on rock and ore chronology and petrogenesis, dynamics, but its ore-forming fluid evolution has been rarely studied. OBJECTIVES To reveal the origin and evolution of ore-forming fluids of the Xiuwacu Mo-W deposit. METHODS Scanning electron microscope (SEM) cathodoluminescence method, and in situ trace element (LA-ICP-MS) and in situ Sr (fs-LA-MC-ICP-MS) isotope analyses of scheelite. RESULTS The occurrences of scheelite and the cathodoluminescence images indicated three generations of scheelite, Ⅰ, Ⅱ, and Ⅲ, with the middle stage scheelite being the most developed. The rare earth element pattern of the scheelite in the early stage was similar to that of the porphyritic granite. It showed a right-inclined pattern with light rare earth enrichment and a moderate negative Eu anomaly (δEu=0.42). The average Mo content was 3.0%, and the average 87Sr/86Sr was 0.7098, close to the specular feldspar granite (0.7075-0.7098). Compared with scheelite in the early stage, the content of light rare earth elements in the scheelite from the middle stage was low, and Eu also had a medium negative anomaly (δEu=0.37). Mo content was reduced to an average of 2445μg/g, and 87Sr/86Sr increased to 0.7113. The rare earth distribution pattern of scheelite in the later stage showed an arched pattern with relative enrichment of middle rare earth and no Eu anomaly (δEu=0.93). Mo content of scheelite decreased to 56μg/g, and average 87Sr/86Sr was 0.7083. Conclusion From early to late, the gradual decrease of light rare-earth elements, especially La and Ce, in scheelite indicates the crystallization of bastnaesite. The increase in δEu and the sharp decrease in Mo content indicate the transformation of ore-forming fluids from oxidation to reduction. The change of Sr isotope composition indicates the change in the source of ore-forming materials. The magmatic fluid contributed a lot in the early stage, and the large-scale interaction between the magma-hydrothermal fluids and surrounding rocks is responsible for the formation of scheelite in the middle stage. The strata provide amounts of Ca for scheelite formation, indicating that strong water-rock interaction played an important role in the formation of the deposit.

BACKGROUND The Nanyangtian scheelite deposit is an important skarn scheelite deposit in Yunnan Province, which is located in Laojunshan W-Sn deposit area, Southeast Yunnan. Due to its complex geological background and multi-stage metallogenic characteristics, its mineralization age and genesis remain controversial. OBJECTIVES To explore the metallogenic age, genesis and material origins of two types of scheelite deposits in order to explore formation patterns. METHODS Molybdenum Re-Os isotope dating was used to constrain the age, whereas in situ trace element and in situ Sr isotopes of scheelite were used to determine the composition of trace elements and Sr isotopes in scheelite. RESULTS The Re-Os isochron age of molybdenite associated with scheelite in the feldspar-quartz mineral vein of Nanyantian was 151.0±1.3Ma, younger than the age of skarn mineralization, indicating a later mineralization event. The skarn-type scheelite was enriched in light rare earth elements with negative Eu anomaly (δEu=0.46). The average content of ∑REE, Mo and Sr in skarn scheelite were 65.60, 240.16 and 883.43μg/g, respectively. Feldspar-quartz vein-type scheelite showed a flat rare earth pattern with positive Eu anomaly (δEu=2.8) and average content of ∑REE, Mo and Sr were 194.40, 16.01 and 129.26μg/g, respectively. respectively. The skarn scheelite had a relatively low and uniform 87Sr/86Sr value of 0.71319 to 0.71491, indicating that the ore-forming fluids were mainly magmatic-hydrothermal in origin, whereas feldspar-quartz vein type scheelite had a wide 87Sr/86Sr range of 0.71537 to 0.72803, with an average of 0.72079, characteristic of metamorphic fluids. CONCLUSIONS The differences in trace and rare earth element contents between two types of mineralization indicate that they have different fluid sources. The negative Eu anomaly of the skarn-type scheelite indicates a high oxygen fugacity environment, whereas the feldspar-quartz vein-type scheelite is formed in a reductive environment in terms of positive Eu anomaly. Sr isotopes of two different types of scheelite display a feature of binary mixing, indicating that feldspar-quartz vein-type scheelite has a superimposed transformation effect on skarn-type scheelite, and the strong metasomatism of ore-forming fluids and surrounding rocks is the key to the formation of scheelite.

BACKGROUND The Huize ultra-large lead-zinc deposit is a typical MVT or HZT type deposit in the lead-zinc polymetallic belt. This deposit is known as a unique metallogenic system and germanium enrichment. Due to the low mineralization temperature and lack of suitable dating minerals, the age of the ore deposits has been controversial. OBJECTIVES To precisely date the mineralization age by Negative Thermal Ionization Mass Spectrometry (NTIMS) Re-Os isotope analyses and discuss the Himalayan metallogenic dynamic process in the Huize ultra-large lead-zinc deposit. METHODS NTIMS Re-Os isotope analyses were carried out on pyrite, galena, and sphalerite samples collected from the Huize ultra-large lead-zinc deposit. The Re-Os isochron age from the pyrite, galena, and sphalerite samples was used to constrain mineralization age. The initial 187Os/188Os values were used to trace the material sources. RESULTS The Re-Os isochron age of the pyrite samples is 40.7±2.6 Ma (2σ, n=9) with a model weighted average age of 40.0±2.6 Ma (2σ, n=8). The sphalerite and galena samples have model ages of 38.24±0.41 Ma and 36.57±0.40 Ma, respectively. Furthermore, the initial 187Os/188Os values of the pyrite samples vary from 0 to 0.26, whereas those of the sphalerite and galena samples are 0.46 and 0.41, respectively. CONCLUSIONS The Re-Os isochron ages indicate that the mineralization for the Huize ultra-large lead-zinc deposit occurred during the Eocene period. Based on regional ore controlling structure, tectono-lithofacies alteration characteristics in Northeastern Yunnan and the isochron ages results, a two-stage (Yanshanian and Himalayan) tectonic-fluid metallogenic model for the Huize Ultra-large lead-zinc deposit is inferred.

BACKGROUND The Kunyang phosphate deposit in central Yunnan is the largest marine sedimentary phosphorite deposit in China. The deposit is hosted in black shale of the Lower Cambrian Meishucun Formation. However, there is still some controversy on the material source of the phosphorite and the deposition age of the black shale. OBJECTIVES To precisely date the black shale and provide direct constraint for the depositional age of the phosphorite and to better understand the successive depositional environment evolution from the phosphorite to black shale in vertical profiles. METHODS Negative Thermal Ionization Mass Spectrometry (NTIMS) Re-Os isotope tracer and dating studies were performed on phosphorite of Zhongyicun Member and black shale of Shiyantou Member in the Kunyang phosphate deposit. RESULTS The Re-Os isochron age of black shale in the Shiyantou Member is 521.9±5.4 Ma, which directly constrains the deposition age of black shale in the Kunyang Phosphate deposit. The phosphorite and black shale samples have initial 187Os/188Os values from 0.6576 to 0.7671 and of 0.887, respectively. The phosphorite and black shale samples have 187Re/188Os values of 2.582-240.5 and 96.24-341.8, respectively. The δEu and δCe values of trace elements in the phosphorite and black shale show changes from low to high in the vertical profile. This evidence indicates that the formation of the Kunyang phosphorus deposit occurred in the period of rapid erosion in the mainland and a large amount of terrigenous debris involvement in diagenesis-mineralization also occurred. CONCLUSIONS Based on previous studies, the atmospheric oxygen content increased rapidly, aggravating the weathering of the continental crust and the input of a large number of highly radioactive terrestrial Os caused the initial 187Os/188Os initial ratio to increase gradually during the Cambrian Period. In addition, due to the rise of the global sea level, the paleo-marine environment of the Lower Cambrian Meishucun gradually changed from shallow water oxidization to deep water reduction. The Kunyang phosphorus deposit formed during the early stages of the sea-inward-cycle sedimentation.