Huang Zhilong

Geochemistry of carbonatites in Maoniuping REE deposit, Sichuan Province, China

Carbonatites in the Maoniuping REE deposit, Sichuan Province, which are spatially and temporally associated with rare earth mineralization, were emplaced at the time of Himalayan. The rocks are carbonatite-syenite complexes, with the mineral assemblages of calcite-aegirine-acmite-arfvedsonite-mica-orthoclase. The rocks are characterized by the enrichment in incompatible elements, such as Sr, Ba and REE, with C and O isotopic compositions of the “primary igneous carbonatites”, relatively high initial 87Sr/86Sr ratios and low ɛnd values. All of these suggest that the rocks were derived from the metasomatic enriched mantle. It is demonstrated by geological and geochemical evidence that the mixing of the Himalayan subducting crustal materials with mantle source EM1 is probably the main factor responsible for the formation of carbonatites. The carbonatite-syenite complexes were generated from liquid immiscibility of CO2-rich alkalic silicate magma, which was derived from partial melting of the metasomatic mantle.

Isotopic Compositions of Sulfur in the Jinshachang Lead-Zinc Deposit Yunnan, China, and its Implication on the Formation of Sulfur-Bearing Minerals

: The Jinshachang lead–zinc deposit is mainly hosted in the Upper Neoproterozoic carbonate rocks of the Dengying Group and located in the Sichuan–Yunnan–Guizhou (SYG) Pb–Zn–Ag multi-metal mineralization area in China. Sulfides minerals including sphalerite, galena and pyrite postdate or coprecipitate with gangue mainly consisting of fluorite, quartz, and barite, making this deposit distinct from most lead-zinc deposits in the SYG. This deposit is controlled by tectonic structures, and most mineralization is located along or near faults zones. Emeishan basalts near the ore district might have contributed to the formation of orebodies. The δ34S values of sphalerite, galena, pyrite and barite were estimated to be 3.6‰–13.4‰, 3.7‰–9.0‰, −6.4‰ to 29.2‰ and 32.1‰–34.7‰, respectively. In view of the similar δ34S values of barite and sulfates being from the Cambrian strata, the sulfur of barite was likely derived from the Cambrian strata. The homogenization temperatures (T≈ 134–383°C) of fluid inclusions were not suitable for reducing bacteria, therefore, the bacterial sulfate reduction could not have been an efficient path to generate reduced sulfur in this district. Although thermochemical sulfate reduction process had contributed to the production of reduced sulfur, it was not the main mechanism. Considering other aspects, it can be suggested that sulfur of sulfides should have been derived from magmatic activities. The δ34S values of sphalerite were found to be higher than those of coexisting galena. The equilibrium temperatures calculated by using the sulfur isotopic composition of mineral pairs matched well with the homogenization temperature of fluid inclusions, suggesting that the sulfur isotopic composition in ore-forming fluids had reached a partial equilibrium.

Signatures of the source for the Emeishan flood basalts in the Ertan area: Pb isotope evidence

The Emeishan flood basalts can be divided into high-Ti (HT) basalt (Ti/Y>500) and low-Ti (LT) basalt (Ti/Y<500). Sr, Nd isotopic characteristics of the lavas indicate that the LT-and the HT-type magmas originated from distinct mantle sources and parental magmas. The LT-type magma was derived from a shallower lithospheric mantle, whereas the HT-type magma was derived from a deeper mantle source that may be possibly a mantle plume. However, few studies on the Emeishan flood basalts involved their Pb isotopes, especially the Ertan basalts. In this paper, the authors investigated basalt samples from the Ertan area in terms of Pb isotopes, in order to constrain the source of the Emeishan flood basalts. The ratios of 206Pb/204Pb (18.31–18.41), 207Pb/204Pb (15.55–15.56) and 208Pb/204Pb (38.81–38.94) are significantly higher than those of the depleted mantle, just lying between EM I and EM II. This indicates that the Emeishan HT basalts (in the Ertan area) are the result of mixing of EMI end-member and EMII end-member.

REE geochemistry of altered tectonites in the Huize base-metal district, Yunnan, China

Hydrothermally altered tectonites (e.g. mylonites, cataclasites) occur in ore-controlling fault zones in the Huize base-metal district. Non-altered wallrocks and altered but non-mineralized tectonites have similar REE characteristics indicating seawater origin of the host carbonate rocks but with significant terrigenous input. Calcite gangues in mineralized (argillaceous/barite-bearing) tectonites and tectonite ores contain the highest REE values and exhibit convex-upward and roughly roof-shaped REE patterns with positive Eu anomalies, which are typical of hydrothermal crustal fluids. Negative Ce and negative La anomalies in calcite gangues imply hydrothermal fluids that previously interacted with marine and terrigenous rocks underlying the carbonate host rocks. Similarities in the REE characteristics of mineralized tectonites with those of the non-altered wallrocks and non-mineralized tectonites support earlier propositions that hydrothermal fluids were derived from the Kunyang Group basement rocks. REE characteristics of mineralized (argillaceous/barite-bearing) tectonites indicate fluid-wallrock interactions during migration of hydrothermal fluids along faults. Convex-upward REE patterns of tectonite ores were likely due to remobilization of early-formed base-metal sulphides whereas convex-upward REE patterns of strongly mineralized tectonites (i.e. with disseminated–massive base-metal sulphides) were likely due to recrystallization of early formed calcite gangues. REE characteristics of altered tectonites due to fluid-rock interactions during fluid migration and metal/mineral remobilization/recrystallization are depicted in Y/Ho–La/Ho, Tb/Ca–Tb/La, and Yb/Ca–Yb/La plots of the data. Migration of hydrothermal fluids along ore-controlling faults was likely induced by seismic pumping associated with tectonic deformation, whereas the remobilization/recrystallization process likely occurred in ‘pressure shadows’ along ore-controlling faults.

REE geochemistry of lamprophyres in Baimazhai nickel deposit, Yunnan Province, China: implication for the mantle source region

Based on the REE geochemistry data from the Baimazhai nickel deposit, Yunnan Province, the authors modeled the composition of the mantle source region by way of petrological mixing calculation, and further discussed the genesis of this type of rocks. Both element geochemistry data and mixing calculation showed that lamprophyres in the Baimazhai nickel deposit were derived from a metasomatism-enrichment mantle and the fluids resulted from dehydration of a subducted slab which is comprised of ALK-, LREE- and incompatible element-rich sediments.Based on the REE geochemistry data from the Baimazhai nickel deposit, Yunnan Province, the authors modeled the composition of the mantle source region by way of petrological mixing calculation, and further discussed the genesis of this type of rocks. Both element geochemistry data and mixing calculation showed that lamprophyres in the Baimazhai nickel deposit were derived from a metasomatism-enrichment mantle and the fluids resulted from dehydration of a subducted slab which is comprised of ALK-, LREE- and incompatible element-rich sediments.

Study on the multi-sources of ore-forming materials and ore-forming fluids in the Huize lead-zinc ore deposit

The Huize large-sized Pb-Zn deposit in Yunnan Province, China, is characterized by favorable metallogenic background and particular geological settings. This suggested that the ore-forming mechanism is relatively unique. On the basis of geological features such as the contents of mineralization elements, the REE concentrations of gangue calcites, the REE concentrations of calcite veins in the NE-trending tectonic zone and the Pb, Sr, C, H and O isotopic compositions of different minerals, this paper presents that the ore-forming materials and ore-forming fluids of the deposit were derived from various types of strata or rocks. This is a very significant conclusion for us to further discuss the mineralization mechanism of the deposit at depth and establish an available genetic model.

Rare-earth elements and genesis of lamprophyres in the Laowangzhai gold orefield, Yunnan Province

The Laowangzhai super-large gold orefield, which is situated in northern Mt. Ailao tectonic zone, Yunnan Province, is a typical gold orefield where lamprophyres are temporally and spatially related to gold mineralization. Major element data show that lamprophyres in the orefield are of alkalic series and can be divided into potassic and K-rich calc-alkaline lamprophyres. The rocks are enriched in rare-earth elements as compared with the primary mantle and mid-ocean ridge basalts(MORB). Modelled calculations by the least squares method of Petrological Mixing show that the mantle source for the lamprophyres is enriched in rare-earth elements. The geotectonic development of western Yunnan, Sr and Nd isotopic compositions, incompatible element patterns and linear programing calculations indicate that the fluids were derived from dehydration of submaine sediments which are enriched in ALK, LREE and incompatible elements and then were carried to mantle wedges as a result of plate subduction. That is the main factor leading to the formation of a metasomalic fertile mantle in the area studied.

The Sr, Nd isotopic composition of lamprophyres in Laowangzhai gold orefield, Yunnan Province

Lamprophyres are widely spread over the Laowangzhai gold orefield in northern Mt. Ailao structure zone, Yunnan Province. Lampmphyres in the orefield are temporally and spatially related to gold mineralization. Lampmphyren in the orefield have anomalous Sr and Nd isotopic compositions, e.g. the87Sr/86Sr ratios (0.706 665–0.707 960, the87Sr/86Sr ratio of sample YLW-44 is 0.709 041) are higher than the modern value of the original mantle (0.704 5), the143Nd/144Nd ration (0.512 463–0.512 551) are lower than the modern value of the original mantle (0.512 638), and the calculated values εSr > 0 (28.1–63.7) and εNd< 0 (- 1.34- -3.07). The results of investigation inete that lampmphyres in the Laowangzhai gold orefield with anomalous Sr and Nd isotopic compositions would not be produced as a result of contamination of the primary magma with the isotopic features of MORB by the crust materials high87Sr/86Sr ratios and low143Nd/144Nd ratios in the ploeaws of rising or in the magma chamber, but the result of metasomatism of source mantle.

The three end members of Li-F granites and their origin of liquid segregation

Li-F granites all over the world can be represented by three end members, i. e., the Na-rich ongonite (O), the K-rich xianghualingite (X) and the Si-rich topazite (T). Characters and criteria are presented for these end-member rocks. Vertical zoning in Li-F granites, as reflected by increasing normative Q and C (corundum) and decreasing ALK (K2O+ Na2O) with increasing content of fluorine, can be explained using the three-end-member scheme in terms of petrochemistry and norms. Considering the difference in melt structure, viscosity and density between the end members, in couple with the regularities that govern the Na-K and SiALK segregation known from field evidence and experiments, it is suggested that the three end members may have resulted from liquid segregation (immiscibility) rather than from crystal fractionation as commonly believed.

Research Progress of the Mineralization of Carbonate-Hosted Pb-Zn Deposits in the Sichuan-Yunnan-Guizhou Pb-Zn Metallogenic Province, Southwest China

The Sichuan-Yunnan-Guizhou(SYG)Pb-Zn metallogenic province in the western Yangtze Block,is a key component of the low-temperature metallogenic domain in South China.In this area,more than 400 Pb-Zn deposits have been discovered,and the total proven reserves are up to 260 million tons with lead and zinc grade reaching 10%,even up to 30%.Another important