Zhilong Huang

Sources and Thermo-Chemical Sulfate Reduction for Reduced Sulfur in the Hydrothermal Fluids, Southeastern SYG Pb-Zn Metallogenic Province, SW China

Located on the western Yangtze Block, the Sichuan (四川)-Yunnan(云南)-Guizhou(贵州) (SYG) Pb-Zn metallogenic province has been a major source of base metals for China. In the southeastern SYG province, structures are well developed and strictly control about 100 Pb-Zn deposits. Almost all the deposits are hosted in Devonian to Permian carbonate rocks. Lead-zinc ores occur either as veinlets or disseminations in dolomitic rocks with massive and disseminated textures. Ore minerals are composed of pyrite, sphalerite and galena, and gangue minerals are calcite and dolomite. Sulfide minerals from four typical Pb-Zn deposits are analyzed for sulfur isotope compositions to trace the origin and evolution of hydrothermal fluids. The results show that δ34S values of sulfide minerals range from +3.50‰ to +20.26‰, with a broad peak in +10‰ to +16‰, unlike mantle-derived sulfur (0±‰). However, the mean δ34Ssulfide and δ34SΣS-fluids values are similar to that of sulfate-bearing evaporites in the host rocks (gypsum: ⊃+15‰ and barite: +22‰ to +28‰) and Cambrian to Permian seawater sulfate (+15‰ to +35‰). This suggests that reduced sulfur in hydrothermal fluids was likely derived from evaporates in the host rocks by thermo-chemical sulfate reduction (TSR). Calculated δ34SΣS-fluids values of the Shanshulin(杉树林), Qingshan(青山), Shaojiwan(筲箕湾) and Tianqiao(天桥) Pb-Zn deposits are +21.59‰, +18.33‰, +11.43‰ and +10.62‰, respectively, indicating sulfur-bearing hydrothermal fluids may be evolved from the Shanshulin to Qingshan and then the Shaojiwan to Tianqiao deposition sites along the Yadu(垭都)-Ziyun(紫云) lithospheric fracture in the southeastern SYG province.

Sources of Ore-Forming Fluids in the Maoniuping REE Deposit, Sichuan Province, China: Evidence from REE, Radiogenic Sr, Nd, and Stable-Isotope Studies

The Maoniuping rare-earth-element (REE) deposit, hosted in a carbonatite-syenite complex, is the second largest light REE deposit in China. Fluorite is one of the main gangue minerals. Fluorites with different colors and REE patterns show uniform initial 87Sr/86Sr ratios and εNd values, similar to carbonatite and syenite, and different from granite. Chondrite-normalized REE patterns of early fluorite and quartz resemble those of carbonatite and syenite, but differ from those of granite and rhyolite. These indicate that the REE ore-forming fluids are closely related to carbonatite and syenite magmas. Because emplacement of the carbonatite was later than that of the syenite, early fluid carrying REE and fluoride mainly evolved from the syenite magma. Mixing of this fluid with a Ca-, carbonatite-derived fluid was the major control of early fluorite deposition. With changes in temperature of the ore-forming fluids, REE mineral deposition occurred as a result of the decreased ligand concentration that accompanied massive later fluorite mineralization. The uniform isotope compositions of fluorite, quartz, and carbonatite show that the REE ore-forming fluids were not contaminated by ground or meteoric water or by country-rock fluids.

Re-Os dating of galena and sphalerite from lead-zinc sulfide deposits in Yunnan Province, SW China

Dating of lead-zinc deposits is of critical importance for better understanding of ore genesis, but has long been a big challenge due to the lack of suitable minerals that can be unequivocally linked to the ore genesis and that can be used for tradition radiometric methods. This kind of deposits have simple mineralogy dominated by galena and sphalerite commonly associated with calcite and other gangue minerals. Both galena and sphalerite have low and high variable Re concentrations and thus Re-Os dating of these minerals have been less promising. In addition, the recovery of Re is extremely low for galena when conventional method was applied, lending additional difficulty in precisely dating galena. In this study, we investigate the recovery of Re using different media for anion exchange separation and reporte a revised preparation method for Re-Os dating of galena and sphalerite. By using the new protocol, two reliable Re-Os isochron ages of galena and sphalerite from the Fule (20.4±3.2 Ma) and Laochang (308±25 Ma) Pb-Zn deposits in Yunnan Province, SW China, are achieved.

New insights into the metallogeny of MVT Zn-Pb deposits: A case study from the Nayongzhi in South China, using field data, fluid compositions, and in situ S-Pb isotopes

Abstract The newly discovered Nayongzhi Zn-Pb deposit (>20 Mt ores at 1.11–15.65 wt% Zn and 0.59–0.97 wt% Pb) in NW Guizhou province, South China, is hosted by late Ediacaran and early Cambrian carbonate rocks. The ore body is structurally controlled by a kilometer-scale reverse fault-anticline system and occurs as stratiform, lentiform, or steeply dipping vein structures. Its geological feature is comparable to that of the Mississippi Valley-type (MVT) Zn-Pb deposits. δ34S values (+11.8 to +33.0‰) of sulfide minerals determined by NanoSIMS have a larger range than those determined by conventional bulk analysis (δ34S = +18.12 to +24.79‰). This suggests that S isotopes determined by in situ analysis can reflect the nature of fractionation involved in mineralization. Furthermore, cores of sulfide crystals have higher δ34S values (+26.1 to +33.0‰) than their rims (+11.8 to +24.5‰). This implies a mixture of multiple S reservoirs or a Rayleigh fractionation of S isotopes occurred during ore formation process. Additionally, both S isotopic compositions determined by in situ and bulk analyses reflect the enrichment of 34S in hydrothermal fluid (δ34Sfluid > +11.8‰), a typical characteristic of marine sulfate-derived S. Such S isotopic signatures also show that thermochemical sulfate reduction (TSR) is the dominant mechanism for the incorporation of S2− from SO42−

Origin of early Triassic rift-related alkaline basalts from Southwest China: age, isotope, and trace-element constraints

\rm SO_{4}^{2-}

Geochemistry and petrogenesis of Late Ladinian OIB-like basalts from Tabai, Yunnan Province, China

. Pb isotopic ratios of galena obtained by femtosecond LA-MC-ICPMS plot in the field that overlaps with the Pb evolution curve of upper crust contributed to the orogeny and the field of modern lower crust, and can be compared to the Proterozoic metamorphic rocks. The means that the majority of Pb metal is sourced from the basement rocks. Although δ13C values (–4.1 to +0.5‰) of calcite separates and corresponding fluids are similar to both fresh limestone (–1.7 to +1.3‰) and typical marine carbonate rocks, the δ18O values (+12.4 to +14.1‰) are significantly lower than both limestone (+24.1 to +25.5‰) and marine carbonate rocks. Such C-O isotopic characteristics suggest that the source of C is ore-hosting carbonate rocks, whereas O has a mixed source of metamorphic fluids and carbonate rocks resulting from water/rock (W/R) interaction. This study demonstrates that (1) fluid mixing caused rapid sulfide precipitation, resulting in significant fractionation of S isotopes; and (2) both the W/R interaction and CO2 degassing controlled local carbonate cyclic process of dissolution → re-crystallization, which provided metastable physical and chemical conditions for giant sulfide mineralization. These two processes are crucial in forming MVT deposits.

REE geochemical indicatrices of Li-F granite liquid segregation

We report new analytical data regarding major and trace element geochemistry, Sr-Nd isotopic composition, and zircon LA-ICP-MS U-Pb analysis from the Kaiyuan alkaline basalts of Yunnan Province, along the southern margin of the Emeishan Large Igneous Province (ELIP). Zircon U-Pb ages and bulk-rock geochemistry indicate that the mafic lavas erupted at 248 ± 6 Ma with OIB-like trace element and isotope ratios similar to the Emeishan high-Ti basalts. These characters suggest that the Kaiyuan alkaline basalts are the products of the post-ELIP magmatism, involving remelting of the plume head after the main ELIP phase. By analogy with the Neogene Red Sea rift system, the Kaiyuan alkaline basalts may have been caused by a Red Sea-like extension along the southwestern margin of the Yangzte during the Early Triassic, during which the hypothesized rift system experienced plate–boundary forces that vanished quickly in the Late Triassic period.

Rare-Earth Element Geochemistry of Eclogites from the Ultra-High Pressure Metamorphic Belt in Central China *

Major and trace elements analysis has been carried out on the Late Ladinian Tabai basalts from Yunnan Province with the aim of studying their petrogenesis. Their SiO2 contents range from 43.63 wt.% to 48.23 wt.%. The basalts belong to the weakly alkaline (average total alkalis Na2O+K2O=3.59 wt.%), high-Ti (3.21 wt.% to 4.32 wt.%) magma series. The basalts are characterized by OIB-like trace elements patterns, which are enriched in large ion lithosphile elements (LILE) including Rb and Ba, and display negative K, Zr and Hf anomalies as shown on the spider diagrams. The Tabai basalts display light rare-earth elements (LREE) enrichment and are depleted in heavy rare-earth elements (HREE) on the REE pattern. Those dates indicate that the parental magma of the Tabai basalts was derived from low-degree (1%–5%) partial melting of garnet peridotite. The magma underwent olivine fractional crystallization and minor crustal contamination during their ascent. The Tabai basalts were related to a relaxation event which had triggered the Emeishan fossil plume head re-melting in the Middle Triassic.

A high temperature and high pressure experimental study on re-bearing capability of sulfide

The results of 118 REE analyses of Li-F granites from South China and other countries indicate that there are three variation types of REE pattern curves with different evolution trends from early to late stages of Li-F granite complex or from lower to upper petrofacies of the Li-F granite body: (1) the decreasing, (2) the increasing, and (3) the saltatory variation types. The first variation type is called the positive evolution type, attributed to crystallization differentiation. The second is called the reversion evolution type, which represents liquid segregation dominated by vapor-liquid distillation. The third is called the saltatory variation type, which is formed from liquid segregation dominated by immiscibility. Therefore, the indicatrices of liquid segregation dominated by immiscibility are the saltatory variation type of REE pattern evolution and the separation of the main evolution trend lines either from the sub-evolution trend lines or from the composition points of Li-F granites in the diagrams of REE-(La/Yb)N and La/Sm-La. The indicatrices of liquid segregation dominated by vapor-liquid fractional distillation are the reverstion evolution type of REE pattern curves and the main evolution trend lines of Li-F granites directing to the upper right-hand on the REE-(La/Yb)N and La/Sm-La diagrams.The results of 118 REE analyses of Li-F granites from South China and other countries indicate that there are three variation types of REE pattern curves with different evolution trends from early to late stages of Li-F granite complex or from lower to upper petrofacies of the Li-F granite body: (1) the decreasing, (2) the increasing, and (3) the saltatory variation types. The first variation type is called the positive evolution type, attributed to crystallization differentiation. The second is called the reversion evolution type, which represents liquid segregation dominated by vapor-liquid distillation. The third is called the saltatory variation type, which is formed from liquid segregation dominated by immiscibility. Therefore, the indicatrices of liquid segregation dominated by immiscibility are the saltatory variation type of REE pattern evolution and the separation of the main evolution trend lines either from the sub-evolution trend lines or from the composition points of Li-F granites in the diagrams of REE-(La/Yb)N and La/Sm-La. The indicatrices of liquid segregation dominated by vapor-liquid fractional distillation are the reverstion evolution type of REE pattern curves and the main evolution trend lines of Li-F granites directing to the upper right-hand on the REE-(La/Yb)N and La/Sm-La diagrams.

Determination of rhenium and osmium by ICP-MS for galena and sphalerite

Based on their REE contents and REE patterns, eclogites from the ultra-high pressure metamorphic belt in central China may be roughly divided into six types including LREE-rich, LREE-rich + positive Eu anomaly, LREE-rich + negative Eu anomaly, REE patternsmooth, MREE-rich and HREE-rich. The LREE-rich, LREE-rich + positive Eu anomaly and LREE-rich + negative Eu anomaly types of eclogites are dominant. REE types of eclogites in different areas can be compared and the REE features of the same REE type of eclogites in different areas are similar. The results of reconstruction of the primary rocks show that the primary rocks of eclogites possibly are dominated by continental tholeiites which are the product of partial melting of relatively fertile mantle and the rocks of tholeiite crystallization-differentiation. There is perfect evolution relationship among the primary rocks of the LREE-rich, LREE-rich + positive Eu anomaly and LREE-rich + negative Eu anomaly types of eclogites and among those of the REE pattern smooth and MREE-rich types of eclogites, the former three types were derived from continental settings and the latter two from nearly oceanic settings. Meanwhile, it is concluded that the mantle sources of primary rocks of the eclogites are inhomogeneous and the primary rocks of eclogites in this area appear to have undergone varying degree of crustal contamination.