Gold and antimony metallogenic relations and ore-forming process of Qinglong Sb(Au) deposit in Youjiang basin,SW China: Sulfide trace elements and sulfur isotopes

In the northwestern margin of the Youjiang basin(NWYB)in SW China,many Carlin-like gold deposits are highly antimony(Sb)-rich,and many vein-type Sb deposits contain much Au.These deposits have similar ages,host rocks,ore-forming temperatures,ore-related alterations and ore mineral assemblages,but the Au and Sb metallogenic relations and their ore-forming process remain enigmatic.Here we investigate the large Qinglong Sb deposit in the NWYB,which has extensive sub-economic Au mineralization,and present a new metallogenic model based on in-situ trace elements(EPMA and LA-ICP-MS)and sulfur isotopes(NanoSIMS and fs-LA-MC-ICPMS)of the ore sulfides.At Qinglong,economic Sb ores contain coarse-grained stibnite,jasperoid quartz and fluorite,whilst the sub-economic Au–Sb ores comprise dominantly veined quartz,arsenian pyrite and fine-grained stibnite.Three generations of ore-related pyrite(Py1,Py2 and Py3)and two generations of stibnite(Stb1 and Stb2)are identified based on their texture,chemistry,and sulfur isotopes.The pre-ore Py1 is characterized by the lower ore element(Au,As,Sb,Cu and Ag)contents(mostly below the LA-ICP-MS detection limit)and Co/Ni ratios(average 0.31)than the ore-stage pyrites(Py2 and Py3),implying a sedimentary/diagenetic origin.The Py2 and Py3 have elevated ore element abundance(maximum As=6500 ppm,Au=22 ppm,Sb=6300 ppm,Cu=951 ppm,Ag=77 ppm)and Co/Ni ratios(average 1.84),and have positive As vs.Au–Sb–Cu–Ag correlations.Early-ore Stb1 has lower As(0.12–0.30 wt.%)than late-ore Stb2(0.91–1.20 wt.%).These features show that the progressive As enrichment in ore sulfides is accompanied by increasing Au,Sb,Cu and Ag with the hydrothermal evolution,thereby making As a good proxy for Au.As-rich,As-poor and As-free zones are identified via NanoSIMS mapping of the Au-bearing pyrite.The As-rich zones in the Qinglong Au-bearing pyrites(Py2 and Py3)and ore stibnites(Stb1 and Stb2)have narrowδ³⁴SH₂S ranges(-8.9‰to +4.1‰,average-3.1‰)and-2.9‰to +6.9‰,average + 1.3‰),respectively,indicating that the Au-rich and Sb-rich fluids may have had the same sulfur source.Published in-situ sulfur isotopic data of pyrite As-rich zones from other Carlin-like Au deposits(Shuiyindong,Taipingdong,Nayang,Getang and Lianhuashan)in the NWYB have similar ore-fluidδSH₂S values(-4.5‰to +6.7‰,average-0.6‰)to those of Qinglong.Therefore,we infer that the sulfur of both Au and Sb mineralization was derived from the same magmatic-related source(0±5‰)in the NWYB.Moreover,the core of pyrites(Py1)has variable S isotope fractionation(-18.9‰to +18.1‰,mostly +3‰to +12‰),suggesting that the higher-³⁴S H₂S was produced by bacterial sulfate reduction(BSR).The hydrothermal pyrite(Py2 and Py3)δ³⁴S values gradually decrease with increasing As concentrations,and ultimately,within the restricted range(-5‰to +5‰)in As-rich zones.This variation implies that the As-rich pyrite was formed through ongoing interactions of the magmatic-hydrothermal fluid with pre-existing sedimentary pyrites,causing the progressive decreasing δ³⁴S values with As content increase,Hence,the fluid/mineral interaction may have generated the observed variation in δ³⁴S and As contents.Overall,comparing the Au and Sb deposits in the NWYB,we favor a magmatic-related source for the Au–Sb–As-rich fluids,but the Au-and Sb-ore fluids were likely evolved at separate stages in the ore-forming system.     

Application of soft computing techniques for shallow foundation reliability in geotechnical engineering

This research focuses on the application of three soft computing techniques including Minimax Probability Machine Regression(MPMR),Particle Swarm Optimization based Artificial Neural Network(ANN-PSO)and Particle Swarm Optimization based Adaptive Network Fuzzy Inference System(ANFIS-PSO)to study the shallow foundation reliability based on settlement criteria.Soil is a heterogeneous medium and the involvement of its attributes for geotechnical behaviour in soil-foundation system makes the prediction of settlement of shallow a complex engineering problem.This study explores the feasibility of soft computing techniques against the deterministic approach.The settlement of shallow foundation depends on the parametersγ(unit weight),e0(void ratio)and CC(compression index).These soil parameters are taken as input variables while the settlement of shallow foundation as output.To assess the performance of models,different performance indices i.e.RMSE,VAF,R^2,Bias Factor,MAPE,LMI,U(95),RSR,NS,RPD,etc.were used.From the analysis of results,it was found that MPMR model outperformed PSO-ANFIS and PSO-ANN.Therefore,MPMR can be used as a reliable soft computing technique for non-linear problems for settlement of shallow foundations on soils.     

Kinetics of oil group-type generation and expulsion: An integrated application to Dongying Depression,Bohai Bay Basin,China

Pyrolysis of two kerogens isolated from the ${\text{E}}_{2\text{-}3}{\text{s}}_3^3$ and ${\text{E}}_{2\text{-}3}{\text{s}}_4^1$ source rocks in the Niuzhuang sag, Dongying Depression, Bohai Bay Basin, China, was performed in a confined system. The products were extracted with solvent and separated using micro-column chromatography into group-type fractions (saturates, aromatics, resins and asphaltenes) with the kerogen residue in each case undergoing swelling with a variety of solvents. The kinetics for generation and retention of crude oil and its group-type fractions from the kerogens were studied and the kinetic parameters applied to modeling generation and retention of crude oil and its fractions from the ${\text{E}}_{2\text{-}3}{\text{s}}_3^3$ and ${\text{E}}_{2\text{-}3}{\text{s}}_4^1$ source rocks on the basis of burial and thermal history of the Niuzhuang sag. The results show that the “normal oil” was generated at about 4.26 Ma and 24.85 Ma ago, but expelled at about 3.96 Ma and 17.46 Ma ago, respectively, from ${\text{E}}_{2\text{-}3}{\text{s}}_3^3$ and ${\text{E}}_{2\text{-}3}{\text{s}}_4^1$ source rocks. The current proportions of the expelled saturates, aromatics and NSOs are about 60%, 15% and 25%, respectively.     

Petrological geodynamics of mantle melting III. AlphaMELTS + multiphase flow: The effect of water

The influence of water is evaluated in this last contribution of a series aiming to study the petrological and dynamic evolution of mantle melting. Water is considered to be either a chemical component in the melt or solid assemblage but it can also be present as a pure water phase in a oversaturated environment. A three-phase-flow model was developed for this purpose.Only a limited set of conditions has been applied to the 1-D upwelling mantle column. A range of fixed temperatures (1150–1450 °C) and water contents in the solid mantle (0, 0.02 wt.%, 0.2 ​wt.%) have been imposed at the entry point (120 ​km deep) for the two melting models introduced in the previous installments, dynamic equilibrium melting (DEM) and dynamic fractional melting (DFM) model.As expected, for a given temperature at the base of the mantle column, the depth of the first melt formation increases with higher water content in the mantle. After the first melt is created, very negligible amount of melt is formed over a certain depth interval which approximately ends at the depth where the first melting of the dry mantle would take place. However melt is present as a dynamic phase thorough the entire region regardless whether the DEM or DFM model has been applied.Under a quasi-steady state regime, the melt and residual mantle compositions vary significantly over depth, depending on the conditions imposed to the model (DEM, DFM, bottom temperature and water content). Several distinctions can be made at the extraction point (top of the mantle column ​= ​15 ​km deep). For DEM and DFM models at this lowest depth, the most influential factor affecting the melt composition after the quasi-steady state condition has been reached is the temperature at the base of the column. In general, for a high temperature model, the input water in the mantle does not seem to play a significant role on the bulk composition of the melt (except for the water content in melt). But at low temperature water does have some noticeable influence on the variation of some chemical components in melt ($Si{O}_2$, $F{e}_2{O}_3$, $CaO$, $N{a}_{2}O$ at T ​= ​1250 °C or lower). A similar conclusion can be made also for the residual mantle composition. The presence of a dynamic free water phase is detected only in absence of melt or in coexistence with a melt phase when the mantle is relatively cold (bottom temperature $\le$1250 °C) and the input water content at the base of the model is relatively high (0.2 ​wt.%).Complete output data for several numerical simulations and six animations illustrating various melting models are available following the instructions in the supplementary material.     

The measurement of D/H ratio in alkenones and their isotopic heterogeneity

Previous paleoenvironmental studies reported the δD values of a mixture of coeluting alkenones. Here, we present a semi-preparative normal-phase high-performance liquid chromatography–mass spectrometry (NP-HPLC–MS) method for purifying long chain (C₃₇ and C₃₈) unsaturated methyl and ethyl ketones (alkenones) on the basis of chain length and degree of unsaturation.The method was applied to purify alkenones in suspended particles and surface sediments from a site in Chesapeake Bay, eastern USA. The hydrogen isotopic composition of di- and triunsaturated C₃₇ and C₃₈ alkenones differed significantly on the basis of chain length and the degree of unsaturation, demonstrating the importance of gas chromatography–isotope ratio-mass spectrometry (GC–irMS) analysis of individual alkenones for accurate paleoenvironmental reconstruction. Constant fractionation factors between alkenones with different chain length but the same degree of unsaturation (${\alpha }_{{\text{C}}_{37:2}''–''{\text{C}}_{38:2}}\text{and}{\alpha }_{{\text{C}}_{37:3}''–''{\text{C}}_{38:3}}=1.01$) and those with the same chain length but different degree of unsaturation (${\alpha }_{{\text{C}}_{37:2}''–''{\text{C}}_{37:3}}\text{and}{\alpha }_{{\text{C}}_{38:2}''–''{\text{C}}_{38:3}}=0.97$) in all samples suggest that the values may represent hydrogen isotope fractionation associated with elongation and desaturation during alkenone biosynthesis.     

Geochemistry of surface and ground water in Guiyang,China: Water/rock interaction and pollution in a karst hydrological system

The chemical compositions of the surface/ground water of Guiyang, the capital city of Guizhou Province, China are dominated by Ca²⁺, Mg²⁺, ${\text{HCO}}_3^{-}\text{and}{\text{SO}}_4^{2-}$, which have been derived largely from chemical weathering of carbonate rocks (limestone and dolomite). The production of ${\text{SO}}_4^{2-}$ has multiple origins, mainly from dissolution of sulfate evaporites, oxidation of sulfide minerals and organic S in the strata, and anthropogenic sources. Most ground water is exposed to soil CO₂ and, therefore, the H₂CO₃ which attacks minerals contains much soil C. In addition, the H₂SO₄ produced as a result of the oxidation of sulfides in S-rich coal seams and/or organic S, is believed to be associated with the chemical weathering of rocks. The major anthropogenic components in the surface and ground water include K⁺, Na⁺, Cl⁻, ${\text{SO}}_4^{2-}\text{and}{\text{NO}}_3^{-}$, with Cl⁻ and ${\text{NO}}_3^{-}$ being the main contributors to ground water pollution in Guiyang and its adjacent areas. The seasonal variations in concentrations of anthropogenic components demonstrate that the karst ground water system is liable to pollution by human activities. The higher content of ${\text{NO}}_3^{-}$ in ground water compared to surface water during the summer and winter seasons, indicates that the karstic ground water system is not capable of denitrification and therefore does not easily recover once contaminated with nitrates.     

Lithospheric stress in Mongolia,from earthquake source data

Lithospheric stress in Mongolia has been studied using mechanisms of 84 M_(LH)≥ 4 earthquakes that occurred in the 20 th century and instrumental seismic moments of 17,375 M_(LH)≥2.5 events recorded between 1970 and 2000.The M_(LH)≥ 3.5 earthquakes mostly have strike-slip mechanisms in southern and central Mongolia,with frequent reverse-slip motions in the west and normal slip in the north,especially,in the area of Lake Hovsgol.The principal stresses are,respectively,S_HS_vS_h in the center and in the south;high horizontal compression with S_HS_hS_v in the west;and a heterogeneous stress pattern with S_vS_HS_h in the north.According to seismic moments of M_(LH)=2.5 events,oblique slip generally predominates over the territory,at S_v≈S_HS_h,while frequent strike slip motions in the west record high horizontal compression(S_HS_vS_h).Earthquake mechanisms show the principal horizontal compression S_H to be directed W-E in the east,NE-SW in the central and Gobi-Altay regions,and approximately N-S in the west of Mongolia.The patterns of principal lithospheric stresses in the territory of Mongolia have undergone three events of dramatic change for a few recent decades,and these events were synchronous with three similar events in the Baikal rift system(BRS):in the latest 1960 s,latest 1970 s to earliest 1980 s,and in the latest 1980 s to earliest 1990 s.The seismicity of Mongolia has been controlled by superposition of variable stresses associated with rifting activity pulses in the neighbor BRS on the background of quasi-stationary super-regional compression.     

Model reconstruction of nitrate pollution of riverbank filtration using 15N and 18O data,Karany, Czech Republic

Stable isotopes of O (δ¹⁸O) in water and N (δ¹⁵N) in ${\text{NO}}_3^{-}$ have been used as natural indigenous groundwater tracers for sources of water and of ${\text{NO}}_3^{-}$ at two riverbank filtration (RBF) water supply systems. Both RBF systems (Skorkov and Sojovice) have wells in unconsolidated Quaternary sediments close to the Jizera River (Czech Republic) that have been affected by increasing ${\text{NO}}_3^{-}$ concentrations. The area is underlain by Turonian sandstones and marls that form a deeper bedrock aquifer. Sources of ${\text{NO}}_3^{-}$ are local sewerage systems and landfills (point sources) and seasonal application of manure and inorganic fertilizers (diffuse sources).At RBF Skorkov recharge to wells can be modelled using a two-component model with 60% river water contribution and 40% of very shallow groundwater with an average residence time of one month. During periods of abundant precipitation, groundwater originates entirely from the unsaturated zone of the Quaternary aquifer; extensive pumping for over 40 a has created new, bypassing flow paths that preferentially drain the contaminated unsaturated zone. During dry periods, wells are recharged by longer residence time groundwater from the Quaternary aquifer.At RBF Sojovice there is an additional recharge component of groundwater from the Turonian aquifer, which is sandier at this locality; this contains denitrified ${\text{NO}}_3^{-}$ with highly positive δ¹⁵N values.