Source of metals related to gold occurrences in Cameroon, Central African Belt

Suites of granitic and metamorphic rocks form a perfect geological environment in which to investigate the source of metals related to gold deposits.In the East Province of Cameroon,the source of metals-related gold(grade~4.6 g/t)that occurs within metamorphic and granitic rocks remains ambiguous.The host rocks were subjected to XRF and ICP-MS whole-rock geochemistry and BSE/EDS mineral analyses to investigate the source(s)of metals related to gold in the Province.Petrographically,chalcopyrite-pyrite and magnetite-ilmenite are the main sulfi des and oxides of granites,respectively.The low-grade metamorphic rocks are sulfi de-rich consisting of arsenopyrite,chalcopyrite,pyrite,and sphalerite,and oxides include magnetite,ilmenite,hematite,and rutile.Cu,Ni,Co,Sb,Sc,and Zn concentrations depleted in high-grade metamorphic rocks and granites compared to low-grade metamorphic rocks.As well,Bi,Cd,Co,Cu,Ni,Sb,V,W,and Zn concentrations decrease with increasing temperatures from low-grade rocks to high-grade rocks and granites.The suite of depleted elements in high-grade rocks and granites is almost identical to those enriched in gold occurrences.We conclude that metals(Bi,Cd,Co,Cu,Ni,Sb,and Zn)related to gold mineralization in the East Province of Cameroon likely originated from metal-rich low-grade metamorphic rocks during prograde metamorphic processes prior to partial melting.

Deciphering fluid origins in the Paleozoic Laoshankou Fe-Cu-Au deposit, East Junggar: Constraints from noble gases and halogens

To constrain the ore-fluid source(s)of the Laoshankou Fe-Cu-Au deposit(Junggar orogen,NW China),we analyzed the fluid inclusion(FI)noble gas(Ar,Kr and Xe)and halogen(Cl,Br and I)compositions in the hydrothermal epidote and quartz.Four hypogene alteration/mineralization stages,including(I)pre-ore Ca-silicate,(II)early-ore amphibole-epidote-magnetite,(III)late-ore pyrite-chalcopyrite,and(IV)post-ore hydrothermal veining,have been identified at Laoshankou.Stage II FIs have salinity of 15.7 wt.%(NaCl eq.),I/Cl molar ratios of 75×10^(−6)-135×10^(−6),and Br/Cl molar ratios of 1.4×10^(−3)-2.1×10^(−3).The moderately-high seawatercorrected Br*/I ratios(0.5-1.5)and low 40ArE/Cl slope(-10−5)indicate the presence of sedimentary marine pore fluid,which was modified by seawater reacting with the Beitashan Fm.volcanic rocks.Stage III fluid is more saline than their stage II and IV counterparts,reaching up to 23.3 wt.%(NaCl+CaCl2 eq.)close to halite saturation(-26 wt.%).The fluid has I/Cl ratios of 75×10^(−6)-90×10^(−6) and Br/Cl ratios of 1.5×10^(−3)-1.8×10^(−3).Considering the increasing 40ArE/Cl trend toward bittern brine and the higher 36Ar content than air-saturated water(ASW),a bittern fluid source is inferred from seawater evaporation,which was modified by interaction with organic-rich marine sedimentary rocks.Stage IV FIs have lower temperature(110-228°C)and Br/Cl(0.90×10^(−3)-1.2×10^(−3)),but higher 36Ar content than ASW,indicative of dissolved evaporite or halite input.Considering also the lowδDfluid(−114‰to−144‰)andδ18Ofluid(2.1‰-3.5‰)values,meteoric water(with minor dissolved evaporites)likely dominated the stage IV fluid.The evaporites may have formed through continuous evaporation of the stage III surface-derived bittern.Involvement of non-magmatic fluids and different ore-fluid origins in stages II and III suggest that the ore-forming process was different from a typical magmatichydrothermal fluid-dominated skarn mineralization,which was previously proposed for Laoshankou.Our noble gas and halogen study at Laoshankou provide new insights on the fluid sources for the Paleozoic Fe−Cu(−Au)deposits in the Central Asian Orogenic Belt(CAOB),and our non-magmatic fluid source interpretation is consistent with the basin inversion setting for the mineralization.

Characteristics and evolution of ore-forming fluids of the Chongjiang copper deposit in the Gangdise porphyry copper belt, Tibet

Petrography, microthermometry, and scanning electron microscope/energy dispersive spectrometer （SEM/EDS） studies were performed on the fluid inclusions in the ore-beating quartz veins and quartz phenocrysts in the porphyry of the Chongjiang porphyry copper deposit. The analyses of the fluid inclusions indicate that the ore-forming fluids were exsolved from magma. They are near-saturated, supercritical, rich in volatile constituents, and have the capture temperature of 362-389℃ and salinities of 17.7wt%- 18.9wt% NaC1 eq. With the decreasing of temperature and pressure, the supercritical fluids were separated into a low salinity vapor phase and a high salinity liquid phase. During quartz-sericitization, the high salinity fluid boiled and separated into a low salinity vapor phase and a high salinity liquid phase. The high salinity inclusions that formed in the boiling process had daughter mineral melting temperatures higher than the homogenization temperatures of the vapor and liquid phases. The late fluids that are responsible for argillization are of lower temperature and salinity.

Effects of the original state of sodium-based additives on microstructure,surface characteristics and filtration performance of SiC membranes

Sodium-contained compounds are promising sintering additives for the low-temperature preparation of reaction bonded SiC membranes.Although sodium-based sintering additives in various original states were attempted,their effects on microstructure and surface properties have rarely been studied.In this work,three types of sodium-based additives,including solid-state NaA zeolite residue(NaA)and liquidstate dodecylbenzene sulfonate(SDBS)and water glass(WG),were separately adopted to prepare SiC membranes,and the microstructure,surface characteristics and filtration performance of these SiC membranes were comparatively studied.Results showed that the SiC membranes prepared with liquid-state SDBS and WG(S-SDBS and S-WG)showed lower open porosity yet higher bending strength compared to those prepared with solid-state NaA(S-NaA).The observed differences in bending strength were further interpreted by analyzing the reaction process of each sintering additive and the composition of the bonding phase in the reaction bonded SiC membranes.Meanwhile,the microstructural differentiation was correlated to the original state of the additives.In addition,their surface characteristics and filtration performance for oil-in-water emulsion were examined and correlated to the membrane microstructure.The S-NaA samples showed higher hydrophilicity,lower surface roughness(1.80μm)and higher rejection ratio(99.99%)in O/W emulsion separation than those of S-WG and S-SDBS.This can be attributed to the smaller mean pore size and higher open porosity,resulting from the originally solid-state NaA additives.Therefore,this work revealed the comprehensive effects of original state of sintering additives on the prepared SiC membranes,which could be helpful for the application-oriented fabrication by choosing additives in suitable state.

中国碳酸岩型稀土矿床:时空分布与成矿过程

中国是世界最大的稀土资源国,约98%稀土资源来自碳酸岩型稀土矿床.对碳酸岩型稀土矿床的成矿背景和矿床成因前人进行了大量的工作,但仍存在认识上的分歧.本文在综合已有研究基础上,对我国碳酸岩型稀土矿床的时空分布、岩浆起源、稀土富集及沉淀机理进行探讨,旨在为我国的稀土成矿理论研究和稀土找矿提供参考.研究表明,我国碳酸岩型稀土矿床主要分布于古老的克拉通边缘,构成了4条时代各异的稀土成矿带.克拉通边缘由于受俯冲板片流体(或熔体)交代形成富稀土的地幔源区,其部分熔融形成稀土成矿母岩浆,初始岩浆成分可能为碳酸盐化硅酸岩浆.母岩浆演化过程中的硅酸盐熔体与碳酸盐熔体的不混溶或多相硅酸岩熔体、磷镁质熔体与碳酸岩熔体的不混溶及基性矿物的结晶分离形成碳酸岩浆,并造成碳酸岩浆中稀土,特别是轻稀土的强烈富集.碳酸岩侵位和冷凝过程中碳酸盐矿物的结晶分离造成了稀土在晚期碳酸岩浆和碳酸岩流体中的进一步富集,因此稀土矿化多发生在碳酸岩浆演化晚期或碳酸岩流体阶段.初始碳酸岩流体以富SO_(4)^(2-)和CO_(2)为特征,具有超高的稀土迁移能力,因此在碳酸岩熔体-流体转化过程中稀土主要富集于富硫酸盐的流体相中.碳酸岩流体演化过程中的硫酸盐熔体与水流体的不混溶造成水流体中SO_(4)^(2-)浓度的快速降低,并导致了稀土的大规模沉淀.由于碳酸岩多以板状侵入体或岩脉形式侵入,快速的减压和降温使碳酸岩流体演化,特别是硫酸盐熔体与水流体的快速分离和稀土的快速沉淀,因此稀土矿化或发生在碳酸岩体内或紧邻碳酸岩体的围岩中.碳酸岩体上部或相对富流体的中心相是最佳成矿部位,向深部或边部,碳酸岩中黑云母等矿物增加,稀土矿化相对减弱.

Fluorescence detection of Escherichia coli on mannose modified ZnTe quantum dots

Rapid detection and identification of Escherichia coli(E.coli)is essential to prevent its quickly spread.In this study,a novel fluorescence probe based on ZnTe quantum dots(QDs)modified by mannose(MAN)had been prepared for the determination of E.coli.The results showed that the obtained QDs showed excellent selectivity toward E.coli,and presented a good linearity in range of 1.0×10~5~1.0×10~8 CFU/mL.The optimum fluorescence intensity for detecting E.coli was found to be at pH 7.0 with a temperature of25℃and incubation time of 20 min.Under these optimum conditions,the detection limit of E.coli was4.6×10~4 CFU/mL.The quenching was discussed to be a static quenching procedure,which was proved by the quenching efficiency of QDs decreased with the temperature increasing.