Cobalt Deposits of China: Classification, Distribution and Major Advances

The important strategic metal cobalt has diverse uses and the majority of world cobalt deposits have been found in China. The deposits can be classified into four types, i.e., magmatic Ni-Cu-Co sulfide deposits, hydrothermal and volcanogenic cobalt polymetallic deposits, strata-bound Cu-Co deposits hosted by sedimentary rocks and lateritic Ni-Co deposits, of which the former two types are the most important. There are six principal metallogenic epochs and seven important metallogenic belts according to their distribution and tectonic position. Although cobalt generally occurs in nickel-copper, copper and iron deposits as an associated metal, great developments in exploration for independent cobalt deposits have happened in China, and, in recent years, many independent deposits with different elementary assemblages and different genetic types have been discovered in the eastern part of the northern margin of the North China platform, the Central Orogenic Belt of China, western Jiangxi and northeastern Hunan. In addition, it is inferred that the Kunlun-Qinling Orogenic Belt has great potential for further exploration of new types of independent cobalt deposits.

Cobalt Deposits in the Central China Orogenic Belt

Cobalt mostly occurs as an associated metal in Cu-Ni sulphide deposits, skarn Fe-Cu-Pb-Zn deposits and volcanic-hosted massive sulphide (VHMS) or sedex deposits. There are different types of cobalt deposits in the Central China orogenic belt. In the Tamu-Kalangu Mississippi-valley type Pb-Zn deposits, many cobalt-nickel sulphide minerals were found. The cobalt content of the ore is 0.064%-0.46% in sedex-type Kendekeke Fe-Pb-Zn-Au deposits, and cobalt sulphide veins with Co contents of 4%-9% have also been found. About 28000 tons of cobalt reserves were delineated in the Dur'ngoi Cu-Co-Zn deposit of VHMS type in the A'nyemaqên Mountains. It is considered that the exploration potential for cobalt is attractive in this district, especially in sedex-type deposits and Co-rich sulphide veins in sedex-type Fe, Cu and Pb-Zn deposits and their surroundings.

China's First Independent Cobalt Deposit and its Metallogenic Mechanism:Evidence from Fluid Inclusions and Isotopic Geochemistry

The Tuolugou cobalt deposit is the first independent large-scale Co- and Au-bearing deposit discovered in northwestern China. It is located in the eastern Kunlun orogenic belt in Qinghai Province, and occurs conformably in low-grade metamorphic volcano-sedimentary rock series with well-developed Na-rich hydrothermal sedimentary rocks and typical hydrothermal sedimentary ore fabrics. Fluid inclusions and isotopic geochemistry studies suggest that cobalt mineralizing fluid is dominated by NaCI-H20 system, accompanied by NaCI-CO2-H20-N2 system responsible for gold mineralization. Massive, banded and disseminated pyrite ores have similar compositions of He and Ar isotopes from the mineralizing fluid, with 3He/4He range between 0.10 to 0.31Ra （averaging 0.21Ra）, and 4~Ar/36Ar between 302 and 569 （averaging 373）, which reflects that Co mineralizing fluids derived dominantly from meteoric water deeply circulating. ~34S values of pyrite approaches to zero （~34S ranging from -4.5%o to ＋1.5%o, centering around -1.8%o to -0.2%o）, reflecting its deep source. Ore lead is characterized by distinctly high radiogenesis, with 2~6pb/2~4pb〉19.279, 2~7pb/2~4pb〉15.691 and 2~spb/2~4pb〉39.627, and its values show an increase trend from country rocks, regional Paleozoic volcanic rocks to ores. This may have suggested that high radiogentic ore Pb derived mainly from country rocks by leaching meteoric water-dominated hydrothermal fluid during its circulation at depth. Cobalt occurs mainly in sulfide phase （such as pyrite）, but cobalt enrichment, and presence and increasing contents of Co-bearing minerals have a positive correlation with metamorphic degree. The Tuolugou deposit and other typical strata-bound Co-Cu-Au deposits have striking similarities in the geological features and metallogenic pattern of primary cobalt. All of them are syngenetic hydrothermal exhalative sedimentation in origin.

Synthesis and characterization of carbon-coated cobalt ferrite nanoparticles

Cobalt ferrite nanoparticles（CFNPs） were prepared via a reverse micelle method. The CFNPs were subsequently coated with carbon shells by means of thermal chemical vapor deposition（TCVD）. In this process, acetylene gas（C2H2） was used as a carbon source and the coating was carried out for 1, 2, or 3 h at 750℃. The Ar/C2H2 ratio was 10：1. Heating during the TCVD process resulted in a NP core size that approached 30 nm; the thickness of the shell was less than 10 nm. The composition, structure, and morphology of the fabricated composites were characterized using X-ray diffraction, simultaneous thermal analysis, transmission electron microscopy, high-resolution transmission electron microscopy, and selected-area diffraction. A vibrating sample magnetometer was used to survey the samples＇ magnetic properties. The deposited carbon shell substantially affected the growth and magnetic properties of the CFNPs. Micro-Raman spectroscopy was used to study the carbon coating and revealed that the deposited carbon comprised graphite, multiwalled carbon nanotubes, and diamond-like carbon. With an increase in coating time, the intensity ratio between the amorphous and ordered peaks in the Raman spectra decreased, which indicated an increase in crystallite size.

Manipulating magnetic anisotropies of Co/MgO(001) ultrathin films via oblique deposition

We present a systematic investigation of magnetic anisotropy induced by oblique deposition of Co thin films on MgO（001） substrates by molecular beam epitaxy at different deposition angles,i.e.,0？,30？,45？,60？,and 75？with respect to the surface normal.Low energy electron diffraction（LEED）,surface magneto–optical Kerr effect（SMOKE）,and anisotropic magnetoresistance（AMR） setups were employed to investigate the magnetic properties of cobalt films.The values of in-plane uniaxial magnetic anisotropy（UMA） constant Ku and four-fold magnetocrystalline anisotropy constant K1 were derived from magnetic torque curves on the base of AMR results.It was found that the value of Ku increases with increasing deposition angle with respect to the surface normal,while the value of K_1 remains almost constant for all the samples.Furthermore,by using MOKE results,the Ku values of the films deposited obliquely were also derived from the magnetization curves along hard axis.The results of AMR method were then compared with that of hard axis fitting method（coherent rotation） and found that both methods have almost identical values of UMA constant for each sample.

A novel coated-particle design and fluidized-bed chemical vapor deposition preparation method for fuel-element identification in a nuclear reactor

Particle coating is an important method that can be used to expand particle-technology applications. Coated-particle design and preparation for nuclear fuel-element trajectory tracing were focused on in this paper. Particles that contain elemental cobalt were selected because of the characteristic gamma ray spectra of 60Co. A novel particle-structure design was proposed by coating particles that contain elemental cobalt with a high-density silicon-carbide （SiC） layer. During the coating process with the high-density SiC layer, cobalt metal was formed and diffused towards the coating, so an inner SiC–CoxSi layer was designed and obtained by fluidized-bed chemical vapor deposition coupled with in-situ chemical reaction. The coating layers were studied by X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy techniques. The chemical composition was also determined by inductively coupled plasma optical emission spectrometry. The novel particle design can reduce the formation of metallic cobalt and prevent cobalt diffusion in the coating process, which can maintain safety in a nuclear reactor for an extended period. The experimental results also validated that coated particles maintain their structural integrity at extremely high temperatures （～1950 °C）, which meets the requirements of next-generation nuclear reactors.