Deposits In China Research Articles

Color Genesis and Compositional Characteristics of Color-Change Sapphire from Fuping, China

The color-change sapphire occurs in sillimanite-biotite gneiss in Fuping County Hebei province, China, is one of most famous sapphire deposits in China. However, the color genesis, mechanisms of color changing and compositional characteristics of the sapphire remain enigmatic. In this contribution, the coloration in the Fuping sapphire, color changing mechanisms and, compositional characteristics were studied by conventional gemological instruments in conjunction with ultraviolet-visible spectroscopy and Laser ablation inductively coupled plasma mass spectrometer. The results show that the Fuping sapphire is characterized by purple-blue-to-purple-red changed effect and column-shaped, waist drum-shaped with higher degree of euhedral crystal. Reddish brown rutile inclusions with 120° crossed cleavage are commonly observed. The dominant coloring element of the Fuping sapphire is Fe3+, and subordinate elements are Fe2+, Cr3+ and V3+. The color-change effect is caused by trace elements Cr3+ and V3+. The chemical compositions of Fuping color-change sapphires are analogous to those of metamorphic blue sapphires. When geochemically compared with sapphires from Isalo/Ilakaka deposit in Madagascar, Ratnapura deposit in Sri Lanka and Mogok in Myanmar, the Fuping color-change sapphires have distinctly higher rare element contents of Fe, Cr and Ga.

Multi-stage metasomatic Zr mineralization in the world-class Baerzhe rare earth element Nb-Zr-Be deposit, China

AbstractMagmatic and metasomatic zircon occurs in many alkaline igneous rocks and both are potential economic reservoirs of Zr, and in some places, rare-earth elements. The Baerzhe deposit in China is an example of a system where both types of zircon occur. Previous studies recognized deuteric and variably altered magmatic zircon in a transsolvus miaskitic granite, as well as four types of metasomatic zircon in a transsolvus agpaitic granite. In this study, the relationships among, and origins of, zircon and how these relate to models for rare-metal mineralization are assessed. In situ backscattered electron (BSE) and cathodoluminescence (CL) imaging, Raman spectroscopy (including mapping), and chemistry of zircon from the agpaitic granite were conducted, combined with evaluation of published data on zircon from Baerzhe. Their textural, spectroscopic, and chemical characteristics suggest that the four types of metasomatic zircon in the agpaitic granite were not subjected to metamictization or intense alteration, with trace-element accommodation largely following a xenotime substitution mechanism. The most abundant type of metasomatic zircon in the agpaitic granite occurs in zircon-quartz pseudomorphs and exhibits comparable CL, Raman spectral, and chemical features to rare zircon that has partially replaced elpidite. This confirms that the pseudomorphs formed by complete replacement of elpidite. The pseudomorph zircon occurs in association with snowball quartz that contains inclusions of zircon, aegirine, and albite, and with secondary quartz containing aegirine. This is consistent with their coeval formation during Na metasomatism. The restriction of Na metasomatism to the agpaitic granite indicates that this event and the associated zircon formation resulted from early autometasomatism of the agpaitic phase. REE- and Be-rich zircon that replaced magmatic amphibole crystallized as a result of reaction with a REE- and Be-rich fluid that most likely was responsible for the later REE-Nb-Be mineralization that affected both the miaskitic and agpaitic granites. The miaskitic granite contains deuteric and altered magmatic zircon with different chemical characteristics to the four types of metasomatic zircon in the agpaitic granite. This suggests that secondary Zr mineralization in the miaskitic granite formed from different fluids to those that metasomatized the agpaitic granite and may also have resulted from autometasomatism. This study reveals a complex picture for the formation of zircon at Baerzhe, the character of which can vary significantly, both temporally and spatially. Such variable chemistry of the various types of zircon resulted not only from their different origins (magmatic vs. metasomatic), but also from localized water-rock interaction that involved multiple stages of fluids. Zircon in both the miaskitic and agpaitic phases was mainly the product of autometasomatism that was constrained to their parental granites.

Geology and Petrogeochemistry of Lijiapuzi Nb-Ta Granitic Pegmatite Deposit: Implications for Ore Genesis and Prospecting

Most of the rare metal pegmatite deposits in China lie in West, Central and South China, and the Lijiapuzi Nb-Ta deposit is the only pegmatite-type Nb-Ta deposit in Northeast China, therefore a detailed study of the Lijiapuzi deposit is of great importance to the metallogeny and exploration of rare metal deposits in Northeast China. The Nb-Ta bearing pegmatites in Lijiapuzi district are composed of a microcline wall zone, a muscovite (lepidolite)-albite intermediate zone and a quartz core, and the rare metal mineralization mainly occurs in the intermediate zone and is intimately related to the albitization. The lithogeochemical features indicate that Lijiapuzi pegmatoids are rich in silicon and alkaline, poor in calcium, magnesium, titanium and phosphorus, and belong to peraluminous granitoid rocks. The enrichment of large ion lithophile elements (LILEs) and depletion of high field-strength elements (HFSEs), the distinct right-inclined REE pattern with obvious Eu negative anomaly, lower ratio of Nb/Ta and higher ratio of La/Nb and Rb/Sr indicate that the pegmatite was of a crustal origin and formed in relatively extensional tectonic setting of post-orogenesis. The pegmatites in Lijiapuzi area can be divided into two categories, i.e., the NW-trending pegmatites are shorter and thicker, with obvious zoning and localized in the upper part of the near-surface, while the NE-trending pegmatites are longer, thinner, devoid of zoning and localized in the lower part of the district. This probably means that excellent ore prospecting potential exists in the lower part of the Lijiapuzi district.

Wealth management products, banking competition, and stability: Evidence from China

Shadow financing through off-balance sheet wealth management products (WMPs) has become increasingly important besides deposits in China. We quantify the economic magnitude of the effect of WMPs on banking stability in an equilibrium model calibrated to Chinese banking sector data. Alternative equilibria emerge which deviate substantially from the observed banking system and lead to severe financial distress and large welfare losses. Rollover costs from the WMP market and negative shocks to the asset market underlying WMPs can exacerbate banking instability. Moreover, we show that smaller and medium sized banks are comparably relevant for financial stability as the systemically important big 4 banks in China.

Study of comprehensive shielding behaviors of chambersite deposit for neutron and gamma ray

Comprehensive shielding behaviors of chambersite deposit in China for neutron and gamma ray were systematically analyzed for the first time. Monte-Carlo method simulation technique, American Evaluated Nuclear Data File (ENDF/B-VIII.0), XCOM program and Phy-X/PSD program were used to perform the analysis. Transmission against different neutron resources and cross section for neutrons, mass attenuation coefficient, half value thickness, effective atomic number and electron density for narrow beam gamma ray at 0.001–100000 MeV, and equivalent atomic number, G-P Fitting Parameters, exposure buildup factors and energy absorption buildup factors against wide beam gamma ray for penetration depths up to 40mfp at 0.015–15 MeV were obtained. Shielding performance of chambersite deposit is excellent for high energy and low energy neutrons because of Mn and B respectively, and better than SWX-210. Shielding ability for gamma ray dependent on the element with high-Z or higher content and is between steel-magnetite concrete and ilmenite concrete. The shielding performance for both thermal neutron and gamma ray of the prepared sample is better than SWX-201 and SWX-261. Thus chambersite deposit will be an excellent shielding raw material for both gamma ray and neutron, also combining it with hydrogen rich materials can improve its attenuation properties and expand its possible uses.

Petrogenesis of Ta-Nb mineralization related Early Cretaceous Lingshan granite complex, Jiangxi Province, southeast China: Constraints from geochronology, whole-rock and in-situ mineral geochemistry, and Nd-Hf isotopic compositions

The Lingshan granite complex, located in the northeast part of the Qin-Hang Belt, Jiangxi Province, southeast China, has produced the largest Ta-Nb deposits in China, i.e., the Huangshan Nb-Ta and Songshugang Ta-Nb-(W-Sn) deposits. This complex is spatially a ring-like multiphase batholith, and comprises a series of granitic rocks from the central to marginal units. Mafic microgranular enclaves (MMEs) occur only in the central unit. Geochronologic results show that the magmatic activities at Lingshan district took place at Early Cretaceous, with similar emplacement ages (133–134 Ma) between the central and marginal units. The Lingshan granites are metaluminous to weakly peraluminous (most A/CNK < 1.1), and display typical A-type affinity. However, the whole-rock REE contents and Zr/Hf and (La/Yb)N ratios exhibit an abnormal increase from the central to marginal units. The Li, Rb and Cs elements of biotite as well as the Zr/Hf ratios of zircon do not exhibit a continuous enrichment trend from the central towards marginal granites. All these features suggest that the generation of Lingshan granites is more complex than the fractional crystallization from a single parental magma. Alternatively, a crystal mush model could be applied to better interpret the geochemical and isotopic contrasts between different granite phases. The marginal granites were likely formed by later crystallization events after the rejuvenation and extraction from the crystal mush reservoirs, while the central granites were formed from the residual crystal-rich mush with a relatively low terminal porosity. Moreover, the Nb and Ta contents of biotite exhibit a gradual enrichment with increasing fluorine contents in the marginal granites. The enrichment of lithium and fluorine in the granitic melt can significantly promote the proportion of non-bridging oxygens (NBOs) for coordinating Nb and Ta in the melt, further enhancing the solubility of columbite and tantalite, and eventually causing the Nb and Ta elements either incorporate into the mineral lattice of micas in the early marginal granites or form columbite-group minerals in the pegmatite/altered granite. In summary, we propose that the Ta-Nb enrichment event in the Lingshan district is spatially and genetically related to the extensive fractionation evolution from central to marginal units.

Syn‐mineralization Uplifting and Exhumation of Porphyry Systems in China: Evidence from Fluid Inclusion Data

AbstractIn order to understand how the metallogenic process of porphyry deposit specifically and directly respond to regional uplifting and exhumation, we compiled previous fluid inclusion data of 32 porphyry deposits in China by recalculating the fluid trapping depths and trapping depth reduction magnitude from early to late mineralization stage veins. The data reveal that the average trapping pressure ratio (Ave TPE/TPL) between early‐ and late‐stage veins of the these deposits are 1.2–18.4, mainly in the range of 1.35–5.83, with average trapping pressure reduction (1–Ave TPL/TPE) from early‐ to late‐ stage veins are 17%–95%, and mainly in the range of 25%–83%. The fluid trapping pressure based mineralization depths most of the porphyry deposits in China had decreased from early to late vein stages by at least 450 m (900–5800 m predominant), or greater than 950 m when take the average depth reduction value, which is greater than the current gap between early‐ and late‐ stage veins of each deposit. We propose that the apparently greater mineralization depth reduction magnitude than the current elevation gaps between early and late veins are likely a consequence of syn‐mineralization uplifting and exhumation process that often occurs in porphyry systems.

Nature and evolution of the ore‐forming fluids in the Shazhou volcanic‐related hydrothermal uranium deposit, Xiangshan ore field, SE China

The Xiangshan uranium (U) ore field in South‐east China has been recognized as the largest volcanic‐related hydrothermal U deposit in China since its discovery in the 1950s. The U mineralization at Xiangshan is mostly hosted in felsic volcanic and sub‐volcanic rocks and occurs mainly in veins, which are controlled by high‐angle normal faults in association with haematite, quartz, fluorite, apatite, and pyrite. Likewise, diverse hydrothermal alterations such as haematitization, silicification, fluoritization, and illitization have been identified adjacent to the ore‐bearing faults and outward for tens to hundreds of metres into the volcanic rocks. Situated to the west in the Xiangshan ore field, the Shazhou deposit is the second‐largest U deposit in the Xiangshan volcanic basin. Based on geological field evidence and petrographic observations, the ore‐forming fluids in the Shazhou U deposit can be classified and separated into three stages (early, main, and late): (a) fluids associated with the early mineralization stage are characterized by the oxidizing feature with U‐O hydroxide complexes as the dominant species; (b) fluids from the main mineralization stage were reducing fluids with black–purple fluorite and sulphide complexes of U‐Ti‐O; and (c) fluids from the late‐stage were weakly oxidizing fluids with light purple fluorite and light red calcite complexes of U‐O as the dominant species in the fluid. Fluid inclusions in alteration minerals from the main and late mineralization stage recorded homogenization temperatures (Th) of 280–340°C and 200–260°C, with salinities of 5–17 and 6–10% NaCleqv, respectively. Ore‐forming fluids contain variable amounts of CO2, O2, and H2, in which the volatile content in the main mineralization stage is higher than that in the late stage. The temperature and salinity of the ore‐forming fluids were fluctuating and gradually decreased as the geologic history of the deposit progressed. The δDW‐SMOW values calculated for the ore‐forming fluids range from −97.4 to −65.1‰. The δ18O values of syn‐ore quartz occur mainly between 5.9 and 15.7‰; calculated δ18OW‐SMOW values are between −1.5 and +8.3‰. The δ34SCDT values of syn‐ore pyrite and galena range from 9.7 to 19.7‰. The ore‐forming fluids in the Shazhou U deposit are derived from different sources with a complex geological evolution history. The ore‐forming fluids from the early mineralization stage with high O2 contents may have been primarily derived from post‐volcanic hydrothermal activity. Subsequently, fluids from the main mineralization stage (with lower O2 and high H2 contents) might have originated from the deep‐sourced fluids, where sulphur was carried from the metamorphic basement. Finally, ore‐forming fluids from the late mineralization stage could have been produced by mixing meteoric hydrothermal fluids. Large‐scale fluid immiscibility and boiling occurred during the main mineralization stage, followed by fluid mixing during the late mineralization stage. Boiling and mixing of fluids were the two dominant mechanisms for the deposition of U in the Shazhou deposit.

3-D Inversion of Gravity Anomalies by Combining Power-Spectrum Derived Adaptive Weighting and Cross-Gradient Regulation: Application to Molybdenum–Copper Deposit

Gravity measurement is an important geophysical prospecting method for mineral exploration. With most of the shallow ore deposits in China being exploited, the future targets for exploration will be aimed at the deep mineral resources about 4-km underground. To improve the resolving ability in the vertical direction of the 3-D density inversion to find deep-source minerals, we propose to achieve the inversion of gravity anomalies by combining power-spectrum derived adaptive weighting and cross-gradient regularization. First, spectral analysis is utilized to conduct the source-depth separation, and the adaptive weighting function is designed depending on the slope of the radial logarithmic power spectrum of the gravity anomaly, which can enhance the correspondence for the field sources with different depths to improve the vertical resolution relatively. Thus, each separated source with different depths could be given an adaptive weighting coefficient in each separated inversion. Second, the cross-gradient technique is introduced as a structural constraint in the objective function to further constrain the separated inversion process. By performing two-cuboid-source cases, it can be seen that this combination calculated approach has great potential to improve the quality of the inversion results. When examining the inversion of the actual gravity data from certain ore district in the west of Zhen’an, South Qinling, we speculate that a potential deep ore body would exist in the deposit via utilizing the recovered density model obtained by the proposed method.

The ore prospecting prediction model for the Huili copper orefield in Sichuan Province, China

The prediction theory and methodology of ore prospecting were developed from an in-depth study of 129 typical deposits in China. It has been verified to be an effective method that is particularly suitable for the initial ore prospecting. In this method, the internal and external factors of metallogenesis are combined together to construct a geological model of prospecting prediction, which consists of metallogenic geological body, metallogenic structure, metallogenic structural plane and metallogenic characteristics. The Huili area is located in the western margin of the Yangtze Plate, where the regional metallogenic geological conditions are superior, and a series of unique iron-copper deposits were formed. In recent years, great breakthroughs and progress have been made in the deep and peripheral areas of the Huili copper orefield. Herein, we take the Huili copper orefield as a typical example to illustrate the specific application of this method in deep ore prospecting of hydrothermal deposits. The metallogenic geological body is the ore-hosting volcanic rocks (albitite in the Hekou Group), and the main metallogenic structure and structural planes are interfaces between basic (intermediate) volcanic rocks and sedimentary rocks and the possible volcanic vent. Combined with the summary of metallogenic characteristics, we constructed a geological model for ore prospecting in the Huili copper orefield.

Trace and minor elements in sulfides from the Lengshuikeng Ag–Pb–Zn deposit, South China: A LA–ICP–MS study

Sphalerite, pyrite and galena are common sulfide minerals in Zn–Pb–(Ag) deposits, containing minor and trace elements that can be used to constrain the ore-forming processes. The Lengshuikeng Ag–Pb–Zn deposit (LSKD) is one of the largest silver deposits in China. The mode of silver occurrence in sulfides remains unclear except for individual silver minerals. In this study, we analyzed the minor and trace element contents of sulfide minerals from massive, vein, and veinlet-disseminated ores by in-situ laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS). The elemental compositions of sulfide minerals are variable. Combining petrographic observations and previous studies, we suggest that the sulfide minerals from two types of mineralization (porphyry and strata-bound types) were formed in a same hydrothermal system, and their content of minor and trace elements mainly is influenced by temperature, alteration of wall rocks and composition change of hydrothermal fluid. The Ag content in galena ranges n*103 ∼ n*104 ppm, whereas that in both sphalerite and pyrite ranges from n*10 ∼ n*103 ppm. Except for galena, a higher content of gold (mean = 0.76 ppm) and silver (mean = 151 ppm) occurs in sphalerite compared with the content of gold (mean = 0.26 ppm) and silver (mean = 69.9 ppm) in pyrite. Generally, altered samples display higher Ag and Au contents in pyrite and sphalerite. Silver occurs in the form of a solid solution in sulfides from samples with massive textures, and as micro-inclusions in sulfides from altered samples. The contents of minor and trace elements (e.g. Cd and In) and their ratios (Ga/In, Zn/Cd and Cd/Fe) are not always sensitive to the temperature and processes of deposit formation. We suggest that sulfides from samples with massive texture and limited alteration are suitable for determining the genetic type of the deposit. Our results show that the hydrothermal fluid is a magmatic fluid related to porphyry granite in the LSKD.

Critical metals in sediment-hosted Pb-Zn deposits in China

<p indent=0mm>Sediment-hosted Pb-Zn deposits are mainly comprised of Mississippi Valley-type (MVT) deposits situated in carbonate-dominated sedimentary rocks and clastic-dominated (CD) deposits located in siliciclastic-dominated sequences. They are significant sources of critical metals such as cadmium, gallium, and germanium, as well as indium, cobalt, and thallium. In China, sediment-hosted Pb-Zn deposits are found in 5 metallogenic belts/districts, namely the Sanjiang belt, the Yangtze Block district, the Tarim Craton district, the Changba belt, and the Langshan belt. They provide 54% of China’s Pb-Zn resources, but their resource endowment and the metallogenic characteristics of these associated critical metals remain unclear. After briefly reviewing the main critical metals in sediment-hosted Pb-Zn deposits and sediment-hosted Pb-Zn deposits in China, this review summarizes the distribution and enrichment mechanisms of critical metals in sediment-hosted Pb-Zn deposits in China and recommends future research. These critical metals are unevenly enriched in sediment-hosted Pb-Zn deposits in China. Compared to the crustal elemental abundances, Cd, Ge, and In are the most enriched, Tl and Co have lower enrichment degrees, and Ga has the lowest enrichment degree. Cd, Ga, Ge, and Tl are rich in MVT deposits, while In and Co are rich in CD deposits. In all five sediment-hosted Pb-Zn belts/districts, Cd is relatively abundant. However, other critical metals are enriched to a different degree in each belt/district. In terms of distribution, Cd is well enriched in all five sediment-hosted Pb-Zn belts/districts, particularly in the Sanjiang belt of the Qinghai-Tibet Plateau, and the Yangtze Block district; Ge is most abundant in the Yangtze Block district, followed by the Changba belt in the Qinling orogenic belt, and Sanjiang belt; In and Co are enriched in the Sanjiang belt, followed by the Yangtze Block district and the Changba belt; Tl is enriched in the Sanjiang belt, the Yangtze Block district, and the Changba belt; and, Ga is most enriched in the Changba belt and Yangtze Block, followed by the Sanjiang belt. Based on these characteristics, two enrichment mechanisms are occurring in sediment-hosted Pb-Zn deposits. First, sediment-hosted Pb-Zn deposits are selective for the enrichment of critical metals, and second, the degrees of enrichment of critical metals in these deposits are different. The first enrichment mechanism results from the similarity in physicochemical properties between the critical metal elements and dominant elements (such as Zn and Fe) in the ore and gangue sulfides (such as sphalerite and pyrite). The second mechanism is associated with substitution forms of critical metal elements and host minerals, as well as physicochemical conditions and tectonic conditions of the deposits and tectonomagmatic processes throughout geological history. Research into critical metals in sediment-hosted Pb-Zn deposits in China abounds in the Yangtze platform Pb-Zn metallogenic belt and MVT Pb-Zn deposits; however, this research is still in the pipeline. A database of critical metal resources hosted by sediment-hosted Pb-Zn deposits in China is urgently needed, as is comprehensive research into the metallogenic mechanism of different critical metals, and the determination of the regional metallogenic regularity of these critical metals.

Meifuite, A New Ferrous Phyllosilicate Mineral With Modulated Tetrahedral Sheets Similar to Minnesotaite

AbstractA new ferrous phyllosilicate, meifuite, has been discovered in the Yinachang Fe-Cu-REE (rare-earth element) deposit in China. The structural formula, calculated using averaged electron probe microanalysis (EPMA) results, is K0.72Na0.20(Fe5.56Mg0.31Mn0.13)Σ6.00(Si6.95Al1.04)Σ7.99O18.84(OH)4.84 Cl1.33, with an ideal formula of KFe6(AlSi7)O19(OH)4Cl2. The structure of meifuite has a P1¯ space group symmetry, with unit-cell parameters of a = 22.7773(13) Å, b = 9.5553(5) Å, c =14.3282(8) Å, α = 99.258(4)°, β = 136.750(3)°, γ = 89.899(4)°, Z = 2, and V = 2077.9(2) Å3. Meifuite has a strip-modulated 2:1 layer (T–O–T) structure similar to that of minnesotaite. About 1/8 of the tetrahedra in the T sheet are occupied by Al instead of Si, and the interlayer cavities are partially occupied by K and Na. Some of the OH sites in the octahedral sheet in the layer structure are fully or partially substituted by Cl, which is apparently the primary reason for the meifuite structure being more stable than stilpnomelane, the most common ferrous layer silicate mineral found at similar temperature and pressure conditions. An updated, more accurate structure model of minnesotaite is also provided for comparison with the meifuite structure. The mineral is named after Meifu Zhou in honor of his outstanding contributions to the field of economic geology.

Earthflow reactivation assessment by multichannel analysis of surface waves and electrical resistivity tomography: A case study

Abstract In this study, we investigated the stability and reactivation of preexisting Tonghua landslide deposits in China, including the adjacent stable slope. We used an integrated approach, combining a multichannel analysis of surface waves (MASW) and electrical resistivity tomography (ERT). We used ERT to determine groundwater seepage paths, weathering conditions, water content, and the depth to bedrock. High-resolution two-dimensional (2D) shear-wave velocity MASW images, on the other hand, played an essential role in detecting both horizontal and vertical compositions, disjointedness, and sliding surfaces related to lithological borders. Based on seismic models, we considered four geological layers encountered in the stable slope, including fractured (gravel) and weathered (phyllite) materials, as a sliding mass. We combined the 2D resistivity profiles obtained to create pseudo-three-dimensional ERT images to estimate water-saturated and unsaturated masses. From the tomography results, we identified different preexisting deposits, including buried arable clay deposits, old accumulated earthflow deposits, a water accumulation zone, and a fissure runoff. Based on the resistivity results, the bottom of the earthflow deposits is susceptible to water, and oversaturation can reactivate the earthflow.

Genesis of the Jinbaoshan PGE-(Cu)-(Ni) deposit: Distribution of chalcophile elements and platinum-group minerals

ABSTRACT The Jinbaoshan platinum group element-(Cu)-(Ni) deposit in southwest China is a sulfide-poor magmatic platinum-group element deposit that experienced multiple phases of post-magmatic modification. The sulfide assemblages of most magmatic Ni-Cu-platinum-group element deposits in China and elsewhere in the world are dominated by pentlandite-pyrrhotite-chalcopyrite with lesser magnetite and minor platinum-group minerals. However, Jinbaoshan is characterized by (1) hypogene violarite-pyrite 1-millerite-chalcopyrite and (2) supergene violarite-(polydymite)-pyrite 2-chalcopyrite assemblages. The platinum-group minerals are small (0.5–10 μm diameter) and include moncheite Pt(Te,Bi)2, mertieite-I Pd11(Sb,As)4, the atokite Pd3Sn – rustenburgite Pt3Sn solid solution, irarsite IrAsS, and sperrylite PtAs2 hosted mainly by violarite, silicates (primarily serpentine), and millerite. The platinum-group minerals occur in two sulfide assemblages: (1) mertieite-I-dominant (with irarsite, palladium, and Pd-alloy) in the hypogene assemblage and (2) moncheite-dominant (with irarsite, sperrylite, and atokite) in the supergene assemblage. Palladium and intermediate platinum-group elements (Os, Ir, Ru) are concentrated mainly in violarite, polydymite, and pyrite 2. Platinum is seldom hosted by base metal sulfides and occurs mainly as discrete platinum-group minerals, such as moncheite, sperrylite, and merenskyite. Violarite and polydymite in the Jinbaoshan deposit contain more Pb-Ag than pentlandite and pyrrhotite in the Great Dyke and Lac des Iles deposit. The formation of the sulfide assemblages in Jinbaoshan can be interpreted to have occurred in three stages: (1) a magmatic Fe-Ni-Cu sulfide melt crystallized Fe-Ni monosulfide and Cu-rich intermediate solid solutions, which inverted to a primary pyrrhotite-pentlandite-chalcopyrite-magnetite assemblage; (2) an early-secondary hypogene voilarite-millterite-pyrite 1-chalcopyrite assemblage formed by interaction with a lower-temperature magmatic-hydrothermal deuteric fluid; and (3) a late-secondary supergene violarite-polydymite-pyrite 2-chalcopyrite assemblage formed during weathering. Late-magmatic-hydrothermal fluids enriched the mineralization in Pb-Ag-Cd-Zn, which are incompatible in monosulfide solid solution, added Co-Pt into violarite, and expelled Pd to the margins of hypogene violarite and millerite, which caused Pd depletion in the hypogene violarite and the formation of mertieite-I. Supergene violarite inherited Pd and intermediate platinum-group elements from primary pentlandite. Thus, the unusual sulfide assemblages in the Jinbaoshan platinum-group element-(Cu)-(Ni) deposit results from multiple overprinted post-magmatic processes, but they did not significantly change the chalcophile element contents of the mineralization, which is interpreted to have formed at high magma:sulfide ratios (R factors) through interaction of crustally derived sulfide and a hybrid picritic-ferropicritic magma derived from subduction-metasomatized pyroxenitic mantle during impingement of the Emeishan plume on the Paleo-Tethyan oceanic subduction system.

Genesis and mechanisms of metal enrichment in the Baimazhai Ni-Cu-(PGE) deposit, Ailaoshan Orogenic Belt, SW China

ABSTRACT The ∼259 Ma Baimazhai Ni-Cu-(platinum-group element) deposit is located in the Ailaoshan-Red River fault zone on the southwest margin of the Yangtze Plate in the Jinping area of southeastern Yunnan Province. The intrusion is lenticular (∼530 m long × 190 m wide × 24–64 m thick) and concentrically zoned (margin to core) from gabbro through pyroxenite to peridotite. It contains ∼50 kt of Ni-Cu-(platinum-group element) mineralization, concentrically zoned (margin to core) from disseminated through net-textured to massive sulfides with an average grade of 1.03 wt.% Ni, 0.81 wt.% Cu, and 0.02∼0.69 ppm Pd+Pt. The sulfide assemblage comprises pyrrhotite, chalcopyrite, and pentlandite, with lesser magnetite, violarite, galena, and cobaltite. The mineralization is enriched in Ni-Cu-Co relative to the platinum-group elements and the host rocks are enriched in highly incompatible lithophile elements relative to moderately incompatible lithophile elements with high Th/Yb and intermediate Nb/Yb ratios. These host rocks, and those at most other Ni-Cu-platinum-group element deposits in the Emeishan Large Igneous Province, have high γOs and intermediate εNd values, indicating that they crystallized from a magma derived from a subduction-modified pyroxenite mantle source and modified by crustal contamination. The initial concentrations of metals in the primary magma are estimated to have been on the order of 200 ppm Ni and 100 ppm Cu, but only 0.4 ppb Pd, 0.2 ppb Pt, 0.005 ppb Rh, 0.02 ppb Ru, and 0.01 ppb Ir. The δ34S values of ores and separated sulfides range from 5.8‰ to 8.6‰, between the ∼10‰ value of sulfides in the metasedimentary country rocks and the 0 ± 0.5‰ value expected for magmas derived from MORB-type mantle, or the –2.5 ± 0.3‰ value expected for subduction-modified mantle, consistent with equilibration at magma:sulfide mass ratios (R factors) of 100–1000. Variations in Ir100 and Pd100 (metals in 100% sulfide) are consistent with 40–60% fractional crystallization of monosulfide solid solution to form Ni-Co-intermediate platinum-group element (Ru, Os, Ir)-rich massive ores and Cu-palladium/platinum-group elements (Pt, Pd, Rh)-Au-rich residual sulfide liquids. This process is also recorded by magnetite: Type I (early magmatic), type II (late magmatic), and type III (secondary) magnetites exhibit progressively lower Cr-Ti-V concentrations. The platinum-group element contents in base-metal minerals are low, and only pentlandite, violarite, and cobaltite contain detectable concentrations of Pd, Rh, and Ru. There is abundant textural evidence for metamorphic-hydrothermal alteration of sulfides in the Baimazhai intrusion, with secondary violarite, chalcopyrite, and pentlandite being enriched (Ag, Sb, Au, Pb) or depleted (Sn) in more mobile chalcophile elements. The different tectonic and petrogenetic settings of the Baimazhai and other deposits in China highlight the potential of Ni-Cu-platinum-group element deposits to occur in subduction or post-subduction settings and demonstrate that the key controls are magma flux and access to crustal S. Exploration potential remains for the Ailaoshan orogenic belt to host additional magmatic Ni-Cu deposits.

Ore Features and Gold Occurrence of the Manlonggou Gold Deposit, Southeast Yunnan Province, China

The Yunnan-Guizhou-Guangxi “Golden Triangle” is one of the famous Carlin-type gold deposits in China and even in the world. Manlonggou gold deposit is a newly discovered gold deposit in this area. The host rocks are mainly lithic quartz sandstone, siltstone and silty mudstone above Caledonian unconformity. The main minerals in ores are natural gold, limonite, hematite, pyrite and so on. The occurrence state of gold is fine exposed and semi-exposed natural gold, as well as gold encased by limonite, carbonate, quartz and silicate minerals. The deposit can be a fine grain hydrothermal altered gold deposit with the origin of tectonic-medium-low temperature hydrothermal percolation.

Microdiamonds in Alkalic Dolerites from the North China Craton: FTIR and C Isotopic Characteristics

Most of the diamond deposits in China are in the North China Craton. In addition to gem diamonds in kimberlite, a large number of microdiamonds have also been discovered in alkaline dolerites. These microdiamonds show very different characteristics from those recovered in kimberlite. Here, we report the morphology, colour, nitrogen contents, and carbon isotopic compositions of the diamonds recovered from the alkalic dolerites in eastern China. The microdiamonds are mainly cube and rhombic dodecahedron with diameters of 0.2 to 0.6 mm. Infrared spectrum analysis shows that these microdiamonds are mostly type Ib with a small amount of type Ia. The Y centre is obvious in type Ib diamond. Modelling mantle residence times for the IaAB diamonds is about 550 Ma. Nitrogen contents of the diamonds range from 4.5–503 ppm, with a median value of 173 ppm. The total δ13C range of the microdiamonds varies between −18.6 and −21.1‰ and are similar to those of ophiolite diamond.

Overview of Gemstone Resources in China

Gemstones are minerals of gem qualities used for adornment and decoration with the attributes of beauty, durability and rarity. Traditionally, although China has been regarded as the most important source for nephrite, over the past decades, a large variety of gemstone resources have been newly discovered in China owing to continuous exploration works. The vast land with various geological and geochemical backgrounds is rich in gemstone resources with potential for new deposits discoveries. In pegmatites, gemstones are related to granitic magma events and mainly occur in pegmatitic cavities, such as tourmaline, aquamarine, spodumene, spessartine, moonstone, quartz, apatite, and topaz. The eruption of Tertiary basaltic magma provides gem-quality sapphire, spinel, olivine, garnet, and zircon. The supergene oxidation zones of some copper and iron deposits in Hubei and Anhui province host gem-quality turquoise and malachite. Moreover, the formation of the nephrite deposit in China is mostly related to the carbonatite and serpentinite rocks involved in the metamorphic-metasomatic processes. This paper comprehensively introduces the distribution of gemstones deposits, as well as the gemological and mineralogical characteristics of gemstones in China. Our present investigation provides insights into the gemstone potential of China for further exploitation.

Genesis of the Baimadong carbonate-hosted uranium deposit, Guizhou, SW China: Constrains from geology, fluid inclusions, and C-O isotopes

The Baimadong uranium deposit is situated in the Yangtze Craton, SW China, and is one of the most representative carbonate-hosted uranium deposits in China. Uranium mineralization has spatial and genetical relationships with black and red alterations that has been documented by previous studies. However, the signature, source, and evaluation of ore-forming fluids producing the alterations and mineralization remain poorly understood. Fluid inclusions hosted in different generations of hydrothermal calcite have been analyzed in this study, including Cal 1 (pre-ore stage), Cal 2 (early ore stage), and Cal 3 (main ore stage). Three types of fluid inclusions were identified: liquid-dominated biphase, vapor-dominated biphase, and vapor-only monophase. Based on fluid inclusion microthermometry using the FIA method, the fluids associated with Cal 2 are characterized by relatively higher temperature (∼243 ℃) and salinity (5.3 wt% NaCl equiv.) compared with fluids associated with Cal 1 (Th = ∼221 ℃; Salinity = 1.9 wt% NaCl equiv.) and Cal 3 (Th = ∼144 ℃; Salinity = 2.5 wt% NaCl equiv.). The results of stable isotopes (C, O, and S) indicate that the carbon in pre-ore stage fluids was dominantly originated from host marine carbonate rocks (δ13Cfluid-PDB = −3.0 to 0.5 ‰; δ18Ofluid-SMOW = 4.8 to 11.3 ‰), the carbon and sulfur in early ore-forming fluids were mainly derived from the Niutitang Formation with minor from deep crust (δ13Cfluid-PDB = −11.2 to −8.4 ‰; δ18Ofluid-SMOW = 7.9 to 11.4 ‰; δ34Sv-CDT = −11.3 to + 2.1 ‰), whereas the main ore-forming fluids were sourced from meteoric fluids (δ13Cfluid-PDB = −8.6 to −4.9 ‰; δ18Ofluid-SMOW = 0.4 to 8.6 ‰). These results reveal that redox reaction as well as fluid-rock reaction are key factors controlling the large-scale uranium mineralization at Baimadong. Combined with these observations, geological setting, and previous geochemical features, we suggest that tectonic system together with overprinting zone of black and red alterations are indicators for exploration of carbonate-hosted uranium deposit in South China and elsewhere worldwide.