Banded iron formations (BIFs) are marine chemical sedimentary rocks comprised of alternating siliceous- and iron-rich bands and deposited from Eoarchean to early Paleoproterozoic. Due to their geological antiquity, BIFs normally have been overprinted by postdepositional tectono-thermal events, leading to large uncertainties with respect to their depositional age and field occurrence. The studied Gongyiming BIF-type iron deposit, which is a typical example of its metamorphosed Archean counterparts, is preserved within the Guyang Greenstone Belt, the North China Craton (NCC). The formation age of this BIF and effects of postdepositional tectono-thermal events on this BIF have not yet been well determined, limiting our understanding of its geological implication and the current occurrence of its orebodies. In this study, we provided new geological and zircon U-Pb geochronological evidence for the Gongyiming BIF that supports a possibly early Neoarchean depositional age (>2.66 Ga). This finding not only helps to fill the early Neoarchean age gap in BIF records in China, but also supports the previously documented multi-stage crustal growth model for the NCC. Furthermore, a metamorphic age of similar to 2.50 Ga is recorded by the BIF-bearing plagioclase amphibolite and monzogranitic gneiss that intruded into the plagioclase amphibolite. This metamorphic age is consistent with the time for an extensively identified late Neoarchean tectonic event in the NCC. The identification of a 1.90 Ga old potassium feldspar granite within this BIF indicates the plausible influence of the regional late Paleoproterozoic tectono-thermal event. This event is likely to have caused the development of a large-scale scale dextral shearing in the Gongyiming mining area, which ultimately shaped the field occurrence of its No. 2 and No. 3 ore bodies. Collectively, a structurally controlled exploration model was established for the Gongyiming BIF-type iron deposit, which facilitates the understanding of its ore body reworking processes and guides further regional iron deposit exploration and prospecting efforts.

The Bayan Obo deposit, located on the northern margin of the North China Plate (NCP), is the world’s largest comprehensive Fe-REE-Nb deposit. After its formation, this deposit was affected by multiple tectonic thermal events, but the ages of these geological events are controversial. To determine the evolutionary history of the Bayan Obo deposit, we conducted a detailed study of the macroscopic and microscopic deformation characteristics of the ore district and selected representative minerals, such as riebeckite and biotite, which are widely present in the banded rocks of the deposit, for an 40Ar-39Ar isotopic analysis. The results show that a large number of deformation structures have developed in the carbonatite and surrounding rocks, including mineral bands, boudins, tight folds, and rotated porphyroclasts, suggesting that the region has undergone intense compression and shearing and that the deformation temperature can reach ~550 °C. 40Ar-39Ar plateau ages of 414.9 ± 1.4 Ma and 264.5 ± 2.5 Ma were obtained for the riebeckite and biotite, respectively. Using these results in conjunction with regional geological data and considering the closure temperature of the mineral isotope system, it was inferred that these two ages corresponded to two distinct reworking events experienced by the deposit during the Early Paleozoic and Late Paleozoic following its initial formation. These events corresponded to the collision between the Bainaomiao Arc and the NCP and the magmatic activity induced by a continental–continental collision during the closure of the Paleo-Asian Ocean (PAO), respectively.

Nioboixiolite-(□) is a new mineral found in a carbonatite sill from the Bayan Obo mine, Baotou City, Inner Mongolia, China. It occurs as anhedral to subhedral grains (100 to 500 μm in diameter) that are disseminated in carbonatite rock composed of dolomite, calcite, magnetite, apatite, biotite, actionlike, zircon, and columbite-(Fe). Most of these grains are highly serrated, with numerous inclusions of columbite-(Fe). The mineral is gray to deep black in color; is opaque, with a semi-metallic luster; has a black streak; and is brittle, with an uneven conchoidal splintery. The Mohs hardness is 6–6½, and the calculated density is 6.05 g/cm3. The reflection color is gray with a blue tone, and there is no double reflection color. The measured reflectivity of nioboixiolite-(□) is about 10.6%~12.1%, close to that of ixiolite (11%–13%). Nioboixiolite-(□) is non-fluorescent under 254 nm (short-wave) and 366 nm (long-wave) ultraviolet light. The average chemical analysis results (wt.%) of twelve electron microprobe analyses are F 0.01, MnO 0.12, MgO 0.15, BaO 0.62, PbO 0.91, SrO 1.49, CaO 2.76, Al2O3 0.01, TREE2O3 1.58, Fe2O3 3.57, ThO2 0.11, SiO2 1.69, TiO2 3.68, Ta2O5 13.95, Nb2O5 47.04, and UO3 21.56, with a total of 99.25. The simplified formula is [Nb5+, Ta5+,Ti4+, Fe3+,□,]O2. X-ray diffraction data show that nioboixiolite-(□) is orthorhombic, belonging to the space group Pbcn (#60). The refined unit cell parameters are a = 4.7071(5) Å, b = 5.7097(7) Å, c = 5.1111(6) Å, V = 138.31(3), and β = 90(1) °Å3 with Z = 4. In the crystal structure of nioboixiolite-(□), all cations occupy a single M1 site. In these minerals, edge-sharing M1O6 octahedra form chains along the c direction. In this direction, the chains are connected with each other via common vertices of the octahedra. The strongest measured X-ray powder diffraction lines are [d in Å, (I/I0), (hkl)]: 3.662(20) (110), 2.975(100) (111), 2.501(20) (021), 1.770(20) (122), 1.458(20) (023). A type specimen was deposited in the Geological Museum of China with catalogue number M16118, No. 15, Yangrou Hutong, Xisi, Beijing 100031, People’s Republic of China.

Bayan Obo niobium deposit is the largest one in China. However, research work on the niobium mineralization process is rare due to the limited size of niobium-bearing minerals and their blurry regularities of distribution. To address these issues, this paper employs geological observations in conjunction with petrological and mineralogical studies to provide a detailed description of the spatial distribution of niobium orebodies, niobium-rich rock types, the occurrence of niobium-bearing minerals and their paragenetic associations in the West Mine, Main Mine, East Mine, and Dongjie Legele Mine within the Bayan Obo deposit. There exists a symbiotic and allo-symbiotic relationship between niobium (Nb) and rare earth element (REE) orebodies in Bayan Obo deposit. Symbiosis is predominantly observed in the West Mine, where Nb orebodies are distributed within slate formations or at the contact zones with surrounding rocks. Allo-symbiosis is mainly found in the Main Mine, East Mine and Dongjie Legele Mine, where Nb orebodies occur within REE orebodies. Petrographic and mineralogical observations reveal that the primary rock types hosting niobium in the West Mine are glimmerites, while in the Main Mine, West Mine and Dongjie Legele Mine, the dominant Nb-rich rocks are carbonatite veins, banded fenites and banded carbonatites, respectively. The major niobium-bearing minerals in Bayan Obo include aeschynite-group minerals, columbite-group minerals, pyrochlore-group minerals, baotite and fergusonite. In the West Mine, columbite and pyrochlore dominate as Nb-bearing minerals, whereas in the Main Mine, East Mine and Dongjie Legele Mine, aeschynite is overwhelming. These variations can be attributed to diverse fluid activities, tectonic settings and wall-rock interactions. The West Mine is associated with potassium fenites, while the East Mine is linked to sodium fenites. Niobium minerals exhibit both magmatic and hydrothermal origins. Magmatic columbite crystallization aligns with carbonatite emplacement, sourcing niobium from carbonatite melts. Hydrothermal processes, particularly fenitization, facilitate the dissolution, aggregation and re-precipitation of niobium, leading to localized enrichment where fenitization and hydrothermal activities intersect. Highly differentiated carbonate magma also promotes unconventional enrichment of niobium and rare earth elements, forming hydrothermal aeschynite in late-stage carbonatite dikes and at Dongjie Legele. This study elucidated the distribution of niobium minerals and their metallogenic processes from which the coupled metallogenic relationship between niobium and rare earth elements was proposed. These findings provide a foundation for niobium exploration and comprehensive utilization in the Bayan Obo region.

Growing evidence suggests that mineralisation of the world-renowned Bayan Obo REE deposit is genetically linked to the intrusion of carbonatite dykes in Archean-Paleoproterozoic sedimentary rocks.Hence,accurate determination of the emplace-ment age of the carbonatite dykes is critically important for understanding the genesis and geodynamic drivers of the giant REE de-posits.Dating carbonatites has proven challenging because they are commonly overprinted by later tectono-thermal events.Previ-ous attempts to date the Bayan Obo carbonatites have yielded younger ages reflecting post-magmatic overprinting(typically 1 300-420 Ma).In this study,we collected samples from the No.1 carbonatite dyke(Wu dyke)and its fenitised wall-rocks and carried out insitu(in polished thin section)U-Th-Pb dating of monazite by Sensitive High-Resolution Ion Microprobe(SHRIMP),which enables us to precisely reconstruct the magmatic and hydrothermal history of the dyke.Monazites in the calcite carbonatite,fenite and metasomatised quartz conglomerate are characterised by extreme depletion of U and high Th/U ratios.The oldest cluster of monazite analyses yielded a weighted mean 208Pb/232Th age of 1 401±39 Ma(MSWD=0.57,n=7),which is the oldest monazite age hitherto obtained from Bayan Obo,and is taken to approximate the onset of intrusion of the carbonatite dykes.This age con-firms that the carbonatite magmatism at Bayan Obo predates the 1.33-1.30 Ga Yanliao Large Igneous Province,but coincides with the separation of North China Craton from the Western Australian Craton as part of the greater breakup of the Nuna/Columbia su-percontinent(1 450-1 380 Ma).Our results also reveal repeated monazite growth during the late Mesoproterozoic through to the early Paleozoic(1 300-420 Ma)as widely documented in previous studies.Notably,our data define a prominent age peak at 529±17 Ma(MSWD=1.01,n=6)indicating Pan-African overprinting,supportive of recent reconstruction placing North China at the northern margin of Gondwana during the earliest Paleozoic.In addition,zircon crystals in the quartz conglomerate were also anal-ysed in this study and yielded concordant 207Pb/206Pb dates between 2.1 Ga and 1.9 Ga,which are interpreted as detrital ages on the basis of crystal morphology and Th-U chemistry of the zircon.In summary,the new monazite geochronology data from the Wu dyke significantly refine the magmatic-hydrothermal timeframe of the Bayan Obo carbonatites,affording new insights into the geo-dynamic drivers and genesis of the giant REE deposits.

Kermesite (Sb2S2O), a needle-like unstable secondary oxysulfide, has made visible advancements in optimizing its triclinic crystal system through twinning discovery. However, research on twinning behavior at micro and nano scales, including its growth mechanisms and impact on kermesite morphologies, remains notably scarce. Our study focuses on kermesite crystal clusters from a private collection in Yunnan, China, confirming the chemical formula as Sb2S1.97O1.03 through EPMA. Single-crystal XRD yielded refined unit cell parameters (a = 8.153(5) Å, b = 10.717(7) Å, c = 5.796(3) Å; α = 102.836(10)°, β = 110.556(8)°, γ = 100.999(12)°), revealing space group P1¯ with Z = 4 and indicating twinning with a ratio of 27.4%. Remarkably, a Transmission Electron Microscope (TEM) provided the first direct observation of twinning in natural kermesite, revealing rotational twins with varying widths and lengths (ranging from 100 nm to several millimeters). Analysis and simulation elucidated that rotational twins, generated by a 180° rotation, align with the mineral’s elongation direction along the [Sb2S2O4]n chains (a-axis), challenging the conventional long-axis direction (b-axis) for crystal growth. This study proposes a symbiotic relationship between kermesite growth and twinning, suggesting that the observed X-shaped growth in crystal clusters results from the collaboration of single crystals (growing along b) and twins (growing along a) in the unit cell. These findings contribute to our understanding of kermesite’s structural complexities and the potential growth and formation mechanism of crystal clusters.

The Bayan Obo deposit is world-famous for its giant rare earth reserves, and also accompanied with 2.2 Mt Nb2O5 resources at an average grade of 0.13 %, renowned as the second largest Nb deposit globally. Previous studies have focused on the origin of carbonatite (igneous/sedimentary), and variation composition during evolution, as well as its super-enrichment of light rare earth elements (LREE), while the metallogenic mechanism of niobium is being overlooked despite the identification of plenty Nb-bearing minerals. In this study, we identify four types of columbite as major Nb-bearing minerals, instead of pyrochlore in the west pit of Bayan Obo. Detailed mineralogical study has revealed large primitive columbite (Clb1-I, 100-200 mu m) is hosted in the coarse-grained Fe-dolomite carbonatite (FeO = 5.46-10.47 wt%), being an ideal target for future mineral beneficiation. Those columbites (Clb1-I) are featured by lowest Sr, Y, and & sum;REE but enriched in iron in composition, revealing its magmatic origin. Sieve-textured columbite (Clb1-II, similar to 100 mu m) dispersed in the fluorination and chloritization dolomite carbonatite, with a U-Pb age of 1359 +/- 31 Ma, contemporary with ages of the regional carbonatite magma intrusion and rift-related magmatism, indicating niobium being sourced from mantle-derived carbonatite. The occurrence of fluorite as inclusions in Clb1-I indicates the solubility of Nb was enhanced by fluxes, and the columbite saturation was easily achieved during the carbonatite magma evolution into ferroan carbonatite. Strong fenitization metasomatism further locally concentrated columbite either within the mineral assemblages of pyrite + phlogopite + allanite (Clb2) or in the mica-dominated fenite (Clb3), and crystallized at 346 +/- 18 Ma and 284 +/- 16 Ma, respectively. The latter metalogenetic epoch is accordant with late Permian granitic magmatism event (ca. 280 Ma) while the former age may attribute to its occurrences related to the early Paleozoic arc-continent collision. Differ from pristine columbite (Clb1-I and Clb1-II), the metamorphic columbite (Clb2 and Cl3, especially Clb3) are enriched in Ta (1803-4092 ppm), Y (560-2029 ppm) and & sum;REE (720-6317 ppm) content, probably suggesting the highest degree of evolution. The similar metallogenesis framework between Nb and REE, combined with the coexistence of columbite and REE minerals assemblages, implies the spatial and temporal coupling of Nb and REE mineralization. This first innovative and systematic mineralogical and geochronological work directly constrains the nature of Mesoproterozoic mantle-derived carbonatite with fertile Fe and fluxes, and the Paleozoic and Permian fenitization metasomatism, are the major factors contribute to the metallogenic specialization of niobium in Bayan Obo.

关键矿产的元素赋存形式对矿产超常富集机制和资源综合利用有着至关重要的作用.然而,关键矿产的元素赋存形式大多以细小矿物、吸附或类质同象的方式存在,不易于直接观察分析,在一定程度上增加了对其进一步认识和综合利用的难度,而透射电子显微镜(Transmission Electron Microscopy,TEM)可以在微纳米尺度上从结构和成分方面提供有效的解决途径.文章扼要地介绍了TEM的基本原理、工作模式、样品制备的方法及工作流程,并根据国内关键矿产的类型与元素赋存形式综述了TEM在关键性稀有金属、稀土金属、稀散金属、稀贵金属、能源金属以及黑色和有色金属等 6 类矿产中成因机制研究的应用进展情况,指出了限制TEM广泛应用的瓶颈问题,并提出了几点浅显的意见和建议.

The Bayan Obo supergiant carbonatite-related rare-earth-element-niobium-iron (REE-Nb-Fe) endogenetic deposit (thereafter as the Bayan Obo deposit), located at 150 km north of Baotou City in the Inner Mongolia Autonomous Region, is the largest rare-earth element (REE) resource in the world. Tectonically, this deposit is situated on the northern margin of the North China Craton and adjacent to the Xing’an-Mongolian orogenic belt to the south. The main strata within the mining area include the Neoarchean Se’ ertengshan Group and the Mesoproterozoic Bayan Obo Group. Generally, the rare earth, niobium, and iron mineralization within the deposit are intrinsically related to the dolomite carbonatites and the extensive alteration of the country rocks caused by the carbonatite magma intrusion. The alteration of country rocks can be categorized into three types: contact metasomatism (anti-skarn and skarn alteration), fenitization, and hornfelsic alternation. As indicated by previous studies and summarized in this review, the multi-element mineralization at Bayan Obo is closely associated with the metasomatic replacement of siliceous country rocks by carbonatite magmatic-hydrothermal fluids. The metasomatic process is comparable to the conventional skarnification that formed due to the intrusion of intermediate-acid magmatic rocks into limestone strata. However, the migration pattern of SiO2, CaO, and MgO in this novel metasomatic process is opposite to the skarn alteration. Accordingly, this review delineates, for the first time, an anti-skarn metallogenic model for the Bayan Obo deposit, revealing the enigmatic relationship between the carbonatite magmatic-hydrothermal processes and the related iron and rare earth mineralization. Moreover, this study also contributes to a better understanding of the REE-Nd-Fe metallogenetic processes and the related fluorite mineralization at the Bayan Obo deposit.

In this paper,geochemical analysis of the ore bearing metasedimentary rocks of the Tebai gold deposit in Alxa Right Banner is carried out,The main lithology is mica quartz schist,metamorphic siltstone,metamorphic lithic quartz sandstone,etc;The average content of SiO 2 is 62.39%,the average content of Al 2 O 3 is 15.40%,the average content of Fe 2 O 3 is 6.57%,the average content of MgO is 3.84%,the average content of CaO is 2.31%,the average content of K 2 O is 2.65%,the average content of Na 2 O is 2.09%.The REE patterns of curves are consistent,LREE/HREE=5.75～8.34,the average value is 7.18,（La/Yb） N =5.39～8.38,the average value is 6.83,Eu negative anomaly is obvious,LREE are obviously enriched relative to HREE;Rb-K 2 O diagram、Ni-TiO 2 diagram and La/Yb-ΣREE diagram show that the parent rocks may originate from granites;Combined with paleocurrent characteristics and detrital zircon age evidence,it is speculated that the provenance may come from granite in Beidashan area.Combined with the rock assemblage characteristics,tectonic combined characteristics and Geochemical characteristics of Ore bearing metasedimentary rocks in Tebai,it is considered that the source rocks were formed in a tectonic environment of continental island-arc.

Granitic gneiss (orthogneiss) and Himalayan leucogranite are widely distributed in the Himalayan orogen, but whether or not the granitic gneiss made a contribution to the Himalayan leucogranite remains unclear. In this study, we present the petrological, geochronological and geochemical results for orthogneisses and leucogranites from the Zhada area, Western Himalayas. Zhada orthogneiss is composed mainly of quartz, plagioclase, K‐feldspar, biotite and muscovite, with accessory zircon and apatite. Orthogneiss zircon cathodoluminescence (CL) images show that most grains contain a core with oscillatory zoning, which indicates an igneous origin. Sensitive high‐resolution ion microprobe (SHRIMP) U‐Pb dating of the zircon cores in the orthogneiss shows a weighted 206 Pb/ 238 U age of 515 ± 4 Ma (early Paleozoic), with spongelike zircon rims of 17.9 ± 0.5 Ma (Miocene). Zhada leucogranite shows 206 Pb/ 238 U ages ranging from 19.0 ± 0.4 Ma to 12.4 ± 0.2 Ma, the weighted average age being 16.2 ± 0.4 Ma. The leucogranites have a low Ca content (<1 wt%), FeO t content (<1 wt%), Rb content (67.0–402 ppm), Sr content (<56.6 ppm), Ba content (3.35–238 ppm) and Rb/Sr ratio (0.5–14.7), which are similar to the geochemical characteristics of the Himalayan leucogranite derived from muscovite dehydration partial melting of metasediments and representative of most Himalayan leucogranites. The highly variable Na 2 O + K 2 O (4.33 wt%–9.13 wt%), Al 2 O 3 (8.44 wt%–13.51 wt%), ∑REE (40.2–191.0 ppm), Rb (67.0–402 ppm) and Nb (8.23–26.4 ppm) contents, 87 Sr/ 86 Sr( t ) ratios (0.7445–0.8605) and ε Nd ( t ) values (–3.6 to –8.2) indicate that the leucogranite is derived from a heterogenetic source. The nonradiogenic Nd isotope values of the studied Zhada leucogranite and orthogneiss range from –8.2 to –3.6 and from –8.7 to –4.1, respectively. Therefore, the general mixing equation was used to perform the Sr and Nd isotope mixing calculations. The results indicate that the heterogenetic source was the Tethyan Himalayan Sequence (THS)/Higher Himalayan Crystalline (HHC) metasediments and Zhada orthogneiss. The Zhada area experienced crustal anatexis during the Miocene and the heterogenetic source of the orthogneiss and metasediment may have experienced crustal anatexis controlled by muscovite dehydration. The Zhada leucogranite inherited not only the geochemical characteristics of the Himalayan metasediment (muscovite dehydration melting), but also the trace elements and Sr‐Nd isotopic characteristics of the Zhada orthogneiss. These results indicate that the Paleozoic Zhada orthogneiss was involved in crustal anatexis at 17.9 ± 0.5 Ma (Miocene) and that the muscovite dehydration of the metasediments in the heterogenetic source produced fluid, which may have caused the orthogneiss solidus lines to decline, triggering a partial melting of the Zhada orthogneiss. It is therefore proposed that Himalayan leucogranite is a crust‐derived granite rather than a S‐type granite, as previously hypothesized.

Tourmaline geochemical and boron (B) isotopic compositions in two‐mica granites (TMG), tourmaline‐bearing leucogranites (Tou‐LG), tourmalites and metapelites from the Gyirong–Malashan areas of the Himalayan orogen provide evidence for country rock assimilation during the intrusion of Himalayan leucogranite. The schorls in Gyirong leucogranitic plutons show low contents of MgO (0.238%–1.160%) and δ 11 B values (–12.1‰ – –11.2‰), while dravites gathered in the contact zone between the leucogranitic veins and metapelites show high contents of MgO (4.815%–6.755%) and δ 11 B values (–10.7‰ – –9.3‰). This geochemical and isotopic variation of tourmalines can also be identified in the Malashan gneiss dome. As a result, three types of tourmaline were identified in the Himalayan orogen: (1) Tou‐I in the TMG and Tou‐LG, which is the most common tourmaline type of schorl; (2) Tou‐II (dravite and high‐Mg schorl) in the Tou‐LG and tourmalite at the margins of the leucogranite; and (3) Tou‐III (mainly dravite, with minor high‐Mg schorl) in metapelites of the High Himalayan Crystalline Sequence. The lenses and veins of Tou‐LG may have experienced metasomatism and assimilation as a result of interaction with the High Himalayan Crystalline Sequence metasedimentary country rocks, which can be traced by the geochemical and isotopic characteristics of the tourmaline therein.

围绕白云鄂博矿山寻找铁矿接替资源的急迫需求,聚焦构造对深部矿体控制作用,开展复杂地形及强干扰地区重力-磁法-电法-高精度反射地震综合勘查示范研究.通过一系列专题地质填图和综合研究,笔者构建了白云鄂博矿床成矿模式和新的勘查模型,提出矿区近东西向逆-平移断层(F2)导致了主矿、东矿深部矿体向东平移的新认识,明确指出深部存在受构造控制的铁矿体,并圈定了找矿靶区3处.通过钻探验证实现了铁矿找矿突破,目前在2号靶区已施工的15个钻孔全部见矿,钻孔控制最大铁矿层累计视厚度达327.2 m.靶区深部厚大铁矿体的发现,是科研指导勘查,降低勘查风险,提高找矿效率的典型实践,大幅度提升了白云鄂博资源保障能力,有效促进了科研成果的及时转化.

With more than 11,000 t of gold resources, the Central Asian orogenic belt is the most significant gold deposit belt in the world. The majority of the orogenic belt's gold resources are found in a layer of carbon-rich black shale. However, there is disagreement regarding the origin and metallogenic process of such a significant quantity of gold. The Haoyaoerhudong gold deposit is located where the northern margin of the North China Craton and the southern margin of the Central Asian orogenic belt converge. It is the most significant black shale gold deposit in the northern margin of North China Craton gold province. The pyrite that typically develops in the Haoyaoerhudong gold deposit has been categorized into five varieties through comprehensive field investigation and mineralogical research, which correspond to five metallogenic stages: Stage 1, sedimentary diagenesis; Stage 2, tectonic deformation; Stage 3, hydrothermal; Stage 4, hydrothermal transformation; Stage 5, late metallogenic. For pyrite in the previous four metallogenic stages, in situ LA-ICP-MS trace element analysis and pyrite sulfide isotope analyses were performed. The results suggest that: The average Au contents in the pyrite of sedimentary diagenesis stage is 0.098 ppm; the average Au contents in the pyrite of the tectonic deformation stage and hydrothermal stage, is below the detection limit mostly; the average Au contents in the pyrite of hydrothermal transformation stage is 0.12 ppm. The results indicate that only 22.4% more gold is present in hydrothermal transformation stage than in sedimentary diagenetic stage overall. It may be inferred that the gold enrichment of Haoyaoerhudong gold deposit mostly took place during the sedimentary diagenetic stage; subsequent brittle-ductile shear and hydrothermal fluid activity did not result in a further enrichment of gold. The sulfur isotope test results of various metallogenic stages in the deposit can be analyzed, and they are generally consistent. The delta 34S values range from +10.15% to +16.47%, with an average value of +13.02%. It suggests that there might be a single source of sulfur. According to extensive analysis, the Haoyaoerhudong gold deposit formed a relatively low-grade ore body during the sedimentary diagenesis stage, and the subsequent tectonic deformation stage and hydrothermal stage provided physical conditions for further activation of gold metal but did not bring corresponding material sources for mineralization.

The Shimensi tungsten-polymetallic deposit, located in Lower Yangtze mineralization province, is a recently-discovered world-class deposit. It is necessary to clarify the source and the evolution of the ore forming fluid. We report Pb isotope results form scheelite, wolframite, molybdenite and chalcopyrite samples as well as K-feldspars from Neoproterozoic biotite granodiorite, and Mesozoic porphyritic biotite granite, fine-grained biotite granite, and granite porphyry. Results show that the Pb isotopes from both the ore minerals and granite K-felspar can be divided into 3 groups. Pb isotope ratios from the ore minerals are similar to those from the early Cretaceous prophyritic biotite granite and fine-grained biotite granite, indicating that the ore components for the Shimensi deposit were mainly originated from these two types of granites. The O isotope equilibrium temperature of the quartz-scheelite ranges from similar to 295.89 degrees C to 435.97 degrees C, the delta O-18 from similar to 7.0%o to 9.6%o, indicating that the mineralization occurred under the condition of high temperature and O isotope equilibrium exchange. It is concluded that the ore-forming fluids for the Shimensi deposite had a magmatic-hydrothermal origin, related to the Early Cretaceous magmatism in an extensional tectonic environment in East China. The granites themselves were probably generated from partially melting of the Neoproterozoic Shuangqiaoshan Group, which contains of 9.13 ppm high tungsten background content.

本文通过对白云鄂博矿区精细的地质填图和剖面测量发现:1)矿区的蚀变矿化均围绕赋矿"白云岩"形成,在横向和纵向上均具有明显的蚀变强弱变化特征,从赋矿"白云岩"到顶底板板岩,蚀变和矿化强度逐渐减弱;2)赋矿"白云岩"呈岩枝状穿切围岩,接触带内带发育萤石化、霓石化、霓辉石化、钠闪石化和磷灰石化等蚀变,外带发育黑云母化、钾化(微斜长石化)、钠闪石化、弱萤石化、弱黄铁矿化和弱磁铁矿化蚀变;3)在白云鄂博矿区的西矿、东介勒格勒和菠萝头矿段的"白云岩"与围岩的内接触带,均发现有碳质板岩、硅质板岩、石英砂岩、闪长(玢)岩和辉长岩捕虏体;4)在赋矿"白云岩"的外部接触带发育与"白云岩"同期侵入的碱性岩,与白云鄂博碳酸岩体共同构成了一个碱性岩套组合;5)在白云鄂博矿区内识别出一条韧性剪切带,矿区内的赋矿"白云岩"均遭受了强烈的韧性变形和动态重结晶作用,各类矿石中的条带状构造既不是沉积层理,也不是岩浆流动的流线(面),而是与韧性剪切带密切相关的构造线(面)理.以上证据表明,白云鄂博赋矿"白云岩"为岩浆成因的白云石碳酸岩,但遭受了强烈的韧性剪切变形和动态重结晶作用.

对白云鄂博超大型稀土-铌-铁矿田内褶皱及断层构造特征进行了剖析和总结,认为矿区内构造活动演化具有多期性,中元古代—海西期至少发育4期构造活动,包括近东西向控岩断层(F1)、近东西向逆-平移断层(F2)、近东西向褶皱和韧性剪切构造、北东向左行走滑正断层(F3),并将其对成岩成矿的影响及控制作用作了详细分析.认为:①沿白云石碳酸岩与顶底板围岩界线分布的近东西向断层控制了白云石碳酸岩的产出和矿体的形成;②白云石碳酸岩侵位之后,近东西向逆-平移断层对矿体进行了第一次破坏,导致主矿、东矿的深部矿体向东平移,钻孔WK14-01的深部矿体应为主矿深部的矿体平移所致;③成矿期后发育一期近南北向的挤压变形事件对矿体进行了第二次破坏,导致矿区白云鄂博群紧闭褶皱的形成和矿体发生透镜体化;④主矿、东矿之间的北东向左行走滑正断层对矿体进行了第三次破坏,导致主、东矿位置的错动.这些认识将对矿区深部及外围找矿工作具有重要的指导意义.

岩石密度测定是获取准确密度值的重要手段,同时密度也是对重力测量结果进行地形校正和中间层校正不可缺少的参数.密度测定精度越高,利用其进行地质解译的精度也越高,但不同版本的测定规范对岩石密度测定前是否需要浸泡处理存在分歧.本文以白云鄂博矿区12种岩(矿)石标本为例,对比浸泡前后的密度变化,得出除云母型铁矿石外,浸泡后的岩石密度均不同程度增大.对于孔隙或裂隙发育的岩(矿)石,浸泡后的密度差百分比大于0.5％.而结构致密的岩(矿)石,浸泡对密度测定的影响低于2倍测定误差,可忽略不计.

The Bayan Obo rare earth element (REE) deposit in Inner Mongolia, northern China, is the largest REE deposit in the world, whose mineralization process remains controversial. There are dozens of carbonatite dykes that are tightly related to the deposit. Here we report the petrological and mineralogical characteristics of a typical dolomite carbonatite dyke near the deposit. The dolomite within the dyke experienced intense post-emplacement fluids metasomatism as evidenced by the widespread hydrothermal REE-bearing minerals occurring along the carbonate mineral grains. REE contents of bulk rocks and constituent dolomite minerals (>90 vol.%) are 1407–4184 ppm and 63–152 ppm, respectively, indicating that dolomite is not the dominant mineral controlling the REE budgets of the dyke. There are three types of apatite in the dyke: Type 1 apatite is the primary apatite and contains REE2O3 at 2.35–4.20 wt.% and SrO at 1.75–2.19 wt.%; Type 2 and Type 3 apatites are the products of replacement of primary apatite. The REE2O3 (6.10–8.21 wt.%) and SrO (2.83–3.63 wt.%) contents of Type 2 apatite are significantly elevated for overprinting of REE and Sr-rich fluids derived from the carbonatite. Conversely, Type 3 apatite has decreased REE2O3 (1.17–2.35 wt.%) and SrO (1.51–1.99 wt.%) contents, resulting from infiltration of fluids with low REE and Na concentrations. Our results on the dyke suggest that post-magmatic fluids expelled from the carbonatitic melts dominated the REE mineralization of the Bayan Obo deposit, and a significant fluid disturbance occurred but probably provided no extra REEs to the deposit.

In the Bayan Obo REE deposit in Inner Mongolia, Northern China, three major orebodies are hosted in dolomite marble of the Bayan Obo Group. There are carbonatite dikes in the ore district. Apatite is a common accessary mineral in the ore-hosting dolomite marble (DM apatite) and in carbonatite dikes (IC apatite). These two types of apatite are both fluorapatite, and have low SiO2, uniform P2O5, and variable CaO contents. Total REY (REEs + Y) contents are correlated with Na2O contents, indicating that REY of both types of apatite enter lattice via the substitution reaction: Na+ + (REY)(3+) = 2Ca(2+). These features, combined with high REY (6230-18,906 ppm) and Sr (9653-17,200 ppm) contents of DM apatite, indicate that DM apatite likely had a carbonatite origin. Some DM apatite grains are partially replaced by albite and quartz. Fluid inclusions crosscutting both apatite and albite or quartz indicate that they formed later than quartz and albite replacement. The back-scattered electron images show that DM apatite grains contain many micro-pores (fluid inclusions), and monazite inclusions formed from the fluid inclusions. However, no monazite inclusions are observed within quartz and albite, excluding the possibility that the monazite inclusions were precipitated directly from the fluids. The monazite inclusions were therefore formed during fluid-induced dissolution-reprecipitation processes, where DM apatite served as the source of LREEs. This also explains the depletion of some LREEs in DM apatite. The formation of monazite inclusions in apatite requires fluids with relatively low Na and Si concentrations, different from the fluids responsible for quartz and albite replacement. DM apatite was affected by two stages of fluid activities: the first stage of metasomatism by alkaline fluids that were likely derived from carbonatite magmas when the deposit first formed (represented by quartz and albite replacement), followed by a second stage of modification that caused LREEs depletion and the formation of new REE minerals. Thus, the Bayan Obo REE ore deposit was modified by a significant thermal event after the formation, which provided negligible or only small amounts of REEs.