Accurately determining the genetic relationships between mafic-ultramafic complexes within the same exploration block is critical for efficient exploration and offers key insights into the ore-forming processes of magmatic nickel-copper sulfide deposits. The Lubei magmatic Ni-Cu sulfide deposit in the Eastern Tianshan orogenic belt comprises two distinct mine fields: Lubei and Yunhai. Geochemical evidence indicates that rocks from the two mine fields have a common high-Mg tholeiitic basaltic parental magma. The Cu/Pd ratios and model calculations suggest that the magma experienced approximately 0.001 wt% prior-sulfide segregation at depth. The variations observed in the magmas suggest a two-stage Ni-Cu sulfide mineralization. The first stage occurred at greater depths with lower oxygen fugacity (from FMQ-1.03 to FMQ + 1.57), resulting in sulfides with higher PGE concentrations in the Lubei mine field. The second stage took place at shallower depths with higher oxygen fugacity (from FMQ + 1.94 to FMQ + 2.30), formed sulfides characterized by lower PGE concentrations in the Yunhai mine field. The negative correlation between initial 87Sr/86Sr ratios and Ni contents in sulfide ores indicates that crustal contamination might have played a role in hindering sulfide saturation. In contrast, olivine crystallization appears to trigger the sulfide saturation, as the modeling of olivines reveals a causal relationship between the olivine crystallization and sulfide segregation processes. The increase in oxygen fugacity may potentially account for the termination of sulfide saturation. At last, this study summarizes the indicators that help determine the evolutionary relationships and relative mineralization potential of different complexes.

Phosphate deposits of both sedimentary and igneous origins are the most important sources of phosphorus in the world. Neoarchean metamorphic series-hosted apatite-magnetite deposits in the northern North China Craton (NCC) are important sources of P and Fe. However, the genesis of some deposits remains controversial, as they are proposed to have formed through sedimentary-metamorphic processes in the phosphorus-deficient Neoarchean environment. The Wulanwusu P-Fe deposit in the Jianping area is a typical example, with the P-Fe mineralization typically composed of plagioclase, amphibole, biotite, apatite and Fe-Ti oxides. This study aims to constrain the geological controls on P-Fe mineralization through petrographic, geochronological, and geochemical analyses of P-Fe ores. Zircon U-Pb geochronology yielded a weighted crystallization age at 1730 +/- 6 Ma, precisely constraining the timing of mineralization to the late Paleoproterozoic. Petrographic observations, whole-rock and apatite geochemistry collectively indicate that the mineralization is associated with a mafic magmatic event, supporting its classification as a late Paleoproterozoic igneous P-Fe deposit. Our results clearly rule out a previously suggested link between P-Fe mineralization and metamorphosed Neoarchean volcanosedimentary rocks. The Nd-Hf isotopic compositions suggest that the parental magma was derived from an enriched subcontinental lithospheric mantle source. Combined with geochronological and geochemical evidence, these results indicate that the formation of the Wulanwusu P-Fe deposit is linked to the late Paleoproterozoic AMCG suite magmatism in the northern NCC and occurred in a post-collisional extensional stage following the convergence of the eastern and western blocks of the NCC.

Paleoproterozoic metamorphic rock series are widely distributed and hosts several iron deposits. The Heiyuting iron (Fe) deposit is hosted by typical Paleoproterozoic leptite of the Li'eryu Formation and represents a key example for constraining the mineralization process of Paleoproterozoic iron deposits within the Liaohe Group. This type of deposit has great exploration potential, but the precise timing of iron mineralization, the sources of ore-forming materials, and iron mineralization processes remain unclear. We conducted zircon and monazite U-Pb geochronology together with monazite electron probe microanalysis (EPMA) to constrain iron mineralization. Zircon cores from the migmatitic granite yield an age of 2174 +/- 23 Ma, representing protolith formation, whereas the rims yield 1892 +/- 14 Ma, consistent with similar to 1900 Ma granulite-facies metamorphism. Monazite grains associated with magnetite yielded an age of 1848 +/- 5 Ma, constraining Fe mineralization and coinciding with regional partial melting (1870-1840 Ma). Monazites observed under back-scattered electron (BSE) imaging show embayed structures and concentric coronas composed of apatite, allanite, and epidote. Based on the major-, trace-, and REE-element compositions of monazite, a metamorphic-hydrothermal origin is suggested. We propose that the apatite-allanite-epidote coronas developed on early-formed monazite through disequilibrium reactions with F-Ca-Fe-Si-Al-rich fluids during the retrograde metamorphic stage. The Li'eryu Formation and the 2.2-2.1 Ga magmatism provided the primary sources of iron. The iron was subsequently concentrated by hydrothermal activity during late metamorphism-anatexis at similar to 1850 Ma. Our results refine the age, source, and mechanisms of iron mineralization in the Heiyuting Fe deposit, provide geochronological and geochemical constraints for similar deposits, and highlight the role of regional metamorphism-anatexis in polymetallic enrichment.

The Xiaojiagou-type titanium-iron ore deposit in the western Shandong region of the eastern North China Craton represents a newly identified important magmatic titanium deposit type in 21st century. The ore minerals, ilmenite and titanomagnetite, are hosted in hornblendite, and its titanium grade is comparable to those of the well-known Panzhihua-type and Damiao-type magmatic deposits in China, yet the timing of rock formation and Fe-Ti oxide mineralization and the ore-forming mechanism of the deposit remain unclear. This study aims to precisely determine the mineralization age of the Xiaojiagou titanium-iron ore, reveal the differentiation and evolution mechanism of its parental magma and the source of ore-forming materials, and explore the tectonic setting of its formation. In this study, Fe-Ti oxide-mineralized hornblendite was taken as the object, and we conducted a comprehensive set of analyses including zircon SHRIMP U-Pb dating, whole-rock major and trace element analysis, Sr-Nd-Hf isotope testing, and electron probe mineral composition analysis. The analytical results indicate that zircon U-Pb dating yields a weighted average age of 1838 +/- 17Ma. The significantly negative epsilon(Hf)(t) values (-20.2 to -0.8), whole-rock epsilon(Nd)(t) values of -1.7 and 0.1, and extremely low initial (Sr-87/Sr-86)i ratios (0.701994 to 0.702421), collectively indicate the parental magma originated from a mantle source region mixed with ancient crustal materials. Whole-rock geochemical data reveal that the hornblendite belongs to a low-silica, high-titanium, and high-iron-magnesium mafic-ultramafic series. Mineral composition data exhibit a systematic decrease in Mg# values of amphibole and pyroxene and increase in TiO2 and FeO contents. Combined with the whole-rock compositions featuring decreasing Fe(2)O3T, MgO, and TiO2 and increasing SiO2, these observations both indicate that fractional crystallization was the dominant process controlling magmatic evolution. Magmatic physicochemical conditions further reveal that early saturation of Fe-Ti oxides, controlled by oxygen fugacity (Delta NNO -0.45 to Delta NNO +0.99), triggered mineralization. Subsequently, as temperature and pressure continued to decline, oxygen fugacity was buffered to moderate conditions, enabling continued enrichment of Fe-Ti oxides during later magmatic evolution. In summary, the large-scale titanium-iron ore deposits in Xiaojiagou was formed approximately 1.84Ga, resulting from the transition from compressional orogeny to post-orogenic extension during the early rifting of the Columbia supercontinent. Their titanium and iron enrichment originated from the partial melting of the lithospheric mantle enriched by ancient crustal materials. The resulting Fe-Ti-rich mafic parental magma subsequently underwent early saturation crystallization of Fe-Ti oxides under moderately to relatively high oxygen fugacity conditions, and continued accumulation and enrichment during subsequent magmatic evolution, ultimately forming economic titanium-iron ore deposits.

High-grade hematite mineralization is widely developed in banded iron formations (BIFs) worldwide. However, in the North China craton where Neoarchean-Paleoproterozoic BIFs are abundant, economic high-grade hematite ores are scarce. High-grade hematite ores hosted in the Paleoproterozoic Yuanjiacun BIFs represent the largest occurrence of this type of ore in the North China craton. It was once viewed that the lack of high-grade hematite ores in the North China was due to the lack of prolonged epigenetic weathering-leaching conditions, but that could not explain the fault-controlled characteristics of high-grade hematite orebodies in Yuanjiacun. On the basis of field contact relationship, petrological and mineralogy analysis, the in-situ U-Pb dating of monazite and xenotime and the fluid inclusion analysis of quartz intergown with hematite was both carried out. The results show that, the timing of high-grade hematite mineralization was at 1.41 to 1.34 Ga, revealing that the deposition of hematite was probably related to tectonic extension in the North China craton related to the breakup of the Columbia/Nuna supercontinent. Petrography and microthermometry of primary fluid inclusion assemblages indicate that the high-grade hematite ore formed from hot (313°–370°C), CO2-rich, and highly saline (about 20 wt % NaCl equiv) hydrothermal fluids. These fluids channeled along faults, which concentrated iron through interaction with the BIFs—a process similar to typical hematite mineralization elsewhere. By comparing to the typical iron deposits worldwide, and combining with the views of the predecessors, we argue that the high-grade hematite ores formed in lower metamorphic-grade BIFs at shallower depths than magnetite mineralization and was largely eroded during later exhumation and uplift of the craton. The determination of ore genesis of the Yuanjiacun high-grade hematite ores is of theoretical and practical significance to enriching the mineralization process of high-grade iron ores and futher prospecting exploration for high-grade iron ores in the Yuanjiacun area.

The rare earth element-iron (REE-Fe) deposits in the Jiao-Liao-Ji belt (JLJB) of the North China Craton (NCC) have significant exploration potential, but their origin remains enigmatic. The Shengtieling REE-Fe deposit is one of the largest occurrences of the sedimentary-metamorphic type, with ores typically consisting of magnetite leptynite enriched in monazite, magnetite, pyrite, and barite. Whole-rock geochemical data of REE-Fe-barren and REE-Fe-rich leptynites suggest a protolith of rhyolite and dacite, which provided the REEs. Zircon grains extracted from magnetite leptynite are characterized by core-rim textures. In situ U-Pb dating of zircon cores and rims yielded weighted mean Pb-207/Pb-206 ages of 2161 +/- 12 Ma and 1837 +/- 9 Ma. The obtained ages indicate the timing of the magmatic protolith formation and the subsequent metamorphism. Additionally, ore mineral monazite grains separated from magnetite leptynite yielded a weighted mean Pb-207/Pb-206 age of 1843 +/- 7 Ma, interpreted as the most reliable estimate for the timing of REE-Fe mineralization. This mineralization was likely linked to the ca. 1.85 Ga metamorphic-hydrothermal event. In situ trace element data of pyrite intergrown with magnetite and monazite indicate that mineralization-related hydrothermal fluids contributed part of the REEs, leached additional REEs from the protolith, and mobilized iron and phosphorus from the Li'eryu Formation under 307-521 degrees C, acidic, reducing, and low oxygen fugacity (fO(2)). Considering that the Co-rich pyrite in the Shengtieling deposit is synchronous with many other occurrences documented in the JLJB, we propose that the similar to 1.85 Ga tectono-magmatic event likely had a significant impact on polymetallic mineralization.

Banded iron formation-hosted high-grade iron ore deposits are among the most important global sources of iron. Although less common than hematite ores, high-grade magnetite ores represent another significant type, occurring mainly in northern North China Craton. These ores are generally considered to have formed through the interaction of high-temperature hydrothermal fluids with-2.55 Ga BIF protore, yet the nature and origin of ore-forming fluids remain uncertain. Two types of high-grade magnetite deposits have been classified based on their size and alteration features: the Gongchangling type and Qidashan type. In situ trace-element and sulfur isotopic analyses were conducted on pyrite from BIFs, high-grade magnetite ores, and altered rocks surrounding high-grade orebodies. In high-grade magnetite deposits, sulfur isotopes may be influenced by multiple factors, making them less effective in constraining the source of ore-forming fluids, whereas trace element analysis of pyrite could provide more precise insights into fluid nature and source. The ore-forming fluids in both deposits exhibit characteristics of hydrothermal systems associated with deep-seated magmatic activity. In the Gongchangling deposit, the ore-forming fluids were primarily derived from magmatic activity at-1.85 Ga, with additional contributions from fluids leaching Paleoproterozoic Co-Ni-rich geological bodies. In contrast, the Qidashan deposit is dominated by As-Se-rich fluids originating from magmatic-hydrothermal activity around-2.5 Ga. We propose that deep-seated magmatic activity is fundamental for forming high-grade iron deposits, whereas the development of large-scale deposits, such as the Gongchangling deposit, requires multi-phase hydrothermal activity involving Co-Ni-rich ore-forming fluids.

Precambrian borate deposits are generally considered to have formed by multiple stages of metamorphic-hydrothermal events subsequent to boron-rich evaporite deposition, but determining the ages of hydrothermal overprinting and remobilization has proven to be challenging. The lack of robust geochronology data has hindered understanding of the geological controls on this type of mineralization. The Houxianyu boron deposit and Wengquangou boron-iron deposit, hosted in 2.05-1.93 Ga metamorphosed evaporites in northern North China Craton, represent the largest occurrences of Precambrian borate deposits. Monazite, molybdenite, baddeleyite and apatite are intergrown with borate minerals of szaibelyite and ludwigite, and thus can be dated to constrain the timing of boron-iron mineralization. In situ U-Pb and Re-Os geochronology yielded consistent Paleoproterozoic ages of 1854 +/- 11 Ma (U-Pb monazite age), 1815 +/- 4 Ma (U-Pb baddeleyite age) and 1825 +/- 22 Ma (Re-Os molybdenite age) related to borate mineralization. These ages constrain the timing of boron and boron-iron mineralization to 1.86-1.81 Ga, which is younger than the similar to 1.90 Ga regional metamorphism but contemporaneous with the similar to 1.85 Ga post-tectonic granitic magmatism. This interpretation is further supported by field relationships which show that hydrothermal quartz-tourmalinite veins cross-cut the schistosity of the leptynites, and by the granitoid-affiliated accessory mineral assemblage (molybdenite, monazite and uraninite). Additionally, chondrite-normalized rare earth element (REE) patterns of apatite intergrown with ludwigite from borate ores show enrichment of LREEs relative to HREEs and strong negative Eu anomalies. These chemical features are similar to those of apatite from similar to 1.85 Ga granites but distinct from those of apatite in metamorphosed rocks. Therefore, we propose that 1.86-1.81 Ga borate mineralization resulted from hydrothermal remobilization associated with the similar to 1.85 Ga granitic magmatism. Our results negate the previously proposed genetic link between borate mineralization and similar to 1.90 Ga regional metamorphism. These results, combined with previously published data, allow us to establish a hydrothermal B-Fe-U-Nb-Ta-Co-Ni metallogenic belt in relation to the similar to 1.85 Ga post-tectonic granitic magmatism in northern North China Craton, potentially valuable for future exploration efforts.

Archean Nb-Ta-bearing granitic rocks linked with crustal growth events are widely developed within cratons worldwide. However, in the North China Craton where crustal growth is extensive, economic Nb-Ta-bearing granitic rocks are scarce. We identified previously unrecognized Nb-Ta-bearing granites in the Qidashan banded iron formation-hosted iron deposit in the Anshan-Benxi area of northern North China Craton. These granites provide a rare example to investigate the rare metal mineralization process within this craton. The U-Pb geochronology conducted on columbite group minerals (CGMs) and cassiterite from the Nb-Ta-bearing granites yielded weighted mean 207Pb/206Pb ages of 2527 +/- 6 Ma and 2535 +/- 5 Ma, respectively, which are indistinguishable from each other within analytical uncertainties. The results indicate a late Neoarchean emplacement age for the Qidashan Nb-Ta-bearing granites. The Qidashan Nb-Ta-bearing granites are characterized by high contents of SiO2, Al2O3, Na2O, K2O and Nb-Ta (average on 190.9 ppm), but low contents of CaO, TFe2O3, MgO, and total rare earth elements (TREE). Additionaly, these granites are enriched in large-ion lithophile elements (LILEs, e.g., Rb, Th, U), are depleted in high-field-strength elements (HFSEs, e.g., Nb, P, Ti), has a low LREE/ HREE ratio, exhibits an obvious negative Eu anomaly, and shows a distinct tetrad effect of REE. These geochemical characteristics indicate that the key factors controlling the formation of Nb-Ta-bearing granites and the subsequent enrichment and mineralization of Nb-Ta rare metals include extensive fractional crystallization of the granitic magma coupled with melt-fluid interactions. The epsilon Nd(t) values of the Qidashan Nb-Ta-bearing granites range from-8.1 to-12.6, with two-stage model ages (TDM2) of 3.56-3.96 Ga, indicating their formation by recycling of mature, old continental crust, similar to the genesis of the 2.50 Ga Qidashan K-rich granites. During the late Neoarchean, the North China Craton entered an extensional tectonic regime, where intense tectono-thermal events triggered extensive granitic magmatism, generating voluminous crust-derived granites. The occurrence of the Archean Qidashan Nb-Ta-bearing granites demonstrates that late Neoarchean tectonic-magmatic activities in the North China Craton possess potential for rare metal Nb-Ta mineralization, offering new insights into the metallogenic prospectivity of Precambrian terranes in this region.

The formation of sediment-hosted CuCo deposits remains controversial, in part due to the lack of a precise age for CuCo mineralization. The Dahenglu deposit is located in the eastern part of the Jiao–Liao–Ji Belt (JLJB), one of the famous sedimentary–metamorphic-type CuCo deposits in China, that is mainly hosted within Palaeoproterozoic epimetamorphic rocks. The orebodies occur as stratoid, lenticular and veined forms in conformity with the carbonaceous sericite phyllite. In this study, we present new ReOs and monazite UPb geochronological data for carbonaceous sericite phyllite, and zircon UPb geochronological data for diorite porphyry associated with the deposit. The ReOs geochronology on carbonaceous rocks from the Dalizi Formation provides a direct and reliable depositional age of 1967 ± 23 Ma. The UPb analyses of metamorphic monazite intergrown with cobaltite yield an age of 1812 ± 8 Ma. Magmatic zircon UPb dating from ore-bearing diorite porphyry yields a weighted mean age of 121.8 ± 0.8 Ma. These results constrain three periods of mineralization in the Dahenglu deposit. Syngenetic sedimentary mineralization and metamorphic mineralization occurred during the Palaeoproterozoic, and magmatic–hydrothermal mineralization occurred during the Early Cretaceous. We suggest that ReOs and UPb geochronology on carbonaceous-bearing epimetamorphic rock and metamorphic monazite can serve as robust chronometers to establish the age and temporal evolution of sedimentary hosted CuCo mineralization.

The formation of sediment-hosted Cu-Co deposits remains controversial, in part due to the lack of a precise age for Cu-Co mineralization. The Dahenglu deposit is located in the eastern part of the Jiao-Liao-Ji Belt (JLJB), one of the famous sedimentary-metamorphic-type Cu-Co deposits in China, that is mainly hosted within Palaeoproterozoic epimetamorphic rocks. The orebodies occur as stratoid, lenticular and veined forms in conformity with the carbonaceous sericite phyllite. In this study, we present new Re-Os and monazite U-Pb geochronological data for carbonaceous sericite phyllite, and zircon U-Pb geochronological data for diorite porphyry associated with the deposit. The Re-Os geochronology on carbonaceous rocks from the Dalizi Formation provides a direct and reliable depositional age of 1967 +/- 23 Ma. The U-Pb analyses of metamorphic monazite intergrown with cobaltite yield an age of 1812 +/- 8 Ma. Magmatic zircon U-Pb dating from orebearing diorite porphyry yields a weighted mean age of 121.8 +/- 0.8 Ma. These results constrain three periods of mineralization in the Dahenglu deposit. Syngenetic sedimentary mineralization and metamorphic mineralization occurred during the Palaeoproterozoic, and magmatic-hydrothermal mineralization occurred during the Early Cretaceous. We suggest that Re-Os and U-Pb geochronology on carbonaceous-bearing epimetamorphic rock and metamorphic monazite can serve as robust chronometers to establish the age and temporal evolution of sedimentary hosted Cu-Co mineralization.

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.

Chromium, a strategic mineral resource in China, is widely used in high-precision equipment manufacturing. As the world’s leading consumer and importer of chromite, China’s external dependence exceeds 99%. The significant imbalance between domestic supply and demand seriously threatens national economic security. This study discusses the state of China’s chromium resource supply from four aspects: the overview of domestic and global chromium resources, China’s chromite production and import volume, the sources of imported chromite, and risk analysis. Considering the chromium industrial chain and factors such as production, consumption, and recovery tendency of chromium-bearing stainless steel, it is forecasted that China’s demand for chromium ore will decline by 2040. This could considerably reduce the security situation of chromium resources. This study proposes five strategies for securing chromium resources: technological innovation, enhancing international cooperation and acquiring overseas resources, constructing a new pattern of “dual circulation” resource guarantee for sea–land transportation, encouraging chromium recycling, and building an emergency management system and strategic reserve mechanism for chromium resources.

Ni-Cu-(PGE) sulfide deposits associated with mafic-ultramafic rocks are the most important sources of Ni and platinum-group elements (PGE) in the world. These deposits also contain significant amounts of Cu. Such deposits are generally considered to have formed by multiple stages of primary magmatic concentration and secondary hydrothermal remobilization. However, constraining the ages of Ni-Cu-(PGE) sulfide deposits has proven challenging, particularly those that have experienced post-magmatic hydrothermal overprinting and remobilization. The lack of robust geochronology data has hindered understanding of the geological controls on this important type of mineralization. The Chibaisong Ni-Cu-(PGE) sulfide deposit in the North China Craton is characterized by disseminated and net-textured ores formed by magmatic processes and overprinted by hydrothermal Cu-rich vein stockwork. The Cu-rich vein stockwork is fracture-controlled, and contains a mineral assemblage of Ni-Cu sulfides (chalcopyrite, pyrrhotite, pentlandite), amphibole and quartz. Chalcopyrite in the hydrothermal stockwork is relatively depleted in Ni but enriched in Ag and Cd compared with disseminated magmatic chalcopyrite, typical of hydrothermal superimposed ores as documented elsewhere. We identified baddeleyite-zircon pairs associated with Ni-Cu sulfides in hydrothermal superimposed ores of the Chibaisong deposit, in which the baddeleyite is unequivocally of primary igneous origin whereas the zircon represents the replacement product of baddeleyite during hydrothermal alteration. In situ SIMS U-Pb dating of baddeleyite and zircon yielded weighted mean 207Pb/206Pb ages of 2181 +/- 21 Ma and 1892 +/- 33 Ma, respectively, interpreted as the timing of magmatic mineralization and subsequent hydrothermal remobilization of the Ni-Cu-(PGE) deposit. Our results explain the large discrepancies in sulfide Re-Os ages previously obtained from this deposit. This study demonstrates that on the basis of detailed BSE imaging, in situ SIMS U-Pb dating of baddeleyite-zircon pairs can provide robust age constraints for both magmatic mineralization and hydrothermal remobilization of Ni-Cu(PGE) sulfide deposits hosted in mafic-ultramafic intrusions, although further studies are needed to test whether the formation of such deposits commonly entails multiple stages of hydrothermal remobilization. Since baddeleyite or baddeleyite-zircon pairs are common accessory minerals in Ni-Cu-(PGE)-bearing mafic-ultramafic rocks, the dating approach employed in this study may be applicable to similar deposits elsewhere.

Nelsonite (Fe-Ti oxide-apatite rock) devoid of silicates offers a rare opportunity to investigate the magma processes for the formation of magmatic Fe-Ti oxide deposits. Both fractional crystallization and silicate liquid immiscibility have been put forward, but the lack of robust evidence has hindered unambiguously distinguishing the role of these two processes in Fe-Ti mineralization. The nelsonite and associated Fe-Ti-P-rich rocks hosted in the Proterozoic Damiao anorthosite complex represent a typical example for studying Fe-Ti ore-forming processes. We recognized a new type of nelsonite (type-I) in the Damiao complex, which is distinct from the two known types of nelsonite (type-II and type-III) from the same complex. The type-I nelsonite is characterized by its coexistence with oxide-apatite gabbronorite and granite in the same dike, and all these rocks have identical emplacement ages (1740 +/- 7 Ma), subparallel REE patterns, and major-element compositions lacking intermediate compositions, suggesting derivation from conjugate Fe- and Si-rich melts generated by silicate liquid immiscibility. The large type-II nelsonite bodies form irregular dikes along fractures in anorthosite and constitute the major ore type. The type-III nelsonite occurs as conformable layers or pods within oxide-apatite gabbronorite and pyroxenite, and occupies the end part of the type-II dike. The latter two types of nelsonites formed by extensive fractional crystallization of residual magma with crystal accumulation and subsequent hydrothermal replacement. During residual magma evolution, silicate liquid immiscibility was crucial for Fe-Ti-P enrichment, fractional crystallization was responsible for enhancing oxide-apatite concentrations, and hydrothermal replacement was effective for mobilizing oxide-apatite concentrations. Our newly recognized nelsonite provides an unambiguous, outcrop-scale, field evidence for the operation of silicate liquid immiscibility process. We show that giant magmatic Fe-Ti oxide orebodies can form by a combination of processes involving silicate liquid immiscibility, fractional crystallization and hydrothermal mobilization.

地球物理探测是深部找矿预测不可或缺的重要手段,但是由于地质条件的复杂性及地球物理信息的多解性导致其地质解释的不确定性,需要通过多种途径加以限定.热电材料的电阻率和热导率具有明显的相关关系,但岩(矿)石的电阻率和热导率的关系鲜有研究.本文通过对前人岩(矿)石热导率和湖南岩(矿)石电阻率研究成果的梳理,发现岩(矿)石的热导率和电阻率具有明显的正相关趋势,认为这一规律有助于限定深部电阻率信息的地质解释.本文以湘南中生代钨锡多金属矿为例,初步探讨了岩(矿)石热导率和电阻率正相关趋势的深部找矿预测意义.

岩浆液态不混溶形成的浆液过渡态熔体是与高度分异花岗岩有关的钨锡多金属成矿流体的重要形式.湘南地区与钨锡多金属成矿有关的浆液过渡态熔体有两种类型,一种富钠富挥发分,以芙蓉矿田矿化蚀变碱长花岗岩中的钠长石电气石石英囊为代表;另一种富钾富挥发分,以界牌岭矿床矿化蚀变花岗斑岩中的锂白云母萤石囊(团块)为代表.两种浆液过渡态熔体可形成于同一矿床,为同期岩浆活动产物,成分上K2O与Na2O负相关,表明它们具有密切的时空和成因联系,熔体-流体包裹体发育,为高度分异的花岗质岩浆液态不混溶产物.两种浆液过渡态熔体富含成矿物质,与成矿关系密切,湘南地区多数钨锡多金属矿床的云英岩型、构造蚀变带型、钾化花岗岩型钨锡多金属成矿可能与富钾富挥发分的浆液过渡态熔体有关,钠化花岗岩型铌钽矿化与富钠富挥发分的浆液过渡态熔体有关.

Based on previous survey and detailed study, the authors focused on the characteristics of the ore-bearing quartz veins and investigated the multistage magmatic activities and mineralization. Besides, the horizontal zoning of metal element and vertical zoning of W-Mo deposit were also summarized. The Gao’aobei deposit belongs to a veinlets-zone type W-Mo deposit that formed at Early Yanshanian period. The W-Mo deposit is characterized by 0.5-5 cm W-Mo-bearing veinlets or micro-veinlets, filling into the upper parts of Indosinian biotite monzogranite, and is covered by the hornfels of Xiangnan Formation in Cambrian, with complete metallogenic system. The quartz veins are distributed in all directions, and the optimum attitude is NWW strike and NNE dip. The main W-Mo orebody is continuous, with a feature of low grade and large tonnage. The main ore minerals are wolframite and molybdenite, with a vertical zoning developed as upper tungsten and lower molybdenum. The discovery of this large-scale veinlets-zone type W-Mo deposit is of great significance to prospecting the same deposits in future in Hunan Province.

铌(Nb)、钽(Ta)广泛应用于全球高新科技领域,是不可替代的稀有金属资源,在中国,铌钽属于紧缺战略性矿产. 铌钽成矿主要与内生作用有关,国内外目前发现的铌钽矿床几乎都产于过铝质花岗岩、花岗伟晶岩、碱性花岗岩、碳酸岩等侵入体中.

1 研究目的(Objective) 铌和钽物理化学性质相似,在自然界中常相伴产出,在内生和外生条件下都可富集成矿.内生铌钽矿床主要与岩浆作用有关,根据赋矿岩石的特征被分为花岗岩型、花岗伟晶岩型、碳酸岩型和碱性岩型.最近,笔者在华北克拉通北缘的辽宁齐大山沉积变质型铁矿中新识别出一种铌钽矿石类型,为富铁矿体边部的富绿泥石蚀变岩型铌钽矿化,与热液作用密切相关,为认识铌钽成矿过程和拓展找矿空间提供了新线索和支撑.