Nb-Ta Deposits Research Articles

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.

Evolution of Nb–Ta Oxide Minerals and Their Relationship to the Magmatic-Hydrothermal Processes of the Nb–Ta Mineralized Syenitic Dikes in the Panxi Region, SW China

Previous geochemical and petrological studies have concluded that initially magmatic Nb–Ta mineralization is often modified by post-magmatic hydrothermal fluids; however, there is still a lack of mineralogical evidence for the syenite-related Nb–Ta deposit. From the perspective of Nb–Ta minerals, the pyrochlore supergroup minerals have significance for indicating the fluid evolution of alkaline rock or related carbonatite type Nb–Ta deposits. The Panzhihua–Xichang (Panxi) region is a famous polymetallic metallogenic belt in southwestern China, abound with a huge amount of Nb–Ta mineralized syenitic dikes. This study focuses on the mineral textures and chemical compositions of the main Nb–Ta oxide minerals (including columbite-(Fe), fersmite, fergusonite-(Y), and especially pyrochlore group minerals) in samples from the Baicao and Xiaoheiqing deposits, in the Huili area, Panxi region, to reveal the magma evolution process of syenitic-dike-related Nb–Ta deposits. The Nb–Ta oxides in the Huili syenites are commonly characterized by a specific two-stage texture on the crystal scale, exhibiting a complex metasomatic structure and compositional zoning. Four types of pyrochlore group minerals (pyrochlores I, II, III, and IV) formed in different stages were identified. The euhedral columbite-(Fe), fersmite, and pyrochlores I and II minerals formed in the magmatic fractional crystallization stage. Anhedral pyrochlore III minerals are linked to the activity of magma-derived hydrothermal fluids at the late stages of magma evolution. The pyrochlore IV minerals and fergusonite-(Y) tend to be more concentrated in areas that have undergone strong albitization, which is a typical phenomenon of hydrothermal alteration. These mineralogical phenomena provide strong evidences that the magmatic-hydrothermal transitional stage is the favored model for explaining the Nb–Ta mineralization process. It is also concluded that the changes in chemical composition and texture characteristics for pyrochlore group minerals could serve as a proxy for syenite-related Nb–Ta mineralization processes.

Mineralogical constraints on Nb-Ta fractionation in Early Cretaceous A-type granites from the Suzhou pluton, SE China

The Suzhou A-type granite pluton in Jiangsu Province, South China, hosts the first Nb-Ta deposit discovered in China. Three granite phases are exposed in the field: porphyritic amphibole- and biotite-bearing granite (Am-BG), medium-grained porphyritic biotite granite (MBG), and fine-grained porphyritic biotite granite (FBG-SZ). The granites have high Nb-Ta contents, yet only FBG-SZ contains minor columbite. Besides, fine-grained porphyritic biotite granite (FBG-DH) and fine-grained zinnwaldite-albite granite (ZAG) are exposed in nearby drill holes. Granites from the boreholes are enriched in Nb-Ta with preliminary inferred grades of 0.008–0.062 wt% Ta2O5 and 0.056–0.157 wt% Nb2O5. Here, we report whole-rock geochemical data, textural and chemical analyses of various Nb–Ta-bearing minerals, and zircon and columbite U-Pb ages for the Suzhou granites. The granitic rocks are metaluminous to weakly peraluminous, which have evolved through progressive fractionation. The granites have high Nb contents (up to 1700 ppm) and a wide range of Nb/Ta ratios (1–154). Niobium and tantalum have an affinity with Ti-bearing host minerals including silicates (e.g. amphibole, titanite and micas) and oxides (e.g. ilmenite, rutile and columbite). The main host minerals for Nb in the Am-BG and MBG are annite, magnetite, ilmenite, titanite ± amphibole (in the Am-BG) ± rutile (in the MBG), whereas in the FBG (including -SZ and -DH) and ZAG the main host minerals for Nb are Li-Fe micas (lithian annite and zinnwaldite), columbite-group minerals (CGMs), ±ilmenorutile and magnetite (in the FBG), and ±tapiolite (in the ZAG). With decreasing whole-rock TiO2 contents, the Nb/Ta ratios first increase gradually and then decrease abruptly, recording fractionation of various Nb-Ta-bearing minerals. Based on columbite U-Pb dating, Nb-Ta mineralization in the FBG occurred at 123 ± 1–121 ± 1 Ma, and is thus slightly younger than the crystallization age of the granites (126 ± 1–125 ± 1 Ma). The metaluminous-peraluminous, low-P (PLP)- type rare-metal granites of the Suzhou pluton, are compositionally and likely genetically different from typically strongly peraluminous Nb-Ta granites in South China. Fractionation at high temperature, high alkalinity and fluid enrichment were important factors for the extreme Nb enrichment in the Suzhou granites. The Suzhou pluton forms one of several metaluminous-peraluminous A-type granites with recognized Nb-Ta mineralization within the Jiangnan Orogen/metallogenic belt, and we thus suggest that Early Cretaceous Nb-Ta mineralization associated with PLP-type rare-metal granites should be the subject of further exploration.

Characterization of Nb22O54 microrods grown from niobium oxide powders recovered from mine tailings

In this work, the possibility of using niobium oxide recovered from tailings from the Penouta Sn–Nb–Ta deposit (located at the North of Spain) as starting material for growing microstructures is demonstrated. The properties of the starting material have been studied to understand its crystal structure, quality and purity. Recovered niobium oxide powders are mainly of TT-Nb2O5. These powders have been used to grow Nb22O54 microrods by an evaporation method in an argon atmosphere. Different characterization techniques (X-Ray diffraction, scanning electron microscopy, micro-Raman spectroscopy, luminescence) have been used to determine the properties of Nb22O54 microrods, mainly focusing on the crystal quality and refractive index. The present study opens the way to the transformation of waste (mine tailings) into a material of high technological value as niobium oxide, and its reintroduction into the value chain for a wide range of applications, from coatings to batteries and supercapacitors.

In-situ boron isotopic and geochemical compositions of tourmaline from the Shangbao Nb–Ta bearing monzogranite, Nanling Range: Implication for magmatic-hydrothermal evolution of Nb and Ta

The enrichment mechanism of tantalum and niobium are still in dispute due to complex textural features of Nb–Ta minerals. Tourmaline is an accurate passive geochemical monitor related to the W-Sn-Nb-Ta-Li mineralization, which can record Nb and Ta variations in melt/fluid. The newly discovered Shangbao Nb–Ta bearing monzogranite is located in Nanling Range, South China, which is characterized by tourmaline wide occurrence. In this paper, we systematically investigate the different types of tourmaline using in-situ major, trace elemental and boron isotope for studying the origin of tourmaline, boron source, and Nb–Ta enrichment process. Three types of tourmaline have been identified, namely, disseminated tourmaline (TD type) in monzogranite, nodular tourmaline (TN type), consisting of the yellow core (TNy type) and blue rim (TNb type), and veined tourmaline (TV type). Almost all tourmalines from the Shangbao Nb–Ta deposit exhibit very low Ca content, X-site occupancy and high ratio of Fe / (Fe + Mg), pertaining to the group of schorl and alkali. Trace elements primarily present the low concentrations of <10 ppm, while the contents of Sc, Li and Zn are higher.Based on the petrography and Al occupations in the Y-site of tourmaline, TD type tourmaline was precipitated straightly from the melt at the late magmatic stage, while TN type tourmaline crystallized during the magmatic-hydrothermal transition process, and TV type tourmaline was the origin of hydrothermal fluid. In-situ boron isotope analyses of TD and TN type tourmaline by MC-ICP-MS show the narrow δ11B values from −17.16‰ to −14.81‰, demonstrating the same boron source. TV type tourmaline shows the weak higher δ11B values of −14.48‰ to −13.46‰ likely resulted by Rayleigh fractionation. The concentration of Nb in TD and TV type tourmaline can reach up to 20 ppm, which is higher than that in TN type tourmaline. However, TN type tourmaline contains higher Ta content than other types, revealing magmatic-hydrothermal transitional stage is critical to Ta enrichment. Compared with tourmaline in other type deposits, tourmaline in Shangbao monzogranite contains high Nb and Ta contents, indicating that it is a suitable tool for exploration, and the tourmaline is available to targeting Nb and Ta mineralization.

Genesis of Late Cretaceous granite and its related Nb–Ta–W mineralization in Shangbao, Nanling Range: Insights from geochemistry of whole-rock and Nb–Ta minerals

The Shangbao mining district, located in Nanling Range, South China, includes a series of middle-large scale granite-related W–Sn–Nb–Ta deposits. The genesis for W-Sn-Nb–Ta mineralization in this region is in fact ambiguous. In addition, the research of the latest mineralized granites in Nanling Range may be contributed to further understand the mineralization mechanism. In this study, we report the geochronological, geochemical and isotopic compositions of the Shangbao granite, together with the texture and element of Nb–Ta bearing minerals. LA-MC-ICP-MS U–Pb dating of zircon and columbite in granite from Shangbao Nb–Ta deposit yields weighted mean 206Pb/238U age of 87.3 ± 0.9 Ma and 86.83 ± 0.8 Ma, respectively, revealing the emplacement of the granites and their mineralization during Late Cretaceous. The major elements of these granites show high contents of K2O + Na2O, Fe2O3, SiO2 and F, low contents of P2O5, CaO, TiO2 and MgO, suggesting high-K calc-alkaline series with slightly peraluminous signature. Besides, they exhibit flat REE pattern and high content of Zr + Nb + Ce + Y, revealing the Shangbao granite affinity of highly fractionated A-type granite. Lu–Hf and Sr–Nd isotopes indicate that the Nb–Ta bearing magma was formed by the mixing crust-mantle materials. Combined with the previous studies, emplacement of Shangbao granite is linked to an expansional geodynamic setting, likely caused by the roll-back of the paleo-Pacific plate subduction.The principal economic Nb–Ta oxides of Shangbao granite are columbite group minerals (CGM). Three major groups are identified given textural and chemical characteristics of CGM, i.e., (i) Group I displays systematic core-rim evolution from columbite to tantalite, and eventually to columbite; (ii) Group II shows that the columbite and tantalite have undergone metasomatism through the wolframoixiolite, and numerous REE-mineral were contained; (iii) Group III is anhedral columbite crystallized together with rutile. As revealed from geochemical characteristics of these three groups, the formation of Nb–Ta oxides within Shangbao granite display three generating stages, supporting the magmatic-hydrothermal origin. The high-degree fractional crystallization of Shangbao granitic magma is the main factor leading to the enrichment of Nb to allow saturation of columbite.

Formation Time, Magma Source and Mineralization in the Zhaojinggou Nb-Ta Deposit, Inner Mongolia: Evidence from Columbite-Group Minerals U-Pb Dating, Rock and Mineral Geochemistry of the Amazonite Granitic Pegmatite

Formation Time, Magma Source and Mineralization in the Zhaojinggou Nb-Ta Deposit, Inner Mongolia: Evidence from Columbite-Group Minerals U-Pb Dating, Rock and Mineral Geochemistry of the Amazonite Granitic Pegmatite

Geochronology, geochemistry, mineralogy and metallogenic implications of the Zhaojinggou Nb-Ta deposit in the northern margin of the North China Craton, China

The large Zhaojinggou Nb-Ta deposit is located in the northern margin of the North China Craton (NCC), Inner Mongolia, China. The deposit is mainly hosted in the mineralized dikes around the Hutoushan pluton and the residual pegmatite shell at the top of the pluton. Samples from the pluton and the mineralized dikes are characterized by high contents of SiO2 (73.3%–84.3%), total alkalis (5.24%–9.60%) and Al2O3 (7.94%–13.8%), and moderate A/CNK values (with an average of 1.04) indicating a weakly peraluminous affinity. The trace element patterns are characterized by Rb, Nb, Ta, Zr, and Hf enrichment and markedly negative Ba, Sr, P, Eu, and Ti anomalies. Zircon U-Pb dating suggests that the emplacement of the pluton and the Nb-Ta mineralization occurred coevally in the Early Cretaceous (126 ± 1 Ma and 127 ± 2 Ma, respectively). Variations in both bulk-rock geochemistry (K/Rb, Zr/Hf, Nb/Ta) and mineral composition (mica and columbite) consistently unveil a magmatic evolutionary trend from the Hutoushan alkali-feldspar granite, through the Hutoushan pegmatite shell, to the mineralized dikes. Typical A-type characteristics of the granite and ancient Hf isotopic features [εHf(t) ranging from −6.80 to −12.95, and crust model ages from 1.61 to 2.00 Ga] indicate that the parental magma was derived from the partial melting of Palaeoproterozoic crust with insignificant mantle material involved. Considering the significantly higher bulk contents of Nb, Ta, and F in the pegmatite shell and the mineralized dikes than that in the alkali-feldspar granite, as well as the similar composition in the biotite from the pegmatite shell and the alkali-feldspar granite, we propose that a residual Nb-Ta-enriched brine-melt phase segregated from the crystal mush at the late stage of crystallization. The progressive concentration of F in the melt was conducive to the solubility of Nb and Ta in granitic melts and decreased the viscosity by depolymerizing the melt, and thus contributed to the high magma differentiation and Nb-Ta concentration. The post-magmatic fluid triggered the fluid-rock interaction, resulting in the extensive albitization, M-type “tetrad effect”, extremely low Nb/Ta ratio (<5), and further mineralization in the mineralized dikes.

Critical mineral resources of Nb, Ta, Zr, and Hf in China

The two element pairs Nb-Ta and Zr-Hf have similar geochemical behaviors and are critical mineral resources due to their specialized applications in modern high-technology industries. Globally, based on the type of host rock, Nb, Ta, Zr, and Hf resources can be divided into granite- and granitic pegmatite-type, carbonatite-type, alkaline rock-type, and related exogenic deposits. Low reserves and a high import dependency on these metals are important issues for China. There are ca. 50 Nb-Ta deposits in China, with estimated reserves of Nb2O5 and Ta2O5 of 2.67 × 106 and 0.17 × 106 t, respectively (excluding the Nb reserves in the Bayan-Obo REE-Nb-Fe deposit). Most of these deposits are hosted in aluminous granites, including peraluminous and metaluminous granite types. Examples include the Yichun peraluminous granite-type Nb-Ta deposit in Jiangxi Province, the Guposhan metaluminous granite-type Nb deposit in Hunan and Guangxi and the granitic pegmatite-type Nanping Nb-Ta-Li deposit in Fujian Province. Other minor deposits include the carbonatite-type (e.g., the Miaoya REE-Nb deposit in Hubei Province) and the alkaline rock-type (e.g., the Ba’erzhe REE-Zr-Nb-Be deposit in Inner Mongolia). Niobium-Ta resources in China are located mainly in the western Pacific domain (e.g., the Nanling Range and Jiangnan orogenic belt), the Paleo-Asian Ocean domain (e.g., the Altay Li-Be-Nb-Ta ore belt), the Tethyan domain (e.g., the Songpan-Ganze Li-Be-Nb-Ta and Himalaya Be-Nb-Ta leucogranite ore belts), and at the margins of the Yangtze and North China cratons (e.g., the Nb deposits in the Qinlin orogenic belt). These deposits formed during the Meso-Neoproterozoic (e.g., the Bayan-Obo REE-Nb-Fe deposit during 1.4–1.3 Ga), Paleozoic (ca. 400–380 Ma), early Mesozoic (Paleo-Tethys tectonism; 250–200 Ma), late Mesozoic (the metallogenic explosion in South China; ca. 160–120 Ma), and Cenozoic (Himalaya leucogranite belt; 44–7 Ma). An estimated 500 ´ 103 t of ZrO2 is hosted in both endogenic and exogenic deposits in China. The endogenic Zr-Hf resources are commonly associated with Nb-Ta deposits, due to their similar geochemical behavior. Most of these are hosted in alkaline-peralkaline granites (e.g., the Ba’erzhe REE-Nb-Ta-Zr deposit), along with minor deposits in aluminous granite and granitic pegmatite (e.g., the Koktokay Li-Be-Nb-Ta-Zr-Hf deposit in Xinjiang). There are no occurrences of carbonatite-type Zr-Hf deposits in China. The endogenic Zr-Hf deposits are located primarily along with deep fractures or in rifted regions, including the ore belts of the Tarim and Northern China cratons (e.g., the Boziguo’er alkaline syenite-type deposit in Xinjiang), the western Yangtze Craton (e.g., the Cida alkaline granite-type deposit in Sichuan Province), and the southern Daxing’an mountain range (e.g., the Ba’erzhe alkaline granite-type deposit). These endogenic Zr-Hf deposits formed during the late Paleozoic and Mesozoic. Although endogenic deposits host the main Zr-Hf resources in China, few have been economically exploited due to their low grade and technical challenges. In contrast, domestically available Zr-Hf resources have been exploited from zircon in Quaternary exogenic deposits, including littoral placers (e.g., the Wenchang placers in Hainan Province), fluvial-alluvial placers (e.g., the No. 725 deposit in Guangxi), and weathered crust-type deposits (e.g., the No. 520 deposit in Guangxi). In these exogenic deposits, the ore minerals commonly include zircon, rutile, monazite-(Ce), ilmenite, and other heavy minerals that were derived mainly from Mesozoic granites. Hainan Province is China’s largest region of mined exogenic Zr deposits, which occur mostly in Wenchang, Qionghai, Wanning, and Lingshui counties along its southeastern coastline. In summary, although China hosts diverse types of Nb-Ta-Zr-Hf resources and its reserves are large, most of the deposits are of low grade and difficult to utilize. Therefore, future research should focus on ore formation mechanisms, mineral exploration, and improvements in resource recycling, mineral processing, and industrial efficiency.

Geochronology and source of the rare-metal pegmatite in the Mufushan area of the Jiangnan orogenic belt: A case study of the giant Renli Nb–Ta deposit in Hunan, China

The Jiangnan orogenic belt hosts many rare-metal deposits that exhibit close ore-forming ages and similar geological backgrounds and is an important Li–Be–Nb–Ta concentration belt located in eastern China. However, the metallogenic mechanism and regularity of these rare-metal deposits have not yet been reported in detail because of the lack of accurate geochronological data and systematic studies on the sources of metallogenic materials. The giant Renli rare-metal deposit, located at the south margin of the Mufushan batholith in the central Jiangnan orogenic belt, is one of the few high-grade granitic-pegmatite-type Nb–Ta deposits in China. Columbite–tantalite U–Pb dating has been developed as a more robust method when compared with the traditional dating methods to constrain the timing of rare-metal mineralization. Six columbite grains, obtained from the microcline–albite pegmatite of the Renli deposit, exhibit a concordant laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb age of 133.0 ± 2.6 Ma, which denotes the Nb–Ta mineralization age. The zircon grains from the columbite-bearing microcline–albite pegmatite subjected to different degrees of alteration by the hydrothermal fluids yield a concordant LA–ICP–MS U–Pb age of 131.2 ± 2.4 Ma, which can be considered to be the age of newly magmatic–hydrothermal growth and recrystallization under the transitional magmatic–hydrothermal conditions observed in case of the Renli deposit. Furthermore, the zircon grains from the host biotite monzogranite yield concordant LA–ICP–MS U–Pb ages of 140.7 ± 0.7 and 140.3 ± 0.7 Ma, whereas the zircon grains from the host two-mica monzogranite yield a concordant LA–ICP–MS U–Pb age of 138.3 ± 0.3 Ma, denoting the intrusion timing of two types of host Mufushan granites of the pegmatite dykes. Finally, the zircon grains from two schist samples of the Lengjiaxi Group yield concordant LA–ICP–MS U–Pb ages of 825.9 ± 5.6 and 834.4 ± 5.3 Ma, constraining the maximum age for the termination of deposition. These ages constitute a clear intrusion-cooling-hydrothermal time series with respect to the Renli deposit.Zircon can retain the original magmatic isotopic composition and is extensively used to trace the petrogenetic processes because it is quickly crystallized from magma. The Mufushan granite and rare-metal pegmatite exhibit consistent negative eHf(t) values (mean eHf(t) values of −7.2 and −7.3, respectively), and their two-stage model ages exhibit similar distribution patterns when compared with that exhibited by the Lengjiaxi Group. Furthermore, the Mufushan granite shows the typical geochemical characteristics of the crustal-derived granite. Thus, the rare-metal pegmatite and host granite of the Renli deposit were concluded to be sourced from the partial melting of the Lengjiaxi Group metasedimentary strata.The compressive torsional nature of the Gajiang fault zone, widespread occurrence of the S-type granite, and absence of basaltic rocks suggest that the central-to-eastern part of the Jiangnan orogenic belt was in a subduction setting during the Early Cretaceous. Thus, this economically important Early Cretaceous (ca. 133–129 Ma) rare-metal metallogenic belt was formed owing to the development of the Jiangnan orogenic belt, and the thick Lengjiaxi Group metasedimentary strata provided the metallogenic material source.

Episodic Nb–Ta mineralisation in South China: Constraints from in situ LA–ICP–MS columbite-tantalite U–Pb dating

South China hosts many Nb–Ta deposits that show evidence for episodic mineralization, which were generated during the emplacement of composite granites. To constrain the spatio-temporal distribution of Nb–Ta mineralisation in the region and to identify future targets for mineral exploration, we used in situ laser ablation-inductively coupled plasma-mass spectroscopy to date 23 columbite-tantalite group mineral (CGM) samples from 14 Nb–Ta deposits. Our CGM U–Pb data, supplemented by previous results, reveal five distinct Nb–Ta mineralisation events in South China as follows: (1) Late Silurian–Middle Devonian (ca. 424–391 Ma; e.g., the Xigang and Nanping deposits in eastern Jiangxi and western Fujian Provinces); (2) Triassic (ca. 248–204 Ma; e.g., the Houxi, Cunxin, Dongtounan, Shenkeng, Limu and Gaoling deposits in western Guangdong Province and northeastern Guangxi Zhuang Autonomous Region; (3) Late Jurassic (ca. 160–150 Ma; e.g., the Gedongping, Yichun, Laiziling, Jianfengling and Jinzhulong deposits in Guangxi, Jiangxi and Hunan Provinces); (4) Early Cretaceous (ca. 130 Ma; e.g., the Huangshan and Songshugang deposits in northeastern Jiangxi province); and (5) Late Cretaceous (ca. 90 Ma; e.g., the Jiepailing deposit, located along the boundary between Hunan and Jiangxi Provinces). We show that Nb–Ta mineralisation in South China was controlled by multiple tectono-magmatic events. Our CGM samples yielded Caledonian (ca. 424–391 Ma), early Indosinian (ca. 248 Ma) and late Yanshanian (ca. 130 Ma) ages, indicating that Nb–Ta mineralisation was abundant during these times and should form the focus for future studies of mineralisation in the region. Early Triassic granite in the Guangning Nb–Ta metallogenic district in western Guangdong Province, Indosinian and early Yanshannian granites in the Miao’ershan–Yuechengling batholith in northeastern Guangxi, and the Late Cretaceous Lingshan batholith in northern Jiangxi Province are identified as targets for future Nb–Ta exploration.

Zr-Ti-Fe placers along the coast of NE Argentina: Provenance analysis and ore guide for the metallogenesis in the South Atlantic Ocean

The Zr-Ti-Fe placers along the coast of Rio Negro and Buenos Aires Provinces, Argentina, evolved within the reaches of the Malvinas Current (1st order hydrodynamic regime). Together with some regional 2nd order local currents it is of major influence on the mineral assemblage of these terrigenous linear shoreline deposits. The nearshore-marine placers came into being in a macro- to mesotidal (San Matias Gulf) and meso- to microtidal regime (Bahia Blanca Estuary).The modern-day placers under study result from a transgressive regime with only moderate detrital input by the contemporaneous river drainage systems. The proto-placers are hallmarked among the heavy minerals (HM) by changes in the redox system which affected predominantly the Fe-Ti oxides and lead to pseudobrookites and kleberite. Light minerals (LM) in the present-day placers played a different role which is mirrored by changes in the alkalinity of the intragranular fluid system. As far as the environment of deposition is concerned in these shoreline deposits, the dune belt and backshore are most prospective as to the concentration of magnetic and non-magnetic HM. The HM assemblage of the coastal placers is a mirror image of the Afro-American part of Gondwana and its break-up history during the Mesozoic and Cenozoic. The HM reflect the alternating orogenic and anorogenic geodynamic processes operative along the passive margin of both continents. While the orogenic regimes contributed to the accumulation of metallogenetically irrelevant HM (e.g. alumosilicates, spinel, garnet, amphibole) of the placers, the anorogenic geodynamic regime may be held accountable for the target elements in the placer deposits Zr, Ti and Fe. Fe-Ti oxides (rutile, ilmenite-titanohematites, titanomagnetites) and zircon form placer deposits in their own rights with zircon playing an additional minor role also as ore guide to rift-related deposits. Titanium dioxides (Nb-Ta rutile s.s.s., struverite) and Nb titanite take the most prominent role as ore guides to rare element-bearing pegmatites, alkali magmatic rocks and carbonatites. In conclusion, the HM suite encountered in the placer deposits denotes a hot-spot mineralization at a triple junction of the South Atlantic, the Antarctic and the Proto-Iapetus Oceans. The Zr-Ti-Fe placer deposits are part of the clastic halo or expressed metaphorical as remnants of this hot-spot metallogenesis encompassing anorogenic Nb-Ta deposits related to alkaline-magmatic rocks, Skaergaard-type Fe-concentration and anorthosite-hosted Fe-Ti deposits.

Magmatic Evolution and Mineralization Process of the Super‐Large Shihuiyao Rb–Nb–Ta Deposit, Southern Great Xing'an Range, China

Magmatic Evolution and Mineralization Process of the Super‐Large Shihuiyao Rb–Nb–Ta Deposit, Southern Great Xing'an Range, China

Metallogenetic systems associated with granitoid magmatism in the Amazonian Craton: An overview of the present level of understanding and exploration significance

The Amazonian Craton hosts world-class metallogenic provinces with a wide range of styles of primary precious, rare, base metal, and placer deposits. This paper provides a synthesis of the geological database with regard to granitoid magmatic suites, spatio temporal distribution, tectonic settings, and the nature of selected mineral deposits. The Archean Carajás Mineral Province comprises greenstone belts (3.04–2.97 Ga), metavolcanic-sedimentary units (2.76–2.74 Ga), granitoids (3.07–2.84 Ga) formed in a magmatic arc and syn-collisional setting, post-orogenic A2-type granites as well as gabbros (ca. 2.74 Ga), and anorogenic granites (1.88 Ga). Archean iron oxide-Cu-Au (IOCG) deposits were synchronous or later than bimodal magmatism (2.74–2.70 Ga). Paleoproterozoic IOCG deposits, emplaced at shallow-crustal levels, are enriched with Nb–Y–Sn–Be–U. The latter, as well as Sn–W and Au-EGP deposits are coeval with ca. 1.88 Ga A2-type granites. The Tapajós Mineral Province includes a low-grade meta-volcano-sedimentary sequence (2.01 Ga), tonalites to granites (2.0–1.87 Ga), two calc-alkaline volcanic sequences (2.0–1.95 Ga to 1.89–1.87 Ga) and A-type rhyolites and granites (1.88 Ga). The calc-alkaline volcanic rocks host epithermal Au and base metal mineralization, whereas Cu–Au and Cu–Mo ± Au porphyry-type mineralization is associated with sub-volcanic felsic rocks, formed in two continental magmatic arcs related to an accretionary event, resulting from an Andean-type northwards subduction. The Alta Floresta Gold Province consists of Paleoproterozoic plutono-volcanic sequences (1.98–1.75 Ga), generated in ocean–ocean orogenies. Disseminated and vein-type Au ± Cu and Au + base metal deposits are hosted by calc-alkaline I-type granitic intrusions (1.98 Ga, 1.90 Ga, and 1.87 Ga) and quartz-feldspar porphyries (ca. 1.77 Ga). Timing of the gold deposits has been constrained between 1.78 Ga and 1.77 Ga and linked to post-collisional Juruena arc felsic magmatism (e.g., Colíder and Teles Pires suites). The Transamazonas Province corresponds to a N–S-trending orogenic belt, consolidated during the Transamazonian cycle (2.26–1.95 Ga), comprising the Lourenço, Amapá, Carecuru, Bacajá, and Santana do Araguaia tectonic domains. They show a protracted tectonic evolution, and are host to the pre-, syn-, and post-orogenic to anorogenic granitic magmatism. Gold mineralization associated with magmatic events is still unclear. Greisen and pegmatite Sn–Nb–Ta deposits are related to 1.84 to 1.75 Ga late-orogenic to anorogenic A-type granites. The Pitinga Tin Province includes the Madeira Sn–Nb–Ta–F deposit, Sn-greisens and Sn-episyenites. These are associated with A-type granites of the Madeira Suite (1.84–1.82 Ga), which occur within a cauldron complex (Iricoumé Group). The A-type magmatism evolved from a post-collisional extension, towards a within-plate setting. The hydrothermal processes (400 °C–100 °C) resulted in albitization and formation of disseminated cryolite, pyrochlore columbitization, and formation of a massive cryolite deposit in the core of the Madeira deposit. The Rondônia Tin Province hosts rare-metal (Ta, Nb, Be) and Sn–W mineralization, which is associated with the São Lourenço-Caripunas (1.31–1.30 Ga), related to the post-collisional stage of the Rondônia San Ignácio Province (1.56–1.30 Ga), and to the Santa Clara (1.08–1.07 Ga) and Younger Granites of Rondônia (0.99–0.97 Ga) A-type granites. The latter are linked to the evolution of the Sunsás-Aguapeí Province (1.20–0.95 Ga). Rare-metal polymetallic deposits are associated with late stage peraluminous granites, mainly as greisen, quartz vein, and pegmatite types.

In situ analyses of micas in the Yashan granite, South China: Constraints on magmatic and hydrothermal evolutions of W and Ta–Nb bearing granites

Most rare-metal granites in South China host major W deposits with few or without Ta–Nb mineralization. However, the Yashan granitic pluton, located in the Yichun area of western Jiangxi province, South China, hosts a major Nb–Ta deposit with minor W mineralization. It is thus important for understanding the diversity of W and Nb–Ta mineralization associated with rare-metal granites. The Yashan pluton consists of multi-stage intrusive units, including the protolithionite (-muscovite) granite, Li-mica granite and topaz–lepidolite granite from the early to late stages. Bulk-rock REE contents and La/Yb ratios decrease from protolithionite granite to Li-mica granite to topaz–lepidolite granite, suggesting the dominant plagioclase fractionation. This variation, together with increasing Li, Rb, Cs and Ta but decreasing Nb/Ta and Zr/Hf ratios, is consistent with the magmatic evolution. In the Yashan pluton, micas are protolithionite, muscovite, Li-mica and lepidolite, and zircons show wide concentration ranges of ZrO2, HfO2, UO2, ThO2, Y2O3 and P2O5. Compositional variations of minerals, such as increasing F, Rb and Li in mica and increasing Hf, U and P in zircon are also in concert with the magmatic evolution from protolithionite granite to Li-mica granite to topaz–lepidolite granite. The most evolved topaz–lepidolite granite has the highest bulk-rock Li, Rb, Cs, F and P contents, consistent with the highest contents of these elements and the lowest Nb/Ta ratio in mica and the lowest Zr/Hf ratio in zircon. Ta–Nb enrichment was closely related to the enrichment of volatile elements (i.e. Li, F and P) in the melt during magmatic evolution, which raised the proportion of non-bridging oxygens (NBOs) in the melt. The rims of zoned micas in the Li-mica and topaz–lepidolite granites contain lower Rb, Cs, Nb and Ta and much lower F and W than the cores and/or mantles, indicating an exotic aqueous fluid during hydrothermal evolution. Some columbite-group minerals may have formed from exotic aqueous fluids which were originally depleted in F, Rb, Cs, Nb, Ta and W, but such fluids were not responsible for Ta–Nb enrichment in the Yashan granite. The interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching, concentrating and transporting W, Fe and Ti. Ta–Nb enrichment was associated with highly evolved magmas, but W mineralization is closely related to hydrothermal fluid. Thus these magmatic and hydrothermal processes explain the diversity of W and Ta–Nb mineralizations in the rare-metal granites.

In situ U–Pb isotopic dating of columbite–tantalite by LA–ICP–MS

Columbite–tantalite (Coltan) is the most important niobium (Nb)- and tantalum (Ta)-bearing economic mineral, commonly occurring in rare metal granite and pegmatite, alkaline granite, syenite and carbonatite. Its high U but low common Pb contents make it an ideal mineral for U–Pb isotopic dating of Nb–Ta mineralization. In order to establish a feasible coltan dating method by in situ laser-ablation (LA) ICP–MS, we determined the U–Pb ages of five coltan samples from different pegmatites and rare-metal granites in China. In order to evaluate the potential matrix effect between different minerals, a 91500 zircon was used as external standard during analyses. The results show that, compared to the recommended ages, approximately 7–15% younger ages were yielded for the analyzed coltan samples in both single spot and line raster scan analytical methods, indicating a significant matrix effect between coltan and zircon. However, by using a coltan standard from Namibia (Coltan139), the coltan sample from Dahe pegmatite (SNNT) has a weighted mean 206Pb/238U age of 363±4Ma (2σ, n=25) and 357±5Ma (2σ, n=20) in single spot and line raster scan analytical methods, respectively; the coltan samples from Altai No.3 pegmatite (713-79), Yichun topaz-lepidolite granite (Yi-1) and Huangshan albite granite (LS-15) have weighted mean 206Pb/238U ages of 218±2Ma (2σ, n=20), 160±1Ma (2σ, n=20) and 130±1Ma (2σ, n=20), respectively, in single spot mode. These ages agree well with the previously published data, and hence support the reliability of our analytical method. Although the analyzed coltan minerals show a large variation of chemical compositions, no significant matrix effect was observed, which suggests that a coltan material should be used as an external standard for U–Pb dating of coltan by LA–ICP–MS. Using the established analytical protocol, we date the Nanping pegmatite (NP155), a main Nb–Ta deposit in China without known age, and obtain a weighted mean 206Pb/238U age of 391±4Ma (2σ, n=20), which is considered as the best estimation of Nb–Ta mineralization time in the area.

Analysis on the Metallogenic Conditions and Perspective of Nb-Ta Mineral in ZhaoJinggou, Inner Mongolia

ZhaoJinggou Nb-Ta deposit was discovered in 1967.After a series of exploration, a summary report of preliminary exploration of ZhaoJinggou Nb-Ta deposit was submitted. The detail exploration was carried out in this mineral aera in 2010.The deposit was sited in the middle part of the northern margin of north China platform, YinShan lifted block and north wing of Daqingshan anticlinorium. A series of metamorphose rocks of Proterozoic to Neoproterozoic were widely distributed in this area. Nb-Ta veins intruded into the structural fissure of dark grey pebbled metamorphic sandstone of Middle Carboniferous Shuanmazhuang Formation. Through verification of deep drilling, it exsited a larger decalcified feldspathized granodiorites and albite granites, which had a relationship with the formation of these veins. The intensity of albitization determined the grade of Nb-Ta minerals.And albitization caused the richment of other rare elements, which had a comprehensive utilization value. Based on the detailed exploration, the Zhaojinggou deposit should have a good mineralize perspective, which may exist the large alkaline albite lithium mica granite Nb-Ta deposits in deep or outer-ring of mining area.

U–Pb dating of the Madeira Suite and structural control of the albite-enriched granite at Pitinga (Amazonia, Brazil): Evolution of the A-type magmatism and implications for the genesis of the Madeira Sn–Ta–Nb (REE, cryolite) world-class deposit

The Madeira Sn–Nb–Ta deposit corresponds to the albite-enriched facies of Madeira granite (Madeira Suite) that is part of a NE–SW alignment of three granitic bodies. Structural analyses suggest that the albite-enriched granite emplacement and development of related structures occurred in a different tectonic setting than earlier facies of the granitic bodies in the NE–SW alignment and that the structure was dominated by a N-NE-trending shortening related to a left-lateral motion along a NE–SW corridor within a Riedel shear. Three types of structures (flat-lying, near vertical fractures, and geodes/miaroles) concentrated the last magmatic-related fluid in the albite-enriched granite. U–Pb in situ zircon dating of the albite-enriched granite yielded an age of 1822±22Ma. The other granitic plutons of the Madeira Suite, Água Boa granite (topaz-granite facies), and Europa per-alkaline granite formed at 1825±14Ma, 1831±11Ma, and 1839±10Ma, respectively. The granite bodies of the Madeira Suite occur in an area occupied by a cauldron complex composed of volcanic sequences (Iricoumé Group) and associated A-type granites (Mapuera Suite), and their formation was controlled by the reactivation of the cauldron structures and the pre-existing structures. The gap between the cauldron complex and the Madeira Suite is no greater than 35Ma. The geological evolution was reanalyzed from the perspective of an entire extensional environment where three successive episodes of A-type magmatism and basin formation (Urupi Formation) occurred. The data and interpretations of this work imply crucial constraints on the petrologic models proposed for the albite-enriched granite and, consequently, on the genesis of the Madeira deposit.

An assessment of a handheld X-ray fluorescence instrument for use in exploration and development with an emphasis on REEs and related specialty metals

Handheld (portable) X-ray fluorescence (pXRF) instruments are designed for use in the exploration for base metals, precious metals, and specialty metals (e.g. rare earth elements (REE), Ta, and Nb) and allow rapid decision-making directly in the field. This paper evaluates the technical merits and limitations of pXRF technology in the exploration for specialty metals using data generated from the analysis of three geochemical standards and a silica blank: Standard Reference Material NIST 2780 from the National Institute of Standards and Technology, Gaithersburg; the Certified Reference Material “TRLK” Rare Earth Ore “CGL 124” from the Mongolia Central Geological Laboratory; the Reference Niobium Ore OKA-1 (CANMET); and a silica blank described as Si (IV) oxide (99.8 % on metal basis) from Alpha Aesar (Ward Hill, MA, USA). The data was acquired over a period of nearly 2 years as a by-product of several distinct specialty metal-related projects using the same pXRF instrument and the same settings. Instrumental analytical accuracy was determined using the percent difference (%diff) between the average concentrations of the pXRF instrument readings and the reported certified values of the standard. Percent relative standard deviation (%RSD) was used as a measure of precision. Smaller %diff and %RSD indicate more accurate and precise data, and the accuracy and precision of the pXRF depended strongly on the elemental concentrations in the standards used. Box and whisker diagrams were used to illustrate characteristics of pXRF data sets (mean, lower and upper quartiles, and range) corresponding to individual standards. The bias of the pXRF determinations (under/overestimation) relative to certified values of individual standards are also depicted on these diagrams. This study indicates that the pXRF was capable of producing readings for Si, K, Al, Fe, Ca, Ti, Pb, Zn, Sr, Ag, Cd, Th, Sb, P, S, Mo, Mn, Mg, As, Nb, Rb, La, Ce, Pr, Nd, and Y within 10 %RSD of the reported certified value in at least one of the three standards measured, depending on the concentrations within that standard. The instrument was able to provide relatively accurate and precise data for Nd, Pr, Ce, La, and Y (%diff, ≤17; %RSD, ≤3.7) when the concentrations were greater than 1,000 ppm (e.g., rare earth ore CGL 124). It generated lower quality data (in terms of %diff and %RSD) when concentrations of these elements were in the hundreds parts per million range or lower (NIST 2780). As for Nb, the best %RSD (2.2) was obtained on the Nb Ore OKA-1 with an accompanying %diff of 34. This indicates that the instrument is suitable for use in the exploration and development of carbonatite-related REE deposits such as: Mountain Pass (California), Bayan Obo (Inner Mongolia), Wicheeda Lake (British Columbia), St Honore, Oka, and Eldor (Quebec). By extension, the instrument is also suitable for the exploration of apatite–monazite veins (Steenkampskraal) and peralkaline intrusion-related deposits such as Kipawa, Nechalacho (Northwest Territories), or Strange Lake (Quebec; Labrador, Newfoundland). A pXRF without a radioactive source cannot be used to analyze for most of the heavy lanthanides; however, Y can be used as a pathfinder for these elements. Limited but effective use of the pXRF in exploration for ion adsorption clay deposits with grades as low as 500 ppm total REE appears possible. The pXRF could also be used in the exploration for carbonatite-related Nb-bearing deposits such as St Honore (Quebec) and Aley (British Columbia), or in the exploration for lower-grade Nb–Ta deposits such as Upper Fir (British Columbia), justifying the need for future case studies.

Study of a series of Ta-minerals in Dajishan W–Nb–Ta Deposit, South China

Study of a series of Ta-minerals in Dajishan W–Nb–Ta Deposit, South China