Mineralization In South China Research Articles

Petrogenesis and REE mineralogical characteristics of Shitouping granites in southern Jiangxi Province: Implication for HREE mineralization in South China

The enrichment of heavy rare earth elements (HREE) in the granitic host-rocks is crucial for generating ion-adsorption HREE deposits in South China. The Shitouping pluton, located in the southern part of Jiangxi Province, South China, develops large-scale HREE deposits in its weathering profile identified by recent geological surveys. These granites can be divided into medium to coarse-grained biotite monzogranite (MGBG), medium to coarse-grained syenogranite (MGSG) and fine-grained alkali feldspar granite (FGAG) based on field observations and mineral assemblages. New geochronologic results show that this composite pluton intruded during the Early Cretaceous (ca. 140 Ma). Three granitic units displaying comparable whole-rock Nd [εNd(t) = −4.5 to −3.4] and zircon Hf compositions [εHf(t) = −4.4 to +1.2], combined with mineral association, hydrothermally altered zircon and whole-rock geochemistry, indicate they were derived from partial melting of hybridized crustal source, followed by intense fractional crystallization and fluid metasomatism in the highly evolved granitic system. The MGSG and FGAG have higher Rb, Nb, HREE contents and Rb/Sr ratios, as well as lower Nb/Ta, K/Rb ratios in comparison with the MGBG, implying they are more evolved units. The overlapping magmatic zircon trace element compositions between MGBG and MGSG, coupled with the subvertical contact boundary between the FGAG and the MGBG, suggest that the generation of Shitouping pluton should be attributed to the periodic magma replenishment, remobilization, and differentiation process in the long-lived magmatic system rather than simple fractional crystallization from a single parental magma. Hydrothermally altered zircon with elevated concentration of HREE and the paragenetic relationship between LREE-phosphate and HREE minerals in the MGSG suggest that the fluid metasomatism promotes the migration and accumulation of HREE. This is consistent with the high HREE concentration recorded in the MGSG, which contains abundant HREE minerals associated with fluorites. Thus, this study highlights that magma differentiation and fluid metasomatism during the late magmatic stage could achieve the relatively high HREE contents in granites to favor the formation of ion-adsorption HREE deposits.

Deeply Derived Magma Controlling the Polymetallic Mineralization at Shuikoushan, South China: Constraints from Mineral U–Pb Dating and Whole-Rock Geochemistry

Various magmatic–hydrothermal activities have resulted in different styles of polymetallic mineralization in South China. Shuikoushan is a large Fe-Cu-Pb-Zn-Au-Ag orefield situated in fold-and-thrust belts within the South China Block. Two types of granodiorite have been identified in recent drilling work. The early-stage, coarse-grained granodiorite has developed magnetite-bearing skarns in the deep level. The late-stage, fine-grained granodiorite is associated with garnet-hematite–magnetite–pyrite–sphalerite–chalcopyrite-bearing skarns in its contact zone. Away from the garnet-bearing skarn are calcite–quartz–pyrite–sphalerite–galena veinlets in faulted breccia. Fieldwork has identified iron mineralization in both skarns, whereas copper mineralization was only discovered in the garnet-bearing skarns. Lead, zinc, gold, and silver mineralization were observed in the garnet-bearing skarns and faulted breccia. Zircon U–Pb analyses suggested the emplacement of two granodiorite at 167.8 ± 0.8 Ma (MSWD = 1.1, N = 31) and 163.6 ± 0.7 Ma (MSWD = 1.3, N = 32). Apatite and garnet U–Pb dating further indicated the magnetite-bearing skarns of 166.2 ± 1.9 Ma (MSWD = 4.5, N = 27), the hematite–magnetite–sulfide-bearing skarns of 158.6 ± 2.8 Ma (MSWD = 1.3, N = 34), and the calcite–quartz–sulfide veinlets of 159.5 ± 5.2 Ma (MSWD = 1.7, N = 24). The time–space relationship between the two intrusions and hydrothermal activities suggests that the fine-grained granodiorite is responsible for polymetallic mineralization. Whole-rock geochemistry analyses demonstrated the enrichment of LILEs and the depletion of Nb and Ta in two granodiorites, with a slight enrichment in LREEs and flat HREE patterns. These granodiorite bodies therefore belong to high-K calc-alkaline magma generated via the crust’s partial melting. The fine-grained granodiorite generally has a lower HREE and higher Dy/Yb, Sr/Y ratios than coarse-grained granodiorite, corresponding to the source of magma in garnet stable lower crust. The residual garnet keeps ferric iron in melts, leaving the fine-granodiorite more oxidized for copper and gold concentration. Through these analyses and our drilling work, a continuous skarn–hydrothermal–epithermal system has been identified for Cu-Pb-Zn-Au-Ag targeting in Shuikoushan.

New Insights into the Mesozoic Large‐scale Intra‐plate Magmatism and Mineralization in South China from Seismic Tomography

AbstractA great amount of new S‐wave data has been combined to image the mantle structure down to lower mantle depth near the southeastern margin of Eurasia and understand the tectonics in South China since the Mesozoic. Our results reveal a large‐scale structure beneath the South China Sea, with a prominent, broad low‐velocity feature of at least 1500‐km wide in and below the mantle transition zone (MTZ) and a pronounced low‐velocity feature of nearly 500‐km wide in the lowermost mantle. Together these features may represent the head‐and‐tail of an upwelling mantle plume that has interacted with and deformed by the subducting plates in the region. The Andaman–Sumatra plate is seen subducting steeply without stagnation in the MTZ over the large‐scale low‐velocity structure, suggesting that the upwelling mantle may have exerted significant influence on the overlying plate tectonics. Our results suggest a long‐term extensional regime near the southeastern margin of Eurasia, which may help to understand the formation of the large‐scale intra‐plate magmatism and mineralization with accumulation of huge amount of rare metal elements in South China during the Mesozoic, and the continental breakup, the southeastward extrusion of Indochina, and the opening of the South China Sea during the Cenozoic.

Origins and chemical evolution of hydrothermal fluids in the Shazhou volcanic-related type U deposit at the Xiangshan district, South China: New insights from LA-ICP-MS analysis of fluid inclusions

The volcanic-related type U mineralization in South China has been associated with the crustal extension occurred since the late Cretaceous. Uranium deposits of this type are spatially related to the Cretaceous red-bed basins and synchronous mafic magmatism. However, the contribution of basinal brines or mantle-derived fluids to the U mineralization is not well understood. This study examines the role of different hydrothermal fluids involved in the U mineralization process and traces their sources by using LA-ICP-MS analysis of fluid inclusions from the Shazhou deposit in the Xiangshan district, which is one of the largest volcanic-related type U ore-fields in the world. Two types of fluids were involved in the U mineralization process. One fluid was of higher salinity, enriched in U, Mo, and Cl, such that having low Br/Cl (0.3–1.0 × 10-3) similar to the basinal brines sourced from meteoric water. The other fluid was of lower salinity, enriched in Th and Sr, yet depleted in U and Mo, with Br/Cl ratios of 1.5–2.5 × 10-3, overlapping the range of mantle-derived fluids associated with the mafic dikes intruded into the felsic wall rocks at the U mineralization age. The high-U fluid and the low-U fluid also show distinct Rb/Na, K/Na, and Rb/Cs, indicating their respective origins of basinal brines and mantle-related fluids. The chemical variation of ore-forming fluids at the Shazhou deposit was comparable to the scenario at the Zoujiashan deposit, as reported in previous studies, suggesting similar fluid evolution history related to U mineralization in the west and the north of the Xiangshan U orefield. Our study suggests in situ analysis of Br/Cl of fluid inclusions can be a useful proxy to discriminate multiple hydrothermal fluids associated with volcanic-related type U mineralization in South China and to individually trace their origins.

Early Cretaceous tectonic transition in South China: Insights from felsic igneous rocks and mafic dikes, eastern Guangdong Province

Large‐scale magmatic activity and associated mineralization in South China are linked to the subduction of the palaeo‐Pacific Plate, although specific processes have remained controversial including the timing of subduction initiation and lithospheric extension. We present new geochemical data and zircon U–Pb and Lu–Hf isotope measurements on volcanic rocks, granites and mafic dikes from coastal south‐eastern China along the Eurasian continental margin. The biotite monzogranites show I–type granitoid affinity and fractional crystallization with zircon εHf(t) values ranging from −10.15 to +0.50, suggesting magma derivation from the melting of lower crust with the addition of juvenile crustal or mantle components. The biotite granites are typical of highly fractionated A‐type granites with εHf(t) values ranging from −3.63 to +1.35, indicating magma hybridization between anatectic granitic and mantle‐derived mafic magmas. The diabase dikes have zircon εHf(t) values ranging from −2.99 to +1.71, with high La/Nb and La/Ta ratios. This suggests derivation from partial melting of a lithospheric mantle metasomatized by fluid from a subducting–slab, with contributions of depleted asthenospheric mantle components. Our data, combined with those from previous studies, suggest that the shallow subduction of the palaeo–Pacific Plate beneath the Eurasian continent had begun by ca. ~170 Ma at least and the subduction orientation changed to oblique with respect to the continental margin. Steepening of the subduction angle likely caused a slab rollback during the Early Cretaceous, resulting in a tectonic transition from compression to extension in South China at ca. 145 Ma.

Tungsten and tin deposits in South China: Temporal and spatial distribution, metallogenic models and prospecting directions

South China is one of the most important tungsten-tin metallogenic areas in the world. Based on the up-to-date geological and chronological data of more than 130 deposits of economic significance, this paper preliminarily summarized the main types and temporal-spatial distribution characteristics of the large-scale tungsten and tin mineralization related to granite in South China. The statistical results show that skarn and quartz-vein types are the most important tungsten metallogenic styles, while skarn and cassiterite-sulfide types are the most important tin metallogenic styles in South China. Tungsten and tin mineralization related to granite in South China are multi-aged, but the largest scale of mineralization is developed within the Yanshanian period. Tungsten mineralization, the majority of which represented by the Nanling and Ganbei metallogenic belts, mainly formed from the Late Jurassic to Early Cretaceous (160 ∼ 120 Ma), while the most important tin mineralization formed in the Late Cretaceous (110 ∼ 80 Ma, peaking at 90 ∼ 80 Ma) and Late Jurassic (160 ∼ 150 Ma) as represented by the Youjiang Basin and Nanling metallogenic belt, respectively. The combined occurrence of different mineralization styles or metal assemblages in individual deposit and sometimes within the same orefield is the most striking feature of granite-related tungsten-tin deposits in South China, and a comprehensive understanding of their patterns are of great significance to guide ore prospecting. To address this issue, this paper proposed several combined metallogenic models and prospecting directions for tungsten-tin mineralization in South China based on recent researches and exploration progresses from typical examples including the Yaogangxian, Chuankou, Maoping, Shizhuyuan, Dachang and Gejiu deposits or orefields. In addition, conventional petrological and mineralogical characteristics that differentiates tungsten and tin granites are summarized, and on this basis the chemical composition of both melt inclusion and early stage fluid inclusion from granitic magmatic-hydrothermal systems were tested as new index to evaluate the tungsten and tin mineralization potential of granitic system.

Early Yanshanian metallogenesis of the Banjing tungsten deposit in Ganxian, Jiangxi province, China: Constraints from geochemistry, Sr–Nd isotopes, zircon U–Pb, molybdenite Re–Os, and mica 40Ar–39Ar dating

The Banjing tungsten deposit, which has been discovered recently, is located in the northernmost part of the Dabu pluton, southern Jiangxi Province, China. In this study, zircon LA‐ICP‐MS U–Pb dating of the fine‐grained porphyritic biotite granite indicate that it was formed in the early Yanshanian (159.4 ± 2.5 Ma–161.6 ± 0.8 Ma). Whole‐rock geochemical studies have shown the fine‐grained porphyritic biotite granite has SiO2 of 75.82%–76.84%, Al2O3 12.50%–12.87%, MgO 0.07%–0.20%, and CaO 0.64%–1.09%, with A/CNK of 1.017–1.038. It has a total rare earth elements content of 93.9–118.9 ppm with strong negative Eu anomalies (δEu = 0.021–0.081). The biotite granite is enriched in Rb, Th, U, Nd and depleted in Ba, Sr, Nb, Ti. These data suggest the Dabu pluton belongs to S‐type granite. This pluton has ISr of 0.71212–0.72929 and εNd(t) from −9.60 to −10.62 with Nd model ages concentrated in 1732–1838 Ma. These isotopic data in combination with zircon Hf isotopes suggest the biotite granite originated from partial melting of the Middle Proterozoic metamorphic supracrustal rocks in South China, with a minor contribution from juvenile crust. Meanwhile, this study has obtained Re–Os isochron ages of the intrusion‐related and quartz vein‐type molybdenum mineralization are 156.3 ± 2.7 Ma and 157.0 ± 1.1 Ma in the Banjing tungsten deposit, respectively. Sericite from the greisen‐type tungsten‐molybdenum ore has an 40Ar–39Ar plateau age of 156.4 ± 1.0 Ma, interpreted as the formation age of this deposit. Collectively, the Banjing tungsten deposit is considered as a product of the early Yanshanian large‐scale peak mineralization in South China, which was formed in an extensional intracontinental environment caused by the subduction of the Palaeo‐Pacific Plate.

Early Paleozoic tin mineralization in South China: Geology, geochronology and geochemistry of the Lijia tin deposit in the Miaoershan-Yuechengling composite batholith

Early Paleozoic Sn mineralization is rarely reported in South China. Here we carried out the detailed studies of deposit geology, cassiterite U-Pb dating, muscovite geochemistry and H-O isotopes on the Early Paleozoic Lijia Sn deposit in South China to constrain its genesis. The Lijia Sn deposit is hosted in the Yuechengling granitic batholith and characterized by greisen-type and quartz vein-type mineralization. Four stages of alteration and veining are recognized according to mineral assemblages and crosscutting relationships: pre-ore tourmalinization and silicification alteration of the Lijia granite (stage I), cassiterite-tourmaline-quartz vein and associated cassiterite greisen (stage II), and post-ore calcite-quartz-fluorite vein and calcite veinlet (stage III and IV, respectively). Two generations of the cassiterite in the cassiterite greisen, identified by cathodoluminescence imaging, yield the U-Pb concordant ages of 430.5 ± 3.7 Ma and 428 ± 2.2 Ma, respectively. The zircon U-Pb ages and geochemical features of the Lijia granite as well as the characteristics of alteration and mineralization indicate that the Lijia granite is Sn-bearing one and brings about the Sn mineralization. H-O isotopic compositions of the quartz from the Lijia granite reveal that the magmatic fluids have the δ18O values of 10.6–10.7‰ and the δD values of −57‰ to −62‰. The ore-forming fluids (δ18O 6.5–7.4‰, δD −64‰ to −69‰) responsible for cassiterite precipitation are derived from the mixing of magmatic fluids with minor meteoric water whereas more meteoric water is involved in the post-ore calcite-quartz-fluorite vein stage. Based on mineral assemblages, internal textures and chemical compositions, muscovite is divided into four generations from early to late: the Mus 1 and Mus 2 in the cassiterite greisen, the Mus 3 in the cassiterite-tourmaline-quartz vein and the Mus 4 in the phyllic alteration in the stage III. From the Mus 1 to the Mus 3, muscovite Rb, Cs, Zn, Li, V, Sc and Ga contents gradually decrease whereas boron shows an increasing trend, which might have been caused by the successive precipitation of hydrothermal minerals such as muscovite. Significantly higher Sr and Ba contents of the Mus 2 than the Mus 1 are likely related to the decomposition of the K-feldspar and plagioclase in the host granite. The combination of the precipitation of the early mineral phases, the decomposition of K-feldspar and the involvement of a large amount of meteoric water gives rise to the decrease of W, Sn, B, Rb, Cs and Sr contents and the increase of Ba, Ti, Mg, Li, Sc, V, Cr, Ga, Nb and Ta contents of the Mus 4 in the stage III. A key mechanism responsible for the formation of the Lijia Sn deposit is the interaction between the ore-forming fluids and the host granite. This study confirms the Early Paleozoic tin mineralization event in South China.

Zircon U-Pb and muscovite 40Ar/39Ar dating of Pb-Zn-(Cu) polymetallic deposits in northeastern Hunan Province, Jiangnan Orogen: Evidence for large-scale mineralization in South China at ca. 150–120 Ma

The Jiangnan Orogen is located between the Yangtze and Cathaysia blocks, and hosts abundant Au, Sb, W, Cu, Pb, Zn, Ag, and Ta-Nb-(Li-Be) deposits. Among these, both the Taolin and Lishan Pb-Zn-(Cu) polymetallic deposits in northeastern Hunan Province are large Pb-Zn deposits, which are located at the northwestern and southern margins of the Late Jurassic to Early Cretaceous Dayunshan-Mufushan composite pluton, respectively. However, the mineralization ages of these deposits remain controversial and poorly constrained. In this study, muscovite 40Ar/39Ar dating of the Taolin and Lishan deposits along with zircon U-Pb dating and geochemical analysis of the Dayunshan-Mufushan composite pluton were undertaken to constrain the age and nature of the Late Jurassic to Early Cretaceous magmatism and related mineralization in South China. Zircon U-Pb dating of the biotite monzogranite and two-mica monzogranite yielded emplacement ages of ca. 149 and 145–136 Ma, respectively. Muscovite from the ore-bearing granitic pegmatites in both the Taolin and Lishan deposits yielded well-defined 40Ar/39Ar ages of ca. 121 and 129 Ma, respectively. These results and previously published data indicate that the Dayunshan-Mufushan composite pluton was emplaced in several stages at ca. 154–148, 146–137, and 136–127 Ma, and experienced associated, multi-stage, granitic pegmatite magmatism at ca. 142, 131, and 125–120 Ma. Two mineralization events occurred at ca. 141–136 and 133–120 Ma in the Pb-Zn-(Cu-Co-Mo), Ta-Nb-Li-Be, and Au deposits in northeastern Hunan Province, including the Dayunshan-Mufushan region. Zircons from the Dayunshan-Mufushan composite pluton record low oxygen fugacity (ƒO2) conditions, indicating the pluton was likely responsible for the large-scale Pb-Zn mineralization.In addition to the 170–160, 160–150, and 120–80 Ma mineralization events, the Late Jurassic to Early Cretaceous (ca. 150–120 Ma) was also an important period of mineralization in South China. This mineralization was likely initiated by Middle Jurassic to Early Cretaceous extension associated with subduction, subsequent slab rollback, and possible break-off of the Paleo-Pacific plate, which led to lithospheric collapse and thinning.

HREE enrichment during magmatic evolution recorded by apatite: Implication for the ion-adsorption HREE mineralization in South China

Understanding the enrichment of heavy rare earth elements (HREE) and high HREE/LREE (light REE) ratios in the granites is critical to understand the ore-genesis of exclusive ion-adsorption HREE deposits in South China. In this study, we conducted geochronological, whole-rock and apatite geochemical, and isotopic studies on the Xinfeng pluton, of which only parts show high HREE/LREE ratios and are ore-related. Both the ore-related granite and ore-unrelated granite from the Xinfeng pluton are characterized by high SiO2 contents, the same Late Jurassic age (ca. 155 Ma), and enriched Nd isotopic compositions. However, the ore-related granite has lower TiO2, CaO, P2O5, Fe2O3, Ba, Sr, Eu, and LREE contents, lower La/Yb, Zr/Hf and Th/U ratios, higher Rb, Cs, Nb, Ta, Pb, and HREE contents, and higher Rb/Sr ratios than the ore-unrelated granite. These features indicate that the ore-unrelated and ore-related granite are cogenetic and their geochemical differences can be explained by magmatic differentiation. The primary igneous apatite from both the ore-unrelated granite and ore-related granite shows negligible hydrothermal alteration. Fractional crystallization of feldspar (∼20%) and allanite (< 0.3%) led to higher HREE contents and HREE/LREE ratios, lower Sr contents, and a more pronounced negative Eu anomaly in the apatite from the ore-related granite. This study highlights that the magma evolution via mineral fractional crystallization could achieve the relatively high HREE contents and HREE/LREE ratios in the granites, and favors the formation of exclusive ion-adsorption HREE deposits in South China.

The deep background of large-scale, Mesozoic Cu-Au-W metallogenesis in northeastern South China: Constraints from Yingshan-Changshan wide-angle seismic reflection/refraction data

To investigate the geodynamic processes of Mesozoic large-scale mineralization in South China, we deployed a 350-km-long, wide-angle seismic reflection/refraction sounding profile between Yingshan in Hubei and Changshan in Zhejiang. This profile traverses the Cu-Au metallogenic belt in the middle and lower reaches of the Yangtze River (YMB), the Jiangnan W-polymetal metallogenic belt (JNMB), and the Qinhang Cu-polymetal metallogenic belt (QHMB). Our imaging results reveal various interesting velocity features along the profile. (1) The velocity structure is characterized by vertical layering and horizontal blocking; (2) the YMB is marked by high velocity and high Vp/Vs ratios in general with a significantly uplifted Moho interface and a thin crust of ∼31 km, and the lower crust contains high-velocity anomalies and has the characteristics of a crust-mantle transition zone; (3) the JNMB is bounded by the Jiangnan fault and Jingdezhen-Huangshan fault and has low-velocity anomalies and low Vp/Vs ratios; and (4) the QHMB is characterized by high-velocity anomalies and high Vp/Vs ratios. The high-velocity anomalies in the YMB and QHMB represent relatively Cu-Au-rich mafic juvenile lower crust. The formation of this kind of crust is considered to be related to mantle-derived magma underplating or residues of Neoproterozoic oceanic crustal materials, and it also provided sources for large-scale Cu-Au mineralization in the Mesozoic. The JNMB has features similar to those of ancient crusts enriched in W-Sn, the partial melting of which played a leading role in the formation of the superlarge W deposits in this belt. Considering these results and other regional geological data, we propose that a large-scale oblique upwelling of the asthenosphere along the collisional belt of the Yangtze and Cathaysia blocks during the Mesozoic was the deep driving mechanism for the explosive mineralization of Cu, Au, and W in northeastern South China. The boundaries of the blocks or terrains and discontinuities of the lithosphere were the main channels for deep heat and magmas and therefore controlled the spatial distribution of the metallogenic belt.

Geochronology and Geochemistry of the Xianghualing Granitic Rocks: Insights into Multi-Stage Sn-Polymetallic Mineralization in South China

Multi-stage magmatic events associated with large tungsten-tin polymetallic deposits in the Nanling Range have been the subject of extensive research spanning many years. In this paper we report the results of a systematic study of the petrology, whole-rock geochemistry, zircon U-Pb chronology, and trace element geochemistry of granite bodies exposed in the Xianghualing ore field. They show that the granites in the study area are characterized by high SiO2 (63.83%–75.29%), Al2O3 (13.12%–18.87%), Rb (565–3260 ppm), Nd (67.3–113.5 ppm) and Ta (23.2–129.0 ppm) and by low MgO (0.02%–0.22%), TiO2 (0%–0.02%), Sr (5.3–80.5 ppm) and Ba (7.9–66.4 ppm). The rocks are highly differentiated A-type peraluminous granite, which originated in an extensional within-plate tectonic setting. Based on U-Pb dating and trace element analysis, the following multi-stage magma-hydrothermal events were identified: (1) Paleozoic (~347 Ma) and Triassic (~206 Ma) magmatic stages (initial enrichment epochs of ore-forming elements), (2) Jurassic (~161 Ma) magmatic-hydrothermal stage (mineralization epoch), and (3) Cretaceous hydrothermal overprinting stage (with peaks in the Early Cretaceous ~120 Ma and Late Cretaceous ~80 Ma). From an economic point of view, the Late Cretaceous appears to have great potential for tungsten-tin mineralization. Zircon trace element geochemistry indicates that the ore-forming fluids related to tin mineralization in the Cretaceous originated from the crust and underwent highly differentiated evolutionary processes under relatively reducing conditions. This paper emphasizes the Cretaceous tungsten-tin metallogenic events in the Nanling Range and provides an essential basis and new ideas for further tin-tungsten exploration.

In situ elemental and Sr-Nd isotopic compositions of hydrothermal apatite from the Shazhou U deposit in the Xiangshan complex: Implications for the origins of ore-forming fluids of volcanic related U deposits in South China

• In situ Sr-Nd isotopes of apatite are effective in tracing origins of ore forming fluids in the Shazhou U deposit. • The reducing U-poor fluid was derived from mantle-derived magma which formed the mafic dikes in wall rocks. • The oxidizing U-rich fluid originated from percolation of meteoric water in the adjacent red-bed basins. • The Late Cretaceous mafic magmatism and red-bed basins are two key factors controlling U mineralization in South China. The origin of ore-forming fluids of volcanic related U deposits remains controversial. This study reports in situ elemental and Sr-Nd isotopic compositions of apatite associated with U mineralization from the Shazhou volcanic related U deposit in South China, which provides a new perspective to constrain the origin and evolution of its ore-forming fluids. Hydrothermal apatites from the hematized rocks and U-mineralized rocks show distinct textures and chemical features, indicating two types of fluids involved in the U mineralization process. The hematitization fluid was oxidizing and enriched in U and Cl. A reducing fluid with lower Cl/F and U was introduced and mixed with the oxidizing hematitization fluid to cause U precipitation. Apatite from the hematized rocks has a lower 87 Sr/ 86 Sr (0.709246–0.714383) than that of apatite in U ore veins (0.710383–0.719318). The εNd(t) of apatite in the hematized rocks is from −7.6 to −9.4, whereas apatite in U ore veins has higher εNd(t) ranging from −1.2 to −8.4, close to that of mafic dikes intruded into the volcanic rocks. In situ Sr-Nd isotopes of apatite indicate the oxidizing fluid originated from the red-bed basins, whilst the origin of the reducing fluid was related to the mantle-derived mafic dikes. The reducing fluid has experienced assimilation by the metamorphic basement rocks to gain higher radiogenic strontium. This study demonstrates that in situ elemental and Sr-Nd isotopic compositions of apatite are effective in identifying different ore-forming hydrothermal fluids and constraining their origins and chemical evolution.

The Jurassic Gangmei Mo-W deposit in Guangdong Province and its implication for Mo-W mineralization in South China

South China developed large-scale Mesozoic magmatism and polymetallic mineralization, especially Jurassic W-Sn and Mo-W mineralization. Compared with W-Sn deposits, Mo-W deposits in South China have received less attention. The recently discovered Gangmei Mo-W deposit, which occurred in Guangdong Province, is the southernmost Jurassic Mo-W mineralization in South China. Here, we report the molybdenite Re-Os isotopic age of the Gangmei deposit and compile the Mo-W- and W-Sn-associated deposits in South China and their Re concentrations in molybdenites, aiming at constraining the ore-forming age of the Gangmei deposit, the scope of Mo-W mineralization in South China and the possible controlling factors of different mineralization types. Four molybdenite samples from the Gangmei deposit were chosen for Re-Os isotopic dating. The Re-Os model ages vary from 162.6 ± 1.6 Ma to 164.1 ± 1.6 Ma with a weighted mean age of 163.1 ± 1.4 Ma and yield an isochron age of 162.2 ± 4.1 Ma (MSWD = 1.01), consistent with the emplacement age of the Gangmei intrusion, indicating a genetic relationship between magmatic activity and mineralization. This age also agrees well with the large-scale Jurassic Mo-W- and W-Sn-associated mineralization in South China, suggesting that the scope of Jurassic Mo-W-associated mineralization can reach the southernmost part of South China. Rhenium concentrations in molybdenites from Jurassic Mo-W-associated and W-Sn-associated deposits in South China suggest that their magma sources are different, and Mo-W-associated deposits may involve more mantle-derived materials. In addition, oxygen fugacity may be another factor controlling different types of mineralization in South China.

Origin and evolution of W mineralization in the Tongshanling Cu–polymetallic ore field, South China: Constraints from scheelite microstructure, geochemistry, and Nd–O isotope evidence

Multistage, skarn-type W mineralization has recently been discovered in the Tongshanling Cu–polymetallic ore field, South China. This contribution reports new results from cathodoluminescence, trace element, and Nd–O isotopic analyses of scheelite samples from Tongshanling, designed to better constrain the W mineralization process and origin of associated metals and metallogenic fluids. Three generations of scheelite were identified that can be attributed to three paragenetic phases: (i) an early prograde skarn stage dominated by massive garnet and diopside intergrown with fine-grained scheelite, (ii) an intermediate retrograde skarn stage characterized by an assemblage of abundant scheelite, medium-grained chlorite and epidote, and (iii) a late sulfide-quartz vein stage typified by coarse-grained, subhedral scheelite grains that are typically intergrown with chalcopyrite, sphalerite, and galena. Our data show that although WO3 and CaO concentrations are similar in scheelite of all three stages and rare earth element (REE) patterns vary, the ∑REE + Y values of scheelite markedly and progressively decrease from the prograde skarn (mean = 901 ppm) to retrograde skarn (70.1 ppm) to the sulfide-quartz vein (34.1 ppm) stages. This signature is consistent with either of the following scenarios: The coprecipitation of REE-enriched minerals (e.g., garnet and scheelite), a change in fluid oxygen fugacity change and/or minor distortions in crystal texture. The δ18OH2O values of fluids linked to the prograde skarn and sulfide-quartz vein stages (5.02‰–6.19‰) are consistent with a magmatic fluid input. The δ18OH2O values of fluids associated with the retrograde skarn stage (2.85‰–3.45‰), on the other hand, are indicative of fluid mixing, possibly reflecting dilution of magmatic fluids by meteoric waters. Interestingly, scheelite samples of the sulfide-quartz vein stage returned low εNd(t) values (−7.46 to − 7.07) and moderate two-stage Nd model ages (T2DM = 1526 –1557 Ma) that are identical to the whole rock Nd isotope composition of an adjacent Jurassic I-type granodiorite porphyry pluton. Overall, the results of our study indicate a close genetic relationship between this pluton and the W mineralization, a scenario that is at odds with the common association between I-type granodiorites and Cu–Pb–Zn mineralization in South China.

Visible/near infrared reflectance (VNIR) spectral features of ion-exchangeable Rare earth elements hosted by clay minerals: Potential use for exploration of regolith-hosted REE deposits

Regolith-hosted ion-exchangeable rare earth element (REE) mineralization in South China dominate the global source of heavy REEs. The lack of studies on spectral features of ion-exchangeable REEs limits the application of visible/near infrared reflectance (VNIR, 350–2500 nm) spectroscopy for rapid identification of regolith-hosted REE deposits in prospective areas. This paper presents a systematic study on VNIR spectral features of ion-exchangeable REEs hosted by a series of synthetic REE-adsorbed clay minerals and natural regolith samples. The results show that ion-exchangeable Nd3+, Dy3+, Ho3+, Er3+ and Tm3+ display diagnostic absorption features at the bands of 730–870, 805, 641, 652, and 684 nm. Specifically, the Nd3+ related absorption bands of regolith samples at ~800 nm show a shoulder at ~802 nm that are distinguishable from unweathered primary REE(−bearing) minerals. The maxima of second derivative curves derived from the Nd3+ absorption at ~802 nm, M802_2nd, can be used to quantify variations of ion-exchangeable REEs in regoliths. Nevertheless, the absorption features of REE3+ ions could be subdued due to an overlapping problem caused by the broad absorption bands of Fe-oxides in the range of 700–900 nm. The obtained VNIR spectra of ion-exchangeable REEs provide critical supplement to spectral library for REE-bearing minerals. This study demonstrates that field-based VNIR spectroscopy can be deployed as a powerful tool for regional and deposit-scale exploration of regolith-hosted ion-exchangeable REE resources.

Tourmaline as an indicator for late-magmatic to hydrothermal fluid evolution of the Neoproterozoic Baotan tin deposit, South China

Neoproterozoic tin mineralization in South China was closely related to the highly-evolved peraluminous granites in the southeastern and western margins of the Yangtze Block. The Baotan (23 Mt @ 0.43 % Sn) is a largest tin deposit in the Jiuwandashan–Yuanbaoshan tin district, northern Guangxi, and the orebodies are mainly hosted in the Lower Neoproterozoic Sibao Group metasedimentary rocks and Early Neoproterozoic mafic rocks intruding the Sibao Group as well as the apex of the Pinying granitic pluton. This deposit shows widely important tourmaline alteration. Based on petrographic observations, four generations and eight occurrences of tourmalines are identified in the Baotan tin deposit. The first generation is late-magmatic tourmalines and occurs as disseminated (Tur1a) and tourmaline–quartz nodule (Tur1b) in the Pingying biotite granite. The pre-ore hydrothermal tourmalines (Tur2) occur as tourmaline–quartz veinlet in the biotite granite and can be subdivided into both the early Tur2a (second generation) and the late Tur2b (third generation) according to microscopic observation and BSE image. The fourth generation is syn-ore hydrothermal tourmalines (Tur3), and they occur as disseminated in mafic- (Tur3a) and metasedimentary (Tur3c) host rocks, or as vein-type tourmaline–quartz–cassiterite–chlorite ores in mafic- (Tur3b) and metasedimentary (Tur3d) host rocks.The different generations of tourmalines have both similarities and distinct differences in their compositions. Both the late-magmatic Tur1a and Tur1b show similar chemical compositions, with high Fe/(Fe + Mg) (0.73 ∼ 0.96, avg. 0.89) and Na/(Na + Ca) (0.87 ∼ 0.98, avg. 0.95) ratios, and Li, Zn, Ga, Nb and Ta contents, and belong to alkali group and schorl tourmaline. Based on mineral textural and compositional features and Mössbauer spectroscopic analyses, it can be speculated that the Tur1b in the tourmaline–quartz nodules and Tur1a are mainly sourced from a late-magmatic immiscible B–Na–Fe-rich hydrous melt in a reduced environment. The pre-ore Tur2a has similar SiO2, Al2O3, TiO2, Na2O, Li, Be, V, Sn and Zr contents, Fe/(Fe + Mg) and Na/(Na + Ca) ratios and total Al (apfu) with the late-magmatic Tur1a and Tur1b, indicating that it also originates from the Pingying granitic magma. The lower compatible elements (e.g., Fe, Mn, Co, Ni and Zn) and higher LILEs (e.g., Sr, Rb, Ba and Cs) in the pre-ore Tur2a and Tur2b suggest that these tourmalines precipitate from the early evolved magmatic hydrothermal fluids. The wide variations of Fe/(Fe + Mg) and Na/(Na + Ca) ranges, elevated Sr and V contents for the syn-ore Tu3a to Tur3d are attributed to the compositional differences of the host rocks and different degrees of interaction between the ore-forming fluids and the host rocks. The increasing Sr content from the late-magmatic Tur1 and pre-ore Tur2 to the syn-ore Tur3 suggests an involvement of the meteoric water. The Mössbauer spectral features of tourmalines from the late-magmatic Tur1 and syn-ore Tur3 confirm that they form under the different redox environments. The early fluids are relatively reduced magma-derived fluids. The addition of recycled meteoric water causes the fluids at the Tur3 stage to become relatively oxidized and also to be Sr-rich. The significant increase of Sn content from the late-magmatic Tur1 and pre-ore Tur2 to the syn-ore Tur3 also reflect a change from the early reduced fluid to the late oxidized fluid. The textural and compositional changes of Tur1 to Tur3 reflect the evolution of the ore-forming fluids. Fluid mixing between an acidic, reduced, Sn-rich magmatic hydrothermal fluid and cooler, oxidizing meteoric water and as well intensive water–rock reaction are considered as the main processes that cause extensive cassiterite precipitation.

Petrogenesis of the Microgranular Enclaves and Their Host Granites from the Xitian Intrusion in South China: Implications for Geodynamic Setting and Mineralization

The South China Block had experienced a significant tectonic transition during the Mesozoic in response to the subduction of the Paleo- and the Pacific Ocean. Large-scale granitic intrusions with massive mineralization are widespread in South China, and their tectonic settings are not defined. The Xitian intrusion is ideal for probing the geodynamic setting and mineralization in South China because they comprise an abundance of microgranular enclaves (MEs) and diverse types of granite associated with mineralization. Age determined by zircon U-Pb dating suggests that the MEs and their host granites are coeval within error, of ca. 152 Ma. The MEs have a similar initial Hf-O isotopic composition as host granites, and the rapid cooling mineral textures indicate that they are autoliths. Geochemical data show that the host granites are high-K, calc-alkaline, and transitional from metaluminous to peraluminous, slightly enriched in light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs), with obvious negative Eu anomalies, belonging to I-type. The Nb/Ta and Zr/Hf ratios indicate the volatile penetrates the magmatic-forming process, and the fluid with abundant volatile could extract metal element effectively from the mantle.

Fluid inclusion, H–O–S isotope and rare earth element constraints on the mineralization of the Dong’an Sb deposit, South China

Systematic geochemical study on the Cambrian strata-hosted Dong’an Sb deposit in the Central Hunan Sb belt would provide key information on the origin of the low-temperature mineralization in South China. In this study, microthermometric, H–O isotopic and fluid composition analyses on ore-bearing quartz, S isotopic analyses on sulfides, and rare earth element (REE) analyses on wall-rocks and monominerals (stibnite, pyrite and quartz) in ores were conducted to constrain the genesis of the Dong’an Sb deposit. Two major stages of mineralization were identified in the Dong’an deposit: (1) an early pyrite-stibnite-quartz stage mineralization with intense wall-rock alteration occurring at depth of the deposit, and (2) a late quartz-stibnite stage mineralization occurring at shallow depths. Microthermometric analyses reveal a low temperature (150 to 230 °C), low salinity (4.5–7.0 wt% NaCl equiv.), low density (0.88–0.96 g/cm3), low pressure (4.5 MPa) and weakly acid (pH = 5.74) fluid for the Sb mineralization. Compositional analyses for fluid inclusions show that the main ion compositions are Na+, K+, Mg2+, Ca2+, F−, Cl− and SO42−, while the gas compositions are dominated by H2O and CO2. This suggests that the ore-forming fluids were enriched in alkali metals, sulfur and halogen. The H–O isotopic compositions (δ18OH2O = 2.52‰ to 7.13‰, δ2HH2O = −88.6‰ to −58.3‰) of fluid inclusions in quartz suggest a mixture of magmatic water, metamorphic rocks-derived brine and meteoric water. The δ34S values of stibnite (−1.32‰ to +2.86‰) and pyrite (+17.4‰ to +23.6‰) are very different, suggesting multi-sulfur sources involving buried magmatic rocks, ore-bearing meta-sedimentary rocks and deep basement rocks. The decreasing of REE contents from early to late mineralization stages reflects a decrease of temperature, reduction of fluid-rock interaction and input of meteoric water along with the stibnite precipitation. We propose that Precambrian strata that underwent regional metamorphism during Early Paleozoic acted as a Sb source bed, whereas strong tectono-magmatism in the early Mesozoic provided thermal driving force for the Sb mineralization occurring under a tensile stress in secondary faults at the shallow crust. This study highlights the use of multi-geochemical methods to constrain the genesis of large-scale Sb mineralization in South China.

Provenances of the Ediacaran sedimentary rocks in the Zhuguangshan area and their implications for granitoid-related uranium mineralization in South China

The terrigenous clastic sedimentary rocks in the Zhuguangshan uranium ore field of the Cathaysia Block, South China, were selected to reveal their petrogenesis and implications for granitoids-related uranium mineralization in South China. LA-ICP-MS U-Pb dating of detrital zircons shows that the Ediacaran terrigenous clastic sedimentary rocks in the Zhuguangshan area are characterized by a significant age peak at ca. 1023 Ma and that the Grenville-aged detritus in the Zhuguangshan area originated from northern India and eastern Antarctica. Elemental geochemical features show that the Ediacaran terrigenous clastic sedimentary rocks in the Zhuguangshan area were derived from a recycled sedimentary source and were deposited in a passive continental margin. The geochemical composition of the source rock is similar to that of intermediate-felsic rocks which are likely composed of andesite-granite. Petrographic and geochemical features unravel that the Ediacaran terrigenous clastic sedimentary rocks in the Zhuguangshan area underwent mildly-intensive chemical weathering. Through the comparison of the terrigenous clastic rocks between the Cathaysia Block and the southeastern margin of the Yangtze Block, we suggest that the high maturity and high U and Th contents of the terrigenous clastic rocks might be the key factors causing the granite-related uranium mineralization in the Cathaysia Block.