24 research outputs found
Short-wave infrared (SWIR) spectral and geochemical characteristics of hydrothermal alteration minerals in the Laowangou Au deposit: Implications for ore genesis and vectoring
No full textThe Laowangou gold deposit is a newly discovered Au deposit in the North Qinling orogenic belt. Based on megascopic and microscopic textural relationships and mineral assemblages, the hydrothermal alteration and mineralization of the Laowangou Au deposit have been divided into porphyry-type (including potassic, chlorite-epidote and mica-quartz alteration stages) and overprinting mineralization periods. Hypogene Au mineralization mainly occurred as muscovite + quartz + Au-bearing pyrite veins during the overprinting mineralization period, and developed in the fault and fracture zone. SWIR analyses indicate that alteration minerals in the Laowangou Au deposit are chlorite (including Mg chlorite, Fe chlorite, and Fe-Mg chlorite), epidote and white micas with less dolomite, brucite and calcite. Two types of white mica are recognized at Laowangou. Type A white mica partially replaces plagioclase and K-feldspar in the Tangzang quartz diorite, representing the mica-quartz stage, whereas Type B white mica coexists with Au-bearing pyrite, quartz, calcite, and mainly developed in the fracture zone, representing the overprinting mineralization period. Compared with metamorphic minerals, Laowangou porphyry-related chlorite shows lower Al, Ti, and As, but higher Sr concentrations; porphyry-related epidote has higher Ti and Bi, but lower As concentrations. Type B white mica has lower Fe and Mg contents, but larger particle sizes and illite crystallinity (IC) values than Type A white mica, similar to geochemical characteristics of metamorphic white mica. These evidences indicate the Laowangou Au mineralization is different from typical magmatic-hydrothermal Au deposits, and the ore-forming fluid related to Au mineralization may have derived from the depth along faults. Higher wavelength of the Al-OH absorption (>2210 nm) and IC values (>1.2) of white mica can be used as effective vector toward high grade Au mineralization (>1 g/t) in the Laowangou Au deposit
Pressure-induced phase transitions in TmVO4 investigated by Raman spectroscopy
No full textThe structural behavior of TmVO4 at pressures up to - 55 GPa was investigated by Raman spectroscopy. The changes in Raman spectra suggest the existence of three phase transitions upon compression. The first phase transition appeared at - 7.7 GPa, which was an irreversible phase transition from the ambient-pressure zircon phase to the scheelite phase, confirming previous X-ray measurements. Subsequently, the second reversible phase transition from the scheelite phase to the fergusonite phase occurred at - 23 GPa. Additional changes in the Raman spectra were observed at - 37 GPa, validating the third phase transition. Based on a comparison to related rare earth orthovanadates, we assumed that the post-fergusonite of TmVO4 has an orthorhombic structure described by space group Cmca. The wavenumbers of the Raman modes and their pressure coefficients for all four phases of TmVO4 are reported. Our study provides the vibrational difference in various polymorphs of TmVO4, which will refine our understanding of the structural behavior of rare-earth orthovanadates
Geochemistry and geochronology of multi-generation garnet: New insights on the genesis and fluid evolution of prograde skarn formation
No full textOrigin of garnet in skarn (magmatic vs. hydrothermal) and the prograde skarn fluid evolution are still controversial. Two generations of garnet (Grt1, Grt2) were identified at the Tongshankou deposit: Grt1 is anisotropic with oscillatory zoning and resorbed boundary, whilst Grt2 grew around Grt1 and formed oscillatory rims. In-situ LA-ICP-MS U-Pb dating of Grt1 and Grt2 yielded a lower intercept 206Pb/238U age of 142.4 +/- 2.8 Ma (n = 57; MSWD = 1.16) and 142.3 +/- 9.6 Ma (n = 60; MSWD = 1.06), respectively, coeval with the ore formation and ore-related granodiorite emplacement. Positive Eu anomaly, non-CHARAC Y/ Ho value and low TiO2 content, together with the mineral assemblages indicate that both Grt1 and Grt2 have a hydrothermal origin. The existence of melt and melt-fluid inclusions in Grt1, together with similar LREE-enriched patterns to the granodiorite, further indicate that Grt1 may have formed in the magmatic-hydrothermal transition. Higher U contents and LREE-enriched patterns of Grt1 indicate that fluid I is mildly acidic pH and low fO2. The inner gray Grt2 rims (Grt2A) is HREE-enriched with low U contents, indicating that fluid II has nearly neutral pH and high fO2. The wider Y/Ho range and LREE-enriched pat-terns of the outer light-gray Grt2 rims (Grt2B) show that the evolved magmatic fluid II had mixed with an external fluid, characterized by being mildly acidic pH and with high fO2. Our results suggest that the pro-grade skarn-forming fluids can be multistage at Tongshankou, and the mixing of meteoric water may have been prominent in the prograde skarn stage.(c) 2022 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/)
Hydrothermal alteration of magmatic titanite: Implications for REE remobilization and the formation of ion-adsorption HREE deposits, South China
No full textIon-adsorption rare earth element (REE) deposits in South China are currently the main source of heavy rare earth elements (HREE). The Gucheng deposit in western Guangdong Province is one example of HREE mineralization hosted in weathered coarse-grained biotite granites (CGBG). Titanite is a common accessory mineral in the CGBG and contains significant amounts of total REE (31 621 to 38 431 ppm), especially HREE (18 906 to 22 249 ppm). Titanite with a U-Pb age of 102.6 +/- 1.9 Ma in the CGBG crystallized under relatively high temperatures (722-798 degrees C), high f(H2O), and high f(O2) conditions in the late magmatic stage, and has similar Nd isotopic compositions similar to the host CGBG:Nd-143/Nd-144 = 0.512062 to 0.512125 and epsilon Nd(t) = -7.4 to -8.6.Backscattered electron (BSE) imaging and TESCAN integrated mineral analyzer (TIMA) measure-ments show that titanite in the CGBG has been altered partly to fergusonite-(Y), rutile, calcite, quartz, and fluorite. The hydrothermal fluid responsible for titanite alteration was enriched in CO32- and F, and was probably exsolved from the granitic magma. HREE released from the alteration of titanite were mostly scavenged by fergusonite-(Y) and rutile, which have been further replaced by gadolinite-(Y) and synchysite-(Ce). In addition, gadolinite-(Y) in the alteration assemblages exhibits further alteration and is characterized by elevated PO43- and SO42- contents in the altered parts. These results demonstrate that magmatic titanite in the CGBG underwent complex hydrothermal alteration, with a preferential accumulation of HREE in fergosnite-(Y) and gadolinite-(Y) in the alteration assemblages. Preferential HREE enrichments in magmatic titanite, and its alteration assemblages, are shown to play significant roles in the formation of the Gucheng HREE deposit
The factors affecting mineralization potential of arc magma: Insights from silicate melt inclusions and zircon composition of igneous lava at Eastern Taiwan Island
No full textSubduction-related Cu-(Au) deposits which represent giant geochemical anomalies of metals and S in the upper crust are commonly associated with arc magmas. However, the fundamental differences between barren and fertile magma producing these deposits still remain highly controversial. In this study, we report the chemical compositions of zircon and silicate melt inclusions (SMIs) from barren arc lavas at eastern Taiwan Island aiming to increase our knowledge on the factors that affect the mineralization potential of arc magma systems. The zircon U-Pb dating shows the magmatism occurred at similar to 0.7 Ma and the andesitic lava formed at similar to 900-950 degrees C with a reduced magmatic environment. The plagioclase-hosted SMIs show an andesitic melt composition and variable Cu content features. The calculated H2O content of parental melt is similar to 3-4 wt.%. The evidence presented above suggests that oxidation state (fO(2)) and H2O content are probably the key controls of Cu-(Au) fertility of arc magmas. We interpret that a reduced and relatively dry magma may be a potential hinderance to cause the absence of porphyry Cu deposits at the eastern Taiwan Island
Late mesozoic magmatism in the Gucheng district: Implications for REE metallogenesis in South China
No full textRegolith-hosted rare earth element (REE) deposits are common in South China. The newly-discovered Gucheng REE deposit in the western part of Guangdong Province, is characterized by HREE enrichment (with SHREE oxides of 55%). Three types of granites have been identified in the Gucheng ore district, a REE-fertile coarsegrained biotite granite (CGBG), a weakly REE-fertile fine-grained biotite granite (FGBG) and the barren mediumgrained biotite granite (MGBG). New LA-ICP-MS zircon U-Pb dating reveals that the MGBG (107.7 +/- 0.4 Ma), CGBG (103.2 +/- 0.6 Ma) and the FGBG (98.9 +/- 0.7 Ma) were all formed in the Late Cretaceous. Mineralogical and geochemical data indicate that the CGBG is an unfractionated I-type granite, whereas the FGBG and MGBG are fractionated I-type granites. The CGBG and FGBG have (87Sr/86Sr) i and eNd(t) ranging from 0.7121 to 0.7140 and 8.6 to 8.0, and 0.7125 to 0.7131 and 8.2, respectively. The source of these granites was mainly composed of two end-members: one having 90% Paleoproterozoic basement and another 10% enriched mantle metasomatized by subduction-related melts. The barren MGBG is also derived from partial melting of a Paleoproterozoic source with a minor contribution of enriched mantle. The involvement of enriched mantle can provide REE into the magmas, which plays an important role in REE enrichment. Geochemical data show that allanite have been crystallized during magma evolution process of all the three types of granites. However, no allanite has been discovered in the MGBG, and the FGBG contains lower abundance of allanite than that of the CGBG, which is due to different degrees of fractionation. The crystallization and separation of allanite has greatly affected the LREE of the three types of granites, which further influences their potential for LREE mineralization. Lower K/Rb and Nb/Ta ratios of the CGBG, FGBG and MGBG indicate that these three types of granites were affected by hydrothermal events after their crystallization. Zircon geochemical data show that the MGBG was formed in a lower oxygen fugacity environment than the CGBG and FGBG. Above all, involvement of enriched mantle, a relatively high oxygen fugacity, crystallization and separation of allanite as well as involvement of hydrothermal events after magmatic crystallization are important factors controlling REE mineralization at Gucheng, of which the hydrothermal events may play the most important role
China: Implications on petrogenesis and tectonic setting
No full textPermian mafic-ultramafic intrusions have great significance for understanding the geodynamic evolution of the Late Palaeozoic eastern Tianshan Orogen due to containing important information on the nature of mantle sources, crust-mantle interaction, and magmatic differentiation. Increasingly, more Permian mafic-ultramafic intrusions are discovered in the Jueluotage belt, especially in the Kangguer ductile shear zone, whereas the mafic-ultramafic intrusions in the Aqishan-Yamansu belt are ill-informed. In this study, we provide zircon U-Pb geochronological, geochemical, and Sr-Nd-Pb-Hf isotopic data of a newly identified hornblende gabbro suite at the Shaquanzi Fe-Cu deposit in the Aqishan-Yamansu Belt. Zircon U-Pb dating results indicate that the Shaquanzi hornblende gabbro was emplaced at Early Permian (ca. 274-265 Ma). The rocks are calc-alkaline and have arc-like geochemical features, including enrichments in large-ion lithophile elements (LILEs: Rb, Ba, K, Pb and Sr) and light rare-earth elements (LREEs: Nb, Ta, Zr, Hf, and Ti), and depletions in high-field-strength elements (HFSEs) with markedly negative Nb and Ta anomalies. The rocks also exhibit depleted-mantle isotopic signatures, with positive bulk-rock epsilon(Nd)(t) values of +3.34 to +4.44 and positive zircon epsilon(Hf)(t) values of +2.8 - +8.7, which are relatively more enriched than those of coeval mafic-ultramafic intrusions from the Kangguer ductile shear zone, but similar to those in the Central Tianshan Massif. We suggest that the Shaquanzi mafic intrusion suite was generated by 10-30% partial melting of a depleted-mantle source at over 85 km depth, corresponding to the garnet to garnet-spinel stability field. And the mantle source had likely been metasomatized by slab-derived fluids of previous subduction. Integrating with geochemical data of the coeval mafic-ultramafic and felsic intrusive rocks in the adjacent tectonic belts of eastern Tianshan Orogen, we speculate that the Shaquanzi mafic intrusion was formed in a post-collision extensional setting, probably triggered by slab breakoff. Metasomatism of the depleted lithospheric mantle had likely occurred during the pre-Permian subduction of the Kangguer oceanic slab
Analysis of the Voltage-Time Dilemma of Metal Oxide-Based RRAM and Solution Exploration of High Speed and Low Voltage AC Switching
No full textIn this paper, the ac electrical characteristics of metal oxide-based resistive random access memory are investigated based on a developed compact model and the experiment. The voltage-time dilemma phenomenon and the impacts of critical factors on resistive switching speed are addressed. Based on predictions of the model, the small parasitic capacitance, low target high resistance, and large thermal resistance are beneficial to accelerate the resistive switching speed both in SET and RESET processes. The high SET speed and low SET voltage can be achieved by tuning the activation energy of oxygen vacancies. While for the RESET process, the barriers of the release of oxygen ions from electrode and the hopping in resistive switching layer should be turned down simultaneously for high switching speed and low operation voltage.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000345087900015&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, Electrical & ElectronicNanoscience & NanotechnologyMaterials Science, MultidisciplinaryPhysics, AppliedSCI(E)[email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]
Chlorite chemistry of Tongshankou porphyry-related Cu-Mo-W skarn deposit, Eastern China: Implications for hydrothermal fluid evolution and exploration vectoring to concealed orebodies
No full textRecent years, the depletion of shallow mineral resources has drawn increasing attention to the exploration of hidden ore bodies in deep of skarn type deposits. Chemical composition of chlorite is an effective tool for tracing the hydrothermal fluid evolution, and has been increasingly used for deep-level exploration of porphyry Cu (-Au) deposits (PCDs). However, the technique was rarely applied onto (porphyry-related)-skarn deposits. The Tongshankou Cu-Mo-W deposit (0.55 Mt Cu @ 0.86%, 0.01 Mt Mo @ 0.10% and 0.12 Mt WO3 @ 0.19%) is one of the largest skarn-porphyry deposits in the Middle-Lower Yangtze River Metallogenic Belt (MLYRB) in Eastern China. In this study, new petrographic and trace element data of the hydrothermal chlorites from Tongshankou were presented to constrain the ore-fluid evolution, and to explore the vectoring potential of the concealed orebodies at Tongshankou. Four types of chlorite have been identified, i.e., G-type chlorite that replaced the original magmatic biotite or hornblende, V-type chlorite in chlorite-quartz-sulfides veins in the granodiorite porphyry (alteration zones I and II), S-type chlorite that replaced garnet in the intensive skarn alteration zone (III) and M-type chlorite-quartz-calcite-sulfides veins that cut the (dolomitic)-marble in the distal alteration zones IV and V.
All the four types of chlorites are typically trioctahedral chlorite. The Fe-Mg, Tschermark and di-trioctahedral substitution mechanisms likely control the geochemical variations of the Tongshankou chlorites. Empirical thermometer indicates that the Tongshankou chlorites were crystallized at 169-322 degrees C. Compared with typical metamorphic chlorites, the higher Zn and Sr contents but lower Al content in the Tongshankou chlorites can potentially distinguish the skarn-type hydrothermal chlorites from typical metamorphic ones. Compared with the chlorites in the typical PCDs, the Tongshankou G-type chlorite has higher Fe, Zn, As and Sn contents, but lower Al, Mg, Co and Cu contents, which likely reflect its protolithic and/or fluid geochemical inheritance. The Tongshankou V-, M- and S-type chlorites have high contents of mobile elements (such as Sr, Ca, Sn and B) and metals (such as Fe, Cu, As, Zn and Pb), indicating that they were directly precipitated from the hydrothermal fluids. From the granodiorite porphyry to the marble wallrocks, the spatial chlorite geochemical variations at Tongshankou indicate that the increasing Zn, Mn, Ga, Ge and Pb contents, and decreasing V, Sc and Ti contents are potential vectors toward concealed mineralized porphyries at Tongshankou. Our study highlights that the chlorite geochemistry is a potential tool for ore-fluid tracer and vectoring tool toward concealed skarn-porphyry orebodies in the MLYRB
Precambrian crust growth and reworking of the eastern Yangtze Craton: insights from xenocrystic zircons in the lamprophyres from the Middle-Lower Yangtze Belt, China
No full textContinental mafic igneous rocks and their xenocrysts provide information on the evolution of deep continent. Here we present new in situ U-Pb and Hf-O isotopes data for xenocrystic zircons discovered from the Late Mesozoic ultrapotassic to K-rich lamprophyres (150 similar to 140 Ma) in the eastern Yangtze Craton to address the poorly understood yet critical issue about the nature, age and evolution of the regional continental crust. The zircon xenocrysts define episodic distribution of Precambrian ages at 2.61 similar to 2.50 Ga, 2.47 similar to 1.63 Ga, 1.13 similar to 1.00 Ga and 0.88 similar to 0.73 Ga, with two-stage model ages of Hf isotopes ranging from 3.19 to 1.61 Ga. The presence of Archean and Paleoproterozoic xenocrystic zircons reveal that the deep crust is probably older than the surface exposures (<= 1.0 Ga) and the Archean-Paleoproterozoic crustal materials maybe widespread in the eastern Yangtze Craton. Hf-O isotopes of the studied Paleoproterozoic and Neopmterozoic xenocrystic zircons, as well as other contemporary xenocrystic zircons from late Mesozoic igneous rocks in the literatures, record the important crust growth and reworking in the eastern Yangtze Craton. The lamprophyres and their xenocrysts provide an important proxy archive of the history of deep continental crust in the eastern Yangtze Craton
