Noble Gas Mass Spectrometer Research Articles

Old but Novel Noble Gas Mass Spectrometer

Old but Novel Noble Gas Mass Spectrometer

Optimizing 40Ar/39Ar analyses using an Isotopx NGX-600 mass spectrometer

40Ar/39Ar geochronology relies on magnetic sector mass spectrometers to determine relative isotopic abundances. Ongoing technological developments within noble gas mass spectrometers over the last decade have led to analysis of increasingly smaller samples and higher precision, but also result in more complex data correction and interpretation. We describe a new multi-collector noble gas spectrometer, the Isotopx NGX-600, that is configured to optimize 40Ar/39Ar measurements. The NGX-600 is equipped with 9 Faraday collectors and one ion counting electron multiplier. Each Faraday is equipped with Isotopx ATONA® amplifier technology, enabling measurements spanning a dynamic range of amplified beam current from below 10−16 A to above 10−9 A. The performance of the NGX-600 is evaluated using both a conventional Nier-type ion source, and a next generation low temperature ion source, which allows for trap current variation from 200 μA to 1000 μA. We have performed over 3000 analyses of atmospheric argon to: (1) assess optimal measurement and integration times for blanks, baselines, and air aliquots of various ion intensities, (2) quantify the sensitivity via measurements of first principles 40Ar/39Ar standards, (3) compare the sensitivity between the conventional and new low temperature Nier-type ion sources, and (4) evaluate corrections associated with inter-Faraday biases, instrumental mass bias, and Faraday-multiplier gain. In addition to optimization experiments, we report a comparative analysis of both single crystal fusion and incremental heating data from Quaternary volcanic rocks obtained using both the 5-collector Nu Instruments Noblesse and the NGX-600 spectrometers.

Performance of the NGX High‐Resolution Multiple Collector Noble Gas Mass Spectrometer

AbstractThis paper describes the design, setup, and performance of a new analytical system installed at Lancaster University, UK, to determine noble gas isotopes in gas samples using an NGX high‐resolution multiple collector noble gas mass spectrometer. The fixed position Faraday cups are configured to simultaneously measure all nine Xe isotopes whilst permitting all other noble gases, such as He, to be analyzed in peak jumping mode. The stability, sensitivity, and reproducibility of the measurements using this new noble gas analytical system were examined by repeating runs of atmospheric air. Reproducibility of the measurements obtained from 90 and 73 air standard runs are 4.2% and 0.4% for 3He/4He and 21Ne/20Ne, respectively. There is no significant difference in the 40Ar/36Ar ratio measurements with various 40Ar abundances, suggesting good sensitivity and pressure linearity of the NGX instrument. The standard errors for 124Xe/130Xe, 126Xe/130Xe, 128Xe/130Xe, 129Xe/130Xe, 131Xe/130Xe, 132Xe/130Xe, 134Xe/130Xe and 136Xe/130Xe in 46 air measurements are 0.782%, 0.804%, 0.053%, 0.029%, 0.029%, 0.029%, 0.030%, and 0.031%, respectively. In contrast, the corresponding reference values from Basford et al. (1973) are 0.342%, 0.505%, 0.148%, 0.139%, 0.153%, 0.076%, 0.156%, and 0.138%, respectively. This suggests that multicollection measurements of Xe isotopes on Faraday cups using the NGX have higher precision than the previous results except for 124Xe and 126Xe, where low abundances affect the measurement precision. Compared to traditional peak jumping single‐collector mass spectrometers, the NGX has significantly decreased analytical time in Xe analysis by allowing simultaneous measurements of all isotopes. As a consequence, high analytical precision can be achieved.

Technical Note: Noble gas extraction procedure and performance of the Cologne Helix MC Plus multi-collector noble gas mass spectrometer for cosmogenic neon isotope analysis

Abstract. We established a new laboratory for noble gas mass spectrometry that is dedicated to the development and application to cosmogenic nuclides at the University of Cologne (Germany). At the core of the laboratory are a state-of-the-art high-mass-resolution multicollector Helix MC Plus (Thermo Fisher Scientific) noble gas mass spectrometer and a novel custom-designed automated extraction line. The mass spectrometer is equipped with five combined Faraday multiplier collectors, with 1012 and 1013 Ω pre-amplifiers for faraday collectors. We describe the extraction line and the automated procedure for cosmogenic neon and the current performance of the experimental set-up. Performance tests were conducted using gas of atmospheric isotopic composition (our primary standard gas), as well as CREU-1 intercomparison material, containing a mixture of neon of atmospheric and cosmogenic composition. We use the results from repeated analysis of CREU-1 to assess the performance of the current experimental set-up at Cologne. The precision in determining the abundance of cosmogenic 21Ne is equal to or better than those reported for other laboratories. The absolute value we obtain for the concentration of cosmogenic 21Ne in CREU is indistinguishable from the published value.

An Automated System for MeasuringIn SituK–Ar Ages

A completely automated system for measuringin situK–Ar ages using laser ablation for argon extraction and potassium measurement, and mass spectrometry for argon determination is described. The system consists of a laser system, an optical spectrometer, a vacuum line, a noble gas mass spectrometer and control software. The automated prototype was designed with ease of use in mind, specifically planned for dating many samples at low cost and reasonable precision. This instrumentation can perform one hundred K–Ar analyses every 24 h with the current setup, including blanks, reference materials and unknowns. Measurement results for the reference materials HDB‐1 biotite, GL‐O glauconite, LP‐6 biotite, Mica‐Mg phlogopite, Alder Creek sanidine and two tektites (moldavite and indochinite) are presented. It is shown that very different sample matrices require specific calibrations. Uncomplicated sample preparation, fast analytical times and uncertainties typically below 5% (1 standard deviation), depending on the age and potassium content, are the hallmarks of the system, which is suitable for many exploratory geology applications (e.g. geological mapping, mineral provenance and dating of drill cores).

The Isotopx NGX and ATONA Faraday amplifiers

Abstract. We installed the new Isotopx ATONA Faraday cup detector amplifiers on an Isotopx NGX mass spectrometer at Lamont-Doherty Earth Observatory in early 2018. The ATONA is a capacitive transimpedance amplifier, which differs from the traditional resistive transimpedance amplifier used on most Faraday detectors for mass spectrometry. Instead of a high-gain resistor, a capacitor is used to accumulate and measure charge. The advantages of this architecture are a very low noise floor, rapid response time, stable baselines, and very high dynamic range. We show baseline noise measurements and measurements of argon from air and cocktail gas standards to demonstrate the capabilities of these amplifiers. The ATONA exhibits a noise floor better than a traditional 1013 Ω amplifier in normal noble gas mass spectrometer usage, superior gain and baseline stability, and an unrivaled dynamic range that makes it practical to measure beams ranging in size from below 10−16 to above 10−9 A using a single amplifier.

Observation of the deep Indonesian throughflow using helium isotopes

Helium isotopes in the ocean are very useful tracers of hydrothermal input and deep-sea circulation. Unlike labile trace elements, noble gases are inert and do not react with other substances in the water column. Previous studies in the Indian Ocean showed that helium isotopes in the region were discharged mainly from the central Indian midocean ridge, convergent boundaries, and the Pacific Ocean via currents that flow through the Indonesian archipelago. These Indonesian waters then exit out as the Indonesian Throughflow (ITF) into the Indian Ocean through shallow sills. The ITF plays a significant role in global climate, because it serves as the main pathway of thermocline waters between the Pacific Ocean and Indian Ocean. We present new helium isotope data from International Indian Ocean Expedition (IIOE-2) at the east Indian Ocean in December 2018. Helium isotopes were measured using a Noble Gas Mass Spectrometer at the Atmosphere and Ocean Research Institute, The University of Tokyo. We compare our data with those from previous expeditions and discuss the source and distribution of helium isotopes near Java. Waters with high excess 3He from the ITF were observed at 1000 m. Application of two-components mixing model enabled us to estimate ITF fraction in the observed area and to clarify the ITF flow in the deep layer. Moreover, flow rate of the deep ITF from Savu sill to Indian Ocean was estimated to be ~ 0.8–1.6 Sv. Based on stations near the Java coast, there could be a deep current or hydrothermal source at 3000 m that advects water enriched in 3He southwards along the Java Island.

Exposure Ages, Noble Gases and Nitrogen in the Ordinary Chondrite Karimati (L5)

Noble gas and nitrogen isotopic compositions of Karimati ordinary (L5) chondrite are presented. Aliquots of the meteorite were studied in two noble gas mass spectrometers. Its cosmic ray exposure (CRE) history, trapped noble gases and nitrogen isotopic systematic are examined. The compositions of Ne and Kr in this meteorite indicate presence of mixture of solar wind and Q trapped components. In addition to the primordial components, radiogenic 129Xe (from the decay of short-lived radioactive 129I) is observed in the two aliquots (129Xe/132Xe ranges between 1.054 and 1.311). The U/Th-4He and K-40Ar ages are discordant. U/Th-4He ages are younger than the K-40Ar ages, indicating loss of helium. The trapped N component is isotopically light analogous to Q gas/solar wind. The cosmic-ray exposure ages of the two aliquots are 16.1 ± 2.7 Ma and 16.6 ± 2.0 Ma based on the cosmogenic 21Nec and 38Arc concentrations.

Constraints on granite-related uranium mineralization in the Sanjiu uranium ore field, SE China provided by pyrite mineralogy, major and trace elements, S–He–Ar isotopes

The Sanjiu uranium ore field, located in the central of Zhuguangshan granitic batholith, is a newly discovered granite-related uranium ore field in South China. The main sulfide in the ore field is pyrite, which is closely related to uranium mineralization. The textures, major and trace elements, S–He–Ar isotopes compositions of pyrites in ores of different grade were observed and/or analyzed by optical microscope, scanning electron microscope, electron microprobe, laser ablation inductively coupled plasma mass spectrometry, and noble gas mass spectrometer (Helix-SFT). It is observed that these U-related pyrites are generally euhedral–subhedral with dissolution textures, anhedral variety with colloform texture, veinlet and fine particles, and the color of the associated minerals is mostly dark hue, such as purple–black fluorite, dark-red hematite, and dark-green chlorite, etc. The analytical results show that the average compositions of major elements in pyrite are FeS1.944. Pyrites are characterized by S-deficiency, low content of Co and Th, and Co/Ni > 1, which indicate that these ores are of low-temperature hydrothermal origin. We found that the higher the grade of ore, the more deficient in S, the more obvious negative δ34S, and the higher REE content (close to U-rich granitic pluton) of pyrite. The S–He–Ar isotopic compositions of various varieties of pyrites indicate that the ore-forming fluids mainly come from crust-derived fluids and mixed with mantle-derived fluids.

Eighth-order virial equation of state and speed-of-sound measurements for krypton.

An eighth-order virial equation of state (VEOS) for krypton, valid for temperatures up to 5000 K, was developed using the accurate potential functions proposed by Jäger et al. [J. Chem. Phys. 144, 114304 (2016)] for the pair interactions and nonadditive three-body interactions between krypton atoms. While the second and third virial coefficients were already calculated by Jäger et al., the fourth- to eighth-order coefficients were determined in the present work. A simple analytical function was fitted individually to the calculated values of each virial coefficient to obtain the VEOS in an easy-to-use analytical form. To enable a stringent test of the quality of the new VEOS, we measured the speed of sound in krypton in the temperature range from 200 K to 420 K and at pressures up to 100 MPa with a very low uncertainty (at the 0.95 confidence level) of 0.005%-0.018% employing the pulse-echo technique. In order to verify that the isotopic composition of the krypton sample conforms to that of natural krypton in air, high-precision measurements of krypton isotope ratios using a high-sensitivity noble gas mass spectrometer were performed. The extensive comparison with the new speed-of-sound data as well as with experimental p-ρ-T and speed-of-sound data from the literature indicates that pressures and speeds of sound calculated using our new VEOS have uncertainties (at the 0.95 confidence level) of less than 0.1% at state points at which the VEOS is sufficiently converged.

Assessment of Helium Isotopes near the Japan Trench 5 Years after the 2011 Tohoku-Oki Earthquake

The helium isotope ratio is an important tracer of mantle-derived fluids. Different reservoirs in nature have distinct helium isotope signatures that make it possible to identify various sources and their mixing. At 5 years after the 2011 Tohoku-Oki earthquake, we continue to investigate possible fluid venting near the epicenter by measuring helium isotopes. We collected seawater and sediment samples in 2016 at the landward slope of the Japan Trench onboard R/V Shinsei Maru. Sediments were collected using a multiple corer. Seawater samples were obtained from different depths using a CTD rosette system. Pore water was extracted from sediments via centrifugation. Gas from each sample was then exsolved from solution and introduced into the in-house purification system equipped with charcoal traps and Ti getter. Helium isotopes were measured using a noble gas mass spectrometer. Our data show less excess 3He in bottom seawater samples than indicated by helium isotope ratios measured after the earthquake, which...

A new unspiked K-Ar dating approach using laser fusion on microsamples.

Issues induced by neutron irradiation makes 40 Ar/39 Ar dating inapplicable in some cases. The first issue is 37 Ar and 39 Ar recoil effects during irradiation that affect fine-grained minerals (<50 μm), such as lunar rocks, glassy groundmass, supergene minerals (e.g., illite, glauconite, Mg-oxide, etc.). The second issue from neutron irradiation is the high radioactivity gain of iron-rich samples such as pyrite, and the third is the production of interference nuclides during irradiation. The inherent drawbacks of conventional K-Ar and current unspiked K-Ar dating make it difficult to assess the reliability of age results. A new approach is proposed using well-calibrated 40 Ar/39 Ar standard minerals to directly quantify 40 Ar, 38 Ar and 36 Ar. Fish Canyon sanidine (FCs), B4M muscovite and MMhb-1 hornblende, the widely used international standard minerals, were analyzed as unknowns to test the approach. Argon isotope analyses were carried out on a noble-gas mass spectrometer using laser fusion on microsamples (n × 0.01 to n × 0.2 mg). A new isochron - an "inverse isochron" for K-Ar dating - was designed. FCs and B4M yielded apparent and inverse isochron ages of 28.1 ± 0.1 and 28.0 ± 0.3 Ma, 18.2 ± 0.1 and 18.2 ± 0.5 Ma, which are consistent with the recommended ages, while the MMhb-1 presented lower apparent and inverse isochron ages (510.8 ± 4.8 and 512.3 ± 17.0 Ma) than the recommended ones. The initial argon compositions for the three standard minerals are 299.2 ± 205.3 (FCs), 294.0 ± 16.4 (B4M) and 290.9 ± 203.1 (MMhb-1), agreeing with that of air. The proposed approach potentially overcomes the issues of 40 Ar/39 Ar rising from irradiation and the drawbacks of K-Ar. By using laser fusion on multiple microaliquots from a same sample, this approach can produce accurate and precise K-Ar ages and give an inverse isochron. This new approach may provide an alternate dating method of geochronology based on argon isotopes.

A new high precision determination of the atmospheric21Ne abundance

We have carried out a series of precise Ne-isotope measurements of atmospheric Ne-separates on a state-of-the-art high mass resolution Thermo-Fisher MC Plus Noble Gas Mass Spectrometer. Assuming an atmospheric22Ne/20Ne ratio of 0.102, we derive the relative mass fractionation corrected21Ne abundance in the terrestrial atmosphere, allowing us to determine a new21Ne/20Ne ratio of 0.0029577 ± 14.

Accurate Determination of the Absolute 3He/4He Ratio of a Synthesized Helium Standard Gas (Helium Standard of Japan, HESJ): Toward Revision of the Atmospheric 3He/4He Ratio

AbstractThe helium standard of Japan, referred to as HESJ, is an interlaboratory standard for the 3He/4He ratio. While the ratio of 3He and 4He of the HESJ was previously determined by a relative comparison to atmospheric helium, the absolute value of the 3He/4He ratio of the HESJ has not been directly determined yet. Therefore, it relies on the early measurements of that of atmospheric helium. The accuracy of the absolute 3He/4He ratios of the atmosphere and other working standards including HESJ is crucial in some applications of helium isotopes, such as tritium‐3He dating, surface‐exposure age determination based on cosmogenic 3He, and the accurate measurement of the neutron lifetime. In this work, new control samples of helium gases with 3He/4He ratios of 14, 28, and 42 ppm were fabricated with accuracy of 0.25–0.38% using a gas‐handling system for a neutron lifetime experiment at Japan Proton Accelerator Research Complex. The relative 3He/4He ratios of these samples and the HESJ were measured using a magnetic‐sector type, single‐focusing, noble gas mass spectrometer with a double collector system. As a result, the absolute 3He/4He ratio of the HESJ was determined as 27.36 ± 0.11 ppm. The atmospheric 3He/4He ratio was determined as 1.340 ± 0.006 ppm, based on this work.

The 40Ar/39Ar dating of quartz: new insights into the metallogenic chronology of the Jinchang gold deposit and its geological significance

The Jinchang gold deposit has been extensively studied, but precise dates for its formation are debated. Native gold mainly occurs as inclusions within pyrite and quartz. In this study, we analysed quartz crystals coeval with gold precipitation from two different types of mineralization using the ArgusVI multi-collector noble gas mass spectrometer by the stepwise crushing technique to resolve the timing and genesis of gold mineralization. 40Ar/39Ar dating of quartz samples (J12Q) from breccia ore yields a plateau age of 109.87 ± 0.86 Ma, and an inverse isochron age of 109.87 ± 0.88 Ma. Quartz samples (J18Q) from vein ore yields a slightly younger plateau age of 107.76 ± 0.85 Ma, with an inverse isochron age of 107.76 ± 0.92 Ma. These dates place the ore-forming age of the Jinchang gold deposit at 107~110 Ma, much younger than previously published radiometric ages, suggesting the gold mineralization is spatio-temporally associated with the granite porphyry. The formation of the Jinchang gold deposit is consistent with the regional late Mesozoic porphyry-epithermal gold mineralization event in the Yanbian-Dongning area. Finally, our study shows that 40Ar/39Ar of quartz can be used as a powerful tool to date the formation ages of hydrothermal ore deposits.

​40Ar/39Ar geochronology of terrestrial pyroxene

Geochronological techniques such as U/Pb in zircon and baddeleyite and 40Ar/39Ar on a vast range of minerals, including sanidine, plagioclase, and biotite, provide means to date an array of different geologic processes. Many of these minerals, however, are not always present in a given rock, or can be altered by secondary processes (e.g. plagioclase in mafic rocks) limiting our ability to derive an isotopic age. Pyroxene is a primary rock forming mineral for both mafic and ultramafic rocks and is resistant to alteration process but attempts to date this phase with 40Ar/39Ar has been met with little success so far.In this study, we analyzed pyroxene crystals from two different Large Igneous Provinces using a multi-collector noble gas mass spectrometer (ARGUS VI) since those machines have been shown to significantly improve analytical precision compared to the previous single-collector instruments. We obtain geologically meaningful and relatively precise 40Ar/39Ar plateau ages ranging from 184.6 ± 3.9 to 182.4 ± 0.8 Ma (2σ uncertainties of ±1.8–0.4%) and 506.3 ± 3.4 Ma for Tasmanian and Kalkarindji dolerites, respectively. Those data are indistinguishable from new and/or published U-Pb and 40Ar/39Ar plagioclase ages showing that 40Ar/39Ar dating of pyroxene is a suitable geochronological tool.Scrutinizing the analytical results of the pyroxene analyses as well as comparing them to the analytical result from plagioclase of the same samples indicate pure pyroxene was dated. Numerical models of argon diffusion in plagioclase and pyroxene support these observations. However, we found that the viability of 40Ar/39Ar dating approach of pyroxene can be affected by irradiation-induced recoil redistribution between thin pyroxene exsolution lamellae and the main pyroxene crystal, hence requiring careful petrographic observations before analysis. Finally, diffusion modeling show that 40Ar/39Ar of pyroxene can be used as a powerful tool to date the formation age of mafic rocks affected by greenschist metamorphism and will likely play an important role in high temperature thermochronology.

The performance of the Noblesse multi-collector noble gas mass spectrometer for 40Ar/39Ar geochronology

Noblesse multi-collector noble gas mass spectrometer is specially designed for multi-collection of Ar isotopes with different beam sizes, especially for small ion beams, precisely, and hence is perfectly suitable for 40Ar/39Ar geochronology. We have analyzed widely used sanidine, muscovite, and biotite standards with recommended ages of ~ 1.2–133 Ma, with the aim to assess the reliability of Noblesse for 40Ar/39Ar dating. An ESI MIR10 30W CO2 laser was used for total fusion or incremental heating samples. Extracted gases were routinely purified by four SAES NP10 getters (one at ~ 400 °C and others at room temperature). A GP50 getter and a metal cold finger cooled by liquid N (− 196 °C) were also attached for additional purification if necessary. The Ar isotopes were then measured by Noblesse using Faraday or multiplier according to the signal intensities. Over a period of 1.5 months 337 air calibrations produced a weighted mean 40Ar/36Ar of 296.50 ± 0.08 (2σ, MSWD = 4.77). Fish Canyon sanidine is used to calculate J-values, which show good linear relationship with position in irradiation. The age of four mineral standards (Alder Creek sanidine, Brione muscovite, Yabachi sanidine, and Fangshan biotite) are within error of the accepted ages. Five Alder Creek sanidine aliquots yielded an age range of 1.174–1.181 ± 0.013 Ma (2σ) which broadly overlaps the established age of the standard and the uncertainty approaches those of the foremost Ar/Ar laboratories in the world. The weighted mean ages of four Brione muscovite aliquots (18.75 ± 0.16 Ma, 2σ), five Yabachi sanidine aliquots (29.50 ± 0.19 Ma, 2σ), and three Fangshan biotite aliquots (133.0 ± 0.76 Ma, 2σ) are consistent with the recommended values of these standards, and the uncertainties are typical of modern Ar/Ar laboratories world-wide.

Multi-phase cooling of Early Cretaceous granites on the Jiaodong Peninsula, East China: Evidence from 40Ar/39Ar and (U-Th)/He thermochronology

The Jiaodong Peninsula at the southeastern periphery of the North China Craton (NCC) has undergone complex changes since the Mesozoic. A striking feature of the NCC is the widespread distribution of Late Mesozoic magmatic rocks, predominantly characterized by granitic intrusions. These igneous plutons are economically important due to their polymetallic mineralization and significant as geodynamic tracers of the regional tectonic evolution. Two representative Early Cretaceous granites (the Yashan and Yuangezhuang plutons) on the Jiaodong Peninsula were selected for multiple-thermochronometer studies to constrain a complete thermal history from their emplacement to near-surface conditions. We obtained biotite 40Ar/39Ar ages of two granites on the new generation Argus VI noble gas mass spectrometer. Two biotites registered identical 40Ar/39Ar plateau ages of ∼117 Ma, which are consistent within the error with their zircon U-Pb ages. This suggested that the two granites were emplaced at the same time and cooled rapidly to about 300 °C. The single crystal zircon (U-Th)/He (ZHe) dating for the two samples gave weighted mean ages of 93.5 ± 4.5 Ma and 93.3 ± 5.0 Ma. Combined with previously published geochronological data and the thermal inversion of the zircon low temperature thermochronological data, three phases of rapid cooling were identified for the two studied plutons: (1) the Early Cretaceous (117–110 Ma); (2) the Late Cretaceous (100–90 Ma); and (3) the Early Tertiary (65–50 Ma). The Early Cretaceous phase of cooling occurred in a regional extensional regime on the NCC characterized by various extensional structures. The Late Cretaceous cooling is consistent with the third episode of the “Yanshan Movement”, which caused a regional basin inversion event on the NCC. In comparison to the first two phases of rapid cooling, the Early Tertiary cooling was more gradual. This phase corresponded to a widely developed Eocene rift on the NCC and the reactivation of major boundary faults, such as the giant Tan-Lu Fault Zone and the Taihangshan Fault.

Minimisation of pressure dependent mass discrimination in the ion source of the Helix MC Plus noble gas mass spectrometer

When tuned for maximum sensitivity, the electron bombardment ion source on the ANU (the Australian National University) Helix MC Plus noble gas mass spectrometer produces an Ar ion beam that is mass discriminated as a function of Ar partial pressure. This effect can be reduced substantially or eliminated by adjusting the repeller and trap voltages, although with a sensitivity loss of up to 50%. A recommended procedure for tuning an ion source to reduce pressure dependent mass discrimination is described. Similar procedures can be applied to other noble gases and other ion sources to ensure that pressure dependent mass discrimination is avoided.

A chondrite strewn field was found in east of Lop Nor, Xinjiang

The meteorites are the most important extraterrestrial samples for understanding the formation and the evolution history of the solar system, although ~382 kg lunar samples and ~1500 asteroid mineral grains have been returned by human space exploration activities. The Northwest region of China, especially the Xinjiang, has a vast area of sandy deserts and Gobi Deserts. The lower annual rainfall and the dry climate of this region provide a good condition for meteorite preservation. In recent years, the number of recovered meteorites from the Gobi Deserts in Xinjiang increased significantly. The Sanfengshan area, located about 65 km east of Lop Nor, is one of the research regions. We first collected three ordinary chondrites in Sanfengshan area on October 9, 2013. Then, we carried out 11 meteorite search campaigns in this area. More than 130 meteorite fragments with a total mass over 160 kg have been recovered. The map of all collected Sanfengshan meteorites depicts a clearly 3 km×11 km elliptic strewn field. The sizes are sorted in the SE-NW-oriented ellipsoid of the strewn field, therefore indicating that the meteor entered the atmosphere from SE at a low angle relative to the ground. In this study, six meteorites (Tuya 002–007) from the Sanfengshan field have been measured using a Scios-FIB field emission scanning electron microscope (SEM), a JXA 8230 electron microprobe analysis (EMA), and a self-made noble gas mass spectrometer. Among all of the collected meteorites, Tuya 002 is the only one unusual sample, which doesn’t show any fusion crust on its surface. We inferred that Tuya 002 is not paired with the other collected meteorites. The well-defined chondrule boundaries and heavy weathering grade, i.e. W3 (the occurrence of large amounts of calcium sulfate in Tuya 002 indicates that it suffered a heavy terrestrial weathering) also support the conclusion that Tuya 002 is obviously different from the other meteorites collected in the Sanfengshan area. In addition to Tuya 002, all the meteorites collected in this region most likely originate from one single meteoric shower. These meteorites all belong to the L5 ordinary chondrite group, with a moderate shock stage of S2 and a heavy weathering grade of W3. The cosmic ray exposure age of Tuya 003 (the representative meteorite of the Sanfenghshan meteoric shower) is 45.6±4.4 Ma. This indicates that the meteoroid that produced the Sanfengshan meteoric shower could be produced in the 45 Ma break-up event on L chondrite parent body. On the other hand, petrographic observations and noble gas measurements shown that Tuya 002 belongs to the L4 ordinary chondrite group. A rather lower CRE age relative to the Sanfengshan L5 chondrites of 17.0±4.1 Ma has been calculated. This also indicates that Tuya 002 is not paired with other L5 meteorites collected in the same strewn field. Our studies shown that the meteorites collected in Sanfengshan area consist of more than one meteorite fall. It includes the main L5 meteorite fall (produced the Sanfengshan L5 strewn field) and the L4 meteorite fall (represented by Tuya 002). This indicates that the Sanfengshan area is not a meteorite dense area. In recent years, several meteorite dense areas (e.g., Loulan Yizhi, Lop Nur, Argan, and Xingdi) have been gradually reported. The limited meteorite types found in such reported meteorite dense areas indicates that these regions are maybe not the real meteorite dense areas, but probably represents the meteorites strewn field. Therefore, it is necessary, in the future, to carry out detailed petrology, mineralogy, cosmic ray exposure age as well as terrestrial age measurements to identify the meteorite dense area in/around the Xinjiang.