Meijuan Yao’s research while affiliated with Sun Yat-sen University and other places

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Publications (5)


Magma Mixing as a Trigger for Sulphide Saturation in the UG2 Chromitite (Bushveld): Evidence from the Silicate and Sulphide Melt Inclusions in Chromite
  • Article
  • Full-text available

October 2017

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158 Reads

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6 Citations

Acta Geologica Sinica

Meijuan YAO

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Ye CAO

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Zongbao REN

It is of great importance to understand the origin of UG2 chromitite reefs and reasons why some chromitite reefs contain relatively high contents of platinum group elements (PGEs: Os, Ir, Ru, Rh, Pt, Pd) or highly siderophile elements (HSEs: Au, Re, PGE). This paper documents sulphide-silicate assemblages enclosed in chromite grains from the UG2 chromitite. These are formed as a result of crystallisation of sulphide and silicate melts that are trapped during chromite crystallisation. The inclusions display negative crystal shapes ranging from several micrometres to 100 μm in size. Interstitial sulphide assemblages lack pyrrhotite and consist of chalcopyrite, pentlandite and some pyrite. The electron microprobe data of these sulphides show that the pentlandite grains present in some of the sulphide inclusions have a significantly higher iron (Fe) and lower nickel (Ni) content than the pentlandite in the rock matrix. Pyrite and chalcopyrite show no difference. The contrast in composition between inter-cumulus plagioclase (An68) and plagioclase enclosed in chromite (An13), as well as the presence of quartz, is consistent with the existence of a felsic melt at the time of chromite saturation. Detailed studies of HSE distribution in the sulphides and chromite were conducted by LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry), which showed the following. (I) Chromite contained no detectable HSE in solid solution. (II) HSE distribution in sulphide assemblages interstitial to chromite was variable. In general, Pd, Rh, Ru and Ir occurred dominantly in pentlandite, whereas Os, Pt and Au were detected only in matrix sulphide grains and were clearly associated with Bi and Te. (III) In the sulphide inclusions, (a) pyrrhotite did not contain any significant amount of HSE, (b) chalcopyrite contained only some Rh compared to the other sulphides, (c) pentlandite was the main host for Pd, (d) pyrite contained most of the Ru, Os, Ir and Re, (e) Pt and Rh were closely associated with Bi forming a continuous rim between pyrite and pentlandite and (f) no Au was detected. These results show that the use of ArF excimer laser to produce high-resolution trace element maps provides information that cannot be obtained by conventional (spot) LA-ICP-MS analysis or trace element maps that use relatively large beam diameters.

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Thermoluminescence (Tl) analysis for otoliths of the wild carps (Cyprinoid) from Baiyangdian lake and Miyun reservior: Some implications for monitoring water environment

August 2012

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3 Reads

Carpathian Journal of Earth and Environmental Sciences

Otolith is a typical biomineral carrier growing on insides of fish skull with prominent zoning structure formed by alternating layers of protein and calcium carbonate growing around the nucleus. Even though thermoluminescence (TL) analysis on biomineral has been widely used to measure the radiation exposure in recent twenty years, the TL characteristics of the fish otolith have not yet been reported in the literature. TL characteristics of otoliths from the wild carps (cyprinoid) living in the Baiyangdian Lake, Hebei Province and Miyun Reservoir, Beijing City was firstly studied, as well as the differences of energy gap (E) between the fish otoliths in the two waters have also been discussed in this paper. The experimental results indicate that TL curve parameters: peak temperature (Tp), luminous intensity (I), integrated intensity (S) and middle width (Wm) for the glow curves of the cyprinoid otoliths from Baiyangdian Lake are greater than those from Miyun reservoir, and the stability of the formers' TL curve parameters value and energy gap (E) is weaker than the latters'. In comparison to the Miyun Reservoir, the analysis manifest that the electrons and vacancies that trapped in the otoliths from Baiyangdian Lake are more likely to escape. According to the investigation, the contaminative degree and eutrophication in the water of Baiyangdian Lake is heavier than that of Miyun Reservoir. So the characteristics of TL growth curves of the cyprinoid otoliths is quite sensitive to heavier contaminated and less contaminated water, and it could be regarded as an important typomorphic biomineral for monitoring the contaminative degree and environment change of the water.


Source and evolution of fluids in the Shihu gold deposit, Taihang Mountains, China: Evidence from microthermometry, chemical composition and noble gas isotope of fluid inclusions

May 2012

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77 Reads

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13 Citations

Geochemistry Exploration Environment Analysis

The well-known Shihu quartz vein-type Au deposit in the Taihang Mountains in the North China Craton (NCC) is hosted by ductile-brittle faults within the Neo-archean-Palaeo-proterozoic Fuping Group metamorphic complex. The deposit exhibit four stages of quartz veins: (1) quartz-K-feldspar-sericite; (2) quartz-pyrite; (3) quartz-polymetallic sulphide; and (4) quartz-carbonate +/- pyrite. Three types of fluid inclusions in quartz are recognized in this study. Solid-bearing high-salinity (Type I) fluid inclusions have homogenization temperatures of up to 390 degrees C and high salinities of 33-47 wt% NaCl equivalent. Two-phase H2O-rich (Type II) fluid inclusions homogenized between 129-396 degrees C and have salinities of 1.7-12.5 wt% NaCl equivalent. Two/three-phase CO2-rich (Type III) fluid inclusions, which are abundant in auriferous quartz veins, have homogenization temperatures of 205-358 degrees C and salinities of 1.63-7.64 wt% NaCl equivalent. Laser Raman spectroscopy and quadrupole mass spectrometry confirmed that the vapour phase in the fluid inclusions is dominated by CO2, H2S, CH4, C2H4, N-2 and Ar besides H2O, whereas the liquid phase is composed of Cl-, SO42-, Na+, and K+ with minor Mg2+ and Ca2+. Fluid inclusions in pyrite associated with quartz ore-stages (2) and (3) have Sigma REE values of 0.61-342.17 ppm with negative Ce, Eu and Y anomalies and LREE enrichment relative to HREE, generally indicating a crustal source of ore fluids. Helium isotope studies of fluid inclusions in pyrites associated with quartz ore-stages (2) and (3) yielded He-3/He-4 ratios of 0.12-0.93 Ra (Ra= 1.4x10(-6) for air) and Ar-40/Ar-36 ratios of 3690-23678. The noble gas data suggest c. 10-20% mantle-derived ore fluids, reflecting an increased interaction of ore fluids with surrounding crustal rocks contributing additional He-4 to the fluids. The present data and various information from published works suggest that the Shihu Au deposit was formed during lithospheric thinning or decratonization beneath the Taihang Mountains. The fluids derived from the lower crust, formed due to partial melting and dehydration of the lithospheric mantle, were mixed with magmatic and meteoric waters, and finally precipitated Au and associated metals in the Shihu deposit.


Fluid evolution and ore genesis of the Qianhe gold deposite, Western Henan province, Central China

February 2012

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25 Reads

Carpathian Journal of Earth and Environmental Sciences

The Qianhe structure-controlled orogenic-mesothermal gold deposit is located in the Late Archean to Early Proterozoic metamorphosed volcanic and sedimentary rocks in the south margin of North China craton (NCC). Three stages of hydrothermal ore-forming processes are recognized, Early (E), Middle (M) and Late (L), characterized by coarse pyrite-quartz veins, fine pyrite-polymetallic sulfide veins and quartz-carbonate veins, respectively. Gold typically occurs as fracture-fillings associated with chalcopyrite and galena in M-stage. Fluid inclusions (FI) were examined in quartz from E-, M- and L-stage samples. FI petrography and microthermometric results suggest that three types of fluid inclusions are present at the deposit. Tm CO2 and Th CO2 in M-stage quartz range from -59.7 to -57.2°C and from 15.4 to 22.1°C, which are lower than those in E-stage quartz of ranging from -57.1 to -56.6°C and from 16.3 to 25.7°C. CO 2-rich inclusions have similar Tm CO2 and Th CO2 to those for CO 2-H 2O inclusions. CO 2-H 2O inclusions show salinities of 5.51 to 10.04 wt.% NaCl equivalent and Th of 242 to 336°C in E-stage quartz, and show salinities of 3.52 to 8.66 wt.% NaCl equivalent and Th of 213 to 240°C in M-stage quartz. Aqueous inclusions have a decreasing trend of salinities and Th from E-stage through M-stage to L-stage. Homogenization pressures of FI are estimated ranging from 367 to 872×10 5 Pa. The M-stage fluid has the lowest contents of ions (e.g., SO 42-, Cl -, K +) and (K+Na)/(Mg+Ca) but highest CO 2/H 2O ratios. The change in ore-forming fluids from K 2SO 4 type to NaCl type indicates the superposition of two hydrothermal mineralizing events. Together with the alkaline and reducing conditions, as indicated by decreased pH and increased Eh values, is most conducive to the deposition of polymetallic sulfides and native Au and electrum. Unlike in E-stage, FI in M- and L-stage quartz shows evidence of fluid immiscibility. The fact that most of gold is associated with M-stage quartz and sulfide but not with that of E-stage suggests that gold deposition occurs at the M-stage of fluid immiscibility. The sudden phase separation led to the deposition of large amounts of gold at the Qianhe deposit.

Citations (3)


... The volume of sulfide minerals in the UG-2 main seam is generally low, typically 1 vol.% (Hey 1999, Naldrett et al. 2009, Junge et al. 2014, Osbahr et al. 2014, Yao et al. 2017, Langa et al. 2021. Pentlandite and chalcopyrite are the most abundant sulfide minerals in the UG-2, and there is little to no pyrrhotite and only minor pyrite (McLaren & De Villiers 1982, Penberthy & Merkle 1999, Naldrett et al. 2009, Osbahr et al. 2014, Rose et al. 2018. ...

Reference:

Sulfide mineral chemistry and platinum-group minerals of the UG-2 chromitite in the northern limb of the Bushveld Igneous Complex, South Africa
Magma Mixing as a Trigger for Sulphide Saturation in the UG2 Chromitite (Bushveld): Evidence from the Silicate and Sulphide Melt Inclusions in Chromite

Acta Geologica Sinica

... Since the Au deposits are much younger than the regional metamorphic events, these deposits are clearly not metamorphicrelated orogenic Au deposits like those occurring in cratonic blocks worldwide (Groves et al. 1998). Instead, many studies argue for a genetic link between the gold mineralization and coeval mafic to intermediate magmatism sourced from metasomatized SCLM (e.g., Yang et al. 2003;Cao et al. 2012;Tan et al. 2012;. ...

Source and evolution of fluids in the Shihu gold deposit, Taihang Mountains, China: Evidence from microthermometry, chemical composition and noble gas isotope of fluid inclusions
  • Citing Article
  • May 2012

Geochemistry Exploration Environment Analysis

... The calibration of the zircon U-Pb isotope ratio was carried out with the Zircon 91500 external standard, with NIST 610 glass serving as the reference standard and 29 Si used as an internal standard for U, Th, and Pb calibration. The analytical procedures closely followed those outlined in previous studies [62,63]. ...

S–Pb isotopic geochemistry, U–Pb and Re–Os geochronology of the Huanggangliang Fe–Sn deposit, Inner Mongolia, NE China
  • Citing Article
  • June 2014

Ore Geology Reviews