Guangzhou Institute of Geochemistry
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Crustal magma oxidation state and endowments in porphyry copper deposits
No full textPorphyry copper deposits (PCDs) supply the majority of the world's copper (Cu) as well as significant amounts of molybdenum (Mo) and gold (Au). The formation of these deposits is controlled by a variety of geological factors, among which the magmatic oxidation is one of the focuses of current research. This study investigates the redox characteristics of arc magmas by analyzing the ratio of vanadium (V) to scandium (Sc) and its correlation with the oxygen fugacity (fO) of magmas from arcs of various crustal thicknesses globally. We compiled an extensive dataset of published V/Sc values and studied the partition coefficients of V and Sc between minerals and silicate melts across various magmatic environments. The results demonstrate that fractional crystallization of magnetite markedly reduces V/Sc values of the residual melt. Furthermore, magnesium number (Mg#) at the onset of magnetite fractionation is strongly positively correlated with fO of the equilibrium magma. Based on this, the oxidation of arc magmas from different crustal thicknesses can be evaluated. The result suggests that magmas generated in crusts thicker than 20 km tend to be more oxidized with increasing crust thickness. This trend is attributed to enhanced intracrustal differentiation processes involving garnet and amphibole, particularly in mature island and continental arcs. In contrast, magmas in thinner arc crusts (<20 km), which are significantly influenced by subducted slab materials, display higher oxidation states than most of their thicker crust counterparts. These findings suggest that both subduction dynamics and crustal thickness play a vital role in determining the oxidation state of arc magmas and, consequently, their capacity to generate PCDs. Highly oxidized, primitive arc magmas are less favorable for PCD formation due to that they tend to experience magnetite fractionation and thus sulfide saturation in the early stage of magma evolution, a process leading to copper depletion. On the contrary, thick arcs where magnetite crystallization is widely suppressed and therefore more conducive to retaining Cu in evolved magmas. This study highlights the coupled roles of subduction input and intra-crustal differentiation in the genesis of arc magmatic oxidation, and provides geochemical indications for the metal endowment of porphyry copper deposits based on the V/Sc systematics
A Pb-free Sn-Bi alloy mount preparation method for secondary ion mass spectrometry (SIMS) analyses
No full textSample preparation is a critical step to achieve reliable in situ chemical analysis. Sample mounting technique with a tin-based alloy was developed in recent years, which is particularly useful for high-precision volatile analyses by secondary ion mass spectrometry (SIMS). However, the success of this technique is hindered by challenges, such as complex alloy preparation and potential Pb contamination. Herein, we introduce a new Sn-Bi alloy preparation method that may overcome these hurdles and assess its potential as a standard preparation method for in situ volatile and isotope analyses. This new alloy can be manufactured with commercially available pure tin and bismuth metal (atomic Sn : Bi = 42 : 58), and its production requires only a heating plate and clean containers. This ensures its high accessibility to laboratories worldwide. The Pb content of the alloy is dependent on the tin and bismuth used. The material (Sn and Bi) from three different manufacturers were evaluated in this study, resulting in the virtually Pb-free MAC alloy (Pb <0.2 mu g g(-1)). The SIMS U-Pb dating results of the zircon standards (Qinghu, Ple & scaron;ovice, and SA01) are consistent with the recommended values (within error). Furthermore, the mounted samples exhibit satisfactory relief on this alloy, suggesting that this alloy material is appropriate for the analysis of oxygen isotopes. The routine external precision of oxygen isotope ratios is better than 0.30 parts per thousand (2sd), on par with that obtained with epoxy mounts. The water background in the SIMS sample chamber can be recovered rapidly after sample transfer from the storage to the sample chamber. Hence, this tin-based alloy is suitable for sample mounting for SIMS volatile and isotope (incl. U-Pb) analyses
Enhanced enrichment of rare earth elements during pedogenesis under subtropical climate
No full textRare earth elements (REEs) are crucial strategic resources, and weathering-crust rare earth deposits are one of the primary sources. To systematically understand the geochemical behaviour (e.g. enrichment and leaching) of REEs in soils (or weathering crusts) formed from diverse parent rocks under varying climatic conditions, 171 soil profiles (weathering crusts) developed from three main types of parent rocks (granite, basalt and carbonate rock) worldwide were studied. Granite shows the highest concentration of REEs at 264 [interquartile range (IQR): 278] ppm with 171 (IQR: 151) ppm and 11.9 (IQR: 36.4) ppm in basalt and carbonate rock, respectively (median test: p < 0.05). The median REE values within the soil profiles were significantly different (median test: p < 0.05), with the concentration of 318 (IQR: 441) ppm, 267 (IQR: 217) ppm and 207 (IQR: 417) ppm in soils derived from granite, carbonate rock and basalt, respectively. Principal component analysis and linear mixed-effects models revealed that soils developed from granite and basalt inherit the mineral characteristics of their parent rocks, with REE concentrations primarily influenced by the REE content of the parent rock and climate. In contrast, the REE concentrations in soils developed from carbonate rocks are predominantly controlled by climate. Linear mixed-effects models and correlation analysis indicate that the enrichment of REEs (Q(REE)) shows a trend of initially increasing and then decreasing with rising temperature and precipitation, due to variations in the host clay minerals. The greatest enrichment occurs in the subtropical region (mean annual temperature = 15-23 degrees C; mean annual precipitation = 1000-2000 mm); weathering-crust type REE deposits are primarily found in the subtropics
Shortwave infrared (SWIR) spectroscopy for greenfield exploration: Investigating the Bayi-Muchang prospect within the Jiama giant Porphyry-Skarn system
No full textJiama is a giant porphyry-skarn system (1,814 Mt ore @ 0.40 % Cu) within the Gangdese porphyry copper belt, Southern Tibet. Recently, copper, molybdenum, and tungsten anomalies, similar to those at Jiama, have been identified in the Bayi-Muchang prospect southwest of the deposit. However, the mineralization potential of this peripheral area and its genetic connection to Jiama remain poorly constrained. This study employs shortwave infrared (SWIR) spectroscopy to map alteration minerals in both the Bayi-Muchang prospect and compare them to those in the southwestern Jiama deposit. SWIR spectral results reveal that the Bayi-Muchang prospect is dominated by chlorite, phengite, quartz, and less carbonates from chlorite-sericite alteration with minor epidote and chlorite vein-halos, as well as pervasive propylitic assemblages with chlorite, epidote, and less carbonates, indicating the presence of an independent hydrothermal center where ore-forming fluids were concentrated and exsolved rather than an extension of the Jiama deposit. Key spectral indicators for mineralized zones, derived from Jiama samples, including wavelength of 2200 nm feature longer than 2207 nm and the illite spectral maturity higher than 1.4 in white mica, as well as the full width at half maximum (FWHM) of 2335 nm feature longer than 36 nm in carbonate minerals. Additionally, carbonate minerals in the Duodigou Formation north of Bayi-Muchang record a contact metamorphism gradient, with the FWHM of the 2335 nm feature increasing from 36 to 56 nm from south to north. The northwest Bayi-Muchang area, near the hydrothermal center, is identified as a favorable target for skarn-type and porphyry-type mineralization. This study highlights the effectiveness of SWIR spectroscopy mapping in supporting exploration strategies within porphyry-skarn systems, particularly for greenfield targets
Co-metabolic Biotransformation of Bisphenol AF by a Bisphenol A-Growing Bacterial Enrichment Culture
No full textThe fluorinated bisphenol A (2,2-bis[4-hydroxyphenyl]propane, BPA) substitute bisphenol AF (BPAF) could be more persistent and toxic than BPA, but little is known about its environmental fate. In this study, we established a co-metabolic BPAF-degrading bacterial enrichment culture with BPA as the growth substrate. BPAF degradation by the enrichment culture was dependent on BPA, and BPAF could be eliminated to below the detection limit with successive additions of BPA. BPAF was mainly degraded via phenolic ring hydroxylation and sequential ring cleavage, which are minor BPA transformation pathway. Conjugated BPAF products were also identified based on the characteristic CF3 - fragment and were found to accumulate during BPAF degradation. Sphingopyxis was the key BPA and BPAF degrader in the aerobic enrichment cultures, which was the most abundant genera in only BPA-added and BPA and BPAF-added cultures and was proven to be able to degrade BPA and BPAF by isolation. The aerobic co-metabolic BPAF degrading community also contain non-BPA and BPAF degraders, such as Pandoraea, which may play a supporting role in the community
Identifying Recycled Materials Using Mo Isotopes in Intraplate Alkali Basalts From the Southeastern Margin of Tibetan Plateau
No full textMantle heterogeneity in lithology and geochemistry is often attributed to recycled subducted materials. While distinct mantle end-members are identified by radiogenic isotopes, the specific recycled materials contributing to this heterogeneity remain debated. This study presents Mo-Sr-Nd-Pb isotopic data for OIB-like alkali basalts from the Maguan area in the southeastern Tibetan Plateau, focusing on slab inputs' role in mantle heterogeneity. The Miocene (ca. 13 Ma) Maguan alkali basalts are divided into two types based on petrographic and geochemical characteristics, showing similar Sr-Nd-Pb isotopic signatures but different Mo isotopic compositions. Type I basalts exhibit a wide delta 98/95Mo range (-0.31 parts per thousand to -1.03 parts per thousand, average -0.47 parts per thousand +/- 0.06 parts per thousand, 2SD = 0.40 parts per thousand, n = 13), while type II basalts have heavy and constant delta 98/95Mo values (-0.11 parts per thousand to -0.17 parts per thousand, average -0.14 parts per thousand +/- 0.01 parts per thousand, 2SD = 0.05 parts per thousand, n = 6). The unique low delta 98/95Mo value (-1.03 parts per thousand) in type I basalts is among the lowest reported in OIB-like continental basalts. Type I basalts likely originate from an enriched asthenospheric mantle metasomatized by melts from recycled dehydrated oceanic crust and sediments, whereas type II basalts are derived from partial melting of an enriched asthenospheric mantle metasomatized by melts from recycled serpentinized peridotites. The residual Tethys oceanic slabs in the deep mantle significantly contribute to the mantle source of the Maguan basalts. The formation of Maguan Miocene magmas may be linked to mantle upwelling induced by the subduction of the West Burma plate. This study highlights the Mo isotopic system's utility in tracing complex slab fluxes generating mantle geochemical heterogeneity
Gold occurrence and mineralization in the Paleozoic Heijianshan Fe-Cu (-Au) deposit, Eastern Tianshan
No full textGold (e.g., electrum) has been reported in the Paleozoic Heijianshan Fe-Cu (-Au) or iron oxide-copper-gold-like (IOCG-like) deposit in the Eastern Tianshan, but relationships between gold occurrence and sulfides are unclear. The Heijianshan Fe-Cu (-Au) (or IOCG-like) deposit underwent five alteration and mineralization stages: Pre-ore epidote alteration (Stage I), syn-ore magnetite/iron mineralization (Stage II) followed by pyrite alteration (Stage III) and Cu (-Au) mineralization (Stage IV), and post-ore late veins (Stage V). This deposit mainly has two types of pyrite (A and B) based on pyrite-hematite and pyrite-pyrrhotite-chalcopyrite assemblages. They are euhedral to subhedral and mainly homogenous, with the former having porous or inclusion-rich domains. Trace elements incorporating into pyrite at Heijianshan are mainly controlled by compositions (e.g., As, Co, and Cu), temperature (e.g., Ni and Se), and oxygen fugacity (fO2; e.g., As and Se) of hydrothermal fluids, respectively. The timeresolved depth-concentration profiles suggest trace elements in pyrite and chalcopyrite occur as solid solution (e. g., Co, Ni, Zn, As, and Se) and micro- to nano-sized mineral inclusions (e.g., Cu, Bi, and Pb). The gold occurrence at Heijianshan is invisible as solid solution in Stage III pyrite and Stage IV chalcopyrite and visible as micronsized Stage IV electrum. Moreover, incorporation mechanisms of invisible gold are Au3+ substituting iron or copper in pyrite A and chalcopyrite, respectively, and Au+ incorporating into the vacancy or defect positions of pyrite B. Sulfides texture and geochemical compositions when combined with previous in-situ sulfur isotope suggest that pyrite formation was resulted from interaction between external basinal brines and altered host rocks under different temperature and fO2 conditions. Ongoing fluid-rock reaction led to formation of chalcopyrite +/- electrum veins as Cu (-Au) mineralization at Heijianshan. This study suggests that the prolonged interaction contributes to sulfide formation and Cu (-Au) mineralization in these Paleozoic Fe-Cu or IOCG-like deposits formed in basin-related setting, and the Aqishan-Yamansu belt, Eastern Tianshan has gold mineralization potential
Co-precipitation of primary dolomite and Mg-rich clays in Deep Springs Lake, California
No full textIn contrast to the prevalence of dolomite [CaMg(CO3)(2)] in the geological record, there are few instances of recent formation. This discrepancy occurs despite supersaturation with respect to dolomite in many modern marine and lacustrine environments. Additionally, laboratory experiments have struggled to precipitate dolomite at ambient temperatures (<40degree celsius) even under highly saturated conditions. However, recent work has found dissolved silica to be an effective catalyst for the direct precipitation of dolomite. To test this hypothesis, the hydrology and mineralogy of Deep Springs Lake, a playa setting with primary dolomite precipitation has been explored. In this study, the central playa sites with the highest sedimentation rates were found to have dissolved silica concentrations close to saturation. Rietveld refinement showed that bulk mineral assemblages of core samples contain 20 to 40% fine-grained, partially ordered dolomite along with a 10 to 20% poorly crystalline clay fraction, while transmission electron microscopy imaging found a co-precipitation relationship between the fine-grained dolomite and Mg-rich smectite clays, where the Mg-rich smectite clays act as a sink for the excess dissolved silica during evaporation. Transmission electron microscopy results indicate that the nanodolomite crystals formed through surface-induced nucleation and growth processes in the presence of dissolved silica as a catalyst. The broad coincidence of conditions for the direct precipitation of dolomite and Mg-rich smectite clays provides evidence that silica may be a key to the dolomite problem, as well as constraining palaeoenvironments such as the Pre-salt Barra Velha Formation
Effects of carbonate on ferrihydrite transformation in alkaline media
No full textAlkaline media widely exist in natural and engineered systems such as semiarid/arid areas, radioactive waste sites, and mine tailings. In these settings, the commonly occurring iron (oxyhydr)oxides differed in their ability to influence the fate of nutrients and contaminants. Due to the substantially increased atmospheric carbon dioxide (CO2) concentration, carbonate stands to increase in these media. However, how increasing carbonate affects the transformation of poorly crystalline iron (oxyhydr)oxides (e.g., two-line ferrihydrite) under alkaline conditions still remains unclear. Here, kinetics of ferrihydrite transformation were evaluated at pH similar to 10 as a function of [carbonate] = 0-286 mM using synchrotron-based X-ray and vibrational spectroscopic techniques. The results showed that carbonate slowed down ferrihydrite transformation slightly and suppressed goethite formation, but promoted hematite formation regardless of its concentration. At low carbonate concentration (11.42 mM), the effect of carbonate on product formation was obvious due to the weak inner-sphere complex; however, at high carbonate concentration (80-286 mM), the effect was retarded because of the adsorption equilibrium of carbonate as well as the initial carbonate adsorption followed by desorption. Moreover, carbonate modified the morphology of hematite from rhombic to ellipsoidal to honeycomb and goethite from rod-like to needle-like to spindle-like due to the inner-sphere adsorption-desorption of carbonate and adsorption of hydroxyl ions on reactive sites of iron (oxyhydr)oxides in alkaline media. The results suggest that the concurrently increasing carbonate with enhanced atmospheric CO2 could control the transformation and occurrence of iron (oxyhydr)oxides in natural and engineered environments and have important implications for the biogeochemical cycles of iron and carbon.
This study indicates that in alkaline media, carbonate slightly inhibits ferrihydrite transformation and suppresses goethite formation, but promotes hematite formation, which has important implications for elemental biogeochemical cycles