Guangzhou Institute of Geochemistry
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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
A modified genetic model for multiple pulsed mineralized processes at the giant Qulong porphyry Cu-Mo mineralization system
No full textPorphyry copper deposits are economically significant sources of Cu and Mo, formed when metal-rich fluids precipitate at shallow levels, exsolving from underlying magmatic reservoirs at depth. However, the origin and evolution of these metal-rich fluids, whether through episodic enrichment from multiple pulses or a single continuous fluid-release event, remain a subject of controversy. To gain deeper insights into these processes, data on cathodoluminescence (CL) imaging, in situ trace elements, and Sr isotopes of newly discovered scheelite (Sch 1, Sch 2, and Sch 3) found in three generations of vein types within the giant Qulong porphyry Cu-Mo mineralization system are presented. The anhedral Sch 1 occurs in quartz + magnetite + anhydrite + chalcopyrite veins, exhibiting no obvious zoning in the CL image. These scheelite samples show high concentrations of Mo, Nb, Ta, and 87Sr/86Sr ratios ranging from 0.70688 to 0.71109. Moreover, they demonstrate enriched rare earth elements (REE) and negative Eu anomalies in the chondrite-normalized pattern, indicative of their formation in relatively oxidized metal-rich fluids during the early high-temperature alteration stage. Among the discovered scheelite varieties, the most volumetrically significant is the subhedral Sch2, which occurs in veins composed of quartz + pyrite + chalcopyrite. In its central region (Sch 2a), Cu-rich cores are dispersed, surrounded by an oscillatory Cu-poor mantle and rim (Sch 2b and 2c), as observed in the CL image. When compared to Sch 1, Sch 2 exhibits lower levels of REE, Nb, Ta, Mo, and 87Sr/86Sr ratios (ranging from 0.70502 to 0.70578), but higher Cu concentration and positive Eu anomalies. The gradual decrease in Cu content from the core to rim in Sch2, along with its rim's intergrowth with sulfide, suggests the precipitation of Cu during the second pulse of fluids. Euhedral Sch 3 is found in relatively moderate-temperature mineral assemblages within quartz + galena + sphalerite + molybdenite veins. It displays an oscillatory pattern with a Mo-rich core (Sch 3a), an extremely Mo-rich mantle (Sch 3b), and a Mo-poor rim (Sch 3c) in the CL image. Sch 3 shows lower REE, Cu, and Pb contents but variable Mo concentrations in different domains while consistently recording 87Sr/86Sr ratios ranging from 0.70498 to 0.70542. These characteristics indicate the precipitation process of Mo and Pb during the third pulse of fluid evolution. The observed shift in mineral assemblages, metal contents, and Sr isotopic components from Sch 1 to Sch 3 reflects the occurrence of different fluid pulses within a cooling porphyry Cu-Mo mineralization system. Overall, the three generations of scheelite found at the Qulong porphyry Cu-Mo deposit indicate the occurrence of multiple pulsed flows of magmatic fluids, revealing a more complex fluid evolution for porphyry Cu deposits than previously recognized. Notably, Sch 1 exhibits relatively high 87Sr/86Sr ratios, similar to the post-ore mafic porphyries, which are higher compared to Sch 2 and Sch 3, showing 87Sr/86Sr ratios similar to the pre- and syn-ore host granite and porphyry. This result implies that mafic magma has significantly contributed to the formation of the first pulse of magmatic fluids, whereas syn-ore granitic magma contributed to the ore fluids responsible for forming the veins containing Sch 2 and Sch 3 in the later stage. Therefore, we propose that volatiles from mafic magma, injected into the porphyry metallogenic system, play a crucial role in the formation of porphyry Cu deposits.
Additionally, for the first time, the presence of Cu-Mo-W metal endowment in the porphyry Cu deposits of the Gangdese magmatic belt is identified, providing valuable new insights into the metallogeny of porphyry Cu deposits and offering promising opportunities for tungsten exploration in the collision zone
Hydrogen isotope fractionation during aromatization to form alkylnaphthalene: Insights from pyrolysis experiments of 1-n-butyldecalin
No full textAlkylnaphthalene homologues are important components of aromatic fraction in sedimentary organic matter and contain significantly geochemical information relative to formation and evolution of the host organic matter. They mainly originate from hydrocarbon aromatization reaction which involves the dehydrogenation of aliphatic rings resulting in the fractionation of stable hydrogen isotopes between aromatic hydrocarbons and their precursors. To examine these processes, this study thermally pyrolysed 1-n-butyldecalin (BD) at different time intervals under 360 degrees C/50 MPa to study the aromatization and hydrogen isotope fractionation during alkylnaphthalene formation and evolution. The relative content of aromatic products, such as naphthalene (N) and 1-methylnaphthalene (1-MN), increases with increasing aromatization. Sulfur enhanced the degree of aromatization during BD thermal evolution, resulting in greater N and 1-MN formation. For the compounds with the same carbon skeleton, i.e. tran-1-methyldecalin (1-MD), 5-methyltetraline (5-MT) and 1-MN, the H-2 enrichment follows the order S2H1-MD < S2H5-MT < S2H1-MN during the low thermal conversion of BD. However, the order was subsequently destroyed with increasing aromatization. The results indicate that hydrocarbon aromatization can enrich aromatic hydrocarbon in 2H, resulting in a higher S2H value of higher aromatic-ringnumber hydrocarbon than that of a lower aromatic-ring-number at low aromatization. However, 2H enrichment will decrease and even result in a reverse order with enhanced aromatization. Our findings are beneficial for understanding genetic mechanism and hydrogen isotope fractionation effect during the formation and evolution of aromatic hydrocarbons
Experimental determination of tin partitioning between titanite, ilmenite, and granitic melts using improved capsule designs
No full textInvestigating mineral/melt Sn partitioning at high temperatures and pressures is a difficult task because Sn is a redox-sensitive multivalent element and easily alloys with noble metal sample capsules. To obtain accurate Sn partition coefficients between titanite, ilmenite, and granitic melts, we developed single capsule Pt or Au and double capsule Pt95Rh5 (or Au)-Re designs to avoid significant Sn loss at a controlled oxygen fugacity (f(O2)). With these new capsule designs, we performed piston-cylinder experiments of Sn partitioning between titanite, ilmenite, and granitic melts. The experimental P-T-f(O2) conditions were 0.5-1.0 GPa, 850-1000 degrees C, and similar to QFM+8 to similar to QFM-4 (quartz-fayalite-magnetite, QFM, buffer), with f(O2) controlled by the solid buffers of Ru-RuO2, Re-ReO2, Co-CoO, graphite, and Fe-FeO. The obtained mineral/melt Sn partition coefficients (D-Sn(min/melt)) are 0.48-184.75 for titanite and 0.03-69.45 for ilmenite at the experimental conditions. The D-Sn(min/melt) values are largely dependent on f(O2), although the effects of temperature and melt composition are also observed. D-Sn(Ttn/melt) strongly decreases with decreasing f(O2), from similar to 46-185 at the most oxidizing conditions (Ru-RuO2 buffer), to similar to 2-16 at moderately oxidizing to moderately reducing conditions (Re-ReO2 to Co-CoO and graphite buffers), to <1 at the most reducing conditions (Fe-FeO buffer). D(Sn)Ilm/melt exhibits a variation trend similar to D-Sn(Ttn/melt) but is always lower than D-Sn(Ttn/melt) at a given f(O2). These D-Sn(min/melt) values can be applied to quantitatively assess the mineralization potential of granitic magmas. Using D-Sn(Ttn/melt), we estimate that Sn contents are similar to 150-400 ppm in the pre-mineralization magmas of the tin-mineralized Qitianling plutons (South China)
Magnesium isotope fractionation during magmatic differentiation in the lower continental crust
No full textThe Mg isotopic compositions display a significant disparity between the lower continental crust and the mantle. However, due to the limited availability of representative samples from the lower crust, our understanding remains incomplete regarding whether Mg isotope fractionation occurred during its formation and its potential influence on the observed isotopic differences. This study addresses this gap by presenting Mg isotopic data for juvenile lower crustal mafic xenoliths from Daoxian, Southeast China, providing new insights into this poorly understood process. The xenoliths, classified as websterites and two-pyroxene granulites, equilibrated at 818-912 degrees C and 10.6-15.4 kbar. They exhibit high Mg# (77-85), Cr (154-1451 ppm), and Ni (143-312 ppm), as well as trace element patterns resembling those of island arcs and evolved Sr-Nd-Pb isotopic compositions (87Sr/86Sri = 0.7046-0.7071; epsilon Nd(t) = -2.44 to +4.62; 206Pb/204Pbi = 18.26-19.03), indicating their derivation primarily from an enriched mantle source. Despite this, these xenoliths display a diverse range of Mg isotopic compositions. Websterite xenoliths exhibit mantle-like S26Mg values (-0.27%o to -0.29%o), indicating no influence from hybridized mantle source or pyroxene fractional crystallization/accumulation on their Mg isotopes. In contrast, granulite xenoliths show lower and variable S26Mg values (-0.26%o to -0.49%o), which positively correlate with Mg#, Cr, and V, but negatively correlate with Na2O + K2O, indicating that magmatic processes likely influenced Mg isotope fractionation in these samples. Petrological features, coupled with correlations between MgO and CaO/Al2O3, Cr, Co, and Ni, indicate that fractional crystallization and/or accumulation of olivine, spinel, clinopyroxene, orthopyroxene, and plagioclase played crucial roles in the formation of the granulite protoliths. Furthermore, the segregation of spinel during magmatic differentiation could have enriched residual melts in light Mg isotopes inherited by the cumulate Cpx + Opx + Pl (i.e., the granulite protoliths). Overall, the weighted average S26Mg value of the lower crust in South China is estimated to be -0.34 +/- 0.04%o. This finding, together with previous studies on granulite xenoliths in North China and Australia, strongly indicates heterogeneous Mg isotopic compositions in the lower continental crust relative to the mantle
Compositional differences of near-critical petroleum from closed pores to wellhead in Gulong shale oil play, Songliao Basin, NE China
No full textThe Gulong shale oil play located in northern Songliao Basin is a promising exploration target in China. Member 1 of Qingshankou Formation (Well H) with high thermal maturity was preferred to obtain pressure-retained cores, long-time exposed cores, and produced petroleum (crude oil and gas). The selected samples were subjected to sequential extraction, GC, GC-MS, thermal desorption-gas chromatography (TD-GC) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. The compositional differences of insitu fluids, residual bitumen trapped in open, confined, and closed pores, as well as wellstream, were systematically investigated. (1) In-situ fluid compositions, with a 30.8% proportion of nC1_ 5 in n-alkanes, were studied by TD-GC analysis on pressure-retained cores. Interestingly, limited amounts of C8- compounds were detected in long-time exposed bulk cores but were almost absent in exposed powder. Primally poor pore connectivity and partially adsorption or absorption of organic matter contribute to the retention of gaseous hydrocarbons. (2) Sequential extraction is a best method for obtaining compositions of fluid in pores with variable sizes. Aliphatic compounds of residual bitumen trapped in open pores are similar to those in confined pores, while polar compounds are more enriched in confined and closed pores. Originally connected pores in early oil window, has turned into confined or closed pores by compaction and cementation with increasing depth. (3) Wellstream compositions are significantly different from in-situ fluid compositions, especially in shale oil extraction. The proportion of gaseous hydrocarbons in the wellstream (76.2%) is considerably higher than that of in-situ fluids (34.1%). Comparison of aromatic hydrocarbons indicated that the wellstream is sourced from free fluids and partially adsorbed hydrocarbons in open pores. (4) Nitrogen and oxide compounds with a higher degree of condensation (higher DBE value) have poor movability, leading to extremely low content or even absence in crude oil. The compositional differences from in-situ fluids to the wellbore through the stimulated fractures are caused by selective adsorption of pore walls, confinement effect of nanopores and fluid phase changing. This study provides a window to the compositional differences of fluids released from different occurrence spaces and confirms compounds heterogeneity
Chemical structure and hydrocarbon generation potentials of cyanobacteria<i> Schizothrix</i><i> calcicole</i> and its resistant biopolymer
No full textMicroalgae have attracted much attention because of their great potential in the development of sustainable biofuel. In this study, cyanobacteria Schizothrix calcicole was fractionated into different fractions and characterized by elemental analyses, Rock-Eval pyrolysis, and C-13 NMR. Closed pyrolysis experiments were carried out on the bulk (BL) sample of S. calcicole and its nonhydrolyzable organic matter (NHOM) fraction. The results suggested the NHOM fraction was composed of a saturated and unbranched or weakly branched hydrocarbon chain with a chain length up to 32, which was highly aliphatic resistant biopolymer similar to algaenan in structure, and exhibited higher oil yield (58.1 %) and oil and gas production potentials (OGPs, 63.9 %) than the BL sample did. Moreover, the n-alkanes for the NHOM fraction showed bimodal distribution and were dominated by long chains higher than C-15. On the contrary, the BL sample exhibited unimodal distribution of n-alkanes, in which middle- and short-chain n-alkanes with chain length <17 were more abundant. In addition, the results indicated C-13 NMR is an effective approach to evaluate hydrocarbon generation potentials. Our investigation identifies aliphatic biopolymers in cyanobacteria S. calcicole and improves the understanding of hydrocarbon generation of its different fractions
Facet-specific photoreduction and immobilization of Cr(vi) on hematite nanocrystals
No full textPhotochemical and adsorptive reactions occurring at the mineral-water interface are of great importance in controlling the fate and transport of contaminants in nature, but the effects of the mineral surface structure on the interplay of these two processes and the underlying mechanisms remain largely unknown. In this work, two different structurally well-defined hematite nanocrystals were employed to explore the coupled photoreduction and immobilization of Cr(vi) on various facets of hematite under light irradiation. Compared with hematite quasi-nanocubes (HNCs) exposing only {012} facets, hematite nanoplates (HNPs) with exposed {001} and {113} facets exhibited higher immobilization ability for Cr(vi) under light irradiation, indicating that the coupled process of photoreduction and adsorption of Cr(vi) strongly relied on the particularly exposed facets of hematite. X-ray photoelectron spectroscopy measurements indicated that the removed Cr(vi) from solution was mainly immobilized on hematite surfaces in the form of Cr(iii) (the reduced products of Cr(vi)). Transmission electron microscopy and electron energy-loss spectroscopy results revealed that the accumulation of Cr species was predominantly on the {113} facets of HNPs and the {012} facets of HNCs. Theoretical calculations show that the work function difference between the {113} and {001} facets was directly linked with the effective separation of photogenerated electron-hole pairs in HNPs, which is beneficial for the reduction of Cr(vi). The results of desorption experiments indicate that the coupling of photoreduction and adsorption processes significantly promotes the long-term immobilization of Cr species and effectively reduces their environmental risks (the desorption of Cr(vi) from the HNP and HNC samples decreased from 35.9% and 33.5% to 0.3% and 1.7%, respectively). Overall, the exposed facets can significantly affect the electron transfer properties of hematite as well as the binding affinity for Cr species, thereby governing the reduction and immobilization behavior of Cr(vi) on various facets of hematite. These results advance our understanding of the speciation and immobilization of redox-sensitive contaminants at the surfaces of semiconducting minerals in nature
Calcium isotopic variability in hotspot lavas controlled by partial melting and source lithological heterogeneity
No full textCrustal recycling can induce significant chemical and lithological heterogeneity of the mantle. Ocean island basalts (OIBs) are the surface expressions of rising mantle plumes from the Earth's deep interior and thus can be a probe of the compositional heterogeneity in the deep mantle. Endmember OIBs sampled the most isotopically extreme mantle components including EM1 (Enriched mantle 1), EM2 (Enriched mantle 2), HIMU (high mu; mu = U-238/Pb-204), and FOZO (Focus zone), but the lithological properties of their source regions are still not well understood. Here we explore the potential of stable calcium (Ca) isotopes in identifying mantle source lithology by investigating OIBs from the type localities for the several mantle components. We find that the delta Ca-44/40 values of classic HIMU OIBs (0.77 +/- 0.09 parts per thousand; 2SD, N = 15) and Louisville FOZO OIBs (0.78 +/- 0.06 parts per thousand; 2SD, N = 4) are indistinguishable from the average MORB (mid-ocean ridge basalt) value (0.84 +/- 0.09 parts per thousand; 2SD, N = 31), while the delta Ca-44/40 values of the Pitcairn EM1 (0.65-0.72 parts per thousand) and the Samoan (Tutuila) EM2 OIBs (0.61-0.71 parts per thousand) are distinctly lower than those of MORBs. Such Ca isotopic distinction cannot be attributed to magmatic differentiation because the EM1 and EM2 OIBs have obviously lower delta Ca-44/40 values than the HIMU and FOZO OIBs even at a same MgO content. Equilibrium fractionation during partial melting of garnet peridotite with bulk silicate Earth (BSE) delta Ca-44/40 (0.94 +/- 0.05 parts per thousand) can explain the Ca isotopic compositions of the HIMU and FOZO OIBs but is unable to reproduce the Ca isotopic variation of all OIBs in this study. Quantitative modeling suggests that the coupling of low delta Ca-44/40 ( 3.5) ratios in the EM1 and EM2 OIBs most likely points to an eclogitic source component with MORB-like or even lower delta Ca-44/40 (e.g., < 0.8 parts per thousand), possibly reflecting contributions from recycled oceanic crust and sediments. A negative correlation between average delta Ca-44/40 and delta Fe-57 values (a useful proxy for mantle source lithology) of all endmember OIBs further confirms this proposal and highlights the significant contribution of distinct source lithologies to the Ca isotopic variations in these basalts. Therefore, our study indicates that Ca isotopes of basalts can be another promising tracer of lithological heterogeneity in the mantle
Big Mantle Wedge and Intraplate Volcanism in Alaska: Insight From Anisotropic Tomography
No full textWe determine high-resolution tomographic models of isotropic P-wave velocity (Vp) and tilting-axis anisotropy of the Alaska subduction zone using a large number of local and teleseismic data recorded at many portable and permanent network stations in and around Alaska. We find a flat high-Vp slab in the mantle transition zone (410-670 km depths) beneath western Alaska, which is connected with the subducting Pacific slab at 0-410 km depths, suggesting that a big mantle wedge has formed under western Alaska. Our tilting-axis anisotropy model reveals complex mantle flows in the asthenosphere. Corner flow in the mantle wedge above the subducting Pacific slab and toroidal flow in the big mantle wedge are revealed, which may cause the Cenozoic intraplate volcanoes in western Alaska and the Bering Sea. In central Alaska, the mantle wedge beneath the Denali volcanic gap is characterized by high-Vp and subhorizontal fast velocity directions normal to the volcanic arc, which may reflect a remnant of the subducted Yakutat slab. In SE Alaska, the shallow subduction of the Wrangell slab is visible above 150 km depth, and hot mantle upwelling through the Wrangell-Yakutat slab gap may contribute to the Wrangell volcanic field.
Alaska is home to over 100 Cenozoic volcanoes, but their formation mechanism is still puzzling. Here we use a large number of seismic data and a novel tomographic technique to obtain high-resolution images of isotropic P-wave velocity (Vp) and anisotropy down to 800 km depth beneath Alaska. Our results show that a flat high-Vp slab exists in the mantle transition zone (410-670 km depths) beneath western Alaska, where a big mantle wedge has formed above the flat slab. Fluids in the big mantle wedge and large-scale mantle flow around it have caused Cenozoic intraplate volcanoes near the Bering Sea. The Denali volcanic gap, different from its neighboring Buzzard Creek-Jumbo Dome volcanoes, has a high Vp mantle wedge with arc-normal fast anisotropy, which may reflect a cool fluid barrier from the Yakutat slab. The high-Vp Wrangell slab is revealed down to similar to 100 km depth beneath the Wrangell volcanic field, Mount Churchill and Prindle volcano. Hot upwelling flows near the Wrangell slab edge may cause these volcanoes.
A big mantle wedge (BMW) has formed above a flat slab in the mantle transition zone under western AlaskaIntraplate volcanism in western Alaska and the Bering Sea is caused by hot upwelling flows in the BMWThe Wrangell volcanic field and Denali volcanic gap are caused by subduction of the Wrangell and Yakutat slabs, respectivel