Earth Science Frontiers

New minerals and their related research innovation and exploration

LI Guowu

2020, 27(5): 1-9.
DOI: 10.13745/j.esf.sf.2020.5.41

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As one of the important basic research directions of mineralogy, the discovery of new minerals and the studies of crystal structure and crystal chemistry have always attracted the attentions of all researchers in the field. The research and discovery of new minerals are such achievements that reflect to some extent the national science and technology advancements and contribution to scientific discovery in this field. I have been involved in the study of some doubtful minerals in recent years, and the 23 new minerals we discovered since 2005 have been approved by the IMA-CNMNC. The approval of these new minerals benefited from the successful acquisitions of composition and diffraction data and structural refinement. In this paper, identification rules, proposal contents and data, classification and naming, and research contents and methods for new minerals are reviewed.

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Local structural environments of bromine in chlorine-rich minerals: Insights from Br K-edge XAS and ⁸¹Br MAS NMR spectroscopy

Yuanming Pan, Ning Chen, Jianfeng Zhu, Neelege Hopps, Eli Wiens, Jinru Lin

2020, 27(5): 10-13.
DOI: 10.13745/j.esf.sf.2020.5.54

Abstract ( 255 )

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Halogens such as Cl and Br as geochemical tracers for constraining the sources and evolution of magmatic, metamorphic and hydrothermal systems require knowledge about their structural environments in both rock-forming minerals and coexisting melts/fluids. However, structural studies of Br in rock-forming minerals are challenging due to its exceedingly low concentrations that are not amendable to most structural techniques. In this study, we have conducted the first structural investigation of Br as a trace constituent in selected Cl-rich rock-forming minerals by use of combined ⁸¹Br magic angle spin nuclear magnetic resonance (MAS NMR) spectroscopy and Br K-edge synchrotron X-ray absorption spectroscopy (XAS). The whiteline positions of the Br K-edge X-ray absorption near-edge structure (XANES) spectra vary systematically with the coordination numbers of the Cl atoms, except for that in boracite. Similarly, fittings of extended X-ray absorption fine structure (EXAFS) data support the substitution of Br^- for Cl^-, with significant local expansions. However, the local structural environment of Br in boracite from EXAFS fittings differs from this of the three-coordinated Cl atom in this mineral but is similar to that of the octahedrally coordinated Br in cubic Mg₃B₇O₁₃Br, suggesting a domain segregation even at the trace level. These local structural data provide new insights into the Br/Cl behavior in geological systems.

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Two dimensional quantitative textural analysis method for igneous rock

YANG Zongfeng, LI Jie, JIANG Xiaojie, QU Linyu, YUAN Ye, LI Yingying, PENG Huizhong, RAO Tong, MA Ben, XU Zhihao

2020, 27(5): 23-38.
DOI: 10.13745/j.esf.sf.2020.5.34

Abstract ( 440 )

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In recent years, quantitative textural studies of igneous rock have shown that by using conventional rock and mineral identification equipment, one can obtain two-dimensional petrographic photos of different scales of igneous rock, so that mineral particles can be identified with naked eyes. Furthermore, by using image processing and textural analysis software the textural characteristics of igneous rocks can be accurately quantify. In this paper, we summarized the advantages and disadvantages of various observation methods commonly used in the two-dimensional quantitative textural analysis in igneous petrology. The quantitative textural parameters of igneous rocks with grain size below millimeter level can be analyzed by two or more observation methods using polarized microscope with transmission, reflective light or cathodoluminescence and back scatter-electron imaging techniques to obtain digital images of high precision and accuracy. All kinds of mafic minerals with crystal size less than 0.03 mm can be analyzed by reflective light and back scatter-electron image. One can assign different colors to look-alike gray-scale mafic mineral images by image processing software to improve mineral identification. Polarized microscope cathodoluminescence can be used for the analyses of felsic and most accessory minerals which are difficult to distinguish under conventional polarized microscope. The rock-forming minerals with mm or above grain size can be quantitatively analyzed by polished large sections or field measurement. In order to facilitate researchers in related fields to use this method, we listed the specific analysis steps in detail. Some detailed analyses are made by combining the quantitative textural data of olivine phenocryst in a basalt sample, focusing on how to accurately identify the boundaries of mineral particles, to determine mineral content and shape, analysis area and crystal numbers, and to distinguish different crystal population. The results show that the intercept and slope of crystal size distribution (CSD), mineral content, alignment factor and crystal shape of granular minerals are not significantly different for particle numbers between 100-500, but the maximum crystal length and degree of particle aggregation are underestimated. For particle numbers less than 300, the R value of crystal spatial distribution pattern will be overestimated by 0.05-0.2, which were largely ignored in previous studies. All textural parameters tend to be stable and precision and accuracy are significantly improved for particle numbers above 500. At the present, most of the textural parameters provided by researchers are usually statistical results and often related to the observation and statistical methods, and the intercept and slope of CSD lack the corresponding original data, which is not convenient for the comparative study among peers. We suggest that detailed analysis steps be provided with the original data when publishing results related to textural parameters in the future. The recommended analysis steps are as follows: (1) Identify boundaries of aggregated minerals or deal with it concretely; (2) Determine crystal three-dimensional shape and whether CSD parameter change among samples is caused by shape parameter change; (3) Obtain minimum particle size of minerals that can be accurately measured; and (4) Estimate sample homogeneity and precision of analysis on samples with large particle numbers so 3-5 repeated measurements can be performed. The original data should (1) contain analysis of at least two different areas of the sample. For multiple authors, at least two independent analyses by different authors is recommended for precision and accuracy evaluation. And (2) the number of crystals in different crystal size intervals of each sample, the original high-resolution mineral outline of the sample or the relevant original parameters of image analysis should be provided in the text or appendix of the article. When multiple crystal populations appear in igneous rocks, the quantitative textural parameters often reflect the mixed characteristics of multiple crystal populations and are related to the proportion of different crystal populations. Future research needs to focus on identifying textural parameters of different crystal populations by combining multiple observation methods and micro-area composition analysis. More effective methods should be developed to identify crystal populations with similar grain size and composition, which is of great significance for the understanding of the genesis of the textural diversity of igneous rocks and magmatic processes.

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The mineral intelligence identification method based on deep learning algorithms

GUO Yanjun, ZHOU Zhe, LIN Hexun, LIU Xiaohui, CHEN Danqiu, ZHU Jiaqi, WU Junqi

2020, 27(5): 39-47.
DOI: 10.13745/j.esf.sf.2020.5.45

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Mineral classification plays an important role in many research fields. Intelligent mineral identification based on deep learning brings a new development direction to these fields, it can effectively save labor costs as well as reducing classification errors. The purpose of this paper is to study an accurate, efficient and versatile intelligent mineral identification method by deep learning. We trained and tested this method on five kinds of minerals: quartz, hornblende, biotite, garnet and olivine. We used the convolution neural network, commonly applies to image analysis, to establish the model and designed the model structure based on residual network (ResNet). In order to support deep learning, we collected microscopic imaging data sets of five kinds of minerals independently, and used them to train, verify and test the model. Besides, we also expanded the data sets for training through reasonable data augmentation. In terms of structural design of the convolutional neural network, we selected ResNets-18 as the framework and finally trained a successful mineral identification model achieving 89% accuracy in the test.

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Mineralogy and geological significance of the melting zone in the Jiaohe upper mantle fragment, Jilin

LIU Jinhong

2020, 27(5): 48-60.
DOI: 10.13745/j.esf.sf.2020.5.50

Abstract ( 215 )

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The Jiaohe mantle rock fragment was brought to the surface by magmatic alkali olivine basalt, of which, 40-55% (in some parts 60%) are mantle fragments of different tile sizes, generally from 4×5×8 cm to 2×3×4 cm, with the largest measuring 20×22×35 cm and so named mantle rock agglomerate lava. The main mantle rock fragments are spinel iherzolite and clinopyroxene. The cement is alkali olivine basalt. Abundant melt microzones with different compositions and shapes have been found. These microzones can be divided according to shape into drop, fan, ball, irregular short vein and ringed edge. The new minerals can be divided into OL, K, Na+Chl, PL, Chl and SP+Chl+Ser types. The structure of the melt zone is the hidden or radial structure between glass bases, with minerals in skeletal crystal or hollow glass forms. The residual glass is devitrified, forming a small number of acicular and black opaque primary crystallites. The morphology, structure and material composition and mineral crystallization of the melt microzones have the characteristics of residual mantle crystalline rocks. The mantle rock underwent an explosion caused by strong volcanic eruption, resulting in the melting of fusible components such as K, Na and Ca and releasing of volatile components such as H₂O and CO₂, creating a rapid crystallization and quenching environment. These melts preferentially occupy mineral gaps, fissures, dislocation or crystal defect sites and gather and fuse nearby metasomatic minerals, continuously expanding space and forming microzone blobs. The melts have different chemical compositions and crystallization characteristics due to different degrees of melting. They represent different initial magmas, including ultrabasic, alkaline basaltic or lamprophyre magmas. Our data indicate that the Jiaohe mantle xenoliths are residue mantle from extracted melts, i.e., lithospheric mantle.

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Mineralogical constraints on the formation of cumulates in layered intrusions in the Pan-Xi region, Sichuan Province, China

LUO Zhaohua

2020, 27(5): 61-69.
DOI: 10.13745/j.esf.sf.2020.5.33

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It is very important for understanding the igneous processes to discover that several crystal populations can be found in an igneous sample. The discovery makes genetic mineralogy again key to revealing the history of a magmatic system, however, this importance is not reflected in the literature. A typical example is the debate on the origin of cumulates in so-called mafic layered intrusions that wether the cumulated minerals are antecrysts or liquidus of the parent magma. In this contribution, we attempt to clarify the origin of cumulate formation in mafic layered intrusions in the Pan-Xi region, Sichuan Province, and to emphasize the importance of genetic mineralogy. Microscopic observations suggest that clinopyroxene cumulate is rich in Fe-Ti oxide exsolution lamellaes (lamellae-bearing pyroxene), indicating the magmatic condition of crystallizing lamellae-bearing pyroxene is obviously different from crystallizing clinopyroxene (lamellae-free pyroxene), which is co-crystallized with plagioclase. The olivine grains included in lamellae-free pyroxene and plagioclase are neaer-rounded, which suggests thermodynamic disequilibrium between olivine and melt. The Fe-Mg partitioning relation between olivine and melt reveals that liquidus olivine Fo value inferred from the parental magma is much lower than the upper limit of the composition range (Fo₆₁-Fo₈₁) of olivine in cumulate. In other words, the observed olivine grains, partly at least, are not of the liquidus phase of the host intrusion. Correlations between Mg^#[Mg/(Mg+Fe)] and minor elements (especially Ni) also suggest multiple olivine crystal populations formed under different thermodynamic conditions. Crystal settling analysis indicates that crystals precipitating from the host magma may not experience rapid gradational settling and cumulate. All the evidences show that the cumulate-forming mineral crystals are mainly arrived from different chambers at depths of the magmatic system, and they are of antecryst and transferred to the terminal magma chamber. Consequently, the cumulated minerals have larger initial grain radius, which is helpful for their rapid settling to the bottom of the intrusion at an earlier stage to form cumulate.

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The mineralogical records of magmatic process: cases from Mesozoic intrusive rocks in the Handan-Xingtai region

ZHANG Juquan, LIANG Xian, YAN Lina, LI Shengrong, SHEN Junfeng, LU Jing, WU Weizhe, LI Qing

2020, 27(5): 70-87.
DOI: 10.13745/j.esf.sf.2020.5.43

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The mineral zoning texture is a good recording of the magmatic process, and the physicochemical conditions of magma could be quantitatively calculated by mineral thermobarometer. In this study, we carried out electron microprobe and LA-ICP-MS element mapping of typical plagioclase phenocrysts of two Mesozoic hypabyssal intrusions in the Handan-Xingtai region, along with electron microprobe analysis and physicochemical condition calculation of amphibole crystals of different genesis. We found that plagioclase phenocrysts in these two samples belong to antecrysts. They are mainly composed of oligoclase in pyroxene diorite porphyrite and andesine and labradorite in porphyritic quartz monzonite. The two intrusions have obviously different zoning textures and record different magma mixing processes. The former records multiple injections of basic magma into acidic magma chamber to obtain eventual volume advantage; the latter records continuous mixing of small amounts of basic magma with large volume of acidic magma to form homogenized magma. There is a tendency of iron enrichment from the core to the rim of plagioclase phenocryst, indicating iron is gradually enriched with magma evolution. The amphibole thermobarometric calculation results show that the depth of magma chamber containing pyroxene diorite porphyrite was about 5.5 km, with a temperature of 850 ℃, oxygen fugacity of ΔNNO+1, and water content of 4.0 wt%. The intrusion finally emplaced at a crust depth of 2.1 km. The porphyritic quartz monzonite intrusion finally emplaced at a crust depth of 2.0 km, with an average hornblende crystallization temperature of 737 ℃, relative oxygen fugacity of about ΔNNO+1.2, and water content in melt of 3.9 wt%.

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Genetic mineralogy of jadeitite from Polar Urals, Russia

MENG Fancong, BAI Shengjin, Alexander B. MAKEYEV, Ksenia V. KULIKOVA

2020, 27(5): 88-98.
DOI: 10.13745/j.esf.sf.2020.5.39

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Subduction zones are major sites for mass circulation between the crust and mantle, while jadeitite is a recorder of the process. In this paper, we summarized the research advance of jadeitite from Polar Urals (Russia). Jadeitite occurs in serpentinized harzburgite as veins or lenses and is composed of jadeite and omphacite. Two generations can be identified based on the color and texture of jadeite. The oscillatory zoning and fluid inclusions (H₂O+CH₄ in composition) in jadeite indicated it is crystallized from fluids. Zircons from jadeitite are hydrothermal at origin, and are enriched in HREE, with La_N/Yb_N and Lu_N/Gd_N ratios ranging between 0.001-0.01, and 10-83, respectively. Cerium shows positive anomalies, with Ce/Ce^* values ranging from 2.8 to 72, and δEu from 0.53 to 1.02. The ¹⁷⁶Hf/¹⁷⁷Hf ratios of zircons ranged from 0.282708 to 0.283017, with initial Hf isotope compositions ranging from +6 to +17. These characteristics resemble those of zircons from depleted mantle-derived magmas. The δ ¹⁸O isotope compositions of zircons ranged from 5.03‰ to 6.04‰ with an average of 5.45‰±0.11‰, similar to those of mantle rocks, suggesting that zircons were acquired from precursor igneous rocks and then transported and reworked by fluids from the subducting slab, or isotopic equilibration was reached between fluid and host harzburgite. Chondrite-normalized REE patterns of jadeitite displayed weak U-shaped distribution, with La_N/Yb_N ratios of 0.82-2.42, and very weak positive Eu anomalies (δEu=1.2-1.6). Jadeitite was enriched in Sr, Ba, Zr and Hf and depleted in Nb, relative to primitive mantle values. The initial Sr isotopic compositions of jadeitite ranged from 0.703400 to 0.703519 (t=368 Ma), and the initial Nd-isotope ratios (ε_Nd=+0.77-+5.61) differed from those of ancient ocean water, oceanic sediments and eclogite, metagranite, and metasediments in the nearby Marun-Keu complex. Mineralogical and petrological evidences support jadeitite precipitation from material mainly produced by fluid interaction with mafic-ultramafic rocks in a subduction zone environment.

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Genesis of the Keluo Au deposit in the Nenjiang-Heihe tectonic melange belt, Heilongjiang Province: evidence from chemical composition and pyrite He-Ar, S, Pb isotopes

LI Chenglu, LI Shengrong, YUAN Maowen, DU Bingying, LI Wenlong, Masroor ALAM, LIU Dongyuan, LIU Hao

2020, 27(5): 99-115.
DOI: 10.13745/j.esf.sf.2020.5.37

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The mid-sized Keluo gold deposit is located in the Heihe-Nenjiang tectonic melange belt, Heilongjiang Province, China. The ore bodies in the deposit occur as both ductile deformed and disseminated-massive types. The deposit has been significantly mined but the genesis of the deposit is elusive. Here we report typomorphic characteristics and He-Ar, S, Pb isotopes of pyrite, intending to establish the ore genesis mechanisms of the Keluo gold deposit. Pyrite from ductile deformed ore body showed lower S/Fe ratios (mean 1.99) and As content (mean 382×10^-6), and higher Au (mean 383×10^-6), Ag (152×10^-6) and Co (1249×10^-6) contents than pyrite from disseminated-massive ores (mean S/Fe, As, Au, Ag, and Co values of 2.01, 503×10^-6, 234×10^-6, 96×10^-6, 845×10^-6, respectively). Trace elements of the two types of pyrite showed similar REE features, i.e. enriched LREE, depleted HREE, and inclined REE patterns. The total REE content of pyrite ranged from 17.00×10^-6 to 66.95×10^-6 with deformed pyrite showing lower REE concentrations, and LREE/HREE ratios ranged from 5.25 to 12.50. The large variations in Y/Ho, Zr/Hf and Nb/Ta ratios indicate an unstable ore-forming environment. Moreover, the ³He and ⁴He values of pyrite were (2.405-10.811)×10^-13 and (3.35-4.99)×10^-7, respectively. The ³He vs. ⁴He and R/R_a vs. ⁴⁰Ar/³⁶Ar discrimination diagrams indicated a dominated mantle source with minor contribution from continental crust, further implying that the meteoric water played a vital role during gold mineralization. The δ ³⁴S values of pyrite ranged from +2.3‰ to +7.6‰ showing lower δ³⁴S values for deformed pyrite than disseminated-massive pyrite, with mean values of +2.65‰ and +5.07‰, respectively. The Pb isotopic study of pyrite showed that the ratios²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ranged in 18.157-18.211, 15.542-15.594 and 38.032-38.218, respectively, and all these values indicate great affinity with ore genesis. Pb isotopic compositions further show that deformed pyrite has relatively low mean values of ²⁰⁶Pb/²⁰⁴Pb (18.171), ²⁰⁷Pb/²⁰⁴Pb (15.542), and ²⁰⁸Pb/²⁰⁴Pb (38.054), as compared with those of disseminated-massive pyrite (18.200, 15.581 and 38.172, respectively). The Co/Ni ratios and Co vs. Ni discrimination diagram indicate that the Keluo deposit belongs to the hydrothermal type, whereas the w(Fe+S) vs. w(As) and Co-Ni-As diagrams indicate that the main mineralization stage exhibits epithermal characteristic. Combined with previous regional deformation events, deposit features, geochronological and fluid inclusion studies, we conclude that there are two stages of mineralization in the Keluo deposit, including the Triassic orogenic and the later Cretaceous epithermal type. Based on this study, we propose that more attention should be paid to orogenic Au during ore prospecting in the Heihe-Nenjiang tectonic melange belt.

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The genesis of color zonation of emerald from Dayakou, Yunnan Province: implication for multi-stage mineralization

YU Xiaoyan, ZHENG Yuyu, ZHANG Tingya, GUO Hongshu, LONG Zhengyu, WAN Jiaxin, ZHANG Cun

2020, 27(5): 116-125.
DOI: 10.13745/j.esf.sf.2020.5.48

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Color zonation with obvious composition variation often appear in emeralds from Dayakou, Yunnan Province, China. However, the origin of color zonation is still controversial, and there has been no reliable evidence for the related multistage mineralization hypothesis. In this study, we analyzed the main and trace elemental signatures of the Dayakou emerald with obvious color zonation by electron microprobe (EMP) and laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We also carried out microthermal analysis of fluid inclusions hosted within emerald and other associate minerals from different types of veins. The composition results showed that the trace elemental contents in emerald increased sharply from the light greenish white core to the green rim, yielding V((970-10077)×10^-6), Rb((9.6-27.4)×10^-6), Cs((535-3108)×10^-6), Fe((1376-2199)×10^-6) and Ga((4-14.7)×10^-6); and the syngenetic black inclusions which only occur at the green crystalline rim were proved to be V-rich intermediate oxy-schorl-dravite. The above evidence strongly suggests that color zonation are formed from multistage crystalline mineralization. Furthermore, the microthermal analysis results showed that salinities of fluid inclusions hosted within minerals from the feldspar-calcite and quartz veins and pegmatite-granofel contact zones were 3.39%-10.36%, 5.71%-12.29% and 8%-18.72%(NaCl_eq), respectively, again indicating different mineralization stages in pegmatite veins and suggesting increasing parent fluid salinity with evolution of the mineralization stage. And the considerable variation of V concentration is also caused by increasing salinity at the greisenization stage.

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Geological signatures of the Baiyun pyrophyllite deposit in Wutai, Shanxi Province: implication for prospecting of Cu-Au ores in deep

ZHANG Huafeng, ZHANG Shaoying

2020, 27(5): 126-135.
DOI: 10.13745/j.esf.sf.2020.5.47

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The Baiyun pyrophyllite deposit is ~15 km away to north of Wutai county, Shanxi Province of China, where the basement rocks belong to the Wutai Complex, north-central of the North China Craton. The main orebody occurs as a lens in fracture of the late Archean meta-volcanic rocks, crosscut by the Mesozoic mafic dikes. The wall rocks exhibit phyllic alteration halos which are weakened outwardly from the pyrophyllite orebody. Auriferous quartz sulfide vein and disseminated gold mineralization occur in the phyllic alteration zone. Mineral assemblages of pyrophyllite ores are dominated by pyrophyllite and quartz, with minor of diaspore, kaolinite, illite, sericite and hematite. Accordingly, the lgf(O₂)-pH diagram is constructed that the pyrophyllic alteration fluids were intensively acidic (pH=2-3) with relatively high oxygen fugacity (>HM buffer). Altered zircon yielded a lower intercepted U-Pb age of (136±7) Ma, similar to those of Cu-Au deposits regionally. Whole-rock H-O isotopic data (δD_SMOW=-34‰--20‰; δ¹⁸O_SMOW=11.2‰-13.9‰) of pyrophyllite ores suggest that the fluids for pyrophyllite alteration are cooling magmatic without pronounced effects of meteoric waters. As to the abundances of metals, the Archean wall rocks are markedly higher than those of the pyrophyllite ores. The concentrations of Au and As in the pyrophyllite ores are below the detected limit, suggesting that the physicochemical conditions of fluids for pyrophyllite alteration are not conductive to gold mineralization, inversely, they can scavenge some metals from wall rocks and transfer them upwardly. Our results suggest that pyrophyllite alteration formed by acid and oxidized fluids might be an early stage of evolving fluids for high sulfidation epithermal deposit. Consequently, a prospective porphyry style or skarn type of Cu-Au deposit in deep is suggested.

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Mineralogy and fluid inclusions study of the Baranevskoye gold-silver deposit, central Kamchatka, Russia

Victor M. Okrugin, Elena D. Skilskaia

2020, 27(5): 136-150.
DOI: 10.13745/j.esf.sf.2020.5.58

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The Baranevskoye gold-silver deposit occurs within the caldera of the Balkhach volcano in the south-east part of the Central Kamchatka mining district. The host rocks are andesite, basalt of Miocene-Pliocene age. The hydrothermal alteration varies as a function of depth and is subdivided into deepest quartize zone, intermediate zones of quartz-sericite(alunite)-pyrite-Fe-Ti-oxides and quartz-sericite-illite-pyrite associations, and shallow quartz-adularia-hydromica-clay-carbonate zone. Mineralogical study reveals three major stages of mineralization. The early stage is present by a highly disseminated copper-rich mineralization with main ore minerals of chalcopyrite, bornite, tennantite-tetrahedrite, and rare gold occurring in the Rzhavaya vein. Tennantite-tetrahedrite series is represented by two end-members of tennantite and tetrahedrite with tetrahedrite preponderating. Later stages are characterized by advanced Au-Ag mineralization containing gold, pyrite, chalcopyrite, sphalerite, galena, tellurides, and sulfosalts. The early Cu-rich mineralization (stage I) is designated as an intermediated state, followed by later low-sulfidation Au-Ag mineralization (stages II and III). Gold was constantly deposited through from Stage I to Stage III. Crystalline gold was also found in void-space in the altered host rocks. Early gold is relatively Ag-rich with Au content of about 59-65% compared to later gold of Stage II and III (Au 64-72%). Fluid inclusion microthermometry shows homogenization temperatures between 190-280 ℃ for the Central vein, 190-240 ℃ for the Rzhavaya vein and 230-310 ℃ for the quartz of the altered host rocks associated with crystalline gold. Low salinity of the fluid inclusions (0.9-2.4 wt.% NaCl eq.) suggests an influx of the meteoric waters. Based on mineralogical and fluid inclusions data the physicochemical conditions of the ore formation are discussed.

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Uplifting and denudation of the Chifeng-Chaoyang gold ore zone in western Liaoning Province since the Early Cretaceous and the implication

SHEN Junfeng, LI Shengrong, XU Kexin, WANG Yehan, ZHANG Shiquan, XU Yuanquan, HE Zeyu, CHI Lei, WU Jinchao

2020, 27(5): 151-170.
DOI: 10.13745/j.esf.sf.2020.5.42

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The viewpoint that the North China Craton (NCC) in eastern China underwent Mesozoic lithospheric destruction has been widely accepted. The Chifeng-Chaoyang gold mineralization zone in western Liaoning Province is a typical ‘destruction’ zone of the north margin because the magmatism and metallogeny of the mineralization zone were a fundamental response to the NCC destruction. Based on the investigation of regional and deposit geologies we studied the two plutons—the Duimiangou intrusive (solidification in 128 Ma) and Dashitougou pluton (solidification in 128-126 Ma) from the Jinchanggouliang and Paishanlou gold mineralization districts, respectively—in terms of mineral assemblage, crystallization temperature, oxygen fugacity, and crystallization pressure. Specifically, we estimated the crystallization pressure of biotite (equal to the crystallization pressure of the pluton) and its average value to be 0.97 kbar and 1.45 kbar, respectively, by Al-in-biotite barometric measurement. We also computed the emplacement depths of the Duimiangou and Dashitougou plutons to be 3.67 km and 5.48 km, respectively, using the above crystallization pressures and a crustal density of 2.7 g/cm³. Combining with the previous data, we estimated the denudation depth in the Chifeng-Chaoyang gold mineralization zone to be 3.67-7.70 km, averaging at 5.27 km. In addition, we compiled the crustal exhumation data on the NCC for comparison. We found that since the early Cretaceous, the total crustal exhumation of the NCC ranged between 2.0-10.0 km; but it is more concentrated between 2.0-6.0 km, averaged at 5.60 km, with varying denudation depths. All above results are very important for the Mesozoic gold prospecting in the NCC.

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Genetic mineralogy of natural heavy placer minerals and its effectiveness in mineral prospecting

DONG Guochen, LI Shengrong, SHEN Junfeng, DONG Pengsheng, LI Huawei, YIN Guodong, TANG Jiahui

2020, 27(5): 171-178.
DOI: 10.13745/j.esf.sf.2020.5.46

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Heavy mineral placers are naturally detached mineral grains (or mineral association) produced by natural weathering, erosion, transportation and deposition processes. Because heavy mineral placers can preserve large amount of genetic information on minerals, such as color, morphology, chemical composition, physical feature and mineral association, it can be utilized for back tracing the original ore bodies or for mineral exploration. Hence an easy and simple method, called natural heavy mineral placer survey, for ore exploration is gradually developed. In this article, based on the survey data, we summarized the mineral types, occurring frequency and distribution characteristics of heavy mineral placers, studied mineral association features of the heavy placers and their genetic mineralogical characteristics, and analyzed the relict of the original ore body, possible transporting distances and typomorphic indicating mineral association. We also discussed the significance in ore prospecting potential when genetic mineral characteristics of natural heavy mineral placer are used. The color, morphology and texture of heavy mineral placer still clearly retain the original typomorphic information as they are inheritable factors corresponding closely to the characteristics of the source host rocks. The placer minerals can be divided into two parts: the residual original heavy minerals including common silica, access and ore minerals, and the newly formed ones during erosion and transportation, including cuprite and malachite, reflecting both the lithology in the source area and the present formation condition. The placer mineral association is mostly inherited from primitive paragenetic mineral assemblages, therefore it can provide information on the mineralization potential. The grain features such as roundness and boundary smoothness reflect placer transport distance, they are favorable properties for identifying the responsible host rocks in the source area to guide mineral exploration.

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Natural mineral photoelectric effect: non-classical mineral photosynthesis

LU Anhuai, LI Yan, DING Hongrui, WANG Changqiu, XU Xiaoming, LIU Feifei, LIU Yuwei, ZHU Ying, LI Yanzhang

2020, 27(5): 179-194.
DOI: 10.13745/j.esf.sf.2020.5.35

Abstract ( 602 )

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Under the ever-existing solar irradiation, the organisms on Earth have evolved with a structurally sophisticated photosynthesis system. However, the inherent impact and response mechanism of solar illumination on the inorganic minerals widespread on the Earth surface has drawn little attention. We discovered for the first time the solar energy conversion system of the “mineral membrane”, which exerts potential oxygen production and carbon sequestration functions on the Earth surface. Our finding shed light on the photoelectric effect and non-classical photosynthesis of the natural semiconducting minerals. We carried out this research on the semiconducting property and photoelectron energy of the typical minerals in the “mineral membrane”. We further discussed the photoelectric effect, oxygen production and carbon sequestration functions of the ferromanganese oxides, as well as the corresponding geological records. We proposed that the sensitive and stable photon-to-electron conversion are performed by birnessite, goethite and hematite, which are semiconducting minerals commonly present in the natural “mineral membrane”. In addition, we put forward the non-classical mineral photosynthesis function as follows: the solar energy conversion system developed by inorganic minerals resembles the biological photosynthesis process regarding to oxygen evolving and carbon fixing; also, the “mineral membrane” may take part in the photocatalytic water-oxidation reaction and in the transformation of atmospheric CO₂ into marine carbonate. Last but not least, minerals might as well have promoted the biologic photosynthesis system as the core complex in the Mn₄CaO₅ photosynthesis system evolved during water-oxidation process to form the structural analog birnessite. Therefore, it is fair to postulate that birnessite could play a role in the initiation of the photosynthesis system of cyanobacteria. On the other hand, minerals could weaken hydrogen bond strength and alter water property, thus to facilitate water oxidation and photosynthesis efficiencies, which would hopefully give further insights into the molecular mechanism of mineral participation in the biologic photosynthesis process.

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The evolutionary process of microbial community structure influenced by photoelectron from semiconducting minerals occurring at the “mineral membrane” on the Earth surface

REN Guiping, LU Anhuai, LI Yan, WANG Changqiu, DING Hongrui

2020, 27(5): 195-206.
DOI: 10.13745/j.esf.sf.2020.5.53

Abstract ( 288 )

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The interaction between minerals and microorganisms involved in the material recycling and energy transformation takes place on the earth's surface. In recently years, research on semiconducting minerals in natural environments has provided a new direction for the study of mineral-microbe interaction. It is one of the core scientific issues in the interdisciplinary study of geomicrobiology to reveal the electron transfer mechanism and its environmental effects on the “sunlight-semiconducting minerals-microorganisms” system. In this study, through examination of natural “mineral membrane” samples, we confirmed that the average photocurrents for karst, red soil and rock varnish samples were about 5.4, 3.4 and 3.2 μA/cm², respectively, in the 1000 min long-term cycling experiments. The results demonstrated that the “mineral membrane” samples have good solar response characteristic, and iron/manganese oxide minerals play a key role in the response process. Moreover, based on our previous studies where we showed that the electroactive genera were enriched in “mineral membrane” and correlated positively with semiconducting mineral distribution, we successfully constructed a simulated photoelectron influencing bacterial community system in red soil. Twenty days later, the α diversity of bacterial community was significantly increased, and the bacterial community had an active response for simulating photoelectron. In addition, bacterial community presented directional evolutions at the electrode and in solution samples. The 16S rRNA sequencing analysis showed that Shewanella, Pseudomonas, Streptococcus, Lactobacillus, Acinetobacter and other electroactive genera were significantly enriched under the influence of simulated photoelectron. In conclusion, the results indirectly confirmed that photoelectron from semiconducting minerals in surface environments could regulate the structure of microbial community and promote enrichment of electroactive genera in the “mineral membrane” over time.

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Relationship between the effects of mineral thermoelectricity and abnormal geoelectricity

SHEN Junfeng, SHEN Xuhui, LI Shengrong, XU Liwei, DU Baisong, WANG Dongli, WANG Shuhao

2020, 27(5): 207-217.
DOI: 10.13745/j.esf.sf.2020.5.61

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There are much more semiconductor minerals in the Earth crust due to inhomogeneous crustal composition and complex physico-chemical environments during mineralization. One of the important characteristics of semiconductor minerals is the multiple potential charge carrier in the crystal because of confounding composition or improper arrangement of atoms. And the potential charge carriers can be activated and move directionally in the crystal driven by temperature gradient field, causing larger thermal disturbance so that thermoelectric potential occurs. This phenomenon is called the thermoelectric effect. Generally, a notably disturbed thermal field often appears under earthquake gestation or during an earthquake, and the temperature difference produced from the thermal field will stimulate the semiconductor minerals to generate the thermoelectric effects and convert thermal energy into electric energy. Therefore we hypothesize that the thermoelectric effects may contribute to the abnormal geoelectric field, which is one of important forewarnings for the volcanic eruption and earthquake, that is, the thermoelectricity model may be valid during volcanic eruption and earthquake. This realization is enlightening for understanding the abnormal geoelectric phenomenon forewarning potential volcanic eruption and earthquake.

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Effect of apatite on the stability of ferrihydrite in lacustrine sediments

LUO Shaoyong, ZHOU Yuefei, LIU Xing

2020, 27(5): 218-226.
DOI: 10.13745/j.esf.sf.2020.5.49

Abstract ( 257 )

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In this study, we set out to investigate the mechanism of apatite-mediated dissolution and transformation of ferrihydrite in lacustrine sediments, and the synergic environmental effect of both minerals. We carried out in-situ ferrihydrite transformation experiments in the Dianchi Lake, Yunnan Province, China. The results show that ferrihydrite remained stable in 1-month cultured samples, whereas in apatite-added samples we observed obvious mineral phase transformation after 3-month culturing. The change of newly formed iron mineral assemblage composition with depth in the top 50 cm sedimentary layer were goethite+magnetite/maghemite → goethite+lepidocrocite → goethiten in the winter experiments, or goethite+lepidocrocite+magnetite/maghemite → goethite+lepidocrocite → no new mineral in the summer experiments. Transmission electron microscopy observations show that magnetic minerals formed in winter are nanosized magnetite and maghemite, while in summer they are mainly magnetite. X-ray photoelectron spectroscopy analysis only found P in 3-month cultured samples in winter at a sedimentary depth of no more than 20 cm. The experimental results suggest that the progressive steps in the apatite-mediated ferrihydrite transformation process in lacustrine sediments are as follows: (1) apatite is dissolved by microorganisms and P is released during dissolution; (2) dissolved P promotes iron-reducing bacterial growth; (3) iron-reducing bacteria promote ferrihydrite reduction and release of dissolved Fe²⁺; and (4) dissolved Fe²⁺ catalyzes the transformation of ferrihydrite to goethite, lepidocrocite, and magnetite. In winter at the sedimentary redox boundary, the functional microorganisms responsible for apatite dissolution and ferrihydrite reduction can grow better, thus the risk of endogenous phosphorus release is much greater.

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Uptake mechanisms of arsenate in gypsum: Structural incorporation versus surface adsorption and implications for remediation of arsenic contamination

Jinru Lin, Ning Chen, Yuanming Pan

2020, 27(5): 227-237.
DOI: 10.13745/j.esf.sf.2020.5.40

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Gypsum (CaSO₄·2H₂O) as the most common and abundant secondary mineral in diverse types of mine tailings potentially plays important roles in the stability and bioavailability of heavy metal(loid)s, including As. Understanding on the behavior of As in gypsum-rich mine tailings and development of effective strategies for remediating related As contamination all require knowledge about the speciation and uptake mechanisms of this metalloid in the dominant mineral. However, quantitative determination of arsenic speciation and uptake mechanisms in gypsum-rich mine tailings at trace levels is analytically challenging. In this contribution, we use combined inductively coupled plasma mass spectrometry (ICP-MS), X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopy to quantitatively determine structural incorporation and surface adsorption of arsenate in synthetic gypsum. Gypsum coprecipitated from aqueous solutions containing 0.02 M sodium hydrogen arsenate heptahydrate (Na₂HAsO₄·7H₂O) at ambient conditions has As contents increasing from 57 ppm at pH=2 to 67470 and 53980 ppm at pH=12 and 14, respectively. Synchrotron As K-edge XANES and powder EPR spectra confirm that arsenate is the dominant species in coprecipitated gypsum. Specifically, As K-edge XANES spectra exhibit systematic variations in post-edge features as a function of pH, consistent with structure-bound arsenate at pH from 2 to 7.5 but different uptake mechanisms at pH from 9 to 14. Similarly, arsenic contents estimated from the structure-bound [AsO₃]^2- radical in powder EPR spectra are in agreement with those determined from ICP-MS analyses for gypsum synthesized at pH from 2 to 7.5, but show large discrepancies for the pH=9, 12 and 14 samples, indicative of a large fraction of non-structure-bound As at high pH. The marked pH dependence of arsenate uptake mechanisms in gypsum has important implications for both understanding the roles of this material in mine tailings and developing its optimal applications for remediation of arsenic contamination in aqueous environments. In addition, the radiation-induced [AsO₃]^2- radical in gypsum with a diagnostic peak at g=~2.33 is potentially useful for EPR/ESR dating and retrospective dosimetry.

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Molecular mechanism and carbon sink effects of microbial transformation in potassium-bearing rocks

LIAN Bin, XIAO Bo, XIAO Leilei, WANG Weiying, SUN Qibiao

2020, 27(5): 238-246.
DOI: 10.13745/j.esf.sf.2020.5.38

Abstract ( 401 )

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Microbial mineral weathering is one of the most active and universal geological processes in the earth surface system. Microorganisms can degrade potassium-bearing rocks (mainly silicate minerals), release elements such as potassium, silicon and calcium, and promote mineral carbonate precipitation under appropriate environmental conditions, functioning as an important link in the geochemical cycles of earth surface elements. Microbial biotransformation of rocks involves growths and metabolic regulations of microorganisms, migration and transformation of elements and evolutionary sequence of secondary minerals-all are important research topics in mineralogy, microbiology and molecular biology. Combining researches in these areas is beneficial for systematically studying the process of microbial weathering of potassium-containing silicate minerals coupled with carbonation and its molecular regulation mechanism. It was confirmed that under the conditions of pure culture experiments, the synergistic effects of acidolysis, chelation, oxidoreduction and other chemical activities are effective in the microbial weathering processes, and the effective weathering can also be achieved by regulating the microbial relevant functional gene expression in response to potassium-deficient environments. Such effects clearly depend on a refined and specific molecular regulation mechanism through long-term evolution of microorganisms. In the soil ecological environment, a significant feature of microbial mineral weathering is the cooperative interaction of microbial communities in the habitats. The participation of microbial carbonic anhydrase in silicate mineral weathering, along with carbonate mineral formation, may be a long-neglected process of earth surface carbon sink. An in-depth exploration of such process will help us further understand the mechanisms of microbial driving carbon migration and transformation in geologic evolutionary history. The utilization of organic fertilizers containing potassium-bearing rock powders has shown positive effects on soil improvement, crop growth and carbon sequestration, which provides a new idea for using the biological weathering of silicate minerals to delay the continuous increase of atmospheric CO₂ concentration. In this paper, we reviewed the molecular mechanisms and carbon sequestration effect of potassium released from biotransformation of potassium-bearing rocks by microorganisms, so as to promote rapid development in this research area.

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Quantitative analysis of pore characteristics of natural and electrochemically treated turquoises based on gas adsorption method and X-ray micro-CT 3D imaging technique

LU Taijin, DAI Hui, TIAN Gengfan, LI Ke, ZHANG Jian, CHEN Hua, KE Jie

2020, 27(5): 247-253.
DOI: 10.13745/j.esf.yx.2020.5.51

Abstract ( 237 )

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Turquoise is a porous material, its pore characteristics directly affect its color, luster, hardness, durability and other properties important for its market value. The main purpose of electrochemical treatment for the enhanced turquoise is to reduce pores and change the porous properties to make it durable and colorful. In this paper, we used a specialized fully automated surface analyzer and X-ray micro-CT (Micro-CT) imaging technique to analyze the pore characteristics of turquoise before and after electrochemical treatment. We found that the pore volume and total porosity, average pore size, and specific surface area of turquoise after electrochemical treatment were all reduced to a certain extend. The slope of the adsorption curve became larger for natural turquoise in the high-pressure region and smaller for turquoise under electrochemical treatment. The pore size distribution curve is parabolic for natural and concave for electrochemically treated turquoises. Micro-CT investigation reveals that some large pores that run through the rock are not completely filled by electrochemical treatment. Natural turquoise has a “ruffled” pore structure along the “ripple”, while the “ruffled” structure disappears and pore distribution became disordered in the treated samples. Starting from the perspective of pore characteristics, we found in this study that natural and electrochemically treated turquoises have obvious different pore characteristics, including adsorption and pore distribution curve characteristics, pore filling conditions, and internal features in pore diameters above 50 nm. It is possible to effectively identify natural turquoise from those treated by electrochemical process based on potassium contents and pore characteristics.

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Nephrite of Eastern Siberia as a basis for development of the original stone-cutting design of the region

Raisa M. Lobatskaya

2020, 27(5): 254-261.
DOI: 10.13745/j.esf.sf.2020.8.1

Abstract ( 254 )

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Nephrite has been used in Eastern Siberia historically as one of the most popular minerals since the Neolithic. The use of nephrite was facilitated by the numerous rich deposits of the stone near the area of Lake Baikal. In Siberia, nephrites come in different colors depending on the genesis of the deposits. There are two fundamentally different genetic types of the stone: apohyperbasite and apocarbonate. Nephrite turned out to be a very good benchmark for reconstructing the development of civilizations over several millennia. The practical role of nephrite in the lives of ancient societies of North Asia and in modern scientific researches has been shown. In this contribution, we discuss the possible ways the natural properties of nephrite can create artistic and artistic-industrial products. We also show the differences between real works of art and serial design products from nephrite.

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Yoko-Dovyren layered dunite-troctolite-gabbro massif, North Baikal region, Russia: Structure, composition and use of mineral raw materials

Svetlana S. Timofeeva, Evgeniy V. Kislov, Lyudmila I. Khudyakova

2020, 27(5): 262-279.
DOI: 10.13745/j.esf.sf.2020.8.2

Abstract ( 186 )

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The Yoko-Dovyren layered dunite-troctolite-gabbro massif is located in a folded frame of the South Siberian Craton (North Baikal region, Russia). The massif structure has been studied in detail in the thickest central part. The base of the section is composed of plagioclase peridotites of the endocontact, turning into the main stratigraphic sequence of five zones corresponding to changes in cumulus associations (from bottom to top): dunite → troctolite → olivine gabbro → olivine gabbronorite → quartz gabbronorites and pigeonite-containing gabbro. Among the mineral resources of the massif are sulfide copper-nickel ores, rocks with low-sulfide mineralization of platinum group elements and other mineralization, and chromitites. In addition, the massif contains various types of nonmetallic raw materials, including boron mineralization, diopside, and magnesium silicate rocks. These include dunites, wehrlites and troctolites, which are of high quality. They are promising for obtaining building materials (cements, concretes, asphalt concretes and building ceramics). The solution to this issue is important from the point of view of the integrated use of mineral raw materials in the development of mineral deposits, which allows for establishing environmentally safe mining works.

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Influences of MgO and Al₂O₃ on the mineralogical properties of calcium ferrite in iron ore sinter

HAN Xiuli, SI Tianhang, LI Mingduo, ZHOU Xiang, LIU Lei, ZHAO Kai

2020, 27(5): 280-290.
DOI: 10.13745/j.esf.sf.2020.5.44

Abstract ( 273 )

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Calcium ferrite is the main binder phase mineral in high basicity sintered ore. Its mineralogical characteristics such as content, crystal form, chemical composition and crystal structure play a key role in the quality of the sintered ore. The content directly affects the formation of calcium ferrite. In this paper, we used the chemically pure reagents of Fe₃O₄, SiO₂, CaO, MgO, and Al₂O₃ as raw materials and carried out micro-sintering experiments in the laboratory. Using XRD, polarizing microscope, electron microprobe and other means we performed quantitative analyses of MgO and Al₂O₃ in the raw material components to investigate the formation of calcium ferrite in sintered ores and its influence on mineralogical properties. The results showed that the increase of MgO content in the raw material had a certain inhibitory effect on the formation of calcium ferrite, especially when the MgO content was 2.0% to 3.0%. The calcium ferrite content in the sinter was significantly reduced, and its crystal morphology also changed from plate columnar and needle-like shape gradually transitioning to an irregular shape. The increase in Al₂O₃ in the raw material promoted the formation of calcium ferrite in the sinter as calcium ferrite content increased significantly with increasing Al₂O₃ and ferric acid contents. The morphology of calcium also changed from columnar and needle-shaped to columnar. Electronic probe composition analysis and mineral chemical formula calculation results show that calcium ferrite is a complex crystal composed of Fe₂O₃, CaO, SiO₂, Al₂O₃ and MgO, and its chemical formula is Ca_2.60Mg_0.44Si_1.07Al_0.96Fe_8.92O₂₀. The changes in MgO and Al₂O₃ contents in the raw materials had little effect on the mole fraction ratio of Fe₂O₃ to CaO in the chemical composition of calcium ferrite, both were close to 3∶2. The above research results are of great guiding significance for an in-depth understanding of the chemical characteristic of calcium ferrite crystal phase under sintering process conditions and its effect on the quality of sinter.

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Mineralogical characteristics and distribution patterns of different types of calcification in a cerebrovascular atherosclerotic lesion

LI Yuan, WANG Changqiu, LU Anhuai, LI Yan, YANG Chongqing, LI Kang

2020, 27(5): 291-299.
DOI: 10.13745/j.esf.sf.2020.5.52

Abstract ( 269 )

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Cerebral artery calcification is an important indication of atherosclerotic plaques and closely related to the atherosclerotic process. In the cerebral artery, calcification mostly appears as spherical or massive mineral aggregates, but the difference between these two types and their spatial distribution patterns in an atherosclerotic lesion are still not clear. Therefore, we collected and analyzed samples with different stages of calcification by environmental scanning electron microscope (SEM) with energy disperse spectroscopy (EDS), transmission electron microscope (TEM) with selected area electron diffraction (SAED) and Raman spectroscopy (Raman). We studied the morphology, structure and spatial distribution of phase and chemical composition of calcification in the atherosclerotic plaque. The results showed that the center of the calcified area develops massive calcification and its surrounding develops spherical calcification. The center of massive calcification is composed of carbonate hydroxyapatite (CHA) while the edge also contains small fraction of amorphous calcium phosphate (ACP). Spherical calcification is composed of whitlockite (WH) and CHA.

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Natural mineral photoelectric effect: mineral non-classical photosynthesis

LU Anhuai, LI Yan, DING Hongrui, WANG Changqiu, XU Xiaoming, LIU Feifei, LIU Yuw

2020, 27(5): 300.
DOI: 10.13745/j.esf.sf.2020.12.3

Abstract ( 505 )

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Under the ever-present solar radiation, photosynthetic organisms on Earth evolved structurally-sophisticated photosynthetic systems. However, little attention has been paid to the inherent impact of sunlight illumination on the inorganic minerals widespread on the Earth surface. We discovered for the first time the solar energy conversion system of the “mineral coatings” on the Earth's surface (aka “mineral membrane”), which exerts potential oxygen-production and carbon-sequestration functions on the Earth surface. Our finding shed a light on the photoelectric effect and non-classical photosynthesis involving natural semiconducting minerals. In this contribution, we studied the semiconducting property and photoelectron energy of typical minerals in the “mineral membrane”, focusing primarily on the photoelectric effect in and oxygen-production/carbon-sequestration function of ferromanganese oxides, as well as relevant geological records. We propose that birnessite, goethite and hematite, the semiconducting minerals commonly found in the “mineral membrane”, can perform sensitive and stable photon-to-electron conversion under solar radiation. The non-classical mineral photosynthetic function we put forth is as follows: Solar energy utilization by inorganic minerals resembles photosynthesis in regarding to oxygen evolution and carbon fixing, and the “mineral membrane” may take part in both photocatalytic water-oxidation reaction and transformation of atmospheric CO₂ into marine carbonate. In addition, minerals might as well have promoted photosynthesis in photosynthetic organisms. During the water-oxidation reaction, the inorganic cluster Mn₄CaO₅ of photosystem II cycles through redox intermediates that are analogous to birnessite both in structure and component. Thus, it is fair to postulate that birnessites could play a role in the initiation of the photosynthesis in cyanobacteria, as minerals could weaken the hydrogen bond strength and alter water properties, thus facilitating water oxidation and photosynthesis. This observation offers further insights into the molecular mechanism of mineral participation in photosynthesis in photosynthetic organisms.

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