Table of Content

20 June 2020, Volume 26 Issue 3

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Genesis and Characteristics of Mantle Sources of Cenozoic Jiande Basalts from Zhejiang Province

HE Ye，CHEN Lihui，ZENG Gang，WANG Xiaojun

2020, 26(3):  241-254.  DOI: 10.16108/j.issn1006-7493.2019043

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The distribution of Cenozoic continental basalts from Zhejiang Province, southeast China are controlled by three northeast-southwest trending faults. According to their outcropping locations and eruption ages, these basalts are divided into three groups: western part, central part and eastern part basalts in Zhejiang province. Here, we carried out a geochemical study on Cenozoic Jiande basalts, the oldest basalts (~40 Ma) cropping out at Jiangshan-Shaoxing fault in the west of Zhejiang, to further explore the nature of mantle source beneath Zhejiang province. These volcanic rocks are mainly alkaline (sodic) basanites with low contents of SiO₂  (41.3-42.3 wt%) and Al₂O₃ (9.70-12.6 wt%), high contents of MgO (8.90-15.6 wt%), CaO (8.92-12.1 wt%), TiO₂ (2.78-3.18 wt%) and Fe₂O₃^T (14.1-16.2 wt%). They are characterized by negative K, Zr, Hf, and Ti anomalies (Hf/Hf*=0.74-0.77, Ti/Ti*=0.70-0.74), and high Zr/Hf (48.5-50.1), Ca/Al (1.02-1.16) ratios, which suggest the contribution of recycled carbonated materials in the mantle source. They show depleted Sr, Nd, Hf isotopic compositions (⁸⁷Sr/⁸⁶Sr=0.7032-0.7034, εNd=5.85-5.95, εHf=7.78-8.56) and have ²⁰⁶Pb/²⁰⁴Pb ratios of 18.491-18.554, ²⁰⁷Pb/²⁰⁴Pb ratios of 15.488-15.518 and ²⁰⁸Pb/²⁰⁴Pb ratios of 38.387-38.523. Compared to weakly alkaline basalts in central and eastern part of Zhejiang, the strongly alkaline basalts in western part of Zhejiang show higher contents of trace elements and more pronounced negative Zr, Hf, and Ti anomalies, which suggest that the strongly alkaline basalts in western part of Zhejiang are generated by low-degree partial melting of a carbonated mantle source. The good correlations of Ti/Ti* with Ba/Th and K/La of Zhejiang Cenozoic basalts suggest a mixing process of two components. Carbonated melts derived from partial melting of carbonate-bearing oceanic crust reacted with the depleted asthenosphere mantle, generating the carbonated mantle source with low Ba/Th, K/La, and Ti/Ti* ratios (reflected in basalts in western part of Zhejiang). Another enriched component is the melting residue of recycled oceanic crust with high Ba/Th, K/La and Ti/Ti* ratios (reflected in basalts in eastern part of Zhejiang). Therefore, the mantle source of Cenozoic Zhejiang basalts, which is mainly controlled by two components with genetic relationship, is heterogeneous.


Characteristics of Cryptoexplosive Breccia from the Chating Copper-Gold Deposits, Xuancheng, Anhui Province and Its Metallogenic Significance

XIE Qiaoqin，SUN Rui，XU Xiaochun，XU Xinyue，AN Yuhua，QIAN Shilong

2020, 26(3):  255-264.  DOI: 10.16108/j.issn1006-7493.2019045

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The Chating copper-gold ore in Xuancheng region is a newly discovered large ore deposit in the Mesozoic-Cenozoic volcanic-sedimentary Nanling-Xuancheng basin in recent years, where the deposits are located at shallow depths of the Middle-Lower Yangtze River. This study is focused on the cryptoexplosive breccia pipe developed in the intrusives of quartz-dioriticporphyrite in the Chating copper-gold ore deposits. Based on the detailed core observations and petrographic analysis, characteristics and types of cryptoexplosive breccia are determined, and the relationship between the cryptoexplosive breccia and the copper-gold mineralization is discussed. The cryptoexplosive breccia in the ore deposits can be divided into three types: cryptoexplosivemelt-crystal-lithicbreccia, cryptoexplosive hydrothermal breccia, and cryptoexplosive fracture breccia based on its textures, compositions and abundance of rubbles. The cryptoexplosive breccia appears as an irregular pipe enveloped by the quartz-dioriticporphyrite and shows a regular spatial distribution. From the center of breccia to wall-rock are quartz-dioriticporphyrite, cryptoexplosivemelt-crystal-lithicbreccia, the cryptoexplosive hydrothermal breccia, and the cryptoexplosive fracture breccia, respectively. The spatial relationship between the alterated, mineralized and the cryptoexplosive breccia pipe shows that there exists a genetic link between formation of cryptoexplosive breccia and mineralization. The cryptoexplosion of the melt, liquid and gas originated from intermediate-acid magma induced the
formation of large amount rubbles and fractures which can cause sudden temperature and pressure changes of ore-forming fluids. In addition, the cryptoexplosive breccia may provide room for migrating, mixing, and ore-forming material unloading for ore-forming hydrothermal fluid that arose from magmatic hydrothermal fluid. The geological features of the Chating copper-gold deposit are similar to those of the porphyry deposits including the intermediate-acid porphyrite host rocks, the alteration types, and zonation of wall rocks, as well as fine-grained dissemination and fine-veined, and net-veined mineralization. However, the mineralization enrichment site is consistent with the cryptoexplosive breccia pipe. Also, the geological features such as breccia, veined, agglomerated mineralization and hydrothermal anhydrite developed intensively in the vein are distinctly different from typical porphyry deposits. Therefore, based on these characteristics, we suggest that the Chating copper-gold ore deposit is a cryptoexplosive breccia type deposit closely related to intermediate-acidic hypabyssal intrusion.

The Mineralogy Study of Shock-induced Melt-veins in Antarctic Meteorite GRV 022115

SI Jiaxin，XIE Zhidong，LI Yang

2020, 26(3):  265-275.  DOI: 10.16108/j.issn1006-7493.2019044

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By micro-analytical techniques, such as electron probe microscopy analysis, scanning electron microscopy，laser Raman pectroscopy and transmission electron microscope, this paper mainly study the mineralogical characteristics of host rock and shock-induced melt vein of the Antarctic meteorite GRV 022115, and discuss the formation mechanism of shock-induced melt veins and the shock conditions of its parent bodies. The host rock of the meteorite GRV 022115 is mainly composed of minerals of olivine, pyroxene, feldspar, and some iron-nickel metal and sulfide. Based on the mineralogical features of the major silicates of the meteorite host rock, the meteorite is classified as L6 type ordinary chondrite with low weathering level (W1) which is similar to the previous classification. While the impact degree for meteorite GRV 022115 is modified as S6 from original S5 based on abundant ringwoodite fragments occurring in several shock-induced melt veins in GRV 022115 meteorite. The shock-induced melt veins are composed of two lithofacies: the melt-vein matrix and host rock fragment inclusions. The vein matrix is mainly composed of μm-scale majorite and nano-scale magnesiowüstite, which were crystallized under equilibrium shock pressure. The original low-pressure silicate minerals of the host rock fragment inclusions in melt-veins, such as olivine, pyroxene and feldspar, mostly went through solid phase transformations under high shock pressure and high temperature. Small olivine grains transformed to ringwoodite completely, while larger olivine grains have ringwoodite rim formed in outside edge of the fragment, and olivine in core part. Some pyroxene grains transformed to perovskite-structured bridgmanite. Feldspar grains transformed to the high-pressure phases of maskelynite and lingunite. Almost all host rock fragments show rounded edges by high temperature effects. The differences of elements’content of same mineral inside and outside melt veins reflects the effects of high temperature mixing and diffusion under high temperature and pressure. Based on the mineral assemblages of majorite and magnesiowüstite in the melt vein matrix of GRV 022115, and the phase diagram of the static high-pressure experiment, combing the formation and crystallization model of the shock-induced melt vein, the shock pressure of the GRV022115 chondrite can be constrained to 23-27 GPa.

Investigation of the Genesis of Glauconite in the Cambrian Xuzhuang Formation in Dabeiwang, Xuzhou

YANG Tianyang，SHEN Yulin，ZHANG Tao，LI Zhuangfu，TONG Gencheng，LIU Jinbang

2020, 26(3):  276-285.  DOI: 10.16108/j.issn1006-7493.2019037

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Different types of glauconites were formed in the Cambrian Xuzhuang Formation in Dabeiwang, Xuzhou. To investigate the genesis of different types of glauconite, analysis of different aspects of glauconite was performed including its mineralogy, geochemistry and sedimentary environment. In addition, polarization microscopy, X-ray diffraction and electron microprobe are used to systematically investigate the different types of glauconite-bearing strata and glauconite to find out the indicative meaning for sedimentary facies of the different types of glauconite. The results show that there are three types of glauconite in the Xuzhuang Formation: granular, detrital illusion, and micellar. Granular glauconite shows medium-high content of potassium, high content of iron, medium-high content of aluminium in sandstone and low content of aluminium in limestone. Detrital illusion glauconite shows a large variety of potassium, iron and aluminium, and maintains the morphological characteristics of its substrates. Micellar glauconite is characterised by high potassium, high iron, and low aluminium. The genesis of granular glauconites can be explained by the verdissement theory and the glauconite in sandstone is susceptible to environmental impacts. The genesis of detrital illusion glauconite follows the layer lattice theory and the pesudomorphic replacement theory, and is subjected to metasomatism and dissolution. The composition of detrital illusion glauconite varies greatly due to strong hydrodynamic conditions. Micellar glauconites are gel-like glauconities precipitated by cementation and are formed in a stable environment.

Effects of Sulfate on the Anaerobic Transformation of Maghemite-Magnetite

GAO Yang，ZHOU Yuefei，XIE Qiaoqin，CHEN Tianhu

2020, 26(3):  286-293.  DOI: 10.16108/j.issn1006-7493.2019032

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Maghemite can transform to magnetite by anaerobic bacteria through solid route. This transformation has important significance both to mineralogy and environmental magnetism. This study investigates the interactions between sulfate-reducing bacteria (SRB) and maghemite, with special emphasis on the effect of bacterial activity on mineral transformation rate. Two types of experiments were designed: one with sulfate and the other without sulfate. After incubating for 31 days, in experiments with SO₄ ^2- and SRB, about 16.7% sulfate was reduced to acid volatile sulfides. Some Fe(II) that was derived from the reduction of maghemite reacted with AVS to form monosulfides, bisulfides, and polysulfides. The decrease in particle sizes of maghemite was associated with the release of Fe(II). In experiments without sulfate, Fe(II) reduced by SRB remained in the mineral and no secondary precipitates was observed. X-ray diffraction and Mössbauer spectroscopy analyses showed that maghemite transformed gradually to magnetite, at a greater rate in experiments with sulfate, which suggests that sulfate promoted both the activity and the electron transfer ability of SRB. Under natural and artificial anaerobic conditions, sulfate could be an important factor that constrains the transformation of maghemite to magnetite.

Uranium Mineralization Characteristics and Metallogenic Potential of the Lower Cretaceous Shahezi Formation, Southeastern Songliao Basin

ZHAO Yue，LI Keyan，XU Qiang，FAN Jingjing，Ding Rong，HUO Chao

2020, 26(3):  294-302.  DOI: 10.16108/j.issn1006-7493.2019069

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Based on the borehole core, logging curve and sample tess and analytical data, the sedimentary facies, sedimentary system and uranium mineralization characteristics of the Lower Cretaceous Shahezi Formation in the southeastern margin of the Songliao Basin are analyzed. From the aspects of uranium source, structure, sedimentation, paleoclimate, and rock geochemistry, the uranium ore-forming conditions are analyzed. In addition, the potential of the Lower Cretaceous uranium mineralization in the southeastern margin of the basin was evaluated. The results show that the sedimentary environment of the upper part of Shahezi, i.e., the ore-bearing target layer, is mainly the micro-facies between the subaqueous distributary channel and the distributary channel in the fan delta front. The uranium mineralization was mainly developed in the fan delta subaqueous distributary channels or near the interface between subaqueous distributary channels and subaqueous interdistributary channel microfacies. The uranium mineralization rock types are sandstone and mudstone, with an average thickness of 0.30 m, an average grade of 0.0259% , an average content of 0.0775 kg/m² of uranium, an average 0.99 radium balance coefficient, and a plate shape of the uranium mineralization layer. The study area is rich in uranium resources, moderate in structural conditions, favorable lithology suitable in paleoclimate, strong in reducing capacity and adsorption capacity of ore-bearing rocks, and large in mineralization potential of sandstone-type uranium deposits. This study provides a
basis for enriching and expanding new areas of uranium prospecting in the basin.

CO₂ Absorption and Precipitation Study Using Magnesium-based Tailings from Salt Lake Potassium Production

WANG Han，ZHU Chen，ZHANG Menglong，ZHAO Liang

2020, 26(3):  303-312.  DOI: 10.16108/j.issn1006-7493.2019048

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In order to achieve the goal of temperature control of 1.5℃ proposed by IPCC, mineral sequestration has been widely studied due to its long-term stability and safety. This paper selects magnesium-based tailings as the raw material for further research. Magnesium-based tailings, as waste of potassium salt production in the salt lake, have been plaguing the local industry due to limited application. If used as a raw material for sequestration of carbon dioxide, it will have great storage potential. In this experiment, two core processes of CO₂ absorption and carbonate precipitation were studied to investigate the reaction rate and path of CO₂ in MgCl₂-NH₃-NH₄Cl system under four different reaction temperatures (0, 20, 50, 80℃ ). It was found that the kinetic reaction rate constant of CO₂ at the gas-liquid interface is an important factor limiting CO₂ mass transfer. Modeling temperature and reaction rate constant and their relationship was found to  k_app=1.4857×10⁵ exp(-1974/T) . In addition, for the CO₂ absorption rate and carbon precipitation rate of the magnesium carbonate precipitation process, the optimal experimental temperature conditions are proposed, indicating the potential for large-scale application.

Sensitivity Analysis of Tight Sandstone Reservoirs of Carboniferous-Permian Coal-series in the Eastern Margin of the Ordos Basin

JIANG Tao，WEI Tao，FAN Xu，XU Weikai，LI Yong

2020, 26(3):  313-322.  DOI: 10.16108/j.issn1006-7493.2019089

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The Upper Paleozoic tight sandstone reservoirs in the Linxing area of the Ordos Basin show various rock and mineral compositions, complex pore structures, and high clay mineral contents, which directly affect the reservoir engineering and development. Based on X-ray diffraction, casting thin sections, gas porosity and permeability test, mercury intrusion porosimetry and sensitivity experiments, the reservoir sensitivity and its influencing factors were systematically investigated. The results show that the sandstones in the study area are of high contents of fragment quartz and lithic, while the feldspar content is low. The sandstones consist mainly of lithic, lithic quartz, feldspar lithic, and quartz sandstones. Clay minerals are mainly of illite, kaolinite, chlorite and illite/smectite (I/S)
mixed layer. The reservoir properties are of low porosity and permeability, with poor pore structure. The sandstones of Taiyuan Formation show the strongest velocity sensitivity, while the Shanxi Formation sandstones are of the weakest, positively correlated with illite and chlorite content, while negatively correlated with kaolinite content. As for water sensitivity, the Xiashihezi Formation sandstones are the strongest while the Taiyuan Formation sandstones are the weakest, which are positively correlated with the I/S contents. The salt sensitivity is similar to water sensitivity, showing a positive correlation with I/S contents. The acid sensitivity of the Shanxi Formation sandstones is the strongest while the Xiashihezi Formation sandstones is the weakest, which is positively correlated with the contents of chlorite and ankerite. The alkali sensitivity is strong in the Shanxi Formation sandstones and weak in Taiyuan Formation sandstones, being associated with the contents of feldspar, quartz, and kaolinite. The results are helpful in guiding well drilling, fracturing and reservoir engineering processes, and also gas drainage controls.

Classified Evaluation of Shale Reservoirs in the Ordovician Wufeng to Silurian Longmaxi Formations in the Southern Sichuan Basin

GUO Jianlin，JIA Chengye，HE Dongbo，LI Lin，ZHU Hanqing，ZHOU Yi，LIU Chang

2020, 26(3):  323-332.  DOI: 10.16108/j.issn1006-7493.2019047

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On the basis of resource evaluation and favorable area evaluation, this paper established a set of classified evaluation criteria for shale reservoirs in the Wufeng-Longmaxi Formations in the southern Sichuan Basin. The criteria for effective reservoir identification include porosity (Φ) greater than 3%, gas saturation (Sg) higher than 30%, density of rock matrix (DEN) below 2.7 g/cm³, brittleness index (BI) over 40% and gas contents (Vt) higher than 1 m³/t. These criteria can distinguish the reservoirs and non-reservoirs. Based on the conception of geological and engineering integration, gas contents (Vt) has been selected to characterize the resource foundation of shale reservoirs, which is positively correlated with porosity and organic matter abundance. The brittleness index (BI) positively correlating with siliceous and carbonate contents has been selected to characterize the compressibility. Gas contents and brittleness index can comprehensively characterize the geological and engineering characteristics of reservoirs. Effective shale reservoirs have been further divided into three types: Type I with gas contents over 4 m³/t and brittleness index greater than 50%; Type II with gas contents lower than 4 m3/t or brittleness index less than 50%; Type III with gas contents from 1 m³/t to 4 m3/t and brittleness index between 40%-50%. Reservoirs in the Wufeng Formation and the low member of the Longmaxi Formation have a good quality which mainly consist of Types I and II and locally Type III. According to the criteria established in this paper, evaluations for reservoir quality of horizontal drillings have been conducted, and correlations between penetration rate of Type I reservoir, testing production and estimate ultimate recovery (EUR) are positive. Horizontal wells with drilling efficiency of Type I reservoir over 50% have probability of 92% for testing production over 15×104 m3/d and the corresponding EUR exceeding 8000×104 m³, meeting the requirements of economic development.

Distribution Pattern of High-quality Reservoirs and Karst Zoning Feature of Carbonate Rocks in Buried Hills: A Case Study from the Bozhong Sag, Bohai Bay Basin, China

HUA Xiaoli，LI Huiyong，SUN Xijia，TAO Li，HU Hewei

2020, 26(3):  333-338.  DOI: 10.16108/j.issn1006-7493.2019059

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A great breakthrough of gas exploration has been gained in deep Paleozoic carbonate reservoirs of Buried Hill in the southwestern Bozhong Sag, Bohai Bay Basin. Drilling wells reveal that the vertical zonation of the Paleozoic gas layers was mainly controlled by karstification in this region. Recognizing the characteristics of vertical karst zoning in the study area is the key to predict the distribution of high-quality reservoirs. According to cores, thin sections, logging characteristics, spectrum logging U values, C-O-Sr isotope compositions, combined with the hydrodynamic magnitude and direction, karst reservoirs can be vertically divided into four zones from top to bottom: surface weathering zone, vertical percolating zone, horizontal underflow zone, and deep slow flowing zone. The differences of lithologic-logging properties and denudation intensity were closely related to the development of high-quality reservoirs. It is showed that the high-quality reservoirs are mainly distributed in the surface weathering zone (20 m under unconformity) and horizontal underflow zone (50 to 200 m beneath unconformity). In addition, the potentially high-quality reservoirs are developed in dolomiteexisting area of deep slow flowing zone with weak denudation. Therefore, clarifying the characteristics of karst vertical zoning and the patterns of reservoir development have important guidance for exploration of oil and gas in the future.

Distribution and Causes of Knickpoints in the Upper Reaches of Minjiang River

LIU Xuan，LIN Zhou，DING Chao

2020, 26(3):  339-349.  DOI: 10.16108/j.issn1006-7493.2019036

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The longitudinal profile of a bedrock channel in an equilibrium state appears as a smooth curve. However, the longitudinal profile of a river in nature often exhibits a transient state characterized by knickpoints, which are caused by the influence of earth's various internal and external dynamic effects. Therefore, the unbalanced channel profile and characteristics of knickpoints can indicate the disturbance of external environment. The drainage system of Minjiang River basin on the eastern margin orogenic belts of Tibetan Plateau is generally characterized by a transient state with widely developed knickpoints. In this study, we extract the spatial distribution of knickpoints based on a digital elevation model. After analyzing causes of the knickpoints, it was found that the formation of these
knickpoints are affected by lithology, glacial action, and tectonics. The knickpoints controlled by lithology were mainly located at the boundary between granite and other strata. High-altitude knickpoints located in the region with low terrain relief are mainly controlled by glacier. The slope-break knickpoints distributed in layers at low altitudes in the basin could be mainly formed by multiple episodes of regional tectonic uplift. In the longitudinal profile of lower part of Minjiang River, the stepped vertical-step knickpoints situated between steep slopes and gentle slopes were mainly caused by seismic landslides. The results help better understand regional geomorphic evolution and its influencing factors. Also, the results suggest that it is necessary to take into account glaciers and landslides in the analysis of the knickpoints in the river longitudinal profile as these factors have important impacts on longitudinal profiles of modern rivers. In addition, the results provide a new perspective for interpreting geomorphological evolution in an orogenic belt.

A Review on Mineral Heating Characteristics and Rock Weakening Effect under Microwave Irradiation

ZHAO Qinhua，ZHAO Xiaobao，ZHENG Yanlong，LI Jianchun，HE Lei，LIU Hanwen，YU Jiawang

2020, 26(3):  350-360.  DOI: 10.16108/j.issn1006-7493.2019041

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With the rapid development of economy, there has been an increasing number of cases where extremely hard rock is encountered. Thus, traditional mechanical excavation methods can hardly guarantee their efficiency and economy. Microwave-assisted rock breaking is a promising technique. Rock is formed by different minerals which have different microwave sensitivity related to their species, crystal forms and iron content. When the rock is exposed to microwave irradiation, differential expansion between minerals of different sensitivity causes thermal stresses inside and along the boundaries of the minerals, thus effectively weakening the rock. Two main factors affecting the weakening effect are microwave parameters and rock properties. Basically, rock strength declines as microwave power and irradiation time increase; a high power and short irradiation can cause a better weakening effect when consuming the same energy. The weakening effect of microwave on rocks can also be enhanced by a certain content of microwave sensitive minerals and a coarser particle size. The physical and chemical properties of minerals are sometimes greatly affected by microwave heating, which in turn affects the heating characteristics and weakening effect of the rock. Surface irradiation tests reveal that microwave can induce radial pattern cracks on the irradiation zone of large-size rock sample, thereby reducing the rock strength and improving the rock breaking efficiency.