Table of Content

20 April 2020, Volume 26 Issue 2

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An Overview of Characteristics and Prospecting of Gold Ore Deposits in China

WANG Bin，LI Jingchao，WANG Chengxi，ZHENG Xiao，SUN Kefeng

2020, 26(2):  121.  DOI: 10.16108/j.issn1006-7493.2019033

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Based on the geodynamic settings of gold metallogenesis and the basic geological features of gold ore deposits, China’s gold deposits can be classified into 11 categories. Among these categories, the structurally-fractured altered-rock type, inner and outer contacting belts type of plutonic intrusives, the Carlin or quasi-Carlin type, hydrothermal type within low-grade metamorphic clastic rocks, and continental volcanic rock types are the types of interest in prospecting. As far as metallogenic ages concerned, those that occurred in Mesozoic and Cenozoic are the major types. According to their geotectonic units, geological evolution, metallogenic geological conditions, spatial-temporal distribution, gold deposit types, regional metallogenic factors, and volumes of mineral resources, totally 42 gold ore concentration areas, which are spatially distributed in clusters, have been preliminarily identified on the basis of China’s III-graded classification scheme of metallogenic zones (belts). According to gold prospecting borehole quantities per unit area, China’s gold ore concentration areas can be categorized into 3 levels, i.e., highly, moderately, and lowly developed. The highly developed ones are mainly distributed in Central and Eastern China. Except the placer gold deposits, about 88.12% boreholes for primary gold (rock gold or associated gold) deposits are less than 500 m with deep in China, suggesting that the quantities and depths of gold exploration drillings in China are less and shallower than in other countries. As for the gold resources exploration potentials, we propose that (1) in Central and Eastern China, the deep parts and the peripheries of the existing gold mines are key locations to be focused on; (2) for Western China, the gold ore concentration areas, which are located especially in Xinjiang Uygur Autonomous Region, Qinghai Province, and Tibet Autonomous Region, are the future key regions with immense potentials for unexplored gold resources.

Geochemical Characteristics and Petrogenesis of Monzogranites from the Xinxian Batholith, Dabie Orogenic Belt

YANG Chunyue，HE Jun，YANG Yizeng，CHEN Fukun

2020, 26(2):  132.  DOI: 10.16108/j.issn1006-7493.2019031

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The Mesozoic intermediate-acid plutons are widespread within the Dabie orogenic belt which is located between the North China Block and the Yangtze Block. This work conducts an integrated study including field geology, zircon U-Pb dating, and elemental and isotopic measurements for the Xinxian batholith, aiming to reveal its geological and geochemical characteristics and to discuss its petrogenesis. The investigation results indicate that the Xinxian pluton consists predominantly of monzogranites. They were crystallized in 133-129 Ma and can be divided into three units based on grain sizes. Paleoproterozoic inherited zircons have been observed from samples of this pluton. The monzogranites are characterized by enrichment of silica and alkaline, depletion in LILEs (e.g., Ba and Sr) and HFSEs (e.g., P and Ti) with indistinct Nb-Ta anomalies on the primitive-mantle normalized spidergrams, and can be grouped into weakly peraluminous high-K calc-alkaline series. The chondrite-normalized REE patterns show strongly enrichment in LREEs, depletion in MREEs, weakly enrichment in HREEs and exhibit distinct negative Eu anomaly. These features indicate that the monzogranites were derived from an amphibole stable zone in an extensional environment of the thickened crust, rather than from a garnet stable zone in the thickened lower crust. The whole-rock εNd(t) values of this pluton range from -20.8 to -18.4, with two-stage Nd model ages of 2.61 to 2.43 Ga, implying that the parent magmas were originated mainly from partial melting of ancient crustal rocks, such as the Kongling and/ or Douling Groups. By comparison the Xinxian monzogranites with the ore-bearing rocks from the Qian’echong and Baoanzhai Mo deposits, it is shown that they have consistent geochemical features, implying that they have closely genetic relationship, and were likely produced from different differentiation stages of the same magma.

Geochronology, Geochemical Characteristics and Its Geological Significance of the Quartz Diorite Pluton from the Dayinshan Gold Deposit in Northern Zhejiang Province

JIANG Xin，NI Pei，DING Junying，CHEN Huanyuan，FAN Mingsen，LI Wensheng，JIA Fei

2020, 26(2):  147.  DOI: 10.16108/j.issn1006-7493.2019035

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The Dayinshan deposit, located in the conjunction zone between the lower Yangtze passive margin and the Jiangnan paleo-island arc, is a skarn gold deposit associated with the quartz diorites. In this study, U-Pb ages and Lu-Hf isotope compositions of zircon grains extracted from quartz diorites were measured combining with major and trace elemental geochemistry, with aims to elucidate the timing of the gold mineralization and the origin of the ore-related quartz diorites. LA-ICP-MS zircon U-Pb dating gives the weighted mean ages of 144 ±1 Ma for quartz diorites. The quartz diorites are high K calcium alkaline to calcium alkaline and aluminum to peraluminous. All the samples are enriched in large ion lithophile elements (Ba, Rb, Sr, K) and depleted in high field strength elements (Nb, Ta, Ti) and heavy rare earth elements, with weakly negative Eu anomalies. The results show that quartz diorites of Dayinshan have a similar characteristics of arc magmatic rocks associated with subduction zone. The quartz diorites also have lower Sr/Y value and higher Y and Yb content, indicating that its magma comes from the thinner continental crust. Zircon Hf isotope model ages vary from 1.51 to 1.82 Ga, with an zircon εHf(t) value of -5.0~-9.9. All of these features are consistent with the gold deposit from the Yangtze River metallogenic belt. Detailed elemental and isotopic data demonstrate that these rocks were derived from partial melting of the lower crust of the Yangtze plate induced by subduction of the paleo-Pacific in late Mesozoic.

Precambrian Crust Components and Its Tectonic Evolution of the Kontum Massif, Central Vietnam

WANG Fangqian，YU Jinhai，NGUYEN DinhLuyen，JIANG Wei

2020, 26(2):  161.  DOI: 10.16108/j.issn1006-7493.2019042

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The Kontum Massif in the central Vietnam is one of the most important Precambrian basement exposures in the Indochina Block. This Massif consists mainly of different periods and different grade of metamorphic rocks. This study presents their petrologic, geochemical, zircon U-Pb and Hf isotopic data, in order to reveal the components of the basement rocks and their formation and tectonic evolution. Petrography and geochemical results indicate that the basement is mainly composed of metasedimentary rocks with a few meta-igneous rocks. Zircon U-Pb dating results suggest that the sedimentary rocks were formed in late Paleoproterozoic to late Neoproterozoic, and can be divided into five stages. First stage of sedimentary rocks were formed in an island-arc setting, second stage of sedimentary rocks were deposited in passive margin setting, third stage of sedimentation evironment is an active continental to continental arc setting, fourth stage is a transition from active continental margin to passive continental margin setting, and fifth stage of sedimentary basin is in an active continental margin setting. The protoliths of two metamorphic igneous rocks are tholeiite and S-type granite, and formed at 1424 Ma and 1485 Ma, respectively. Tholeiite is enriched in Rb, Ba and Sr and depleted in Nb, Ta, Zr and Ti. These features are consistent with the geochemical characteristics of typical island arc basalts. Most zircon εHf(t) values are positive with a mean value of + 5.66, except two grains, indicating that its parental magma originated from the depleted lithospheric mantle.Geochemical characteristics suggest that this tholeiite was formed in the island arc setting, in accordance with the deposition environment of coeval sedimentaryrocks. S-type granite has high SiO2, ALK and A/CNK (>1.1), and medium REE content and medium Eu negative anomaly. The magmatic zircon εHf(t) values varies from +5.97 to +12.11, suggesting that the clasts of the meta-sedimentary rocks in the source mainly came from the juvenile crust. Similarities of the formation time and geochemical features of Mesoproterozoic igneous rocks suggest that the Kontum Massif probably was connected with Hainan Island in Mesoproterozoic, and they were on the edge of the Columbia supercontinent during the disintegration of the supercontinent based on their tectonic setting.

Geophysical Characteristics and Prospecting of the Huazishan Area in Taqian-Fuchun Metallogenic Belt, Northeastern Jiangxi Province

LIN Jianyong，LUO Fan，CHEN Hui

2020, 26(2):  175.  DOI: 10.16108/j.issn1006-7493.2019070

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The Huazishan area belongs to the Taqian-Fuchun Metallogenic Belt in the Northeastern part of Jiangxi Province. It has complicated geological structures but superior conditions for deep metallogeny. For the complicated geological conditions, a combination of a variety of geophysical methods can help detect deep geologic strcutures. The difference in physical properties of rocks is the basis for the application of geophysical methods. First, the physical analysis of rock specimens in the Huazishan area was carried out. Then, two (8-line and 11-line) gravity, magnetic and controllable source audio magnetotelluric integrated geophysical profiles were obtained from the Huazishan area. The integrated geophysical profiles are interpreted in combination with geological, physical and drilling data. The high gravity and low resistance anomaly zone is interpreted to result from mineralization, and the magnetic anomaly zone was likely caused by alteration. Finally, by analyzing the integrated geophysical profile, the distribution of high-density, high-magnetic and low-resistance high-polarity region in the underground is mapped, and the key area for prospecting is located in the southwest direction of the upper strata of the Niutouling Formation of the Wannian Group. The findings of this study will aid in future ore-deposit prospecting work in the Huazishan area.

The Impacts of Injection-Production Parameters on Physico-Mechanical and Wave Characteristics of Hot Dry Rocks in Songliao Basin

CUI Hanbo，TANG Jupeng，JIANG Xintong，QIU Yuman

2020, 26(2):  185.  DOI: 10.16108/j.issn1006-7493.2019065

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In order to investigate the impacts of injection-production parameters on physico-mechanical and wave characteristics of hot dry rocks (HDR) in Songliao Basin, a uniaxial compressive test and wave velocity tests of longitudinal and shear waves of granite after high temperature treatments with subsequent water cooling under different injection-production conditions were performed. Considering the relationships between various injection-production parameters (rock sample temperature, water temperature, and cycles of high temperature with water) and granite physico-mechanical characteristics (shape, peak intensity, elastic modulus, and Poisson's ratio), and wave characteristics (longitudinal and shear wave velocity), we established the fitting curves of mechanical characteristics and wave characteristics under different injection-production conditions. Moreover, the variations of physico-mechanical and wave characteristics of granite under different rock sample temperatures and different water temperatures during the shelving process were studied. The results show that: (1) at the initial stage of shelving process, the higher the temperature of the rock sample was, the greater the magnitude of decrease in mass, longitudinal and shear wave velocity and elastic modulus can be. With increasing water temperature, the magnitude of decrease in mass, longitudinal and shear wave velocity, and elastic modulus first show an increase and subsequently a decrease; (2) among the injection and production parameters of the rock mass physical mechanics and wave characteristics on the temperature of the target area, parameters with the degree of influence from high to low are the target area temperature, the number of water injection cycles, and the water injection temperature. With the increase in the temperature of rock samples and cycles of high temperature with water, both the mechanical and wave characteristics of granite gradually decreased; while their variations can be opposite when the water injection temperature increases. After the treatment at the high temperature of 600℃ , the longitudinal wave velocity, shear wave velocity, peak intensity and elastic modulus of granite decreased by 53.44% , 58.02% , 66.56% , 79.84% , respectively. After 5 cycles of high temperature and water cooling treatments, the longitudinal wave velocity, shear wave velocity, peak intensity and elastic modulus of granite decreased by 33.61% , 33.63% , 34.22% , 56.00% , respectively. (3) The injection-production
parameters that affect the correlation between granite mechanics and wave characteristics, with the extent from large to small, are the temperature of the rock samples, cycle numbers of high temperature with water, and the water temperature. This study provides a useful reference for selecting injection-production parameters on thermal extraction in Songliao Basin.

Research Progress on Ordering and Rheological Properties of Dolomite

ZHENG Zhong，WANG Qin

2020, 26(2):  197.  DOI: 10.16108/j.issn1006-7493.2019039

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Dolomite CaMg(CO3)2 widely occurs in dolostone, limestone and marble. The wide P-T stability conditions of dolomite make it an important mineral for understanding deformation in subduction channels, global carbon cycle and mantle metasomatism. The degree of cation order in dolomite probably relates with recrystallization process. Cation ordering in dolomite is controlled by temperature, and weakly dependent on pressure. At pressure of 1-3 GPa, complete disordering in dolomite is achieved at 1150-1200℃. The addition of Fe, Mn and Cd could significantly decrease the order/disorder transition temperature of dolomite. Naturally deformed dolomite often develops the crystallographic preferred orientation due to activation of c slip. According to flow laws of dolomite, under the natural strain rate of 10-15-10-12 s-1, diffusion creep is the dominant deformation mechanism in fine-grained dolomite above 400℃ and in coarse-grained dolomite above 600-700℃. Below these temperature, dislocation creep controls ductile deformation of dolomite. Decomposition reaction or dynamic recrystallization can significantly decrease strength of dolomite and results in strain localization. The increasing of critical shear stress of c slip in dolomite with increasing temperature may be related with the cation order. The influence of confining pressure, water fugacity and composition on rheology of dolomite is still not clear. Quantitative study of the correlation between cation order and rheological properties of dolomite will provide new information to trace petrogenesis and deformation history of carbonates and marble.

Palaeoenvironmental Evolution and Human Activities of Xiawangdu Site in Zhejiang Province during the Mid-Late Holocene

SUN Jue，MA Chunmei，LI Yongning，DENG Yunkai，SHANG Guangchun，HUANG Zhenhui

2020, 26(2):  209.  DOI: 10.16108/j.issn1006-7493.2019029

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Based on pollen analysis and geochemical elements of the Xiawangdu Site in Ningfeng Plain, Zhejiang Province, and combined with 5 AMS14C dates and the archaeological cultural layers, regional environmental changes and human activities were revealed during the late cultural period of Hemudu and Liangzhu periods. The results show that the warm and humid climate conditions contributed to the settlement of the ancestors of Hemudu and evergreen deciduous broad-leaved mixed forest dominated in regional vegetation lanscape. Evidences from sporopollen, and geochemical elements show that the transgression of the Middle Holocene led to a cultural disruption in the area, and the impact of the ocean began to decrease from the fourth stage of Hemudu culture. Starting from
this period, the proportion of herbaceous pollen has vastly exceeded that of trees and shrub, especially increased pollen of Poaceae associated with cultivated crops with larger than 37 μm in size. This suggested increased human activities related to land use, as well as the rice cultivation in moderate scale near Xiawangdu site.

Sedimentary Characteristics of the Lower Member of the Zhiluo Formation in Middle Jurassic and Its Uranium Metallogenic Significance in Bayinqinggeli-Sutaimiao Area, Ordos Basin

ZHANG Bin，LIU Hongxu，DING Bo，YI Chao，ZHANG Yan

2020, 26(2):  218.  DOI: 10.16108/j.issn1006-7493.2019058

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The lower member of the Middle Jurassic Zhiluo Formation in northern Ordos Basin is the main ore-hosting layer of sandstone-type uranium deposits. The genetic type, geometric shape, and physical properties of sandstone-bearing strata control the size and spatial distribution of sandstone-type uranium deposits. Previous studies on the genesis, geometric shape and physical properties of ore-bearing sand bodies that are controlled by sedimentation and diagenesis have effectively supported the exploration of sandstone-type uranium deposits in the Eastern North of the Ordos Basin. However, continental sedimentary environments are characterized by relatively rapid changes and significant regional variations. The sedimentary environment, the genesis and spatial distribution of the sand body of J2z1 in Bayinqinggeli-Sutaimiao area on the western side of the northern basin are still unclear. In order to expand the prospecting space, we studied the 5300 m long cores and logging data from 35 wells in the lower member of Zhiluo Formation, and carried out core inspection, microscopic identification, single well analysis, cross-well profile analysis and sand content isoline analysis of this stratigraphic unit in the western periphery of the northern basin. The results show that: (1) the sandstone types in the lower member of the Zhiluo Formation in the Bayinqinggeli-Sutaimiao area are mainly medium-coarse grain lithic feldspar sandstone and feldspar lithic sandstone; (2) delta plain subfacies were mainly developed in the study area, which can be further subdivided into branching channel, crevasse fan, interdistributary bay, swamp and mud microfacies; (3) based on the analysis of ore-bearing construction, uranium source characteristics, and tectonic characteristics, it is concluded that the eastern part of the study area has a great metallogenic potential to necessitate further exploration work in this area. The finding of this study provides an important geological basis for the exploration of sandstone-type uranium deposits in the Western peripheral areas.

Study on the Impact Patterns of Multiple Geological Resources during Urban Underground Development

ZHOU Dankun，LI Xiaozhao，MA Yan，GE Weiya

2020, 26(2):  231.  DOI: 10.16108/j.issn1006-7493.2019034

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Urban underground generally contains 4 geological resources: underground space, groundwater, shallow geothermal energy and geological materials. They coexist in a geological environment system and are interconnected with each other. The development of one resource may have a significant impact on the development potential of other resources. In order to make full use of various underground resources for urban sustainable development and reduce the conflict between resource utilization, the development mode of urban underground resources needs to change from one-sided development that only for a certain resource to collaborative development that considers all resources comprehensively. Based on the literature review, this paper identifies 9 typical impact patterns between the 4 geological resources mentioned above, concluded that the influence between multiple resources has the characteristics of mutual
feedback, chain reaction and dynamic change, and lists some typical cases of collaborative development of multiple geological resources,expected to provide support for maximizing the benefits of urban underground development.