25 February 2021, Volume 24 Issue 1

    

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   Geochronology of mineralization and tectonic setting of Baishidong skarn－ type iron deposit in Helong area of Yanbian，Jilin Province，NE China

  NIE Xitao, ZHANG Yajing, WANG Fuliang and SU Zumin

  Global Geology. 2021, 24(1): 1-14.

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   The Baishidong iron deposit is the only skarn-type iron deposit discovered in the study area． Accord-

  ing to mineral assemblage and paragenesis，the mineralization can be divided into four metallogenic stages: ear-

  ly garnet-diopside skarn stage，late magnetite-tremolite-epidote skarn stage，early quartz-pyrite-chalcopyrite

  stage and late quartz-calcite-pyrite stage． Through LA-ICP-MS zircon U-Pb dating of diorite，which is closely

  related to mineralization，the results show that the weighted average age is 164． 6 ± 1． 4 Ma，which limits the

  mineralization time of Baishidong iron deposit during or slightly later than Middle Jurassic． The diorite rocks are

  rich in sodium (Na 2 O/K 2 O = 1． 24--1． 76)，aluminium (Al 2 O 3 = 17． 41%--18． 76%)，LＲEE and large-ion

  lithophile elements (Ba，K and Sr)，depleted in HＲEE and high-field-strength elements (Y，Nb，Ta，P and

  Ti)，and show strongly fractionated patterns (LＲEE/HＲEE =6． 58--9． 93)，no apparent Eu anomalies (δEu =

  0． 91--1． 13)，which shows similar characteristics to island arc or active continental margin arc magma． The zir-

  con εHf(t) values range from －22． 6 to 5． 9，and the age of the two-stage model (t DM2 ) is 836--2 633 Ma．

  Above data combined with the geochemical characteristics，it is indicated that the magma was a mixture of mul-

  tiple sources，composed of ancient materials and newly formed crust． During the process of evolution and ascending of magma，separation and crystallization occurred，and a large amount of continental crust material was mixed at the same time． Combined with regional tectonic evolution，the formation of this deposit may be related to the westward subduction of the Paleo-Pacific Plate to the Eurasian Plate． 
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   Three － dimensional geological modelling and direction of hydrothermal alteration of Horne deposit， Blake Ｒiver Group，Quebec，Canada

  TIAN Liya，YU Yunliang and XU Haibo

  Global Geology. 2021, 24(1): 15-22.

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   The Horne deposit with rich Cu and Au in Noranda region of Black Ｒiver Group in Quebec has high economic significance． Current researches on Horne deposit are mostly based on two-dimensional maps and statistical data． It is hard to reflect the spatial structure and characteristics of Horne orebody directly． In this paper，GIS was used to digitize the mining plan-view maps at different depths，stope maps，the boundary of the massive sulfide in drilling trajectories as well as the grade data of Au and Cu of Horne deposit． Meanwhile，the authors established the grade attribute database． Subsequently the three-dimensional ( 3D) geological model and grade attribute model of Horne orebody were established by Geological Object Computer Aided Design ( GOCAD) ． Positions of two vents and directions of hydrothermal alteration in Horne deposit were inferred based on the property of the major fault，characteristics of hydrothermal alteration，the enrichment morphology and spatial distribution of high-grade Cu in the Cu attribute model．
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   Qiyugou auriferous breccia pipes: A low － sulphidation epithermal system linked with transition of tectonic regime from collisional compression to extension，Xiong＇ershan，Henan，China

  ZHANG Yuanhou,ZHANG Shihong and Pirajno Franco

  Global Geology. 2021, 24(1): 23-42.

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   The Xiong＇ershan area，as a part of a metallogenic province in cetral China，contains substantial Leimengou porphyry molybdenite deposit，Qiyugou breccia gold deposits and vein gold deposit occurred in fault zone，as well as previously refer to as orogenic gold deposit． Around or nearby the Mesozoic porphyry granite， the typical porphyry deposit，much more breccia pipes and breccia gold deposit are developed in the area． In this paper we focus on reporting preliminary results obtained from field，petrographic work on the Leimengou porphyry molybdenite and the Qiyugou breccia gold deposit，as well as laser Ｒaman microspectroscopy and microprobe analyses carried out on samples from the Au-bearing Qiyugou breccia pipes． An adularia-calcite assemblage is reported in these breccia gold deposits． Two stages of hydrothermal alteration，pervasive and vein，are identified． The first stage consists of the alteration of the breccia clasts and rock flour by actinolite，green biotite，epidote，chlorite and minor sericite． This hydrothermal activity is likely to relate to the molybdenite mineralisation episode． The second stage is characterised by quartz veining and adularia and calcite filling openspaces． Vein ores associated with quartz，sericite，and minor calcite alteration occur in NE-trending fault that cut the first stage of alteration． The adularia-calcite alteration is genetically associated with gold mineralization． The adularia-calcite assemblage in the area suggest that the Qiyugou pipes are of low-sulphidation epithermal in nature． The Qiyugou breccia pipes are coeval and spatially associated with the nearby Leimengou porphyry Mo deposit，which together conform to an alkalic mineralising system． We propose a model for the development and evolution of the breccia pipes in conjunction with a model that describes the genesis of the porphyry Mo and auriferous breccia pipes as a unified magmatic-hydrothermal system，which is linked with transition from collisional compressional to extensional geodynamic regime.
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   Application of high － density resistivity method for assessing construction safety of Shimodong tunnel in Helong City of Jilin Province

  LI Zhuoyang,HAN Jiangtao,LIU Lijia and XIN Zhonghua

  Global Geology. 2021, 24(1): 43-48.

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   Some unfavorable geological conditions can affect the construction of tunnels． In order to evaluate the damage degree of tunnel construction and determine the surrounding rock grade and stability of the tunnel，the authors used high-density resistivity method to detect the surrounding rocks of Shimodong tunnel in Xicheng Town of Helong City． The underground resistivity structures of the entrance，exit and middle parts of the tunnel are obtained． Through analysis，it is found that there are no bedrock faults near the tunnel，although some joints and fissures are developed in some locations，which are characterized by low-resistivity anomalies． The tunnel structures are stable overall，favorable for safe and efficient construction． The study also proves the good application effect of the high-density resistivity method in tunnel safety detection.
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   Multi － scale separation of aeromagnetic abnormality based on dual － tree complex wavelet

  GONG Mingxu,ZENG Zhaofa,ZHANG Jianmin and JIANG Dandan

  Global Geology. 2021, 24(1): 49-57.

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   Bit-field separation is an important part of gravity and magnetic data processing． In order to extract different levels of anomaly information better，this paper introduces the dual-tree complex wavelet multi-scale separation to the processing of bit-field data firstly and uses the geological model of different buried depth to verify its feasibility． Finally，the dual-tree complex wavelet is applied to the aeromagnetic anomaly in Jinchuan copper nickel mining area． The results show that the method can effectively separate the anomaly information of different scales and analyze the output results with relevant geological data．
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   Application of high － density resistivity method in archaeological investigation of Sumicheng ancient city site

  XIN Zhonghua,HAN Jiangtao,WANG Zhigang,LIU Lijia and LI Zhuoyang

  Global Geology. 2021, 24(1): 58-63.

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   The authors employ the high-density resistivity method during an archaeological investigation of Sumicheng site，an ancient city of the Tang Dynasty，to find evidence of human activities and locate a favorable target for archaeological excavation in the southern part of the outer city． There are two obvious high-resistivity structures，the south wall of the inner city and an ancient building near the south gate along the outer city wall， of which the resistivities are indicative of rammed soil foundations． The south wall of the inner city is continuous but is cut off abruptly to the east，which we suggest it is due to either wall damage or destruction． The resistivity signature of the target area is verified by archaeological excavation，proving the feasibility and effectiveness of implementing the high-density resistivity method for archaeological exploration．
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   Analysis of effects of operating parameters on rate of penetration in drilling process with air down － the － hole hammer

  HO Yinchol,PAK Kumdol,PENG Jianming,ＲI Jaemyong,KIM Yongnam and CHOE Cholho

  Global Geology. 2021, 24(1): 64-70.

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   Air down-the-hole ( DTH) hammer drilling has long been recognized to have the potential of drilling faster than conventional rotary drill，especially in some hard rocks such as granite，sandstone，limestone，dolomite，etc． with the same weight on bit ( WOB) and rotations per minute ( ＲPM) ． So，it has been widely used in many drilling fields including mineral resource exploration drilling，oil and gas drilling and geothermal drilling． In order to reduce drilling cost by selecting optimal drilling parameters，rate of penetration ( ＲOP) should be estimated accurately and the effects of different factors on ＲOP should be analyzed． In this research，ANN model with several multi-layer perception back propagation ( BP) networks for predicting ＲOP of air DTH hammer drilling was developed using controllable parameters such as impact energy，impact frequency，WOB， ＲPM and bit operating time for the formations with a certain drillability index of rock． Several BP neural networks with the different neurons in hidden layers were developed and compared for selecting optimal architecture of ANN． The effects of the drilling parameters such as impact energy，impacting frequency，WOB，ＲPM and bit operating time on the ＲOP of air DTH hammer drilling were investigated by trained ANN． From the analyses，the optimum range of drilling parameters for providing high ＲOP were determined and analyzed for a formation with a certain drillability index of rock． The methodology proposed in this study can be used in many mathematical problems for optimization of drilling process with air DTH hammer．