Geophysical Exploration Method of Epithermal Gold Deposit in Shallow Overburden Area:A Case Study of Alinghe Mining Area in Heihe City,Heilongjiang Province
1.Harbin Center for Integrated Natural Resources Survey,China Geological Survey,Harbin 150081,Heilongjiang,China
2.Northeast Geological S&T Innovation Center of China Geological Survey,Shenyang 110034,Liaoning,China
3.Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Central South University),Ministry of Education of the People’s Republic of China,Changsha 410083,Hunan,China
4.School of Geophysics and Information Technology,China University of Geosciences(Beijing),Beijing 100083,China
5.Scientific Monitoring and Research Station of Earth Critical Zone on Black Soil in Harbin,Ministry of Natural Resources of the People’s Republic of China,Harbin 150086,Heilongjiang,China
In shallow overburden area,acquiring geological prospecting information via geological outcrops presents significant challenges.Consequently,there is an urgent requirement for the implementation of geophysical technologies to enhance the optimization of prospecting target areas and the strategic placement of boreholes.Typically,epithermal gold deposits do not directly produce geophysical anomalies.The geophysical properties of gold ore bodies,alteration zones,and their surrounding lithologies remain insufficiently understood.The Alinghe mining area,located within the forested region of northeast China,is characterized by shallow soil cover.The scarcity of rock outcrops has rendered traditional geological and mineral mapping techniques largely ineffective,underscoring the necessity for an increased reliance on geophysical prospecting methods in gold exploration.In response,we conducted high-resolution 1∶5 000 magnetic surveys over areas exhibiting soil gold anomalies,alongside 1∶5 000 induced polarization (IP) measurements using gradient arrays in selected hydrothermal alteration zones.Through the integrated analysis of resistivity and polarizability anomalies,we identified areas with favorable gold mineralization potential.Subsequently,electrical resistivity tomography (ERT) was employed to delineate vertical geological characteristics.In conclusion,verification of drilling and logging activities was conducted.The aforementioned geophysical exploration study yielded the following findings:(1) A series of parallel magnetic anomaly stripes were identified within the andesite distribution area.The observed low magnetic anomalies are attributed to the demagnetization effect resulting from hydrothermal alteration.Hydrothermal activity can reduce the magnetic susceptibility of andesite by up to 1 000 nT.(2) Induced polarization (IP) measurements revealed that the distribution of low apparent resistivity aligns closely with the regions of low magnetic anomalies.The apparent resistivity in the hydrothermally altered area is 100 Ω·m lower than that of the surrounding regions,indicating a water-rich shallow hydrothermal alteration zone.The anomaly of high apparent polarizability suggests a relatively pyrite-rich area associated with epithermal gold ore bodies.(3) Occam’s inversion of electrical resistivity tomography (ERT) data effectively delineates vertical geological features,including surrounding rock,hydrothermal channels,and pyritization zones,which are closely associated with gold mineralization.(4) The geological and alteration assumptions derived from the aforementioned geophysical data were validated by borehole ZK01 along the ERT line,resulting in the identification of two gold-bearing horizons and six gold mineralized bodies within a depth of 100 meters.Through the analysis of curves and crossplots of various logging parameters,the geophysical characteristics of the six gold mineralized bodies were categorized into channel type and terminal type.These two types of gold deposits are distributed on both the upper and lower sides of the high polarizability anomaly,suggesting that a high polarizability anomaly alone is not a direct indicator of a gold ore body,although it holds significant implications for prospecting.In this study,the epithermal gold deposit was systematically targeted for detection.A range of surface geophysical exploration methods was employed to progressively and effectively refine the exploration target area.Subsequent borehole verification confirmed the presence of several gold mineralized bodies,thereby validating the efficacy of the employed methods.The two distinct types of gold-mineralized bodies,categorized based on the combination of geophysical parameters and spatial distribution differences,indicate a terminal position within the mineralization system and suggest minimal erosion post-mineralization.This distinction holds significant implications for the interpretation of geophysical data and has practical relevance for prospecting and exploration efforts.
浅成低温热液型金矿床因成矿深度浅(小于2 km)和成矿温度低(低于300 ℃)而得名,在成因上与浅成、超浅成侵入作用和陆相火山、次火山作用有关,往往伴随着多期侵入的中酸性岩体发育(Hedenquist et al.,1994)。浅成低温热液型金矿可划分为低硫型、中硫型和高硫型。在全球范围内,浅成低温热液型金矿主要位于环太平洋成矿带、特提斯成矿带和劳亚成矿带3个巨型成矿域,具有重要的研究价值和意义(Sillitoe,1997,2010;Lipson,2014)。金矿体的边界品位一般界定为0.3×10-9~0.5×10-9,金含量非常低,金矿体本身的物性与未矿化的围岩没有明显的差别,不足以产生明显的地球物理异常,因此无法直接对金矿进行地球物理探测。金矿体成矿过程明显受控于特定的地质条件,含金热液在运移过程中对地质体产生的物理、化学变化构成了金矿勘查的对象(Henley,1991;Hedenquist et al.,2000; Sillitoe et al.,2003)。
野外采集数据采用EarthImager2D进行处理和反演。二维反演算法采用Occam进行反演,该方法也被称为平滑模型反演法(Smooth Model Inversion)。反演过程中,正演方法采用有限元法,正演求解器为乔里斯基(Cholesky)分解,边界条件采用狄利克雷(Dirichlet),电阻率反演初始模型采用拟断面,最大均方误差为3%,视充电率反演采用线性感应极化反演法,圆滑系数和阻尼系数均为10。
在金矿测井资料研究方面,以往研究主要集中于与金矿体、黄铁矿体分布一致的中—高硫型(Li et al.,2018;Huang et al.,2022),而关于低硫型浅成低温热液型金矿的测井响应及其与地面电法反演剖面的对比研究偏少。本次研究测井响应特征,先对测井曲线进行深度校正和突变处理,然后参考岩心编录和试验测试等资料开展研究工作,分析各类岩性、蚀变和含矿层位的测井响应特征,从而指导地面地球物理找矿工作。
本研究发现具有不同地球物理特征组合的金矿体具有不同的空间分布特征,这可能与成矿流体中硫化物和金的析出先后不同有关,该过程与温度等物理化学条件的变化有关(Brathwaite et al.,2002;Farsang et al.,2024)。地球物理方法本身无法对该问题进行深入研究,需要开展岩石地球化学和高温高压试验研究,来明确黄铁矿与金矿体之间的关系,从而提升利用极化率异常寻找金矿体的指导意义。此类金矿体与黄铁矿空间分布差异可能是低硫型浅成低温热液型金矿的地球物理特征,末端型金矿体位于浅成低温热液型成矿系统的末端,是金矿床后期遭遇较少剥蚀的证据,可能暗示着此类金矿体位于多宝山成矿带内大型浅成低温—斑岩型成矿系统的末端(Sillitoe,2010),研究区深部具有较大的找矿潜力。
AllisR G,1990.Geophysical anomalies over epithermal systems[J].Journal of Geochemical exploration,36:339-374.
[2]
BaiChenglin, XieGuiqing, ZhaoJunkang,et al,2024.Metallogenic characteristics and ore deposit model of porphyry copper-epithermal gold system in the Duobaoshan ore field,eastern margin of the Central Asian Orogenic Belt[J].Earth Science Frontiers,31(3):170-198.
[3]
BrathwaiteR L, FaureK,2002.The Waihi epithermal gold-silver-base metal sulfide-quartz vein system,New Zealand:Temperature and salinity controls on electrum and sulfide deposition[J].Economic Geology,97(2):269-290.
[4]
ChenMan, ZhouDianyu, LiDexin,2008.Analysis and verification of Au geochemical exploration anomaly in forest landscape area,great Xing’an range[J].Gold Science and Te-chnology,16(1):24-27.
[5]
ChengLin,2017.Ore genesis of the Sandaowanzi Telluride-Gold Deposit in Heilongjiang Province[D].Changchun:Jilin University.
[6]
CuiFeng,1990.Analysis of relations of apparent charging rate and chargeability[J].Jiangsu Geloogy,(3):51-53.
[7]
DoyleH A,1990.Geophysical exploration for gold—A review[J].Exploration Geophysics,17:169-180.
[8]
FarsangS, ZajaczZ,2024.Sulfur species and gold transport in arc magmatic fluids[J].Nature Geoscience,(12):1-15.
[9]
FatehiM, AsadiH H,2019.Geophysical signatures of the gold rich porphyry copper deposits:A case study at the Dalli Cu-Au porphyry deposit[J].Journal of Economic Geology,10(2):639-675.
[10]
GeXinmin, FanYiren, LiJun,et al,2019.Experimental studies and investigations on the dual lateral log response of near borehole fractures[J].Chinese Journal of Geophysics,62(1):354-360.
[11]
HaoTianyao, LiuYike, DuanChuang,1996.Approaching fault system of the east China and adjacent area from gravity and magnetic data[J].Acta Geophysica Sinica,36(Supp.1):141-149.
[12]
HaoYujie,2015.Mineralization and Metallogenic Regularity of Duobaoshan Ore Concentration Area in Heilongjiang Province,Northeast China[D].Changchun:Jilin University.
[13]
HedenquistJ W, ArribasR A, Gonzalez-UrienE,2000.Exploration for epithermal gold deposits[J].Reviews in Economic Geology,13:245-277.
[14]
HedenquistJ W, LowensternJ B,1994.The role of magmas in the formation of hydrothermal ore deposits[J].Nature,370:519-527.
[15]
HenleyR W,1991.Epithermal Gold Deposits in Volcanic Terranes[M]//Foster R P.Gold Metallogeny and Exploration.Boston:Springer.
[16]
HoschkeT G,2011.Geophysical Signatures of Copper-Gold Porphyry and Epithermal Gold Deposits,and Implications for Exploration[M].Tasmania:University of Tasmania.
[17]
HoschkeT, SextonM,2005.Geophysical exploration for epithermal gold deposits at Pajingo,North Queensland,Australia[J].Exploration Geophysics,36(4):401-406.
[18]
HuangK, XieG Q, DuanL A,et al,2022.Identification of Paodaoling large intermediate-sulfidation epithermal gold deposit in Middle-Lower Yangtze River Valley metallogenic belt and its implication for mineral exploration[J].Mineral Deposits,41(2):440-448.
[19]
KawasakiK, OkadaK, KubotaR,1986.Geophysical surveys in the Hishikari mine area[J].Mining Geology,36:131-147.
[20]
LiChenglu,2018.Gold Metallogeny and Prospecting in the Nenjiang-Heihe Tectonic Melange Zone,Heilongjiang Province [D].Beijing:China University of Geosciences.
LiS N, NiP, BaoT,et al,2018.Geology,fluid inclusion,and stable isotope systematics of the Dongyang epithermal gold deposit,Fujian Province,southeast China:Implications for ore genesis and mineral exploration[J].Journal of Geochemical Exploration,195:16-30.
[23]
LipsonR,2014.The promise and perils of porphyry deposits in the future of gold production[J].SEG Newsletter,98:1-21.
[24]
LiuBaoshan, ChengZhaoxun, ShaoJun,et al,2022.Latest pro-specting progress and exploration direction of copper-gold polymetallic deposit in Nenjiang-Heihe area,Heilongjiang Province [J].Geology and Resources,31(3):331-341.
[25]
LiuDongming, LiangMingxing, FengJie,et al,2024.Response characteristics and its prospecting signs of geophysical well logging in Xiaotongjiabuzi gold deposit,Eastern Liaoning Province[J].Earth Science,49 (3):1066-1080.
[26]
LiuShanli, LiWei, SunGuosheng,et al,2011.Applications of high-precision magnetic measurement in checking Kelidai gold deposit,Inner Mongolia[J].Global Geology,30(4):666-670.
[27]
LiuXiaoyu,2021.Magnetostratigraphy and Discussion on J/K Boundary of LK-1 Borehole in Lingshan Island[D].Beijing:China University of Petroleum.
[28]
LiuYongjiang, FengZhiqiang, JiangLiwei,et al,2019.Ophiolite in the eastern Central Asian Orogenic Belt,NE China[J].Acta Petrologica Sinica,35(10):3017-3047.
[29]
MaDexi, YuAijun, GeLiangsheng,et al,2008.Application of multi-electrode electrical method in gold ore prospecting[J].Geology and Prospecting,44(3):65-69.
[30]
MaoGuangwu, CaoLiang, YanXieping,et al,2015.A review of research on epithermal gold deposits[J].Contributions to Geology and Mineral Resources Research,30(1):121-132.
[31]
RicharteD, Correa-OttoS, KlingerF L,et al,2023.Geophysical characterization of a low sulfidation epithermal gold and silver deposit,Mendoza,Argentina[J].Journal of South American Earth Sciences,123:1-10.
[32]
SeigelH O, JohnsonI, HennesseyJ,1984.Different methodology:Geophysical aids to gold exploration[J].The Leading Edge,3(6):32-36.
[33]
ShiDongyan, ZhangKun, ZhangYupeng,et al,2021.Geophysical and geochemical characteristics and prospecting criteria of shallow overburden area in Heilongjiang Province:A case study of 340 Highland gold mineralization in Heihe City[J].Journal of Jilin University(Earth Science Edition),51(4):1042-1053.
[34]
SillitoeR H,1997.Characteristics and controls of the largest porphyry copper-gold and epithermal gold deposits in the circum-Pacific region[J].Australian Journal of Earth Sciences,44(3):373-388.
Sillitoe R H,Hedenquist J W,2003.Linkage between volcanotectonic settings, compositionore-fluid,and epithermal precious metal deposits[C]//Simmons S F,Graham I.Volcanic,Geothermal and Ore-Forming Fluids:Rulers and Witnesses of Processes within the Earth.Society of Economic Geologists Special Publication,10:315-343.
[37]
SunJinggui, LiuYang, XuZhikai,et al,2023.Large-scale epithermal mineralization of late Mesozoic and the constraints of deep geological processes on mineralization in the continental margin of NE China[J].Journal of Jilin University(Earth Science Edition),53(3):651-692.
[38]
SunJingpeng,2016.Rock Magnetism and Paleomagnetism of Upper Cretaceous Volcanic Rocks from CCSD-LK-I,in Jiaolai Basin,Shandong [D].Beijing:The University of Chinese Academy of Sciences.
[39]
SunZhongren, WeiWenbo,2004.Application of the high density resistivity method in gold exploration work[J].Oil Geophysical Prospecting,39(B11):118-122.
[40]
WanFei,2013.Characteristics,Genesis and Prospecting Criteria of the Mesozoic Epithermal Gold Deposits in Yanbian Area[D].Changchun:Jilin University.
[41]
WangHongyu, LiTao,2016.The application of dual frequency IP method to the exploration of mineral resources in Western Australia[J].Geophysical and Geochemical Exploration,40(5):923-928.
[42]
WangXin’e, XuDonghui, SunZhifu,et al,2014.Wireline logs analysis and application of Shandong gold resources scientific drilling[J].Advances in Earth Science,29(3):397-403.
[43]
WuGuoxue,2007.High accuracy magnetic prospecting on earth surface in gold mine exploration—Take the Shisangongli exploring area out of Wulaga gold deposit in Heilongjiang Province as an example[J].Progress in Geophysics,22(5):1637-1641.
[44]
YinQichun, WangYuanjun, ZhouDaorong,et al,2022.Application of complex resistivity method to shale gas exploration in the Nanling Basin,Anhui Province[J].Geophysical and Geochemical Exploration,46(3):668-677.
[45]
ZhangFucheng, YangYanchen, LiXiangwen,et al,2015.The effect of applying geophysical and geochemical anomalies to the Shiwuliqiao gold deposit in Heilongjiang Province[J].Geophysical and Geochemical Exploration,39(2):262-267.
[46]
ZhaoLifang, LiXiyuan, LiChengli,et al,2022.Recognition of concealed porphyry body and deep prospecting practice in Duobaoshan ore concentration area based on gravity,magnetic and electromagnetic surveys[J].Minerals Deposits,41(6):1217-1231.
[47]
ZhaoZhonghai, CuiXiaomeng, SunJinggui,et al,2024.Deep metallogenic prediction based on 3D geological-geophysical model:A case study of Yongxin gold deposit in Heihe area[J].Journal of Jilin University(Earth Science Edition),54(2):498-515.
[48]
ZhaoZhonghai, QuHui, GuoYan,et al,2011.Metallogenic rules and prospecting orientation of gold deposit in the Duobaoshan area,Heilongjiang Province[J].Geology and Resources,20(2):89-95.
[49]
ZhuLian,2014.Synthetic Metallogenic Prognosis of Au Deposit on Dong’an-Tangwanghe Region,Heilongjiang Province[D].Beijing:China University of Geosciences(Beijing).