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黄金科学技术, 2023, 31(5): 707-720 doi: 10.11872/j.issn.1005-2518.2023.05.090

矿产勘查与资源评价

胶东大尹格庄金矿床成矿过程数值模拟及其找矿意义

单文法,1,2,3,4, 毛先成,2,3, 刘占坤2,3, 邓浩2,3, 陈进2,3, 张维2,3,5, 王海正6, 杨鑫6

1.中南大学计算地球科学研究中心,湖南 长沙 410083

2.中南大学地球科学与信息物理学院,湖南 长沙 410083

3.中南大学有色金属成矿预测与地质环境监测教育部重点实验室,湖南 长沙 410083

4.湖南大众传媒职业技术学院,湖南 长沙 410100

5.湖南城市学院市政与测绘工程学院,湖南 益阳 413099

6.招金矿业股份有限公司,山东 招远 266009

Numerical Simulation of Metallogenic Processes of Dayingezhuang Gold Deposit in Jiaodong Peninsula and Its Prospecting Significance

SHAN Wenfa,1,2,3,4, MAO Xiancheng,2,3, LIU Zhankun2,3, DENG Hao2,3, CHEN Jin2,3, ZHANG Wei2,3,5, WANG Haizheng6, YANG Xin6

1.Computational Geosciences Research Centre, Central South University, Changsha 410083, Hunan, China

2.School of Geosciences and Info-Physics, Central South University, Changsha 410083, Hunan, China

3.Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, Central South University, Changsha 410083, Hunan, China

4.Hunan Mass Media Vocational and Technical College, Changsha 410100, Hunan, China

5.School of Municipal and Geomatics Engineering, Hunan City University, Yiyang 413099, Hunan, China

6.Zhaojin Mining Industry Co. , Ltd. , Zhaoyuan 266009, Shandong, China

通讯作者: 毛先成(1963-),男,湖南常德人,教授,从事矿产资源三维预测研究工作。mxc@csu.edu.cn

收稿日期: 2023-06-15   修回日期: 2023-08-22  

基金资助: 国家自然科学基金重点项目“矿床时空结构定量表征与智能理解”.  42030809
湖南省自然科学基金青年项目“不确定性随机扰动下的三维成矿预测与风险评估”.  2022JJ40022

Received: 2023-06-15   Revised: 2023-08-22  

作者简介 About authors

单文法(1983-),男,安徽宿州人,博士研究生,从事成矿过程数值模拟研究工作wenfashan@qq.com , E-mail:wenfashan@qq.com

摘要

大尹格庄金矿床的形成涉及到构造变形、流体活动、热量传递和水岩反应等过程的相互耦合作用。利用FLAC3D数值模拟软件,结合现代矿化率概念,开展了大尹格庄金矿床力—热—流—化耦合的数值模拟,以探讨断裂、体积形变与化学过程耦合对金矿体就位的控制作用。研究结果表明:正体积应变、流体汇聚和金析出量(负矿化率)的高值区均位于控矿招平断裂倾角由陡倾向缓倾转换部位以及断裂局部起伏部位,与金矿体的实际空间分布相吻合,反映出成矿流体更多地汇聚、停留在这些部位,并发生强烈的化学反应,引起金的沉淀析出。这种多物理—化学过程在相同部位的耦合可能是控制大尹格庄金矿床形成的关键因素,基于该成矿规律,推测大尹格庄金矿区深部具有较大的成矿潜力。

关键词: 蚀变岩型金矿 ; 数值模拟 ; 成矿流体 ; 控矿因素 ; 矿化率 ; 大尹格庄金矿床

Abstract

The formation of the Dayingezhuang gold deposit involves the coupled effects of tectonic deformation,pore-fluid transport,heat transfer,and hydrogeochemical reactions.In this paper,FLAC3D nume-rical simulation software and modern mineralization rate concept were used to carry out numerical simulation of force-heat-fluid-chemical coupling of Dayingezhuang gold deposit,so as to explore the controlling effect of fracture structure,bulk deformation,and chemical process coupling on the emplacement of gold orebody.The simulation results demonstrate the following findings: From the perspective of physical process,the steep-slow transition and its local undulation zones along the Zhaoping fault tend to develop larger volume strains with differences of up to 1% compared to the surrounding rocks.This uneven strain distribution leads to the formation of uneven ore-holding spaces and pore pressure variation distribution.Significantly differences between high values of positive and negative pore pressure gradients are observed near the zones with large volume strains,while the differences in other zones are less notable.From the perspective of chemical process,mineralizing fluids tend to converge and stagnate at sites with high volume strain during their migration from the deep to the shallow parts.This convergence of mineralizing fluids leads to a greater precipitation of gold orebodies (mineralization rate less than 0),indicating the occurrence of intense water-rock reactions.In contrast,the areas where the mineralizing fluids don’t converge exhibit a predominance of positive mineralization rate dis-tribution,suggesting the absence of significant gold orebody precipitation.Furthermore,the ROC curve analysis with an AUC value of 0.815 provides quantitative evidence of the strong correlation between the mineralization rate and known gold orebodies,suggesting that this coupling of multiple physical-chemical processes at the same sites may be a key factor governing the formation of Dayingezhuang gold deposit. Based on these observations,it can be inferred that the deep-seated regions of Dayingezhuang deposit hold considerable mineralization potential.

Keywords: altered rock type gold deposit ; numerical simulation ; ore-forming fluid ; ore-controlling factor ; mineralization rate ; Dayingezhuang gold deposit

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单文法, 毛先成, 刘占坤, 邓浩, 陈进, 张维, 王海正, 杨鑫. 胶东大尹格庄金矿床成矿过程数值模拟及其找矿意义[J]. 黄金科学技术, 2023, 31(5): 707-720 doi:10.11872/j.issn.1005-2518.2023.05.090

SHAN Wenfa, MAO Xiancheng, LIU Zhankun, DENG Hao, CHEN Jin, ZHANG Wei, WANG Haizheng, YANG Xin. Numerical Simulation of Metallogenic Processes of Dayingezhuang Gold Deposit in Jiaodong Peninsula and Its Prospecting Significance[J]. Gold Science and Technology, 2023, 31(5): 707-720 doi:10.11872/j.issn.1005-2518.2023.05.090

胶东半岛是我国最大的金矿集中区,已探明金资源量超过5 000 t(杨立强等,2019Zhang et al.,2020Song et al.,2021a)。金矿床集中形成于晚白垩世(~120 Ma),是构造变形—流体活动—热质输运—化学反应多种因素耦合的产物(Fan et al.,2003Song et al.,2015Liu et al.,2021a),这些矿床具有相似的成矿机制,表现为类似的构造背景、地球化学特征和物质来源等。通常情况下,构造形变能够促进断裂及次级构造(如裂隙、节理)的发育,形成成矿流体运移的高渗透断裂网络,提高了岩石渗透率,为成矿流体的运移和停留提供空间。与此同时,成矿流体与岩石相互作用引发了水岩反应,导致矿物质沉淀,扰乱了原有岩石结构的稳定性,进一步促进岩石渗透率的发育(Zhao et al.,202020212022a2022bLin et al.,2019)。因此,成矿过程涉及复杂的力—热—流—化耦合作用。Zhao et al.(20082020)基于化学热力学、流体力学和固体力学等经典理论推导并提出矿化率概念,即:某种金属矿物在单位体积、单位时间内重量的变化,它能够有效模拟成矿流体运移过程中矿化空间发育机制,再现成矿系统的演化进程。因此,运用矿化率概念将会显著加深对多物理—化学过程耦合机制控制矿体就位的理解。

大尹格庄金矿床位于招平断裂带中段,累计探明金矿储量超过280 t,属于典型的构造蚀变岩型金矿床(Yuan et al.,2019)。金矿化交替分布在断裂倾角变缓的破碎蚀变带,表现出相同部位在时空上物理过程和化学过程高度耦合的紧密关系(Mao et al.,2019宋明春等,2020)。为了查明这一耦合关系,前人开展了大量研究工作,如:毛先成等(2019)通过分析不同控矿因素特征与金矿化之间的关系,指出成矿流体汇聚、滞留与断裂坡度有关,这些因素显著影响了热液交代或成矿作用的持续;杨斌等(2020)通过分析大尹格庄成矿前挤压、成矿期拉张宏观特征,发现缓倾斜部位有利于形成构造扩容空间,为成矿热液对流循环提供有利空间;宋明春等(2020)通过分析岩浆活动与金矿化之间的关系,以及构造与矿体之间的耦合关系,指出胶东地区金矿床具有相似的成矿机制。大规模的含矿流体活动和交代蚀变作用是胶东金矿集中产出的基础条件,而物理和化学条件控制了矿体的就位。这些研究已从断裂、流体活动和岩石蚀变等方面探讨了大尹格庄金矿床的构造控矿作用,但尚未从构造变形、流体流动、热传递和化学反应的动态耦合演化过程理解矿体就位的时空规律。而这种时空规律在理解大尹格庄金矿床成因和深部成矿预测过程中具有重要的理论和实践意义(Chen et al.,2004Song et al.,2012Mao et al.,2019Liu et al.,2021b邓浩等,2021)。

本文运用成矿动力学数值模拟方法,在建立大尹格庄金矿床三维地质模型的基础上,应用FLAC3D(Itasca Consulting Group,2012)软件,结合现代矿化率概念,开展应力场、温度场、流体场及化学场耦合过程数值模拟,分析在成矿期体积应变、温度梯度、孔压梯度、流体运移和矿化析出(矿化率<0)的空间分布规律,建立成矿物理条件、化学条件与构造几何特征之间的关系,探讨断裂、物理过程与化学过程耦合对金矿体就位的控制作用,以此深化对大尹格庄金矿床成矿过程的理解,为大尹格庄乃至胶东半岛金矿床的控矿规律、成矿机制和深部找矿提供新见解。

1 地质背景

胶东半岛位于华北克拉通东缘,被NE走向的五莲—烟台断裂分割成胶北地体和苏鲁造山带2个构造单元(李洪奎等,2016),其中胶北地体产出胶东地区绝大多数金矿(图1)。这些金矿床按矿化特征可划分为蚀变岩型和石英脉型,其中蚀变岩型金矿资源量占胶东半岛矿集区金资源量的80%以上,绝大多数大型、超大型金矿床均属于蚀变岩型金矿(Wang et al.,2021)。

图1

图1   胶东半岛金矿分布和区域地质图(修改自杨立强等,2019Deng et al.,2022

1.古近纪沉积物;2.白垩纪沉积物和火山岩;3.新元古代蓬莱群变质岩(1.1~0.8 Ga);4.古元古代荆山/粉子山群变质岩(2.2~1.9 Ga);5.中—新太古代胶东变质杂岩;6.超高压变质岩;7.早白垩世晚期艾山花岗岩类;8.130~125 Ma郭家岭花岗闪长岩;9.160~155 Ma玲珑/昆嵛山花岗岩;10.晚三叠世花岗岩;11.岩石圈断层;12.区域断层;13.蚀变岩型金矿;14.石英脉型金矿;15.其他类型金矿

Fig.1   Distribution and regional geological map of gold deposits in Jiaodong Peninsula

(modified after Yang et al.,2019Deng et al.,2022


大尹格庄金矿床位于招平断裂带中段(图2),产于断裂主裂面之下的黄铁绢英岩化碎裂岩和黄铁绢英岩化花岗质碎裂岩中。矿体严格受断裂带控制,主要沿断裂倾角平缓部位和由陡变缓的转折部位分布(Mao et al.,2019)。矿床发育有2个矿体(1号和2号矿体),二者以近EW向大尹格庄断裂为界。金矿体平行或近平行于主裂面,集中发育在下盘碎裂岩中,沿倾伏方向延伸大于2.5 km,宽度在2~30 m之间。

图2

图2   胶东大尹格庄金矿床地质简图

(修改自Mao et al.,2019

1.第四系沉积物;2.晚侏罗世玲珑花岗岩;3.脉岩;

4.中—新太古代胶东变质杂岩;5.黄铁绢英岩化蚀变带;

6.金矿体;7.断层;8.勘探线

Fig.2   Geological map of Dayingezhuang gold deposit in Jiaodong (modified after Mao et al.,2019


研究表明,大尹格庄金矿床的形成与一定埋藏深度的物理化学条件有关,即满足特定地球化学和物理化学条件临界边界则有利于矿物质沉淀(杨立强等,2019宋明春等,2020)。矿石中石英的流体包裹体(CO2-H2O、富CO2和 H2O溶液)温度在180~300 ℃之间,埋藏深度范围为-2.775~-6.600 km(戴雪灵,2012吕承训等,2022)。成矿流体从深部运移至浅部的过程中,当遇到近似等压条件的断裂带缓倾部位时,会以横向缓慢运移,延长了与围岩接触的时间,促进了流体—岩石之间的交代反应,加大了H2S的消耗,诱发Au(HS)2-失稳分解,最终导致金主要以黄铁矿中裂隙金和少量包体金的形式沉淀,同时伴有其他多金属硫化物的沉淀(Wen et al.,2016Yang et al.,2016Song et al.,2021b)。

2 原理及模型设置

2.1 模拟流程

FLAC3D是一种采用显式有限差分算法的数值模拟软件,被广泛应用于成矿系统中的力—热—流耦合模拟研究(Li et al.,2017Eldursi et al.,2020Liu et al.,2022),但不支持对化学反应的耦合模拟。本文基于大尹格庄矿区成矿期力—热—流耦合模拟结果,引入矿化率耦合水岩反应,以实现物理过程和化学过程的耦合模拟,主要划分为以下4个步骤(图3):

图3

图3   大尹格庄金矿床成矿过程数值模拟流程(修改自Zhao et al.,20022008毛先成等,2020

(modified after Zhao et al.,20022008Mao et al.,2020

Fig.3   Numerical simulation process of ore-forming process of Dayingezhuang gold deposit


(1)模型构建。用于构建大尹格庄矿区的模型数据主要包括2幅地形地质图、63幅勘探线剖面图、21幅中段平面图和172幅钻孔柱状图。模型的每个组成部分被分割为多个大小近似、连续的四面体单元,然后,将这些单元加载至FLAC3D软件中(Oliver et al.,2006)。

(2)力—热—流耦合模拟。在FLAC3D软件平台上,采用Mohr-Coulomb本构模型(弹性—塑性),开展大尹格庄矿区成矿过程的岩石变形、热量传递和流体流动耦合模拟。

(3)力—热—流—化耦合模拟。编写相应的计算机程序,从FLAC3D软件中提取数值模拟结果中的流体温度、压强和速度等数据,计算模型中每个节点的温度梯度和孔压梯度,结合Au(HS)2-的化学平衡浓度常数,按照矿化率理论开展耦合化学反应的计算。

(4)探讨多物理—化学过程的耦合规律。建立数值模拟结果中的体积应变、温度梯度、孔压梯度、金析出量(负矿化率)与已知矿体的空间分布对应关系,并运用ROC曲线定量表达金析出量与已知矿体之间的关系,探讨金成矿过程多物理—化学过程耦合机制,进而识别成矿潜力区。

2.2 矿化率的数学模型

通过研究矿床成矿过程中热液流动、热液—围岩的蚀变反应以及成矿物质结晶沉淀的机制,借助能量守恒、质量守恒和达西定律等经典物理规律,推导并提出矿化率概念,即:某种金属矿物在单位体积、单位时间内重量的变化(Zhao et al.,20022008)。若矿化率为正,则表示在成矿系统中单位体积、单位时间内溶解该金属矿物的重量;相反,若矿化率为负,则表示在成矿系统中单位体积、单位时间内析出该金属矿物的重量。其数学方程表达式(Zhao et al.,20022008)如下:

uCkx+vCky+wCkz=φD02Ckx2+2Cky2+2Ckz2+φRk (k=1,2,,n)

式中:uvw分别为流体在xyz方向的速度;Ck为化学物种k的浓度;Rk为源/汇项;n为定义特定成矿系统中矿物种类的总数;φ为岩石的孔隙率;D0为化学物种的扩散率。在成矿系统中,式(1)右侧平流项远大于扩散项,因此,可将式(1)近似表达为

MRk=φRk=uCkex+vCkey+wCkez

式中:MRk为矿物k的矿化率。一般来说,特定矿物质的化学平衡浓度是一个集成温度、孔隙流体压力和有关化学物质的函数,其数学模型为

Cke=f(T,P,C1,C2,,Cn)

式中:T为温度;P为流体压力;n为化学反应中化学物种的平衡浓度所需的相关化学物种的数量;Cr(r=1,2,,n)为物种r的浓度。基于链式法则,将等式(3)代入等式(2)可获得以下方程:

MRk=CkeTuTx+vTy+wTz+CkePuPx+vPy+wPz+         r=1nCkeCruCrx+vCry+wCrz

2.3 Au平衡浓度

大尹格庄金矿床的含金热液为微酸性,成矿流体中的金主要以Au(HS)2-的形式运移(Fan et al.,2003Williams-Jones et al.,2009Wen et al.,2016Yang et al.,2016)。在水岩反应过程中,流体中的CO2浓度降低、温度下降和pH值升高,导致络合物的失稳,引起金的沉淀(Yang et al.,2016)。在此关键的化学反应方程式表示为

Fe2+ + 2H2S (aq)+ 1/2O2= FeS2+ H2O + 2H+
4Au(HS)2-+2H2O+4H+R4Au0(s)+8H2S(aq)+O2(aq)

式中:R为化学总反应速率常数。

本文采用CHNOSZ软件(Dick,2019)计算大尹格庄金矿床Au(HS)2-在180~400 ℃条件下的化学平衡浓度常数。依据矿石的矿物组合(黄铁矿—石英)和流体包裹体研究,大尹格庄金矿成矿流体中含有H2O、CO2、Fe、S、Si、Na和K等。Au(HS)2-化学平衡浓度常数随温度变化呈近似抛物线[图4(a)],可采用最小二乘法进行拟合,其数学模型表达式如下:

logTi=aTi2+bTi+c i=1,2,,n
f(T)=minwilog(Ti)-ei2 (i=1,2,,n)

式中:Tiei是从图5上获取的第i个坐标点;logTiAu(HS)2-Ti处的平衡浓度对数;wi为采集点i的权重;abc分别为3个待定系数。其中,通过误差平方和最小化[式(8)]来确定式(7)中的参数,以此获得成矿流体中Au(HS)2-化学平衡浓度常数随温度变化的数学模型,表示为

logCAu(HS)2-e=-7.857×10-5T2+0.068T-20.7                   180 T400 , P=200 MPa

式中:CAu(HS)2-eAu(HS)2-随温度变化的平衡等式浓度。类似地,Au(HS)2-随孔压变化[图4(b)]的平衡等式浓度表示为

logCAu(HS)2-e=-5.5×10-9P-9.15                   T=200 ,1.0E+08P3.0E+08
logCAu(HS)2-e=-2×10-9P-8.2                   T=250 ,1.0E+08P3.0E+08
logCAu(HS)2-e=-2×10-9P-7.1                   T=300 ,1.0E+08P3.0E+08

式中:流体相对于温度和孔隙流体压力的一阶导数分别如图4(c)和图4(d)所示。

图4

图4   CAu(HS)2-e及其梯度平衡浓度随温度、孔压的变化

Fig.4   Variations of CAu(HS)2-e and its gradient equilibrium concentration with temperature and pore pressure


图5

图5   大尹格庄金矿床成矿期数值模拟模型及其构造应力背景

Fig.5   Numerical simulation model of metallogenic period of Dayingezhuang gold deposit and its tectonic stress background


2.4 模型构建及相关参数

为确保大尹格庄金矿床勘探范围(0~3 km)内模型的完整性,首先从勘探线剖面图、钻孔资料和测斜数据出发,对断裂带和矿体进行浅部三维建模。然后,综合深部大地电磁测深数据、地震勘探数据和构造地球化学数据等多源数据,开展深部推断建模(毛先成等,2020)。通过合并岩性较近的岩石和忽略岩性占比较少的类别,将模型划分为胶东杂岩、断裂带和玲珑花岗岩。考虑到大尹格庄金矿床侵蚀覆盖层的影响,结合成矿期矿体形成的深度,将模型垂向向上延展5 km(图5)。

本文设定模型的上表面温度为25 ℃,向下温度梯度递增为20 ℃/km。前人研究表明,大尹格庄金成矿温度范围为230~340 ℃(Song et al.,2014Yang et al.,2014)。考虑到成矿流体在运移过程中存在热量损失的情况,将成矿流体的初始温度设定为400 ℃。本文模型遵循通用模型(Fournier,1999)的约束条件,即完全饱和岩石孔隙空间。在数值模拟过程中,允许孔隙流体在模型顶部边界自由流动,而在底部和垂直边界处禁止流出。同时,选取大尹格庄矿区的地应力原位应力试验数据和成矿期构造应力场测试数据为模型初始应力参考,其最大主应力方向为NW-SE向拉张(杨立强等,2019)。

由于岩石岩性随环境因素的变化(埋深等因素)而改变,导致不同位置的岩石物性参数可能存在差异。对此,基于前人研究成果(Yang et al.,2007Song et al.,2021a),结合《岩石物理手册》(Schön,1988)和FLAC3D帮助文档,确定了研究区岩石的物性参数范围,并进行反复对照验证试验以确定每个参数的值,其物性参数设置如表1所示。

表1   模拟中的岩石参数

Table 1  Rock parameters used in the simulation

参数名称玲珑花岗岩断层破碎带胶东杂岩
密度/(kg∙m–32 5802 5002 870
体积模量/(×1010 Pa)1.340.501.71
剪切模量/(×109 Pa)2.580.301.80
内聚力/(×107 Pa)5.704.705.30
抗拉强度/(×106 Pa)3.770.405.16
膨胀角/(°)3.204.705.30
摩擦角/(°)28.0014.8033.00
孔隙度/%20.0031.0021.00
渗透率/(×10-121.8010.002.50
热导率/(W∙m–1∙K–13.602.752.80

新窗口打开| 下载CSV


3 结果与讨论

在大尹格庄矿区,矿化呈现出不均匀分布的特征,主要分布在断裂倾角变缓处,且呈现出空间不连续的分布特点,这种分布可能暗示着断裂带对矿体产出的控制作用。本文结合剖面图矿体分布特征,对比分析力—热—流—化耦合的数值模拟结果,以查明内在控制机制。

3.1 体积应变

体积应变高值随着断裂带陡、缓转换交替发育在缓倾部位,呈现不连续分布的特征[图6(a)~6(c)],与“阶梯式”分布规律一致(Song et al.,2012)。在图6(a)~6(c)剖面中,正体积应变均位于断裂面以下,在断裂带明显陡缓转换部位具有快速收窄、尖灭趋势,而在无明显陡倾变化部位收窄变缓,这与断裂缓倾部位矿化特征一致。将图6(c)剖面与图6(a)、6(b)剖面进行对比发现,断裂陡缓转换较大的图6(c)剖面在断裂缓倾部位的正体积应变分布较为连续,体积应变集中在0.2%~0.5%之间,这与图6(III)号剖面中矿体分布连续、均匀的规律相吻合。将图6(b)剖面与图6(a)、6(c)剖面进行对比发现,图6(b)剖面中断裂有较多局部起伏,在局部起伏的缓倾处显示明显的正体积应变,陡倾处体积应变变小,总体呈交替性分布,而图6(a)、6(c)剖面中断裂较平滑,体积应变变化幅度较小。

图6

图6   大尹格庄金矿床典型勘探线剖面模拟的体积应变及其对应的剖面图[Ⅰ(60)、Ⅱ(76)和Ⅲ(88)]

1.钻孔;2.金矿体;3.断裂带;4.绢英蚀变岩;5.绢英岩质破碎带

Fig.6   Simulated volumetric strain of typical exploration line profile of Dayingezhuang gold deposit and its corresponding profiles[Ⅰ(60)、Ⅱ(76) and Ⅲ(88)]


断裂倾角转换及其局部起伏部位为应力、能量集中和释放的陡变区域(宋明春等,2020),这些部位改变了局部应力状态的均匀分布,加大了在低倾角部位的正体积应变(Mao et al.,2019)(图6),破坏了附近围岩的完整性,有利于向围岩传递正体积应变,形成连续、高渗透性的容矿空间。而高倾角部位未形成明显的正体积应变(图6),难以提供良好的容矿空间。正体积应变随着断裂带高倾角与低倾角的交替变化而变化,形成多个构造圈闭,使成矿流体在断裂低倾角部位横向缓慢运移或滞留,有利于长时间发生水岩反应,从而沉淀成矿(宋明春等,2020)。

3.2 孔压梯度与温度梯度

孔压梯度在断裂带中分布不均匀,正、负孔压梯度分别发育在断裂带上部和下部,在断裂缓倾部位两侧显著波动,沿着断裂面对称地形成了正、负孔压梯度局部极值,但是,垂向上均呈渐进变化、相互联通;而在高倾角部位附近垂向上均呈迅速尖灭、不连续发育的特点[图7(a)~7(c)]。相反地,正、负温度梯度分别形成于断裂下部和上部,在断裂高倾角部位两侧显著波动,而在缓倾部位附近趋于尖灭[图8(a)~8(c)]。

图7

图7   大尹格庄金矿床典型勘探线剖面Z轴方向孔压梯度及其对应的剖面图[Ⅰ(60)、Ⅱ(76)和Ⅲ(88)]

1.钻孔;2.金矿体;3.断裂带;4.绢英蚀变岩;5.绢英岩质破碎带

Fig.7   Z-direction pore-fluid pressure gradient of typical exploration line profile of Dayingezhuang gold deposit and its corresponding profiles[Ⅰ(60)、Ⅱ(76) and Ⅲ(88)]


图8

图8   大尹格庄金矿床典型勘探线剖面Z轴方向温度梯度及其对应的剖面图[Ⅰ(60)、Ⅱ(76)和Ⅲ(88)]

1.钻孔;2.金矿体;3.断裂带;4.绢英蚀变岩;5.绢英岩质破碎带

Fig.8   Z-direction temperature gradient of typical exploration line profile of Dayingezhuang gold deposit and its corresponding profiles[Ⅰ(60)、Ⅱ(76) and Ⅲ(88)]


模拟结果显示,孔压梯度和温度梯度的分布特征与不均匀的体积应变分布密切相关(图6~图8)。正体积应变会破坏岩石的完整性,产生容矿空间,使其孔压低于附近围岩,形成显著的孔压梯度陡变带。孔压梯度能够改变成矿流体的运移方向(Zhao et al.,2008),驱动成矿流体向分布着正体积应变的断裂缓倾部位流动、充填和聚集(图6图7)。运移中成矿流体的温度(>300 ℃)往往高于围岩,不断与围岩发生热量传递。实际上,在断裂低倾角部位分布有较大的正体积应变,意味着岩石破碎程度大,能与高温的成矿流体充分接触,加快了热量传递的进行,从而形成平稳变化的温度梯度;在断裂高倾角部位未形成明显的正体积应变,岩石相对完整、渗透率较低,难以与高温的成矿流体充分接触,不利于热量传递的进行,维持着岩石与成矿流体之间的温度差异,从而形成了陡变的温度梯度(图6图8)。

3.3 矿化率

从化学过程的视角来看,招平断裂带正体积应变部位为成矿流体发生化学反应提供了空间。矿化率可用于进一步估算金属矿化的空间分布,以及成矿过程相关的控制因素(Zhao et al.,20022008)。在剖面图[图9(a)~9(c)、图10(a)]中,负矿化率(金析出)主要在断裂带倾角陡缓转换的缓倾部位积累,且随着与断裂距离的增加,矿化率由负值逐渐转变为正值(金溶解),这与已知矿床主要分布在断裂缓倾部位附近且随着与断裂距离的增大矿化程度逐渐减弱相一致(图9图10)。同时,利用ROC曲线下面积(Area Under Curve,AUC)来定量评估大尹格庄矿化率的精准度,AUC值达到0.815(图11),说明金矿床与负矿化率在空间上具有较好的匹配关系。

图9

图9   大尹格庄金矿床典型勘探线剖面矿化率及其对应的剖面图[Ⅰ(60)、Ⅱ(76)和Ⅲ(88)]

1.钻孔;2.金矿体;3.断裂带;4.绢英蚀变岩;5.绢英岩质破碎带

Fig.9   Mineralization rate of typical exploration line profile of Dayingezhuang gold deposit and its corresponding profiles[Ⅰ(60)、Ⅱ(76) and Ⅲ(88)]


图10

图10   大尹格庄金矿床70~90号勘探线剖面(a)及其对应的矿化率图(b)

Fig.10   Profile of No.70~No.90 exploration line (a) and its corresponding mineralization rate map(b) of Dayingezhuang gold deposit


图11

图11   大尹格庄金矿床矿化率与已知矿体的ROC曲线

Fig.11   ROC curve between mineralization rate and known orebodies of Dayingezhuang gold deposit


负矿化率与正体积应变、孔压梯度陡变部位在空间上存在重叠,并具有显著的相关性(图6图7图9)。正体积应变形成的容矿空间及孔压梯度对成矿流体的驱动力联合促进了成矿流体向断裂缓倾部位流动、充填和汇聚(Li et al.,2018Poh et al.,2020Liu et al.,2021c)。成矿流体富含CO2SO42-Au(HS)2-等,呈微酸性,能够与附近围岩发生水岩反应,其强烈程度受成矿流体多少及其停留时间长短的影响。因此,较多成矿流体汇聚、停留在断裂带缓倾处[图6(a)~6(c)],就会发生剧烈的水岩反应,产生强烈的绢英岩化蚀变并沉淀析出金,而在断裂陡倾处成矿流体分布少且流速快,不能为水岩反应提供充足的时间。

3.4 找矿意义

如前所述,正体积应变和负矿化率联合表征了大尹格庄金矿床是多物理—化学过程耦合的结果,这种多物理—化学过程在相同部位的耦合可能对找矿工作具有一定的指示意义。基于数值模拟结果,观察到大尹格庄金矿床2号矿体深部呈现出正体积应变和负矿化率重叠的特征,位于招平断裂陡缓转换的缓倾处,集中在断裂面下盘,与已知矿体的定位规律一致,说明2号矿体深部属于有利的成矿部位(图10)。

综合考虑数值模拟结果和前人研究成果(张瑞忠等,2008邓浩等,2020),在74~82号勘探线之间的延伸方向,圈定了1处找矿靶区,深度大致在-1 300~-1 900 m之间,可能揭示了深部成矿流体通道的空间分布[图10(b)]。由此,认为2号矿体向深部延伸部位具有一定的找矿潜力,建议作为未来深部勘探的重点区域。

4 结论

(1)数值模拟结果显示,招平断裂带在构造变形过程中,在断裂缓倾转换及其局部起伏部位发育正体积应变和负矿化率,而在断裂陡倾部位容易形成负体积应变和正矿化率(不利于成矿)。认为二者交替性分布形成构造圈闭,成为成矿流体滞留并与围岩发生水岩反应的有利场所。随着温度降低、孔压释放,诱发Au(HS)2-失稳分解,最终导致金沉淀,形成矿床。

(2)矿化率能够反映在单位时间内单位体积岩石矿物重量的变化,能够定量表达成矿系统中多物理—化学过程的耦合结果。成矿流体倾向于在控矿断裂倾角陡、缓变化的较缓部位及断裂局部起伏部位聚集并沉淀成矿(负矿化率),形成了阶梯式的分布规律。

(3)这种多物理—化学过程在相同部位的耦合可能是控制大尹格庄金矿床形成的关键因素。根据这一成矿规律,推测大尹格庄金矿床74~82号勘探线的深部属于有利的成矿部位,建议作为未来深部勘探的重点区域。

http://www.goldsci.ac.cn/article/2023/1005-2518/1005-2518-2023-31-5-707.shtml

参考文献

Chen Y JPirajno FLai Yet al2004.

Metallogenic time and tectonic setting of Jiaodong gold province,eastern China

[J].Acta Petrologica Sinica,204):907-922.

[本文引用: 1]

Dai Xueling2012.

Study on Petrogenesic-Metallogenic Mechanism in Dayingezhuang Gold Deposit,Zhaoyuan Country,Shandong Province

[D].ChangshaCentral South University.

Deng HaoWei YunfengChen Jinet al2021.

Three-dimensional prospectivity mapping and quantitative analysis of structuralore-controlling factors in Jiaojia Au ore-belt with attention convolutional neural networks

[J].Journal of Central South University(Science and Technology),529):3003-3014.

Deng HaoZheng YangChen Jinet al2020.

Deep learning-based 3D prediction model for the Dayingezhuang gold deposit,Shandong Province

[J].Acta Geoscientica Sinica,412):157-165.

Deng JWang Q FLiu X Fet al2022.

The formation of the Jiaodong gold province

[J].Acta Geologica Sinica(English Edition),966):1801-1820.

[本文引用: 2]

Dick J M2019.

Chnosz: Thermodynamic calculations and diagrams for geochemistry

[J].Frontiers in Earth Science,7180.

[本文引用: 1]

Eldursi KChi GBethune Ket al2020.

New insights from 2- and 3-D numerical modelling on fluid flow mechanisms and geological factors responsible for the formation of the world-class Cigar Lake uranium deposit,Eastern Athabasca Basin,Canada

[J].Mineralium Deposita,567):1365-1388.

[本文引用: 1]

Fan H RZhai M GXie Y Het al2003.

Ore-forming fluids associated with granite-hosted gold mineralization at the Sanshandao deposit,Jiaodong gold province,China

[J].Mineralium Deposita,386):739-750.

[本文引用: 2]

Fournier R O1999.

Hydrothermal processes related to movement of fluid from plastic into brittle rock in the magmatic-epithermal environment

[J].Economic Geology,981193-1211.

[本文引用: 1]

Itasca Consulting Group,2012.

FLAC3D user’s guide

[Z].version 5.0. Minneapolis:Itasca Consulting Group.

Li HongkuiGeng KeZhuo Chuanyuanet al2016.Tectonic Setting and Mineralization of the Jiaodong Gold Deposit[M]. BeijingGeological Publishing House.

Li ZChi GBethune K Met al2017.

Structural controls on fluid flow during compressional reactivation of basement faults:Insights from numerical modeling for the formation of unconformity-related uranium deposits in the Athabasca Basin,Canada

[J].Economic Geology,1122):451-466.

[本文引用: 1]

Li ZChi GBethune K Met al2018.

Numerical simulation of strain localization and its relationship to formation of the Sue unconformity-related uranium deposits,eastern Athabasca Basin,Canada

[J].Ore Geology Reviews,10117-31.

[本文引用: 1]

Lin YGao FZhou K Pet al2019.

Mechanical properties and sta-tistical damage constitutive model of rock under a coupled chemical-mechanical condition

[J].Geofluids,(6):1-17.

[本文引用: 1]

Liu LCao WLiu Het al2022.

Applying benefits and avoiding pitfalls of 3D computational modeling-based machine learning prediction for exploration targeting: Lessons from two mines in the Tongling-Anqing district,eastern China

[J].Ore Geology Reviews,142104712.

[本文引用: 1]

Liu Z KMao X CJedemann Aet al2021a.

Evolution of pyrite compositions at the Sizhuang gold deposit,Jiaodong Peninsula,Eastern China:Implications for the genesis of Jiao-dong-type orogenic gold mineralization

[J].Minerals,114):344.

[本文引用: 2]

Liu Z KHollings PMao X Cet al2021b.

Metal remobilization from country rocks into the Jiaodong-type orogenic gold systems,Eastern China:New constraints from scheelite and galena isotope results at the Xiadian and Majiayao gold deposits

[J].Ore Geology Reviews,134104126.

[本文引用: 1]

Liu XXiao CZhang Set al2021.

Numerical modeling of deformation at the Baiyun gold deposit,northeastern China:Insights into the structural controls on mineralization

[J].Journal of Earth Science,321):174-184.

Chengxun Zhang DaXu Yaqinget al2022.

Calculation of metallogenic depth in the Jiaodong gold deposits:Tectoniccorrection method and metallogenic prediction

[J].Earth Science Frontiers,291):427-438.

Mao X CRen JLiu Z Ket al2019.

Three-dimensional prospectivity modeling of the Jiaojia-type gold deposit,Jiao-dong Peninsula,Eastern China:A case study of the Dayingezhuang deposit

[J].Journal of Geochemical Exploration,20327-44.

[本文引用: 6]

Mao XianchengWang MijunLiu Zhankunet al2019.

Quantitative analysis of ore-controlling factors based on exploration data of the Dayingezhuang gold deposit in the Jiaodong Peninsula

[J].Earth Science Frontiers,264):84-93.

Mao XianchengWang QiChen Jinet al2020.

Three-dimensional modeling of deep metallogenic structure in northwestern Jiaodong Peninsula and its gold prospecting significance

[J].Acta Geoscientica Sinica,412):166-178.

[本文引用: 1]

Oliver N H SMcLellan J GHobbs B Eet al2006.

Numerical models of extensional deformation,heat transfer,and fluid flows across basement-cover interfaces during basin-related mineralization

[J]. Economic Geology,1011-31.

[本文引用: 1]

Poh JYamato PDuretz Tet al2020.

Precambrian deformation belts in compressive tectonic regimes:A numerical perspective

[J].Tectonophysics,777228350.

[本文引用: 1]

Schön J H1998.Physical Properties of Rocks:Fundamentals and Principles of Petrophysics[M].OxfordPergamon-Elsevier.

Song M CDeng JYi P Het al2014.

The kiloton class Jiaojia gold deposit in eastern Shandong Province and its genesis

[J].Acta Geologica Sinica(English Edition),88801-824.

[本文引用: 1]

Song M CLi JYu X Fet al2021a.

Metallogenic characteristics and tectonic setting of the Jiaodong gold deposit,China

[J].Solid Earth Sciences,64):385-405.

[本文引用: 2]

Song M CLi S ZSantosh Met al2015.

Types,characteristics and metallogenesis of gold deposits in the Jiaodong Peninsula,Eastern North China Craton

[J].Ore Geology Revie-ws,65612-625.

[本文引用: 1]

Song M CXue G QLiu H Bet al2021b.

A geological-geophy-sical prospecting model for deep-seated gold deposits in the Jiaodong Peninsula,China

[J].Minerals,1112):1393.

[本文引用: 1]

Song M CYi P HXu J Xet al2012.

A step metallogenetic model for gold deposits in the northwestern Shandong Peninsula,China

[J].Science China (Earth Sciences),55940-948.

[本文引用: 2]

Song MingchunLin ShaoyiYang Liqianget al2020.

Metallogenic model of Jiaodong Peninsula gold deposits

[J]. Mineral Deposits,392):215-236.

Wang ZXu ZCheng Het al2021.

Precambrian metamorphic crustal basement cannot provide much gold to form giant gold deposits in the Jiaodong Peninsula,China

[J].Precambrian Research,354106045.

[本文引用: 1]

Wen B JFan H RHu F Fet al2016.

Fluid evolution and ore genesis of the giant Sanshandao gold deposit,Jiaodong gold province,China:Constrains from geology,fluid inclusions and H-O-S-He-Ar isotopic compositions

[J]. Journal of Geochemical Exploration,17196-112.

[本文引用: 2]

Williams-Jones A EBowell R JMigdisov A A2009.

Gold in solution

[J]. Elements,55):281-287.

[本文引用: 1]

Yang BinZhou XinDuan Leiet al2020.

Tectonic evolution and ore control effect in Dayingezhuang gold district,Jiaodong Peninsula

[J]. Gold,419):35-40.

Yang L QDeng JGuo L Net al2016.

Origin and evolution of ore fluid,and gold deposition processes at the giant Taishang gold deposit,Jiaodong Peninsula,eastern China

[J].Ore Geology Reviews,72585-602.

[本文引用: 3]

Yang L QDeng JWang Q Fet al2007.

Numerical modeling of coupling metallogenic dynamics of fluid flow and thermal transportation in Jiaodong gold ore cluster area,China

[C]//Proceedings of IAMG’07: Geomathematics and GIS Analysis of ResourcesEnvironment and Hazards.12th Conference of the International. Association for Mathematical Geology, Beijing, China, August 26-3139-43.

[本文引用: 1]

Yang L QDeng JWang Z Let al2014.

Mesozoic gold metallogenic system of the Jiaodong gold province,eastern China

[J].Acta Petrologica Sinica,302447-2467.

[本文引用: 1]

Yang LiqiangDeng JunSong Mingchunet al2019.

Structure control on formation and localization of giant deposits:An example of Jiaodong gold deposits in China

[J].Geotectonica et Metallogenia,433):431-446.

[本文引用: 1]

Yuan Z ZLi Z KZhao X Fet al2019.

New constraints on the genesis of the giant Dayingezhuang gold (silver) deposit in the Jiaodong district,North China Craton

[J]. Ore Geology Reviews,112103038.

[本文引用: 1]

Zhang LWeinberg R FYang L Qet al2020.

Mesozoic orogenic gold mineralization in the Jiaodong Peninsula,China:A focused event at 120±2 Ma during cooling of pregold granite intrusions

[J].Economic Geology,1152):415-441.

[本文引用: 1]

Zhang RuizhongGao BangfeiGuo Chunyinget al2008.

Ore-body locating and mineral prospecting in Dayingezhuang gold deposit,Shandong Province

[J].Gold,294):9-13.

Zhao CHobbs B EOrd A2008.

Convective and Advective Heat Transfer in Geological Systems

[M]//Advances in Geophysical and Environmental Mechanics and Mathematics. BerlinSpringer.

[本文引用: 7]

Zhao CHobbs B EOrd A2020.

Transient-state instability analysis of dissolution-timescale reactive infiltration in fluid-saturated porous rocks:Purely mathematical approach

[J].Science China Technological Sciences,63319-328.

[本文引用: 2]

Zhao CHobbs B EOrd A2021.

An accurate porosity-velocity-concentration approach for solving reactive mass transport problems involving chemical dissolution in fluid-saturated porous media with arbitrarily initial porosity distributions

[J].International Journal for Numerical Methods in Engineering,1227354-7377.

[本文引用: 1]

Zhao CHobbs B EOrd A2022a.

Semi-analytical finite element method for simulating chemical dissolution-front instability problems in fluid-saturated porous media

[J]. Engineering Computations,391781-1801.

[本文引用: 1]

Zhao CHobbs B EOrd A2022b.

Two different mathematical schemes for solving chemical dissolution-front instability problems in fluid-saturated rocks

[J]. Science China Technological Sciences,65147-156.

[本文引用: 1]

Zhao CLin GHobbs B Eet al2002.

Finite element modelling of reactive fluids mixing and mineralization in pore-fluid saturated hydrothermal/sedimentary basins

[J].Engineering Computations,19364-387.

[本文引用: 5]

戴雪灵2012.

山东招远大尹格庄金矿成岩—成矿机理研究

[D].长沙中南大学.

[本文引用: 1]

邓浩魏运凤陈进2021.

基于注意力卷积神经网络的焦家金矿带三维成矿预测及构造控矿因素定量分析

[J].中南大学学报(自然科学版),529):3003-3014.

[本文引用: 1]

邓浩郑扬陈进2020.

基于深度学习的山东大尹格庄金矿床深部三维预测模型

[J].地球学报,412):157-165.

[本文引用: 1]

李洪奎耿科禚传源2016.胶东金矿构造环境与成矿作用[M].北京地质出版社.

[本文引用: 1]

吕承训张达许亚青2022.

胶东金矿成矿深度的构造校正测算及成矿预测

[J].地学前缘,291):427-438.

[本文引用: 1]

毛先成王迷军刘占坤2019.

基于勘查数据的胶东大尹格庄金矿床控矿地质因素定量分析

[J].地学前缘,264):84-93.

[本文引用: 1]

毛先成王琪陈进2020.

胶西北金矿集区深部成矿构造三维建模与找矿意义

[J].地球学报,412):166-178.

[本文引用: 2]

宋明春林少一杨立强2020.

胶东金矿成矿模式

[J].矿床地质,392):215-236.

[本文引用: 5]

杨斌周鑫段磊2020.

胶东大尹格庄金矿区构造演化与控矿作用

[J].黄金,419):35-40.

[本文引用: 1]

杨立强邓军宋明春2019.

巨型矿床形成与定位的构造控制:胶东金矿集区剖析

[J].大地构造与成矿学,433):431-446.

[本文引用: 4]

张瑞忠高帮飞郭春影2008.

胶东大尹格庄金矿床矿体定位与成矿预测

[J].黄金,294):9-13.

[本文引用: 1]

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