秦向辉,陈群策,郝越进,孟 文,孙东生

1)中国地质科学院地质力学研究所,北京 100081;2)国土资源部新构造运动与地质灾害重点实验室,北京 100081;3)安徽省地质矿产勘查局313地质队,安徽六安 237010



安徽金寨沙坪沟矿区地应力测量与现今应力场研究

秦向辉1,2),陈群策1,2),郝越进3),孟 文1,2),孙东生1,2)

1)中国地质科学院地质力学研究所,北京 100081;
2)国土资源部新构造运动与地质灾害重点实验室,北京 100081;
3)安徽省地质矿产勘查局313地质队,安徽六安 237010

摘 要:安徽金寨沙坪沟钼矿位于秦岭—大别山成矿带东段,是近年来我国发现的世界级特大钼矿,其开采设计和地质安全评价备受重视。为了查明沙坪沟矿区现今应力场特征,指导矿区开采设计,在矿区3个700～1000 m深钻孔中开展了水压致裂法地应力测量工作,测量结果表明:(a)矿区最大、最小水平主应力随深度增加梯度系数分别为0.0226和0.0166,与区域地应力背景值基本一致;(b)矿区实测最大水平主应力优势方位为NE−NEE向,与区域构造应力场方向一致;(c)实测地应力数据揭示的应力结构与区域结果存在差异,分析认为,沙坪沟矿区所在的桐柏—大别构造带特殊的构造位置和构造活动机制可能是造成这种差异的主要原因。进一步,利用库伦滑动摩擦准则评价了实测地应力数据,探讨了其对矿区开采设计的意义,结果表明,矿区现今地应力强度不足以导致以断裂失稳活动或地震为表现形式的地应力状态调整事件的发生,从地应力角度讲,沙坪沟矿区目前总体处于稳定的构造应力环境。本文结果,对于沙坪沟矿区开采设计、地质安全评价及大别山造山带东段构造应力场研究有重要意义。

关键词:沙坪沟钼矿;地应力;水压致裂法;现今地应力状态;库伦滑动摩擦准则

www.cagsbulletin.com www.地球学报.com

本文由深部探测技术与实验研究专项(编号:Sinoprobe-06-03)、中国地质调查局地质矿产调查专项项目(编号:1212011220122)和中国地质科学院地质力学研究所基本科研业务费项目(编号:DZLXJK201404)联合资助。

赋存于地质体内未受扰动的应力称之为地应力,地壳浅表层变形和内部构造运动及其导致的地质灾害都与地应力密切相关(Zoback et al.,1993;Hardebeck and Hauksson,2001;Liao et al.,2003;郭啟良等,2009;Chang et al.,2010;Lin et al.,2013)。地质学家一直尝试通过揭示地壳浅表部地应力状态及作用规律,解决断裂失稳活动、地震地质灾害机理、工程领域岩体稳定性等问题(吴满路等,2002,2005;陈群策等,2010;Lin et al.,2013;Qin et al.,2014;谭成轩等,2014;曹辉等,2015)。对于深部矿产开采、地下空间开发而言,详细查明工程区现今地应力场特征,对于地下工程设计和岩体稳定性分析有重要作用,也可为可能出现的工程地质问题的合理解决提供支持(吴满路等,2002,2005;谭成轩等,2006)。

安徽省金寨县沙坪沟钼矿位于东秦岭—大别成矿带东段,是我国近年来发现的特大斑岩型钼矿,资料显示,沙坪沟钼矿基本探明钼金属储量可达245×104t(苏晓静等,2013)。目前,众多科研机构和学者对矿区地质构造与成矿地质特征、成矿年代、成矿机理和成矿岩体矿物学特征等进行了深入研究并取得了丰硕成果(张红等,2011;孟祥金等,2012;张怀东等,2012),但是对于矿区现今构造应力场研究较少,且尚无实测地应力数据支持。此外,沙坪沟钼矿所处的北淮阳带曾作为三叠纪华南与华北陆块碰撞造山带的缝合线,其莫霍面错断至今仍保存(董树文等,1993,1998),查明矿区现今构造应力场特征,对这一关键构造区带构造应力场研究、中国大陆现今构造应力场分区研究都有重要意义。为此,我们利用沙坪沟钼矿部分勘探钻孔,开展了水压致裂法地应力测量工作。

本文首先简述了沙坪沟钼矿区域地质条件,概述了地应力测量方法,给出了地应力测量结果;进而,利用实测数据计算了矿区地壳浅表层地应力状态特征参数,分析了矿区现今构造应力场特征;最后,利用库伦滑动摩擦准则评价了实测地应力数据,并探讨了地应力测量结果对于矿区开采的意义。

沙坪沟钼矿地处豫皖鄂交界的金寨县境内,构造上属于大别山造山带,大别造山带是扬子地块向华北地块俯冲形成的碰撞造山带,它是以深大断裂构造所围限的“东宽西窄”的楔形地质块体,夹于华北与扬子地块之间;大别造山带总体构造格局被北西向断裂控制,同时被数条近于平行的北北东向断裂切割。具体来讲,沙坪沟钼矿位于桐柏—大别山构造带内,桐柏—桐城断裂带和商城—麻城断裂带的交汇部位的北东侧,亦即桐柏—桐城断裂与泗河—银山断裂(商城—城断裂的派生断裂)汇构成的“入”字型构造锐角处(张红等,2011;孟祥金等,2012;张怀东等,2012)(图1)。沙坪沟矿区基底构造层为中元古界卢镇关岩群,由形成于新元古代变形变质侵入体和变质表壳岩组成,后者为一套中基性的火山-沉积岩组合;受燕山期岩浆活动的强烈影响,该套地层已被肢解、侵蚀而零星分布,多呈残留体和捕虏体产出。沙坪沟矿区岩性主要为黑云母斜长片麻岩、角闪斜长片麻岩、硅质大理岩以及花岗片麻岩等,局部可见超镁铁质变质岩块(张怀东等,2012)。矿区内的构造主要表现为浅层次的压性、压扭性断裂,主要有北东向和北西向两组,多为成矿后断裂。沙坪沟矿区地貌属大别山中低山区,为构造剥蚀类型,海拔高度200～745 m,地形切割较深,山势陡峻,沟谷横截面多呈“V”型,少量规模较大的沟谷呈“U”型,地形坡度25°～40°。

1 地应力测量方法与结果

1.1 地应力测量方法

在沙坪沟矿区深孔中开展的地应力测量,采用了水压致裂法。作为一种二维地应力测量方法,水压致裂法通过水力压裂诱发裂缝方式来测量地应力,是目前常用的地应力测量方法,也是国际岩石力学学会(ISRM)推荐的五种地应力测量方法之一(Haimson and Cornet,2003)。水压致裂法测量的可靠性和准确性在理论上和实践中得到了广泛认可,其测量原理、程序等参见Amadei和Stephansson(1997)、Haimson和Cornet(2003)、Zoback(2007)等人著述。

水压致裂法测量时使用了单回路水压致裂地应力测量系统(Qin et al.,2014),现场试验程序均严格按照ISRM建议步骤及要求进行(Haimson and Cornet,2003)。对获得的水压致裂参数进行处理时,也采用ISRM建议方法进行,尤其对闭合压力(Ps)这个关键参数,综合了单切线法、dt/dP vs P法(Lee and Haimson,1989)和dP/dt vs P法(Hayashi and Haimson,1991)进行取值,以提高闭合压力计算结果准确性,进而提高主应力计算结果的准确性。在计算主应力值时,孔隙压力根据已有研究结果,取近似等于静水压力处理(Barton et al.,1995;Zoback and Townend,2001)。

图1　沙坪沟钼矿构造位置示意图(据孟祥金等,2012修改)Fig.1 Tectonic map of the Shapinggou molybdenum deposit(modified after MENG et al.,2012)

图2　沙坪沟矿区水压致裂地应力测量曲线Fig.2 Typical test-interval pressure-time curves obtained from hydraulic fracturing tests in the Shapinggou molybdenum deposit

图3　沙坪沟矿区水压致裂地应力测量中诱发裂缝形态Fig.3 Typical induced fracture trace impressed on packer in the Shapinggou molybdenum deposit

1.2 地应力测点

沙坪沟矿区三个地应力测量钻孔均分布于金寨县关庙乡银山村附近(见图1),相距较近,其地质概况如下:

工程勘查钻孔(GCZK2)位于银山村银山沟,孔深887 m,孔径95 mm;钻探揭露显示,钻孔岩性以花岗岩及蚀变正长岩为主,岩芯总体完整,静水位58.00 m;由于260 m深度以上岩石较破碎,地应力测量在此深度以下开展。

主井钻孔(ZJZK)位于银山村蔡湾,孔深1020 m,孔径75 m;钻孔揭露显示,钻孔岩性主要以花岗岩、黑云斜长片麻岩、正长岩为主,局部存在变质特征,并且在个别深度上出现了饼化岩芯,岩芯总体完整,静水位16.00 m;测量在400 m深度以下裸孔进行。

副井钻孔(FJZK)位于银山村沙坪沟,孔深730 m,孔径95 mm;钻孔揭露显示,地层岩性以花岗岩、正长岩、片麻岩为主,除455 m深度附近存在着严重破碎带外,岩芯总体完整,静水位8.00 m。

表1　沙坪沟矿区水压致裂地应力测量结果Table 1 Results of hydraulic fracturing in-situ stress measurements in the Shapinggou molybdenum deposit

1.3 地应力测量结果

在沙坪沟矿区三个钻孔中共成功进行了29段压裂试验和12段印模试验,图2给出了三个钻孔中不同深度的3段典型测试曲线,图3给出了一段典型印模结果,表1给出了三个钻孔水压致裂地应力测量主要参数以及主应力值计算结果。

2 沙坪沟矿区现今应力场特征

基于表1数据,我们评价了沙坪沟矿区地壳浅表层应力状态,包括:地应力大小、最大水平主应力方向以及应力结构,图4a给出了实测主应力随深度变化特征,而以线性拟合方式对沙坪沟矿区最大、最小主应力随深度变化计算结果为:

图4a、公式(1)和(2)表明,沙坪沟矿区实测地应力值总体上表现为随着深度的增加而增大,符合已有认识和规律。为了更加准确地评价沙坪沟钼矿地应力分布规律,我们首先对比了沙坪沟钼矿和中国大陆浅层地应力随深度增加梯度系数(景锋等,2007;王艳华等,2012;杨树新等,2012),结果显示两者基本一致,但是沙坪沟矿区地应力地表值偏高(即拟合公式截距),表明沙坪沟矿区近地表水平构造作用较强。进一步,我们缩小对比范围,将沙坪沟矿区结果与矿区外围地应力测量资料对比(谢富仁等,2003),结果显示,沙坪沟矿区地应力水平明显高于矿区外围,尤其是在450 m深度附近(图4),进一步分析后发现,沙坪沟矿区450 m深度附近数据主要分布于FJZK钻孔中,而FJZK钻探揭露显示,450 m深度附近岩芯十分破碎,结合该测点附近地形地貌特征,我们推断此深度附近的地应力测试数据可能受到了地形、断层等因素的影响(Cuisiant et el.,1992;陈群策等,2004;Tan et al.,2004;谭成轩等,2006),至于那种因素起主控作用,有待进一步分析。

图4b和4c进一步给出了沙坪沟钼矿现今应力状态特征参数KHv和KHh的计算结果,KHv和KHh可以反映水平构造应力和水平差应力强度,KHv和KHh计算结果表明,沙坪沟矿区KHv分布特征与已有研究结果大致吻合,而KHh值随深度变化较小,其稳定值约为1.75,略高于已有研究结果(景锋等,2007;王艳华等,2012;杨树新等,2012)。

图5给出了沙坪沟矿区实测最大水平主应力方向随深度分布特征。分析表明,除个别测点外,沙坪沟矿区最大水平主应力方向总体分布在NE−NEE之间(数学平均值为N63°E),对比图6给出的华北地区构造应力场图发现,通过水压致裂法获得的沙坪沟矿区最大水平主应力方向与区域构造应力场方向基本一致(谢富仁等,2003)。

图4　沙坪沟矿区地应力值随深度变化图(实心代表沙坪沟矿区数据,空心表示矿区外围数据)Fig.4 Variation of measured stresses with depth in the Shapinggou molybdenum deposit(the solid and hollow logos represent data of the Shapinggou molybdenum deposit and the periphery,respectively)

公式(1)和(2)及图4a还揭示,沙坪沟矿区实测主应力之间关系总体表现为SH>Sh>Sv,应力结构为逆冲型,但是800 m深度以下,有转向SH>Sv>Sh的趋势(其应力结构为走滑型),由于800 m深度以下数据很少,对此暂不能下定论,但是可以确定的是,上述实测数据均揭示沙坪沟矿区现今应力场以水平应力作用为主导。对比图4和图6给出的资料,发现矿区实测地应力数据揭示的应力结构和其他资料揭示的测区外围应力结构存在差异。至于造成这种差异的原因,从构造地质角度讲,沙坪沟矿区构造位置特殊,其所处的桐柏—大别构造带内是华北地块和扬子地块多次碰撞缝合和长期构造演化的结果,存在着多旋回碰撞缝合,构造环境特殊,构造活动演化复杂;进一步,从构造活动力源方面分析,华北地块构造活动的力源主要来自西太平洋板块的俯冲,以弱张剪作用为主,而扬子地块构造活动的力源主要来自菲律宾板块的推挤作用,以中强压剪作用为主,桐柏—大别构造带则是两者综合作用的结果,加之沙坪沟矿区又被数条深切断裂围限,其应力结构又在一定程度上叠加了断裂的影响,这也恰是豫皖—苏北应力区的应力环境特点,而测区外围的应力结构资料(尤其是震源机制解资料)更多的是反应华北和华南板块的构造应力环境,矿区实测数据揭示的应力结果与外围区存在差异也不难理解了。因此,我们认为除测试数据量及深度差别可能存在的影响外,沙坪沟矿区和外围应力结构的差异主要与其所处特殊构造位置和构造活动机制有关。

图5　沙坪沟矿区实测最大水平主应力方向随深度分布特征Fig.5 Variation of the orientations of the maximum horizontal stresses with depth in the Shapinggou molybdenum deposit

图6　华北现今构造应力场图(据谢富仁等,2003修改)Fig.6 Recent tectonic stress field in North China(modified after XIE et al.,2003)

3 沙坪沟矿区地质安全评价与讨论

本文第二部分揭示了沙坪沟矿区现今地应力状态,那么矿区现今构造应力环境是否稳定,会不会以断层活动或地震的形式导致地应力状态调整呢？研究表明,现代构造运动的性质与强度,取决于区域地应力状态和岩体力学性质(Zoback and Healy,1992;Zoback et al.,1993;Boatwright and Cocco,1996;陈庆宣等,1998;Townend and Zoback,2000;Zoback and Townend,2000;Rivera and Kanamori,2002;Chang et al.,2010)。Townend和Zoback(2000)认为地壳处于破裂极限状态,并且通过断裂的失稳活动或地震事件的发生,地壳应力状态能够保持一个均衡的状态,Zoback和Townend(2001)分析大量地应力实测资料后认为地壳浅部应力状态是受断裂控制的,且其强度的极限状态可以用库伦摩擦滑动准则来描述,并指出在使用库伦摩擦滑动准则时,粘聚力可以忽略,而摩擦系数可以使用Byerlee(1978)基于大量室内实验而提出的除少数岩石外地壳岩石的内摩擦系数为0.6～1.0这一结论(即著名的Byerlee定律)。在引入主应力和有效应力概念后,上文提到的用来描述地壳浅部强度极限状态的库伦摩擦滑动准则变成:

图7　基于地应力实测数据的沙坪沟矿区库伦摩擦滑动计算结果Fig.7 Plots displaying calculation results of measured in-situ stress data obtained in the Shapinggou molybdenum deposit using Coulomb frictional failure criterion

式中,S1,S3分别为断裂外围最大与最小主应力;P0为孔隙压力,其值与静水压力大致相等(Barton et al.,1995;Zoback and Townend,2001)。

使用上式评价某个地区现今地应力强度时,可将实测地应力值带入上式,若由实测地应力数据计算的公式(3)左侧结果大于右侧,那表明该区域现今地应力强度达到地壳浅表部强度极限,可能通过断层失稳活动或地震事件的发生来调整地应力状态;反之,则表明该区域现今地应力强度未达到强度极限,地应力状态不会调整,暂时处于稳定状态。

图7给出了利用库伦摩擦滑动准则对沙坪沟矿区实测地应力数据评价结果,结果表明,沙坪沟钼矿实测地应力数据均未达到地壳浅表部强度极限的上限值(即摩擦系数µ=1.0时限值),也仅有一小部分数据(<30%)超过了强度极限的下限值(即摩擦系数µ=0.6时限值),而这部分数据又主要分布在FJZK钻孔中,如前所述,这部分数据还可能叠加了地形和断裂的影响,由此可以认为沙坪沟矿区现今地应力强度不足以导致断裂失稳活动或地震事件的发生,从地应力角度讲,沙坪沟矿区目前处于稳定构造应力环境。

上述分析从构造应力场角度进行,实际上对于矿产开采而言,更为关心的是在巷道或竖井开挖是否会出现岩爆、片帮剥落等工程问题,由于缺少其他关键资料,暂时不能对此类问题进行具体的分析,后续研究中将重点关注此问题。此外,对于面积较大且构造与地形条件复杂的沙坪沟矿区来讲,继续补充地应力实测数据,对于具体工程问题的解决也十分有益(谭成轩等,2006;王成虎等,2009)。

4 结论

本文采用水压致裂法在金寨沙坪沟矿区3个深孔中开展了地应力测量工作,获得了实测地应力数据,初步揭示了金寨沙坪沟矿区地壳浅表层现今应力状态,同时利用库伦摩擦滑动准则,探讨了实测地应力数据对矿产开采的意义。通过以上分析,可以得到如下结论:

(1)沙坪沟矿区最大、最小水平主应力随深度增加梯度系数分别为0.0226和0.0166;地应力状态特征参数KHv分布特征与已有认识一致,而KHh随深度变化很小,总体分布在1.75左右;上述结果表明,沙坪沟矿区地壳浅表层现今构造应力场以水平向应力作用为主导。

(2)实测地应力数据反映,沙坪沟矿区地壳浅表层最大水平主应力优势方向总体为近NE‒NEE向,与区构造应力场方向基本一致;但是,实测地应力数据揭示的应力结构总体表现为逆断型,与其他资料解释的区域应力结构存在差异,初步认为这种差异主要由矿区所在桐柏—大别构造带与其两侧地块构造位置和构造活动机制差异造成。

(3)基于实测应力数据,使用库伦滑动摩擦准则,结合Byerlee定律,对沙坪沟矿区实测地应力结果分析表明,矿区现今地应力强度不足以导致断裂失稳活动或地震事件的发生,从地应力角度讲,矿区处于稳定构造应力环境。

Acknowledgements:

This study was supported by the Science and Technology Project(No.Sinoprobe-06-03),China Geological Survey(No.1212011220122)and the Central Public-interest Scientific Institution Basal Research Fund(No.DZLXJK201404).

参考文献:

曹辉,孙东生,孟文,赵卫华,万串串.2015.安第斯山中段现今地应力测量及地震相关性分析[J].地球学报,36(2):250-254.

陈庆宣,王维襄,孙叶,黄庆华,王连捷.1998.岩石力学与构造应力场分析[M].北京:地质出版社.

陈群策,安其美,孙东生,杜建军,毛吉震,丰成君.2010.山西盆地现今地应力状态与地震危险性分析[J].地球学报,31(4):541-548.

陈群策,毛吉震,候砚和.2004.利用地应力实测数据讨论地形对地应力的影响[J].岩石力学与工程学报,23(23):3990-3995.

董树文,孙先如,张勇,黄德志,王刚,戴世坤,于邦存.1993.大别山碰撞造山带基本结构[J].科学通报,38(6):542-545.

董树文,吴宣志,高锐,卢德源,李英康,何义权,汤加富,曹奋扬,侯明金,黄德志.1998.大别造山带地壳速度结构与动力学[J].地球物理学报,41(3):349-361.

郭啟良,王成虎,马洪生,王崇艮.2009.汶川Ms 8.0级大震前后的水压致裂原地应力测量[J].地球物理学报,52(5):1395-1401.

景锋,盛谦,张勇惠,罗超文,刘元坤.2007.中国大陆浅层地壳实测地应力分布规律研究[J].岩石力学与工程学报,26(10):2057-2062.

孟祥金,徐文艺,吕庆田,屈文俊,李先初,史东方,文春华.2012.安徽沙坪沟斑岩钼矿锆石U-Pb和辉钼矿Re-Os年龄[J].地质学报,86(3):486-494.

苏晓静,王根节,周艳,陈秀忠,王波华.2013.金寨县沙坪沟钼矿的隐爆特征及成矿意义[J].安徽地质,23(3):195-199.

谭成轩,孙炜锋,孙叶,王连捷.2006.地应力测量及其在地下工程应用的思考[J].地质学报,80(10):1627-1632.

谭成轩,张鹏,丰成君,秦向辉,孙伟烽,陈群策,吴满路.2014.探索首都圈地区深孔地应力测量与监测及其在地震地质研究中应用[J].地质学报,88(8):1436-1452.

王成虎,郭啟良,丁立丰,刘立鹏.2009.工程区高地应力判据研究及实例分析[J].岩土力学,30(8):2359-2364.

王艳华,崔效峰,胡幸平,谢富仁.2012.基于原地应力测量数据的中国大陆地壳上部应力状态研究[J].地球物理学报,55(9):3016-3027.

吴满路,廖椿庭,袁佳音.2002.荒沟蓄能电站地下厂房地应力状态与工程稳定性研究[J].地球学报,23(3):263-268.

吴满路,张春山,廖椿庭,区明益.2005.风火山隧道地应力测量及工程稳定性分析[J].地球学报,26(1):71-74.

谢富仁,陈群策,崔效锋,李宏,杨树新,陈连旺.2003.中国大陆地壳应力环境研究[M].北京:地质出版社.

杨树新,姚瑞,崔效峰,陈群策,黄禄渊.2012.中国大陆各活动地块、南北地震带实测应力特征分析[J].地球物理学报,55(12):4207-4217.

张红,孙卫东,杨晓勇,梁华英,王波华,王瑞龙,王玉贤.2011.大别造山带沙坪沟特大型斑岩钼矿矿床年代学及成矿机理研究[J].地质学报,85(12):2039-2059.

张怀东,王波华,郝越进,程松,项斌.2012.安徽省沙坪够斑岩型钼矿地质特征及综合找矿信息[J].安徽地质,31(1):41-51.

References:

AMADEI B,STEPHANSSON O.1997.Rock stress and its measurement[M].London:Chapman &Hall.

BARTON C A,ZOBCK M D,MOOS D.1995.Fluid flow along potentially active faults in crystalline rock[J].Geology,23:683-686.

BOATWRIGHT J,COCCO M.1996.Frictional constraints on crustal faulting[J].Journal of Geophysical Research,101(B6):13895-13909.

BYERLEE J D.1978.Friction of rocks[J].Pure and Applied Geophysics,116(4-5):615-626.

CAO Hui,SUN Dong-sheng,MENG Wen,ZHAO Wei-hua,WANG Chuan-chuan.2015.In Situ Stress Measurement in the Central Section of Andes and Its Relation to Seismicity[J].Acta Geoscientica Sinica,36(2):250-254(in Chinese with English abstract).

CHANG C D,LEE B J,KANG T S.2010.Interaction between regional stress state and faults:complementary analysis of borehole in situ stress and earthquake focal mechanics in southeastern Korea[J].Tectonophysics,485:164-177.

CHEN Qing-xuan,WANG Wei-xiang,SUN Ye,HUANG Qing-hua,WANG Lian-jie.1998.Rock mechanics and analysis of tectonic stress field[M].Beijing:Geological Publish House(in Chinese).

CHEN Qun-ce,AN Qi-mei,SUN Dong-sheng,DU Jian-jun,MAO Ji-zhen,FENG Cheng-jun.2010.Current In-situ Stress State of Shanxi Basin and Analysis of Earthquake Risk[J].Acta Geoscientica Sinica,31(4):541-548(in Chinese with English abstract).

CHEN Qun-ce,MAO Ji-zhen,HOU Yan-he.2004.Study on influence of topography on in-situ stress by interpretation of measurement data of in-situ stress[J].Chinese Journal of Rock Mechanics and Engineering,23(23):3990-3995(in Chinese with English abstract).

CUISIANT F D,HAIMSON B C.1992.Scale effects in rock mass stress measurements[J].Int.J.Rock.Mech.Min.Sci.&Geomech.Abstr.,29(2):99-117.

DONG Shu-wen,SUN Xian-ru,ZHANG Yong,HUANG De-zhi,WANG Gang,DAI Shi-kun,YU Bang-cun.1993.Basic structure of Dabieshan Orogen[J].Chinese Science Bulletin,38(6):542-545(in Chinese).

DONG Shu-wen,WU Xuan-zhi,GAO Rui,LU De-yuan,LI Ying-kang,HE Yi-quan,TANG Jia-fu,CAO Fen-yang,HOU Ming-jin,HUANG De-zhi.1998.On the crust velocity levels and dynamics of the Dabieshan orogenic belt[J].Acta Geophysica Sinica,41(3):349-361(in Chinese with English abstract).

GUO Qi-liang,WANG Cheng-hu,MA Hong-sheng,WANG Chong-gen.2009.In-situ hydro-fracture stress measurement before and after the Wenchuan Ms8.0 earthquake of China[J].Chinese Journal of Geophysics,52(5):1395-1401(in Chinese with English abstract).

HAIMSON B C,CORNET F H.2003.ISRM suggested methods for rock stress estimation—part 3:hydraulic fracturing(HF)and/or hydraulic testing of pre-existing fractures(HTPF)[J].International Journal of Rock Mechanics &Mining Sciences,40:1011-1020,doi:10.1016/j.ijrmms.2003.08.002.

HARDEBECK J L,HAUKSSON E.2001.Crustal stress field in southern California and its implications for fault mechanics[J].Journal of Geophysical Research,106(B10):21859-21882.

HAYASHI K,HAIMSON B C.1991.Characteristics of shut-in curves in hydraulic fracturing stress measurements and determination of in situ minimum compressive stress[J].Journal of Geophysical Research,96(B11):18311-18321.

JING Feng,SHENG Qian,ZHANG Yong-hui,LUO Chao-wen,LIU Yuan-kun.2007.Research on distribution rule of shallow crustal geostress in China mainland[J].Chinese Journal of Rock Mechanics and Engineering,26(10):2057-2062(in Chinese with English abstract).

LEE M Y,HAIMSON B C.1989.Statistical evaluation of hydraulic fracturing stress measurement parameter[J].Int.J.Rock Mech.Min.Sci.&Geomech.Abstr.,26:447-456.

LIAO C T,ZHANG C S,WU M L.2003.Stress change near the Kunlun fault before and after the Ms8.1 Kunlun earthquake[J].Geophysical Research Letters,30(20):2027-2030,doi:10.1029/2003GL018106.

LIN Wei-ren,CONIN M,MOORE C,CHESTER F M,NAKAMURA Y,MORI J J,ANDERSON L,BRODSKY E E,EGUCHI N.2013.Stress state in the largest displacement area of the 2011 Tohoku-Oki earthquake[J].Science,339:687-690,doi:10.1126/science.129379.

MENG Xiang-jin,XU Wen-yi,LÜ Qing-tian,QÜ Wen-jun,LI Xian-chu,SHI Dong-fang,WEN Chun-hua.2012.Zircon U-Pb Dating of Ore-Bearing Rocks and Molybdenite Re-Os age in Shapinggou Porphyry Molybdenum Deposit,Anhui Province[J].Acta Geologica Sinica,86(3):486-494(in Chinese with English abstract).

QIN Xiang-hui,TAN Cheng-xuan,CHEN Qun-ce,WU Man-lu,FENG Cheng-jun.2014.Crustal stress state and seismic hazard along southwest segment of the Longmenshan thrust belt after Wenchuan earthquake[J].Journal of Earth Science,25(4):676-688.

RIVERA L,KANAMORI H.2002.Spatial heterogeneity of tectonic stress and friction in the crust[J].Geophysical ResearchLetters,29(6):12-1-12-4.

SU Xiao-jing,WANG Gen-jie,ZHOU Yan,CHEN Xiu-zhong,WANG Bo-hua.2013.Cryptoexplosion features and their implications to mineralization of the Shapinggou molybdenum ore deposit,Jinzhai County[J].Geology of Anhui,23(3):195-199(in Chinese with English abstract).

TAN Cheng-xuan,ZHANG Peng,FENG Cheng-jun,QIN Xiang-hui,SUN Wei-feng,CHEN Qun-ce,WU Man-lu.2014.An Approach to Deep Borehole Crustal Stress Measuring and Real-time Monitoring and Its Application in Seismogeology Research in Capital Beijing Region[J].Acta Geologica Sinica,88(8):1436-1452(in Chinese with English abstract).

TAN Cheng-xuan,SUN Wei-feng,SUN Ye,WANG Lian-jie.2006.A Consideration on In-Situ Crustal Stress Measuring and Its Underground Engineering Application[J].Acta Geological Sinica,80(10):1627-1632(in Chinese with English abstract).

TAN Cheng-xuan,WANG Rui-jiang,SUN Ye,LEI Wei-zhi,WU Shu-ren,YANG Mei-ling,SUN Wei-feng.2004.Numerical modeling estimation of the ′tectonic stress plane′(TSP)beneath topography with quasi-U-shaped valleys[J].International Journal of Rock Mechanics &Mining Sciences,(41):303-310,doi:10.1016/S1365-1609(03)00096-0.

TOWNEND J,ZOBACK M D.2000.How faulting keeps the crust strong [J].Geology,28(5):399-402.

WANG Cheng-hu,GUO Qi-liang,DING Li-feng,LIU Li-peng.2009.High in-situ stress criteria for engineering area and a case analysis[J].Rock and Soil Mechanics,30(8):2359-2364(in Chinese with English abstract).

WANG Yan-hua,CUI Xiao-feng,HU Xing-ping,XIE Fu-ren.2012.Study on the stress state in upper crust of China mainland based on in-situ stress measurements[J].Chinese Journal of Geophysics,55(9):3016-3027(in Chinese with English abstract).

WU Man-lu,ZHANG Chun-shan,LIAO Chun-ting,OU Ming-yi.2005.Stress Measurement and Engineering Stability Analysis at Fenghuoshan Tunnel[J].Acta Geoscientica Sinica,26(1):71-74(in Chinese with English abstract).

WU Man-lu,LIAO Chun-ting,YUAN Jia-yin.2002.A Study of Stress State and Engineering Stability of Underground Houses at the Huanggou Accumulation Power Station[J].Acta Geoscientica Sinica,23(3):263-268(in Chinese with English abstract).

XIE Fu-Ren,CHEN Qun-ce,CUI Xiao-feng,LI Hong,YANG Shu-xin,CHEN Lian-wang.2003.Crustal stress in China[M].Beijing:Geological Publish House(in Chinese).

YANG Shu-xin,YAO Rui,CUI Xiao-feng,CHEN Qun-ce,HUANG Lu-yuan.2012.Analysis of the characteristics of measured stress in Chinese mainland and its active block and North-South seismic belt[J].Chinese Journal of Geophysics,55(12):4207-4217(in Chinese with English abstract).

ZOBACK M D,APEL R,BAUMGÄRTNER J,BRUDY M,EMMERMANN R,ENGESER B,FUCHS K,KESSELS W,RISCHMÜLLER H,RUMMEL F,VERNLK L.1993.Upper-crustal strength inferred from stress measurements to 6 km depth in the KTB borehole[J].Nature,365:633-635.

ZOBACK M D,HEALY J H.1992.In-situ stress measurements to 3.5 km depth in the Cajon Pass scientific research borehole:implications for the mechanics of crustal faulting[J].Journal of Geophysical Research,97(B4):5039-5057.

ZOBACK M D,TOWNEND J.2001.Implications of the hydrostatic pore pressures and high crustal strength for the deformation of intraplate lithosphere[J].Tectonophysics,336(1-4):19-30.

ZOBACK M D.2007.Reservoir Geomechanics[M].Cambridge:Cambridge University Press.

ZHANG Hong,SUN Wei-dong,YANG Xiao-yong,LIANG Hua-ying,WANG Bo-hua,WANG Rui-long,WANG Yu-xian.2011.Geochronology and Metallogenesis of the Shapinggou Giant Porphyry Molybdenum Deposit in the Dabie Orogenic Belt[J].Acta Geological Sinica,85(12):2039-2059(in Chinese with English abstract).

ZHANG Huai-dong,WANG Bo-hua,HAO Yue-jin,CHENG Song,XIANG Bin.2012.Geological characteristics and comprehensive ore-prospecting information of Shapinggou porphyry-type molybdenum deposit in Anhui Province[J].Mineral Deposits,31(1):41-51(in Chinese with English abstract).

Estimation on In-situ Stress Measurements and Present-day Stress Field in the Shapinggou Molybdenum Deposit,Jinzhai County,Anhui Province

QIN Xiang-hui1,2),CHEN Qun-ce1,2),HAO Yue-jin3),MENG Wen1,2),SUN Dong-sheng1,2)
1)Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081;
2)Key Laboratory of Neotectonic Movement &Geohazard,Ministry of Land and Resources,Beijing 100081;
3)No.313 Geological Party,Anhui Bureau of Geology and Mineral Resources,Lu′an,Anhui 237010

Abstract:The Shapinggou molybdenum deposit located in the East Qinling-Dabie metallogenic belt is a superlarge porphyry molybdenum deposit discovered in recent years.Much attention has been paid to the exploitation designing and geological safety evaluation of this deposit.To thoroughly understand the present-day stress field in the Shapinggou molybdenum deposit and put forward suggestions for the exploitation designing,the authors conducted in-situ stress measurement using hydraulic fracturing method in three drill holes at the depths of 700～1000 m in the Shapinggou molybdenum ore district.The measurement results reveal that the grade coefficients of the maximum,minimum horizontal principal stresses versus depths are 0.0226 and 0.0166,respectively,which are consistent with previous results representing the regional tectonic stress field.The measured in-situ stress data also indicate that the dominant direction of the maximum horizontal stress in the Shapinggou molybdenum ore district is in NE−NEE direction,which is consistent with the regional tectonic stress field.However,the stress regimes inferred from the measured in-situ stress data are not consistent with regional results inferred from other methods.The unique tectonic location and the tectonic evolution mechanism of thebook=224,ebook=99Tongbai-Dabie tectonic belt where the Shapinggou molybdenum deposit occurs are considered to be the main factors inducing the discrepancy between the Shapinggou molybdenum deposit and the regional results.Furthermore,the measured in-situ stress data and their implications for the exploitation designing of the Shapinggou molybdenum deposit were estimated by using the Column frictional failure criterion.It is noted that the measured in-situ stress levels in the ore district are lower than those expected to induce the stress field adjustment in the form of fault slipping or earthquake,and thus the Shapinggou molybdenum deposit can be considered to be in the relatively stable tectonic stress state now.The results achieved in this study will contribute to exploitation of the Shapinggou molybdenum deposit and geological safety evaluation as well as to the study of tectonic stress field of the Dabieshan orogenic belt.

Key words:Shapinggou molybdenum deposit;in-situ stress;hydraulic fracturing;present-day stress field;Column frictional failure criterion

作者简介:第一秦向辉,男,1984生。硕士,助理研究员。主要从事地应力测量与监测、区域地壳稳定性评价等工作。E-mail:qinxiangh03@126.com。

收稿日期:2015-08-18;改回日期:2015-11-17。责任编辑:魏乐军。

中图分类号:P618.65;P553

文献标志码:A

doi:10.3975/cagsb.2016.02.10