岩石学报  2017, Vol. 33 Issue (7): 2273-2284   PDF    
湘东北杨山庄金矿床流体成矿机制
刘育1,2, 张良1, 孙思辰1, 綦鹏1, 吴胜刚3, 高磊3     
1. 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083;
2. 河北地质大学资源学院, 石家庄 050031;
3. 湖南黄金洞矿业有限责任公司, 岳阳 414507
摘要: 杨山庄金矿床位于江南造山带中部,矿体严格受NW-NWW向断裂控制,赋存于新元古代浅变质的绢云母板岩和粉砂质板岩中,成矿期分为三个阶段:石英-毒砂-黄铁矿(少量)-自然金-白钨矿-白云石-白云母(阶段Ⅰ)、石英-毒砂-黄铁矿-自然金-黄铜矿-方铅矿-闪锌矿-绢云母(阶段Ⅱ)和石英-方解石(阶段Ⅲ)。成矿Ⅰ、Ⅱ阶段流体包裹体以两相水溶液包裹体为主,含有少量的气相包裹体和含CO2的三相包裹体,气相包裹体成分为CH4-N2-CO2、N2-CO2和N2。成矿温度集中在240~320℃,盐度集中在7%~9% NaCleqv,成矿流体为中-低温、中低盐度H2O-NaCl-CO2体系。在成矿Ⅰ、Ⅱ阶段,成矿流体与围岩发生交代反应,流体发生相分离,使液相CO2含量降低,引起Au(HS)2-溶解度降低,导致金发生沉淀。
关键词: 流体包裹体     杨山庄金矿床     黄金洞金矿田     江南造山带    
Mineralization mechanism of Yangshanzhuang gold deposit, northeastern Hunan Province
LIU Yu1,2, ZHANG Liang1, SUN SiChen1, QI Peng1, WU ShengGang3, GAO Lei3     
1. State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Beijing 100083, China;
2. School of Resources, Hebei GEO University, Shijiazhuang 050031, China;
3. Hunan Huangjindong Mining Co. Ltd., Yueyang 414507, China
Abstract: The Yangshanzhuang gold deposit, located in the middle part of the Jiangnan orogenic belt, is hosted by the Neoproterozoic low-grade metamorphic sericite slate and silty slate and is strictly controlled by NW-NWW-trending faults. According to intergrowth and crosscutting relationships among different minerals, three paragenetic stages were identified, which are quartz-arsnopyrite-pyrite-native gold-scheelite-dolomite-muscovite (stage Ⅰ); quartz-arsnopyrite-pyrite-native gold-chalcopyrite-galena-sphalerite-sericite (stage Ⅱ) and quartz-sericite (stage Ⅲ). Fluid inclusions in stage Ⅰ and Ⅱ are mainly aqueous inclusions with minor gaseous inclusions and H2O-CO2 inclusions. Raman spectroscopy analysis indicates that gaseous inclusions are consist of N2, CH4 and CO2. Mineralization temperature and salinity of the ore-forming fluid are restricted in ranges of 240~320℃ and 7%~9% NaCleqv, respectively. The combined microthermometry and Raman spectroscopy studies suggest a H2O-NaCl-CO2 fluid system characterized by medium-low temperature and medium-low salinity. Fluid phase separation occurred during the process of wall rock metasomatism in Stage Ⅰ and Stage Ⅱ. The concentration of liquidus CO2 decreased because of phase separation might further facilitate the deposition of gold.
Key words: Fluid inclusion     Yangshanzhuang gold deposit     Huangjindong gold field     Jiangnan orogenic belt    
1 引言

江南造山带内新元古代浅变质岩中发育金-多金属矿床250余个,黄金储量超过600t(图 1, Goldfarb and Santosh, 2014; Deng and Wang, 2016; 文志林等, 2016; 陈爱清, 2012),此类矿床均发育在NE向深大断裂附近,矿脉展布受NW-NWW向断裂控制(毛景文, 1997; 黄诚等, 2012; Xu et al., 2017)。湘东北地区位于江南造山带中部,已控制黄金储量超过200t,是华南重要的金-多金属矿集区,区内一系列NNE向深大断裂将该区分割成相间的断陷和断隆,金-多金属矿床位于断隆带或隆-拗带的转换部位(许德如等, 2009, 2015)。

图 1 江南造山带内金矿床分布(据陈爱清, 2012修编) Fig. 1 Distribution of gold deposits in Jiangnan Orogenic Belt (modified after Chen, 2012)

对于此类金矿床的成矿时代,韩凤彬等(2010)采用Rb-Sr法测定杨山庄和万古金矿床成矿年龄为462±18Ma和425±33Ma;许德如等(2015)获得了与金矿化相关辉钼矿Re-Os 138±5.7Ma的等时线年龄;Deng et al. (2017c)根据连云山侵入岩锆石U-Pb年龄和成矿期白云母40Ar-39Ar年龄,将成矿年龄限定在142~130Ma,进而认为早白垩世是湘东北地区大规模金矿化的主要时期。在矿床成因方面,贾宝华和彭和求(2005)马东升和刘英俊(1991)依据含矿建造特征,将此类金矿床划分为层控型金矿床;董国军等(2008)依据成矿地质条件和矿化特征,认为此类金矿床是浅成造山有关的金矿床。此外,前人对于此类金矿的地质特征和成矿规律做了大量的工作,但目前关于此类金矿的成矿机制还缺乏深入研究,这制约了对此类矿床的理解和找矿勘查工作,因此湘东北金矿床成矿机制是亟需解决的科学问题。

大部分地质过程均离不开流体的参与,尤其是与流体活动密切相关的热液矿床(Yang et al., 2006, 2008, 2009a, b; Deng et al., 2003a, 2005),通过流体包裹体研究,可以获得成矿流体的温度、压力和组成等,对于研究对确定成矿流体性质、成矿机制和成矿背景具有重要意义(Yang et al., 2016a, c, 2017a; Deng et al., 2003b, 2008, 2011, 2017a, b; Deng and Wang, 2016)。对于湘东北金矿床成矿流体特征和演化,前人做了大量的研究(李杰等, 2011; 叶传庆等, 1988; 刘荫椿, 1989),但由于实验所采集样品地质意义不明确,或未基于可靠的成矿阶段,目前仍没有令人信服的结果。在金成矿机制研究方面,李杰等(2011)认为金的沉淀与温度降低和成矿流体的混合作用有关,但文中并未列举流体混合的证据,因此金成矿机制仍需进一步研究。

杨山庄金矿床为一大型金矿床,位于湘东北黄金洞金矿田内,前人对该矿床的地质特征和成因类型具有较深入的研究,是研究湘东北金矿床成矿机制的理想选区。本文拟通过对杨山庄金矿床野外地质调研和室内薄片、光片分析,在精确厘定成矿阶段的基础上,研究成矿流体特征与演化,进一步探讨金成矿机制。

2 区域与矿床地质 2.1 区域地质

湘东北地区位于江南造山带中段(图 2),在江南造山带经历了多次裂解、碰撞和拼接过程中,形成了NNE和NW向大型走滑断裂系统控制的盆岭山链构造、陆内岩浆岩带和金-多金属成矿带(Liu et al., 1993; 傅昭仁等, 1999)。区内出露地层主要为新元古代浅变质的火山碎屑岩和新生代地层。断裂主要为新宁-灰汤、长沙-平江和浏阳-醴衡3条NNE向深大断裂,将湘东北划分成盆岭相间的构造格局。区内发育多期次的岩浆活动,包括晋宁期、加里东期、海西-印支期和燕山期。区内金-多金属矿床发育在断隆带和隆-坳转换部位,如黄金洞金矿田、雁林寺金矿田和七宝山铅-锌-铜-金多金属矿床(许德如等, 2009)。

图 2 湘东北区域地质图(据贺转利等, 2004; 毛景文, 1997修编) 1-第四系-白垩系;2-三叠纪-泥盆纪粉砂岩、灰岩、白云岩;3-志留纪-震旦纪白云岩、灰岩;4-新元古界板溪粉砂质板岩、粉砂岩;5-新元古界冷家溪群绢云母板岩、粉砂质板岩、粉砂岩;6-燕山期花岗岩;7-印支期花岗岩;8-加里东期花岗岩;9-新元古界花岗岩;10-深断断裂/次级断裂;11-韧性剪切带;12-向斜/背斜;13-倒转向斜/倒转背斜;14-金矿床(点)/铜铅锌金多金属矿床.Ⅰ-汨罗断陷盆地;Ⅱ-幕阜山-望湘断隆;Ⅲ-长沙-平江断陷盆地;Ⅳ-浏阳-衡东断隆;Ⅴ-醴陵-攸县断陷盆地;A-九岭-清水韧性剪切带;B-连云山-长沙韧性剪切带;C-青草-株州韧性剪切带 Fig. 2 Regional geologic map of Northeastern Hunan Province (modified after He et al., 2004; Mao, 1997)
2.2 矿床地质

黄金洞金矿田位于雪峰山弧形构造隆起处东段,江西九岭复式背斜西南倾伏段北侧(罗献林, 1988; 李杰等, 2011)。杨山庄金矿床位于黄金洞金矿田东部(图 3a),赋矿围岩为新元古代冷家溪群厚层状绢云母板岩、粉砂质板岩和条带状板岩。矿区内发育长平断裂、泥湾断裂、坑上断裂及一系列近NW-WNW向层间压性断裂和切层压性断裂。矿区内发育10条层间压性断裂,其中F1控制201号矿脉,断裂走向长300~1730m,倾向N或NE,倾角41°~66°;切层压性断裂较层间压性断裂晚,为一组的共扼剪切断裂,多数为N倾断裂,倾向2°~15°,倾角60°~73°,S倾断裂倾向160~175°,倾角55~65°(伍德胜, 1993)。矿区内岩浆岩不发育,仅在矿区南侧约2km处见小规模的斜闪煌斑岩脉(罗献林, 1988)。

图 3 黄金洞金矿田地质图(a)和201号矿体和202号矿体剖面图(b)(据罗献林, 1988; 伍德胜, 1993; 李杰等, 2011修编) Fig. 3 Geological map of Huangjindong gold filed (a) and profiles of ore body 201 and ore body 202 (b) (modified after Luo, 1988; Wu et al., 1993; Li et al., 2011)
2.2.1 矿体地质

矿体主要呈脉状、透镜体状或不规则状,发育在断裂下盘(图 4)。已发现15条NW-WNW向大致平行的矿脉,其中201、202、203、4-2号矿脉为工业矿体,201和202号矿体储量占矿区总储量的87%(伍德胜, 1993)。201号矿脉受层间断裂控制,产于断裂下盘0~3m,矿脉地表走向长1730m,倾向300°~40°,倾角37°~64°,矿脉厚0.06~4.09m,平均品位3.08g/t;202矿脉受切层断裂控制,矿脉地表走向长2220m,矿脉倾向300°~56°,倾角66°~80°,厚0.24~3.47m,平均品位5.53g/t;202号矿体与201号矿体深部呈“Y”状相交(图 3b)。矿区围岩蚀变类型主要为硅化、绿泥石化和绢云母化,蚀变发育在断裂带下盘,远离断裂逐渐变弱,蚀变带一般宽2~5m,少数可达15m(图 5)

图 4 杨山庄金矿床矿石类型 (a)石英硫化物脉型矿石;(b)硅化板岩型矿石;(c、d)石英角砾岩型矿石 Fig. 4 Mineralization types of ores in Yangzhuangshan gold deposit (a) quartz sulfide veins; (b) gold-bearing alterated rocks; (c, d) gold-bearing quartz brecciated

图 5 杨山庄金矿床围岩蚀变特征 Fig. 5 Wallrock alteration in Yangzhuangshan gold deposit
2.2.2 石类型与矿物组合

根据矿物组合和矿石组构特征,矿石类型划分为石英硫化物脉型(图 4a图 6a, b)、硅化板岩型(图 4b)和石英角砾岩型(图 4c, d图 6g, h)。石英硫化物脉矿石呈条带状分布,其中发育半自形-自形结构,稀疏浸染状毒砂和黄铁矿(图 6c, d),矿石矿物为毒砂、黄铁矿和自然金,极少量黄铜矿和白钨矿,脉石矿物为石英、白云石等。硅化板岩型矿石发育于石英硫化物脉型矿体或断裂带下盘,矿石矿物主要为长柱状毒砂和粗粒黄铁矿,呈星点状或浸染状分布。石英角砾岩型矿石产于断裂带下盘,其中角砾为早阶段形成的贫矿乳白色石英,胶结物为后期形成的热液石英,矿石矿物为黄铁矿,为毒砂、自然金、偶见黄铜矿、方铅矿和闪锌矿(图 6i, j),脉石矿物为石英、白云石、绢云母。黄铁矿和毒砂为他形-半自形,呈网脉状分布与早期形成的贫矿石英脉或绢云母板岩型中(图 6k, l),石英呈角砾状、细脉状,细脉状石英具有鳞片变晶结构(图 6k, l),绢云母呈鳞片状分布裂隙内(图 6l)。

图 6 杨山庄金矿床矿石手标本及镜下特征 (a、b)石英硫化物脉型矿石;(c)石英硫化物脉型内发育浸染状毒砂和黄铁矿;(d)石英硫化物型矿石内毒砂形成较早,黄铁矿形成较晚;(e)毒砂和黄铜矿共生;(f)石英硫化物矿石单偏光照片;(g)石英角砾岩型矿石;(h、i)石英角砾型矿石内发育黄铁矿;(j)石英角砾岩型矿石黄铁矿、黄铜矿和方铅矿共生;(k、l) Ⅰ阶段石英脉破碎,沿裂隙发育绢云母和黄铁矿;(m、n) Ⅲ阶段石英方解石脉;(o)石英方解石脉镜下照片 Fig. 6 Photographs and photomicrographs of ore samples from the Yangshanzhuang gold deposit (a, b) quartz sulfide veins; (c) disseminated arsenopyrite and pyrite in quartz sulfide; (d) arsenopyrite is earlier than pyrite in quartz sulfide; (e) symbiotic arsenopyrite and chalcopyrite; (f) quartz sulfide (-); (g) gold-bearing quartz brecciated; (h, i) pyrite in gold-bearing quartz brecciated; (j) pyrite, chalcopyrite and galena are symbiosis in gold-bearing quartz brecciated; (k, l) Ⅰ stage quartz broken, and sericite and pyrite occur along the fracture; (m, n) quartz calcite veins in the stage Ⅲ; (o) quartz calcite veins (-)
2.2.3 成矿阶段划分

根据野外的脉体的穿插关系和共生矿物组合(图 6),杨山庄金矿床成矿过程分为3个阶段(图 7)。Ⅰ阶段为石英-毒砂(少量黄铁矿)阶段,特征矿物组合为石英-毒砂-黄铁矿(少量)-自然金-白钨矿-白云石-白云母;Ⅱ阶段为石英-多金属硫化物阶段,特征矿物组合为石英-毒砂-黄铁矿-自然金-黄铜矿-方铅矿-闪锌矿-绢云母;晚阶段为石英-方解石阶段,发育于矿体较远的裂隙中。金矿化主要发育在Ⅰ和Ⅱ阶段,金呈可见金分布于毒砂裂隙内或石英脉中,部分呈不可见金赋存于毒砂晶格内(刘英俊等, 1989)。

图 7 杨山庄金矿床矿物生成顺序图 Fig. 7 Paragenetic assemblage and sequence of mineral in Yangshanzhuang gold deposit
3 流体包裹体研究 3.1 样品采集与测试方法

本次研究采集了杨山庄金矿床202号矿脉180m、120m、80m、-140m和-180m不同成矿阶段流体包裹体样品共10件(表 1)。首先将样品磨制成厚约0.3mm双面抛光的包裹体片,进行包裹体岩相学和类型分析,然后选择代表性样品进行显微测微和激光拉曼探针分析。

表 1 流体包裹体研究样品采样位置及特征 Table 1 Characteristics and Sampling location of specimen for fluid inclusion research

流体包裹体显微测温分析在中国地质大学(北京)资源勘查实验室LinkamTHMS600型冷热台进行,利用FLUIDINC公司的合成流体包裹体标样对冷热台进行温度标定。该冷热台测温范围为-196~600℃,在-196~30℃精度为±0.2℃,在30~300℃精度为±1℃、在300~600℃精度为±2℃。流体包裹体测试过程中,开始时升或降温速度为10~20℃/min,相变点附近速度降至~1℃/min。流体包裹体盐度根据Bodnar (1993)提供的盐度-冰点关系表求得,流体包裹体密度根据NaCl-H2O溶液包裹体密度公式:D=A+Bt+tC2求得。

单个包裹体的激光拉曼探针分析在中国地质大学(北京)资源勘查实验室InVia型激光拉曼光谱仪进行,使用Ar原子激光器,波长514.5nm,所测光谱计数时间为10~30s,每1cm-1(波数)计数一次,1000~4000cm-1波段依次取峰,激光束斑最小直径约1μm,光谱分辨率1~2cm-1

3.2 岩相学特征与类型

杨山庄金矿床不同阶段石英脉中普遍发育包裹体,原生包裹体分布均匀,在毒砂晶体周围较发育(图 8a, c, e)。次生包裹体较小,呈带状分布,切过了石英晶面纹。通过流体包裹体在升温和降温过程中相态变化(Diamond, 2001),区分出以下3类包裹体:

图 8 杨山庄金矿床流体包裹体显微照片 (a、b) Ⅰ阶段C型和L型包裹体;(c) Ⅰ阶段L型和V型包裹体;(d) Ⅱ阶段C型、L型和V型包裹体共生;(e) Ⅱ阶段L型和V型包裹体;(f) Ⅲ阶段L型包裹体 Fig. 8 Microscopic photos of fluid inclusions in Yangshanzhuang gold deposit (a, b) C-style inclusion and L-style inclusion in quartz of stage Ⅰ; (c) L-style inclusion and V-style inclusion in quartz of stage Ⅰ; (d) C-style, L-style and V-style inclusion coexist in quartz of stage Ⅱ; (e) L-style inclusion and V-style inclusion in quartz of stage Ⅱ; (f) L-style inclusion in quartz of stage Ⅲ

水溶液两相包裹体(L型):此类包裹体最常见,呈长条状或椭球状,粒径3~15μm。室温下为LH2O和VH2O两相,气液比多集中在5%~15%,少量可达20%~40%(图 8b, e, f)。

含CO2三相包裹体(C型):此类包裹体较少,多呈椭球状和不规则状,粒径6~15μm,室温下为LH2O、LCO2和VCO2三相,CO2含量15%~40%(图 8b, d)。

气体包裹体(V型):此类包裹体较常见,灰黑色,呈椭圆状和不规则状,大小5~15μm(图 8c, d, e, )。

3.3 流体包裹体显微测温

在成矿阶段划分和流体包裹体岩相学观察的基础上,对成矿期Ⅰ、Ⅱ和Ⅲ阶段石英脉中原生L型和C型包裹体进行显微测温分析,结果见表 2

表 2 杨山庄金矿床流体包裹体显微测温结果 Table 2 Microthemometric data of fluid inclusions in Yangshanzhuang gold deposit

Ⅰ阶段热液石英脉中的L型包裹体均一温度为225~353℃,集中在280~320℃(图 9),冰点温度分布范围-7.3~-3.2℃,对应盐度在5.26%~10.86% NaCleqv,流体密度0.71~0.89g/cm3;C型包裹体完全均一温度264~305℃,集中在280~300℃,部分均一温度24.5~27.1℃,笼合物消失温度4.1~6.3℃,固态CO2融化温度为-61.0~-56.9℃,盐度6.97%~10.44% NaCleqv,流体密度0.80~0.86g/cm3

图 9 杨山庄金矿床不同成矿阶段均一温度和盐度直方图 Fig. 9 Histograms of homogenization temperature and salinity of fluid inclusions in Yangshanzhuang gold deposit

Ⅱ阶段热液石英中L型包裹体均一温度177~343℃,集中在240~280℃(图 9),冰点温度-6.4~-2.5℃,对应流体盐度4.18%~10.61% NaCleqv,流体密度0.71~0.96g/cm3;C型包裹体完全均一温度234~264℃,集中在240~260℃,部分均一温度24.2~26.5℃,笼合物消失温度4.8~6.7℃,固态CO2融化温度为-59.4~-56.2℃,盐度6.29%~9.39% NaCleqv,流体密度0.84~0.88g/cm3

Ⅲ阶段无矿热液石英脉中的L型包裹体均一温度116~226℃,集中在120~160℃(图 9),冰点温度-7.5~-2.3℃,对应流体盐度在4.2%~9.8% NaCleqv,流体密度密度0.88~1.01g/cm3,总体上从成矿Ⅰ阶段到Ⅲ阶段,温度逐渐降低,但盐度变化不大(图 10)。

图 10 不同成矿阶段包裹体均一温度-盐度协变图 Fig. 10 Covariation diagram of homogenization temperature and salinity of fluid inclusions
3.4 激光拉曼探针分析

包裹体激光拉曼测试结果显示,各阶段的石英内的L和C型包裹体内除了寄主矿物石英特征峰外,均可以检测到的液态H2O(3443cm-1)峰(图 11a);在C型包裹体中气相成分中出现了明显的CO2特征双峰(1386cm-1和1282cm-1)和N2峰(2328cm-1)(图 11b)。V型包裹体气体成分均显示出明显的N2峰(2328cm-1)(图 11c),少量的V型包裹体具有CO2双峰,或同时具有CO2特征双峰和CH4特征峰(2915cm-1)(图 11d)。

图 11 流体包裹体原位激光拉曼光谱分析谱图 (a) Ⅰ阶段C型包裹体液相成分谱图;(b) Ⅰ阶段C型包裹体中CH4和N2峰值;(c) Ⅰ阶段V型包裹体CO2和N2峰值;(d) Ⅰ阶段V型包裹体CO2、CH4和N2峰值 Fig. 11 Laser-Raman microspectra of the fluid inclusions (a) H2O spectrum peak in the L-style inclusion of stage Ⅰ; (b) CH4 and N2 spectrum peak in L-style inclusion of stage Ⅰ; (c) CO2 and N2 spectrum peak in the V-style inclusion of stage Ⅰ; (d) CO2, CH4 and N2 spectrum peak in the V-style inclusion of stage Ⅰ
4 讨论 4.1 成矿流体性质与演化

成矿期不同阶段热液石英脉中的流体包裹体能够反映成矿流体的性质并反演其演化过程(Ulrich et al., 2001; Yang et al., 2008, 2009a, b; Deng et al., 2003a, 2005, 2009)。杨山庄金矿床成矿期热液石英脉中普遍发育原生包裹体,其中水溶液两相包裹体最常见,还含有少量的纯气相包裹体和CO2三相包裹体,气相包裹体成分组成主要有CH4-N2-CO2、N2-CO2和N2。包裹体均一温度范围主要为120~320℃(图 8),属于中-低温热液的范围。在热液期石英脉中的包裹体中并未发现盐类子矿物,通过计算求得包裹体盐度主要分布在7%~9% NaCleqv之间,为中低盐度。因此杨山庄金矿床成矿流体为中低温、中低盐度的H2O-NaCl-CO2体系。

成矿Ⅰ阶段包裹体均一温度集中在280~320℃,盐度范围5.26%~10.86% NaCleqv,密度范围0.71~0.89g/cm3;Ⅱ阶段均一温度集中在240~280℃,盐度范围4.18%~10.61% NaCleqv,密度范围0.71~0.96g/cm3;Ⅲ阶段均一温度集中在120~160℃,盐度范围3.87%~11.1% NaCleqv,密度范围0.88~1.01g/cm3。从Ⅰ阶段到Ⅲ阶段,均一温度降低,盐度有略微降低的趋势,流体密度略微增大。

4.2 成矿机制

成矿流体中金主要以二硫化物和氯化物的络合物形式迁移(Gammons et al., 1994; Mikucki, 1998; Wang et al., 2015; Yang et al., 2016b, 2017b)。在压力为2000bar,温度200~400℃的中性到弱碱性流体中,金主要以Au(HS)2-形式运移(Benning and Seward, 1996)。杨山庄金矿床成矿温度240~320℃,石英角砾岩型矿石中热液作用形成的绢云母-长石矿物组合指示成矿环境为弱碱性(Mikucki, 1998),因此杨山庄金矿床成矿流体中金以Au(HS)2-形式运移。

成矿流体中Au(HS)2-溶解度降低导致金发生沉淀作用,而Au(HS)2-溶解度与成矿流体中H2S含量密切相关,H2S含量降低可使Au(HS)2-溶解度呈几何倍数降低(Mikucki, 1998)。成矿流体中H2S含量降低主要有两种方式,一种为硫化反应(H2S与围岩内含铁矿物反应生成硫化物),另一种为流体发生沸腾作用,H2S呈气态逃逸(Mikucki, 1998)。杨山庄金矿床赋矿围岩为粉砂质板岩和绢云母板岩,其中广泛发育低变质作用形成了大量含铁绢云母,但围岩中通过硫化作用形成的硫化物并不发育,表明硫化作用对金沉淀贡献不大。采用激光拉曼对单个包裹体气相成分进行分析,并未检测到H2S,刘荫椿(1989)对杨山庄金矿床包裹体进行了群成分分析,在气相成分中也未发现H2S,指示沸腾作用没有产生气相H2S或产生了极少量的气相H2S,因此,沸腾作用使H2S呈气态逃逸也并非矿区内金沉淀的主导成矿机制。

产于中-低变质地体中的脉状金矿床的形成往往与低盐度含CO2和/CH4热液系统有关(Naden and Shepherd, 1989),卢焕章(2008)研究表明当CO2作为缓冲剂时,Au(HS)2-溶解度最大,在成矿流体围岩发生交代发应过程中,流体将发生相分离,分离出富H2O和相对富气相CO2的流体,进而使液相CO2含量降低,引起Au(HS)2-溶解度降低,导致金发生沉淀。杨山庄金矿床流体包裹体气相成分表明,成矿Ⅰ、Ⅱ阶段的CO2含量远高于除H2O之外的其他气体(刘荫椿, 1989),指示成矿流体发生了相分离,产生了大量的气相CO2。因此,杨山庄金矿床主导成矿机制为成矿流体与围岩交代反应而引起的相分离。

5 结论

(1) 杨山庄金矿床成矿期分为三个阶段,Ⅰ阶段特征矿物组合为石英-毒砂-黄铁矿(少量)-自然金-白钨矿-白云石-白云母;Ⅱ阶段特征矿物组合为石英-黄铁矿-毒砂-自然金-黄铜矿-方铅矿-闪锌矿-绢云母;Ⅲ阶段特征矿物组合为石英-方解石,金矿化主要发育在成矿Ⅰ和Ⅱ阶段。

(2) 成矿期石英脉中流体包裹体以两相包裹体为主,含有少量的气相包裹体和含CO2的三相包裹体,气相包裹体成分为CH4-N2-CO2、N2-CO2和N2。成矿温度集中在240~320℃,盐度集中在7%~9% NaCleqv,成矿流体为中低温、中低盐度的H2O-NaCl-CO2体系。

(3) 成矿Ⅰ、Ⅱ阶段,流体与围岩发生交代反应,流体发生相分离,使液相CO2含量降低,引起Au(HS)2-溶解度降低,导致金发生沉淀。

致谢 研究工作得到了中国地质大学(北京)王中亮老师、刘跃博士和郭林楠博士的指导和帮助;野外工作得到了杨山庄金矿床相关工作人员的帮助和支持;流体包裹体测温和激光拉曼测试工作得到了中国地质大学(北京)资源勘查实验室褚海霞博士和刘丽老师的协助;博士生杨镇、张炳林和赛盛勋也参与了部分工作; 在此一并致以诚挚的感谢!
参考文献
[] Benning LG, Seward TM. 1996. Hydrosulphide complexing of Au (Ⅰ) in hydrothermal solutions from 150~400℃ and 500~1500bar. Geochimica et Cosmochimica Acta, 60(11): 1849–1871. DOI:10.1016/0016-7037(96)00061-0
[] Bodnar RJ. 1993. Revised equation and table for determining the freezing point depression of H2O-NaCl solutions. Geochimica et Cosmochimica Acta, 57(3): 683–684. DOI:10.1016/0016-7037(93)90378-A
[] Chen AQ. 2012. Study on mineralization regularity and formation mechanism of scheelite and wolframite in the Woxi Au-Sb-W deposit in Hunan Province. Master Degree Thesis. Beijing:China University of Geosciences, 1-75 (in Chinese with English summary)
[] Deng J, Liu W, Sun ZS, Wang JP, Wang QF, Zhang QX, Wei YG. 2003a. Evidence of mantle-rooted fluids and multi-level circulation ore-forming dynamics:A case study from the Xiadian gold deposit, Shandong Province, China. Science in China (Series D), 46(Suppl.1): 123–134.
[] Deng J, Yang LQ, Sun ZS, Wang JP, Wang QF, Xin HB, Li XJ. 2003b. A metallogenic model of gold deposits of the Jiaodong granite-greenstone belt. Acta Geologica Sinica, 77(4): 537–546.
[] Deng J, Yang LQ, Sun ZS, Wang JP, Wang QF, Cheng XM, Zhou YH. 2005. Late Paleozoic fluid systems and their ore-forming effects in the Yuebei basin, northern Guangdong, China. Acta Geologica Sinica, 79(5): 673–687.
[] Deng J, Wang QF, Yang LQ, Zhou L, Gong QJ, Yuan WM, Xu H, Guo CY, Liu XW. 2008. The structure of ore-controlling strain and stress fields in the Shangzhuang gold deposit in Shandong Province, China. Acta Geologica Sinica, 82(4): 769–780.
[] Deng J, Yang LQ, Gao BF, Sun ZS, Guo CY, Wang QF, Wang JP. 2009. Fluid evolution and metallogenic dynamics during tectonic regime transition:Example from the Jiapigou gold belt in northeast China. Resource Geology, 59(2): 140–152. DOI:10.1111/rge.2009.59.issue-2
[] Deng J, Wang QF, Wan L, Liu H, Yang LQ, Zhang J. 2011. A multifractal analysis of mineralization characteristics of the Dayingezhuang disseminated-veinlet gold deposit in the Jiaodong gold province of China. Ore Geology Reviews, 40(1): 54–64. DOI:10.1016/j.oregeorev.2011.05.001
[] Deng J, Wang QF. 2016. Gold mineralization in China:Metallogenic provinces, deposit types and tectonic framework. Gondwana Research, 36: 219–274. DOI:10.1016/j.gr.2015.10.003
[] Deng J, Liu XF, Wang QF, Dilek Y and Liang YY. 2017a. Isotopic characterization and petrogenetic modeling of Early Cretaceous mafic diking-lithospheric extension in the North China craton, eastern Asia. GSA Bulletin, doi:10.1130/B31609.1
[] Deng J, Wang QF and Li GJ. 2017b. Tectonic evolution, superimposed orogeny, and composite metallogenic system in China. Gondwana Research, doi:10.1016/j.gr.2017.02.005
[] Deng T, Xu DR, Chi GX, Wang ZL, Jiao QQ, Ning JT, Dong GJ, Zou FH. 2017c. Geology, geochronology, geochemistry and ore genesis of the Wangu gold deposit in northeastern Hunan Province, Jiangnan Orogen, South China. Ore Geology Reviews, 88: 619–637. DOI:10.1016/j.oregeorev.2017.01.012
[] Diamond LW. 2001. Review of the systematics of CO2-H2O fluid inclusions. Lithos, 55(1-4): 69–99. DOI:10.1016/S0024-4937(00)00039-6
[] Dong GJ, Xu DR, Wang L, Chen GH, He ZL, Fu GG, Wu J, Wang ZL. 2008. Determination of mineralizing ages on gold ore deposits in the eastern Hunan Province, South China and isotopic tracking on ore-forming fluids-re-discussing gold ore deposit type. Geotectonica et Metallogenia, 32(4): 482–491.
[] Fu ZR, Li ZJ, Zheng DY. 1999. Structural pattern and tectonic evolution of NNE-trending strike-slip orogenic belt in the border region of Hunan and Jiangxi provinces. Earth Science Frontiers, 6(4): 263–272.
[] Gammons CH, Williams-Jones AE, Yu Y. 1994. New data on the stability of gold (Ⅰ) chloride complexes at 300℃. Mineral. Mag., 58A: 309–310. DOI:10.1180/minmag
[] Goldfarb RJ, Santosh M. 2014. The dilemma of the Jiaodong gold deposits:Are they unique?. Geoscience Frontiers, 5(2): 139–153. DOI:10.1016/j.gsf.2013.11.001
[] Han FB, Chang L, Cai MH, Liu SY, Zhang SQ, Chen Y, Peng ZA, Xu M. 2010. Ore-forming epoch of gold deposits in northeastern Hunan. Mineral Deposits, 29(3): 563–571.
[] He ZL, Xu DR, Cheng GH, Xia B, Li PC, Fu GG. 2004. Gold-polymetallic ore-forming geochemistry of Yanshanian intracontinental collision orogen, northeastern Hunan Province. Mineral Deposits, 23(1): 39–51.
[] Huang C, Fan GM, Jiang GL, Luo L, XU ZL. 2012. Structural ore-controlling characteristics and electron spin resonance dating of the Yanlinsi gold deposit in northeastern Hunan Province. Geotectonica et Metallogenia, 36(1): 76–84.
[] Jia BH, Peng HQ. 2005. Precambrian Geology and Mineralization in Northeast Hunan Province. Beijing: Geological Publishing House: 1-144.
[] Li J, Chen BH, An JH, Tan SM, Zhang XG, Yao YJ. 2011. Characteristics of fluid inclusions of the Huangjindong gold deposit, Hunan Province. Geology and Mineral Resources of South China, 27(2): 163–168.
[] Liu YC. 1989. Geochemical signatures of the Huangjindong gold deposit. Geology and Prospecting, 25(11): 43–48.
[] Liu YJ, Sun CY, Cui WD, Ji JF. 1989. Study on the occurrence of gold in arsenopyrite of Huangjindong gold deposit in Hunan Province. Contributions to Geology and Mineral Resources Research, 4(1): 42–49.
[] Liu YJ, Li Y, Qiu DT, Ji JF. 1993. Ore-controlled mechanism and geochemical characteristics of gold-bearing formation in northwest Jiangxi terrain. Science in China (Series B), 36(10): 1263–1275.
[] Lu HZ. 2008. Role of CO2 fluid in the formation of gold deposits:Fluid inclusion evidences. Geochimica, 37(4): 321–328.
[] Luo XL. 1988. On the genesis and metallogenic model of the Huangjindong gold deposit from Hunan. Journal of Guilin College of Geology, 8(3): 225–240.
[] Ma DS, Liu YJ. 1991. Geochemical characteristics and genesis of gold-type gold deposits in Jiangnan metallogenic belt. Science in China (Series B)(4): 424–433.
[] Mao JW. 1997. Geology and Genesis of the Wangu Gold Deposit in Hunan Province, China. Beijing: Atomic Energy Press: 1-33.
[] Mikucki EJ. 1998. Hydrothermal transport and depositional processes in Archean lode-gold systems:A review. Ore Geology Reviews, 13(1-5): 307–321. DOI:10.1016/S0169-1368(97)00025-5
[] Naden J, Shepherd TJ. 1989. Role of methane and carbon dioxide in gold deposition. Nature, 342(6251): 793–795. DOI:10.1038/342793a0
[] Ulrich T, Günther D, Heinrich CA. 2001. The evolution of a porphyry Cu-Au deposit, based on LA-ICP-MS analysis of fluid inclusions:Bajo de la Alumbrera, Argentina. Economic Geology, 96(8): 1743–1774. DOI:10.2113/gsecongeo.96.8.1743
[] Wang ZL, Yang LQ, Guo LN, Marsh E, Wang JP, Liu Y, Zhang C, Li RH, Zhang L, Zheng XL, Zhao RX. 2015. Fluid immiscibility and gold deposition in the Xincheng deposit, Jiaodong Peninsula, China:A fluid inclusion study. Ore Geology Reviews, 65: 701–717. DOI:10.1016/j.oregeorev.2014.06.006
[] Wen ZL, Deng T, Dong GJ, Zou FH, Xu DR, Wang ZL, Lin G, Chen GW. 2016. Characteristics of ore-controlling structures of Wangu gold deposit in northeastern Hunan Province. Geotectonica et Metallogenia, 40(2): 281–294.
[] Wu DS. 1993. Study on ore-controlling conditions of Yangshanzhuang gold deposit in Pingjiang, Hunan Province. Gold Geological Science and Technology(1): 13–17, 67.
[] Xu DR, Wang L, Li PC, Chen GH, He ZL, Fu GG, Wu J. 2009. Petrogenesis of the Lianyunshan granites in northeastern Hunan Province, South China, and its geodynamic implication. Acta Petrologica Sinica, 25(5): 1056–1078.
[] Xu DR, Dong GJ, Deng T, Ning JT, Wang ZL, Zou FH. 2015. Large-scale gold mineralization and geodynamic background in northeast of Hunan Province. Acta Mineralogica Sinica(Suppl): 85.
[] Xu DR, Deng T, Chi GX, Wang ZL, Zou FH, Zhang JL, Zou SH. 2017. Gold mineralization in the Jiangnan Orogenic Belt of South China:Geological, geochemical and geochronological characteristics, ore deposit-type and geodynamic setting. Ore Geology Reviews, 88: 565–618. DOI:10.1016/j.oregeorev.2017.02.004
[] Yang LQ, Deng J, Guo LN, Wang ZL, Li XZ, Li JL. 2006. Origin and evolution of ore fluid, and gold-deposition processes at the giant Taishang gold deposit, Jiaodong Peninsula, eastern China. Ore Geology Reviews, 72: 585–602.
[] Yang LQ, Deng J, Zhang J, Guo CY, Gao BF, Gong QJ, Wang QF, Jiang SQ, Yu HJ. 2008. Decrepitation thermometry and compositions of fluid inclusions of the Damoqujia gold deposit, Jiaodong gold province, China:Implications for metallogeny and exploration. Journal of China University of Geosciences, 19(4): 378–390. DOI:10.1016/S1002-0705(08)60071-0
[] Yang LQ, Deng J, Li N, Guo CY. 2009a. Geology, geochemistry of ore-forming fluids and hydrothermal alteration dynamics of the Zhaoping gold belt in northwestern Jiaodong Peninsula, eastern China. Geochimica et Cosmochimica Acta, 73(Suppl): A1477.
[] Yang LQ, Deng J, Guo CY, Zhang J, Jiang SQ, Gao BF, Gong QJ, Wang QF. 2009b. Ore-forming fluid characteristics of the Dayingezhuang gold deposit, Jiaodong gold province, China. Resource Geology, 59(2): 181–193. DOI:10.1111/rge.2009.59.issue-2
[] Yang LQ, Deng J, Guo RP, Guo LN, Wang ZL, Cheng BH, Wang BH, Wang XD. 2016a. World-class Xincheng gold deposit:An example from the giant Jiaodong gold province. Geoscience Frontiers, 7(3): 419–430. DOI:10.1016/j.gsf.2015.08.006
[] Yang LQ, Deng J, Wang ZL, Guo LN, Li RH, Groves DI, Danyushevsky LV, Zhang C, Zheng XL, Zhao H. 2016b. Relationships between gold and pyrite at the Xincheng gold deposit, Jiaodong Peninsula, China:Implications for gold source and deposition in a brittle epizonal environment. Economic Geology, 111(1): 105–126. DOI:10.2113/econgeo.111.1.105
[] Yang LQ, Deng J, Li N, Zhang C, Ji XZ, Yu JY. 2016c. Isotopic characteristics of gold deposits in the Yangshan Gold Belt, West Qinling, Central China:Implications for fluid and metal sources and ore genesis. Journal of Geochemical Exploration, 168: 103–118. DOI:10.1016/j.gexplo.2016.06.006
[] Yang LQ, Gao X and Shu QH. 2017a. Multiple mesozoic porphyry-skarn Cu (Mo-W) systems in Yidun Terrane, East Tethys:Constraints from zircon U-Pb and molybdenite Re-Os geochronology. Ore Geology Reviews, doi:10.1016/j.oregeorev.2017.01.030
[] Yang LQ, Guo LN, Wang ZL, Zhao RX, Song MC, Zheng XL. 2017b. Timing and mechanism of gold mineralization at the Wang'ershan gold deposit, Jiaodong Peninsula, eastern China. Ore Geology Reviews, 88: 491–510. DOI:10.1016/j.oregeorev.2016.06.027
[] Ye CQ, Dai WJ, Liu YC, Han XJ. 1988. Discussion on the origin and prospecting significance of Huangjindong gold deposit. Gold Geology(2): 24–36.
[] 陈爱清. 2012. 湖南沃溪Au-Sb-W矿床中白钨矿与黑钨矿的成矿规律及成因机制的研究. 硕士学位论文. 北京: 中国地质大学, 1-75 http://cdmd.cnki.com.cn/Article/CDMD-11415-1012365223.htm
[] 董国军, 许德如, 王力, 陈广浩, 贺转利, 符巩固, 吴俊, 王智琳. 2008. 湘东地区金矿床矿化年龄的测定及含矿流体来源的示踪——兼论矿床成因类型. 大地构造与成矿学, 32(4): 482–491.
[] 傅昭仁, 李紫金, 郑大瑜. 1999. 湘赣边区NNE向走滑造山带构造发展样式. 地学前缘, 6(4): 263–272.
[] 韩凤彬, 常亮, 蔡明海, 刘孙泱, 张诗启, 陈艳, 彭振安, 徐明. 2010. 湘东北地区金矿成矿时代研究. 矿床地质, 29(3): 563–571.
[] 贺转利, 许德如, 陈广浩, 夏斌, 李鹏春, 符巩固. 2004. 湘东北燕山期陆内碰撞造山带金多金属成矿地球化学. 矿床地质, 23(1): 39–51.
[] 黄诚, 樊光明, 姜高磊, 罗亮, 徐增连. 2012. 湘东北雁林寺金矿构造控矿特征及金成矿ESR测年. 大地构造与成矿, 36(1): 76–84.
[] 贾宝华, 彭和求. 2005. 湘东北前寒武纪地质与成矿. 北京: 地质出版社: 1-140.
[] 李杰, 陈必河, 安江华, 谭仕敏, 张孝国, 姚宇军. 2011. 湖南黄金洞金矿成矿流体包裹体特征. 华南地质与矿产, 27(2): 163–168.
[] 刘荫椿. 1989. 黄金洞金矿床地球化学特征. 地质与勘探, 25(11): 43–48.
[] 刘英俊, 孙承辕, 崔卫东, 季峻峰. 1989. 湖南黄金洞金矿床毒砂中金的赋存状态的研究. 地质找矿论丛, 4(1): 42–49.
[] 卢焕章. 2008. CO2流体与金矿化:流体包裹体的证据. 地球化学, 37(4): 321–328.
[] 罗献林. 1988. 论湖南黄金洞金矿床的成因及成矿模式. 桂林冶金地质学院学报, 8(3): 225–240.
[] 马东升, 刘英俊. 1991. 江南金成矿带层控金矿的地球化学特征和成因研究. 中国科学(B辑)(4): 424–433.
[] 毛景文. 1997. 湖南万古地区金矿地质与成因. 北京: 原子能出版社: 1-33.
[] 文志林, 邓腾, 董国军, 邹凤辉, 许德如, 王智琳, 林舸, 陈根文. 2016. 湘东北万古金矿床控矿构造特征与控矿规律研究. 大地构造与成矿学, 40(2): 281–294.
[] 伍德胜. 1993. 湖南平江杨山庄金矿床控矿条件的初步研究. 黄金地质科技(1): 13–17, 67.
[] 许德如, 王力, 李鹏春, 陈广浩, 贺转利, 符巩固, 吴俊. 2009. 湘东北地区连云山花岗岩的成因及地球动力学暗示. 岩石学报, 25(5): 1056–1078.
[] 许德如, 董国军, 邓腾, 宁钧陶, 王智琳, 邹凤辉. 2015. 湘东北地区大规模金成矿作用及地球动力学背景. 矿物学报(增刊): 85.
[] 叶传庆, 戴文剑, 刘荫椿, 韩秀军. 1988. 试论黄金洞金矿床成因及找矿意义. 黄金地质科技,(2): 24–36.