Dating of Early Jurassic volcanic rocks in the Mohe foreland basin of northern Greater Khingan Mountains, northeast China
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摘要:
黑龙江省大兴安岭地区大面积分布的中基性火山岩的时代厘定对研究大兴安岭中生代火山岩带的构造演化及地层划分具有重要意义。本次基于开展的黑龙江省盘古林场幅、布鲁克里河幅1∶5万区域地质矿产调查项目,对该区原划为中—晚侏罗世塔木兰沟组的中基性火山岩进行了系统的LA-ICP-MS锆石U-Pb年代学、岩石学、岩石地球化学等方面研究。其中2件粗安岩年龄分别为(185.8±8.1)Ma、(196.8±2.1)Ma,玄武安山岩年龄为(196.3±2.7)Ma,时代为早侏罗世,表明在塔木兰沟组中存在一套早侏罗世中基性火山岩。通过岩石地球化学研究表明,该套中基性火山岩总体属于准铝质,以高钾钙碱性-钙碱性系列为主,显示富集Ba、K、La、Ce、Sr、Zr等大离子亲石元素和轻稀土元素,亏损Th、Nb、P、Zr、Ti等高场强元素和重稀土元素特征。认为该套早侏罗世中基性火山岩的形成与蒙古—鄂霍茨克洋板块向额尔古纳地块下的俯冲作用关系密切,构造环境为活动陆缘环境。
Abstract:Intermediate-basic volcanic rocks are largely distributed in Greater Khingan Mountains of Heilongjiang Province, and the determination of their ages is of great significance to understanding the regional tectonic evolution and petrogenesis of the Mesozoic volcanic belt in the Great Xing'an Range. Based on the 1:50000 regional geological and mineral resources survey in the study area, the LA-ICP-MS zircon U-Pb geochronology, petrology and petrogeochemistry of the intermediate-basic volcanic rocks previously attributed into the Middle-Late Jurassic Tamulangou Formation were systematically studied. Zircon U-Pb dating of the two trachyandesite samples and one basaltic andesite sample yields (185.8±8.1)Ma, (196.8±2.1)Ma and (196.3±2.7)Ma respectively, which indicates that there exists a set of early Jurassic intermediate-basic volcanic rocks in the Tamulangou Formation. These Early Jurassic volcanic rocks belong to metaluminous, mainly high-K calc-alkaline series generally enriched in large ion lithophile elements (such as Ba、K、La、Ce、Sr、Zr) and LREE, but depleted in high field strength elements (such as Th、Nb、P、Zr、Ti) and HREE. Combined with the regional tectonic evolution, it is conclude that the early Jurassic intermediate-basic volcanic rocks were formed in an active continental margin setting related to the southward subduction of the Mongol-Okhotsk oceanic plate beneath the Erguna Massif during the Early Jurassic.
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1. 引言
造山型金矿床作为重要的金矿床类型,其占世界黄金资源的30%以上(Groves et al., 1988)。造山带中形成的造山型金矿床主要位于由挤压或走滑变形中应力相对低的区域,如次级断裂构造中(McCuaig et al., 1988)。大多数造山型金矿床是在绿片岩相变质条件下形成的(Goldfarb et al., 2001, 2015; Deng and Wang, 2016)。造山型金矿的成矿流体和金的来源是至今尚未解决的问题(卢焕章等, 2018)。一般认为成矿流体中的Au(HS)2-络合物是金元素运输及富集的载体(McCuaig et al., 1988)。金成矿流体来源多样,包括:(1)岩石变质作用(Groves et al., 2003); (2)含碳沉积物(Large et al., 2011); (3)岩浆热液(Tomkins et al., 2013); (4)海水(Chang et al., 2008); (5)变质脱水(Phillips and Powell, 2009, 2010)。事实上各个时代的大多数造山型金矿床的成矿流体具有盐度低(≤10%NaCleqv),高碳(CO2 + CH4含量为5%~30%),低Cl和高S含量等特征(卢焕章等, 2018)。而造山型金矿床成矿流体的一致性,说明它们可能来自相同或者是多阶段形成的热液流体(卢焕章, 1991;卢焕章和池国祥, 1995)。此外,造山型金矿的成矿时代也是其研究的热点,争论的焦点主要在于是形成于变质峰期前(Phillips and Powell, 2009, 2010;Tomkins, 2010)还是变质峰期与峰期后(Groves et al., 1998;Goldfarb et al., 2005)。前者主要认为造山带在抬升剥蚀过程中,变质峰期与地壳的深度有关,即越深则达到峰期的时间越晚,且也可能受到之后变质作用的叠加,从而表现出成矿时代比围岩变质时期晚(Phillips and Powell, 2010)。后者则基于造山型金矿的成矿时代统计(Knight et al., 1993, 2000;Dziggel et al., 2010;Kolb et al., 2015),并结合变质时代、蚀变特征、穿切关系等。同时,前人研究发现这些造山型金矿的成矿峰期与陆壳增生速率的峰期和超大陆拼合峰期吻合较好(Goldfarb et al., 2001)。
造山型金矿床也是中国重要的黄金来源,广泛分布于天山造山带(Chen et al., 2012),哀牢山构造带(Zhang et al., 2018),华北克拉通北缘(Hart et al., 2002)和中国西北的造山带(Mao et al., 2000; Zhang et al., 2009;李猛等,2020)。柴达木盆地北缘(简称柴北缘)造山带是中国西北部的重要的造山带之一,含有一系列Au、Cu、Pb和Zn矿床(Zhang et al., 2009)。本区是中国重要的金成矿带,目前发现9个金矿床,金矿化点十余处,远景资源量在300 t以上。前人研究认为这些金矿与造山作用密切相关,但缺乏系统性总结,从而限制了我们对柴北缘造山型金矿的理解。本文在前人研究和最新地质资料的基础上,对柴北缘造山型金矿进行初步探讨,希望能够对柴北缘造山型金矿的找矿工作有所启迪。
2. 地质背景
柴北缘造山带整体走向为西北-东南,长约900 km,宽25~160 km(图 1)。北邻祁连造山带,南接柴达木地块(柴达木盆地)(Song et al., 2014; 蔡鹏捷等,2019)。欧龙布鲁克—牦牛山断裂将柴北缘从欧龙布鲁克地块向北分离(Chen et al., 2009)。在其西北端,造山带被阿尔金断裂切割(Wittlinger et al., 1998)。前人研究表明,柴达木盆地北部在早奥陶世发生俯冲,与祁连地块的碰撞发生在晚奥陶世到中泥盆世(Yang, 2002; 蔡鹏捷等, 2018)。
1—胜利沟金矿;2—野骆驼泉金矿;3—千枚岭金矿;4—红柳沟金矿;5—青龙沟金矿;6—滩间山金矿;7—鱼卡金矿;8—双口山金矿;9—赛坝沟金矿Figure 1. Schematic map showing the major tectonic units in northwest China (a, modified from Song et al., 2013) and simplified map showing the tectonic framework of the northern Qaidam(b, modified from Zhang et al., 2009)1-Shengligou gold deposit; 2-Yeluotuoquan gold deposit; 3-Qianmeiling gold deposit; 4-Hongliugou gold deposit; 5-Qinglonggou gold deposit; 6-Tanjianshan gold deposit; 7-Yuka gold deposit; 8-Shuangkoushan gold deposit; 9-Saibagou gold deposit柴北缘的主要岩石地层单位包括古元古界达肯大板岩群、中—新元古界鱼卡河岩群、滩间山岩群和下古生界弧相关的火山和沉积岩(Zhang et al., 2017a, b)。柴北缘作为著名的超高压变质带,前人通过对高压/超高压变质岩(榴辉岩和片麻岩)和花岗岩的地质年代学和地球化学研究,建立了一个大陆碰撞造山带从早期海底俯冲(>440 Ma)、大陆俯冲和碰撞(440~ 420 Ma)、俯冲板块的剥露(420~390 Ma)和最终造山带崩塌(390~360 Ma)的演化模型(Song et al., 2014;张建新等, 2015;Zhang et al., 2017a, b)。
3. 柴北缘造山型金矿床地质概况
俯冲相关增生造山作用的成矿模型预测,柴北缘有利于造山型成矿(Goldfarb et al., 2001, 2015; Deng and Wang, 2016)。柴北缘造山带已发现大量的造山型金矿床,包括胜利沟、野骆驼泉、千枚岭、红柳沟、青龙沟、滩间山、赛坝沟、鱼卡和双口山,以蚀变岩型和石英脉型为主(国家辉, 1998;张德军, 2001, 2005, 2007a, 2007b;Zhang et al., 2009;范贤斌, 2017;孟和, 2017;蔡鹏捷等, 2018)。
柴北缘造山型金矿的地质特征见表 1。总体上,柴北缘的造山带金矿体主要赋存于中元古界、寒武系和奥陶系低品位变质岩发育的剪切带中(Deng and Wang, 2016)。其中胜利沟、野骆驼泉、千枚岭、红柳沟、鱼卡和双口山金矿主要产于寒武—奥陶系滩间山群,青龙沟和滩间山金矿产于中元古界万洞沟群,赛坝沟金矿的赋矿围岩为中粗粒花岗闪长岩-英云闪长岩。基本上所有金矿的围岩蚀变包括硅化、绿泥石化、绢云母化,部分还有碳酸盐化(千枚岭、红柳沟、滩间山、鱼卡、双口山),黄铁绢英岩化(赛坝沟金矿)。多数金矿体的展布与NW向的韧性剪切或断层破碎带相关,少数还与次级构造有关(野骆驼泉、千枚岭、青龙沟、滩间山、双口山)。矿石构造大部分为浸染状、细脉浸染状,部分可见团块状矿石(滩间山和鱼卡)。这些金矿的元素组合均表现为Au-As。
Table 1. Geological characteristics of the orogenic gold deposits in Northern Qaidam4. 金矿成矿温度特征
对柴北缘造山型金矿与成矿相关的流体包裹体均一温度、冰点、盐度等进行统计(表 2,图 2):野骆驼泉(CO2-H2O型:峰值177~261℃和270~341℃,盐度为1.6%~8.9%;H2O-NaCl型:119~437℃,冰点为-7.8~-0.9℃,盐度为1.6%~11.4%)(张德全等, 2001)、滩间山(CO2-H2O型:峰值在186~250℃和280~296℃,盐度为1.4%~7.9%;H2O-NaCl型:121~ 449℃,冰点为-7.0~-0.9℃,盐度为1.6%~10.5%) (张德全等, 2001)、千枚岭(CO2-H2O型:峰值191~ 243℃,299℃,盐度为2.4%~7.3%;H2O-NaCl型:124~358℃,冰点-6.9~-1.5℃,盐度为2.6%~10.3%) (张德全等, 2001)、青龙沟(CO2- H2O型:200~ 245℃,293~299℃,盐度为1.8%~8.3%;H2O-NaCl型:129~418℃,冰点为-6.0~-0.7℃,盐度为1.2%~ 9.2%)(张德全等, 2001)、红柳沟(CO2-H2O型:213~ 245℃,295℃,盐度为2.4%~8.1%;H2O-NaCl型:129~420℃,冰点为- 5.9~- 1.2℃,盐度为2.1% ~ 9.1%)(张德全等, 2001)、鱼卡(CO2-H2O型:193~ 249℃;H2O- NaCl型:188~285℃,冰点为- 7.5~-0.7℃,盐度为1.22%~11.10%)(范贤斌, 2017;蔡鹏捷, 2018)、双口山(CO2-H2O型:252~290℃,320~ 358℃;H2O-NaCl型:161~365.6℃,冰点为-5.6~ -3.0℃,盐度为1.91%~14.25%)(孟和, 2017)、胜利沟(H2O- NaCl型:120~209℃,206~385℃,冰点为-9.7~-1.8℃,盐度为3.06%~13.62%)(黄亚, 2013)。
Table 2. Temperature measurement data of fluid inclusions of orogenic gold deposits in the northern Qaidam (datas from Zhang et al., 2001; Huang, 2013; Fan, 2017; Meng, 2017; Cai et al., 2018)Figure 2. Histogram showing homogenization temperature of fluid inclusions of the orogenic gold deposits in the northern Qaidam (after Zhang et al., 2001; Huang, 2013; Fan, 2017; Meng, 2017; Cai et al., 2018c)不难看出,成矿流体的均一在各个矿床之间存在一定的差异。这种差异应该是与成矿作用时的压力-温度不同有关,也与围岩的组成有关。但这些矿床的成矿温度还是在200~400℃,仅有几十度的差别,均在造山型金矿的成矿温度(卢焕章等, 2018)。大部分矿床(点) 中呈双峰态分布, 只有少部分矿床(点)中呈单峰态分布。张德全(2007)对柴北缘—东昆仑金矿流体包裹体研究认为,这可能与不同造山时期的成矿作用有关,且对应了低盐度的H2O-CO2-NaCl-CH4(晚加里东碰撞造山期)和H2O-CO2-NaCl±CH4(晚华力西—印支碰撞造山期)两种不同的成矿流体。
一般认为金成矿具有多个成矿阶段, 从早期的高温阶段到后期的低温阶段(卢焕章等, 2018)。金矿化主要包含了4个阶段:①乳白色石英黄铁矿阶段;②含金石英黄铁矿阶段;③含金多金属硫化物石英阶段;④碳酸盐阶段(卢焕章等, 2018)。前人对柴北缘造山型金矿流体包裹体的研究主要针对与金矿的成矿流体相关第二和第三阶段。对柴北缘造山型金矿的流体包裹体显微观察,均发现有富CO2型、含CO2水溶液型(CO2-H2O型)和水溶液型(H2O-NaCl型) 三类,这与典型的造山型金矿中流体包裹体类型是一致的(Groves et al., 1998; Kerrich et al., 2000; Hagemann and Cassidy, 2000; 陈衍景等, 2007)。
5. 金成矿流体与物质来源
5.1 氢、氧同位素特征
利用与成矿相关的氢、氧同位素,能够有效地揭示成矿流体的来源,区分其来源岩浆水、变质水或大气降水,从而有助于判别流体的演化轨迹和矿床成因(杨利亚等, 2013)。造山型金矿的成矿流体往往经历了长距离迁移,其氢、氧同位素组成除了反映源区性质之外,可能表征沿着流体通道的水/岩反应、源区和围岩或后期流体的混合特征(Ridley and Diamond, 2000; Beaudoin and Pitre, 2005; 蔡鹏捷, 2019)。
柴北缘造山型金矿成矿流体中δ18OH2O-SNOW = -1.7‰ ~ 10.31‰和δDV- SMOW = -113.8 ‰~ -41.6 ‰ (表 3,图 3),其中滩间山金矿δ18OH2O-SNOW = 9.15‰ ~ 10.31‰,δDV-SMOW=-69.9‰ ~ -50‰;青龙沟金矿δ18OH2O - SNOW =- 1.7‰ ~ 5.5‰,δDV- SMOW=- 95.1‰ ~ -71.4‰;鱼卡金矿δ18OH2O-SNOW =5.2‰ ~ 6.01‰,δDV-SMOW=-58.5‰ ~-41.6‰;双口山金矿δ18OH2O-SNOW = 5.75‰ ~ 6.45‰,δDV-SMOW=-113.8‰ ~ -99.8‰。柴北缘这些金矿的H-O同位素特征,是无法用单一大气水或原生岩浆水的参与解释,只有是在复杂的造山过程中变质流体受到岩浆水及大气水等共同作用所导致。从图 3也可见,整个柴北缘金矿的H-O同位素基本上也与华北克拉通北缘、小秦岭、西秦岭、东昆仑等造山带中的造山型金矿范围重叠。
表 3 柴北缘造山型金矿H-O同位素Table 3. δ18O and δD values of the orogenic gold deposits in the northern Qaidam图 3 柴北缘造山型金矿δD与δ18Owater比值图(底图据Deng and Wang, 2016)1—双口山金矿;2—滩间山金矿;3—青龙沟金矿;4—鱼卡金矿Figure 3. δD (‰) vs. δ18Owater (‰) diagram of the orogenic gold deposits in the northern Qaidam (modified from Deng and Wang, 2016)1-Shuangkoushan gold deposit; 2-Tanjianshan gold deposit; 3- Qinglonggou gold deposit; 4-Yuka gold deposit5.2 硫、铅同位素特征
硫化物的硫同位素组成对于追踪成矿物质来源和约束成矿过程是非常有效的(Hodkiewicz et al., 2009)。柴北缘金矿中含金黄铁矿的δ34S在0.5‰~ 11‰,主要集中在5‰~9‰(表 4,图 4),其中滩间山金矿δ34S为5.31‰~8.54‰;青龙沟金矿δ34S为5.0‰ ~11.0‰;鱼卡金矿δ34S为0.5‰~7.4‰;双口山金矿δ34S为6.0‰ ~10.0‰;红柳沟金矿δ34S为3.9‰ ~4.4‰。总体柴北缘金矿黄铁矿的δ34S与金矿类型进行对比,主要落在造山型金矿和卡林型金矿范围内,源区特征主要落在变质岩类型的范围内(图 4),推测成矿流体在上升过程中与通道围岩发生水-岩作用而产生的混合硫,总体上指示了带内的金矿应属于造山型金矿。
表 4 柴北缘造山型金矿S同位素特征Table 4. Analytical results of S isotope of the orogenic gold deposits in Northern Qaidam图 4 柴北缘造山型金矿与其他类型S同位素对比(据Deng and Wang, 2016修改)Figure 4. Comparison of S isotopes between orogenic gold deposits in the northern margin of Qaidam and other types of gold deposits矿石的铅同位素同样是一类对成矿来源的有效示踪工具(Doe and Stacey, 1974; Zartman and Doe, 1981)。柴北缘金矿中黄铁矿或共生方铅矿的206Pb/204Pb为18.238~19.296,207Pb/204Pb为15.547~ 15.773,208Pb/204Pb为37.918~38.978,∆β为14.15~ 29.79,∆γ为11.95~51.92(表 5)。其中胜利沟金矿中方铅矿的206Pb/204Pb为18.300~18.374,207Pb/204Pb为15.602~15.688,208Pb/204Pb为38.054~38.346,∆β为14.15~20.28,∆γ为11.95~18.38(表 5);滩间山金矿中黄铁矿的206Pb/204Pb为18.476~19.296,207Pb/204Pb为15.547~15.641,208Pb/204Pb为37.918~38.211,∆β为18.55~24.41,∆γ为28.66~36.42(表 5);鱼卡金矿中黄铁矿的206Pb/204Pb为18.238~18.62,207Pb/204Pb为15.59~ 15.618,208Pb/204Pb为38.039~38.775,∆β为16.96~ 18.78,∆γ为15.29~34.82(表 5);双口山金矿中方铅矿的206Pb/204Pb为18.437~18.567,207Pb/204Pb为15.617~ 15.773,208Pb/204Pb为38.466~38.978,∆β为15.33~ 29.79,∆γ为32.26~51.92,黄铁矿的206Pb/204Pb为18.435~18.460,207Pb/204Pb为15.604~15.634,208Pb/204Pb为38.431~38.531,∆β为18.24~20.91,∆γ为26.03~ 30.10(表 5)。柴北缘金矿含金矿物的Pb同位素投点可见主要落在了上地壳和造山带演化线之间(图 5),这些Pb同位素特征说明柴北缘金矿的成矿物质大多来源于地幔—上地壳的混合作用(图 6),且一定程度上受到了岩浆作用的影响,也指示了其应该与造山作用相关。
表 5 柴北缘造山型金矿Pb同位素特征Table 5. Pb-isotpic compositions and characteristic parameters of orgen gold deposits in the northern Qaidam图 5 柴北缘造山型金矿Pb同位素构造图解(底图据Zartman and Doe, 1981)1—双口山金矿;2—滩间山金矿;3—胜利沟金矿;4—鱼卡金矿Figure 5. Pb isotope diagrams of the orogenic gold deposits in the northern Qaidam (basic diagram modified from Zartman and Doe, 1981)Pb isotope diagrams of the orogenic gold deposits in the northern Qaidam (basic diagram modified from Zartman and Doe, 1981)图 6 柴北缘造山型金矿Pb同位素Δβ-Δγ图解(底图据朱炳泉等, 1998)1—地幔源Pb; 2—上地壳源Pb; 3—上地壳与地幔混合的俯冲带Pb (3a—岩浆作用; 3b—沉积作用); 4—化学沉积型Pb; 5—海底热水作用Pb; 6—中深变质作用Pb; 7—深变质下地壳Pb; 8—造山带Pb; 9—古老页岩上地壳Pb; 10—退变质作用Pb;11—双口山金矿;12—滩间山金矿;13—胜利沟金矿;14—鱼卡金矿Figure 6. Pb isotope Δβ-Δγ diagram of the orogenic gold deposits in the northern Qaidam (basic diagram modified from Zhu et al., 1998)1- mantle lead; 2-upper crust lead; 3- subduction zone lead mixed with upper crust and mantle(3a -magmatism; 3b- deposition); 4- chemical deposition lead; 5- submarine hot water lead; 6-mesometamorphism lead; 7- katametamorphism lower crust lead; 8-orogenic belt lead; 9- ancient shale upper crust lead; 10- retrograde metamorphism lead; 11-Shuangkoushan gold deposit; 12-Tanjianshan gold deposit; 13-Shengligou gold deposit; 14-Yuka gold deposit6. 柴北缘造山型金成矿时代
前人对柴北缘构造带中的金矿相关的成岩成矿时代进行了厘定(表 6):野骆驼泉金矿成矿时代为(246.0±3.0)Ma(张德全等, 2005);青龙沟金矿成矿时代为(409.4±2.3)Ma(张德全等, 2005)、(410.3± 5.8)Ma(张德全等, 2005)、274.6 Ma(林文山等, 2006);滩间山金矿成矿时代为409.4 Ma(张德全等., 2001)、401 Ma(张德全等, 2001)、(394±6)Ma (Li, 2011)、385.8 Ma(崔艳合等, 2000)、(356±2.8) Ma(贾群子等, 2013)、(350.4 ± 3.2)Ma(张博文, 2010)、(344.7±2)Ma(李世金, 2011)、(344±2.2)Ma(张博文, 2010)、(330±24.3)Ma(张德全等, 2001)、(288.9±7.3)Ma(崔艳合等, 2000)、(289.6±6)Ma(崔艳合等, 2000)、288 Ma(Zhang et al., 2009)、(284.04±2.95)Ma(张德全等, 2005)、284 Ma(张德全等, 2005)、(275.9 ± 7.2)Ma(崔艳合等, 2000)、(268.94 ± 4.31)Ma(崔艳合等, 2000)、268.9 Ma (Zhang et al., 2009)、209 Ma(国家辉, 1998);鱼卡金矿成矿时代为(376.9±4.0)Ma、(387.5±7.2)Ma(范贤斌, 2017);双口山金矿成矿时代为(357.7±5.28)Ma (孟和, 2017);赛坝沟金矿成矿时代为(425.5±2.1) Ma(丰成友等, 2002)、(426±2)Ma(张德全等, 2005)、(210±3)Ma(丰成友等, 2002)。上述成矿时代指示了柴北缘造带中的金矿大多与复合造山过程有关。
表 6 柴北缘造山型金矿相关成岩与成矿时间Table 6. Diagenetic and metallogenic ages of orogenic gold deposits in the northern Qaidam将柴北缘金矿成矿时期与岩浆活动和构造运动分期进行对比(图 7),综合前人研究,可见寒武—奥陶纪时期,柴北缘的洋盆逐渐关闭,洋壳俯冲导致岛弧火山岩(滩间山岩群)的形成,洋壳俯冲结束后,柴达木地块与欧龙布鲁克微陆块开始碰撞,形成了加里东期的柴北缘碰撞造山带(赵志新,2018),造山期后的一系列岩浆活动奠定了柴北缘造山型金矿形成的基础(张德全等, 2001, 2005;Zhang et al., 2009)。整个柴北缘造山型金矿的成矿期主要集中在426~376 Ma、357~330 Ma和288~246 Ma三个时期。第一个成矿期与区域的加里东期碰撞造山过程相关,第二成矿期与陆内裂解的岩浆活动有关,第三成矿期则与晚华力西—印支期造山过程有关。其中加里东晚期,柴达木陆块向祁连陆块的俯冲由正向俯冲变成斜向俯冲,导致区域上形成了一条右行剪切走滑构造带,同时柴北缘这种应力的转变也进一步促进了岩浆活动的加剧及地层的褶皱变形,从而导致成矿热液流体沿原有构造体系发生叠加富集(丰成友等, 2002; 张德全等, 2005)。从时间上,不难看出,第一时期是属于柴北缘超高压变质峰期之后,该期矿床成矿时代的差异应该是所处不同位置及成矿深度导致。第二成矿期属于柴北缘碰撞造山后地壳增厚后减薄时期,岩浆活动对金矿的进一步富化。第三成矿期则是古特提斯洋的开合导致该区新的造山活动,热液与岩浆新的叠加作用。事实上,一般认为挤压或者从伸展到挤压的转换阶段,才是造山型金矿最有利的形成时期(王庆飞等,2019)。柴北缘大部分的造山型金矿都属于一次造山作用的产物,而带内滩间山、青龙沟、塞巴沟等经历了两期以上,其中滩间山金矿的三期复合成矿作用可能是导致其成为柴北缘最大金矿的原因。
图 7 柴北缘构造事件、岩浆活动与金矿成矿时代耦合图(据赵志新,2018修改)1—青龙沟金矿;2—滩间山金矿;3—鱼卡金矿;4—双口山金矿;5—赛坝沟金矿;6—野骆驼泉金矿;7—镁质钙性-钙碱性花岗岩;8—钙碱性花岗岩;9—钙碱-碱钙性花岗岩;10—钙碱花岗岩、拉斑质基性岩;11—碱性花岗岩Figure 7. Coupling diagram showing tectonic event, magmatic activity and metallogenic age of gold deposits in the northern Qaidam (modified from Zhao Zhixin, 2018)1-Qinglonggou gold deposit; 2-Tanjianshan gold deposit; 3-Yuka gold deposit; 4-Shuangkoushan gold deposit; 5-Saibagou gold deposit; 6- Yeluotuoquan gold deposit; 7-Magnesian calc alkaline granite; 8-Calc alkaline granite; 9-Calc alkaline- alkali calcium granite; 10-Calc alkaline granite, tholeiitic basic rock; 11-Alkaline granite7. 结论
(1) 柴北缘造山型金矿主要赋存在中元古代、寒武系和奥陶系低品位变质岩发育的剪切带中,且多数矿体的展布与NW向的构造相关。
(2) 柴北缘造山型金矿大部分矿床(点) 成矿温度呈双峰态分布, 只有少部分矿床(点)中呈单峰态分布,指示了受到多期流体作用。
(3) 柴北缘造山型金矿的成矿流体中δ18OH2O-SMOW=-1.7‰ ~ 10.31‰和δDV-SMOW = -113.8 ‰ ~ -41.6 ‰,指示其变质流体受到岩浆水及大气水等共同作用。含金硫化物(黄铁和方铅矿)的δ34S在0.5‰ ~11‰,主要集中在5‰ ~9‰,206Pb/204Pb为18.238~19.296,207Pb/204Pb为15.547~15.773,208Pb/204Pb为37.918~38.978,指示了成矿物质来源于地幔-上地壳,且一定程度上都受到了岩浆作用的影响。
(4)柴北缘的复合造山运动导致造山型金矿存在(426~376)Ma、(357~330)Ma和(288~246)Ma三个成矿期。
致谢: 感谢黑龙江省地球物理地球化学勘查院张树岐等为本文提供资料;同时感谢匿名审稿人和编辑部老师在成稿过程中提出的宝贵意见。 -
图 1 中国东北大地构造略图(a)、大兴安岭地区构造分区图(b)和研究区地质简图(c)(a, b据刘晨等, 2017)
1—第四系沉积物;2—新生代火山岩;3—中生代火山岩;4—古生代火山岩;5—前寒武纪火山岩;6—燕山期花岗岩;7—印支期花岗岩;8—海西期花岗岩;9—加里东期花岗岩;10—断裂或缝合带;11—国界线;12—下白垩统光华组;13—下侏罗统塔木兰沟组;14—上侏罗统秀峰组;15—早白垩世次火山岩;16—采样位置及年龄
Figure 1. Tectonic subdivisions of northeast China(a)、tectonic map of Greater Khingan (b) and simplified geological map of the study area (c)(a, b modified from Liu Chen et al., 2017)
图 5 塔木兰沟组火山岩TAS岩石化学图解(a)、K2O-SiO2图解(b)、K2O-Na2O图解(c)和A/NK-A/CNK图解(d)(据Peccerillo & Taylor, 1976)
Figure 5. Diagrams of TAS (a)、K2O-SiO2 (b)、K2O-Na2O (c) and A/NK-A/CNK (d) of volcanic rocks in the Tamulangou Formation(after Peccerillo & Taylor, 1976)
图 6 塔木兰沟组火山岩稀土微量配分图(球粒陨石和原始地幔标准化值据Sun & McDonough, 1989)
Figure 6. Chondrite-normalized REE patterns and primitive mantle-normalized trace element patterns of the Tamulangou Formation volcanic rocks (Chondrite and primitive mantle values referring to Sun & McDonough, 1989)
图 7 塔木兰沟组火山岩构造环境判别图Rb-(Y+Nb)图解(a)、Ta-Yb图解(b)、Th/Yb-Ta/Yb图解(c)和Th/Yb-Sr/Nd图解(据Pearce et al., 1984;Labanieh et al., 2012)
CA—钙碱性系列;SHO—橄榄玄武质;TH—拉班系列;E—MORB-富集大洋玄武岩;N-MORB—正常大洋玄武岩;OIB—洋岛玄武岩;PM—原始地幔
Figure 7. Rb-(Y+Nb) (a)、Ta-Yb(b)、Th/Yb-Ta/Yb (c) and Th/Yb-Sr/Nd (d) diagram showing discrimination of tectonic environment of the Tamulangou Formation volcanic rocks(after Pearce et al., 1984; Labanieh et al., 2012)
CA-Calc-alkaline; SHO-Shoshonitic basalt; TH-Tholeiitic; E-MORB-Enriched mid ocean ridge basalt; N-MORB-Normal mid ocean ridge basalt; OIB-Ocean island basalt; PM-Primitive Mantle
表 1 粗安岩锆石U-Pb同位素LA-ICP-MS测试结果(D0001)
Table 1 LA-ICP-MS U-Pb dating results of zircons from the trachyandesite in the study area (D0001)
表 2 玄武安山岩锆石U-Pb同位素LA-ICP-MS测试结果(D0007)
Table 2 LA-ICP-MS U-Pb dating results of zircons from the basalt andesite in the study area (D0007)
表 3 粗安岩锆石U-Pb同位素LA-ICP-MS测试结果(D6395)
Table 3 LA-ICP-MS U-Pb dating results of zircons from the trachyandesite in the study area (D6395)
表 4 塔木兰头组火山岩主量元素分析结果表(%)
Table 4 Major element compositions of the Tamulangou Formation volcanic rocks(%)
表 5 塔木兰沟组火山岩微量元素分析结果表(K元素含量/10-2,其他元素含量/10-6)
Table 5 Trace element compositions of the Tamulangou Formation volcanic rocks
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