地质力学学报  2022, Vol. 28 Issue (3): 406-416
引用本文
娄元林, 唐侥, 郭威, 李毅, 袁永盛, 杨桃. 西藏隆子县那穷锑金矿地质特征及找矿前景分析[J]. 地质力学学报, 2022, 28(3): 406-416.
LOU Yuanlin, TANG Yao, GUO Wei, LI Yi, YUAN Yongsheng, YANG Tao. Geologic characteristics of the Naqiong Sb-Au deposit and prospecting prediction for Au-polymetallic deposits in Longzi County, Tibet[J]. Journal of Geomechanics, 2022, 28(3): 406-416.
西藏隆子县那穷锑金矿地质特征及找矿前景分析
娄元林1, 唐侥1, 郭威1, 李毅1, 袁永盛2, 杨桃3    
1. 中国地质调查局长沙自然资源综合调查中心, 湖南 长沙 410600;
2. 中国地质调查局昆明自然资源综合调查中心, 云南 昆明 650100;
3. 常德职业技术学院, 湖南 常德 415000
摘要:那穷锑金矿是近年来通过区域地质矿产调查在西藏自治区隆子县新发现的金多金属矿床,其矿化带受断裂构造控制。目前该矿床研究程度相对较低,若对其成矿地质条件、地质特征及找矿潜力等内容进行专门性和系统性研究,可为该矿床的下步找矿勘探工作提供依据。文章通过总结区域成矿地质背景,分析了该矿床地质特征、地球物理与地球化学异常特征、包裹体地球化学特征,并结合遥感地质特征和异常查证开展相关研究工作,结果表明:矿体主要产于上三叠统涅如组中,受东西向次级断裂构造带控制,目前共发现3条破碎蚀变带;土壤地球化学剖面测量工作中,选择了Sb、Au、As、Bi、Cu作为Sb及多金属成矿指示元素,共圈定单元素异常10处,各元素异常套合较好;激电中梯测量共圈定极化体2条,视极化率异常3处;与成矿有关的流体包裹体类型主要为富液包裹体,并推测矿区流体为含微量CO2、N2气体的中低温低盐度NaCl-H2O热液体系。综合分析认为那穷锑金矿区具备优越的成矿条件,具有寻找金多金属矿的潜力。
关键词那穷锑金矿    地球化学和地球物理特征    地质特征    找矿前景分析    西藏    
DOI10.12090/j.issn.1006-6616.2021143     文章编号:1006-6616(2022)03-0406-11
Geologic characteristics of the Naqiong Sb-Au deposit and prospecting prediction for Au-polymetallic deposits in Longzi County, Tibet
LOU Yuanlin1, TANG Yao1, GUO Wei1, LI Yi1, YUAN Yongsheng2, YANG Tao3    
1. Changsha Natural Resources Comprehensive Survey Center, China Geological Survey, Changsha 410600, Hunan, China;
2. Kunming Natural Resources Comprehensive Survey Center, China Geological Survey, Kunming 650100, Yunnan, China;
3. Changde Vocational Technical College, Changde 415000, Hunan, China
Abstract: The Naqiong Sb-Au deposit is a newly discovered Au-polymetallic deposit in Longzi county, Tibet. Recent years of regional geological surveys reveal that its mineralized zone is controlled by fault structure. In view of the relatively low research degree of this deposit, specialized and systematic research on its metallogenic geologic conditions, geologic characteristics and prospecting potentials will lay a foundation for further prospecting and exploration work of this deposit. The geologic characteristics, geophysical and geochemical anomaly characteristics, and inclusion geochemical characteristics are analyzed based on the regional metallogenic geological background. The analysis results in combination with the remote sensing geologic characteristics and anomaly verification work show that the ore bodies mainly occur in the Nieru formation of the upper Triassic and are controlled by the EW-trending secondary fault structural belt. Three fractured alteration zones have been found. Through the soil geochemical profile survey, Sb, Au, As, Bi and Cu are selected as the indicator elements for Sb and polymetallic mineralization. Altogether there are ten single element anomalies, showing good match with each other. Two polarization bodies and three apparent polarizability anomalies are defined by induced polarization intermediate gradient measurement. The fluid inclusions related to mineralization are mainly liquid-rich inclusions. It is inferred that the fluid in the mining area belongs to a medium-low temperature and low salinity NaCl-H2O hydrothermal system containing traces of CO2 and N2. Overall, the available data support the notion that the Naqiong Sb-Au mining area has superior metallogenic conditions for Au-polymetallic deposits.
Key words: Naqiong Sb-Au deposit    geochemical and geophysical characteristics    geologic characteristics    potential for deposits    Tibet    

那穷锑金矿位于西藏自治区山南市隆子县那穷一带,矿区已通行简易公路,交通较为便利。该矿床位于藏南特提斯-喜马拉雅金锑多金属成矿带内,该带具优越的成矿地质条件,已成为勘探金锑铅锌多金属矿产的热点地区,目前发现了众多典型金属矿床,其中有位于矿区西南部的扎西康大型铅锌锑矿床(郑有业等,2012梁维等,2014于淼,2015),东北部的查拉普大型金矿(郑有业等,2007周天成等,2015许国雨,2020),西部的马扎拉中型锑金矿床(王军等,2001王军和张均,2001张建芳等,2011李应栩等,2018),附近还有象日锑矿床(娄元林等,2018a)、古堆锑矿床、那嘎迪金矿床(娄元林等,2018b)、恰嘎锑矿床(董富权等,2015娄元林等, 2016, 2018c)、邦卓玛金矿床(陈东太等,2016娄元林等,2019)。那穷锑金矿是近年来长沙自然资源综合调查中心在开展中国地质调查局项目中,通过区域地质矿产调查新发现的矿床,是在1:50000水系沉积物测量异常中圈定的那穷综合异常(HS-5-B2)基础上,通过异常查证工作取得的找矿成果。相关学者对该矿床更多的是从区域上总结其所属区带上的成矿规律、控矿因素、成矿作用等基础地质方面的研究,对该矿床的成矿地质条件、地质特征及找矿潜力等内容的专门性和系统性研究不够。文章系统梳理了地物化遥及科研等方面研究成果后(王建等,2019薛玉山等,2020),通过详细野外调查和室内综合分析研究,总结了那穷锑金矿的矿床地质特征,分析了其找矿潜力,为进一步的找矿勘探工作提供了依据。

1 区域成矿地质背景

那穷锑金矿在大地构造上处于青藏高原南部喜马拉雅特提斯造山带中东部,北邻冈底斯,属雅鲁藏布缝合带(YS)与藏南拆离系(STDS)的过渡部位(陈智梁和刘宇平,1996尹安,2001江元生等,2009杜泽忠等,2011黄小东,2011),是寻找金锑铅锌等多金属矿产的重要成矿带之一(冯孝良和杜光树,1999付伟等,2005张洪瑞等,2010席伟杰和肖克炎,2016娄元林等,2016)。该成矿带断裂构造较发育,自泛非运动开始强烈活动,经历了冈瓦纳古陆北缘长期沉积-构造演变;在此背景下,区域内以北西西向的拉孜-邛多江缝合带、近南北向勒金康桑和洞嘎断裂、近东西向绒布生长和洛扎生长断层为边界,构造了区域羊卓雍措-哲古错断陷盆地。该区强烈的岩浆活动和变质作用造成了复杂多样的构造样式、构造组合及构造层次(图 1a),具有优越的构造-岩浆-成矿地质条件(潘桂棠等,2004戚学祥等,2008卞爽等,2021许云鹏,2021)。

1—第四纪冲积、冰积堆积;2—侏罗纪-白垩纪滨浅海碎屑岩建造,含火山碎屑岩建造;3—侏罗纪海相碎屑岩建造,含火山碎屑岩建造、碳酸盐岩建造;4—晚三叠世海相碎屑岩建造,含火山碎屑岩建造;5—中新世二云二长花岗岩;6—始新世石英闪长岩;7—晚白垩世辉绿玢岩;8—未分岩脉;9—伸展剥离断层;10—韧性剪切带;11—实测平推断层;12—推测平推断层;13—实测断层线;14—推测断层线;15—平行不整合界线;16—角度不整合界线;17—背斜轴线;18—向斜轴线;19—地质界线;20—典型锑铅锌矿;21—典型锑金矿;22—典型锑矿;23—典型锌矿;24—典型金矿;25—典型铜矿;26—地名;27—那穷锑金矿及矿区范围;Ⅰ—雅拉香波变质核杂岩;Ⅱ—卓木日-俗坡下逆冲推覆带;Ⅲ—甲坞-多日褶皱冲断带
a—古堆-隆子地区大地构造略图;b—那穷锑金矿周边矿产分布图
(a) Sketch map showing the tectonic units in the Gudui-Longzi area; (b) Distribution of mines in the Naqiong Sb-Au deposit and surrounding areas
1-Quaternary alluvial-glacial accumulation; 2-Jurassic-Cretaceous littoral and shallow sea clastic rock formation, volcanic clastic rock formation; 3-Jurassic marine clastic rock formation, volcanic clastic rock formation, carbonate rock formation; 4-Late Triassic marine clastic rock formation, volcanic clastic rock formation; 5-Miocene Ermo-feldspar granite; 6-Eocene quartz diorite; 7-Late Cretaceous diabase porphyrite; 8-Undetermined dikes; 9-Extensional detachment fault; 10-Ductile shear zone; 11-Measured transcurrent fault; 12-Inferred transcurrent fault; 13-Measured fault line; 14-Inferred fault line; 15-Parallel unconformity boundary; 16-Angular unconformity boundary; 17-Anticline axis; 18-Syncline axis; 19-Geologic boundary; 20-Typical Sb-Pn-Zn deposit; 21-Typical Sb-Au deposit; 22-Typical Sb deposit; 23-Typical Zn deposit; 24-Typical Au deposit; 25-Typical Cu deposit; 26-Place names; 27-The Naqiong Sb-Au deposit and its mining areas; Ⅰ-Yalashangbo metamorphic core complex; Ⅱ-Zhuomuri-Supoxia thrust nappe belt; Ⅲ-Jiawu-Duori fold and thrust belt
图 1 西藏古堆-隆子地区区域构造纲要及矿产分布图(据娄元林等,2019许云鹏,2021修改) Fig. 1 Regional tectonics and mine distribution in the Gudui-Longzi area, Tibet (modified from Lou et al., 2019; Xu, 2021)

地层属喜马拉雅地层区中的康马-隆子地层分区,总体为一套相对稳定的碎屑沉积岩,主要有古生界、上三叠统、侏罗系、下白垩统及第四系地层发育。其中,上三叠统涅如组二、三段富集金矿,下侏罗统日当组富集铅锌锑银矿,中下侏罗统陆热组和中侏罗统遮拉组地层富集锑矿,而上侏罗统维美组地层中发育金锑矿,显示出一定的成矿专属性(娄元林等,2019)。

构造以大量逆冲断层和复式倒转褶皱为主,发育穹窿构造,整体处于康马-隆子褶冲带中,以东西向为主,其次为北东、北西和南北向断层,整个区域被伸展剥离断层和古堆隆子断层分为3个区:北部(Ⅰ区)为雅拉香波变质核杂岩,中部(Ⅱ区)是卓木日-俗坡下逆冲推覆带,南部(Ⅲ区)以甲坞-多日褶皱冲断带为主(图 1b),这些构造形成了“导矿、容矿、储矿”三位一体控矿体系(娄元林等,2016)。

岩浆岩活动较频繁,岩石类型齐全,分布也较广泛,空间上以脉岩为主的侵入岩分布在东北部和西部;时间上以中生代、新生代中—酸性岩为主;成因上碰撞型、后碰撞型均有发育(任冲等,2015任冲,2015张达等,2021)。除第四系松散沉积外,其他各时代的地层均有不同程度的变质,但变质岩组合较简单,多为板岩、片岩、变砂岩类,变质作用类型表现为区域变质、动力变质和接触变质。

区域产出的典型金属矿床成因类型主要有沉积-构造-热液型矿床(扎西康铅锌锑矿床)、卡林型金矿床(查拉普金矿床)、沉积-次火山岩浆热液叠加改造型矿床(马扎拉锑金矿床)(许云鹏,2021)。

2 矿床地质特征

那穷锑金矿出露地层的时代比较单一,主要为上三叠统涅如组(T3n)灰黑薄层状绢云母粉砂质板岩夹岩屑变质长石石英杂砂岩,局部夹有硅铁质条带;该组地层在区域上可细分为五段,矿区仅出露一、二、三岩性段。一段(T3n1),仅少量在矿区西北角可见,岩性为灰黑色页岩、灰黑色薄层砂岩夹中厚层长石石英砂岩为主,局部夹硅质条带,硅质条带顺层产出;二段(T3n2),出露于矿区北部,岩性为灰黑—黑色薄层状绢云母粉砂质板岩夹少量薄层状杂砂岩,砂岩厚度1~10 cm不等,局部夹有硅铁质条带及透镜体;三段(T3n3),出露于矿区南部,岩性为灰—深灰色粉砂质绢云母板岩夹中厚层状细粒变质岩屑长石石英杂砂岩,砂岩厚度10~50 cm不等,在变质长石石英杂砂岩中可见波痕,发育斜层理和底模及虫迹(图 2)。

1—第四系;2—上三叠统涅如组第三段;3—上三叠统涅如组第二段;4—上三叠统涅如组第一段;5—辉绿岩;6—玄武安山岩;7—地质界线;8—断层及编号;9—视极化率异常及编号;10—1:50000水系沉积物测量金异常及编号;11—1:50000水系沉积物测量锑异常及编号;12—土壤地球化学剖面测量金异常及编号;13—土壤地球化学剖面测量砷异常及编号;14—土壤地球化学剖面测量锑异常及编号;15—土壤地球化学剖面测量铋异常及编号;16—土壤地球化学剖面测量银异常及编号;17—土壤地球化学剖面测量铜异常及编号;18—破碎蚀变带及编号;19—探槽及编号;20—金品位/厚度;21—激电中梯剖面测量测线及编号 1-Quaternary; 2-The third member of the Upper Triassic Nieru Formation; 3-The sccond member of the Triassic Nieru Formation; 4-The first member of the Upper Triassic Nieru Formation; 5-Diabase; 6-Basaltic andesite; 7-Geologic boundary; 8-Fault and number; 9-Apparent polarizability anomaly and number of geophysical prospecting; 10-Au anomaly and number in 1:50000-scale stream sediment survey; 11-Sb anomaly and number in 1:50000-scale stream sediment survey; 12-Au anomaly and number in soil geochemical profile survey; 13-As anomaly and number in soil geochemical profile survey; 14-Sb anomaly and number in soil geochemical profile survey; 15-Bi anomaly and number in soil geochemical profile survey; 16-Ag anomaly and number in soil geochemical profile survey; 17-Cu anomaly and number in soil geochemical profile survey; 18-Fractured alteration zone and number; 19-Exploration trench and number; 20-Au grade/thickness; 21-Lines and numbers of the induced polarization intermediate gradient survey profile 图 2 那穷锑金矿综合地质图 Fig. 2 A generalized geological map of the Naqiong Sb-Au deposit

该矿床整体处于卓木日-俗坡下逆冲推覆带中,在矿区内近东西、北西向断层构造发育。阿涡夺-多拉则日断层(F1)为一低角度逆冲推覆断层,从矿区中部穿过,走向北西西,倾向北,倾角较缓,一般为16°~30°。在构造运动的作用下,形成一条强劈理化带,带内板岩由于被强烈的劈理化改造后显得较为破碎。扎布旗断层(F2)为一逆冲断层,从矿区中部穿过,整体走向为北西,倾向北东,倾角略陡,一般为41°~64°,在矿区内,上盘岩层较为破碎。矿区控矿构造主要为近南北向张性裂隙,如①号、②号破碎蚀变带,另有北东走向构造裂隙,如③号破碎蚀变带(图 2)。

矿区内出露有辉绿岩,主要呈近东西向侵入,另在矿区北部可见少量玄武安山岩。辉绿岩呈灰绿—暗绿色,块状构造,少数脉岩边部具气孔杏仁状构造、块状构造,可见有变余辉绿结构,部分呈变余辉长辉绿结构、变余嵌晶含长结构和变余斑状结构等。主要矿物为基性斜长石(约60%),单斜辉石(约15%);副矿物为磁铁矿(小于5%);次生矿物为绿泥石(约20%)。

矿区内各时代岩层遭受不同程度的低温动力变质作用,局部发生接触变质作用和动力变质作用。低温动力变质作用主要形成有板岩、片岩和变质砂岩。接触变质作用发生于达拉岩体周边,以及其他岩体围岩的接触带附近,主要为一些斑点岩化、角岩化及碳酸盐化的岩石。动力变质作用发生在脆性断裂带和逆冲推覆带附近的强劈理化带内,岩石上发生破碎、形变,岩石主要为脆性系列,形成构造角砾岩、碎裂岩等,未见韧性动力变质形成的糜棱岩等岩石。

通过路线地质调查工作及相关探矿工程揭露,目前矿区共揭露到3条破碎蚀变带(图 2),具体特征如下。

① 号破碎蚀变带由TC001单工程控制,主要由破碎带夹石英脉及团块组成,宽约16.3 m,岩石破碎强烈,蚀变主要为泥化和弱硅化,矿化主要为褐铁矿化、辉锑矿化等。出露于破碎泥质粉砂岩与辉长岩接触部位,呈断层接触,产状318°∠63°,矿脉厚1.74 m,金品位0.49×10-6

② 号破碎蚀变带由TC006单工程控制,主要由硅化蚀变岩夹石英脉及团块组成,宽约7.2 m,蚀变主要为泥化、弱绢云母化、绿泥石化等,主要有黄铁矿化、辉锑矿化、褐铁矿化等金属矿化,矿化带走向近南北,近直立产出,厚0.23 m,金品位0.60×10-6

③ 号破碎蚀变带由TC004(图 3)、TC054控制,主要由破碎泥质粉砂岩夹石英脉及团块组成,宽约6.9 m,岩石破碎强烈,发育泥化、弱硅化、绿泥石化等蚀变,矿化主要有褐铁矿化、辉锑矿化、黄铁矿化等,辉锑矿呈针柱状、毛发状,矿化带出露于破碎泥质粉砂岩与辉长岩接触部位,呈断层接触,产状280°∠85°,矿脉厚2.30 m,锑品位2.84%。

1—第四系;2—辉绿岩;3—板岩;4—破碎板岩;5—辉锑矿化;6—采样及编号;7—产状;8—等线方位及坡角 1-Quaternary; 2-Diabase; 3-Slate; 4-Fractures slate; 5-Stibnite mineralization; 6-Sampling point and number; 7-Occurrence; 8-Direction and Angle of conductor 图 3 那穷锑金矿TC004素描图 Fig. 3 A sketch map of TC004 in the Naqiong Sb-Au deposit

矿石类型主要为石英脉型和构造破碎蚀变岩型(图 4),矿石结构主要有自形—半自形晶结构、柱状结构等,矿石构造为块状构造、细脉状构造等,组成矿石的金属矿物主要有辉锑矿、少量的黄铁矿,脉石矿物主要有石英、方解石等。

a—TC004揭露的3号矿化带;b—辉锑矿石(破碎蚀变岩);c—含石英脉的粉砂岩(围岩) (a) No.3 mineralized zone revealed by TC004; (b) Stibnite ore (fractured altered rock); c-Siltstone with quartz veins (surrounding rock) 图 4 那穷锑金矿矿石露头照片 Fig. 4 Photos showing the outcrops in the Naqiong Sb-Au deposit

由于工作程度有限,各构造破碎蚀变带深部延伸情况暂未进行钻孔布设控制。总体上,该矿区地表矿化蚀变情况良好,已发现的矿化带产出部位于辉长岩与破碎泥质粉砂岩的接触带上或其附近,且岩石发生强烈的破碎,主要由破碎带夹石英脉组成,有时可见少量石英团块,围岩蚀变强烈,具明显的分带性,主要为弱硅化、泥化、弱绢云母化、绿泥石化等,主要有褐铁矿化、黄铁矿化、辉锑矿化等金属矿化。

3 成矿条件与找矿潜力分析 3.1 遥感地质特征与控矿条件

根据遥感影像特征及遥感解译显示,那穷锑金矿位在影像图上位于一个较大的环形影像附近,且处于次级东西向与近南北向线性构造交汇部位,属线性、环形构造复杂区,另外发育中基性辉绿岩体(脉),在岩体边部围岩可见较弱的蚀变现象。遥感蚀变异常呈片状展布,且较为集中,主要集中在岩体及附近地区,强矿化(蚀变)则分布在多组线性构造相互交汇与环形构造相叠合部位,多种构造叠合部位及铁染和羟基各级蚀变异常强矿化(蚀变)的分布范围与矿区内矿化体分布范围套合紧密,这与区域上的扎西康铅锌锑矿床、马扎拉锑金矿床具相似的地质构造环境(张刚阳,2012娄元林等,2018a)。野外调查时,在该区内发现较好的锑、铅、锌矿化线索,该区具有明显的以金、锑元素为主的化探异常,且辉长岩脉边部发现具有矿化及蚀变的石英脉,成矿条件较为有利,推断该区具有良好的找矿前景。

区域遥感找矿标志:多个环形构造重叠或交叉的边部、多组线性构造的交叉部位或线环构造的交汇叠加部位,遥感矿化蚀变强(娄元林,2016),是寻找锑金多金属矿床的良好场所。

3.2 地球化学特征与控矿条件

在1:50000水系沉积物测量过程中发现了那穷异常(HS-5-B2),该异常总面积约19.1 km2,异常呈不规则椭圆状东西走向,主要由锑、金、砷、铋、铜等5种元素组成。异常强度及规模大,各元素套合较好,该异常产于涅如组粉砂质绢云板岩夹灰色变质细粒岩屑石英砂岩,南侧为辛那铅锌矿点。

在矿区对套合较好的金锑单元素异常地段开展了1:10000土壤地球化学剖面测量工作,圈定金异常3处,铋异常1处,砷异常2处,锑异常2处,铜异常2处(表 1)。由表 1可知,Au-1、Bi-1、As-1元素套合较好,Au最高值为8.25×10-9,平均值为4.75×10-9

表 1 那穷锑金矿土壤剖面测量异常特征表 Table 1 Anomaly characteristics of the soil profile survey in the Naqiong Sb-Au deposit

区域地球化学找矿标志:地球化学异常衬度值高,规模大,锑、金、砷、铋等各元素异常套合紧密,具明显浓度分带和浓集中心的化探异常是找矿有利部位。

3.3 地球物理特征与控矿条件

通过1:10000激电中梯测量,矿区共圈定极化体2条,分别为J-1、J-2,视极化率异常3处,分别为ηs-1、ηs-2、ηs-3(图 5)。

a—视极化率剖面平面图;b—视极化率等值线异常图 (a) Apparent polarizability profile plane; (b) Apparent polarizability contour anomaly diagram 图 5 那穷锑金矿激电中梯视极化率剖面平面图及等值线异常图 Fig. 5 Intermediate gradient apparent polarizability profile plane and contour anomaly diagram in induced polarization of the Naqiong Sb-Au deposit

极化体J-1大体呈近南北走向,沿走向延伸约2000 m,水平投影宽度约100 m,推测可能为含矿构造带或蚀变带;极化体J-2大体呈北北东走向,沿走向延伸约800 m,水平投影宽度约100 m,推测可能为含矿构造带或蚀变带。

异常ηs-1视极化率较高,极化较强,由于该异常连续性较差,异常受中梯剖面线控制较少,异常可靠性较低,异常性质需要进一步开展工作以确定。

异常ηs-2视极化率较高,极化较强,整体呈条带状分布,局部的高极化区域呈串珠状分布,异常圈闭性较好,视电阻率平均值较低,异常西侧已揭露到矿化蚀变破碎带,推测为矿致异常。

异常ηs-3视极化率较高,极化较强,整体为细长条带状,异常东部和南部均未封闭,视电阻率平均值较低,推测为矿致异常,但需要进一步工作以确定异常东部和南部地下介质的激电特征(表 2)。

表 2 那穷锑金矿激电中梯异常特征表 Table 2 Anomaly characteristics of intermediate gradient in induced polarization(IP) in the Naqiong Sb-Au deposit

区域地球物理找矿标志:低阻高极化异常区域可能是硫化物含量丰富地区,电阻率、极化率梯度带可能是控矿构造分布区,可成为找矿有利地段。

3.4 流体包裹体地球化学特征

对那穷锑金矿的矿体流体进行研究分析表明,包裹体多在石英矿物内成群分布,部分为成带状分布,主要为无色—灰色的富液包裹体。富液包裹体分布非常广泛,大约占包裹体总数的95%以上,可见少量呈深灰色的气体包裹体发育;包裹体成群(带)分布,形态呈不规则状、椭圆状,大小在3 μm×4 μm~15 μm×25 μm之间,气液比一般为10%~20%;主要呈透明无色状,局部可见呈无色—灰色状包裹体。气体包裹体极少,仅个别视域内见,呈深灰色(图 6),在测温、盐度、成分方面,矿区均一温度直方图显示存在两个峰值,分别为190~200 ℃与205~220 ℃区间,富液相包裹体盐度5.56%~8.41%,激光拉曼分析数据显示成矿流体的气体成分以CO2为主,并含有部分N2,推断矿区流体为含微量CO2、N2气体的中低温低盐度NaCl-H2O热液体系(付伟等,2005李洪梁等,2017谢玉玲等,2019许国雨,2020许云鹏,2021)。

L—液相; V—气相
a—包裹体成带状分布;b—包裹体成群分布;c—富液包裹体和气体包裹体;d—富液包裹体
(a) Banded distribution of inclusions; (b) Clustered distribution of inclusions; (c) Liquid-rich inclusions and gas inclusions; (d) Liquid-rich inclusions
L-Liquid phase; V-Vapor phase
图 6 那穷锑金矿流体包裹体显微镜下照片 Fig. 6 Microscope photos of fluid inclusions in the Naqiong deposit
4 结论

虽然目前那穷锑金矿研究程度相对较低,但已经发现的破碎蚀变带明显受构造控制,且主要集中在上三叠统涅如组地层中,表现出明显的成矿专属性,另外,岩浆岩及脉岩的侵入,促使区内初始矿源层的形成,同时为成矿流体运移和矿质富集提供了热动力。

区内开展了土壤地球化学剖面和激电中锑测量工作,圈定单元素异常10处,极化体2条,视极化率异常3处,遥感解译显示区内多组线性构造和环形构造发育,且线环构造、线线构造相互交汇、交截和叠加,铁异常和羟基异常较发育,成矿地质条件较为有利;在矿区南部物化探异常套合较好部位,通过工程揭露到了3条破碎蚀变带。流体包裹体的岩相学研究结果表明,包裹体体积较小,与成矿有关的流体包裹体类型主要为无色—灰色的富液包裹体;激光拉曼光谱分析结果显示,气体成分以CO2为主,并含有部分N2;显微测温结果方面,均一温度190~220 ℃,为中低温,盐度5.56%~8.41%,推测矿区流体为含微量CO2、N2气体的中低温低盐度NaCl-H2O热液体系。

综上所述,那穷锑金矿的成矿地质特征、地球化学特征、地球物理特征及遥感地质特征均显示该矿床具备优越的成矿条件,受限于工作量和经费投入,特别是在矿区北部及外围Au、As、Sb单元素异常套合较好部位尚未开展查证工作,具有进一步的工作价值,该矿床具有寻找金多金属矿的潜力。

致谢: 感谢原武警黄金第十一支队李武毅总工程师、陈东太、陈武工程师,中国地质调查局长沙自然资源综合调查中心王步清研究员在野外工作和成文过程中给予的悉心指导,审稿专家及编辑部提出了宝贵的修改意见,在此一并表示衷心感谢。

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