胡古月, 范昌福*, 李延河, 侯可軍, 劉 燚, 陳 賢

1)中國地質科學院礦產(chǎn)資源研究所, 國土資源部成礦作用與資源評價重點實驗室, 北京 100037; 2)金瑪寬甸礦業(yè)有限公司, 欒家溝硼礦, 遼寧丹東 118200; 3)中國地質大學(北京)地球科學與資源學院, 地質過程與成礦作用國家重點實驗室, 北京 100083

遼東磚廟礦區(qū)硼礦床的海相蒸發(fā)成因
——來自硼、硫、碳同位素的證據(jù)

胡古月1), 范昌福1)*, 李延河1), 侯可軍1), 劉 燚2), 陳 賢3)

1)中國地質科學院礦產(chǎn)資源研究所, 國土資源部成礦作用與資源評價重點實驗室, 北京 100037; 2)金瑪寬甸礦業(yè)有限公司, 欒家溝硼礦, 遼寧丹東 118200; 3)中國地質大學(北京)地球科學與資源學院, 地質過程與成礦作用國家重點實驗室, 北京 100083

遼寧磚廟硼礦區(qū)的硼礦體呈層狀或透鏡狀賦存于遼河群里爾峪組火山-沉積建造下部的蛇紋石化大理巖中, 內部含有大量鎂橄欖巖包裹體。本研究利用LA-MC-ICP-MS技術對磚廟硼礦區(qū)內的硼礦石硼同位素進行了微區(qū)原位分析, 對礦石及大理巖圍巖的硫、碳穩(wěn)定同位素進行了系統(tǒng)研究。硼礦石的δ11BNISTSRM-951為12.6‰~13.9‰, 具海相蒸發(fā)沉積特征; 硼礦石和大理巖的δ34SV-CDT為11.6‰~24.3‰, 具海相沉積成因特征; 礦體上下層位中蛇紋石化大理巖的 δ13CV-PDB為–5.0‰ ~ –0.5‰, 部分未蛇紋石化大理巖的δ13CV-PDB為4.1‰~4.6‰, 具有古元古代海相碳酸鹽巖特有的碳同位素正異?，F(xiàn)象。據(jù)此提出, 磚廟礦區(qū)的硼礦床可能形成于海相蒸發(fā)沉積和火山噴發(fā)旋回交替的濱海環(huán)境, 隨后同期噴發(fā)的超基性火山巖覆蓋于海相蒸發(fā)沉積成因硼礦體之上, 保護了易溶的硼酸鹽礦物, 經(jīng)后期變質和熱液改造, 形成目前獨特的硼酸鹽礦物, 碳酸鹽巖與超基性巖巖石組合。

遼河群; 里爾峪組; 磚廟硼礦區(qū); 硼同位素; 硫同位素; 碳同位素

華北克拉通東部基底在古元古代時打開, 形成遼吉裂谷(Zhang et al., 1988; Zhai et al., 2011; Zhao et al., 2012), 在遼東地區(qū)沉積了一套火山-沉積建造, 被命名為遼河群, 其中賦存有大規(guī)模的層控硼酸鹽類礦床(張秋生, 1984; Zhang et al., 1988; Peng et al., 1995, 1998, 2002; Jiang et al., 1997; 劉敬黨等, 2007)。相對于廣為人知的土耳其西安拉托尼亞地區(qū)和美國加利福尼亞地區(qū)的第三系(或更年輕)硼酸鹽礦床, 遼東地區(qū)的硼酸鹽礦床以其特殊的礦物組合(遂安石-硼鎂石型和硼鎂鐵礦-硼鎂石型)和古老的成礦時代(古元古代)而倍受關注。遼東硼礦形成于火山活動(李守義, 1994; 孫敏等, 1996; 肖榮閣等, 2007)與蒸發(fā)沉積作用(Peng et al., 1995, 2002; Jiang et al., 1997)旋回交替的環(huán)境, 后期經(jīng)歷了達綠片巖相-角閃巖相的變質作用(張秋生, 1984; 劉敬黨等, 1993; 孫敏等, 1996),屬沉積-變質型礦床, 主礦區(qū)包括后仙峪、翁泉溝和磚廟—楊木桿。由于遼東硼礦后期經(jīng)歷強烈的混合巖化作用和蛇紋石化蝕變作用(張秋生, 1984),原始沉積特征遺失殆盡, 導致對硼來源的認識存在兩種迥異的觀點: (1)火山熱泉供硼-非海相蒸發(fā)沉積(Peng et al., 1995, 1998, 2002; Jiang et al., 1997; Wang et al., 1998; Xu et al., 2004); (2)海底火山噴發(fā)形成礦源層, 后期混合巖化成礦(馮本智等, 1998; 肖榮閣等, 2007; 劉敬黨等, 2005, 2007; 王翠芝等, 2008a)。本研究試圖通過分析遼東磚廟礦區(qū)硼礦床的礦石和蛇紋石化大理巖圍巖中的硫、硼、碳同位素地球化學特征和變化規(guī)律, 探討硼礦的成礦環(huán)境。

1 地質背景

1.1 區(qū)域地質

以綠片巖和花崗片麻巖為主的鞍山群于古元古代時期打開而形成遼吉裂谷, 并接受了一套火山沉積建造, 形成遼河群。遼河群中賦存有硼礦、菱鎂礦、滑石、岫巖玉等一系列大型-特大型非金屬礦床。遼吉古元古代裂谷呈近東西向展布, 西窄東寬呈楔形橫貫遼寧東部與吉林南部。西以復縣華銅、蓋州、大石橋一帶為界, 向東經(jīng)岫巖、鳳城、寬甸、桓仁延伸進入吉林長白山、朝鮮, 南北寬約100 km, 東西長約300 km(翟裕生等, 2008)。根據(jù)巖相建造與構造特征, 裂谷帶橫向上被劃分為北緣斜坡(鞍山—桓仁北緣濱海斜坡), 中央凹陷(大石橋—寬甸軸部淺海凹陷), 南緣淺臺(岫巖—丹東南緣濱海淺臺)三個構造巖相區(qū)(陳榮度, 1990)(圖1)。沉積地層遼河群底部石英巖不整合于鞍山群變質巖之上, 自下而上劃分為五個組: 浪子山組, 里爾峪組, 高家峪組, 大石橋組和蓋縣組, 屬一套火山-沉積建造, 普遍遭受綠片巖相至角閃巖相的變質作用(姜春潮, 1987)。其中里爾峪組歷來有南里爾峪組(屬遼河群中央凹陷區(qū)和南緣淺臺區(qū))和北里爾峪組(屬遼河群北緣斜坡區(qū))之分。南里爾峪組含有大量酸性火山巖和硼礦, 硼含量較高而被稱為“含硼巖系”(張秋生, 1984), 而北里爾峪組則不含硼礦?？偟目磥? 里爾峪組主要為層狀分布的條痕狀花崗巖、變粒巖、淺粒巖和大理巖, 最大厚度達 1400余m。

1.2 礦區(qū)地質及成礦時代

磚廟硼礦區(qū)位于遼寧省寬甸縣硼海鎮(zhèn)以東20 km處, 自西向東可細分為大陽溝、二人溝、老人溝、花園溝、磚廟溝、欒家溝和小湯石等7個小型礦床和礦點, 本次工作重點研究了其中的二人溝、花園溝、磚廟溝和欒家溝四個小型硼礦床(圖2)。礦區(qū)內含硼巖系整體走向近東西(90°~110°), 傾角較陡(65°~80°)。含礦地層普遍經(jīng)角閃巖相變質和強烈褶皺變形作用, 因受到多條北北東和北北西向斷裂切割(圖2), 有較大錯移(Lu et al., 2005)。礦區(qū)含硼巖系的巖石類型主要為一套變粒巖和淺粒巖(圖 2), 代表性的礦物組合為黑云母-角閃石-鈉長石-石英-鉀長石-電氣石(Sun et al., 1993), 在變粒巖層位中發(fā)育一套夾雜有鎂橄欖石, 普通輝石和透輝石等基性礦物(圖 3a, b)的硼礦石和(蛇紋石化)大理巖(圖3c, d), 構成礦床的主體。后期有時代不明的煌斑巖、偉晶巖(圖3d)和閃長巖等脈巖穿切磚廟礦區(qū)的含硼巖系和硼礦體。礦體總體呈層狀和似層狀產(chǎn)出, 明顯受層位控制。主要的礦石礦物有纖維硼鎂石、遂安石(圖 3a), 其次有極少量的柱狀硼鎂石、板狀硼鎂石和硼鎂鐵礦。脈石礦物主要是白云石、蛇紋石, 其次有鎂橄欖石、金云母、透輝石、粒硅鎂石、斜硅鎂石、水鎂石和透閃石等(劉敬黨等, 2007)。

圖1 遼東裂谷中硼礦床的分布簡圖(據(jù)陳榮度, 1990; 郝德峰等, 2004; Li et al., 2006修改)Fig. 1 Simplified geological map showing locations of boron deposits (modified after CHEN, 1990; HAO et al., 2004; Li et al., 2006)

磚廟礦區(qū)外圍分布有大量條痕狀花崗巖, 屬含硼巖系的底層巖石(姜春潮, 1987), 前人得到的條痕狀花崗巖的鋯石TIMS, LA-MC-ICP-MS和SHRIMP年齡數(shù)據(jù)集中分布在2.17~2.24 Ga之間(Sun et al., 1993; Lu et al., 2006; Li et al., 2007), 原巖可能為酸性火山-沉積巖(張秋生, 1984; 姜春潮, 1987; 趙鳳順等, 1989; 劉敬黨等, 2007)。由于硼礦屬于沉積變質型礦床, 因此, 由酸性火山巖原地重熔而成的條痕狀花崗巖的巖漿鋯石年齡直接將遼東地區(qū)硼礦的沉積成礦時代下限限定在2.2 Ga左右。

圖2 遼東磚廟硼礦區(qū)含硼巖系中段的地質簡圖(據(jù)Lu et al., 2005修改)Fig. 2 Geological sketch map of the middle parts of boron-bearing sequence in the Zhuanmiao borate ore district, eastern Liaoning Province (modified after Lu et al., 2005)

2 分析方法

2.1 LA-MC-ICP-MS微區(qū)原位硼同位素測試

圖3 遼東磚廟礦區(qū)的硼礦石和圍巖照片F(xiàn)ig. 3 Photographs of Mg-borate ores and wall rocks in the Zhuanmiao borate ore district, eastern Liaoning Province

LA-MC-ICP-MS微區(qū)原位硼同位素分析在中國地質科學院礦產(chǎn)資源研究所 MC-ICP-MS實驗室完成, 所用標準為美國國家標準技術研究所 NIST SRM951硼酸樣品(11B/10BNISTSRM951=4.05003), 所用儀器為Neptune型MC-ICP-MS及與之配套的New Wave UP 213激光剝蝕系統(tǒng)。激光剝蝕所用斑束直徑為 25 μm, 頻率為 10 Hz, 能量密度約為 8 J/cm2, 以 He氣為載氣(0.8 L/min)。10B和11B 分別用法拉第杯 L3、H4靜態(tài)同時接收, LA-MC-ICP-MS激光剝蝕采樣采用單點剝蝕的方式,數(shù) 據(jù) 分 析 前 用 電 氣 石 IAEA B4(δ11B為(–8.36±0.58)‰)調試儀器, 使之達到最優(yōu)狀態(tài), 以電氣石IMR RB1(δ11B為–(12.97±0.97)‰)為內標, 以電氣石IAEA B4(δ11B為(–8.36±0.58)‰)為外標進行校正。測試過程中每測定 3個樣品前后重復測定兩次IMR RB1(δ11B為(–12.97±0.97)‰)對樣品進行校正,精度(2σ)均為1‰左右。詳細過程見侯可軍等(2010)和Hou等(2010)。在花園溝和二人溝采集的4件硼礦石的微區(qū)原位測試結果列于表1。

2.2 硫同位素

磚廟硼礦區(qū)硼礦石和圍巖大理巖的硫同位素分析在國土資源部成礦作用與資源評價重點實驗室完成。先用艾氏卡試劑(Eschka)將硼酸鹽巖和碳酸鹽巖中的硫酸根轉化為硫酸鈉, 然后用BaCl2溶液將硫酸鹽類轉化為BaSO4沉淀, 沉淀經(jīng)過濾、清洗、烘干后,用V2O5氧化劑制備SO2, 使用氣體質譜儀MAT-253進行硫同位素測試, 分析精度為±0.2‰, 結果以相對國際標準為 V-CDT的 δ34SV-CDT值表示, 在花園溝,二人溝和磚廟溝采集的4件硼礦石和12件大理巖樣品的硫同位素測試結果見表1。

2.3 碳同位素

磚廟硼礦區(qū)蛇紋石化大理巖和大理巖的碳同位素分析在國土資源部成礦作用與資源評價重點實驗室MAT-253型質譜計上完成。碳同位素測試采用100%磷酸法, 結果以相對國際標準為 V-PDB的δ13CV-PDB值表示, 精度優(yōu)于±0.2‰。在花園溝, 欒家溝, 二人溝和磚廟溝采集的 10件大理巖樣品的碳同位素測試結果見表1。

3 結果與討論

3.1 硼同位素

在磚廟礦區(qū)的花園溝和二人溝硼礦床采集的4個硼礦石(12HYG-1, 12HYG-6, 12ERG-6和12ERG-7)的δ11BNISTSRM951值為12.2‰~13.9‰(表1), 數(shù)據(jù)分布集中而穩(wěn)定, 與前人得到的磚廟礦區(qū)硼礦石的δ11BNISTSRM951值(8.8‰~12.6‰)基本一致(Peng et al., 2002)。硼在地殼中儲庫主要包括碎屑沉積巖, 海相蒸發(fā)巖和陸相蒸發(fā)巖(Peng et al., 1995)。全球已探明的兩個最大硼礦區(qū), 土耳其西安拉托尼亞地區(qū)和美國加利福尼亞地區(qū)的硼酸鹽礦床均屬于陸相蒸發(fā)鹽型硼礦床; 而哈薩克斯坦印德硼礦區(qū)的硼酸鹽礦床則屬于海相蒸發(fā)成因硼礦(劉敬黨等, 2007)。陸相硼酸鹽礦物主要分布在陸相咸化湖泊, 硼主要來源于與火山活動有關的熱泉和熱液(Alonso et al., 1988);海相硼酸鹽礦物則主要分布在海相蒸發(fā)沉積地層,來自于海水硼的蒸發(fā)富集(Swihart et al., 1986; Kloppmann et al., 2001; 肖應凱等, 2005; Tan et al., 2010)。陸相咸化湖泊沉積碳酸鹽巖的 δ11B值與海洋碳酸鹽巖的δ11B值具有明顯的差異, 兩者的δ11B值分別為(–7±10)‰和(25±4)‰(Swihart et al., 1986), B同位素組成可有效判別海相或非海相蒸發(fā)鹽(Vengosh et al., 1992)。遼東地區(qū)古元古代磚廟礦區(qū)硼礦石的δ11BNISTSRM951值為8.8‰~13.9‰, 處于非海相蒸發(fā)巖和海相蒸發(fā)巖之間(圖4)。

表1 磚廟礦區(qū)的硼礦石和大理巖中硫、硼、碳同位素測試結果Table 1 Sulfur, boron and carbon isotopic compositions of borate ores and marbles in the Zhuanmiao borate ore district

含硼礦物的變質和脫水作用可導致礦物的δ11B值降低(Peacock et al., 1999), 由于幾乎無法避免后期變質和流體作用, 前寒武紀海相碳酸鹽巖的 δ11B值均處于零值附近(δ11BNISTSRM951為–6.2‰~4.4‰) (Barth, 1993; Kasemann et al., 2005)。遼東硼礦普遍遭受了綠片巖相-角閃巖相的變質作用, 因此古元古代的遼東磚廟礦區(qū)的硼礦床初始沉積時的δ11BNISTSRM951值可能比測定值高, 暗示硼礦床可能形成于海相蒸發(fā)沉積環(huán)境。另外, 根據(jù)地球上海水中硼同位素的一般演化規(guī)律以及目前得到的早前寒武紀海相碳酸鹽和海相地層中電氣石礦物的δ11B值普遍較低的地球化學現(xiàn)象, Chaussidon等(1992)估算得到太古代海水的δ11BNISTSRM951值為(27±11)‰, 明顯低于現(xiàn)代海水的值。因此, 在古元古代海水蒸發(fā)沉積形成的硼酸鹽類礦物的δ11B值也比現(xiàn)代海相蒸發(fā)沉積硼酸鹽的值低。

圖4 不同地質體中δ11B值的分布范圍(數(shù)據(jù)來自Swihart et al., 1986; Chaussidon et al., 1992, 1995; Peng et al., 2002; Tan et al., 2010)Fig. 4 Range of δ11B values from different boron sources (except for data from the Zhuanmiao Mg-borate ore district of eastern Liaoning province, all data from Swihart et al., 1986; Chaussidon et al., 1992, 1995; Peng et al., 2002; Tan et al., 2010)

3.2 硫同位素

磚廟礦區(qū)的 4個硼礦石 δ34SV-CDT分布在16.1‰~23.7‰, 平均值為18.8‰。12個圍巖大理巖的 δ34SV-CDT分布在 11.6‰~24.3‰, 平均值為19.1‰。與硼礦石共生的硬石膏 δ34SV-CDT分布在20.7‰~24.9‰, 平均值為22.7‰(黃作良等, 1996)。碳酸鹽巖和硼酸鹽礦物的δ34SV-CDT值相對于圍巖中石膏單礦物值偏低 3‰左右。在整體上, 花園溝硼礦床的蛇紋石化大理巖的δ34SV-CDT值相對于蝕變較輕的二人溝硼礦床大理巖的值偏低(表1)。變質和熱液作用通常使巖石中的硫元素發(fā)生逸失和再分配,使變質巖的硫同位素組成均一化(Andreae, 1974),而在硫同位素體系中硫酸鹽的 δ34SV-CDT值最高, 在變質過程中其δ34SV-CDT值降低幅度可能更大。因此,圍巖大理巖和石膏中 δ34SV-CDT的最高值(24‰)可能大致代表了其沉積時海水硫酸鹽的硫同位素組成。太古代海水中的硫主要來自火山, 以還原硫的形式存在(Ono et al., 2009), 具有接近地幔的S同位素組成(圖5), 古元古代早期(2.4~2.0 Ga)“大氧化事件”使得陸殼中大量硫化物氧化而進入海洋, 形成了古元古代海水硫酸鹽儲庫(Canfield, 2005; Schroder et al., 2008), 海水 δ34SV-CDT值升高(Reuschel et al., 2012), 太古代缺氧環(huán)境中光化學反應形成的非質量硫同位素分餾現(xiàn)象結束(Pavlov et al., 2002)。顯生宙海相蒸發(fā)巖 δ34S值維持在 11‰~36‰的范圍(Strauss et al., 1997), 而現(xiàn)代海相蒸發(fā)硫酸鹽 δ34S值比較穩(wěn)定, 為20‰左右(鄭永飛等, 2000)。由圖5可看出, 磚廟硼礦區(qū)同沉積海洋硫酸鹽的 δ34SV-CDT值高于世界其他地區(qū)同期海洋硫酸鹽的值, 也暗示磚廟礦區(qū)的硼礦石和含硫酸鹽大理巖可能形成于封閉的蒸發(fā)海洋沉積環(huán)境, 這與根據(jù)硼同位素得到的結果一致。

圖5 遼東磚廟礦區(qū)的硼礦石和大理巖的硫同位素組成(背景數(shù)據(jù)來自Bottomley et al., 1992及其中的參考文獻,為前寒武紀海相沉積碳酸鹽巖, 硫酸鹽巖的硫同位素組成)Fig. 5 Sulfur isotopic composition of disseminated sulfur in borate ores and marbles from the Zhuanmiao Mg-borate ore district, eastern Liaoning Province (background data from Bottomley et al., 1992 and the references therein, representing sulfur isotopic composition of Precambrian marine carbonate and sulfate)

3.3 碳同位素

遼東磚廟礦區(qū)硼礦體的直接容礦圍巖——蛇紋石化大理巖的δ13CV-PDB為–5.0‰ ~ –0.5‰; 少量未發(fā)生蛇紋石化大理巖的δ13CV-PDB為 4.1‰~4.6‰(表 1)。在碳同位素體系中, 碳酸鹽的δ13CV-PDB值最高, 而海相碳酸鹽的 δ13CV-PDB值又明顯高于非海相, 正常海相碳酸鹽的 δ13CV-PDB值多分布在0值左右(鄭永飛等, 2000)。變質作用和后期熱液改造常使海相碳酸鹽的δ13CV-PDB值降低(Veizer et al., 1999; Jacobsen et al., 1999; Melezhik et al., 2005)。磚廟礦區(qū)硼礦體的直接容礦圍巖——蛇紋石化大理巖的δ13CV-PDB值較外圍未蝕變大理巖的值明顯降低(圖6), 可能為大理巖遭受強烈蝕變的結果。因此, 磚廟礦區(qū)初始沉積碳酸鹽的 δ13CV-PDB值可能較大理巖的值要高, 表明其可能形成于海相蒸發(fā)環(huán)境, 這與根據(jù)硼、硫同位素得到的認識是一致的。

前人獲得遼東硼礦下盤普遍出露的條痕狀花崗巖的鋯石TIMS, LA-MC-ICP-MS和SHRIMP年齡數(shù)據(jù)分布在2.14~2.24 Ga左右(Sun et al., 1993; Lu et al., 2006; Li et al., 2007), 可作為遼東硼礦的沉積成礦時代下限。同一時期, 在2350~2000 Ma(Shields et al., 2002)或2220~2060 Ma(Karhu et al., 1996)期間海相碳酸鹽發(fā)生碳同位素正異常的Lomagundi事件。古元古代蒸發(fā)環(huán)境在全球多有分布, 可能是造成部分局域封閉環(huán)境海相碳酸鹽碳同位素正異常的原因(Melezhik et al., 2005), 因此磚廟地區(qū)海相大理巖的碳同位素正異常也有可能是古元古代Lomagundi事件引起的。

圖6 地質歷史時期海相碳酸鹽巖沉積(數(shù)據(jù)來自Shields et al., 2002)與遼東磚廟硼礦區(qū)的大理巖和蛇紋石化大理巖的碳同位素組成Fig. 6 Carbon isotopic evolution of marine carbonate (after Shields et al., 2002), and carbon isotopic compositions of marbles and serpentinized marbles in the Zhuanmiao Mg-borate ore district of eastern Liaoning Province

超基性噴發(fā)巖在遼東硼礦各個礦區(qū)普遍以礦體直接容礦圍巖的形式存在(王翠芝等, 2006a, b, 2008b; 王翠芝, 2007; 肖榮閣等, 2007), 在磚廟礦區(qū)則主要是以鎂橄欖石和普通輝石的形式與礦石交錯伴生(圖3a, b)(Peng et al., 2002; 王翠芝等, 2007)。超基性火山巖可能在海相蒸發(fā)沉積成礦過程中噴發(fā)并覆蓋在硼礦體之上, 在后期的角閃巖相變質過程中起到了保護硼礦體的作用。因此, 超基性火山噴發(fā)巖及相關熱液活動可能是導致蒸發(fā)沉積型硼礦體附近鎂質碳酸鹽發(fā)生蝕變, 形成蛇紋石化大理巖,碳同位素值降低的主要因素。

4 結論

遼東磚廟礦區(qū)硼礦石的δ11BNISTSRM951為8.8‰~13.9‰, 硼礦石及圍巖的 δ34SV-CDT分布在11.6‰~24.3‰, 未蝕變的大理巖圍巖的 δ13CV-PDB為4.1‰~4.6‰, 三者均顯示明顯正異常, 表明磚廟礦區(qū)的硼礦可能形成于古元古代海相蒸發(fā)環(huán)境; 同期的超基性火山巖噴發(fā)覆蓋對硼酸鹽在變質和后期改造中免遭破壞及硼礦的最終形成起到了很好的保護作用。

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Marine Evaporative Genesis of Mg-borate Deposits in the Zhuanmiao Ore District, Eastern Liaoning Province: Evidence from B, S, C Isotopes

HU Gu-yue1), FAN Chang-fu1)*, LI Yan-he1), HOU Ke-jun1), LIU Yi2), CHEN Xian3)
1) MRL Key Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037; 2) Luanjiagou Boron Mine, Jinma (Kuandian) Boron Co., Ltd., Dandong, Liaoning 118200; 3) State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Resources, China University of Geosciences(Beijing), Beijing 100083

Zhuanmiao Mg-borate ore bodies exhibit layered or lenticular structure in the wall rocks of serpentinized marbles, which are located in the lower strata of volcanic-sedimentary Lieryu Formation in Kuandian County of eastern Liaoning Province. The authors applied LA-MC-ICP-MS in-situ technology to analyze the B isotopic composition of borate ores in the Zhuangmiao Mg-borate ore district, and systematically studied the S and C stable isotopic compositions of the ores and marbles. The δ11BNISTSRM-951values of Mg-borate ores vary from 12.6‰ to 13.9‰, showing marine evaporative characteristics; the δ34SV-CDTvalues of Mg-borate ores and serpentinized marble vary from 11.6‰ to 24.3‰, suggesting marine sedimentary characteristics; (3) the δ13CV-PDBvalues of serpentinized marble vary from –4.6‰ to –0.5‰, while those of marble vary from 4.1‰ to 4.6‰, exhibiting positive carbon isotopic anomaly of Paleoproterozoic marine carbonates. Therefore, the ore-forming environment of the Mg-borate deposit in Zhuanmiao area was probably an alternate cycle of marine sedimentation and volcanism of the littoral facies, while a suite of homochronous Mg-rich ultrabasic volcanicrocks covered the borate deposits and preserved the borate ores during hydrothermalism and metamorphism at late stages, and formed a unique rock unit of borate minerals, carbonates and ultrabasic minerals.

Liaohe Group; Lieryu Formation; Zhuanmiao Mg-borate ore district; boron isotope; sulfur isotope; carbon isotope

P578.93; P571; P597.2

A

10.3975/cagsb.2014.04.06

本文由國土資源部公益性行業(yè)科研專項(編號: 201211074-2; 200911043-20)資助。

2013-09-23; 改回日期: 2014-01-10。責任編輯: 閆立娟。

胡古月, 男, 1985年生。博士研究生。主要從事同位素地球化學和分析化學研究。E-mail: wanghuguyue@126.com。

*通訊作者: 范昌福, 男, 1979年生。副研究員。長期從事地質環(huán)境研究。E-mail: fancf@cags.ac.cn。