黔西北杉树林铅锌矿床微量和稀土元素地球化学特征及其地质意义
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摘要
杉树林铅锌矿床是黔西北地区最具代表性的中型矿床,相关地质地球化学研究程度较低,成因认识有较大分歧。本文利用电感耦合等离子体质谱(ICP-MS)分析该矿床主成矿阶段硫化物(闪锌矿和方铅矿)的微量和稀土元素组成,以期从元素地球化学角度揭示该矿床的成因机制。结果表明,硫化物中的Cu、As、Cd、Sb、Tl和Bi明显富集,而其它微量元素则相对亏损或没有明显富集。这些元素的富集特征表明该矿床既有较高温元素组合,亦有低温元素组合,暗示杉树林矿床成矿作用的复杂性。此外,Cu和Cd在闪锌矿中更为富集,而Sb、Tl和Bi在方铅矿中更为富集,可见这些微量元素与不同寄主矿物的亲缘性。此外,杉树林铅锌矿床中闪锌矿的颜色较深,以深棕色为主,且闪锌矿和方铅矿中的Ga/In比及均值都明显大于1,而它们的Zn/Cd均值在500附近,暗示该矿床形成温度较高(>250℃),这与闪锌矿-方铅矿矿物对计算S同位素平衡温度(135～292℃)较一致。硫化物总REE含量很低(ΣREE<1×10-6),Eu正异常显著(δEu=1.6～2.5),但Ce负异常明显(δCe=0.2～0.6),而方解石中总REE含量相对较高(ΣREE=12.71×10-6),但Eu呈负异常明显(δEu=0.7),且Ce亦呈负异常显著(δCe=0.25),推测杉树林矿床成矿流体的演化经历了从还原到氧化的变化过程,其中的REE来源于多个潜在源区岩石。综合已有的地质、地球化学研究成果,本文认为杉树林铅锌矿床是较高温度流体与较低温流体混合的产物,成矿过程经历了还原向氧化环境转变的过程,其属于后生热液矿床,与低温盆地卤水成因的典型MVT矿床存在一定差异。
The Shanshulin Pb-Zn deposit is a representative medium-sized deposit in NW Guizhou province. Due to the relatively low degree of relevant geological and geochemical researches on this deposit, there is still a wide divergence in understanding of its genesis. In this paper, inductively coupled plasma-mass spectrometry(ICP-MS) was used to analyze concentrations of trace elements and rare earth elements in sulfides(sphalerite and galena) of the main ore-stage, in order to reveal the genetic mechanism of the deposit from the perspective of elemental geochemistry. The results show that Cu, As, Cd, Sb, Tl, and Bi of sulfides were significantly enriched, while other trace elements were relatively depleted or not obviously enriched. The enrichment of these elements implies that the deposit contains a combination of both medium temperature elements and low temperature elements, indicating the complexity of ore genesis of the Shanshulin deposit. In addition, Cu and Cd are much more concentrated in sphalerite, while Sb, Tl, and Bi are more abundant in galena, suggesting the affinity of these trace elements to relevant host minerals. Sphalerite of the deposit is mainly in color of dark brown. The sphalerite and galena have the Ga/In ratios and their mean values of over 1, and the Zn/Cd ratios of around 500, suggesting that the deposit was formed in medium temperature(>250 ℃), which is similar to temperatures(135-292 ℃) calculated on the basis of the assumed S isotopic equilibrium between sphalerite and galena. The sulfides have very low total REE contents(ΣREE<1×10-6), with obvious positive Eu anomalies(δEu =1.6-2.5), but obvious negative Ce anomalies(δCe = 0.2-0.6). The calcite has relatively high total REE contents(ΣREE = 12.71×10-6), with obvious negative Eu anomalies(δEu = 0.7) and Ce negative anomalies(δCe = 0.25). Therefore, the authors have speculated that the ore-forming fluids of the Shanshulin Pb-Zn deposit were evolved from reduction to oxidation states. The REE of the Shanshulin Pb-Zn deposit could be originated from multiple potential source rocks. With the integration of previous geological and geochemical researches, it is believed that the Shanshulin Pb-Zn deposit could be produced by the mixing of higher temperature fluids with lower temperature fluids, with the ore-forming process experienced the transformation from reduced to oxidized environments. It belongs to the epigenetic hydrothermal deposit, and is certainly different to the typical brine originated MVT deposits in the low temperature basin.
The Shanshulin Pb-Zn deposit is a representative medium-sized deposit in NW Guizhou province. Due to the relatively low degree of relevant geological and geochemical researches on this deposit, there is still a wide divergence in understanding of its genesis. In this paper, inductively coupled plasma-mass spectrometry(ICP-MS) was used to analyze concentrations of trace elements and rare earth elements in sulfides(sphalerite and galena) of the main ore-stage, in order to reveal the genetic mechanism of the deposit from the perspective of elemental geochemistry. The results show that Cu, As, Cd, Sb, Tl, and Bi of sulfides were significantly enriched, while other trace elements were relatively depleted or not obviously enriched. The enrichment of these elements implies that the deposit contains a combination of both medium temperature elements and low temperature elements, indicating the complexity of ore genesis of the Shanshulin deposit. In addition, Cu and Cd are much more concentrated in sphalerite, while Sb, Tl, and Bi are more abundant in galena, suggesting the affinity of these trace elements to relevant host minerals. Sphalerite of the deposit is mainly in color of dark brown. The sphalerite and galena have the Ga/In ratios and their mean values of over 1, and the Zn/Cd ratios of around 500, suggesting that the deposit was formed in medium temperature(>250 ℃), which is similar to temperatures(135-292 ℃) calculated on the basis of the assumed S isotopic equilibrium between sphalerite and galena. The sulfides have very low total REE contents(ΣREE<1×10-6), with obvious positive Eu anomalies(δEu =1.6-2.5), but obvious negative Ce anomalies(δCe = 0.2-0.6). The calcite has relatively high total REE contents(ΣREE = 12.71×10-6), with obvious negative Eu anomalies(δEu = 0.7) and Ce negative anomalies(δCe = 0.25). Therefore, the authors have speculated that the ore-forming fluids of the Shanshulin Pb-Zn deposit were evolved from reduction to oxidation states. The REE of the Shanshulin Pb-Zn deposit could be originated from multiple potential source rocks. With the integration of previous geological and geochemical researches, it is believed that the Shanshulin Pb-Zn deposit could be produced by the mixing of higher temperature fluids with lower temperature fluids, with the ore-forming process experienced the transformation from reduced to oxidized environments. It belongs to the epigenetic hydrothermal deposit, and is certainly different to the typical brine originated MVT deposits in the low temperature basin.
引文
[1]Zhou JX,Huang ZL,Lv ZC,et al.Geology,isotope geochemistry and ore genesis of the Shanshulin carbonate-hosted Pb-Zn deposit,southwest China[J].Ore Geology Reviews,2014,63:209-225.
[2]金中国,周家喜,黄智龙,等.贵州普定纳雍枝铅锌矿矿床成因:S和原位Pb同位素证据[J].岩石学报,2016,32(11):3441-3455.
[3]陈士杰,蔡继锋,王志经,等.生物地层相对杉树林铅锌矿床的控矿意义[J].地质与勘探,1984,(11):16-19+24.
[4]郑传仑.贵州杉树林铅锌矿床碳酸盐岩浊流沉积与成矿的关系[J].桂林冶金地质学院学报,1992,12(4):323-334.
[5]付绍洪,顾雪祥,王乾,等.扬子地块西南缘铅锌矿床Cd、Ge与Ga富集规律初步研究[J].矿物岩石地球化学通报,2004,23(2):105-108.
[6]张羽旭,朱传威,付绍洪,等.川滇黔地区铅锌矿床中锗的富集规律研究[J].矿物学报,2012,32(1):60-64.
[7]Zhou J,Huang Z,Zhou M,et al.Constraints of C-O-S-Pb isotope compositions and Rb-Sr isotopic age on the origin of the Tianqiao carbonate-hosted Pb-Zn deposit,SW China[J].Ore Geology Reviews,2013,53:77-92.
[8]Zhou JX,Xiang ZZ,Zhou MF,et al.The giant Upper Yangtze Pb-Zn province in SW China:Reviews,new advances and a new genetic model[J].Journal of Asian Earth Sciences,2018,154:280-315.
[9]周家喜,黄智龙,周国富,等.黔西北赫章天桥铅锌矿床成矿物质来源:S、Pb同位素和REE制约[J].地质论评,2010,56(4):513-524.
[10]Zhou J,Huang Z,Zhou G,et al.Trace elements and rare earth elements of sulfide minerals in the Tianqiao Pb-Zn ore deposit,Guizhou Province,China[J].Acta Geologica Sinica,2011,85(1):189-199.
[11]周家喜,黄智龙,周国富,等.贵州天桥铅锌矿床分散元素赋存状态及规律[J].矿物学报,2009,29(4):471-480.
[12]叶霖,李珍立,胡宇思,等.四川天宝山铅锌矿床硫化物微量元素组成:LA-ICPMS研究[J].岩石学报,2016,32(11):3377-3393.
[13]金中国.黔西北地区铅锌矿控矿因素、成矿规律与找矿预测[M].北京:冶金工业出版社,2008:1-105.
[14]周家喜,黄智龙,周国富,等.黔西北天桥铅锌矿床热液方解石C、O同位素和REE地球化学[J].大地构造与成矿学,2012,36(1):93-101.
[15]Qi L,Hu J,Gregoire D C.Determination of trace elements in granites by inductively coupled plasma mass spectrometry[J].Talanta,2000,51(3):507-513.
[16]Taylor S R,McLennan S M.The geochemical evolution of the continental crust[J].Reviews of Geophysics,1995,33(2):241-265.
[17]Boynton WV.Cosmochemistry of the rare earth elements meteorite studies.In:Henderson P.(ed)Rare Earth Element Geochemistry[M].Amsterdam:Elsevier,1984,63-114.
[18]刘英俊,曹励明,李兆麟,等.元素地球化学[M].北京:科学出版社,1984:360-420.
[19]涂光炽,高振敏,胡瑞忠,等.分散元素地球化学性质及成矿机制[M].北京:科学出版社,2003:1-407.
[20]刘铁庚,叶霖,周家喜,等.闪锌矿中的Cd主要类质同象置换Fe而不是Zn[J].矿物学报,2010,30(2):179-184.
[21]Ma Y,Liu C.Trace element geochemistry during weathering as exemplified by the weathered crust of granite,Longnan,Jiangxi[J].Chinese.Sci.Bull.,1999,44:2260-2263.
[22]Chen Y,Fu S.Variation of REE patterns in early Precambrian sediments:Theoretical study and evidence from the southern margin of the northern China craton[J].Chinese Sci.Bul1.,1991,36(l3):1100-1104.
[23]Li B,Zhou JX,Huang ZL,et al.Geological,rare earth elemental and isotopic constraints on the origin of the Banbanqiao Zn-Pb deposit,southwest China[J].Journal of Asian Earth Sciences,2015,111:100-112.
[26]Huang Z,Li X,Zhou M,et al.REE and C-O Isotopic Geochemistry of Calcites from the World-class Huize Pb-Zn Deposits,Yunnan,China:Implications for the Ore Genesis[J].Acta Geologica Sinica(English Edition),2010,84(3):597-613.
[2]金中国,周家喜,黄智龙,等.贵州普定纳雍枝铅锌矿矿床成因:S和原位Pb同位素证据[J].岩石学报,2016,32(11):3441-3455.
[3]陈士杰,蔡继锋,王志经,等.生物地层相对杉树林铅锌矿床的控矿意义[J].地质与勘探,1984,(11):16-19+24.
[4]郑传仑.贵州杉树林铅锌矿床碳酸盐岩浊流沉积与成矿的关系[J].桂林冶金地质学院学报,1992,12(4):323-334.
[5]付绍洪,顾雪祥,王乾,等.扬子地块西南缘铅锌矿床Cd、Ge与Ga富集规律初步研究[J].矿物岩石地球化学通报,2004,23(2):105-108.
[6]张羽旭,朱传威,付绍洪,等.川滇黔地区铅锌矿床中锗的富集规律研究[J].矿物学报,2012,32(1):60-64.
[7]Zhou J,Huang Z,Zhou M,et al.Constraints of C-O-S-Pb isotope compositions and Rb-Sr isotopic age on the origin of the Tianqiao carbonate-hosted Pb-Zn deposit,SW China[J].Ore Geology Reviews,2013,53:77-92.
[8]Zhou JX,Xiang ZZ,Zhou MF,et al.The giant Upper Yangtze Pb-Zn province in SW China:Reviews,new advances and a new genetic model[J].Journal of Asian Earth Sciences,2018,154:280-315.
[9]周家喜,黄智龙,周国富,等.黔西北赫章天桥铅锌矿床成矿物质来源:S、Pb同位素和REE制约[J].地质论评,2010,56(4):513-524.
[10]Zhou J,Huang Z,Zhou G,et al.Trace elements and rare earth elements of sulfide minerals in the Tianqiao Pb-Zn ore deposit,Guizhou Province,China[J].Acta Geologica Sinica,2011,85(1):189-199.
[11]周家喜,黄智龙,周国富,等.贵州天桥铅锌矿床分散元素赋存状态及规律[J].矿物学报,2009,29(4):471-480.
[12]叶霖,李珍立,胡宇思,等.四川天宝山铅锌矿床硫化物微量元素组成:LA-ICPMS研究[J].岩石学报,2016,32(11):3377-3393.
[13]金中国.黔西北地区铅锌矿控矿因素、成矿规律与找矿预测[M].北京:冶金工业出版社,2008:1-105.
[14]周家喜,黄智龙,周国富,等.黔西北天桥铅锌矿床热液方解石C、O同位素和REE地球化学[J].大地构造与成矿学,2012,36(1):93-101.
[15]Qi L,Hu J,Gregoire D C.Determination of trace elements in granites by inductively coupled plasma mass spectrometry[J].Talanta,2000,51(3):507-513.
[16]Taylor S R,McLennan S M.The geochemical evolution of the continental crust[J].Reviews of Geophysics,1995,33(2):241-265.
[17]Boynton WV.Cosmochemistry of the rare earth elements meteorite studies.In:Henderson P.(ed)Rare Earth Element Geochemistry[M].Amsterdam:Elsevier,1984,63-114.
[18]刘英俊,曹励明,李兆麟,等.元素地球化学[M].北京:科学出版社,1984:360-420.
[19]涂光炽,高振敏,胡瑞忠,等.分散元素地球化学性质及成矿机制[M].北京:科学出版社,2003:1-407.
[20]刘铁庚,叶霖,周家喜,等.闪锌矿中的Cd主要类质同象置换Fe而不是Zn[J].矿物学报,2010,30(2):179-184.
[21]Ma Y,Liu C.Trace element geochemistry during weathering as exemplified by the weathered crust of granite,Longnan,Jiangxi[J].Chinese.Sci.Bull.,1999,44:2260-2263.
[22]Chen Y,Fu S.Variation of REE patterns in early Precambrian sediments:Theoretical study and evidence from the southern margin of the northern China craton[J].Chinese Sci.Bul1.,1991,36(l3):1100-1104.
[23]Li B,Zhou JX,Huang ZL,et al.Geological,rare earth elemental and isotopic constraints on the origin of the Banbanqiao Zn-Pb deposit,southwest China[J].Journal of Asian Earth Sciences,2015,111:100-112.
[26]Huang Z,Li X,Zhou M,et al.REE and C-O Isotopic Geochemistry of Calcites from the World-class Huize Pb-Zn Deposits,Yunnan,China:Implications for the Ore Genesis[J].Acta Geologica Sinica(English Edition),2010,84(3):597-613.