山西省五台白云叶蜡石矿地质特征及其对深部找矿的启示

doi:10.13745/j.esf.sf.2020.5.47

摘要/Abstract

摘要：

山西五台县北约15 km的白云村一带出露有叶蜡石矿及金矿化点,其形成特点与关系对区域深部找矿具有重要启示意义。该叶蜡石矿体产于经历古元古代绿片岩相变质的新太古代酸性火山岩之中(绢英片岩),切割区域片理并被晚期的辉绿玢岩截切。矿体总体呈透镜状产出,倾向北西,近东-西向延伸大于5 km,最厚处约1 km,未见底。该叶蜡石矿形成于中生代早白垩世。矿石矿物以叶蜡石和石英为主,含少量绢云母、伊利石、硬水铝石和赤铁矿等,反映出蚀变流体酸性及氧化的特征。叶蜡石矿体外围发育黄铁绢英岩化带,强度由近及远逐渐减弱。在靠近叶蜡石矿的黄铁绢英岩中,硫化物颗粒边缘常见赤铁矿化现象,应与叶蜡石化流体叠加有关。以上蚀变特征与叶蜡石化细脉灌入黄铁绢英岩相吻合。叶蜡石矿体上盘的黄铁绢英岩化带宽约0.4 km,其内发育一小型石英脉型金矿(岭底金矿),下盘的黄铁绢英岩化带最宽约1.5 km,局部发育金矿化现象((1~18)×10^-6)。黄铁绢英岩中硫化物以黄铁矿为主,可见少量黄铜矿、斑铜矿和辉铜矿。金矿化黄铁绢英岩以发育大量浸染型黄铁矿为特征,该类黄铁矿无韧性变形,未见其他共生硫化物,SEM-EDS分析结果显示其内发育有明显的不可见金。黄铁绢英岩化可依据矿物变形与否分为两期。早期的蚀变分布局限,见于新太古代糜棱岩化奥长花岗岩与酸性火山岩(绢英片岩)接触带,其中的黄铁矿、绢云母和石英等矿物发育韧性变形特征;晚期的蚀变带内硫化物、绢云母和石英均无韧性变形特征。依据样品的岩相学及全岩Au、As含量特征,可以确认金矿化与晚期黄铁绢英岩化有关,与早期蚀变无关。叶蜡石矿石的H-O同位素组成(δ¹⁸O_V-SMOW=11.2‰~13.9‰;δD_V-SMOW=-34‰~-20‰)显示流体以气相为主,且缺乏大气水的混合。上述特征说明白云叶蜡石矿是深部岩浆侵位固结后出溶的以气相为主的热液与浅部新太古代变质火山岩反应的结果,类似于斑岩成矿系统中普遍发育的高级泥化带(岩帽)的底部蚀变特征。

关键词: 叶蜡石化, 金矿作用, 热液蚀变, 五台山, 深部找矿

Abstract:

The Baiyun pyrophyllite deposit is ~15 km away to north of Wutai county, Shanxi Province of China, where the basement rocks belong to the Wutai Complex, north-central of the North China Craton. The main orebody occurs as a lens in fracture of the late Archean meta-volcanic rocks, crosscut by the Mesozoic mafic dikes. The wall rocks exhibit phyllic alteration halos which are weakened outwardly from the pyrophyllite orebody. Auriferous quartz sulfide vein and disseminated gold mineralization occur in the phyllic alteration zone. Mineral assemblages of pyrophyllite ores are dominated by pyrophyllite and quartz, with minor of diaspore, kaolinite, illite, sericite and hematite. Accordingly, the lgf(O₂)-pH diagram is constructed that the pyrophyllic alteration fluids were intensively acidic (pH=2-3) with relatively high oxygen fugacity (>HM buffer). Altered zircon yielded a lower intercepted U-Pb age of (136±7) Ma, similar to those of Cu-Au deposits regionally. Whole-rock H-O isotopic data (δD_SMOW=-34‰--20‰; δ¹⁸O_SMOW=11.2‰-13.9‰) of pyrophyllite ores suggest that the fluids for pyrophyllite alteration are cooling magmatic without pronounced effects of meteoric waters. As to the abundances of metals, the Archean wall rocks are markedly higher than those of the pyrophyllite ores. The concentrations of Au and As in the pyrophyllite ores are below the detected limit, suggesting that the physicochemical conditions of fluids for pyrophyllite alteration are not conductive to gold mineralization, inversely, they can scavenge some metals from wall rocks and transfer them upwardly. Our results suggest that pyrophyllite alteration formed by acid and oxidized fluids might be an early stage of evolving fluids for high sulfidation epithermal deposit. Consequently, a prospective porphyry style or skarn type of Cu-Au deposit in deep is suggested.

Key words: pyrophyllite alteration, gold mineralization, hydrothermal alteration, Wutai complex, ore prospecting

中图分类号:

张华锋, 张少颖. 山西省五台白云叶蜡石矿地质特征及其对深部找矿的启示[J]. 地学前缘, 2020, 27(5): 126-135.

ZHANG Huafeng, ZHANG Shaoying. Geological signatures of the Baiyun pyrophyllite deposit in Wutai, Shanxi Province: implication for prospecting of Cu-Au ores in deep[J]. Earth Science Frontiers, 2020, 27(5): 126-135.

图/表 7

图1 华北克拉通五台杂岩及其中生代构造与岩浆分布简图(图b据文献[11]修改;图c据文献[23]修改) YXZ—义兴寨金矿;SH—石湖金矿;XSM—西石门金矿;YDG—银洞沟钼矿;YJG—闫家沟钼矿;TS—滩上钼矿;LD—岭底金矿。

Fig.1 Geological skeleton map of the Wutai Complex(b) and distribution of the Mesozoic magmatism and structures(c) (b modified from [11]; c modified from [23])

图2 山西五台白云叶蜡石矿区地质图

Fig.2 Geological map of the Baiyun pyrophyllite deposit,Wutai of the Shanxi Province

图3 五台白云叶蜡石矿及其围岩矿物特征(矿物缩写据文献[32]) a—叶蜡石矿石矿物以叶蜡石和石英为主;b—叶蜡石矿石中的赤铁矿化;c—叶蜡石矿体下盘的金矿化围岩(黄铁绢英岩)中黄铁矿充填片理方向特征;d—叶蜡石矿石中黄铁矿颗粒边缘赤铁矿化。Py—黄铁矿,Prl—叶蜡石,Qtz—石英,Hem—赤铁矿。

Fig.3 Microscope photos of altered rocks from the Baiyun pyrophyllite deposit, Wutai of Shanxi Province. Mineral abbreviations adapted from [32].

图4 山西五台白云叶蜡石矿热力学相图[10,31]

Fig.4 Thermodynamic phase diagram for pyrophyllite and pyrite-phyllic alteration of the Wutai pyrophyllite deposit, Shanxi Province[10,31]

图5 五台白云叶蜡石矿氢氧同位素及金属元素含量特征(a引自文献[31];b中数据引自文献[10]) 金属元素含量为Au+Ag+As+Cu+Pb+Zn+Mo+Sb+Bi+Se的总含量。

Fig.5 (a)δ18O versus δD of quartz/whole rocks from pyrophyllite and gold deposits of the Wutai area; (b) SiO2 concentrations vs total metal abundances (a after [31]; data of b from [10])

图6 斑岩体系蚀变矿物组合的特瑞pH-温度演化关系[7] 流体演化路径自右向左,最终可能会演化为两条路径:(1)演化为高硫型低温热液矿床。流体保持氧化和强酸性,H-O同位素保持岩浆水特征。(2)从高级泥化反转向泥化带(绿色区)或外青磐岩化(深绿色)方向演化,形成低硫型低温热液矿床。可能在开放体系下有大气降水参与,结果导致pH变为弱酸性到中性,H-O同位素显示程度不等的大气降水参与特征。Ab—钠长石;Act—阳起石;Ad—冰长石;Al—明矾石;And—红柱石;Bio—黑云母;Cb—碳酸盐;(Ca,Mg,Mn,Fe) Ch—绿泥石;Chab—菱沸石;Chd—玉髓;Ch-Sm—绿泥石-胶岭石;Cl—方解石;Cor—刚玉;Cpx—单斜辉石;Cr—方石英;Dik—地开石;Do—白云石;Dp—硬水铝石;Ep—绿帘石;Fsp—长石;Ga—石榴石;Hal—多水高岭石;Heu—片沸石;I—伊利石;I-Sm—伊利石-胶岭石;K—高岭石;Lau—浊沸石;Mica—白云母;Mor—丝光沸石;Mt—磁铁矿;Nat—钠沸石;Op—蛋白石;Pyr—叶蜡石;Q—石英;Ser—绢云母;Sid—菱铁矿;Sm—蒙脱石;Stb—锑华;Tr—透闪石;Tri—鳞石英;Ves—符山石;Wai—斜钙沸石;Wo—硅灰石;Zeo—沸石

Fig.6 Terry's pH-T evolution chart for common mineral alteration assemblages in porphyry system[7]

图7 斑岩体系的高硫化矿床示意图(无矿的叶蜡石化、绢英岩化蚀变带据文献[8];斑岩成矿体系模型改自文献[35]) 五台叶蜡石化带应位于高硫型低温热液矿床底部和斑岩型之间的过渡带;图中红色为矿化体。

Fig.7 Model for the high sulfidation epithermal deposit of porphyry system[8,35]

参考文献 44

[1]	WANG L, ZHANG M, REDFERN S A, et al. Dehydroxylation and transformations of the 2∶1 phyllosilicate pyrophyllite at elevated temperatures: an infrared spectroscopic study[J]. Clays and Clay Minerals, 2002, 50(2):272-283. DOI URL
[2]	MUKHOPADHYAY T K, GHATAK S, MAITI H S. Pyrophyllite as raw material for ceramic applications in the perspective of its pyro-chemical properties[J]. Ceramics International, 2010, 36(3):909-916. DOI URL
[3]	ZEN E A. Mineralogy and petrology of the system Al₂O₃-SiO₂-H₂O in some pyrophyllite deposits of North-Carolina[J]. American Mineralogist, 1961, 46(1/2):52-66.
[4]	PHILLIPS G. Widespread fluid infiltration during metamorphism of the Witwatersrand Goldfields: generation of chloritoid and pyrophyllite[J]. Journal of Metamorphic Geology, 1988, 6(3):311-332. DOI URL
[5]	EVANS B W, GUGGENHEIM S. Talc, pyrophyllite, and related minerals[J]. Reviews in Mineralogy and Geochemistry, 1988, 19(1):225-294.
[6]	DAS B, MOHANTY J K. Mineralogical characterization and beneficiation studies of pyrophyllite from Orissa, India[J]. Journal of Minerals and Materials Characterization and Engineering, 2009, 8(4):329-338. DOI URL
[7]	CORBETT G J, LEACH T M. Southwest Pacific Rim gold-copper systems: structure, alteration and mineralization[M]. Denver: Society of Economic Geologists, 1998, 6:238.
[8]	SILLITOE R H. Porphyry copper systems[J]. Economic Geology, 2010, 105(1):3-41. DOI URL
[9]	SEEDORFF E, DILLES J H, PROFFETT J M, et al. Porphyry deposits: characteristics and origin of hypogene features[J]. Economic Geology, 2005, 29:251-298.
[10]	张少颖, 张华锋. 叶蜡石化蚀变过程中的元素活动性与流体性质: 以山西五台地区白云叶蜡石矿为例[J]. 岩石学报, 2017, 33(6):1872-1892.
[11]	白瑾, 王汝铮, 郭进京. 五台山早前寒武纪重大地质事件及其年代[M]. 北京: 地质出版社, 1992.
[12]	沈保丰, 骆辉, 毛德宝, 等. 五台山—恒山绿岩带金矿床地质[M]. 北京: 地质出版社, 1998.
[13]	ZHAO G C, WILDE S A, CAWOOD P A, et al. Archean blocks and their boundaries in the North China Craton: lithological, geochemical, structural and p-T path constraints and tectonic evolution[J]. Precambrian Research, 2001, 107(1/2):45-73.
[14]	WILDE S A, CAWOOD P A, WANG K Y, et al. Determining Precambrian crustal evolution in China: a case study from Wutaishan, Shanxi Province, demonstrating the application of precise SHRIMP U-Pb geochronology[J]. Geological Society, London, Special Publications, 2004, 226(1):5-25. DOI URL
[15]	WILDE S A, CAWOOD P A, WANG K Y, et al. Granitoid evolution in the Late Archean Wutai Complex, North China Craton[J]. Journal of Asian Earth Sciences, 2005, 24(5):597-613.
[16]	PENG P, ZHAI M G, ZHANG H F, et al. Geochronological constraints on the Paleoproterozoic evolution of the North China Craton: SHRIMP zircon ages of different types of mafic dikes[J]. International Geology Review, 2005, 47(5):492-508.
[17]	LI Q, SANTOSH M, LI S R, et al. Petrology, geochemistry and zircon U-Pb and Lu-Hf isotopes of the Cretaceous dykes in the central North China Craton: implications for magma genesis and gold metallogeny[J]. Ore Geology Reviews, 2015, 67:57-77.
[18]	LI S R, SANTOSH M, ZHANG H F, et al. Inhomogeneous lithospheric thinning in the central North China Craton: zircon U-Pb and S-He-Ar isotopic record from magmatism and metallogeny in the Taihang Mountains[J]. Gondwana Research, 2013, 23(1):141-160.
[19]	LI S R, SANTOSH M, ZHANG H F, et al. Metallogeny in response to lithospheric thinning and craton destruction: geochemistry and U-Pb zircon chronology of the Yixingzhai gold deposit, central North China Craton[J]. Ore Geology Reviews, 2014, 56:457-471.
[20]	刘凤岐, 真允庆. 晋东北“金三角”地区金、银矿床成矿构造环境[J]. 地质找矿论丛, 1994, 9(1):27-38.
[21]	真允庆. 五台山—恒山一带金、银多金属矿床同位素地球化学及其成矿模型[J]. 桂林工学院学报, 2004, 24(2):127-137.
[22]	张文亮, 李朝辉, 陈宇鹏, 等. 五台山区燕山期侵入岩特征及控矿作用[J]. 地质找矿论丛, 2005, 20(增刊):49-52.
[23]	葛良胜, 王治华, 杨贵才, 等. 晋东北燕山期岩浆活动与金多金属成矿动力学[J]. 岩石学报, 2012, 28(2):619-636.
[24]	庞尔成, 席伟杰, 施光海, 等. 山西代县滩上钼多金属矿床辉钼矿Re-Os同位素测年及其地质意义[J]. 地球学报, 2012, 33(5):787-793.
[25]	张文义. 五台县岭底金矿区矿体特征[J]. 华北国土资源, 2012, 48(3):84-85.
[26]	毛景文, 谢桂青, 张作衡, 等. 中国北方中生代大规模成矿作用的期次及其地球动力学背景[J]. 岩石学报, 2005, 21(1):169-188.
[27]	李双保, 李俊建. 山西恒山义兴寨脉金矿田成矿地球化学特征[J]. 前寒武纪研究进展, 1997, 20(2):1-21.
[28]	田永清, 王安建, 余克忍, 等. 山西省五台山—恒山地区脉状金矿成矿的地球动力学[J]. 华北地质矿产杂志, 1998, 13(4):301-456.
[29]	王自力, 牛树银, 郭鹏志, 等. 冀西石湖地区多金属矿床成矿流体氦氩碳氢氧同位素特征及地质意义[J]. 中国地质, 2014, 41(2):577-588.
[30]	LI S R, SANTOSH M. Geodynamics of heterogeneous gold mineralization in the North China Craton and its relationship to lithospheric destruction[J]. Gondwana Research, 2017, 50:267-292. DOI URL
[31]	ZHANG S Y, ZHANG H F. Genesis of the Baiyun pyrophyllite deposit in the central Taihang Mountain, China: implications for gold mineralization in wall rocks[J]. Ore Geology Review, 2020, 120: 103313 https://doi.org/10.1016/j.oregeorev.2020.103313.
[32]	WHITNEY D L, EVANS B W. Abbreviations for names of rock-forming minerals[J]. American Mineralogist, 2010, 95(1):185-187.
[33]	HEMLEY J J, MONTOYA J W, MARINENKO J W, et al. Equilibria in the system Al₂O₃-SiO₂-H₂O and some general implications for alteration/mineralization processes[J]. Economic Geology, 1980, 75(2):210-228. DOI URL
[34]	ZHENG Y F. Calculation of oxygen isotope fractionation in anhydrous silicate minerals[J]. Geochimica et Cosmochimica Acta, 1993, 57(5):1079-1091.
[35]	ROBERT F, BROMMECKER R, BOURNE B T, et al. Models and exploration methods for major gold deposit types[J]. Ore Deposits and Exploration Technology, 2007, 48:691-711.
[36]	GOD R, ZEMANN J. Native arsenic-realgar mineralization in marbles from Saualpe, Carinthia, Austria[J]. Mineralogy and Petrology, 2000, 70(1):37-53.
[37]	MOREY A, TOMKINS A G, BIERLEIN F P, et al. Bimodal distribution of gold in pyrite and arsenopyrite: examples from the Archean boorara and bardoc shear systems, Yilgarn Craton, Western Australia[J]. Economic Geology, 2008, 103(3):599-614. DOI URL
[38]	REICH M, KESTER S E, UTSUNOMIYA S, et al. Solubility of gold in arsenian pyrite[J]. Geochimica et Cosmochimica Acta, 2005, 69(11):2781-2796.
[39]	AN F, ZHU Y F. Native antimony in the Baogutu gold deposit (West Junggar, NW China): its occurrence and origin[J]. Ore Geology Reviews, 2010, 37(3):214-223. DOI URL
[40]	ZHU Y F, AN F, TAN J J. Geochemistry of hydrothermal gold deposits: a review[J]. Geoscience Frontiers, 2011, 2(3):367-374.
[41]	CABRI L J, NEWVILLE M, GORDON R A, et al. Chemical speciation of gold in arsenopyrite[J]. The Canadian Mineralogist, 2000, 38(5):1265-1281. DOI URL
[42]	TARAN Y, BERNARD A, GAVILANES J, et al. Native gold in mineral precipitates from high-temperature volcanic gases of Colima volcano, Mexico[J]. Applied Geochemistry, 2000, 15(3):337-346. DOI URL
[43]	SIMON G, KESLER S E, CHRYSSOULIS S L. Geochemistry and textures of gold-bearing arsenian pyrite, Twin Creeks, Nevada: implications for deposition of gold in carlin-type deposits[J]. Economic Geology, 1999, 94(3):405-421. DOI URL
[44]	CAMUTI K. Clay minerals in alteration systems: terry leach symposium[J]. Australian Institute of Geoscientists Bulletin, 2008, 48:13-18.