一个与岩浆作用有关的独立铅锌成矿系统的建立——以西藏纳如松多铅锌矿床为例
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国家973资助项目(2011CB403104);中国地质调查项目(1212011220908);国家自然科学基金(41320104004,41403043);国际地质对比计划(IGCP/SIDA-600);科技部创新方法工作专项项目(2010IM031100)


The establishment of an independent Pb-Zn mineralization system related to magmatism: A case study of the Narusongduo Pb-Zn deposit in Tibet
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    摘要:

    通过对西藏纳如松多铅锌矿床4套矿化型式的系统梳理,根据地质事实和相关同位素证据,初步建立了一个独立的和岩浆作用相关的热液铅锌成矿系统模式。纳如松多铅锌矿化和石英正长斑岩密切相关,目前已发现了产在斑岩外围的古新世典中组凝灰岩地层中的隐爆角砾岩型矿化、产在斑岩与二叠纪下拉组灰岩接触带上的矽卡岩型矿化、产在斑岩外围典中组凝灰岩与二叠纪昂杰组砂板岩岩性分界面上的矿层型矿化以及产在凝灰岩或砂板岩内部先存裂隙中的脉型矿化等4种铅锌矿化型式。它们均以绿帘石绿泥石化、硅化绢云母化和碳酸盐化为主要围岩蚀变类型,矿石矿物为方铅矿+闪锌矿,主要脉石矿物为黄铁矿+黄铜矿+石英+绢云母+方解石,蚀变和矿物组合特征指示它们发育在同一矿化系统中,但成矿热液温度逐渐降低。隐爆角砾岩型和矽卡岩型矿化成矿流体δDV-SMOW值分布范围较大(-177‰~-118‰和-164‰~-139‰),δ18OV-SMOW值分布范围较小(-2.76‰~3.29‰和-5.46‰~-4.58‰),反映其主要来自发生了去气作用的岩浆水,并混合了少量大气降水。4种矿化型式的S同位素值按照隐爆角砾岩型(4.15‰)、矽卡岩型(7.92‰)、矿层型(8.49‰)和脉型(8.80‰)的顺序逐渐增大,反映其主要来自发生了H2S去气作用的残余岩浆相。矿区成矿斑岩与冷水坑斑岩型铅锌矿床的成矿斑岩极为相似,推测矿区深部也有斑岩型铅锌矿化的可能。一个独立的和岩浆作用相关的铅锌成矿系统模式由此建立,它包括了发育在挤压环境中所有和岩浆作用相关的铅锌矿化类型,可简述如下:新特提斯洋壳俯冲回转,地幔楔及上覆地壳部分熔融,纳如松多独具特色的斑岩岩浆形成;岩浆上升侵位,H2O及H2S去气,流体初溶,岩浆内部和顶部分别汇集了富氧化性质S和金属物质及富还原性质S和金属物质的残余岩浆流体;岩浆进一步侵位,温度降低,矿物结晶,SO2水解,斑岩型铅锌矿化形成;岩浆侵位到凝灰岩地层中,凝灰岩高压致爆,硫化物沉淀,隐爆角砾岩型铅锌矿化形成;富成矿物质残余岩浆水向外运移,伴随H2S进一步去气,矽卡岩型、矿层型、脉型铅锌矿化在不同岩性地层和构造位置中形成。

    Abstract:

    In the compressive environment, intrusion-related Pb-Zn mineralization includes porphyry, crytoexplosive breccia, skarn, manto, and vein types. However, examples of all of them occurring in the same mineralization system are less known. Narusongduo is a superlarge Pb-Zn deposit in the Gangdise metallogenic belt, Tibet. Except porphyry type, all Pb-Zn mineralization types mentioned above have been found in this deposit, which makes this deposit an excellent case to study the scientific question mentioned above. In this study, the authors present a preliminary description about the four Pb-Zn mineralization types and oxygen, hydrogen and sulfur isotopic analyses, and establish a descriptive and genetic model that involves all the mineralization types in an independent Pb-Zn mineralization system related to magmatism. The Pb-Zn mineralization in the Narusongduo deposit has close relationship with the quartz syenite porphyry. Four Pb-Zn mineralization types have been found, i.e., crytoexplosive breccia type formed in the tuff strata of the Dianzhong Formation in Paleocene, skarn type formed in the contact between limestone of the Xiala Formation in Permian and quartz syenite porphyry, manto type formed in the contact between sandstone and slate in the Angjie Formation in Permian and tuff in the Dianzhong Formation, and vein type formed in pre-existing fractures in tuff and sandstone-slate strata. Epidotization, chloritization, silicification, sericitization and carbonation are main alteration types for the four mineralization types, galena and sphalerite are ore minerals, and pyrite, chalcopyrite, quartz, sericite and calcite are main gangue minerals. In accordance with the order of cyrtoexplosive type, skarn type, manto type and vein type, the host rock alteration becomes weaker, the epidote, chlorite, quartz, sericite and chalcopyrite decrease and eventually disappear, and the carbonate increases. These characteristics indicate a cooling evolution in a unified mineralization system. As for the fluids of crytoexplosive breccia type and skarn type Pb-Zn mineralization, the δDV-SMOW values have large ranges (-177‰~-118‰ and -164‰~-139‰, respectively) and the δ18OV-SMOW values have narrow ranges (-2.76‰~3.29‰ and -5.46‰~-4.58‰, respectively). These data suggest that the ore fluids were derived from magmatic hydrothermal fluid which had undergone degasification in an open system and was mixed with meteoric water. The δ34S values vary in a narrow range and become larger in order of cyrtoexplosive type (4.15‰), skarn type (7.92‰), manto type (8.49‰) and vein type (8.80‰), which indicates that the sulfur came from magmatic hydrothermal fluid which had undergone H2S degasification in an open system, and the degasification degree became stronger and stronger. The chemical geology of the quartz syenite porphyry is similar to that of porphyry hosting the Lengshuikeng porphyry Pb-Zn deposit, so the authors infer that some porphyry-type Pb-Zn mineralization might have also occurred in the depth of the Narusongduo porphyry. On such a basis, an independent Pb-Zn mineralization system, which includes all the Pb-Zn mineralization types related to magmatism occurring in compressed environment, has been built. The model can be described as follows: With the subduction and revolution of the Neo Tethys oceanic crust, the mantle wedge and the overlying crust became melted, forming the Narusongduo porphyry magma with unique chemical geology. With the magma ascending, H2O and H2S became degassing, the fluid became exsolved, oxidized magmatic fluid with oxidized S and metals was concentrated in the center of the magma, and reduced magmatic fluid with reduced S and metal was concentrated on the top of the magma. With further ascending, the temperature of the magma decreased, the magma crystallized, SO2 became hydrolytic, and the porphyry Pb-Zn mineralization occurred. When the magma ascended into the tuff strata, the compact rocks caused the pressure of the hydrothermal fluid to be higher than the rocks, which led to the crytoexplosion of the tuff, and the crytoexplosive type Pb-Zn mineralization occurred. At the same time, with the stronger H2S degasification, magmatic fluid rich in metal and sulfur also moved to the host rocks far away from the magma, and then skarn-type, manto-type and vein-type Pb-Zn mineralization occurred in different locations with different lithologies and structures.

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刘英超,纪现华,侯增谦,田世洪,李振清,赵晓燕,周金胜,马旺,杨竹森,2015,一个与岩浆作用有关的独立铅锌成矿系统的建立——以西藏纳如松多铅锌矿床为例[J].岩石矿物学杂志,34(4):539~556. LIU Ying-chao, JI Xian-hua, HOU Zeng-qian, TIAN Shi-hong, LI Zhen-qing, ZHAO Xiao-yan, ZHOU Jin-sheng, MA Wang, YANG Zhu-sen,2015,The establishment of an independent Pb-Zn mineralization system related to magmatism: A case study of the Narusongduo Pb-Zn deposit in Tibet[J]. Acta Petrologica et Mineralogica,34(4):539~556.

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  • 收稿日期:2014-06-10
  • 最后修改日期:2015-01-16
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  • 在线发布日期: 2015-07-22
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