【作者】 徐受民；

【导师】 莫宣学； 曾普胜；

【作者基本信息】 中国地质大学（北京） ， 矿物学、岩石学、矿床学， 2007， 博士

【摘要】 首次对北衙富碱斑岩进行了锆石SHRIMP U-Pb年龄测定，厘定了北衙矿区成矿石英正长斑岩的SHRIMP U-Pb年龄为34～33Ma。结合前人所报道的年龄，认为北衙矿区存在三期岩浆活动：早期是石英钠长斑岩和煌斑岩在60～65Ma侵位；中期石英正长斑岩在33～34Ma侵入，并伴有煌斑岩的侵入，该期斑岩与成矿关系密切；晚期的黑云母石英正长斑岩在3.7Ma侵位。通过对北衙地区富碱斑岩常量、微量元素和Pb，Sr，Nd同位素地球化学等方面的研究揭示：北衙富碱斑岩具有埃达克岩的地球化学特征，但又以高w（Na₂O+K₂O），高w（K₂O）／w（Na₂O）比值，低w（MgO），低w（Cr），低w（Ni）不同于典型的埃达克岩。含矿斑岩为低Y，中Ba，且Nb／Y＞1，反映了与熔体有关的富集作用占主导。扬子板块的俯冲和脱水作用及软流圈物质上涌所提供的热能和流体，使加厚地壳部分熔融，形成具埃达克岩性质的富碱岩浆。发现北衙富碱斑岩正长石斑晶具有富Or的环边。表明在岩浆结晶过程中出现了独立的流体相，为含矿热液来自岩浆提供了岩石学依据，是含矿斑岩的标志。首次较为全面系统地研究了矽卡岩组成，分带和矿床成因：北衙金矿床具典型的矽卡岩型矿床的特征。接触带中矽卡岩具明显的分带特征，多数矿体产于其中。在矽卡岩中叠加有后期的交代蚀变，并伴有大量磁铁矿、金和铜的沉淀。原生矿床成因类型为以矽卡岩型铁金矿为主，兼有斑岩型金铜矿和热液脉型铁金矿铅锌矿的复合类型。从岩体内部向外，从深部到地表，元素组合为（Au）Cu→（Cu）Au→Au-（Cu）-Fe（Pb+Zn），元素分带明显，反映了从高温→低温元素组合的变化。在岩体走向上，从北向南，随着岩体向南倾伏，高温的Cu、Fe、Ag含量有降低的趋势，而中低温的Au、Pb+Zn含量则逐渐增高，也体现了从高温→低温元素组合的变化。讨论了原生矿床和表生矿床的成矿时代。认为北衙金-多金属矿床成矿时代为33～28Ma，岩浆热液系统的持续寿命约5Ma。依据地质体的接触关系和测年数据，丽江组下段及表生成矿作用的时代应在始新世之后。建立了北衙金多金属矿床的成矿模式。北衙金多金属矿床位于金沙江—红河大型走滑断裂带及隐伏东西向断裂交叉部位，处于晚碰撞时期压扭到张扭应力转换阶段。成矿金属和成矿流体来自富碱斑岩岩浆。矿体主要产出于中三叠统北衙组碳酸盐岩与石英正长斑岩接触带中，近南北向断裂及破碎带控制了矿体的分布。碳酸盐岩活泼的化学性质和力学性质有利于矿质的沉淀和充填。挥发组分是成矿元素运移、富集和沉淀的主要因素。成矿作用有三期：斑岩矿化期，矽卡岩矿化期，表生矿化期。还总结了北衙矿床在岩浆岩、构造，围岩蚀变、矿化、地球物理和地球化学方面的找矿标志。更多还原

【Abstract】 It is the first time that we obtain 34～33Ma of the ore-bearing quartz syenite porphyry in Beiya ore area by using SHRIMP U-Pb zircon dating. Combined with the ages reported by former researchers, we suggest that there were three periods of magmatism. The earliest one is quartz albitophyre and lamprophyre in 60～ 65 Ma, then quartz syenite porphyry in 30～34Ma, which has a close relationship with mineralization process, and associated with lamprophyre, and the last is the biotite quartz syenite porphyry at 3.7Ma.Based on geochemistry of major elements, trace elements, and Pb, Sr, Nd isotopes, the Beiya alkali-rich porphyries have the same geochemical characteristics as adakite, but are different from the typical adakite in higher w（Na₂O+K₂O）, w（K₂O）/w（Na₂O） ratio, and lower w（MgO）, w（Cr） and w（Ni）. Low Y, medium Ba and Nb/Y > 1 of the ore-bearing porphyries indicate that the enrichment process related to melts had played an important role. Heat and fluids released by subduchtion and dehydration of Yangzi block and asthenosphere upwelling might cause partial melting of the thickened crust and then formed such alkali-rich magma.Orthoclase phenocrysts with Or-rich rims in the Beiya alkali-rich porphyries suggests that fluid phase occurred during the magma crystallization, which is a symbol of ore-bearing porphyries and could be the evidence that the ore-bearing hydrothermal solution came from the magma.A systemic research on composition, zonation and metallogeny of skarns has been conducted. The Beiya Au deposit has the typical characteristics of skarn-type ores. Zonation was developed in skarns at the contact between porphyries and wall rocks, in which most ore bodies are distributed. Later metasomatic alteration was overlapped on skarns with precipitation of a great deal of magnetite, gold and copper. According to our study, the Beiya deposit is a composite deposit, within which skarn-type Fe-Au deposit is predominant, and associated with porphyry-type Au-Cu, and hydrothermal vein-type Fe-Au-Pb-Zn mineralization.From the inside to outside and from the deep to surface, the alkalic-rich porphyries are clearly zoned in element assemblage from （Au）Cu to （Cu）Au, and to Au-（Cu）-Fe（Pb+Zn）, corresponding to temperature decreasing. While the contents of Cu, Fe and Ag （high temperature） gradually decreased along the strike from north to south, Au、 Pb+Zn （medium to low temperature） increased..In this thesis, we discussed the timing of mineralization of the primary and supergene deposits. The timing of Beiya Au and polymetallic deposit is considered to be a period of 33～28Ma, and the hydrothermal system of magma had been lasted for about 5Ma. According to geological relationship, the lower section of Lijiang formation and the timing of supergene ore-forming process should be younger than Eocene.A metallogenetic model is proposed for Beiya gold and polymetallic deposit in this thesis. The deposit is located at the junction of the large Jingshajiang-Red River strike-slip fault and W-E buried faults during a transitional period from transpressional to transtensional state in the late collisional time. Ore-forming fluids and metals mainly came from the magma of alkalic-rich porphyries. The ore bodies, controlled by the N-S faults and fracture zones, mainly occurred in the contact zone between the middle Triassic carbonates of Beiya formation and quartz syenite porphyries. The actively chemical and mechanic characteristics of carbonate are in favor of precipitation of metallogenetic materials. Volatiles are very important factors for ore-forming elements to be transported, accumulated and concentrated. There are three epochs of ore-forming processes, namely, epochs of prophyries, skarn and supergene, respectively. Finally, indicators for prospecting of the Beiya deposit has been summarized in aspects of magma rocks, structural geology, alternation of wallrocks, geophysics and geochemistry.更多还原