【作者】 孟祥金；

【导师】 侯增谦；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2004， 博士

【摘要】 冈底斯斑岩铜矿带位于西藏造山带南部拉萨地体南侧冈底斯花岗岩基的中东部东西长约350km、南北宽达80kin的带状区域内。带内分布有十余个斑岩型铜矿床（点）。含矿斑岩形成于中新世，侵入于冈底斯花岗岩基和火山岩以及沉积岩地层中。它们在空间分布上受横跨拉萨地体的正断层系统和平行于造山带的逆冲带共同控制，具有东西成带、南北呈串的展布特点。成矿作用时间与含矿斑岩活动时间一致，在14～17Ma之间，岩浆活动与成矿事件发生在印度-亚洲大陆碰撞后的地壳伸展时期。含矿斑岩体为浅成复式岩体，岩性为二长花岗斑岩、花岗斑岩，少量为石英二长斑岩，石英正长斑岩、碱性花岗斑岩和花岗闪长斑岩。岩石化学特征显示含矿斑岩属于高钾钙碱性岩石系列。岩石明显高SiO₂、Al₂O₃、K₂O，Mg^#，低Y和HREE，富集大离子亲石元素（LILE）K、Rb、Th、U、Sr、Pb和LREE，亏损高场强元素（HFSE）Nb、Ta、Ti、Yb，高Sr／Y比值，具有埃达克岩浆亲合性。岩石的微量元素组成与Sr-Nd-Pb同位素组成特征表明含矿斑岩岩浆起源与增厚的下地壳和／或残存在上地幔的俯冲洋壳板片熔融有关，形成环境明显不同于岛弧、大陆边缘的俯冲环境。冈底斯斑岩铜矿带由其南侧的斑岩型铜矿化带和北侧的铜多金属矿化带组成，南带的斑岩型Cu、Mo矿化与北带的矽卡岩型铜多金属矿化共同构成了冈底斯斑岩铜矿成矿系统。矿化类型与斑岩体侵位的围岩环境有关。斑岩体内为单一的细脉浸染状Cu或Cu-Mo矿化，铜矿体多出现在钾硅酸岩化蚀变带。在碳酸盐岩围岩中形成矽卡岩型脉状、块状、似层状铅锌铜多金属矿化。斑岩铜矿的蚀变分带特征类似于Lowell和Guilbert模式，从中心向外依次为钾硅酸岩化带→石英绢云母化带→青磐岩化带。与岛弧、陆缘弧环境斑岩蚀变不同，冈底斯斑岩铜矿的蚀变分带简单，蚀变矿物组合稳定，泥化蚀变不发育，矿化主要发生在钾硅酸岩化带。冈底斯斑岩铜矿的成矿流体特征与成矿作用与岛弧、陆缘弧环境的斑岩铜矿基本相似。与成矿有关的流体包裹体可以分为气相包裹体、液相包裹体、含子晶的多相包裹体三类。包裹体内的子晶以石盐为主，并有较多的黄铜矿子晶分布于高盐度的包裹体内。成矿流体为高盐度流体，盐度变化范围为（1.91～66.75）wt NaCl％。流体成分组成显示成矿流体属于Na⁺-K⁺-SO₄^2--Cl^--H₂O-CO₂型。包裹体均一温度为（191～＞550）℃，主要集中于（300～550）℃之间。均一压力变化范围为（64.33～236.42）×10⁵Pa。成矿流体的氧逸度（lgfo₂=-20.763～-38.078）和硫逸度(lgf_s2=-2.21～-7.62)较高。含矿斑岩和金属硫化物的S、Pb同位素组成、流体的H、O同位素组成、流体成分特点以及流体活动的环境参数表明成矿流体与成矿物质直接来自于岩浆，具有高氧逸度的含矿斑岩岩浆在就位后于较为封闭的环境中演化；冈底斯斑岩铜矿的蚀变与矿化是岩浆流体单向演化的结果，外来流体对成矿贡献不大。成矿作用主要发生在岩浆期后高温阶段（钾硅酸岩化蚀变阶段）。高温阶段岩浆流体的二次沸腾作用和流体混合作用是冈底斯斑岩铜矿成矿的两个重要方式。冈底斯斑岩铜矿具有快速成矿特点。含矿斑岩中长石矿物年龄与矿石辉钼矿Re-Os年龄对比显示出冈底斯单个斑岩铜矿床成矿流体活动持续时间多在2Ma以内，矿化活动维系时间约1Ma左右。在与不同构造背景下斑岩铜矿进行对比的基础上，提出了冈底斯含矿斑岩构造控制模式，初步建立了碰撞造山带冈底斯中新世斑岩铜矿的区域成矿模式。更多还原

【Abstract】 The Gangdese porphyry copper belt is located in the central-east segment of the Gangdese granitoid batholiths, southern margin of the Lhasa terrane in the Tibetan collisional orogen, paralleling with the Yarlung-Zangbo suture. The Miocene mineralized porphyry bodies, intruded the Gangdese granitoid batholiths and surrounding the Triassic-Cretaceous sedimentary sequence as multiple hypabyssal intrusions, were locally controlled by either near NS-striking normal faults or the intersection of thrust zone with normal fault. Across the batholiths, these intrusive appear as beaded clusters trending within the normal faulting systems or graben basins.The ¹⁸⁷Re- ¹⁸⁷Os isochron ages yielded by molybdenite samples from the deposits in the belt vary from14 Ma to 17 Ma, suggesting that Cu （-Pb-Zn） mineralization took place in the middle-late stage of the lifetime of the Miocene magmatic Cu systems during post-collisional crustal extension period.The dominant porphyries are granitic, and monzogranitic, with subordinate quartz monzoniti1, quartz synitic, granitic, and granodiorite. The porphyries characterized by high-SiO₂, Al₂O₃, K₂O, and Mg# and low Y, and HREE contens with high Sr/Y are shoshonitic and high-K ealc-alkaline. The rocks are enriched in LILE（e.g. K, Rb, Th, U, Sr, Pb） and LREE, and depleted in HFSE（e.g. Nb, Ta, Ti, Yb）, showing adakite magmatic affinity. The characteristics of the rare elements compositions and the signatures of Sr, Nd, and Pb isotope of the rocks inferred that the mineralized porphyry related to the partial melting of the subducted oceanic slab remaining in the mantle and of the lower crust under Gangdese and to the interaction between slab-derived melt and overlying mantle.The Gangdese porphyry copper belt consists of two mineralize subzones, viz. porphyry type copper mineralize zone in the south Gangdese belt and skarn type copper polymetal mineralize zone in the north Gangdese belt, which form the metallogenic system of Gangdese porphyry copper deposit. Two styles of mineralization can be recognized in the porphyry deposits. One style is the Cu or Cu-Mo mineralization in the interior of porphyry intrusions with veinlet-disseminated and fine veinlet pyrite + chalcopyrte+molybdenite+bornite assemblages, the Cu orebodies mostly occurred in K-silicate zone whereas Mo orebodies in quartz-sericite zone. The second mineralization predominantly produced stratiform or lenticular Pb-Zn-Cu polymetallic orebodies, mainly associated with the skarn bodies along the contact between the porphyries and surrounding carbonate rocks.Multiple hydrothermal alterations progressing from early central K-silicate styles to late sericitic, silicification and argillic types were extensively developed around mineralizing intrusions. Three zones can be distinguished according to the altered mineral assemblages. The concentric alteration zones from the inner outward are successively the K-silicate zone, the quartz-sericite zone, and the propylitic zone. The orebodies mostly occur in the K-silicate alteration zones. The argillic alteration controlled by structure locally occurs as patches, overprinted the other alteration zone.The feature of the inclusions in quartz phenocrystal, vein quartz and anhydrite and the compositions of the ore-fluid in the deposits indicate that the fluid is the type of Na⁺-K⁺-SO₄^2--Cl^--H₂O-CO₂. The salinities of the fluid vary remarkable from 1.91 to 66.75 wt%NaCl equivalent. The homogenization temperatures of the fluid inclusions are various, ranging from 191℃to 550℃, with mostly between 300℃and 550℃. The range of the homogenization pressures is from 64.33×10⁵Pa to 236.42×10⁵Pa. The fugacity of oxygen and that of sulfur are high, varying from -20.763～-38.078 （lgfo₂） and -2.21～-7.62 (lgf_s2, respectively. The compositions of hydrogen, oxygen isotope of the fluid and the signatures of sulfur, lead isotopes of the rocks and the sulfide from the deposits indicate that the ore fluid and ore-forming matter are directly from the magmas developed closely in high fugacity of oxygen. The mineralization mainly took place in the postmagmatic stage in high temperatures. The alterations and the mineralization resulted from the unilateral evolution of the magmatic fluid. The secondary boiling of the magmas in high temperature and the mixing of different fluids are two important mineralizing ways in the copper deposits in the Gangdese belt. The size of the single copper deposit in Gangdese is restricted by the limited scale of the oceanic slab remaining in the mantle under the Gangdese.The comparison of the age date yielded by the phenocrystal plagioclases and by the molybdenites from the mineralized porphyry intrusions suggests that the ore fluid developed in a short session with time limit of active no more than 2 Ma, and the time span of mineralizing is even more shorter, 1 Ma or so, implying the speciality of rapid mineralizing of the copper deposits in Gangdese.Based on the mineralization characteristics of the Gangdese copper deposits and the contrast of the copper deposits occurred in different settings, the tectonic model of the mineralized magmas and the metallogenic model of the Gangdese Miocene porphyry copper deposits in the Tibetan collisional orogen have been proposed in this paper.更多还原