摘要
多不杂富金斑岩铜矿床位于斑公湖-怒江缝合带北侧多不杂构造岩浆弧中,成矿与侵位于中侏罗统雁石坪群和早白垩统美日切组地层中的石英闪长玢岩、花岗闪长斑岩有关。由于斑岩体的侵位,在岩体内及其围岩中形成强烈蚀变且分带明显,由含矿斑岩中心向外可划分出钾硅化带、中级泥化带、泥化带、伊利石-水白云母化-褐铁矿化带-角岩带或青磐岩化带(围岩是中基性火山岩时)。矿化为细脉-浸染状,含矿斑岩全岩矿化,少量矿化产于围岩中,成矿为铜-金组合,为典型的富金斑岩铜矿。初步识别出(1)钾化带中主要发育M型、EB型、A型及部分B型脉;(2)绿泥石化带(中级泥化带)中发育B型、C型、石英-绿泥石脉及S型、G型脉;(3)在粘土化带(泥化带)中主要发育C型脉、G型脉及S型细网脉;(4)在围岩中主要发育B型、C型、D型及G型细网脉以及碳酸盐脉、M型脉等。矿区范围内发育丰富的热液磁铁矿、赤铁矿、金红石等,铜、金沉淀与热液磁铁矿的形成关系密切;矿石中主要为黄铜矿、少量斑铜矿和辉铜矿,而黄铁矿很少,总体上为黄铜矿>斑铜矿,黄铜矿》黄铁矿。在石英斑晶及各种脉系中识别出三个大类和十个亚类的流体包裹体。包裹体显微测温数据表明最高(达935℃、压力200MPa)的均一温度出现在石英斑晶中,这种由含不透明子矿物、简单多相、含硅酸盐子矿物、赤铁矿多相包裹体类型构成的具45%NaCleq盐度的多相包裹体可能代表本矿床最原始的成矿流体组成;这种成矿流体上升到3km左右、冷却到580℃左右发生沸腾,分离出超高盐度(60%～80%NaCl eq)流体包裹体和富气相包裹体,并导致大量磁铁矿的结晶和还原硫的释放,且伴随部分金属硫化物及部分金沉淀,形成早期的M、A型脉;随着温度的进一步降低和分离出的流体包裹体的聚集,在500℃～480℃之间、22～40MPa之间、深度约1.5km发生沸腾,大量释放出的硫与金属离子结合,导致了大量铜、金的沉淀,形成如B型脉等一系列脉系及浸染状的铜矿化。在450℃～400℃之间、压力20～32MPa之间、深度1.1km左右又发生了明显的沸腾事件,形成了如C型脉、S型等含铜脉系。在370℃～200℃之间、压力5～30MPa之间,包裹体以液相包裹体和多相包裹体为主,其盐度变化较大,可能是由于岩浆流体的稀释作用或少量大气降水参与循环所致,形成了D型脉及面状硅化。我们的研究结果揭示多不杂富金斑岩铜矿是主要由直接从岩浆熔体中出溶(600℃～950℃)的具高氧化性、(超)高盐度的富含成矿元素的岩浆流体形成的,是斑岩矿床系列中正岩浆端元的典型代表。
The Duobuza gold-rich porphyry copper deposit, located in the Duobuza tectono-magmatic arc at northern margin of the Bangonghu suture zone, is occurred in high-level, early-Cretaceous compositionally quartz diorite porphyrite to granodiorite porphyry which intruded into the strata of the middle Jurassic Yanshiping Formation volcano-sedimentary rocks and the early Cretaceous Meiriqie Group volcanic rocks. Intensively alterations in stock and wall-rocks resulted from emplacement of the intrusion have obvious zonation, as follows： potassic alteration, moderate phyllic alteration, argillization, illite-hydromuscovite and propylitization from centre outwards. Early hydrothermal alteration produced potassic assemblage （biotite-K-feldspar） in the central part of the intrusion, but in the peripheral and upper part of the intrusion occurred later phyllic alteration and argillization, overprinting the earlier potassic alteration. Illite or hydromuscovite and silicification, propylitization occurred in the hosted volcano-sedimentary rocks and volcanic rocks. Mineralization is characterized by multiple generations of stockwork and sheeted quartz, K-feldspar, magnetite, stringer chalcopyrite and gold-bearing veins. Copper and gold mineralization is accompanied by potassic and phyllic alterations. Mineralization is Cu-Au association, belonging to typical gold-rich porphyry copper deposit. Eight main types of veins have been identified, namely M, EB, A, B, C, D, S and G veins. Three major inclusion types and ten subs are distinguished from quartz phenocrysts and various quartz veins. Based on microthermometric analyses of fluid inclusions from quartz phenocrysts and early to late-stage veins, the highest temperature multiphase inclusions （up to 935℃ ; average salinity 45% NaCl eq, P-200MPa） , containing a number of solids, e.g. opaque, silicate melt, hematite at room temperature, are mainly recorded in quartz phenocrysts, locally in A and C veins. This result indicates that fluids exsolved from magma are high temperature, high salinity, strong oxidation and ore metal-rich ore-forming fluids. They represent the most primitive magmatic fluid recorded at the deposit. When primitive magmatic fluid ascended up to 3km and cooled down to 580℃, they were separated to multiphase fluid inclusions of salinity 60% - 80% NaCleq and lower salinity vapor-rich fluid inclusions of salinity 6.9% NaCleq by boiling. This process resulted in formation early M and A veins, and deposition of sulfides mainly, as well as some gold in certain location. Later B, C and D veins were generated by the orthomagmatic fluids boiling episodically. Our research suggests that the Duobuza gold-rich porphyry deposit is representative of the typical orthomagmatic end member of the porphyry continuum.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第5期935-952,共18页
Acta Petrologica Sinica
基金
国家自然科学基金(40672068)
国家重点基础研究发展规划"973"项目"冈底斯-藏东斑岩铜矿成矿作用课题"(2002CB412605)联合资助
关键词
富金斑岩铜矿
蚀变脉系
流体包裹体
原始岩浆流体
流体沸腾
多不杂
西藏班公湖
Gold-rich porphyry copper deposit, Vein systems, Primitive magmatic fluid, Fluid inclusion, Boiling, Duobuza, Bangonghu arc, Tibet
作者简介
李光明,男,1964年生,博士,主要从事金属矿床成矿作用及成矿预测研究,E-mail：liguangming0505@yahoo.com.cn
