青藏高原碰撞造山背景造山型金矿床:构造背景、地质及地球化学特征

Orogenic gold deposits formed in Tibetan collisional orogen setting:Geotectonic setting,geological and geochemical features

青藏高原碰撞造山背景下形成了雅鲁藏布江缝合带及哀牢山造山带两条造山型金矿带。雅鲁藏布江缝合带包含马攸木、念扎、邦布及折木朗金矿等;该矿带形成于拉萨地块及特提斯喜马拉雅地层序列地壳初始缩短加厚的背景(59~44Ma),与林子宗火山岩和高压变质岩同期形成。控矿构造主要以EW向展布。金以自然金形式赋存在石英硫化物脉及石英脉两侧以绿片岩相变质为主的千枚岩及板岩中。哀牢山造山带包含镇沅、金厂、大坪及长安金矿等,主要形成于35~26Ma,成矿背景为区域发生大规模走滑剪切,矿区内分布有成矿前期的煌斑岩及富碱斑岩。控矿构造主要以NW-SE向展布,围岩变质级低于雅鲁藏布江缝合带。C-S-H-O-Pb同位素变化较大,整体雅鲁藏布江缝合带及哀牢山造山带造山型金矿成矿流体主要来源于深部地幔流体、围岩地层的变质流体及岩浆流体,成矿围岩的差异性也会导致同位素的变化性。

There are two orogenic gold belts： Yarlung Zangbo suture zone and Ailaoshan orogenic belt,formed in Tibetan collisional orogenic setting. Orogenic gold deposits formed on the Yarlung Zangbo suture zone include Mayum,Nianzha,Bangbu and Zhemulang gold deposit,etc. This gold belt formed in compression structural setting in which the crust of Lhasa Terrane and Tethyan Himalaya Sequence shortened and thickened at the beginning of Tibetan collisional orogen（ 59 - 44Ma）. It is coeval with Linzizong volcanic rock and high-pressure metamorphic rocks. Orogenic gold deposits on the belt are controlled by EW-striking structure. Gold is concentrated as native gold in sulfide-quartz veins,as well as in greenschist facies host rocks surrounding sulfide-quartz veins,mainly as slate and phyllite. Orogenic gold deposits formed on the Ailaoshan orogenic belt include Zhenyuan,Jinchang,Daping and Chang ＇an gold deposit,etc. These deposits mainly formed in 35 - 26 Ma,dominated by large strike-slip faults in the district. They are controlled by NW-SE striking structure and the metamorphic grade of the lithologies surrounding the Ailaoshan orogenic gold deposits is lower than the Yarlung Zangbo＇s. Cenozoic lamprophyre and alkali rich porphyry formed during the early mineralization distribute wildly in the ore district. C-S-H-O-Pb isotopes vary widely between deposits. Ore-forming fluids of the Yarlung Zangbo suture zone and Ailaoshan orogenic belt mainly derived from deep reduced mantle fluids,metamorphic fluids coming from dehydration of host stratum and magmaic fluid. The different lithology of host rocks can also cause the variability of isotope compositions.