西藏马攸木金矿床的矿床类型讨论

Discussion on genetic type of Mayum gold deposit in Tibet

位于青藏高原西段的马攸木金矿床，是由西藏地热队于2001年新发现的岩金矿床。通过对马攸木金矿床开展的野外实地调查和初步的室内研究，结果表明：①马攸木金矿床产于绿片岩相以上的变质地体；②其成矿年龄约为（59．34±0．62）Ma，反映成矿作用发生于青藏高原碰撞造山的高峰期；③金矿体呈脉状产于超地壳断裂带附近的韧性剪切带内；④矿石类型主要为构造蚀变岩型和石英脉型，含金石英脉呈较为致密的块状，并未见在低温石英脉中常见的皮壳状、条带状等结构构造以及玉髓等低温矿物；⑤初步的石英流体包裹体研究表明，成矿流体主要为富CO2的低盐度NaCl—H2O流体，成矿温度介于240～280℃间，峰值为270℃；⑥初步的氢氧同位素资料表明，成矿流体主要为变质流体与天水的混合产物。上述这些特征总体符合造山型金矿床的基本特征，因此认为马攸木金矿床可能属于造山型金矿床，而不是曾被认为的热泉型金矿床。

The Mayum gold deposit in western Tibet plateau was discovered in 2001 by the Tibet Geothermal and G-e- ological Party of Tibet Bureau of Geology and Mineral Exploration and Development. It was once considered to be of the hot spring type. The authors＇ study, however, reveals that the Mayum detxxsit should belong to the orogenic gold deposit. This conclusion is based on the following evidence： ① ore bodies are hosted by greenschist of the metamorphic terrain; ② the ore-forming age is about （59.34 ±0.62） Ma, suggesting that minera- lization took place at the culminatiom period of the Indo-Asian collision. ;③ ore bodies occur along the ductile zones near the supra-crustal fault belt; ④ ores are mainly of quartz vein and altered rock types, and auriferous quartz veins are massive, with no low-temperature crustose and banded structures and chalcedony observed among ores; ⑤ preliminary fluid inclusion studies show that the ore fluid is mainly of low salinity and CO2-rich NaCl-H2O type, and ore-forming temperatures are between 240 and 280℃, with the mode being 270℃ ; ⑥ oxygen and hydrogen isotope geochemistry indicates that the ore fluid seems to be a mixture of metamorphic fluid and meteoric water.