西藏甲玛斑岩成矿系统闪锌矿矿物学特征及其地质意义

Mineralogical characteristics and geological significance of sphalerite from Jiama porphyry metallogenic system,Tibet

闪锌矿作为甲玛斑岩成矿系统远端热液流体形成的典型金属硫化物之一,也是揭示成矿流体演化和成矿作用差异的重要指示矿物。甲玛超大型铜多金属矿床是西藏冈底斯成矿带碰撞型斑岩成矿系统的典型代表,其远端成矿流体的性质有待进一步完善。甲玛矿床中闪锌矿可分为产于远端硅灰石矽卡岩型矿体中的闪锌矿(进一步分为主矿段和南坑矿段)、大理岩中Manto型矿体的闪锌矿和角岩型矿体中的闪锌矿。采用电子探针测定闪锌矿的元素组成及含量,研究结果表明,甲玛闪锌矿相对富集Fe、Mn、Cd等元素,其中,角岩型矿体中的闪锌矿的Fe和Cd含量最高,其次为硅灰石矽卡岩型矿体和大理岩中Manto矿体的闪锌矿。甲玛闪锌矿的颜色较丰富,且与Fe元素的含量具有较强相关性,颜色越偏红褐色的闪锌矿Fe含量越高,颜色越偏蓝黑色的闪锌矿Fe含量越低。距离斑岩成矿中心较近的角岩型矿体中的闪锌矿铁含量最高,形成温度最高,为中偏高温;远离斑岩成矿中心的远端硅灰石矽卡岩型矿体中闪锌矿的形成温度中等;更远端的大理岩中Manto矿体的闪锌矿形成温度最低,为中低温。距离热液成矿中心越远,闪锌矿中的Fe和Cd含量逐渐降低,形成温度越低,据此可将闪锌矿作为斑岩成矿系统判定热源和流体源的找矿标识之一。

Sphalerite as one of the typical metal sulfides formed by hydrothermal fluid at the distal end of the Jiama porphyry metallogenic system,is also an important indicator mineral to reveal the evolution of ore-forming fluid and the difference of mineralization.The Jiama super-large copper polymetallic deposit is a typical representative of collision-type porphyry metallogenic system in Tibeten Gangdisi metallogenic belt,and the nature of its distal mineralising fluids needs further refinement.The sphalerite in Jiama mining area can be divided into sphalerite in remote wollastonite skarn type orebody(further divided into main ore section and Nankeng ore section),sphalerite in Manto type orebody in marble and sphalerite in hornfels-type orebody.The article uses electron microprobe to determine the elemental composition and content of sphalerite,and the results of the study show that Jiamma sphalerite is relatively enriched in Fe,Mn,Cd,among which,the sphalerite in hornfels-type orebody has the highest Fe and Cd content,followed by the sphalerite in wollastonite skarn type orebody and Manto type orebody in marble.The color of sphalerite from Jiama is abundant,and has a strong correlation with the content of Fe.The more reddish brown the color is,the higher the Fe content is;and the more bluish black the color is,the lower the Fe content is.The sphalerite has the highest Fe content in the hornfels-type orebody close to the porphyry metallogenic center,and its ore-forming temperature is the highest,which is medium to high temperature.The ore-forming temperature of sphalerite in the remote wollastonite skarn orebody far from the porphyry center is moderate.The ore-forming temperature of sphalerite from the Manto orebody is the lowest,which is at low temperature.The farther away from the hydrothermal metallogenic center,the Fe and Cd contents in sphalerite gradually decrease,and the formation temperature becomes lower.Therefore,sphalerite can be used as one of the prospecting criteria to judge the heat source and fluid source of porphyry skarn metallogenic system.