CAJ | 학술논문

知不拉矽卡岩铜多金属矿床位于西藏冈底斯成矿带中段驱龙斑岩铜矿南侧2~3 km 处,铜资源量接近大型规模,矽卡岩矿体主要呈似层状、透镜状和大脉状产出,主要受角岩化凝灰岩–大理岩岩性界面和断层破碎带控制。本文以最新勘查工作中钻孔揭露的花岗闪长岩为研究对象,通过岩相学观察、LA-ICP-MS锆石U-Pb定年和Hf同位素分析,对知不拉矿床成矿母岩认识给出新指示。花岗闪长岩与角岩化凝灰岩、大理岩的接触带可见不同程度的矽卡岩化发育,由角岩化凝灰岩至花岗闪长岩有角岩化凝灰岩–矽卡岩化角岩–矽卡岩–矽卡岩化花岗闪长岩–花岗闪长岩的分带规律,岩体内可见长石被石榴子石、绿帘石等矿物交代,指示该岩体与矽卡岩矿体形成关系密切。测试结果显示,花岗闪长岩内锆石15个有效测点给出了206Pb/238U加权平均年龄为16.0±0.4 Ma,该年龄代表花岗闪长岩的结晶年龄,与矽卡岩内成矿年龄16.9±0.6 Ma在误差范围内一致；锆石的176Hf/177Hf(i)值为0.2829~0.2831,εHf(t)为3.2~12,单阶段模式年龄tDM在209~563 Ma 之间,具有与驱龙中新世侵入岩相似的 Hf 同位素地球化学特征,岩浆可能起源于软流圈物质上涌引起的新生下地壳部分熔融。知不拉矽卡岩矿床的成矿母岩为中新世花岗闪长岩,与驱龙斑岩矿床属于同一岩浆房演化出溶岩浆,分别是侵位于向形和背形构造中的热液作用产物。
지불랍석잡암동다금속광상위우서장강저사성광대중단구룡반암동광남측2~3 km 처,동자원량접근대형규모,석잡암광체주요정사층상、투경상화대맥상산출,주요수각암화응회암–대리암암성계면화단층파쇄대공제。본문이최신감사공작중찬공게로적화강섬장암위연구대상,통과암상학관찰、LA-ICP-MS고석U-Pb정년화Hf동위소분석,대지불랍광상성광모암인식급출신지시。화강섬장암여각암화응회암、대리암적접촉대가견불동정도적석잡암화발육,유각암화응회암지화강섬장암유각암화응회암–석잡암화각암–석잡암–석잡암화화강섬장암–화강섬장암적분대규률,암체내가견장석피석류자석、록렴석등광물교대,지시해암체여석잡암광체형성관계밀절。측시결과현시,화강섬장암내고석15개유효측점급출료206Pb/238U가권평균년령위16.0±0.4 Ma,해년령대표화강섬장암적결정년령,여석잡암내성광년령16.9±0.6 Ma재오차범위내일치；고석적176Hf/177Hf(i)치위0.2829~0.2831,εHf(t)위3.2~12,단계단모식년령tDM재209~563 Ma 지간,구유여구룡중신세침입암상사적 Hf 동위소지구화학특정,암장가능기원우연류권물질상용인기적신생하지각부분용융。지불랍석잡암광상적성광모암위중신세화강섬장암,여구룡반암광상속우동일암장방연화출용암장,분별시침위우향형화배형구조중적열액작용산물。
The Zhibula skarn-type copper polymetallic deposit is a large copper deposit. It is located 2–3 km south of the Qulong porphyry copper deposit, in the middle section of the Gandise metallogenic belt in Tibet. The ores are commonly bedded, stratoid and vein-like hosted in the interformational detachment zone between tuff and marble and in the fracture zone. The granodiorite was discovered lately in the drill holes. The contact zone between granodiorite and tuff or marble is skarnized. The skarn-type ore deposit is closely related to the granodiorite as was demonstrated by the gradual change from the tuff, hornfels, and skarn, to the skarnized granodiorite. LA-ICP-MS zircon U-Pb dating yields a weight average 206Pb/238U age of 16.0±0.4 Ma, which is close to the Re-Os isochron age (16.9±0.6 Ma) of molybdenites from the ores. The granodiorite hasεHf(t) values in range of 3.2–12 and single-stage model ages between 209–563 Ma, which are similar to those of the Miocene intrusives in the Qulong areas. The zircon Hf isotopic compositions of the granodiorite indicate that the magma is likely resulted from partial melting of the juvenile lower crust. The granodiorites are determined as the ore-forming intrusive of the Zhibula skarn-type deposit, and they are derived from the same magma system with those associate with Qulong deposits. Both of them are are of hydrothermal origin.