锆石Ge含量和年龄对云南临沧锗矿床物质来源的约束

云南临沧锗矿床产在以临沧花岗岩为基底的中新世断陷盆地中。已有研究表明,成矿元素Ge来自基底花岗岩,但临沧花岗岩是复式岩基,具有多期次的岩浆活动,而Ge来自哪期岩浆活动并不清楚。文章对采自晓街、临沧、勐库和勐海的7个花岗岩样品(纵贯临沧岩基)进行了LA-ICP-MS锆石原位Ge元素含量分析和U-Pb年代学研究。研究结果表明,岩基主体岩浆活动时代与前人研究成果一致,为(215.6±2.7)Ma~(236.9±3.7)Ma,同时也有少量继承锆石(303~2533 Ma);w(Ge)在主岩浆期的锆石中为0.23×10-6~4.21×10-6,平均0.53×10-6,在继承锆石中为0.34×10-6~3.43×10-6,平均1.18×10-6;而在本次研究中新发现的年龄为106.5 Ma和87.7 Ma的年轻锆石中w(Ge)高达102×10-6。因此,推测临沧锗矿床中Ge来源于晚期岩浆或热液作用。这个结果为成矿理论的深入研究提供了新依据。

Zircon germanium and age constrains on source of Lincang germanium deposit, Yunnan Province

The Lincang deposit occurs in the Miocene fault depressions overlying the Lincang batholith in Yunnan Province. It is generally accepted that Ge in the deposit was sourced from the underlying granites. However, the Lincang batholith is a composite one, and has experienced multi-magmatic pulses. It remains unclear which magmatic stage provided germanium to the deposit. This paper reports in-situ LA-ICP-MS Ge and U-Pb isotopic measurements of zircons in granites collected near Xiaojie, Lincang, Mengku and Menghai, which pass southwards through the Lincang batholith. The results achieved show that the timing of the main magmatic stage is between (215.6±2.7) Ma and (236.9±3.7) Ma, and zircons of these granites have low Ge concentrations (0.23×10^-6~4.21×10^-6, 0.53×10^-6 on average). Inherited zircons with ages between 303 Ma and 2533 Ma also have low Ge concentrations (0.34×10^-6~3.43×10^-6, 1.18×10^-6 on average). In contrast, the newly identified zircons 106 Ma and 87 Ma in age have high Ge concentrations up to 102×10^-6. It is proposed that Ge in the Lincang deposit was likely sourced from late stage magmatic or hydrothermal activities.