斑岩矿床成矿时间尺度的研究进展:以藏东玉龙斑岩铜(钼)矿床为例

Advances in research of the time scales of porphyry deposits: A case study of the Yulong porphyry Cu-Mo deposit in the eastern Tibet

精确限定多期次岩浆-热液活动的时间尺度一直是剖析斑岩矿床形成过程的热点和难点。借助矿物的高精度同位素定年、热力学数值模拟以及石英的钛扩散模型等方法,斑岩矿床中岩浆-热液活动的时间尺度已经被限定在几万年之内。本文以三江特提斯超大型玉龙斑岩铜(钼)矿床为例,重点识别含矿热液脉中普遍存在的石英,利用钛元素的扩散年代学方法,精确限定斑岩矿床中多期岩浆-热液流体活动的时间尺度。扩散模型表明玉龙斑岩矿床热液活动的时间尺度为32000~870000年,有力支持了超大型斑岩矿床可以在几万至几十万年甚至更短时间内形成的观点。此外,为避免钛扩散模型产生较大的误差,需要在精确测定石英中钛含量的基础上,结合矿床地质背景或其他实验方法合理地估测温度和压力条件。研究认为,将矿物的高精度同位素定年与元素的扩散年代学相结合,可以在更为精细的尺度上完善斑岩矿床岩浆-热液活动的时间框架。

Accurate determination of the time scales of multiple magmatic-hydrothermal pulses is a critical and difficult problem that could provide key information needed to better constrain the genesis of porphyry deposits. Recent high-resolution dating, diffusion chronometry in quartz, and numerical modeling of thermal processes have revealed that the time scales of individual ore deposition cycles may be constrained in tens of thousands of years. Taking the giant Yulong porphyry Cu-Mo deposit in Sanjiang Tethys metallogenic belt as an example, this study focuses on the ubiquitous quartz in hydrothermal veins through the titanium diffusion chronology to accurately determine time scales of multistage magma-related hydrothermal events in the porphyry deposit. Diffusion modeling for different quartz generations indicates that the time scale of hydrothermal pulses in the Yulong deposit can form in a short period of 70000 to 900000 years. These findings provide strong support that giant porphyry deposits can be formed in tens of thousands to hundreds of thousands of years or even less. Based on accurately determining titanium contents in quartz, in order to avoid tricky errors, the diffusion modeling needs to reasonably estimate the temperature and pressure combined with the geological background or other experimental methods to avoid errors. This study suggests that the combination of high precision dating and diffusion chronology models can further constrain the time frame of magmatic-hydrothermal events in porphyry deposits.