ScienceDirect：

https://www.sciencedirect.com/science/article/pii/S0009254118301104

Abstract

Increasingly more data have indicated that the ⁴⁰Ar/³⁹Ar crushing technique provides a very useful approach to determine the mineralization ages of hydrothermal ore deposits. In this study novel gas mixing lines are proposed based on the data of two quartz samples by ⁴⁰Ar/³⁹Ar crushing. Electron microprobe analyses indicate that the quartz grains contain K-rich silicate microlites. Both quartzs by crushing yield two mixing lines with ages corresponding respectively to those of K-feldspar or sericite (post-mineralization fluids) and muscovite samples (ore-forming fluids). This is the first report that both ages of secondary and primary fluid inclusions (SFIs and PFIs) are confirmed correspondingly by those of the K-rich minerals. This study strongly indicates that the ⁴⁰Ar/³⁹Ar crushing technique is very useful to determine the ages of geofluid activities. The newly proposed gas mixing patterns are shown on the inverse and normal isochron diagrams, indicating: (1) the mixtures are in different proportions of the PFIs and SFIs in different crushing steps; (2) the gas mixing lines yield PFI ages with low initial ⁴⁰Ar/³⁶Ar ratios; (3) an intermediate age between PFI and SFI ages cannot be obtained because the progressive crushing technique never release gas mixtures with a constant PFI/SFI proportion for each step. The gas mixing lines are thus interpreted to yield significant geological ages. The mixing patterns will help us better understand the ⁴⁰Ar/³⁹Ar dating results and be used for references to other isotopic mixing isochron systems.

Keywords

• ⁴⁰Ar/³⁹Ar crushing technique; 

• Gas mixing line; 

• Fluid inclusion; 

• Tungsten mineralization age; 

• Inverse isochron

Gas mixing lines of hydrothermal non‑potassium minerals based on the data of quartz 09PT37Q by ⁴⁰Ar/³⁹Ar progressive crushing. A – modern atmosphere. P and S represent the radiogenic components of the PFIs (or muscovite) and SFIs (K-feldspar or sericite) respectively. E – parentless excess ⁴⁰Ar. The red arrows show the trend of data point distribution as the crushing procedure progresses. EX – the SFI isochron line containing excess ⁴⁰Ar. PA – the PFI isochron line. SA – ⁴⁰Ar_ex-free SFI isochron line, or isochron line of post-mineralization K-feldspar and sericite. PM – gas mixing line of PFIs and ⁴⁰Ar_ex-free SFIs, corresponding to the PFI age and a low initial ⁴⁰Ar/³⁶Ar ratio. SN – a potential gas mixing line by dominant post-mineralization components with minor residual PFIs. BA – an impossible gas mixing line with a constant PFI/SFI proportion. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

https://www.sciencedirect.com/science/article/pii/S0009254118301104