Progress in Methodology of Low Temperature Thermochronometry

Objective Thermochronometry is based on the temperaturedependent radiogenic/fissionogenic products（e.g.,fission track or a particle）or the radiation effects of a radioactive isotopic system for a single mineral.The characteristics of a thermochronological system can be described by its closure temperature.

GEOLOGICAL AND GEOCHEMICAL FEATURES AND GENESIS BY FLUID CONVECTION FOR PERMIAN Cu-BEARING Cu-Ag TYPE DEPOSITS AT THE SOUTHWESTERN EDGE OF THE SICHUAN BASIN

Kupferschiefer type Cu-Ag deposits occur in the Upper Permian Xuanwei Formation in the Leshan-Muchuan region at the southwestern edge of the Sichuan Basin. Evidences from geology, major element, REE and thermolurninescence analyses suggest that these Kupferschiefer type CuAg deposits were formed during diagenesis and the ore-forming fluids were derived frorn the underlying basalt. Fluid dynamic analyses show that the ore-forming fluids migrated in a unicellular convection, fluids migrated through the basalt, leaching Cu and Ag frorn basalt and forming orebearing solutions, up the western basement highs, moved laterally along the Xuanwei Formation toward the basin centers, presumably to sink back down into the basalt, completing a convection cycle which was about 15 km long, 300 m high and subhorizontal. Further analysis and calculation suggest that there are good geological, tectonic and fluid-dynamic conditions to form middle-scale Cu and giant Ag Kupferschiefer type deposits, but superlarge deposits are unlikely to be formed in this region.

Spectral study on feldspar thermoluminescence process

Feldspar thermoluminescence fading phenomena were investigated here by using newly-constructed thermoluminescence spectrometer on the basis of charge-cou-pled detector,and thereafter the discussion and explanation on feldspar TL fading mechanism were presented. The experimental results show that the fading rate of feldspar TL depends on both wavelength and stimulated temperature,and normally the feldspar TL in every region of wavelength and temperature shows different traits,namely the low temperature TL (170℃-190℃) fading at the rate of logarith-mic function and furthermore the TL of different wavelengths fading at approxi-mately the same rate on the condition of 160℃ preheating. While the medium and high temperature TLs (290℃-400℃) do not show much thermal fading,their fading rate at room temperature invariably correlates well with their wavelength,namely the longer TL wavelength,the slower TL fading rate. The thermal instability of traps and the quantum-mechanical tunneling effects can explain the above fading phe-nomena respectively. It is recognized that feldspar TL fading depends on its wave-length,and furthermore new aspects of the solid thermoluminescence process can be displayed by the combination of three-dimensional TL spectral analysis and thermal fading or anomalous fading of TL for feldspar.