The hydrothermal alteration assemblages of Duobaoshan porphyry copper district indicate a spatial distribution of ore bodies and ore belts. They are mainly divided into K-silicate alteration zone, quartz-sericite alteration zone and chlorite-epidotecalcite alteration zone. Some K-rich hydrothermal minerals, produced in K-silicate zone and quartz-sericite zone:K-feldspar, biotite, sericite and illite, are considered to be directly associated with the hydrothermal events of mineralization and ore forming period.The experiment used laser microprobe 40Ar/39Ar dating technique equipped with a Nd-YAG pulsing laser. The background level of mass spectrometer is 36Ar≈1×10-15mol, 37Ar≈4×10-16 mol, 39Ar≈2×10-15 mol, 40Ar≈9×10-15 mol, with a measurement of atmospheric Ar isotopes being (40Ar/36Ar)A≈295.3±1.0(1σ). We determined two K-rich standard samples:K-feldspar (SB-778, K-Ar method, recommend.ed as (1.84±0.08)Ma) and muscovite (KF-1M, Rb-Sr method, recommended as 803Ma). The results of laser microprobe 40Ar/39Ar dating are (2.6±0.1) Ma and (785.5 ±6.5) Ma, respectively.Following electron microprobe studies, the whole rock samples collected from mineralization zone were made of a thin section about 0.5 mm in thickness. Then,the hydrothermal minerals are measured in situ by means of laser microprobe 40Ar/39Ar technique under a microscope’s location. The age results of ten samples show that there are two major periods of hydrothermal events:253-220 Ma and 184-162 Ma,respectively, corresponding to the Late-Variscan and the Early-Yanshanian magmatic activities in the district.It is considered that Late-Variscan magmatic activities formed the mineralization intrusion of granodiorite and granodiorite porphyry bodies, and Early-Yanshanian magmatic intrusion mostly emerged in the northwest of structural belts of the district without porphyry copper mineralization. Therefore, the period of hydrothermal mineralization is 253-220 Ma while another hydrothermal period, 184-162 Ma,reflects an superimposed influence of magmatic-hydrothermal activities on the mineralization zones.
Liu Chi,Mu Zhiguo,Liu Ruxi et al. 40Ar/39Ar LASER MICROPROBE DATING ON HYDROTHERMAL MINERALS FROM DUOBAOSHAN PORPHYRY COPPER MINING DISTRICT, HEILONGJIANG PROVINCE, CHINA[J]. Chinese Journal of Geology, 1995, (4): 329-337.