Micro-Raman spectral characteristics and implication of FeS2 from Augen granites in west of Guangdong

Some FeS2 samples among Augen granite from Guanshanzhang mass in the west of Guangdong Province were retrieved to characterize the spectral signature of Raman. The results show that three distinct scattering modes active of Fe-[S2]2- Liberational Motion (Eg), Fe-[S2]2- Stretching Motion (Ag) and S--S Stretching Motion (Tg) are observed from all samples. Detailed analyses indicate that Raman shift (Δυ), Modes intensity (I) and full width at half maximum (FWHM) are different between each type pyrite. The spectra show that there are three peaks respectively about 318 cm(-1) (Δυ1), 381 cm(-1) (Δυ1) and 440 cm(-1) (Δυ1) in Banded pyrite and three peaks in others samples about 344 cm(-1) (Δυ1), 379 cm(-1) (Δυ1) and 430 cm(-1) (Δυ1). Under compression to Alterated pyrite, all modes (Eg, Ag and Tg) shift continuously to higher frequencies from Deformed samples to Euhedral type. Eg mode is much intenser than Ag mode as well as the latter is intenser than Tg mode too in Banded samples (I(Eg) >> I(Ag) >> I(Tg)), the intensity of Ag mode is higher than Eg mode, and the latter is much higher than Tg mode in other samples (I(Ag) > I(Eg) >> I(Tg)). Compared with Alterated pyrite, all modes of Eg, Ag and Tg intense continuously to higher frequencies from Euhedral samples to Deformed type. Those spectral characteristics above evidence that, the Raman shift and intensity of Banded samples is similar to marcasite, while those of others show characteristics of the pyrite. The crystallization temperature of Euhedral pyrite is higher than Deformed as well as Euhedral is higher than Alterated too. The formation pressure of Euhedral samples is higher than Alterated pyrite the same as Deformed pyrite hingher than Euhedral one too. Thus, The authors' studies suggest that the forming conditions of FeS2 in Guanshanzhang mass experienced marcasite period-->high-pressure pyrite period--> high-temperature pyrite period-->Alterated pyrite period.