Terahertz time-domain spectroscopy of alteration minerals in the Guocheng orogenic gold deposit as indicators for exploration

Abstract The spatial distribution of alteration minerals in orogenic gold deposits and their correlation with mineralization are important parameters for exploration. The Guocheng gold deposit, located on the northeastern margin of the Jiaolai Basin, contains multiple alteration assemblages, which are an ideal target for studying the relationship between alteration minerals and mineralization. By integrating petrographic observations with terahertz time-domain spectroscopy (THz-TDS). we systematically analyzed samples from distal host rock, proximal host rock, and orebody positions. The deposit is characterized by predominant silicification-pyritization, chloritization-epidotization, and carbonatization. Our results demonstrate that the absorption coefficient of the marble at 0.9 THz increases from 75.1 cm−1 in the distal host rock to 85.3 cm−1 in the proximal host rock and 98.9 cm−1 in the orebody. The quartz-rich granofel orebody sample has a higher bulk refractive index (2.63 at 0.9 THz) than the proximal host rock sample (∼2.45), whereas the strongly chloritized and epidotized granofel ore displays lower bulk absorption and refractive-index values than the proximal host rock. These distinctive spectral fingerprints, specifically the combined absorption coefficient and refractive index patterns serve as effective discriminators between the mineralization center from the host rock. We propose that the THz-TDS may therefore provide a rapid, non-destructive screening method complementary to petrographic, mineralogical, and geochemical investigation.