Application of Visible-Near Infrared and Short-Wave Infrared Spectroscopy for Hydrothermal Alteration of the Yangyang Iron Oxide-Apatite (IOA) Deposit, Korea

The Yangyang Iron Oxide-Apatite (IOA) deposit is characterized by distinct mineral assemblages with calcic, potassic, and phyllic alteration indicators such as amphibole, mica and sericite. Fe-P mineralization is closely associated with calcic-potassic and potassic alteration zones. In the alteration products associated with calcic-potassic and potassic zones, mica can be distinguished by different color and composition of green, brown and white under microscope. Hydrothermal alteration of the Yangyang deposit is defined using visible-near infrared (VNIR) and short-wave infrared (SWIR) spectrometry. Difference features for an absorption observed by VNIR-SWIR spectrometer are consistent with the mineralogy data obtained from EPMA. Brown mica shows low Mg# (0.55) and high Ti, whereas green mica exhibits high Mg# (0.75) and low Ti. The abundance of green mica indicates that a decrease in Fe, Ti and Al concentrations corresponds to an increase in Mg and Si. It is suggested that white mica occurred in an overprinting main fluid channel in intensely altered mylonitic rocks, whereas green and brown mica formed preferentially distal to low-grade iron mineralization on the margin of altered shear zones.