Characteristics of short wave infrared spectroscopy of sericite group minerals and their implications for exploration in the Yulong porphyry copper deposit, Tibet

The late phyllic and clay alteration of Yulong porphyry copper deposit is strongly superimposed within the early potassic alteration, blurring alteration zonation and its correlation with copper mineralization. Using short-wave infrared spectroscopy (SWIR) can identify OH-bearing alteration minerals in porphyry copper deposits and identify alteration mineralization centers based on their spatial distribution. In this paper, we conduct detailed alteration-mineralization catalogs and SWIR analysis of three drill holes near the porphyry center of the Yulong copper deposit. Based on the identification of kaolinite, montmorillonite, sericite group minerals (sericite and phengite), chlorite and other alteration minerals,the spatial distribution patterns of sericite group minerals and their correlations with copper mineralization are emphatically analyzed. This study reveals that the deep Cu-rich ore bodies (>0.6 wt%) are immediately adjacent to the intrusion center of the porphyry body and are spatially associated with sericite. The phengite is relatively developed in the center of the rock body, and the absorption peak wavelength of the Al-OH of sericite group minerals is larger (Pos2200>2207 nm) and the crystallinity is high (IC>2.0). The Pos2200 values and IC values of the sericite group minerals are relatively smaller (2206~2207 nm) and lower (1.0~2.0) when close to the peripheral ore body of rock center. Therefore, high Pos2200 values (>2207 nm), high IC values (>2.0) of sericite group minerals and occurrence of phengite can be used as the bottom boundary of ore bodies, while the relatively lower Pos2200 values (2206~2207 nm) and lower IC values (1.0~2.0) of sericite group minerals can be used as an indication of the occurrence of deep copper-rich ore bodies.