TARGETING ALUNITE IN EPITHERMAL AND PORPHYRY COPPER DEPOSITS BY USING ASTER IMAGERY IN THE SIERRA MADRE OCCIDENTAL, CHIHUAHUA, MEXICO

In this present work, a new method is applied to target alunite (KAl₃(SO₄)₂(OH)₆) which is a sulfate mineral that is commonly found in argillic alteration zones of porphyry and epithermal systems. The area of interest is in Sierra Madre Occidental Chihuahua, Mexico, which has many deposits, but it is hard to access because the area is rugged and large. In the past, confusion and errors have existed in attempting to distinguish alunite from carbonates, clays, iron oxides, and iron sulfates because their absorption is similar to the 2.2 μm OH^- absorption exhibited by alunite. The technique is used ASTER bands 12 (9.1 μm) and 13 (10.6 μm), which straddle the center wavelength (9 μm) of the SO₄ ^2- because of a deep and broad absorption feature associated with SO₄ ^2- in alunite which is present in the TIR. This absorption can be used to distinguish alunite from clays. Moreover, targeting the negative slope between band 3 (0.8 μm) and 4 (1.65 μm) which can differentiate alunite from both iron oxides and sulfates, which have a positive slope. Ten new locations of alunite have been identified. Two of them are located in actual mines, which are Moris and Alamaos. Six locations of alunite will be explored in the area of interest where there is not located any prior exploration. This method is essential for mining companies since ASTER satellite imagery is cheap and widely available dataset.