GRSG Conference 2022: Orbit to Outcrop

Title: Hydrothermal alteration mapping using ASTER data within Akhalsofeli Ore Field Areas (Kakheti Segment of Caucasus, Georgia)

Author: Giorgi Mindiashvili


In the work ore hydrothermal alteration mapping using ASTER data within Akhalsofeli Ore Field Areas. Akhalsopeli ore field covers the territory of the Shorokhevi-Areshi-Lako river basins. It is structured by intensively folded and crushed lower Jurassic clay-shales, sandstones, carbonaceous rocks in small quantities, and dacite-andesite-basalt sheets; in relief, they make Kakhetian anticline structure of a general Caucasian strike, leaning into South.

Numerous hydrothermally changed zones of the general sub-latitudinal strikes are famous in this territory. Within their areas, local perspective sites are selected: Gokhiana (West), Adalaskedi (central part), Arashi (South-East), and Lako (North-East).

This project consists of interpretations of more than 40 data obtained by remote sensing analyses and techniques in order to detect geological features and potential of probable Akhalsofeli ore fields in the area located in the Kakheti segment of Caucasus Georgia using Terra ASTER Multispectral satellite data.
Technical specifications for the ASTER data used are as follows:
Granule ID: AST3A1 0409160806091107270062
Processing Level: 3
Acquisition Date: 20040916
Scene ID: [171, 87, 1]
Processed Bands: “01023N3B0405060708091011121314”
Cloud Coverage: 2

The area is quite intensive in terms of vegetation, snow, glacier, and cloudiness. Therefore, the best satellite data among all ASTER images have been ordered that could represent the area the best way and which has the least snow and cloud cover. The acquisition date of the satellite data is 6.05.2008. It is noticeable that although the time of acquisition is autumn season, excess snow covers still remain on mountain tops.

The ASTER image used in this study has approximately 2% cloudiness, 20% vegetation, and 35% snow cover in the whole region. In this very highly vegetated territory, there have been detected different rock types covering 10% of the study area and lithological descriptions, mineral mapping techniques, and analysis towards determination of geological features have been made.

Ground truth studies on license areas should also be made after all these analyses have been performed to check for the anomalies observed. Since the area is actually too small to run for such processes, all analyses have been carried out using the full ASTER image to detect all other geological features available in the region.

Performed analyses and results obtained using ASTER data are given below. During these analyses, VNIR, SWIR, and TIR spectral bands have been used. Wavelength intervals of these bands are especially useful in the determination of alteration minerals. ASTER SWIR bands have been used during the mapping of acidic alteration minerals such as alunite, kaolinite, phyllic, and alteration minerals such as sericite and muscovite.

The reason for the usage of this mineral mapping technique is important in terms of revealing the environments of the formation of metallic minerals in the study area. Especially, alteration minerals give several clues for metallic formations.

Using the remote sensing method, hydrothermally altered zones were distinguished and the areas of geochemical anomalies were contoured. The data obtained by this method literally repeat the contours of the existing ore manifestations. It is important that several new substantial ore manifestations were revealed by this method.

Resulted of the remote sensing method provided by us at the Akhalsopeli ore field, hydrothermally changed areas were selected, where elevated contents of ore mineralization were observed.

After all, of that, visiting the site and testing of mentioned mineralized zones took place. Resulted of provided investigations, it turned out that the Akhalsopeli ore field represents a perspective site and deposits of industrial significance may be revealed by properly planned geological works.