TY - JOUR

T1 - Alteration Mineral Mapping of the Shadan Porphyry Cu-Au Deposit (Iran) Using Airborne Imaging Spectroscopic Data

T2 - Implications for Exploration Drilling

AU - Asadzadeh, Saeid

AU - Chabrillat, Sabine

AU - Cudahy, Thomas

AU - Rashidi, Bahman

AU - Filho, Carlos Roberto de Souza

N1 - Funding Information: This study was supported by the EnMAP scientific preparation program (grant 50EE1923) under the DLR Space Agency with resources from the German Federal Ministry for Economic Affairs and Climate Actions and also GFZ Potsdam. The authors are thankful to A. Houshmandzadeh (deceased June 2023) and Karand Sadr Jahan for granting access to geochemical and geophysical data and to Espeer Mining Services for assistance in collecting the sample suite used for laboratory spectroscopy. We are grateful to Farhad Bouzari (University of British Colombia) for his constructive discussions and to the Geoinformatics Deputy of the Geological Survey of Iran for facilitating our access to the HyMap hyperspectral data used in this study. The authors are thankful to two anonymous reviewers for their useful comments and suggestions.

PY - 2024/1

Y1 - 2024/1

N2 - Porphyry copper deposits are associated with large alteration footprints, and alteration mapping plays a key role in the exploration of these deposits. Imaging spectroscopy is commonly deployed for exploration targeting, yet it has rarely been used to map deposit-scale alteration patterns before initiating drilling. To close this gap, the Shadan porphyry Cu-Au deposit was thoroughly studied using the HyMap hyperspectral data (visible near-infrared–short-wave infrared) at 5-m resolution corroborated by rock geochemistry, magnetometry, and laboratory spectroscopy. Shadan is a well-exposed deposit with near-perfect zonation located in the volcanic belts of eastern Iran containing >135 Mt of ore at 0.3% Cu and 0.4 g/t Au. Thirteen minerals, including white mica, Al smectite, kaolinite, ferric/ferrous minerals, biotite, actinolite, epidote, chlorite, tourmaline, and jarosite, were mapped by applying the multifeature extraction methodology. The propylitic zone was partitioned into actinolite, epidote, and chlorite subfacies. The compositions of biotite and white mica were observed to become Fe and Al rich, respectively, toward the mineralized zones. The chemistry of actinolite was observed to change from Fe to Mg rich inward, providing a new vectoring tool for porphyry copper exploration. The study provided significant information about fluid-rock interactions and the chemistry of the circulating fluids including the oxidation-reduction states and acidity. By integrating the mineral maps with other data sets using the fuzzy logic method, the promising (ore) zones were identified and used to plan the next-stage drilling. This work demonstrated that imaging spectroscopy can be effectively used to better understand porphyry systems and provide deposit-scale vectors toward the mineralized centers, facilitating drilling.

AB - Porphyry copper deposits are associated with large alteration footprints, and alteration mapping plays a key role in the exploration of these deposits. Imaging spectroscopy is commonly deployed for exploration targeting, yet it has rarely been used to map deposit-scale alteration patterns before initiating drilling. To close this gap, the Shadan porphyry Cu-Au deposit was thoroughly studied using the HyMap hyperspectral data (visible near-infrared–short-wave infrared) at 5-m resolution corroborated by rock geochemistry, magnetometry, and laboratory spectroscopy. Shadan is a well-exposed deposit with near-perfect zonation located in the volcanic belts of eastern Iran containing >135 Mt of ore at 0.3% Cu and 0.4 g/t Au. Thirteen minerals, including white mica, Al smectite, kaolinite, ferric/ferrous minerals, biotite, actinolite, epidote, chlorite, tourmaline, and jarosite, were mapped by applying the multifeature extraction methodology. The propylitic zone was partitioned into actinolite, epidote, and chlorite subfacies. The compositions of biotite and white mica were observed to become Fe and Al rich, respectively, toward the mineralized zones. The chemistry of actinolite was observed to change from Fe to Mg rich inward, providing a new vectoring tool for porphyry copper exploration. The study provided significant information about fluid-rock interactions and the chemistry of the circulating fluids including the oxidation-reduction states and acidity. By integrating the mineral maps with other data sets using the fuzzy logic method, the promising (ore) zones were identified and used to plan the next-stage drilling. This work demonstrated that imaging spectroscopy can be effectively used to better understand porphyry systems and provide deposit-scale vectors toward the mineralized centers, facilitating drilling.

UR - http://www.scopus.com/inward/record.url?scp=85174818101&partnerID=8YFLogxK

U2 - 10.5382/econgeo.5041

DO - 10.5382/econgeo.5041

M3 - Article

AN - SCOPUS:85174818101

VL - 119

SP - 139

EP - 160

JO - Economic geology

JF - Economic geology

SN - 0361-0128

IS - 1

ER -