Structural interpretation of the Iso-Kuotko area, Lapland, with implications to gold precipitation

• Main Author: Silvonen, Olli
• Other Authors: Matemaattis-luonnontieteellinen tiedekunta, Faculty of Science, Kallioperägeologia, Bedrock Geology, Maantieteen ja geologian laitos, Department of Geography and Geology
• Format: Other/Unknown Material
• Language: English
• Published: 2023
• Subjects: structural geology; orogenic gold; Central Lapland Greenstone Belt; 3D modelling; rakennegeologia; orogeeninen kulta; Keski-Lapin vihreäkivivöyhyke; 3D mallinnus; Kati; Kiistala; Northern Finland; Lapland
• Online Access: https://www.utupub.fi/handle/10024/176315

Central Lapland Belt (CLB) in Northern Finland hosts multiple orogenic gold deposits from which Iso-Kuotko gold deposit is one. The Iso-Kuotko deposit comprises three mineralizations: Kati, Retu and Tiira. Previous studies have focused on the geochronology and geochemical attributes of the deposit, whereas the structural geometry of the deposit, and the linkage between gold-bearing veins and shear features remains partly unknown. The main goal of this study is to describe both the ductile and brittle deformation structures of the study area and to link them together. The secondary objective is to identify and compare the orientations distribution of diverse vein sets occurring within the mineralized areas, and further compare them with the mineralization. The study is based on new field observations and structural measurements from drill core and bore hole videos, which complement the pre-existing datasets available from several parts of the study area. Moreover, a structural interpretation of magnetic anomaly maps was conducted, and previously gathered drill core measurements were used in the study. The data were eventually gathered into digital 3D models and lower hemisphere projections. The Kati area is dominated by gently NE dipping foliation which has been sheared during a thrusting event. The Kati area is also cross-cut by NW trending, likely dextral, sub-vertical shear bands splaying out from the Kiistala Shear Zone (KiSZ). Additionally, in the Kati area there is a E-W trending, sub-vertical, shear band possibly splaying out from the NW trending shear bands. The Retu area is dominated by sub-horizontal foliation which is undulating around gently NE plunging fold axis. According to this study, shear deformation occurred along the sub-horizontal foliation surface, and the foliation was cross-cut by the main branch of the NE trending sub-vertical KiSZ and parallel subsidiary shear bands. In total five mineralogically varying vein types were observed: 1) quartz, 2) quartz + Fe-carbonate, 3) quartz + ...