Decoding multiple ore mineral remobilization processes during polyphase deformational phases from the Precambrian Pyhäsalmi VMS deposit halo, Central Finland: new insights from mineralogy, mineral chemistry and micro-CT
2025
Islam, Sk Rakibul | Heilimo, Esa | Kuva, Jukka | Mäkilä, Ermei | Mäki, Timo | Geologian tutkimuskeskus | Geological Survey of Finland
The Precambrian bimodal Pyhäsalmi Zn-Cu-Ag-Au VMS deposit in the Svecofennian domain of Finland has undergone various degrees of metamorphism and deformation, which have altered the composition and texture of the minerals, resulting in sulfide remobilization. However, studies on metamorphism and its influence on the ore mineral remobilization in the Pyhäsalmi region are lacking. Our study provides insights into the remobilization history of ore minerals during polyphase deformational and metamorphic events in the deposit halo region by integrating mineralogical, textural, mineral chemical, microtextural, and 3D micro-CT analyses. We propose that the Pyhäsalmi deposit has experienced two distinct ore mineral remobilization stages: (a) The first stage, associated with D1-D2 deformational phase, is dominated by solid-state (mechanical) remobilization processes demonstrated by cataclastic flow, foliated, elongated sulfide, which possibly occurred before the metamorphic peak denoted by staurolite + garnet + cordierite, and (b) The second stage, linked to D4 deformational phase, is characterized by mixed-state remobilization processes evidenced by the spatial distribution of disseminated pyrrhotite around the grain boundaries of silicate porphyroblasts, attenuation of sulfides around the hinge zone of the crenulation cleavages and fracture filling sulfides, which possibly occurred during metamorphic peak conditions represented by sillimanite + garnet + cordierite + biotite. Published studies on ore remobilization often overlook the potential of linking ore minerals to metamorphic mineral assemblages through petrographic and microstructural observations. Our study addresses this gap by providing a framework to decode the ore mineral remobilization events in polyphase deformational and metamorphic environments using metamorphic mineral assemblages, garnet porphyroblasts, and microstructural analysis.
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