Geochronology, geochemistry and structural setting of the Uunimäki gold mineralisation, SW Finland

Abstract

<p>The Uunimäki gabbro was studied by zircon U-Pb geochronology which yielded an age of ~1.89 Ga, making it one of the oldest plutonic rocks in the Häme Belt. Geochemical analysis of the gabbro reveals that it lacks several characteristics for typical subduction zone rocks: (i) it does not have a negative Ta-Nb anomaly compared to average NMORB-composition, (ii) it shows a rather unfractionated REE pattern, (iii) it lacks clear enrichment of fluid-mobile elements (e.g. Ba, Rb, Th, Pb). Structurally, the Uunimäki gabbro is located at the intersection of several regional features: (i) steep NE-plunging folds, (ii) a ENE-WSW-trending deformation zone immediately to the north and (iii) a large N-S-trending deformation zone to the west. The gabbro itself has been deformed under both brittle and ductile conditions by primarily NW-SE-trending faults and shears.<br /></p>