The internal architecture of the Reinfjord ultramafic complex from high resolution magnetic, gravity and petrophysical data

More than 17000 km³ of igneous melts intruded into the deep crust at ca. 560-580 Ma and formed a large complex of mafic and ultramafic intrusions known as the Seiland Igneous Province. The province, now a part of the Middle Allochthon of the North Norwegian Caledonides, is believed to represent a cross section of the deep plumbing system of a large igneous province. Its layered intrusions share geological features with large ore-forming exploration provinces. Here, we investigate one of the four major ultramafic complexes of the province, the Reinfjord ultramafic Complex (RUC). This was emplaced during three magmatic events in a time span of 4 Ma and consists of a cylindrically zoned complex with a slightly younger dunite core surrounded by wehrlite and lherzolite dominated series. The country rocks of the RUC are layered gabbros and metamorphosed sedimentary rocks. Deep drill cores logging indicates that the RUC hosts Ni-Cu-and a platinum group elements (PGE) within the dunite, which make the RUC an interesting prospect. A comprehensive dataset consisting of high-resolution magnetic helicopter data, complemented by ground magnetic data, gravity data, and an extensive petrophysical data collection, has been used to model the complex. We developed a 3D gravity and magnetic model for the RUC using densities and magnetic attributes constrained by petrophysical data from both oriented surface samples, and samples from deep drill cores. The model indicates the RUC has a root with a minimum depth of 1400 m that narrows and plunges below the gabbro which borders the complex on the eastern side. This model refines the geological interpretation of the RUC at depth by mapping the extent of the ultramafic rocks and identifying areas of serpentinization.