Resource evaluation of the Målvika tungsten deposit, Nordland

Abstract

Nordic Mining contacted NGU in spring 2007 in order to re-evaluate the resource and grade of the Målvika tungsten deposit in Tosbotn municipality in Nordland, Norway. \rThe Målvika tungsten deposit is a tungsten skarn mineralisation which extends 900 m NNW-ward from the northern coastline of Tosenfjord towards mountain Landnubben and ends at an altitude of about 500 m a.s.l. The skarn zone comprises marbles, metasomatic calc-silicate rocks (skarn sensu strictu), skarn-altered gneisses and granites. The ore-bearing diopside and garnet-diopside skarns form individual boudins (lenses) usually smaller than 5 m in length and 2 m in width, aligned in vein-like structures commonly 2 m wide and up to two hundred metres long. Scheelite ore is accumulated in 1-20 cm large batches distributed very heterogeneously within complexly folded and boudinaged skarns. \rThe deposit has previously been the target of three exploration phases with contrasting results since its discovery in 1972 by P. Skaarup. Some results indicate that the Målvika skarn in a world-class tungsten resource having an ore tonnage of 2 509 000 t with a grade 0.7 to 0.9 wt.% WO3, while a drilling project performed in 1983 by Sulfidmalm AS indicated only traces of tungsten.\rFieldwork was carried out during two campaigns in July and October 2007. The first campaign included 393 in situ analyses of the tungsten concentration of different rock types in the mineralised zone using a portable X-ray fluorescence diffraction spectrometer. During the second campaign, 66 bulk rock trench samples were taken, transecting nine different skarn layers.\rThe results indicate that the Målvika skarn zone is a minor tungsten deposit with possible mineable ore tonnage of 750 000 t diopside and garnet-diopside skarn with an ore grade of about 0.44 wt.% WO3. The granites of the Visttindane massif sampled 0.5 to 1 km E of Målvika have a high average tungsten content of 121 ppm reflecting an extreme enrichment of tungsten in the granite magmas. Thus, these granites are the most likely source of the tungsten and the Målvika deposit is an intrusion-related skarn. The mineralisation was presumably formed 430-440 Ma years ago. This result suggests that there is the possibility of finding more tungsten deposits within a radius of 5 km around the Visttindane granite massife, or within the pluton.