The Laver prospect: Characterization of rock-, vein- and alteration types
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
In 2012, Boliden Mineral AB announced the discovery of a new mineral deposit in the Laver-area, c. 40 km west of Älvsbyn, Norrbotten, Sweden. The deposit was classified as large volume, low grade Cu-Au-Mo mineralization. This discovery resulted from intense exploration activities in an area c. 1 km south of the historic Laver mine. Geological descriptions in the area are old and restricted to the old Laver mine, which differs in the style of mineralization. For this reason, two M.Sc projects were initiated as collaboration between Boliden Mineral AB, Technische Universität Bergakademie Freiberg (TUBAF) and Luleå University of Technology (LTU). This report summarizes the results of the LTU M.Sc project, which focused on petrography, alteration and vein types, and the relationship between these features and the mineralization. Three profiles have been studied, through drill core logging with emphasis on rock types, veins and alteration types. In addition, 43 polished thin sections were carefully examined with optical microscope, combined with further examination in SEM and electron microprobe. Furthermore, 15 lithogeochemistry samples, mainly from porphyritic intrusions, have been studied. The Laver deposits are located in the south-west part of the Karelian craton, in the Arvidsjaur-group volcanic rocks, interpreted as deposited in an active continental margin or continental arc. The wall rock in the study area consists of volcanic-sedimentary, mainly felsic rocks, interpreted as post-eruptive mass flow deposit. The intrusive rocks consist of plagioclase-quartz to plagioclase-hornblende-porphyritic intrusions of intermediate to felsic composition. Both wall rock and intrusions have a calc-alkaline affinity. No temporal or spatial correlation of mineralization to specific intrusions has been identified, yet non-porphyritic mafic dykes cut all other rock types including mineralization. Mineralization at Laver is vein- and alteration-related, not bound to specific rock types and most likely related to hydrothermal activity, caused by the intrusion of the porphyritic intrusions. Chalcopyrite is strongly correlated with epidote, and, to a lesser degree, with biotite in veins and in the alteration zones. Molybdenite is observed in quartz-veins and, to a lesser degree, in the groundmass, commonly associated with chlorite. Most veins in the study area carry at least minor sulphides. Mineralized veins cut and displace barren veins, but are themselves cut by barren veins, often with clear displacements along the vein contacts. Furthermore, chalcopyrite and pyrite have locally been tectonically remobilized into ‘ladder-vein´ structures on a small scale. These observations are consistent with a syn-tectonic timing of vein formation and mineralization. Alternatively, the observations could be interpreted as syn-tectonic sulphide remobilization during deformation of existing veins, or a combination of both. The style of the mineralized vein systems and associated alteration, the spatial affinity of mineralization to porphyritic intrusions, the low grade/high tonnage style of mineralization, as well as the indication of a syn-tectonic timing of mineralization at Laver is similar to porphyry systems worldwide. However, a major difference is the fact that the vein systems and alteration zones at Laver commonly contain a higher proportion of calcic minerals (e.g. epidote) than in typical porphyry systems. This may have resulted from telescoping at a late stage, whereby original potassic and sericitic alteration assemblages have been overprinted by propylitic assemblages.
Place, publisher, year, edition, pages
2013. , 152 p.
Life Earth Science
Bio- och geovetenskaper, Geologi, Prospektering, Laver, Porphyry-deposit
IdentifiersURN: urn:nbn:se:ltu:diva-53632Local ID: aa12cd4b-fdda-4b30-b252-98315a773b87OAI: oai:DiVA.org:ltu-53632DiVA: diva2:1027007
Subject / course
Student thesis, at least 30 credits
Geosciences, master's level
Validerat; 20130917 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved