Geology and mineral resources of the Lövstrand Pb(-Zn) mineralization, Dorotea area, north-central Sweden

Abstract: The Dorotea district is situated in North Central Sweden and is the host of
many small sized sandstone-hosted lead-zinc deposits such as Lövstrand,
Bellviksberg and Granberget. The mineralized areas were discovered during
the 1930s through an extensive exploration campaign along the Caledonian
Front. Boliden Mineral AB has investigated the Lövstrand zone for about ten
years (from 1947 to 1958) but even with X drill-holes and a mine-testing
excavation, the mineralization was estimated to contain too low lead grades
and too limited tonnage to be considered economic.

The present study aims to improve the knowledge about the Lövstrand
mineralization. The Lower Cambrian Sandstones, deposited in a fluvial
dominated deltaic system and rich in organic matter, were involved in
thrusting during the Scandian Event 425 million years ago. They are now
included in the Lower Allochthonous Unit of the Tåsjön Décollement and host
a stratabound galena-(sphalerite) mineralization at Lövstrand. The organic
matter (indicating a high probability of sulfide presence due to high
authigenic pyrite content) associated with intergranular clayey minerals,
together with a lower alteration of the porosity, are the most likely
causes for the precipitation of the sulfides in the sandstones.
Because of the high rock fracturing due to the thrusting process, the
mineralization has been partly remobilized and spread along faults,
lowering the grades to sub-economic levels.
The lead content in mineralized rocks is strongly correlated with silver.
The high-grade parts of zinc mineralization are spatially separated from
the lead even though both still seems to be linked to the same mineralizing
event. The latter is likely to be of same nature as the mineralizing event
described in Laisvall.

The resource estimation indicates that the Lövstrand mineralization
contains X Mt of inferred resources with an average of X % lead and X %
zinc. In addition, the area contains a potential mineralization estimated
at X Mt with an average of X % lead and X % zinc. Using the
correlation between lead and silver, the silver grade has been estimated to
be around X g/t.
The observation of the spatial separation between high zinc grades and high
lead grades, together with the low number of zinc assays, indicates the
possibility of further zinc mineralization.