Overview
In May 2023, District Metals received approval from the Bergsstaten (Mining Inspectorate) for the Ardnasvarre nr 1 mineral license application located in the Norrbottens County, northern Sweden (Figures 1 and 2).
The Ardnasvarre Property hosts several uranium, lead-zinc-silver and copper mineralized occurrences that were historically drilled by the Swedish Geological Survey and Boliden, respectively.
Ardnasvarre Property Highlights:
- The Ardnasvarre nr 1 mineral license is located within the Arjeplog-Arvidsjaur uranium province and covers an area of 9,708 hectares (ha) that is prospective for uranium, copper, zinc, lead, and rare earth elements (REE).
- Straddles the unconformity between exposed Svecofennian basement rocks and overlying Caledonide sedimentary rocks where targets include stratabound, unconformity- and intrusive-related uranium and REE mineralization. Additional targets include sandstone-hosted lead and zinc mineralization, similar to the nearby historic Laisvall deposit.
- Labbas Uranium Zone: drilling by the SGU in the 1970’s and 1980’s resulted in a historical resource estimate of 86,478 tonnes at an average grade 0.12% U3O8 containing 228,780 lbs of U3O8 using a polygon resource estimation method6. The Labbas zone contains elevated molybdenum and zirconium, and remains open in all directions.
This above mineral resource estimates are considered to be “historical estimates” under National Instrument 43-101 – Standards of Disclosure for Mineral Projects (“NI 43-101”). A Qualified Person has not done sufficient work to classify the historical estimate as a current mineral resource, and the Company is not treating these historical estimates as current Mineral Resources. The Company would need to conduct an exploration program, including twinning of historical drill holes in order to verify the Labbas Uranium Zone historical estimate as a current mineral resource.
- Labbas Uranium Zone: A single hole (LAB08-001) was drilled in 2008 by Continental Precious Minerals that returned 7.0 m at 0.17% U3O8 from 50.0 to 57.0 m including a higher grade interval of 0.8 m at 0.94% U3O8 from 53.5 to 54.3 m (Table 1).
Figure 1: Location Map
Geological Setting
The regional geology where Ardnasvarre is situated is part of the Sveckokarelian Province of the Pre-Cambrian Baltic Shield which runs from south of Stockholm to the far north of Sweden where Lapponian - Jatulian rocks of Archaean age occur. The Sveckokarelian province is bounded to the west by thrust nappes of sedimentary and volcanic rocks of Caledonian age and its eastern boundary lies across the Baltic Sea in Finland1.
The basement of the Svecokarelian Province developed before and in conjunction with the Svecokarelian orogenesis that occurred ~1,800 to 1,850 million years ago. The basement is dominated by plutonic rocks, usually granitoids, that are ~1,600 to 1,900 million years old, though successive generations of ‘post-orogenic’ or younger granites continued to be intruded until ~1,500 Mya and are found throughout the entire province. The earliest granitoids are believed to be of mantle origin, and have suffered high-grade metamorphism, anatexis and major deformation, whereas the younger granitoids believed to be of crustal origin, are largely unaffected2.
Dolerites are common intrusives occurring as dyke swarms of marking crustal sutures and major fracture zones throughout the area. They are aged ~900 to 1,500 million years ago1.
The supracrustal rocks of the Sveckokarelian Province are composed of Svecofennian
terrestrial meta-sediments and metavolcanics dating from ~1,950 to 1,800 million years old. Basal meta-greywackes and meta-argillites predominate in the Svecofennian sedimentary rocks, with rare overlying meta-arenites, meta-arkoses and marbles. The stratigraphically higher metavolcanics are predominantly silicic to intermediate in composition e.g. metarhyolites; while basic metavolcanics occur towards the southeastern part of the province. In many cases, regional metamorphism was of such a high grade that the supracrustals have partly migmatised into gneisses.
Tectonism has commonly caused the supracrustals to become tightly folded, often with
multiple generations of folding. Major regional fracture systems, generally trending north to northeastwards, developed during the major D2 deformational event some ~1,820 to 1,870 million years ago3.
Svecofennian metasediments and metavolcanics are particularly abundant in central Norrland, which is a central area containing uranium deposits. Large areas with acid volcanic rocks can be found in an area extending from Kiruna down towards Arvidsjaur and further to the south. The younger granites are commonly highly differentiated alkali granites enriched in uranium relative to the older granites, particularly in a 300 km long area adjacent to the Caledonian [tectonic] front in the region of the towns of Arjeplog and Arvidsjaur4. The Ardnasvarre Property is within this region, which is known as the Arjeplog-Arvidsjaur-Sorsele Uranium Province5 and is an area of general uranium enrichment1.
Figure 2: Ardnasvarre Property Mineral License
Ardnasvarre Property Deposit Types
Intrusive-Related Uranium
The Labbas Uranium Zone is part of the intrusive-related uranium deposit spectrum. Uranium mineralization appears to be directly related to devolatilization during tectonism in terms of distribution, mineralization control, structure, and associated mineralogy.
Deposits of this spectrum are widely known in Sweden and globally.
The Labbas Uranium zone was discovered by boulder hunting in 1971 and was drill tested with 4,740 m in 35 holes between 1973 and 1980. Disseminated to impregnation style uranium mineralization is hosted by foliated meta-granites and amphibolites. The historic mineral resource estimate indicates that mineralization extends for at least 100 m in strike length and averages 2 m in width7 and remains open in all directions.
Drilling by the SGU in the 1970’s and 1980’s at the Labbas Uranium Zone resulted in a historical resource estimate of 86,478 tonnes at an average grade 0.12% U3O8 containing 228,780 lbs of U3O8 using a polygon resource estimation method6. The Labbas Uranium Zone also contains elevated molybdenum and zirconium and remains open in all directions. This above mineral resource estimates are considered to be “historical estimates” under National Instrument 43-101 – Standards of Disclosure for Mineral Projects (“NI 43-101”). A Qualified Person has not done sufficient work to classify the historical estimate as a current mineral resource, and the Company is not treating these historical estimates as current Mineral Resources. The Company would need to conduct an exploration program, including twinning of historical drill holes in order to verify the Labbas Uranium Zone historical estimate as a current mineral resource.
Uranium mineralization at Labbas is epigenetic in origin, and the source of uranium could either be the Archaean basement or, probably more likely, remobilization from early uranium enriched rhyolites by a sodium metasomatic event that took place ~1,750 million years ago1.
Unconformity Uranium
An unconformity is a boundary between two rock units that reflects a time gap. The rocks below the unconformity surface are older than the rocks above and were exposed to erosion for a longer period of time. Most unconformity uranium deposits formed between about 1.75 and 1.4 billion years ago, during a time known as the Proterozoic. Nearly all unconformity uranium deposits are closely associated with fault systems, which play a major role in the ore-forming process by providing a conduit for fluids to cross the unconformity. These deposits are further divided into perched or sandstone-hosted, unconformity-hosted, and basement-hosted.
Unconformity uranium deposits are generally thought to have formed as a result of reduced fluids coming out of the basement and mixing with oxidized basin fluids to trigger uranium deposition. While uranium is the main economic element, these deposits often contain other valuable metals such as rare earth elements, nickel, copper, cobalt, lead, and gold.
The Ardnasvarre Property strategically straddles the unconformity contact between the basement intrusive rocks and eastern Scandinavian Caledonides sedimentary rocks where the potential for unconformity uranium deposits has never been previously investigated.
Stratabound Lead-Zinc-Silver
The Labbas and Ardnesjaure lead-zinc-silver occurrences represent stratabound mineralization on the Ardnasvarre Property. Numerous sandstone-hosted lead-zinc-silver deposits occur along the present-day erosional front of the eastern Scandinavian Caledonides. This type of mineralization shares characteristics of both SEDEX and MVT-style deposits, but the term Laisvall-type has often been used8.
The Ardnasvarre Property (Figure 1) is located approximately 30 km north from the historic sandstone-hosted Laisvall Pb-Zn deposit, which was Europe’s largest former lead mine (1941 to 2001: 64.3 Mt @ 4.0% Pb, 0.6% Zn and 9 g/t Ag)7. Typically, mineralized zones occur along sedimentary bedding and consist of disseminated galena and sphalerite and lesser amounts of calcite, fluorite, baryte, pyrite and sericite forming a cement that fill interstitial pores in Neoproterozoic/Eocambrian (eg. Laisvall) to Cambrian (eg. Vassbo) sandstones. Deposits occur both in autochtonous and allochtonous sedimentary rocks, and a broad consensus exists about their epigenetic nature, their spatial relationships to syn-sedimentary faults and that ore fluids have scavenged metals from the crystalline basement8.
The Labbas lead-zinc-silver zone (357 m in 9 holes) and Ardnesjaure lead-zinc-silver zone (1,781 m in 28 holes) have been explored and drilled in 1954 and 1969 respectively by Boliden to identify the autochthonous stratigraphy above the basement rocks, which includes the Laisberg Formation hosting the Laisvall deposit. This formation represents a transgressive, sandstone-dominated sequence with epigenetic, disseminated, mottled or banded galena-sphalerite mineralization hosted in two sandstone paleoaquifers (Lower and Upper Sandstone)9.
References:
1 Phillips AH, 2005: Revised introductory technical report on eight uranium properties in Northern Sweden; Telluride & Associates for Continental Precious Minerals Inc; revised report 20 Sep 2005; SEDAR filing.
2 Lundqvist T., and Bygghammar, B., 1994 “The Swedish PreCambrian” in Geology : National Atlas of Sweden. Editor Fredén, C.. Royal Swedish Academy of Sciences. First Edition, 208 pgs.
3 Weihed, J.B., 2001 Palaeproterozoic deformation zones in the Skellefte and Arvidsjaur areas, northern Sweden. In Weihed J., (Editor) Economic geology Research. Vol. 1, 1999-2000. Uppsala 20001. Sveriges Geologiska Undersökning, C 833, pgs 46 to 68.
4 Wilson, M.R. and Åkerblom, G.V, 1982 Uranium-enriched Granites in Sweden. Pgs 367-385. In “Metallization Associated with Acid Magmatism”, Editor Evans, A.M., IUGS International Correlation Programme. John Wiley & Sons. 385 pgs.
5 Adamek P.M. and Wilson, M.R., 1977 RECOGNITION OF A NEW URANIUM PROVINCE FROM THE PRECAMBRIAN OF SWEDEN. Proc. Tech. Comm., Vienna, IAEA, pgs 199-215.
6 Svensson, S., 1981. Uranium Prospecting in Norrland, Interim Report Nov. 1981. Sveriges Geologiska Undersökning. Uranrapport 1981-8.
7 Ohlsson, L-G., 1992. Mineraliseringar och Industrimineralförkomster inom Arjeplogs Kommun, Report 10 Oct. 1992. Sveriges Geologiska Undersökning. Brap 94033.
8 K. Billström, C. Broman, A. Larsson, A. Schérsten, M. Schmitt, 2020. Sandstone-hosted Pb-Zn deposits along the margin of the Scandinavian Caledonides and their possible relationship with nearby Pb-Zn vein mineralisation, Ore Geology Reviews, Volume 127.
9 Saintilan, N.J. et al, 2015. A Middle Ordovician Age for the Laisvall Sandstone-Hosted Pb-Zn Deposit, Sweden: A Response to Early Caledonian Orogenic Activity. Economic Geology 110, p1779-1801.