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Geological and geophysical characteristics of the Pb-Zn sandstone-hosted autochthonous Laisvall deposit in the perspective of regional exploration at the Swedish Caledonian Front
2010 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The Laisvall Pb-Zn sandstone-hosted deposit is located in the autochthonous rocks at the Eastern Front of the Swedish Caledonides. Amounted to 64 Mt at 4,6% Pb, 0,6% Zn and 9 g/t, it is the largest known deposit of this type. The global tectonic history of the Caledonian Orogen is rather well known. Despite the mineralisation processes at Laisvall have been extensively studied, a satisfactory genetic model in the tectono-stratigraphic frame of the Caledonides is yet to be proposed. Review of previous studies and construction of a 3D sedimentary model enabled defining the key geological requirements for favourable hosts. On the other hand interpretation of geophysical magnetic data helped identifying such geological suitable targets for future regional exploration. These consideration laid the basis of a constructive review of the genetic model from available studies. Stratabound mineralisation occurs in the two lowermost permeable units, that happen to be the cleanest clay-free sandstone members. The lowermost Kautsky Ore Member which is the most important orebody, rests on the flank of a basement high while the second orebody (Nadok Ore Member) appears to be tightly linked to the Nadok normal fault. A fluid-basement interaction mineralising model is proposed. This model, updated after Kendrick et al. (2004), invokes an oilfield brine expelled from a deep sedimentary basin during the Caledonian Orogeny. It would be driven through the permeability-enhanced fractured basement to the site of mineralisation where it infiltrates the sandstone unit through reactivated Proterozoic basement fault during Scandian compression. Precipitation of sulphides in the aquifer would result from fluid mixing processes between the basement expelled sulphate metal-rich brine and a fluid resulting from reduction of trapped seawater in the sandstone. It is herein demonstrated that synsedimentary faulting could account for mineralisation in the Nadok Member separated from the Kautsky Member by a clay-rich impermeable sandstone. Ore controlling factors were also weighted. Basement paleotopography was of major importance on the ore localisation and directly governed the depositional environment of the favourable host units. A prospectivity map is produced over a 100x50 km area around Laisvall to help focus future regional exploration in the autochthonous rocks of the Caledonian Front.

Place, publisher, year, edition, pages
Keyword [en]
Life Earth Science, Laisvall, Sandstone-hosted, Caledonian front, 3d modelling, ore, model, exploration, lead, zinc, Proterozoic basement, Aeromagnetic, geophysics
Keyword [sv]
Bio- och geovetenskaper
URN: urn:nbn:se:ltu:diva-59375ISRN: LTU-PB-EX--10/039--SELocal ID: fe8a1db6-1615-4fa0-92c8-364f26a5f370OAI: diva2:1032762
Subject / course
Student thesis, at least 30 credits
Educational program
Geosciences, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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