Studies on the genesis of the Laisvall sandstone lead-zinc deposit, Sweden

• Published in: Economic Geology
• Main Authors: Rickard, D, Willden, M.Y., Marinder, N.E., Donnelly, T.H.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Society of Economic Geologists 1979
• Subjects: Laisvall; Lappland
• Online Access: https://orca.cardiff.ac.uk/id/eprint/120049/; https://doi.org/10.2113/gsecongeo.74.5.1255

The Laisvall deposit in Swedish Lappland is one of a series of sandstone lead-zinc deposits at the border of the Caledonian mountains. The total ore reserves were estimated to be 80 million tons of 4 percent lead and zinc.The ore is located mainly in two thin sandstone horizons in a late Precambrian-Cambrian autochthonous sedimentary sequence overlying a Proterozoic crystalline basement and covered by nappe slices related to the Caledonian orogeny. The sandstones were deposited on a stable platform at the shallow, tidal margin of the proto-Atlantic.Nappe translation into the area was accompanied by minimal disturbance of the Laisvall autochthonous sediments. Disruption of the alum shales, which formed the sole of the lowermost nappe, flexure folding, and some faulting are the major tectonic effects. The ore has suffered folding, faulting, and overthrusting, and thus predates the arrival of the Caledonian nappes into the area. An illite crystallinity study reveals that thermal effects of the overthrusting were limited to within 20 m of the lowermost nappe. This is consistent with textural observations on the sandstones and ore minerals suggesting that the major metamorphic effect on the ore was caused by low-temperature loading. Total recrystallization or remobilization of the deposit is precluded.The minerals of the ore association include galena, sphalerite, calcite, fluorite, and barite. They infill the pore spaces in the sandstones. No definitive paragenesis can be unraveled at Laisvall. The minerals are commonly mutually exclusive and several generations of each mineral exist. However, there is a marked tendency for sphalerite to be generally older than galena, which in turn usually precedes the calcite, barite, and fluorite. The deposit is zoned, particularly with respect to galena and sphalerite, with zinc being dominant in the Upper Sandstone to the northwest and very minor in the galena-rich Lower Sandstones.A fluid inclusion study on the sphalerites shows that the ore was precipitated from a ...