Hydrocarbons associated with lead–zinc ores at Laisvall, Sweden

Abstract

BITUMEN and a series of normal alkanes (C₁₈ to C₂₇) have been identified in sphalerite from the Laisvall lead–zinc deposit. This is a stratabound lead–zinc ore in Eocambrian sandstone, situated at the eastern border of the Swedish Caledonides. The deposit is an aberrant member of the Mississippi Valley ore class¹. The main ore minerals are galena and sphalerite, associated with minor amounts of calcite, barite and fluorite. These infill interstices around the sandgrains, often following sedimentary structures². The lead is markedly radiogenic J-type with a ²⁰⁶Pb/²⁰⁴Pb ratio of more than 20 (ref. 3). Fluid inclusion studies on the sphalerite give homogenisation temperatures around 150 °C (ref. 4). Laisvall is the largest lead concentration (original resources of about 60 × 10⁶ t of 4% Pb) in the 1,000km long lead- and zinc-rich Caledonian border zone, which includes deposits such as Dorotea and Vassbo.