Mapping polymetallic-sulfide-TOC associations in Swedish alum shales

Description

Scandiavian alum shale and other black shale formations of different age can act as important source of metals or host of economically important mineral deposits. Knowledge on the depositional and diagenetic environment of black shales and their associated trace metals (TM’s) is of significant importance for prospecting, mining and extracting critical metals from shales as well their impact on the surficial environment such as soil and groundwater. Modern studies and mapping of black shales are needed in Sweden, as a response to the Governments Official Investigations (SOU 2020:71). The focus of this proposal is therefore on the geochemical composition and its regional spatial variation of the Swedish alum shale, to increase the knowledge of how TM’s associate with mineralogy, carbon (organic and inorganic) and/or sulfur and phosphate content, metamorphic grade and depositional environment of alum shales. We are planning to use traditional geochemical and mineralogical methods with the aim to improve knowledge about black shale-hosted mineral deposits and to forecast possible risks related to black shale natural weathering and potential exploitation.

The main focus will be to investigate the TM association with sulfides, phosphates and kerogens (and/or graphites) in Paleozoic alum shales in Sweden, and compare the results with the Proterozoic black shales in Skelleftefältet and Finland to better understand TM migration in black shales of different grade of maturity, preservation and alteration and to get a better overview of the spatial distribution of TM’s in the Swedish black shales. Several redox sensitive and bio-essential trace metals, such as U, Cu, As, V, Mo, Ni, Mn, V, Hg, Sb and W, are commonly enriched in black shales as a function of its depositional and preservational environments. Identification of metal sources (incl. seawater-derived and hydrothermal sources) and entrapment mechanisms are important for putative future identification of economically important deposits of metals and their association with ore deposits.