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FLUIDS-INC: Fluids in critical mineral systems

The FLUIDS-INC project is investigating the character of hydrothermal fluids associated with critical and strategic raw material mineralization in Sweden.

Project Overview

This project investigates the petrography, mineralogy and fluid characteristics of critical raw material (CRM) mineralization in Sweden. An integrated textural, paragenetic, geochemical and fluid inclusion (FI) study of ore and gangue minerals from three mineral system types (Li, W and REE) linked to granitic rocks will be undertaken. Associated barren granitic/pegmatitic rocks will also be investigated to compare fluid compositions and assess fluid evolution. Project results will constrain the geochemical fingerprints and PVTX conditions of magmatic-hydrothermal fluids linked to the mineralization, and provide new insights into the genesis of these important CRM systems. FI analysis will be conducted at the new Geofluids Lab at LTU (see below), and will help generate diagnostic pathfinder signatures relevant for intrusion-related CRM mineral systems to aid more efficient mineral exploration. Results will also advance understanding of granite-pegmatite emplacement conditions during Paleoproterozoic orogenesis.

Funding for the FLUIDS-INC project has been provided by the Geological Survey of Sweden (SGU)

Case studies

(1) LCT pegmatites in the Bothnian Basin, central Sweden

Fluids associated with lithium-caesium-tantalum (LCT) pegmatite mineralization in central Sweden will be investigated. Target deposits include the Varuträsk and Järkvissle pegmatite systems in Västerbotten and Västernorrland, respectively (below).

Clockwise images from top left: Green elbaite intergrown with pinkish lepidolite in Varuträsk pegmatite. Coarse, pink rubellite and fine-grained lepidolite (upper right) in Varuträsk pegmatite. Detail view of spodumene pegmatite with black cassiterite crystals, Järkvissle. Note narrow tourmaline halo at wall rock contact. Outcrop view of spodumene pegmatites at Järkvissle.

(2) Granite-skarn W mineralization, Bergslagen

Fluids associated with granite-skarn W-F-Mo mineralization in Bergslagen will be investigated. Target deposits include the Wigström and Yxsjöberg mineral systems. Pictures below show examples of the skarn mineralization.

Left image: Drill core of garnet-pyroxene skarn with scheelite, fluorite and quartz, Wigström. Right image: Drill core of garnet-quartz-pyroxene-fluorite-scheelite skarn rock also from Wigström.

(3) Granite-related REE mineralization, Jämtland

Fluids associated with granite-related rare earth element (REE) mineralization will be investigated. The target occurrence is the Näverån Th-U-REE system in Jämtland, hosted by a deformed granite.

Geofluids Lab at LTU

The FLUIDS-INC project supports and consolidates research activities within the new (2025) Geofluids Lab at LTU. The lab is centred around a Linkam MDS600 microthermometry heating-freezing stage coupled to a Nikon Eclipse E600 polarising microscope (below). An optional Linkam Imaging Station is also available. The Geofluids Lab fits within a research workflow for the petrographic and geochemical characterisation of minerals and fluid inclusions that includes optical microscopy (transmitted and reflected light), SEM-EDS/WDS imaging and analysis, and micro-XRF for mineral and chemical mapping (in collaboration with the Process Mineralogy Lab at LTU). Fluid inclusion standards for stage calibration have been kindly supplied by R.J. Bakker at the Fluid inclusion Lab, Technical University of Leoben.

Fluid inclusion studies

Direct insights into the character of mineralizing hydrothermal fluids are provided by fluid inclusions (FIs). These micro-scale mineral cavities (typically < 30 microns) contain minute volumes of the paleofluid from which ore and gangue minerals precipitate, or trap later fluids associated with overprinting hydrothermal activity linked to metamorphism and/or deformation (see pics below). FI analysis provides key information about the physicochemical nature and evolution of metal- and ligand-bearing hydrothermal fluids and their role in mineral deposit genesis, as well as other geological processes.