Viscaria Cu-Co spacetime

A multi-chronometer approach to date the Viscaria Cu-Fe ± Co deposit, Kiruna. Results will constrain the timing of Cu mineralization at Viscaria and refine the tectonic spatiotemporal framework for this type of Cu deposit in the Northern Norrbotten ore province.

This project will assess the structural setting, chemical character, and age of petrographically well-constrained Cu-Fe ± Co mineralization at the Viscaria deposit in Kiruna. The project includes a state-of-the-art sample characterization workflow spanning a range of analytical techniques including 3D drill core tomography, SEM-EDS analysis, and micro-XRF imaging. Key mineral phases will be identified, characterized, and dated using bulk and in situ geochronology methods. Current research at Viscaria is a partnership between the Ore Geology group at LTU and Copperstone Resources, supported by the LTU-SUN strategic research initiative.

Project rational

Despite being a copper mine in the 1980’s−90’s and subsequent exploration activities, limited geological research has been undertaken at Viscaria and the age of the deposit remains unknown. Thus, the metallogenic relationship between Viscaria Cu-Fe ± Co mineralization and iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG) mineralization in Northern Norrbotten remains uncertain. Whereas Viscaria is hosted by Rhyacian (2.1 Ga) supracrustal rocks (Kiruna greenstone group) and has an overall stratiform character, other Cu ± Au ± Fe ± Co mineralization in northern Norrbotten typically occurs in Orosirian (1.9 Ga) supracrustal rocks and shows epigenetic characteristics (e.g., Aitik, Rakkurijärvi). New robust radiometric dating at Viscaria will constrain the age of the deposit, affirm its syngenetic and/or epigenetic character, and help guide future exploration strategies for Cu ± Co mineralization in Norrbotten greenstone belts.

Project implementation

To develop efficient and scientifically based exploration strategies for Viscaria-type copper mineralization, this project focuses on radiometric dating of structurally and chemically well-characterized Cu ± Co mineralization in different paragenetic settings from the three main ore zones (A-, B- and D-zones). Re-Os dating of chalcopyrite and pyrite will constrain the timing of Cu mineralization in the A- and B-zones. Presently, a scoping study to identify apatite ± monazite in D-zone magnetite-rich zones suitable for in situ U-Pb dating is underway.

Expected results and implications

New radiometric dating will constrain the absolute timing of Cu-Fe ± Co mineralization at Viscaria for the first time. The new dating results will confirm or refute a previously hypothesized syn-volcanic origin for Viscaria at c. 2.1 Ga and assess what role tectonothermal (re)mobilization has played in deposit formation. From a regional perspective, the results will evaluate potential genetic links between Viscaria and IOA- or IOCG-type mineralization in Norrbotten, assess Cu ± Co prospectivity in Rhyacian greenstone belts, and refine the current tectonic-metallogenic framework for the Norrbotten ore province.

This work is co-funded by the strategic area SUN – Natural Resources for Sustainability Transitions at Luleå University of Technology and Copperstone Resources.