Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland

Abstract

The Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.

Vein-type gold formation during late extensional collapse of the Eastern Desert, Egypt: the Gidami deposit

“…These variable ranges of the Co/Ni ratios may have been related to fluctuating salinity and temperature of the ore fluids as the mineralization progressed (e.g. Brugger et al 2016;Vasilopoulos et al 2021).…”

Nemesfémkutatások a Kelet-Mecsekben: egy új orogén aranyércesedés felfedezése a Mecsekalja-zónában

“…GOLDFARB et al (2005 szerint a turmalin megelőzheti az arany kiválását, és csak ritkán utólagos a megjelenése, de minden esetben az aranytartalmú kvarcerek részét képezi, melyekben a leggyakoribb szulfidfázisok a pirit és arzenopirit, valamint a különféle Bi-Te-ásványok főként szulid, szulfoarzenid és tellurid formájában. MOLNÁR et al (2016), BEAUDOIN & PITRE (2016), VASILOPOULOS et al (2021 és számos más szerző alapján a turmalin megjelenése az orogén aranytelepekben rendszerint egyidős az arany képződésével. Az Ófalunál kibukkanó Studervögyi Gneisz érces kvarcitjában előforduló turmalin töredezettsége és a palásság síkjába ívesen besimuló turmalinfragmentumok alapján feltételezhető, hogy a turma linosodás is a milonitosodáshoz kötődően, a kvarc dinamikus átkristályosodását megelőzően vagy annak során jöhetett létre.…”

Potential Benefits and Constraints of Development of Critical Raw Materials’ Production in the EU: Analysis of Selected Case Studies

“…The region has been an area of intense mineral exploration for decades. It is a highly prospective area for gold and cobalt, and to some extent also for copper, rare earth elements, uranium and diamonds [70,71]. The deposit's mineralization is hosted by sericite quartzite, and volcanic and hypabyssal mafic and ultramafic rocks (Figures 5 and 6) [74].…”

“…All the mineralized rocks have, apparently, the same ore-mineral assemblage. According to [71], the metal association in the Juomasuo deposit was formed by spatially coincident, multiple hydrothermal processes. These type of deposits have been classified by, e.g., the authors of [75] as 'orogenic gold deposits with an atypical metal association'.…”