The conceptual approach used in this study incorporates spatial analysis techniques for data integration and analysis to perform reconnaissance-scale mineral prospectivity mapping for iron oxide copper -gold (IOCG) mineralisation in Finland. The known IOCG occurrences in Finland are characterised by the following features: (i) an epigenetic magnetite-rich host-rock; (ii) an association of Fe -Cu -Au + Co + U; (iii) ore minerals comprising magnetite, chalcopyrite, pyrite or pyrrhotite, and native gold; (iv) a gangue dominated by Ca-amphibole + diopside, albite and biotite; (v) enrichment in Ag, Au, Bi, Ca, CO 2 , Cu, Fe, S, Te + As, Ba, Cl, Co, K, LREE, Mo, Na, Pb, Rb, Sb, Se, U; (vi) multi-stage alteration; (vii) formation in the P -T range of 400 -6008C, 150 -350 MPa; and (viii) a distinct structural control in regions that have experienced both extensive compression and extension. The datasets used for the prospectivity analysis include a 1:1 000 000 scale geological map, high-resolution airborne geophysics, regional-scale multi-element till-geochemistry data, and a mineral occurrence database. The derived parameters used in the conceptual analysis include: (i) proximity to the craton margin; (ii) intersecting fault structures; (iii) presence of granitic intrusions particularly those with compatible and incompatible element enrichment; (iv) Cu, Co and Fe concentrations in till samples; (v) presence of hematite; and (vi) airborne magnetic highs and radiometric U data. A conceptual fuzzy-logic model was used to predict and locate the most prospective or favourable areas for IOCG exploration in the study area using the above-mentioned data layers. The models identify several permissive and highpotential areas within a significantly reduced potential exploration area. Validation of the modelling was conducted by quantifying the spatial association between the predicted endowment as favourability classes on the prospectivity map and the known mineral deposit sites with IOCG affinities using the Bayesian weights-of-evidence method.
15Compared with present-day global plate tectonics, Archaean and Palaeoproterozoic plate tectonics may have involved faster 16 moving, hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle. This scenario also 17 fits with the complex geodynamic evolution of the Fennoscandian Shield from 2.06 to 1.78 Ga when rapid accretion of island 18 arcs and several microcontinent-continent collisions in a complex array of orogens was manifested in short-lived but intense 19 orogenies involving voluminous magmatism. With a few exceptions, all major ore deposits formed in specific tectonic settings 20 between 2.06 and 1.78 Ga and thus a strong geodynamic control on ore deposit formation is suggested. 21All orogenic gold deposits formed syn-to post-peak metamorphism and their timing reflects the orogenic younging of the 22 shield towards the SW and west. Most orogenic gold deposits formed during periods of crustal shortening with peaks at 2.72 to 23 2.67, 1.90 to 1.86 and 1.85 to 1.79 Ga. 24The ca. 2.5 to 2.4 Ga Ni-Cu F PGE deposits formed both as part of layered igneous complexes and associated with mafic 25 volcanism, in basins formed during rifting of the Archaean craton at ca. 2.5 to 2.4 Ga. Svecokarelian ca. 1.89 to 1.88 Ga Ni-Cu 26 deposits are related to mafic-ultramafic rocks intruded along linear belts at the accretionary margins of microcratons. 27All major VMS deposits in the Fennoscandian Shield formed between 1.97 and 1.88 Ga, in extensional settings, prior to 28 basin inversion and accretion. The oldest bCyprus-typeQ deposits were obducted onto the Archaean continent during the onset of 29 convergence. The Pyhäsalmi VMS deposits formed at 1.93 to 1.91 Ga in primitive, bimodal arc complexes during extension of 30 the arc. In contrast, the Skellefte VMS deposits are 20 to 30 million years younger and formed in a strongly extensional intra-arc 31 region that developed on continental or mature arc crust. Deposits in the Bergslagen-Uusimaa belt are similar in age to the 32 Skellefte deposits and formed in a microcraton that collided with the Karelian craton at ca. 1.88 to 1.87 Ga. The Bergslagen- ARTICLE IN PRESS33 Uusimaa belt is interpreted as an intra-continental, or continental margin back-arc, extensional region developed on older 34 continental crust. 35Iron oxide-copper-gold (IOCG) deposits are diverse in style. At least the oldest mineralizing stages, at ca. 1.88 Ga, are 36 coeval with calc-alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to 37 continental arcs or to magmatic arcs inboard of the active subduction zone. Younger mineralization of similar style took place 38 when S-type magmatism occurred at ca. 1.80 to 1.77 Ga during cratonization distal to the active N-S-trending subduction zone 39 in the west. Possibly, interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore 40 formation. 41Finally, the large volumes of anorthositic magmas that characterize the S...
Widespread orogenic gold deposits are hosted by practically all rock types over the range of metamorphic grades in the Archaean Yilgarn Craton, Western Australia. They are normally located in second- or third-order structures, most commonly near crustal- to regional-scale deformation zones, in brittle, brittle–ductile and ductile deformational environments. Despite this extreme variability, the alteration and geochemical features of these deposits are strikingly consistent. Each gold deposit is enveloped by an alteration-zoning sequence. In greenschist facies, the alteration zones are, from distal to proximal and according to the diagnostic minerals: calcite–chlorite, calcite–ankerite and sericite. In amphibolite facies, two zones are normally detected, a distal biotite and a proximal calc-silicate zone with no intermediate zone. The ores are enriched in Ag, As, Au, Ba, CO 2 , K, Rb, S, Sb, Si, Te and W, and depleted in Na and Y relative to host-rocks. Base metals, Fe, Mg and Mn are rarely mobile in these settings. From the available, albeit limited, database there is little correlation between rock type or metamorphic grade and the elements enriched in the gold deposit. All enriched components may form primary dispersion haloes around the deposits. Parameters that most consistently define dispersion haloes for those deposits studied in the Yilgarn Craton are As, Au, Sb, Te, W, and the carbonation and sericitization indices. In nearly all cases, at least one of the parameters defines an anomaly significantly more extensive than that defined by Au alone. In some cases, Se or Y anomalies also extend beyond the Au anomaly. Importantly, there is also at least one pathfinder element whose primary dispersion extends beyond the alteration halo based on mineral assemblages, whereas the alteration–index anomalies normally do not extend beyond these limits. The primary geochemical dispersion halo may extend laterally for >200 m, and along strike for a few kilometres, from the gold orebody. A single geochemical parameter rarely defines an extensive and consistent vector towards gold ore. However, useful directional information can be achieved when trends defined by several geochemical parameters are combined.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.