Cross-section of slow-spreading ridges, showing the different occurrences of melt in the oceanic crust (based on Sinton and Detrick, 1992; Dick et al., 2008). Gabbro s.l. includes troctolite, olivine-gabbro, gabbro, gabbronorite and ferrogabbro. Also dunite occurs along the Moho. Young hot crustal gabbro reacts (i.e., partial melting, hybridization, recrystallization) with invading primitive mantle-derived melt. Crystals, rocks and melt chemistry and texture are modified.
The deposits of Bor and Cukaru Peki are important contributors to the Apuseni–Banat–Timok–Srednogorie (ABTS) belt’s metallogenic endowment. We use decision tree and random forest algorithms applied to zircon geochemistry data from Bor, Cukaru Peki and a selection of other localities within the ABTS. The resulting predictions, supported by high scores on the test set predictions for the random forest algorithm, suggest that it is possible to fingerprint the studied deposits and localities from the ABTS belt based on zircon geochemistry. These results take into account the multivariate geochemical patterns and can be used in combination with a widely accepted Eu anomaly indicator or assist in finding more subtle geochemical differences for systems where applying a single cut-off value does not result in a good separation between barren and mineralized rocks.
Bor and Cukaru Peki are world-class porphyry deposits spatially and
genetically associated with the Cretaceous Timok magmatic complex. This
research was conducted to determine the age and geochemical affinity of the
magmatic rocks that formed these ore deposits. Our new geochemical analyses
of magmatic rocks from Bor and Cukaru Peki deposits imply they comprise
adakite-like compositions that have undergone the amphibole fractionation
and sulphide saturation processes. The zircon ages indicate that the Bor
system was formed in the age span between 84.5-82 Ma, while the Cukaru Peki
system was created in the age span between 86.5-85 Ma.
The Cu-Au deposit of Bor (Serbia) represents a continuum of mineralization styles, from porphyry-style ore occurring in quartz-magnetite-chalcopyrite veins and chalcopyrite disseminations to high-sulfidation epithermal Cu-Au ores in pyrite-chalcopyrite and anhydrite-sulfide veins. Decisive for the great economic importance of Bor is the presence of exceptionally rich high-sulfidation massive sulfide orebodies, composed of pyrite + covellite + chalcocite/digenite and minor anhydrite and enargite. They form irregular bodies measuring 0.5–10 million tons of ore grading up to 7% Cu, hosted by andesites and surrounded by intense argillic alteration. This study focuses on a small but rich underground orebody mined out recently, where limited drillcore is preserved for quantitative geochemical study. This paper documents the vein relationships within the deep porphyry-style orebody of Borska Reka, the transitional porphyry-epithermal veins, and the overlying and laterally surrounding epithermal massive sulfides of the Bor deposit. Geological observations indicate that the formation of massive sulfide orebodies concludes the ore formation. Mass balance calculations, recast into geologically realistic bulk fluid-rock reactions, confirm textural evidence that near-isovolumetric replacement of andesite host rocks is the dominant formation mechanism of massive sulfide orebodies at Bor, whereby all lithophile elements including Si are dissolved and only Ti stays relatively immobile. While net volume changes for individual mineralization styles within the massive sulfide orebody vary from − 16% volume loss to + 127% volume gain, overall volume change for the whole massive sulfide orebody was probably slightly negative. Brecciation is important only as means of creating channelways for reactive fluid that turns the andesite protolith into massive sulfide, whereas net breccia infill occurred only locally.
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