The link between hydrothermal nickel mineralization and an iron oxide-copper–gold (IOCG) system: Constraints based on mineral chemistry in the Jatobá deposit, Carajás Province
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The hydrothermal alteration types, which have affected intrusive and volcanic rocks from Nistru ore deposit, are related to fluids composition varied in their evolution within hydrothermal systems. The early stage of the hydrothermal activity has produced extensive propylitisation and potassic alteration (orthoclase, biotite, sericite) associated with the central part of the quartz-micromonzodioritic porphyry stock. The late stage of the fluids differentiation is determined by the hydrogen-ion metasomatism (phyllic alteration, argillic alteration), characterized by a large vertical variation. The hydrogen-ion metasomatism is associated with the bor metasomatism, generated by acid solutions and at a high temperature. The vertical and lateral zoning character of the hydrothermal alterations is related to differences in rock composition and variation in physical-chemical conditions during the periods of subvolcanic intrusion and mineralization.
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Bornite
Actinolite
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Polymetallic replacement deposit
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Amphibole
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The Late Cretaceous Silistar intrusion comprises of gabbros, gabbro-diorites to quartz-diorites and aplites, that were emplaced into a volcano-sedimentary succession of similar age. Structural data suggest that this intrusion is part of a larger, partially exposed body. A dense network of primary and secondary joints, in many places filled with various ore and gangue minerals, is a conspicuous feature of the intrusion. Hydrothermal alteration affecting the intrusion and the wall rocks includes: uralitization (amphibole-epidote), secondary biotitization and propylitization. Propylitic alteration occurred in two stages: high temperature (epidote-actinolite- chlorite) and middle to low temperature (sericite-chlorite-carbonate-epidote and chlorite-sericite-carbonate). Products of later alteration events include quartz-adularia, quartz-carbonate, carbonate, quartz-zeolites and zeolites. Apart from previously recognized contact-metasomatic mineralization, the presence of stockwork-type and disseminated pyrite and chalcopyrite mineralization, hosted by both the intrusion and the host rocks, is documented here. Two types of magnetite and pyrite (magmatic and metasomatic) are recognized. Based upon the alteration products and ore minerals, the presence of two differing zones is suggested. The first zone, which closely coincides with the intrusion, is potassic and hosts py-ma-cpy-hm-(ilm). The second zone is propylitic with py-ma-cpy-hm-(ilm)+(sph+ga)+(bo+hz). Cu is the main ore element; Mo contents are very low or nil. The types of ore mineralization and alteration products, along with structural data, show elements of both porphyry copper and epithermal systems and suggest their occurrence of such (and the first recognition of such) in the incipient rift zone of the Eastern Srednogorie Zone.
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The copper deposits of Perú consist of porphyry Cu±Mo, Au, Ag, breccia pipe Cu-Mo, enargite vein and replacement Cu±Au, Ag, Zn, Pb, calcic skarn Cu±Fe, Au, Zn, amphibolitic skarn Cu±Fe, volcanogenic massive sulfide Cu-Zn, vein and manto Cu±Ag, Pb, Zn, Sn, W, and sandstone ("red bed") Cu types. The vast majority of these deposits formed during the Andean Orogeny and are geographically and chronologically distributed in well-defined metallogenic domains. These domains correlate with geochemically distinct magmatic episodes.The magmatic and metallogenic domains appear to be controlled in part by transverse growth-faults in the Mesozoic and older basement rocks underlying the intensely folded and thrust-faulted Mesozoic and Tertiary rocks of the higher structural levels of the Cordillera. During the Andean Orogeny the extent of magmatism and the corresponding metallogenic provinces were influenced by subducted plate segmentation and by continental margin basement tectonics. In addition, the lithologic nature of the host rocks played an important role in determining the types of copper deposits formed.Porphyry Cu, breccia pipe Cu-Mo and calcic skarn Cu deposits are related to the Pomahuaca, Coastal and Caldera batholiths, as well as to felsic Cordilleran volcanism between 8° and 12°S. However, the largest and richest porphyry Cu deposits are related to the Caldera batholith. The Cobriza Cu-bearing skarn is the only significant copper deposit of pre-Mesozoic age.Perú has many ore deposits associated with the Miocene felsic extrusive and intrusive rocks along the Cordillera, forming veins and disseminations in igneous rocks and noncarbonate sedimentary rocks, and replacement mantos, pipes and veins in limestones. Several are large and high-grade enargite-type deposits containing mainly Cu, Ag, Au, Pb and Zn, accompanied by significant amounts of Cd, Te, Se, In, Bi and Tl. Others are veins and mantos containing Cu±Ag, Pb, Zn, Sn, W.The Mesozoic volcanosedimentary sequences along the coast host volcanogenic massive sulfide Cu-Zn and vein/manto-type amphibolitic skarn Cu±Fe deposits.Red bed Cu deposits are relatively unimportant in Perú.The following information on the history of copper mining in Perú has been condensed largely from Samame (1979), Petersen et al.(1990) and Benavides (1990).In Perú, gold and silver were apparently used before copper. The latter was first mined and processed by the pre-Inca Chimú culture along the northern coast and by the Tiahuanaco civilization in the Lake Titicaca region.Copper became an important metal during the Inca period,
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The intracratonic Paleoproterozoic Nonacho Basin, deposited on the western margin of the Rae craton, contains historic polymetallic (i.e., U, Cu, Fe, Pb, Zn, Ag) occurrences spatially associated with its unconformable contact with underlying crystalline basement rocks and regionally occurring faults. This study presents the paragenesis, mineral chemistry and geochemistry of uranium mineralized rocks and minerals of the MacInnis Lake sub-basin of the Nonacho Basin, to evaluate the style and relative timing of uranium mineralization. Mineralization is restricted to regionally occurring deformation zones, and post-dates widely spread and pervasive albitization and more local Ba-rich K-feldspar alteration of host rocks. Uranium mineralized rocks show elevated concentration of Cu, Ag and Au relative to variably altered host rocks. Microscopic and compositionally heterogeneous altered uraninite occurs (i) as overgrowths on partially dissolved Cu-sulphides with magnetite in chlorite ± quartz, calcite veins, and (ii) with minor uranophane in hematite-sericite-chlorite ± quartz breccia and stockwork. Both uraninite types are Th poor (<0.09 wt.% ThO2) and variably rich in SO4 (up to 2.26 wt.%), suggesting a low-temperature hydrothermal origin in a relatively oxidized environment. Rare-earth element (+Y) concentrations in type-i uraninite are high, up to 9.5 wt.% Σ(REE+Y)2O3 with CeN/YN values > 1, similar to REE compositions of uraninite in metasomatic iron and alkali-calcic systems (MIAC), including low-temperature hematite-type IOCG-deposits (e.g., Olympic Dam, Gawler Craton, Australia) and albitite-hosted uranium deposits (e.g., Southern Breccia, Great Bear Magmatic Zone, Canada, and Gunnar Deposit, Beaverlodge District, Canada). Both uraninite types are variably rich in Ba (up to 3 wt.% BaO), a geochemical marker for MIAC systems, provided by the dissolution of earlier secondary Ba-rich K-feldspar. Chemical U-Th-Pb dating yields resetting ages of <875 ± 35 Ma for type-ii uraninite-uranophane, younger than strike-slip movement along regional structures of the basin that are spatially associated with the uranium occurrences. We suggest that MacInnis Lake uranium occurrences formed from oxidized hydrothermal fluids along previously altered (albitized, potassically altered) regional-scale faults. Uranium minerals precipitated on earlier Fe-rich sulfides (chalcopyrite, bornite), which acted as a redox trap for mineralization, in low-temperature (~310–330 °C, based on Al-in-chlorite thermometry) breccias and stockwork zones, late in a metasomatic iron and alkali-calcic alteration system.
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