Franco Pirajno - Academia.edu (original) (raw)
Papers by Franco Pirajno
Precambrian Research, 2002
Gondwana Research, Sep 1, 2016
Springer eBooks, 1992
The Earth’s outer layers, namely, the lithosphere and the asthenosphere have an important role in... more The Earth’s outer layers, namely, the lithosphere and the asthenosphere have an important role in the mechanisms of plate tectonics. The outermost layer of our planet is the relatively strong and rigid lithosphere — about 100 km thick — broken up into a number of major and minor plates, whose present-day configuration is shown in Fig. 6.1. The boundaries between plates, divergent (rifting, spreading zones), convergent (subduction and collision zones) and transform faults, are the sites of intense geological activity including earthquakes, volcanism, mountain building and of course mineralisation. The lithosphere overlies the asthenosphere, a weak region of the upper mantle about 200 km thick, where temperatures approach melting point. The boundary, which is probably gradational, between these two layers is by no means well defined, and is not to be confused with the crust-mantle boundary which is defined by the Mohorovicic discontinuity. Although the reason for the movement of the lithospheric plates is not entirely understood, it is generally agreed that mantle convective motions, possibly driven by radiogenic heat, may be responsible. The spreading motion of the oceanic crust is indicated by the characteristic magnetic stripes, symmetrically disposed on either side of a mid-ocean ridge, and first described by Vine and Matthews (1963). In this chapter we examine plate tectonic settings and associated types of hydrothermal mineralisation. A schematic view of plate tectonic settings is shown in Fig. 6.2.
Springer eBooks, 1992
The theory of sea-floor spreading and the “new” global tectonics, including the more recent ideas... more The theory of sea-floor spreading and the “new” global tectonics, including the more recent ideas on accretionary tectonics, has permitted a much clearer understanding of the genesis of mineral deposits. This understanding is essentially provided by a unifying framework within which processes of ore genesis can be integrated. In this way mineralisation types can be related to time-space positions, in specific lithospheric plate settings, and within continuously evolving crustal geodynamic patterns. The spatial distribution of mineral deposits as related to plate tectonic processes has been widely discussed in many papers, especially during the 1970–1980 decade. Consequently, excellent textbooks on the topic were published soon after, which in spite of subsequent advances in more recent years, remain important texts for providing the geologist with an essential background in the study of mineral deposits. The books referred to are those published by Mitchell and Garson (1981), Hutchison (1983) and Sawkins (1990). Equally important in models of ore genesis is an understanding of the evolutionary trends of mineral deposits through the geological ages. This field of study is obviously connected with the evolution of plate configurations and their interactions through time. The works of Watson (1973,1978), Reed and Watson (1975), Cloud (1976), Goodwin (1981), Lambert and Groves (1981), Meyer (1981, 1988), Hutchinson (1980), and Windley (1984) all deal with these evolutionary trends.
Earth and Planetary Science Letters, 2022
Ore Geology Reviews, 2022
Modern Approaches in Solid Earth Sciences, 2022
Ore Geology Reviews, 2021
Abstract The multiphase hydrothermal superposition phenomena on porphyry deposits, the mineral co... more Abstract The multiphase hydrothermal superposition phenomena on porphyry deposits, the mineral complexity and characteristics of the alteration-associated assemblages limit the further determination for the magmatic-hydrothermal evolution in porphyry deposits. The Taiyangshan porphyry Cu-Mo deposit in the northern margin of the Triassic West Qinling orogenic belt exhibits a multi-stage, alteration-related quartz sulfide veins that recorded element migration processes during fluid-rock reactions. In this study, we investigated hydrothermal veins in the Taiyangshan deposit focusing on vein compositions and structures as well as the evolution of ore formation using quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and iron isotope analyses. The formation of the early K-feldspar-biotite-quartz-magnetite-apatite veins is closely associated with the early potassic alteration, and during the fluid-rock reactions, Si, S, Fe, and K migrated in, while Mg, Ca and Na migrated out. K-feldspar-chlorite-pyrite-chalcopyrite-quartz veins correlated to the propylitic alteration, dominantly caused the migration of Si, Fe, S, Ca Mg, Al and K. Quartz-sericite-pyrite veins corresponding to the phyllic alteration processes that occurred in a relatively late stage, during the fluid-rock reactions of which, Si, Fe, S, and K migrated into the system. The δ56Fe whole-rock values of altered porphyries range from 0.08 ‰ to 0.31 ‰, and δ56Fe values of pyrite from quartz veins range from 0.30 ‰ to 0.57 ‰. Iron isotope compositions of both pyrites of the ore-bearing wall rocks and the quartz-sulfide veins of the Taiyangshan Cu-Mo deposit are generally uniform, which indicate the same source origin between the ore-bearing porphyry and the iron isotope compositions of the metal sulfide in the quartz veins, and additionally highlights that the ore-forming source is closely related to the ore-bearing porphyry. Magnetite precipitated in the early stage of potassic alteration, resulting in the enrichment of the light Fe isotope in the early fluids. Crystallization and precipitation of pyrite mainly occurred during processes of propylitic and phyllic alteration, leading to an absorption of the light Fe isotope, and elsewhere, an enrichment of the heavy Fe isotope in the fluids. During the fluid-rock reactions of propylitic and phyllic alteration, a large amount of S migrated into the veins, thereby promoting the fractionation of Fe isotope. Moreover, the development of the ore-forming fluids enriched with heavy Fe isotope from early potassic- to late phyllic alteration, are indicative of isotopic progressions from the early lithostatic pressure to the late hydrostatic pressure. Our current research on the Taiyangshan Cu-Mo porphyry deposit helps to explain the evolutionary processes of the magmatic–hydrothermal system, and also improves our understanding of a porphyry metallogenic evolution model.
Gondwana Research, 2021
Abstract In this contribution, we present the more or less consistent banding (mm to several cm) ... more Abstract In this contribution, we present the more or less consistent banding (mm to several cm) from Fe-rich to silica-rich chemical sediments associated with the venting that leads to the formation of banded sediments in several hydrothermal mineral systems, such as volcanogenic massive sulphides (VMS) and sedimentary exhalative (SEDEX) deposits. However, in this contribution we specifically refer to the banded sediments that are commonly known as Algoma-type iron formation (BIF). Algoma-type BIF does provide a somewhat unusual and poorly investigated case of chemical sediments banding. The banding of these chemical sediments in terms of Fe oxides and silica is related to their alternate dominance in the upwelling fluids in a variety of settings ranging from a sea floor spreading centre to continental rift-related settings. Equally important is the concept that Algoma-type BIF may well be associated with and a distal expression of sulphide-bearing mineral systems.
Scientific Reports, 2020
Large-scale mantle convective processes are commonly reflected in the emplacement of Large Igneou... more Large-scale mantle convective processes are commonly reflected in the emplacement of Large Igneous Provinces (LIPs). These are high-volume, short-duration magmatic events consisting mainly of extensive flood basalts and their associated plumbing systems. One of the most voluminous LIPs in the geological record is the ~ 2.06 billion-year-old Bushveld Igneous Complex of South Africa (BIC), one of the most mineralised magmatic complexes on Earth. Surprisingly, the known geographic envelope of magmatism related to the BIC is limited to a series of satellite intrusions in southern Africa and has not been traced further afield. This appears inconsistent with the inferred large size of the BIC event. Here, we present new radiometric ages for alkaline magmatism in the Archean Yilgarn Craton (Western Australia), which overlap the emplacement age of the BIC and indicate a much more extensive geographic footprint of the BIC magmatic event. To assess plume involvement at this distance, we prese...
Nature Communications, 2019
The cycling of iron and organic matter (OM) is thought to have been a major biogeochemical cycle ... more The cycling of iron and organic matter (OM) is thought to have been a major biogeochemical cycle in the early ferruginous oceans which contributed to the deposition of banded iron formations (BIF). However, BIF are deficient in OM, which is postulated to be the result of near-complete oxidation of OM during iron reduction. We test this idea by documenting the prevalence of OM in clays within BIF and clays in shales associated with BIF. We find in shales >80% of OM occurs in clays, but <1% occurs in clays within BIF. Instead, in BIF OM occurs with 13C-depleted carbonate and apatite, implying OM oxidation occurred. Conversely, BIF which possess primary clays would be expected to preserve OM in clays, yet this is not seen. This implies OM deposition in silicate-bearing BIF would have been minimal, this consequently stifled iron-cycling and primary productivity through the retention of nutrients in the sediments.
Applied Earth Science, 2018
Modern Approaches in Solid Earth Sciences, 2018
Precambrian Research, 2002
Gondwana Research, Sep 1, 2016
Springer eBooks, 1992
The Earth’s outer layers, namely, the lithosphere and the asthenosphere have an important role in... more The Earth’s outer layers, namely, the lithosphere and the asthenosphere have an important role in the mechanisms of plate tectonics. The outermost layer of our planet is the relatively strong and rigid lithosphere — about 100 km thick — broken up into a number of major and minor plates, whose present-day configuration is shown in Fig. 6.1. The boundaries between plates, divergent (rifting, spreading zones), convergent (subduction and collision zones) and transform faults, are the sites of intense geological activity including earthquakes, volcanism, mountain building and of course mineralisation. The lithosphere overlies the asthenosphere, a weak region of the upper mantle about 200 km thick, where temperatures approach melting point. The boundary, which is probably gradational, between these two layers is by no means well defined, and is not to be confused with the crust-mantle boundary which is defined by the Mohorovicic discontinuity. Although the reason for the movement of the lithospheric plates is not entirely understood, it is generally agreed that mantle convective motions, possibly driven by radiogenic heat, may be responsible. The spreading motion of the oceanic crust is indicated by the characteristic magnetic stripes, symmetrically disposed on either side of a mid-ocean ridge, and first described by Vine and Matthews (1963). In this chapter we examine plate tectonic settings and associated types of hydrothermal mineralisation. A schematic view of plate tectonic settings is shown in Fig. 6.2.
Springer eBooks, 1992
The theory of sea-floor spreading and the “new” global tectonics, including the more recent ideas... more The theory of sea-floor spreading and the “new” global tectonics, including the more recent ideas on accretionary tectonics, has permitted a much clearer understanding of the genesis of mineral deposits. This understanding is essentially provided by a unifying framework within which processes of ore genesis can be integrated. In this way mineralisation types can be related to time-space positions, in specific lithospheric plate settings, and within continuously evolving crustal geodynamic patterns. The spatial distribution of mineral deposits as related to plate tectonic processes has been widely discussed in many papers, especially during the 1970–1980 decade. Consequently, excellent textbooks on the topic were published soon after, which in spite of subsequent advances in more recent years, remain important texts for providing the geologist with an essential background in the study of mineral deposits. The books referred to are those published by Mitchell and Garson (1981), Hutchison (1983) and Sawkins (1990). Equally important in models of ore genesis is an understanding of the evolutionary trends of mineral deposits through the geological ages. This field of study is obviously connected with the evolution of plate configurations and their interactions through time. The works of Watson (1973,1978), Reed and Watson (1975), Cloud (1976), Goodwin (1981), Lambert and Groves (1981), Meyer (1981, 1988), Hutchinson (1980), and Windley (1984) all deal with these evolutionary trends.
Earth and Planetary Science Letters, 2022
Ore Geology Reviews, 2022
Modern Approaches in Solid Earth Sciences, 2022
Ore Geology Reviews, 2021
Abstract The multiphase hydrothermal superposition phenomena on porphyry deposits, the mineral co... more Abstract The multiphase hydrothermal superposition phenomena on porphyry deposits, the mineral complexity and characteristics of the alteration-associated assemblages limit the further determination for the magmatic-hydrothermal evolution in porphyry deposits. The Taiyangshan porphyry Cu-Mo deposit in the northern margin of the Triassic West Qinling orogenic belt exhibits a multi-stage, alteration-related quartz sulfide veins that recorded element migration processes during fluid-rock reactions. In this study, we investigated hydrothermal veins in the Taiyangshan deposit focusing on vein compositions and structures as well as the evolution of ore formation using quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and iron isotope analyses. The formation of the early K-feldspar-biotite-quartz-magnetite-apatite veins is closely associated with the early potassic alteration, and during the fluid-rock reactions, Si, S, Fe, and K migrated in, while Mg, Ca and Na migrated out. K-feldspar-chlorite-pyrite-chalcopyrite-quartz veins correlated to the propylitic alteration, dominantly caused the migration of Si, Fe, S, Ca Mg, Al and K. Quartz-sericite-pyrite veins corresponding to the phyllic alteration processes that occurred in a relatively late stage, during the fluid-rock reactions of which, Si, Fe, S, and K migrated into the system. The δ56Fe whole-rock values of altered porphyries range from 0.08 ‰ to 0.31 ‰, and δ56Fe values of pyrite from quartz veins range from 0.30 ‰ to 0.57 ‰. Iron isotope compositions of both pyrites of the ore-bearing wall rocks and the quartz-sulfide veins of the Taiyangshan Cu-Mo deposit are generally uniform, which indicate the same source origin between the ore-bearing porphyry and the iron isotope compositions of the metal sulfide in the quartz veins, and additionally highlights that the ore-forming source is closely related to the ore-bearing porphyry. Magnetite precipitated in the early stage of potassic alteration, resulting in the enrichment of the light Fe isotope in the early fluids. Crystallization and precipitation of pyrite mainly occurred during processes of propylitic and phyllic alteration, leading to an absorption of the light Fe isotope, and elsewhere, an enrichment of the heavy Fe isotope in the fluids. During the fluid-rock reactions of propylitic and phyllic alteration, a large amount of S migrated into the veins, thereby promoting the fractionation of Fe isotope. Moreover, the development of the ore-forming fluids enriched with heavy Fe isotope from early potassic- to late phyllic alteration, are indicative of isotopic progressions from the early lithostatic pressure to the late hydrostatic pressure. Our current research on the Taiyangshan Cu-Mo porphyry deposit helps to explain the evolutionary processes of the magmatic–hydrothermal system, and also improves our understanding of a porphyry metallogenic evolution model.
Gondwana Research, 2021
Abstract In this contribution, we present the more or less consistent banding (mm to several cm) ... more Abstract In this contribution, we present the more or less consistent banding (mm to several cm) from Fe-rich to silica-rich chemical sediments associated with the venting that leads to the formation of banded sediments in several hydrothermal mineral systems, such as volcanogenic massive sulphides (VMS) and sedimentary exhalative (SEDEX) deposits. However, in this contribution we specifically refer to the banded sediments that are commonly known as Algoma-type iron formation (BIF). Algoma-type BIF does provide a somewhat unusual and poorly investigated case of chemical sediments banding. The banding of these chemical sediments in terms of Fe oxides and silica is related to their alternate dominance in the upwelling fluids in a variety of settings ranging from a sea floor spreading centre to continental rift-related settings. Equally important is the concept that Algoma-type BIF may well be associated with and a distal expression of sulphide-bearing mineral systems.
Scientific Reports, 2020
Large-scale mantle convective processes are commonly reflected in the emplacement of Large Igneou... more Large-scale mantle convective processes are commonly reflected in the emplacement of Large Igneous Provinces (LIPs). These are high-volume, short-duration magmatic events consisting mainly of extensive flood basalts and their associated plumbing systems. One of the most voluminous LIPs in the geological record is the ~ 2.06 billion-year-old Bushveld Igneous Complex of South Africa (BIC), one of the most mineralised magmatic complexes on Earth. Surprisingly, the known geographic envelope of magmatism related to the BIC is limited to a series of satellite intrusions in southern Africa and has not been traced further afield. This appears inconsistent with the inferred large size of the BIC event. Here, we present new radiometric ages for alkaline magmatism in the Archean Yilgarn Craton (Western Australia), which overlap the emplacement age of the BIC and indicate a much more extensive geographic footprint of the BIC magmatic event. To assess plume involvement at this distance, we prese...
Nature Communications, 2019
The cycling of iron and organic matter (OM) is thought to have been a major biogeochemical cycle ... more The cycling of iron and organic matter (OM) is thought to have been a major biogeochemical cycle in the early ferruginous oceans which contributed to the deposition of banded iron formations (BIF). However, BIF are deficient in OM, which is postulated to be the result of near-complete oxidation of OM during iron reduction. We test this idea by documenting the prevalence of OM in clays within BIF and clays in shales associated with BIF. We find in shales >80% of OM occurs in clays, but <1% occurs in clays within BIF. Instead, in BIF OM occurs with 13C-depleted carbonate and apatite, implying OM oxidation occurred. Conversely, BIF which possess primary clays would be expected to preserve OM in clays, yet this is not seen. This implies OM deposition in silicate-bearing BIF would have been minimal, this consequently stifled iron-cycling and primary productivity through the retention of nutrients in the sediments.
Applied Earth Science, 2018
Modern Approaches in Solid Earth Sciences, 2018