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Intracontinental rift-related deposits: A review of key models

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Mineral systems associated with extensional fault systems in continental environments and not related to magmatic activity involve various deposit models that can be grouped into a single system which would plausibly explain the source and chemical composition of fluids, the formation depth, the source of heat and the structural history within a common geologic setting. Mineral deposits related to this tectonic setting are those described within the detachment-related model, including massive replacements, stockworks and veins of Cu and Fe oxides (with or without Au), polymetallic sulfide veins, barite and/or fluorite veins and stratabound and vein Mn deposits. This paper reviews the abovementioned deposits as well as others related to this tectonic setting, such as Se-rich polymetallic deposits, Almadén type Hg deposits, U-Ni-Co-As-Ag polymetallic deposits with subordinated Bi-Cu-Pb-Zn (five element deposits), simple polymetallic Pb-Ag-Zn deposits, and the members of the IOCG clan (including the Au-Ag detachment-related deposits) involved in the Cu-Fe (-Au) model deposits. All these mineral deposits are the result of fluid motion unrelated to magmatism in areas of thermal anomalies. These fluids collect certain elements producing a district mineralogical specialization with inhomogeneities in the distribution of mineralization types along the region affected by rifting. Fluid homogenization temperatures and salinities range between 60° and 430 °C, and 0 and 27 equivalent wt% NaCl, respectively. The O, S and D isotope composition is consistent with basinal poral fluids derived from meteoric waters under different P-T conditions in an active faults environment. Pb isotopes suggest that Pb derives from a mixture of rocks with a long period of residence in the upper crust and rocks deformed along repeated orogenic cycles with a contribution of Pb from the lower crust and even the mantle. Fluid flow along fault planes leads to different types of hydrothermal alterations depending on P-T conditions, particularly propylitization and low temperature potassium metasomatism. All such deposits can be found in two different geotectonic environments of metallogenic interest involving extensional faults associated with detachment zones in depth; i.e., 1) continental extension in a back-arc environment and 2) extension with rift development and generation of oceanic crust in a passive continental margin. Although the economic importance of this group of deposits is mainly related to industrial minerals, non-magmatic IOCG deposits could significantly augment the economic potential of this setting. The rift setting itself, without relation to detachments, is favorable for concentrating metals in stratabound deposits such as SEDEX ores. Additionally, the development of deposits directly related to magmatic activity contributes to the economic interest of this environment.

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... The Acoite Formation records the maximum transgression of the Eopaleozoic basin (Moya, 1988). During this event, high values of Ba, Cu, Ag, Pb, As, Ni, Co, Zn and U were registered in the black shales facies (López, 2012;Zappettini et al., 2017), therefore this unit may be a potential source of some of the metals of the Purísima-Rumicruz veins. ...
... In many FEDs, this "natural fracking" (sensu Markl et al., 2016) may lead to the mixing of hydrocarbon-bearing fluids and metal-rich hydrothermal fluids producing ore precipitation (Markl et al., 2016). These fluids circulate along direct faults associated with the detachment zones in a rifting setting ( Fig. 8; Jenkin et al., 1997;Zappettini et al., 2017). ...
... Five-element deposits were frequently related to a continental rifting environment (Kissin, 1988(Kissin, , 1992Canals et al., 1992;Essarraj et al., 2005;Staude et al., 2012;López, 2012;Zappettini et al., 2017;Guilcher et al., 2021b). Bagheri et al. (2007) and Bagheri (2015), based on structural, mineral texture and fluid inclusion analysis, propose a hiatus between the Cu mineralization and the Ni-Co sulfide paragenesis. ...
Article
The Purísima-Rumicruz vein system is a Ni–Co–Fe-arsenide type or Five-Element deposit located in the Cordillera Oriental, northwestern Argentina. The host rocks are Ordovician black shales of the Acoite Formation. Three vein types, were identified (a) sulfides/sulfoarsenides + carbonates ± quartz; (b) barite; and (c) crystalline quartz veins. Sulfide-carbonate veins are narrow and exhibit multi-episode infill and are NW-SE and E-W oriented. Four successive stages of mineral precipitation were established. The first stage, sulfide-rich, comprises galena, pyrite, chalcopyrite, bornite, and Zn-rich tetrahedrite-tennantite. A second stage corresponds to native silver, arsenides, Ni-sulfarsenides and pitchblende, indicative of a rise in the As/S ratio in the hydrothermal fluids. The third stage evidences a decrease in the As/S ratio with sulfide precipitation of silver sulfides, chalcocite, chalcopyrite, tetrahedrite-tennantite, bornite and millerite. Finally, a supergene event with covellite, digenite, limonite and Cu-carbonates occurred. Microthermometric studies of Stage 1 quartz yield Th between 185 and 276 °C and 5.2–12 wt% eq. NaCl. Salinities. Stage 3 calcite yield Th 110-240 °C and salinities in two ranges, 1–11 and 16.8–24 %wt. NaCl eq. The δ³⁴S values in chalcocite and galena range between +5.8 and + 7‰, and the δ¹⁸OSMOW values from quartz, are between +6.2 and + 9.0‰. δ¹⁸OSMOW and δ¹³CPDB values in calcite samples range between +10.9 and +14.7‰, and −3.05 to −4.07‰, respectively. Isotope data indicate a cortical source of the fluids, probably from connate waters. Early Cretaceous rifting produced a thermal anomaly and direct faults and fractures. Deep-seated brines mixed with connate fluids of the Acoite Formation led to the formation of the Purísima-Rumicruz veins.
... Pb-Zn-Ag veins hosted in clastic sedimentary sequences (CSS Pb-Zn-Ag veins) are a distinct class of mineral deposits associated with crustal-scale faults that could be genetically related to magmatic activity. This class of mineral deposit is included within the regional model for intracontinental rift-related deposits recently proposed by Zappettini et al. (2017) based on the "detachment-related mineralization model" of Long (1992), which also includes Mn bedded and vein deposits, Ba-F veins, Cu-Fe-Pb-Ag-Au replacement and veins, five-element veins and Se-rich polymetallic veins. Several Pb-Zn-Ag deposits related to Mesozoic intraplate extensional tectonic settings have been documented around the world, e.g. the Cierco ore (Pyrenees, Johnson et al. 1996) and Linares-La Carolina ores (Lillo, 1992) in Spain, Freiberg district (Baumann, 1994) and Harz Mountains (Haack and Lauterjung, 1993;Graaf et al. 2019) in Germany and he Purcell Basin in Canada (Paiement et al., 2012). ...
... The reactivation of E-W faults which controls the veins emplacement would be indicating the inception of the Andean deformation by the Middle Cretaceous in the PUVD area. In CSS Pb-Zn-Ag veins deep crustal faults are considered to be first-order hydrothermal fluid channels that connect deep-seated C, Pb, and fluid reservoirs with upper crustal C, S, Pb, and fluid reservoirs types (Zappettini et al., 2017;Beaudoin and Sangster, 1992). In the PUVD, the channeling of the mineralizing fluids could be favored by the location of the Cuyo basin in a weakened zone reactivated during different deformation cycles in which crustal scale faults affecting different stratigraphic levels controlled the deformation. ...
... Based on this new information we conclude that the PUVD occurred during the beginning of the compressive Andean Orogeny. Our finding reveals that CSS deposits can form not only in active rift environments as has been considered so far (Zappettini et al., 2017) but also during the compressive reactivation of an inactive rift system. . ...
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The Paramillos de Uspallata deposit, located in the Cuyo rift basin, is a Pb–Zn–Ag vein deposit hosted by Mesozoic Triassic volcano-sedimentary sequences. In the present study, new geological and isotopic data is used to constrain the age, source and structural controls of the ore forming fluids. The isotopic data suggest a Middle Cretaceous age for the mineralization and that mineralizing fluids were formed from a mixture of sources that includes the Permian volcanic rocks from the basin basement and the Triassic basalts, with Pb (and Sr) isotopic composition typical of the upper crust. Regional structural analysis allowed to conclude that the veins formed within large-scale reactivated structures that affect the basin basement. Local structural analysis showed that the mineralization was controlled by extensional and shear-extensional WNW-ESE to NW-SE and shear E-W trending structures. Kinematic analyses performed in the veins evidenced a transtensional environment with a NE extension direction and E-W dextral shear. In this scenario fluids were channeled by a strike-slip-faulting system connected with a deep weakness zone during the beginning of the Andean Orogeny. This study provides new insights into the genesis and the geodynamic scenario of Pb–Zn–Ag vein deposit.
... The fluorite deposits in China are mainly characterized by epigenetic vein-type mineralization Pei, 2018;Zhang et al., 2014). These fluorite vein systems which typically fill shear zones, tension fractures and tectonic breccias have contributed the main source of fluorine worldwide Zappettini et al., 2017). ...
... Fluorite is the sole mineral of economic value found in the mining area. The above signatures are similar to the fluorite districts located along the Rio Grande graben in western USA and the Baikal rift zone in Russia and Mongolia (Zappettini et al., 2017). According to the exploration reports, ore grade is quite variable with an average value ranging from ~45% to ~88% (Pei, 2018). ...
Article
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The Linxi fluorite district is located in the southern Great Xing’an Range and tectonically belongs to the eastern segment of the Central Asian Orogenic Belt. Previous studies mainly focus on the metal deposits in this region, but relatively little attention has been paid to the fluorite mineralization. The Linxi district contains more than 60 fluorite deposits while the formation age, nature of mineralized fluids, and ore-forming processes are poorly understood. This study focuses on geology, geochronology and geochemistry of the fluorite deposits in the Linxi district which share similar and relatable geological features. Fluorite veins are strictly controlled by ∼S-N-, NNE-SSW- and NE-SW-striking fault zones. Ore mineral assemblages are quite simple and mainly include fluorite, quartz and calcite. Geochronological data indicate that the main-stage fluorite vein mineralization in the Linxi district occurred approximately at 137–132 Ma. Fluid inclusions hosted in fluorite, quartz and calcite mainly homogenize at 140–220°C, corresponding to low salinities (mainly 0.3–1.2 wt% NaCl equivalent). Ore-forming fluids are characterized by low temperatures, low salinities and low densities of the H2O−NaCl system. The carbon, hydrogen and oxygen isotopic compositions of samples obtained from the Linxi fluorite district indicate an origin of meteoric water. Combined with trace element geochemistry, fluorite, quartz and calcite in this area share a common hydrothermal origin. The large-scale fluorite mineralization in this region may link to the Late Mesozoic metal metallogenic events in the southern Great Xing’an Range associated with the extensional tectonic setting.
... Fluorite can form over a wide range of physicochemical conditions (Eppinger & Closs, 1990) and often acts as a paragenetic associated mineral in Sn (-W-Mo), Fe-rare earth elements (REEs)-Nb, and base metal deposits (e.g., Galindo et al., 1994;Piqué et al., 2008;Yang et al., 2009;Smolyanskii & Bogomolov, 2011;Assadzadeh et al., 2017). Of these, fluorite epigenetic vein deposits are the main source of fluorine worldwide (Zappettini et al., 2017). Late Mesozoic fluorite vein systems are widespread throughout Eastern China, Southeastern Transbaikalia, and Eastern Mongolia (Hu et al., 1998;Nie et al., 2008;Smolyanskii & Bogomolov, 2011;Xu & Zhang, 2013;Fang, 2014;Wang et al., 2015a). ...
... During this period, tectonic extension occurred over the whole SGXR, and accordingly, extensive magmatism and related mineral deposits were generated (Ouyang et al., 2015). It is worth noting that, although the contribution of the input of magmatic fluids is negligible according to our study, coeval magmatism might have provided the power to drive the hydrothermal circulation system, which is similar to the situation described by Broom-Fendley et al. (2017), Pei et al. (2017) and Zappettini et al. (2017). ...
Article
The recently discovered Xiaobeigou fluorite deposit is situated in the southern part of the Southern Great Xing'an Range metallogenic belt. Fluorite‐bearing veins are rather common over the whole area. So far, 11 mineralized veins have been delineated at the Xiaobeigou deposit. Orebodies of the deposit are mainly hosted in Permian and Jurassic volcano‐sedimentary rocks. The orebodies in this mining district exhibit a well‐developed vertical zonation: from top to bottom, the orebodies can be divided into upper, central, and lower zones. The central zone is the most important part for mining operations, and it shows lateral zonation of fluorite mineralization. Rare earth element (REE) contents of the investigated samples are relatively low (less than 30.2 ppm). Furthermore, the REE contents of the fluorite grains from early to late ore stages exhibit a decreasing trend. All the fluorite samples show no or slightly positive Eu anomalies. Three types of fluid inclusions (FIs) are distinguished in the quartz and fluorite samples, including pure‐liquid single‐phase (PL‐type), liquid‐rich two‐phase (L‐Type), and vapor‐rich two‐phase (V‐type) FIs. The FIs hosted in early‐stage quartz were homogenized at 159.5–260.7°C (mainly 160–240°C); their salinities range from 0.18 to 1.22 wt.% NaCl eqv. The FIs hosted in early‐stage fluorite yield slightly lower homogenization temperatures of 144.4–266.8°C (peaking at 140–220°C), which correspond to salinities of 0.18–0.88 wt.% NaCl eqv. Homogenization temperatures and salinities for the late stage are 132.5–245.8°C (mainly 160–180°C) and 0.18–1.40 wt.% NaCl eqv., respectively. Laser Raman spectroscopy of FIs shows that both the vapor and liquid compositions of the inclusions are dominated by H2O. The H–O isotopic compositions at Xiaobeigou suggest that the ore‐forming fluids are predominantly of meteoric water origin. The Xiaobeigou deposit can be classified as a typical low‐temperature hydrothermal vein‐type fluorite deposit. Combined with regional data, we infer that the fluorite mineralization occurred during the Late Mesozoic in an extensional setting.
... In contrast, the second model suggests that the region developed as an intracontinental rift basin without generating new oceanic crust (i.e., the "intracontinental rift basin" model; Chen et al., 2020a;Zhao et al., 2022). These two models make specific predictions regarding the occurrence of prerifting basement rocks, rock assemblages and sedimentary characteristics, and deformation styles within the Zongwulong Shan-Qinghai Nanshan region (e.g., Zappettini et al., 2017;Corti et al., 2018;Leprêtre et al., 2018;Boone et al., 2019;Morley, 2020;Chenin et al., 2022;Manatschal et al., 2022;Wang et al., 2021a). For example, the ocean basin model predicts subduction-related magmatism and deformation and the absence of pre-extensional basement rocks, whereas the intracontinental rift basin model requires the occurrence of pre-extensional basement rocks comparable to those of the North Qaidam and South Qilian regions. ...
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Suture zones located across the Tibetan region clearly demarcate the rift-and-drift and continental accretion history of the region. However, the intraplate responses to these marginal plate-tectonic events are rarely quantified. Our understanding of the Paleo-Tethyan orogenic system, which involved ocean opening and closing events to grow the central Asian continent, depends on the tectonic architecture and histories of major late Paleozoic−early Mesozoic orogenic belts. These opening and collision events were associated with coupled intracontinental deformation, which has been difficult to resolve due to subsequent overprinting deformation. The late Paleozoic−early Mesozoic Zongwulong Shan−Qinghai Nanshan belt in northern Tibet separates the Qilian and North Qaidam regions and is composed of Carboniferous−Triassic sedimentary materials and mantle-derived magmatic rocks. The tectonic setting and evolutional history of this belt provide important insight into the paleogeographic and tectonic relationships of the Paleo-Tethyan orogenic system located ∼200 km to the south. In this study, we integrated new and previous geological observations, detailed structural mapping, and zircon U-Pb geochronology data from the Zongwulong Shan−Qinghai Nanshan to document a complete tectonic inversion cycle from intraplate rifting to intracontinental shortening associated with the opening and closing of the Paleo-Tethyan Ocean. Carboniferous−Permian strata in the Zongwulong Shan were deposited in an intracontinental rift basin and sourced from both the north and the south. At the end of the Early−Middle Triassic, foreland molasse strata were deposited in the southern part of the Zongwulong Shan during tectonic inversion in the western part of the tectonic belt following the onset of regional contraction deformation. The Zongwulong Shan−Qinghai Nanshan system has experienced polyphase deformation since the late Paleozoic, including: (1) early Carboniferous intracontinental extension and (2) Early−Middle Triassic tectonic inversion involving reactivation of older normal faults as thrusts and folding of pre- and synrift strata. We interpret that the Zongwulong Shan−Qinghai Nanshan initiated as a Carboniferous−Early Triassic intracontinental rift basin related to the opening of the Paleo-Tethyan Ocean to the south, and it was then inverted during the Early−Middle Triassic closing of the Paleo-Tethyan Ocean. This work emphasizes that pre-Cenozoic intraplate structures related to the opening and closing of ocean basins in the Tethyan realm may be underappreciated across Tibet.
... These ores often occur in terrigenous and carbonate-argillaceous formations and bear signs of syngenetic and/or diagen e t i c d e p o s i t i o n f r o m w a r m s a l i n e b r i n e s ( 1 0 0 -200°C) in the texture of ores, which were exposed to the near-bottom space along consedimentary faults. As this occurs, mineralization can be associated with deep sources in regional extension settings (Zappettini et al., 2017). Ores in the MVT deposits have an epigenetic appearance; they occur in subplatform carbonate complexes in hydrocarbon-related intracratonic and pericratonic basins of the passive margin. ...
Article
The results of recent study of the Earth’s crust based on the gravity data of the GOCE satellite were used for a comparative metallogenic analysis of the geodynamic settings of polymetallic deposits in the folded frame of Siberian and East European platforms. It is shown that deposits of the SEDEX type are more often located in the earth’s crust with the predominant development of the lower “basalt” layer. Pyrite copper and lead-zinc deposits (VMS), as well as some occurrences of the SEDEX type, are known in subduction island-arc and accretionary settings on the crust with the predominant development of the middle “granite” layer. Pb–Zn ores of the MVT-type are localized in deep pericratonic sedimentary oilgas basins on the shelf and continental slope, with no spatial relationship with the stratification of the earth’s crust. The Ag-polymetallic mineralization of Taimyr and Western Verkhoyansk are confined to deep pericratonic rift troughs on the passive continental margin, have a similar ore-bearing environment and may be considered as a single silver-polymetallic Taimyr-West Verkhoyansk belt. The obtained results to confirm the prospects of Pb–Zn deposits in Central and Eastern Taimyr, as well as the Saurey ore region (Polar Urals) and the need for their further research.
... These ores often occur in terrigenous and carbonate-argillaceous formations and bear signs of syngenetic and/or diagen e t i c d e p o s i t i o n f r o m w a r m s a l i n e b r i n e s ( 1 0 0 -200°C) in the texture of ores, which were exposed to the near-bottom space along consedimentary faults. As this occurs, mineralization can be associated with deep sources in regional extension settings (Zappettini et al., 2017). Ores in the MVT deposits have an epigenetic appearance; they occur in subplatform carbonate complexes in hydrocarbon-related intracratonic and pericratonic basins of the passive margin. ...
... Some basin-fill deposits such as the evaporite potash are directly a mineral resource. Veining from flow of mineral-rich fluids along faults related to deep penetrating detachments, and also shallower hydrothermal systems are also a valuable resource, particularly for metals (Zappettini et al., 2017). Fortunately, the porous and permeable rock formations that make good hydrocarbon reservoirs are also capable of storing vast amounts of CO 2 , making large-scale carbon capture and storage (CCS) a potentially important contributor to future global CO 2 emission reductions (IPCC, 2005). ...
... Globally, alkaline igneous complexes with carbonatites host significant orthomagmatic to hydrothermal PO 4 , Nb and REE deposits (Simandl and Paradis 2018;Goodenough et al 2016). Extension with a strong detachment vector may induce fluid convection that is unrelated to magmatism and causes formation of, for example, base metal, barite and fluorite deposits (Zappettini et al 2017). ...
Article
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Metallogeny is the science of ore and mineral deposit formation in geological space and time. Metallogeny is interdisciplinary by nature, comprising elements of natural science disciplines such as planetology to solid state physics and chemistry, and volcanology. It is the experimental forefront of research and bold thinking, based on an ever-growing foundation of solid knowledge. Therefore, metallogeny is not a closed system of knowledge but a fast-growing assemblage of structured and unstructured information in perpetual flux. This paper intends to review its current state and trends. The latter may introduce speculation and fuzziness. Metallogeny has existed for over 100 years as a branch of Earth Science. From the discovery of plate tectonics (ca. 1950) to the end of the last century, metallogeny passed through a worldwide phase of formally published ‘metallogenetic’ maps. In the last decades, a rapidly growing number of scientists, digitization and splendid new tools fundamentally boosted research. More innovations may be expected by the growing use of an evolving systematic ‘Geodata Science’ for metallogenic research by an increasingly global human talent pool. Future requirements for metallic and mineral raw materials, especially the critical natural elements and compounds that are needed for the nascent carbon-free economy, already drive activities on stock markets and in the resource industry. State geological surveys, academia and private companies embrace the challenges. The new age requires intensified metallogenic backing. In this paper, principles of metallogeny are recalled concerning concepts and terms. A metallogenic classification of ore and mineral deposits is proposed, and the intimate relations of metallogenesis with geodynamics are sketched (ancient lid tectonics and modern plate tectonics). Metallogenic models assemble a great diversity of data that allow an ever better understanding of ore formation, foremost by illuminating the geological source-to-trap migration of ore metals, the petrogenetic and geodynamic–tectonic setting, the spatial architecture of ore deposits and the nature and precise timing of involved processes. Applied metallogeny allows companies to choose strategy and tactics for exploration investment and for planning the work. Based on comprehensive metallogenic knowledge, mineral system analysis (MSA) selects those elements of complex metallogenic models, which are detectable and can guide exploration in order to support applications such as mineral prospectivity mapping, mineral potential evaluation and targeting of detailed investigations. MSA founded on metallogenic models can be applied across whole continents, or at the scale of regional greenfield search, or in brownfields at district to camp scale. By delivering the fundamental keys for MSA, supported by unceasing innovative research, the stream of new metallogenic insights is essential for improving endowment estimates and for successful exploration.
... Increased confidence in the F concentration of Hansonburg mineralizing fluids would also improve understanding of the origin of Hansonburg and fluorite-rich carbonate-hosted Zn -Pb deposits generally. For example, the association of fluorite deposits with continental rifts and lineaments has long been recognized and surmised to be the result of Frich fluids emanating from the mantle (Worl, 1974;Van Alstine, 1976;Zappettini et al., 2017). The Illinois-Kentucky district fits this model in that it is located in a rift setting and formed from fluids that had a strong mantle component as indicated by 3 He/ 4 He ratios (Kendrick et al., 2002) and were apparently F-rich. ...
Article
The Hansonburg, New Mexico district in the southwestern U.S.A. contains anomalously fluorite rich carbonate-hosted base metal sulfide deposits. A long-standing hypothesis for this fluorite enrichment is that the Hansonburg mineralizing fluids were correspondingly enriched in F relative to the typical sedimentary brines that formed carbonate-hosted base metal deposits. The purpose of the present study was to test this hypothesis by determining the F concentration in fluid inclusions hosted by drusy quartz that paragenetically overlaps fluorite. The fluid inclusions were thermally decrepitated creating evaporative solute mounds, which were then analyzed via scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Fluorine was detected in all evaporative solute mounds analyzed, equating to fluid inclusion F concentrations of 320 to 2500 ppm. These F concentrations are significantly greater than the F concentrations of tenth's to 10s of ppm F typical of sedimentary brines. Further, these high F concentrations indicate that the Hansonburg mineralizing fluid must have been very acidic during the time of fluorite mineralization with a pH of 1 to 2.4. This pH is much lower than the pH of 4.3 to 5.1 predicted in earlier studies and also much lower than the pH of 4 to 5.5 considered typical of carbonate-hosted ZnPb mineralizing fluids. High mineralizing fluid F concentrations in combination with low pH would have provided conditions favorable for the formation of the observed Hansonburg mineral assemblage, i.e. fluorite-barite rich and metal sulfide mineral poor.
... As discussed in section 6.2.3, the occurrence of fluorite deposits in the Gonzalito district might be linked to the rift-related regional fluoritemineralization. The NW-oriented regional belt of the fluorite-rich event reaches the Gonzalito district area and it is attributed to the Upper Triassic -Lower Jurassic magmatism, showing a Sm-Nd isochrone age of 205 ± 11 Ma (Zappettini et al., 2014;Rubinstein and Zappettini, 2015). ...
Article
The Gonzalito polymetallic mining district is located within the northeast tip of the 600 km-long NE-trending polymetallic belt of the North Patagonian Massif, in Patagonia, Argentina. It comprises Paleozoic igneous-metamorphic rocks of the Mina Gonzalito complex, which are intruded by Middle Triassic trachytic-andesitic dykes of the Monasa Fm. through a complex system of high-angle fractures. Rhyolitic dykes crosscut the pre-Jurassic rocks. Numerous semi-parallel vein-like mineral deposits, whose classification and age have been subject of debate, sharply crosscut the igneous-metamorphic, trachytic-andesitic and rhyolitic units. Mineralization shows a strong structural control through a complex system of semi-parallel NW-N-NE oriented fracture-hosted mineral deposits. Extensional jogs and open dilational fractures allow multiband vein infills, vein-like hydrothermal and fault-tectonic breccias, stockwork veins and veinlets with primary growth open-space and boiling-derived textures, indicating a brittle geological setting that is properly of the epithermal environment. Based on the structural setting, sulfide-gangue-alteration mineral assemblages and textures, sulfide mineral chemistry and whole-rock geochemical analyses, two different styles of hydrothermal deposits can be distinguished: massive-sulfide intermediate sulfidation epithermal Pb – Zn ± Ag ± Cu ± In and disseminated-sulfide low sulfidation Au ± Pb ± Ag ± Zn. The first has a main-stage pyrite – In-rich sphalerite – chalcopyrite – galena ore assemblage in scarce quartz - carbonates gangue. The second shows disseminated pyrite ± sphalerite ± chalcopyrite ± galena with economic grades of Au in abundant quartz – adularia ± fluorite gangue. SHRIMP U–Pb zircon data of rhyolites reveal Early Jurassic ages of 193 ± 2 and 191 ± 2 Ma and, along with their bulk-rock geochemical features, they can be included within the Chon Aike magmatic province, locally known as Marifil volcanic complex. Crosscutting relationships between the Lower Jurassic rhyolites and the epithermal veins in the Gonzalito district, and the presence of Oligocene basalts partially covering the epithermal deposits toward the western area, constrain the mineralization event between the Lower Jurassic and the Oligocene. However, the crosscutting relationships of this district along with the already proven genetic, temporal and spatial links between epithermal ore and fluorite-rich deposits and the Jurassic magmatism-rifting of Patagonia suggest that the studied epithermal deposits might be yielded closer or during the Lower Jurassic.
... Base-metal-poor deposits can be interpreted as detachment fault-controlled lowsulfidation gold mineralization. Mineralizations are in the form of massive, tabular ore bodies within the fault zone and they are open-space ore filling type in listric faults (Zappettini et al., 2017). Ores are observed in the areas showing intense silicification and brecciation taken place simultaneously with the detachment fault. ...
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Yeşilyurt (Malatya) fluorite-gold mineralization is located within the provincial borders of Malatya (Yeşilyurt) and Adıyaman (Çelikhan) in the East Anatolian Region. This mineralization is one of the gold deposits which correlated with low-angle normal/detachment fault. Low-angle normal fault associated with a tectonic setting which is potential extensional in Tertiary term. Marble-recrystallize limestone which belongs to the metamorphic core are the dominant rock (footwall) type in the bottom plate of the fault zone. There are deformed graphitic calcschists (hanging wall) in the upper plate of the fault zone. The fault zone is characterized by fault clay, cataclasite and breccia. While the cataclasite, and breccia are the principal ore host, there is more weakly mineralization in fault clay. Alteration assemblages are: (1) silica replacements/veinlets and, (2) quartz-pyrite replacements /veinlets. Gang minerals are; quartz, calcite, limonite, hematite, semi-graphite, realgar, orpiment and fluorite. High gold contents are closely related to silicification and quartz-pyrite alteration which damaged the primary textures. Small volume syn-tectonic intrusives are simultaneous and typically monitored in the silicified areas which are border on the high-grade gold mineralization. Metalliferous fluids precipitated sulfides in the relatively low-pressure, low-temperature environment along the low-angle fault zone at Yeşilyurt deposit. Mineralization is a non-basemetalliferous Au system which contains Au/Ag ~ 1,07, As (~%0,27), F (%1,59) and trace amount of Sb. The resource calculations made by MTA shows that Yeşilyurt is a small scaled gold deposit which contains 1.900.000 ton ore and 1gr Au/ton. This deposit will lead to finding new gold deposits in Eastern Taurus Orogenic Belt. 10.19111/bulletinofmre.797729
... This calls into question the source of Cu-Au mineralisation which has been suggested as IOCG (Iron Oxide Copper Gold)-type or IPB (Iberian Pyrite Belt)-type mineralisation (Pirajno et al., 2016). IOCG-type deposit have been reported with fluid values between δ 18 O −1 and 7.5‰ and δD -40-10‰ (Skirrow, 2000;Torresi et al., 2012), and δ 18 O values between −5 and 8‰ have been reported for Cu-Au mineralisation associated with detachment-fault zones, a variant of non-magmatic IOCG deposits (Zappettini et al., 2017). It is possible that the circulation of formation fluids can transport and concentrate Cu-Au mineralisation without magmatic fluid. ...
Article
The Abra Pb-Ag-Ba-Zn-Cu-Au deposit in the Capricorn Orogen, Western Australia is primarily a lead and silver resource currently estimated at 47.8 Mt (indicated and inferred) of 7.3–10.1% Pb and 18–28 gt⁻¹ Ag, although significant Cu-Au zones are also identified. The deposit is unique within sediment-hosted Pb-Zn deposits for its low Zn content, significant Cu-Au zone and high Fe content, providing a case study where the source of fluid and ore-forming processes are contentious. The combination of whole-rock hydrogen and oxygen isotope data, in situ oxygen isotope data in quartz, and in situ sulphur isotope data of pyrite and chalcopyrite, has been used to reconstruct a complex history of overprinting, involving stages of sedimentation, diagenesis and hydrothermal activity. The host sedimentary rocks consist of detrital quartz (δ¹⁸O ∼11–18‰) and whole rock δ¹⁸O values (∼9–16‰) reflecting the combined composition of detrital and authigenic minerals, diagenetic-metamorphic exchange, chlorite and iron content. Quartz in recrystallised chemical sedimentation, quartz cementation, and quartz-barite veins at low temperatures (∼100–250 °C) involved predominantly surface and formation fluids with a wide range of fluid δ¹⁸O values between ∼ -5‰ and 2.6‰. Quartz in chloritized host rock with disseminated pyrite and chalcopyrite-galena veins at 250–320 °C reflect exchange with fluids(s) having a narrow range of δ¹⁸O values (∼5–9‰), most likely formation fluids. The fluid responsible for iron oxide, pyrite and polymetallic carbonate veins appears to be a mixture of formation and lighter surface fluids, with a range of fluid δ¹⁸O values (∼0.8–5.5‰). In situ sulphur isotopes are consistent with reduced seawater sulphate source in all samples, therefore it is likely that metal-rich formation fluids have interacted with reduced sulphate in the host sediments to precipitate as sulphide. Mineralisation and associated alteration at Abra has caused whole rock δ¹⁸O values to decrease in the deposit which may be useful as a tool for exploration in similar sediment-hosted base-metal deposits. We have shown the combination of different isotopic systems, and utilisation of in situ techniques, can constrain the sources and evolution of fluid and sulphur involved in basin formation, hydrothermal alteration and base metal mineralisation. Isotopic values can be directly related to different mineral populations within a relative temporal framework and can be used to distinguish fluids between multiple events.
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Rifting and continental break-up are major research topics within geosciences, and a thorough understanding of the processes involved as well as of the associated natural hazards and natural resources is of great importance to both science and society. As a result, a large body of knowledge is available in the literature, with most of this previous research being focused on tectonic and geodynamic processes and their links to the evolution of rift systems. We believe that the key task for researchers is to make our knowledge of rift systems available and applicable to face current and future societal challenges. In particular, we should embrace a system analysis approach and aim to apply our knowledge to better understand the links between rift processes, natural hazards, and the geo-resources that are of critical importance to realise the energy transition and a sustainable future. The aim of this paper is therefore to provide a first-order framework for such an approach by providing an up-to-date summary of rifting processes, hazards, and geo-resources, followed by an assessment of future challenges and opportunities for research. We address the varied terminology used to characterise rifting in the scientific literature, followed by a description of rifting processes with a focus on the impact of (1) rheology and stain rates, (2) inheritance in three dimensions, (3) magmatism, and (4) surface processes. Subsequently, we describe the considerable natural hazards that occur in rift settings, which are linked to (1) seismicity, (2) magmatism, and (3) mass wasting, and provide some insights into how the impacts of these hazards can be mitigated. Moreover, we classify and describe the geo-resources occurring in rift environments as (1) non-energy resources, (2) geo-energy resources, (3) water and soils, and (4) opportunities for geological storage. Finally, we discuss the main challenges for the future linked to the aforementioned themes and identify numerous opportunities for follow-up research and knowledge application. In particular, we see great potential in systematic knowledge transfer and collaboration between researchers, industry partners, and government bodies, which may be the key to future successes and advancements.
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Rifting and continental break-up is a key research topic within geosciences, and a thorough understanding of the processes involved, as well as of the associated natural hazard and natural resources is of great importance to both science and society. As a result, a large body of knowledge is available in the literature, yet most of previous research focuses on tectonic and geodynamic processes and their links to the evolution of rift systems. However, we believe that the key challenge for researchers is to make our knowledge of rift systems available and applicable to face new societal challenges. In particular, we should embrace a system analysis approach, and aim to apply our knowledge to better understand the links between rift processes, natural hazards, and the geo-resources that are of critical importance to realize the energy transition and a sustainable future. The aim of this paper is therefore to provide a first-order framework for such an approach, by providing an up-to-date summary of rifting processes, hazards, and geo-resources, followed by an assessment of future challenges and opportunities for research. We address the varied terminology used to characterise rifting in the scientific literature, followed by a description of rifting processes with a focus on the impact of (1) rheology and stain rates, (2) inheritance in three dimensions, (3) magmatism, and (4) surface processes. Subsequently, we address the considerable natural hazards and risks that occur in rift settings, which are linked to (I) seismicity, (II) magmatism, and (III) mass wasting, and provide some insights in how the impacts of these hazards can be mitigated. Moreover, we classify and describe the geo-resources occurring in rift environments as (a) non-energy resources, (b) geo-energy resources, (c) water and soils, and (d) opportunities for geological storage. Finally, we discuss the key challenges for the future linked to the aforementioned themes, and identify numerous opportunities for follow-up research and knowledge application. In particular, we see great potential in systematic knowledge transfer and collaboration between researchers, industry partners and government bodies, which may be the key to future successes and advancements.
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This study focuses on the origin of fluorite ore deposits that are associated with the Eocene alkaline igneous suite of the Tamazert complex in the Moroccan High Atlas. Based on field observations and mineralogy, two major ore styles were identified: 1) a disseminated purple fluorite in aegirine-rich nepheline syenites (stage 1) and 2) a banded purple-white fluorite ore in karstic cavities and veins hosted in the Jurassic carbonate (stage 2). Both fluorite mineralization stages are commonly accompanied by calcite. The distribution of fluorite deposits at the peripheries of syenite and the surrounding Jurassic carbonates suggests the development of long-lived hydrologic systems around the shallow intrusion. Based on fluid inclusion, Rare Earth Elements and Yttrium (REY), and C–O isotopic constraints, this study reveals that different fluid systems were responsible for the deposition of fluorite ores in and around the Tamazert alkaline igneous complex. The disseminated interstitial fluorite precipitated from a F-rich magmatic-hydrothermal fluid, which exsolved from the highly evolved alkaline-silicate melt and was subsequently altered by Na–Ca metasomatic brines. Vein-type fluorite deposits hosted in the Jurassic carbonates precipitated from low salinity (1.6–8.5 wt% NaCl equiv.) and heated (Th = 118–157 °C) meteoric fluids, which migrated in response to the heat flow around the shallow intrusion. Fluid cooling, fluid interaction with Jurassic carbonates, and pressure fluctuations were the most important fluorite deposition mechanisms. The evolved melt provided F and REY for the interstitial fluorites, whereas meteoric fluids leached F− from syenites and other F-bearing igneous rocks. Based on the fractionation pattern, the REY inventory of the vein fluorites was acquired by interaction of meteoric fluids with Jurassic carbonates.
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Continental rifts can form when and where continents are stretched. If the driving forces can overcome lithospheric strength, a rift valley forms. Rifts are characterised by faults, sedimentary basins, earthquakes and/or volcanism. With the right set of weakening feedbacks, a rift can evolve to break a continent into conjugate rifted margins such as those found along the Atlantic and Indian Oceans. When, however, strengthening processes overtake weakening, rifting can stall and leave a failed rift, such as the North Sea or the West African Rift. A clear definition of continental break-up is still lacking because the transition from continent to ocean can be complex, with tilted continental blocks and regions of exhumed lithospheric mantle. Rifts and rifted margins not only shape the face of our planet, they also have a clear societal impact, through hazards caused by earthquakes, volcanism, landslides and CO2 release, and through their resources, such as fertile land, hydrocarbons, minerals and geothermal potential. This societal relevance makes an understanding of the many unknown aspects of rift processes as critical as ever.
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Este libro contiene los resúmenes de trabajos presentados en la XVII Reunión de Tectónica, llevada a cabo en la ciudad de La Rioja, Argentina, entre los días 3 y 5 de septiembre de 2018. Estudiantes y profesionales de Ciencias de La Tierra presentan y discuten los avances científicos originales alcanzados o en desarrollo sobre temáticas relacionadas a la tectónica y geología estructural a diversas escalas, desde la microestructuras hasta la arquitectura litosférica. Las áreas temáticas incluyen: evolución de basamentos cristalinos (deformación y adición magmática), tectónica preandina, tectónica Andina, modelado y geofísica, neotectónica, y análisis estructural aplicado y riesgo sísmico (geotecnia, minería, sistemas petroleros riesgo sísmico).
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The Paramillos de Uspallata deposit, previously considered as genetically linked to a Miocene porphyry deposit, is located in the Mesozoic Cuyo Basin, which was formed during the beginning of the break-up of Gondwana. In the present study, both previous information and new geological, mineralogical, and isotopic data allowed outlining a new descriptive model for this deposit. Stratigraphic and structural controls allowed considering this deposit as contemporaneous with the Mesozoic rifting, with the mineralization resulting from a Pb–Zn stage followed by an Ag–Cu–Pb stage. The hydrothermal fluids were found to have low temperature and low to moderate salinity, and to result from the mixing between metamorphic and meteoric fluids, with the lead sourced by the igneous Paleozoic basement and the sulfur partly derived from a magmatic source. These characteristics allow describing Paramillos de Uspallata as Pb–Zn–Ag veins hosted in clastic sedimentary sequences genetically linked to a rift basin and redefining it as detachment-related mineralization.
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The Bay of La Paz region of Baja California Sur is critical for understanding the southwestern Gulf of California’s stratigraphic, structural, and tectonic evolution from a convergent margin before ~12 Ma to highly oblique-divergent plate boundary since ~8 to 6 Ma. This study focuses on the San José Island accommodation zone and addresses the gap in geologic knowledge between the San Juan de la Costa and Timbabichi areas to the south and north, respectively. New mapping of pre-rift, Oligocene-Miocene, forearc basin and arc rocks of the Comondú Group, between latitudes 24°30' N and 25°05' N, suggests vertical stratigraphic trends and lateral correlations. Timing of events is constrained by field observations and ten new isotopic ages for key volcanic and volcaniclastic units. The 40Ar/39Ar ages, ranging from 23.34 ± 0.21 Ma to 18.23 ± 0.20 Ma, indicate a change from marine to terrestrial conditions at ~24 Ma in the southern study area. Between 23.34 ± 0.21 and 19.37 ± 0.06 Ma, fluvial facies became more conglomeratic. At ~19 Ma, there was a major change to dominantly proximal and core volcanic facies. Major vertical facies changes represent a westward migration of the Comondú volcanic arc between 19.37 and 18.64 Ma, similar to the Loreto area. Rhyolitic tuffs ranging from 23.34 to 19.37 Ma correlate around much of the Bay of La Paz and possibly with those in the state of Nayarit. The western margin of the Gulf of California between La Paz and Timbabichi includes the structurally simple, ~100 km-long La Paz rift segment to the south and ~50 km-long Timbabichi rift segment to the north. The segments are separated by the structurally complex, 45 km-long San José Island accommodation zone. Mapping and kinematic analysis of faults in the accommodation zone elucidate the role of structural overprinting related to the change from dominantly orthogonal rifting that commenced ~12 Ma to dominantly transtensional rifting that initiated about 8 to 6 Ma. The accommodation zone, which includes San Francisquito and San José Islands, is characterized by alternating sets of dominantly NW-SE-striking and NE-SW-striking normal faults, with offsets ranging from 10s to 100s of meters, and is strongly overprinted by the modern oblique-divergent plate boundary. The accommodation zone therefore represents a transition from strong regional strain partitioning to the south to little or no strain partitioning to the north and is mechanically linked to the broad dextral shear couple of the Gulf of California. ________________________________________________________________________________ LINKS TO PLATES: https://www.researchgate.net/publication/324455130_Drake_2005_Plate_1 https://www.researchgate.net/publication/324455129_Drake_2005_Plate_2 https://www.researchgate.net/publication/324454970_Drake_2005_Plate_3 https://www.researchgate.net/publication/324455216_Drake_2005_Plate_4 https://www.researchgate.net/publication/324455215_Drake_2005_Plate_5 https://www.researchgate.net/publication/324455048_Drake_2005_Plate_6
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Manning (2012) has challenged our suggestion that dissolution by hydrofl uoric acid (HF) contributed to the formation of the Olympic Dam breccia complex (McPhie et al., 2011b). Manning has summarized the outcome of considerable experimental and other research on HF-granite interactions under magmatic and near-magmatic temperature and pressure conditions. Under these conditions, a reaction takes place, rather than dissolution, and produces a crystalline quartz-topaz assemblage. However, these conditions are not relevant to our proposal that HF played a role in the formation of the Olympic Dam breccia complex.
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Las mineralizaciones vinculadas con sistemas de fallas extensionales en ambiente continental han sido reconocidas como tales recientemente, e individualizadas con modelos genéticos propios, ya que en el pasado no habían sido diferenciadas de otras mineralizaciones epitermales. Un grupo de depósitos ha sido agrupado por el Servicio Geológico de Estados Unidos bajo el modelo de ?Mineralizaciones relacionadas a fallas de despegue? . En este modelo, las fallas de despegue (fallas normales de bajo ángulo relacionadas a extensión regional) separan un bloque inferior caliente con evidencias de milonitización asociada y un bloque superior en el que se han desarrollado fallas lístricas y planares normales que limitan cuencas de hemigraben. Las mineralizaciones asociadas se presentan como reemplazos masivos, stockworks y vetas de óxidos de cobre y hierro, vetas de sulfuros polimetálicos, vetas de baritina y/o fluorita y vetas de óxidos de manganeso. También se vinculan a este ambiente mineralizaciones de manganeso estratoligado formadas en ambiente lacustre. El objetivo del presente trabajo es analizar el modelo relacionado a fallas de despegue y los diversos tipos de depósitos que pueden generarse en este ambiente con el fin de: 1. Completar la tipología de depósitos minerales en ambientes extensionales en general. 2. Ampliar el modelo relacionados con fallas de despegue. 3. Proponer un nuevo modelo metalogenético de tipo regional que sirva como base para analizar la potencialidad minera de áreas afectadas por rifting y orientar la prospección en términos de los metalotectos definidos. En particular, la revisión y nuevos estudios presentados en esta publicación sobre mineralizaciones que se interpretan vinculadas al rifting mesozoico en la República Argentina, permiten enmarcarlas en el nuevo modelo propuesto y postular hipótesis genéticas alternativas para varios de ellos. Con este nuevo enfoque se espera contribuir con la evaluación de la prospectividad del territorio en relación a los modelos de depósitos analizados y de otros potencialmente asociados. Para cumplir con estos objetivos se analizan los antecedentes sobre mineralizaciones vinculadas a rifting tanto de depósitos de Argentina como del resto del mundo, que son característicos de los diversos tipos de depósitos analizados, de manera de establecer una síntesis en cuanto a las caracterísitcas de los fluidos mineralizantes y al origen de los elementos. Desde un punto de vista local se sintetiza el conocimiento sobre los procesos de rifting acaecidos entre el Triásico y el Cretácico en el territorio argentino, se describen mineralizaciones relacionadas con esta etapa en el noroeste argentino, Precordillera, Cordillera Frontal, Bloque de San Rafael, Sierras Pampeanas y Macizo Nordpatagónico, se aporta nueva información geocronológica, isotópica y geoquímica que permite precisar la relación entre mineralizaciones, magmatismo y fuente de fluidos, así como acotar la edad de los depósitos estudiados y, finalmente, se dan pautas para establecer la potencialidad económica del metalotecto.
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Tajo lode, Paramillos de Uspallata. Mendoza, Characteristics of hydrothermal system. The Pb-Ag-Zn Tajo lode lies within the Paramillos de Uspallata mining district in which a porphyry copper mineralisation had also been found. The lode strikes NW-SE, extends for about 400 m, has an average thickness of 0,40m and dips vertically. The country rocks are Triassic volcanic and sedimentary rocks of the Cachcuta Group covered unconformably by Tertiary sedimentary rocks. The mineralisation is related to a Miocene intrusive stock. In the Tajo lode, the mineralisation occurs as fracture fillings and breccia cements. It has crustification textures in which the most common order of deposition is siderite, sphalerite, galena and quartz. Textural evidence indicates that some of quartz was deposited as chalcedony. Fluid inclusions in quartz, siderite and sphalerite suggest that the lode was formed by a hydrothermal fluid with a temperature between 180-240°C, low to medium salinity (5 to 19 % wt eq. NaCl) and without any evidence of boiling. The textural, mineralogical and fluid inclusion evidence indicates that the mineralization was formed in a hydrothermal system near the surface, with isotopic values for the sulphides, quartz and carbonates suggesting a mixed depositional source of magmatic and meteoric waters in which the magmatic pulses increase the salinity values. The lack of a boiling hypersaline fluid precludes a close spatial relationship with a porphyry copper mineralization. The Tajo lode has potential of containing enhanced gold contents with depth.
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Plumbotectonics is an attempt to model the geochemical behaviour of U, Th and Pb, among major terrestrial reservoirs in agreement with observational data. By recycling rock through the orogenic environment, a dynamically communicating upper crust, lower crust, and mantle can produce the required patterns of lead-isotope evolution.
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The sierra de Chacaico (Neuquén Argentina) is one of the most important localities to study the Upper Triassic-Lower Jurassic syn-rift sequence of the Neuquén Basin. Structural and sedimentological analyses have been carried out in order to depict the stratigraphic evolution of the infill. The syn-rift sequence evolved in a volcano-sedimentary environment. For the entire column, three sections have been recognized. The lowest section is composed of basic to intermediate volcanic rocks associated with coarse-grained volcaniclastic deposits. The middle section is dominated by pyroclastic flow and fall deposits closely associated with volcaniclastic sandstones and minor conglomerates. Lacustrine carbonates and basaltic lavas were recognized at the top of the middle section. The upper section is characterized by coarse-grained conglomerates and breccias and pyroclastic fall and flow deposits. The whole area formed a unique depocentre during syn-rift evolution, its margins trending E-W/ENE-WSW. The southern margin acted as the main active border of the trough, where the thickest section was deposited. The syn-rift depocentre was inverted during later tectonic events leading to the generation of a complex pattern of anticlines and reverse faults. Some of these anticlines were formed by the inversion of oblique trending (north-east) normal faults suggesting the presence of internal steps within the depocentre. The structural and stratigraphic pattern observed at sierra de Chacaico is similar to the main framework of the Huincul high, one of the most prominent tectonic elements of the southern Neuqu Basin.
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The Benue trough is Nigeria’s main, but not exclusive source of barite mineralisation. There are at least ten barite fields in the trough, each containing swarms of veins or concordant stratiform minerals flats of hydrothermal origin. There are only two vein trends in the trough: the NW-SE trend, which tends to be orthogonal to the axis of the trough; and the N-S to NNE-SSW trend, which is younger than the former. Both vein sets are formed from ac tension joints reflecting different post-sedimentary deformation phases in the trough. The NW-SE veins are also more frequent than the N-S veins, almost in the ration of 2:1. Although 86 veins have been studied, not one was found oriented parallel to the axis of the trough, a good indication of structural control on mineral vein orientations. The dips of the veins tend to be high (>80o), a condition that favours manual mining. Veins tend to display a simple block profile and their widths vary from a few centimetres to as much as 6m, though the most frequently occurring widths are between 50cm and 1m. The implication of this is that BaSO4 concentrations in hydrothermal fluids in the trough were probably low during the Cretaceous period. In many veins, there is barite quality contrast between the top part and the lower portions. Higher quality barite tends to come from the lower portions. Hence it is expected that much of the low quality stigma associated with Nigerian barite from the trough would be relieved when mining gets down to good depths. For this reason, mining in those veins of low quality barite should proceed by vertical stripping.
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El yacimiento de uranio Las Termas, ubicado en la provincia geológica de Sierras Pampeanas, Argentina, se aloja en basamento precámbrico en las proximidades del contacto con el granito Los Ratones, de edad carbonífera. Este yacimiento fue originalmente vinculado a la greisenización asociada a la actividad magmática granítica. Sin embargo, las edades U/Pb (113,6 Ma y 51,4 Ma) recientemente obtenidas para uraninita (variedad “pechblenda”) y la relación espacial de la mineralización con el volcanismo alcalino asociado al rifting cretácico que tuvo lugar en el área, permiten plantear un nuevo modelo genético alternativo en dos etapas. Durante la primera habría tenido lugar la lixiviación del uranio del granito por acción de la greisenización carbonífera. En la segunda etapa se habría desarrollado un sistema hidrotermal por acción del magmatismo asociado al rifting cretácico, el cual habría concentrado la mineralización dando origen a este yacimiento.
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High-velocity lower crust (HVLC) and seaward-dipping reflector (SDR) sequences are typical features of volcanic rifted margins. However, the nature and origin of HVLC is under discussion. Here we provide a comprehensive analysis of deep crustal structures in the southern segment of the South Atlantic and an assessment of HVLC along the margins. Two new seismic refraction lines off South America fill a gap in the data coverage and together with five existing velocity models allow for a detailed investigation of the lower crustal properties on both margins. An important finding is the major asymmetry in volumes of HVLC on the conjugate margins. The seismic refraction lines across the South African margin reveal cross-sectional areas of HVLC 4 times larger than at the South American margin, a finding that is opposite to the asymmetric distribution of the flood basalts in the Paraná–Etendeka Large Igneous Province. Also, the position of the HVLC with respect to the SDR sequences varies consistently along both margins. Close to the Falkland–Agulhas Fracture Zone in the south, a small body of HVLC is not accompanied by SDRs. In the central portion of both margins, the HVLC is below the inner SDR wedges while in the northern area, closer to the Rio Grande Rise-Walvis Ridge, large volumes of HVLC extend far seaward of the inner SDRs. This challenges the concept of a simple extrusive/intrusive relationship between SDR sequences and HVLC, and it provides evidence for formation of the HVLC at different times during the rifting and breakup process. We suggest that the drastically different HVLC volumes are caused by asymmetric rifting in a simple-shear-dominated extension.
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The Monakoff iron oxide–Cu–Au (IOCG) deposit, located to the north east of Cloncurry within the Eastern Succession of the Mount Isa Inlier, Queensland, Australia, is characterised by high concentrations of F and Ba, with a host of other enriched elements including Co, Ag, Mn, REE, U, Pb, Zn and Sr. This gives the deposit a characteristic gangue assemblage dominated by fluorite, barite and calcite. The nearby E1 deposit, located 25 km to the NNE of Monakoff, and the large Ernest Henry deposit, 3 km to the west of E1, also contain abundant fluorite, barite and calcite in late stage assemblages. The three deposits, therefore, constitute a distinct group of IOCG deposits within the district, based on their F-rich geochemical and mineralogical affinities.
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La presente contribución intenta esclarecer la ubicación de los yacimientos de selenio de la sierra de Cacho, que antiguamente se consideraban situados en la sierra de Umango, a través de una revisión bibliográfica y una actualización geográfica-geológica. También se compilan los datos existentes sobre las mineralizaciones y se discute sobre las interpretaciones genéticas.
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The Santa Rosa Mn–Ba deposit is located southwest of the town of San Nicolás and south of the Concepción Peninsula in Baja California Sur (Mexico). It consists of a manganese oxide vein–breccia striking NNW with a subvertical dip to the ENE that is exposed discontinuously over 500 m. The deposit is hosted in conglomerates that belong to the Los Volcanes member of the Pliocene age San Nicolas Formation. The mineralization is characterized mainly by banded and brecciated structures with manganese oxides (romanèchite and pyrolusite), along with barite, opal, quartz, calcite, magnetite–maghemite and minor goethite.
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Metamorphic core complexes and associated detachment faults of the North American Cordillera represent gently dipping, normal-displacement shear zones (detachment zones) along which hot, deeper levels of the crust were transported upward and outward from underneath a brittlely distended upper plate. Structures that formed during the ductile-to-brittle evolution of detachment zones can be used to reconstruct the relative magnitudes of fluid pressure and deviatoric stress at different levels within the shear zones. Mylonitization, which occurred along deeper segments of detachment zones below the brittle-ductile transition, was locally accompanied by tensile failure, indicative of low deviatoric stress and high fluid pressure. This condition persisted into the earliest phases of brittle deformation, after which shear fractures formed due to both a reduction in fluid pressure and an increase in deviatoric stress. Brittle deformation of upper-plate rocks occurred largely under conditions of low fluid pressure. Structural and geochemical data suggest that normal displacement on detachment zones results in establishment of two fluid systems: (1) an upper-plate system driven by convection and dominated by meteoric and connate fluids at near-hydrostatic pressures and (2) a system within deeper levels of the shear zone, where fluids are largely derived from igneous sources and fluid migration is aided by dilatancy pumping. The late phases of normal displacement on detachment zones structurally juxtaposed rocks affected by the two fluid systems and locally caused the shear-zone rocks to be overprinted by mineralization related to the upper-plate fluid system.
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The Ada Tepe gold deposit, 230 km SE of Sofia, formed in the eastern part of the Rhodope Mountains that underwent extension and metamorphic core complex formation, followed by normal faulting, basin subsidence, and silicic to mafic magmatism during the Maastrichtian-Oligocene. The region comprises numerous volcanic-hosted epithermal and base-metal vein deposits spatially and temporally associated with the Oligocene magmatism. Ada Tepe is a typical low-sulfidation epithermal gold deposit, unusual in that it is older than adjacent magmatic-related deposits and is hosted in Maastrichtian-Paleocene sedimentary rocks above a detachment fault contact with underlying Paleozoic metamorphic rocks. Gold mineralization is located in: (1) a massive, tabular ore body above the detachment fault; and (2) open space-filling ores along predominantly east-west oriented listric faults. The ores are zones of intensive silicification and brecciation synchronous with detachment faulting. Brittle deformation opened spaces in which bands of opaline silica and electrum, quartz, pyrite, massive and bladed carbonates were deposited. Mineralization is exclusively a Au system with Au/Ag ∼3, trace As and no base metals. Alteration consists of quartz, adularia, chlorite, sericite, calcite, pyrite and clay minerals. Adularia and abundant bladed carbonates indicate boiling within the entire span of the deposit, whereas bands of opaline silica with dendritic gold suggest that silica and gold were transported as colloids. The physical setting of formation of the Ada Tepe deposit was very shallow and low temperature. The Sr and Pb isotope ratios of carbonates and pyrite reflect hydrothermal fluid signatures derived predominantly from the metamorphic rocks. The age of mineralization and association with the detachment fault suggest that gold mineralization at Ada Tepe is more closely linked to the Kessebir metamorphic core complex rather than to local magmatism.
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Fuchsite and other Cr-rich phyllosilicates, paragenetic with dolomite, are present in some ultramafic enclaves from the ‘frailesca’ rock (a lapilli- to block-size pyroclastic lithic-tuff), in the Almade ´n mercury mining district, Spain. Analyses (EMPA and TEM) of fuchsite and Cr-chlorite showed a relatively large range in levels of Cr2O3. Petrographic relationships between these phyllosilicates and primary relics of Cr-spinel crystals, as well as their high Cr content, indicate that these Cr-rich minerals originated from primary chromian spinels through an early hydrothermal alteration stage. The hydrothermal fluids accounting for this early alteration would be of relatively high temperature, high aCO2and aK, and variable aNa/K. In a later alteration stage, fuchsite was partially or totally replaced by illite and Cr-illite, giving rise to an argillitic alteration.
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The Fe oxide(-Cu-Au-REE-P-U) family of Cu, Fe, and/or Au deposits (or IOCG) represents a geochemically coherent but geologically diverse group that formed globally from the Archean to the Holocene. IOCG systems exhibit intense, voluminous Na-Ca-K-Fe(-H) hydrothermal alteration related to flow of moderately to highly saline metal-rich, sulfur-poor brines. These fluids account for the characteristic sulfide-poor, oxide-rich mineralogy and the alkali-rich character of the alteration and for the varied contents of Cu, Au, and other metals. Associated igneous rocks range from mafic to felsic, subalkaline to alkaline. Metal enrichments vary with host-rock type and sulfur availability. Geologic settings are tectonically diverse but commonly have evidence for contemporaneous or older evaporitic environments. Magmatism drives most systems, yet clearly amagmatic examples occur. Geochemical and petrologic studies demonstrate igneous-dominated sources for some solutes and permissive evidence for a connection to magmatic fluids. In many cases, a central role for nonmagmatic saline fluids is evident. The geochemistry of the latter fluids rationalizes the key distinguishing features of the IOCG family. The diversity of the IOCG family parallels that seen in other major families of deposits; their distinctive attributes indicate that they comprise a separate class of (mainly) terrestrial hydrothermal systems.
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Five-element veins are open-space fillings, which characteristically occur as features developed late in the tectonic history of older crystalline or sedimentary-volcanic terranes. Their major characteristics include: 1) occurrence in areas of continental crust, where a spatial and temporal relation to rifting or other extensional tectonics is often prominent; 2) development from the early Proterozoic to the Tertiary; 3) association of mild propylitic alteration with sequential deposition of distinct vein assemblages; 4) deposition at initially high (up to 450°C) temperatures from highly saline solutions, which decreased in temperature and became more reducing through the depositional sequence; 5) isotopic characteristics generally suggestive of a non-magmatic origin and derivation of components from diverse sources; and 6) frequent association of ore lodes with structural traps, reductants, and evidence of intermittent boiling at shallow depths. The weight of evidence seems to suggest that the non-magmatic model, in which the driving mechanism is continental rifting, and the solution is mobilized formational water, provides the best explanation for a widely scattered group of deposits. -from Author
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Ferroselite from Trogtal, the type locality of the cobalt selenide trogtalite, in the Harz Mountains, Germany, forms a trogtalite-ferroselite assemblage in pockets of massive clausthalite in which specular hematite is dispersed. The pockets occur in hematite-impregnated carbonate veins, emplaced in a reddened greywacke of Lower Carboniferous age. Ferroselite contains similar to 0.2- 5.0 ppm Au; trogtalite has even higher Au contents. Ferroselite has Co/Ni ratios mostly above unity. These characteristics likely reflect oxidizing brines with Co/Ni > 1, such as those involved in the formation of sediment-hosted copper deposits.
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Olympic Dam is a supergiant Fe oxide Cu-U-Au-Ag ore deposit (similar to 9 x 10(9) t) that is also enriched in rare earth elements (REEs) and fluorine (F). The immediate host to the ore is hydrothermal breccia within granite and volcanic rocks of a Mesoproterozoic silicic large igneous province. Analyses of melt inclusions in quartz phenocrysts in rhyolite show that the silicic magmas of this province were unusually rich in F (up to 1.3 wt%). Fluorite and other F-rich minerals that crystallized from these magmas provided a gigantic reservoir of F. As a result, the Olympic Dam ore-forming fluid was F-rich and had exceptional capacity to transport diverse elements. Further, we infer that hydrofluoric acid, the most corrosive acid known, contributed to hydrothermal breccia formation by dissolution that in turn increased permeability and accelerated the rate of fluid-rock interaction. It is no accident that the world's largest hydrothermal ore deposit occurs in an F-rich silicic large igneous province.
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The San RafaelMassif is characterized by widespread fluorite and manganese epithermal ore deposits whose origin has been under debate to the present. Isotopic (Sm/Nd and K/Ar) and geochemical (trace elements and REE) data of fluorite and manganese ore allowed to establish the age and genesis of the deposits and to propose a regional genetic model. The fluorite deposits were formed during the Upper Triassic–Lower Jurassic as a result of the Triassic rifting that launched a hydrothermal activity at regional scale. The hydrothermal fluids had low T and high fO2 with fluorine probably derived from a mantle source and REE scavenged from the volcanics of the Gondwanan Choiyoi Magmatic Cycle upper section. The manganese deposits were formed by oxidizing hydrothermal fluids that collected Mn from deep sources and also leached REE from the upper section of the Choiyoi Magmatic Cycle during two mineralization episodes. One episode was linked to the rift tectonic setting that remained active up to the Upper Cretaceous and the other was related to an Early Miocene back-arc extensional geodynamic setting. Both manganese and fluorite deposits were formed in extensional tectonic settings within an epithermal environment near the surface, and can be ascribed to the general model of detachmentrelated deposits.
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The Almadén mine has been the largest among several mercury deposits that represent the biggest mercury concentration in the world. The deposits form a mining district which is located in a 30 km long and up to 15 km wide WNW–ESE oriented syncline, where a thick Lower Ordovician–Upper Devonian siliciclastic sedimentary sequence outcrops. Most of the deposits are located in the south subvertical syncline flank, which has an opposite vergence to the rest of the region. Of special note is the presence of important NW–SE to WNW–ESE crustal structures that played a major role at several times during the regional geological history and controlled the sedimentary unit distribution, volcanism and deformation. One of these structures seems to have played an important role in the Almadén area, probably having been responsible for the anomalous syncline geometry. This structure acted during the E–W Variscan shortening as a ductile–fragile sinistral shear zone that resulted in a subvertical attitude of the southern Almadén Syncline flank, affecting the sedimentary sequence longitudinally. The Hg deposits in the region correspond to two types, stratabound and stockworks. The former are hosted in well-defined “Criadero Quartzite” orthoquartzite levels of Ordovician–Silurian age. These deposits were folded and sheared during the Variscan deformation. The stockwork deposits filled fractures and veins and partially replaced the volcanic rocks affected by the Variscan shear zones. The replacement process took place at the end of the E–W Variscan shortening
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The Mesoproterozoic Purcell Basin in Canada contains three different types of veins: (1) type 1 Pb-Zn-Ag veins are composed of Fe-rich sphalerite, pyrrhotite, galena, freibergite, and pyrite with minor quartz gangue; (2) type 2 Pb-Ag-Cu-Au veins are characterized by galena, pyrite, freibergite, and gold in a quartz gangue; and (3) type 3 Ag-Pb-Zn vein and replacement deposits contain Fe-poor sphalerite, galena, pyrite, and freibergite in a quartz-dolomite gangue that locally replaces host dolostone. The sulfur isotope composition of type 1, 2, and 3 vein and replacement deposits closely reflects their respective stratigraphic positions. Type 1 and 2 veins hosted in lower Purcell sedimentary rocks have light sulfur isotope compositions (−4.8 to +2.5‰) similar to diagenic pyrite disseminated in clastic sedimentary host rocks. Type 3 veins and the replacement deposits hosted in upper Purcell Supergroup rocks have heavy sulfur isotope compositions (8.3–17.2‰) indicative of thermo-chemical reduction of marine sulfate in carbonate host rocks. Quartz from type 1 Pb-Zn-Ag veins has δ18OSMOW values ranging from 7 to 17‰, whereas type 2 and 3 vein and replacement deposits have δ18O values ranging from 9 to 20‰. The range of δ18O values for type 1, 2, and 3 veins is the result of mixing of metamorphic fluids with a δ18O value higher than 11.5‰ and an upper crustal fluid with a δ18O lower than 1.2‰, in equilibrium with the host rocks during Proterozoic (type 1) and Mesozoic-Cenozoic (type 2 and 3) hydrothermal events. Galena and freibergite lead isotope compositions plot in two groups, consistent with previous studies. Type 1 Pb-Zn-Ag veins have a nonradiogenic lead signature (206Pb/204Pb: 16.322–16.435) and are considered Proterozoic in age. Type 2 Pb-Ag-Au-Cu veins and type 3 Ag-Pb-Zn vein and replacement deposits have a radiogenic lead signature (206Pb/204Pb: 17.842–19.347) and are interpreted to be Mesozoic-Cenozoic in age. Hydrothermal sericite from the type 3 Ptarmigan replacement deposit yields a 40Ar/39Ar age of 133.1 ± 0.7 Ma, indicating a Cretaceous age for type 3 deposits. Type 1 veins are interpreted to be the result of hydrothermal fluids generated during the Proterozoic East Kootenay Orogeny, whereas type 2 and 3 veins and replacement deposits are interpreted to be the result of Late Cretaceous-Paleocene tectonism.
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The Late Triassic-Early Jurassic rift basins of Iberia, offshore eastern Canada, and the continental shelf of western Europe are fragments of a formerly coherent northeast-trending rift system that probably formed as a result of tensional stress between Europe, Africa, and North America. The separation of Europe, North America, and Iberia was preceded by a Late Jurassic-Early Cretaceous rifting phase that is clearly distinct from the earlier Mesozoic rifting episode and was little influenced by it. The two periods of rifting are separated by a Middle Jurassic relatively tectonically quiet period. The distribution of hydrocarbon finds within the rift basin suggests that the best prospects are in areas where the two rifting episodes are superimposed. Lack of mature source rocks in the later Mesozoic rift basins and an unfavorable temporal relationship between hydrocarbon generation and tectonic activity in the early Mesozoic basins are proposed as explanations for the apparently poor hydrocarbon prospectivity of large areas of the Mesozoic basins.
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Abstract Vertical and horizontal profiles from the North and South Pacific Oceans demonstrate,the existence of three species of dissolved selenium: selenite, selenate, and organic selenide (opera- tionally defined). In surface waters, organic selenide makes up about 80% of the total dissolved selenium, selenite concentrations are uniformly low, and selenate concentrations rise with increased vertical mixing. The organic selenide maximum,(thought to consist of seleno-amino acids in peptides) coincides with the maxima of primary productivity, pigments, bioluminescence, and dissolved free amino acids. Deep ocean waters are enriched in selenite and selenate, while organic selenide is nondetectable. In suboxic waters of the tropical northeastern Pacific, organic selenide concentrations rise, while selenite values decrease. The downward flux of particulate selenium generally decreases with depth, and fluxing particulate selenium is found to be primarily in the (-2) oxidation state. These data allow a re-evaluation of the internal biogeochemical,cycle of selenium. This cycle includes selective uptake, reductive incorporation, particulate transport, a multistep regeneration, and kinetic stabilization of thermodynamically unstable species. The,marine,biogeochemical,cycles,of many,trace elements,include,the processes of uptake from dissolved to particulate form, particulate transport, and regeneration back to the dissolved,state. Uptake,can occur pas- sively by adsorption,onto,particle surfaces and coprecipitation into solid phases, or ac- tively by,selective incorporation,into bio- logical tissues and,skeletal,material. The vertical transport,of trace elements,from,the surface zone,to the deep,sea via detrital mat- ter is a function,of the type,of carrier and of sinking,rates. The regeneration,of a par- ticulate-bound,trace,element,to,the,dis- solved state can occur by simple,dissolution of the carrier or by the complex,microbial process,of oxidative,degradation.,The,re-