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Cartoon to show kinematic controls on orebody geometry at Golden Pig mine, Southern Cross greenstone belt, Yilgarn craton, Australia. Lineation and vorticity vector plunge very gently to the south, indicating a pure shear-dominated shear zone. Permeability and/or extension lead to the elongation of orebodies in this direction. The geometric controls are similar to (A) in Figure 5.
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The structural geology and tectonic setting of hydrothermal gold deposits are paramount for understanding their genesis and for their exploration. Strong structural control on mineralization is one of the defining features of these deposits and arises because the permeabilities of crustal rocks are too low to allow the formation of hydrothermal dep...
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Context 1
... the foliation and lineation, there is consistent evidence for reverse shear, while roof views parallel to the lineation and perpendicular to the foliation show sinistral and dextral asymmetries from deformed veins. The vorticity vector appears to be parallel to the lineation, suggesting a pure shear-dominated shear zone, with a reverse component (Fig. 6). The large amount of flattening may be related to the position of the shear zone between two adjacent granite domes. Orebody long axes (U axes) plunge parallel to the lineation and vorticity vector ( Nugus et al., ...
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... This structural relationship, together with the observed overprinting of the vein alteration halos by the cleavage, suggests that the veins were emplaced during D2, as were most gold deposits in the southern Abitibi greenstone belt (Dubé and Mercier-Langevin, 2020), including the nearby Donalda deposit (Riverin et al., 1990;Robert et al., 1996). The north-northwest strike of the veins is largely controlled by the mechanical anisotropies created by rheological contrasts between the mafic dikes and host tonalite (e.g., Belkabir et al., 1993;Blenkinsop et al., 2020). Because the strike of the mafic dikes is within ~20° of the north-south bulk shortening direction during the D2 event (Fig. 14B), the diketonalite contacts acted as planes of weakness that underwent a dextral shear traction as they opened up parallel to the bulk extension direction (e.g., Sibson, 2001;Lafrance, 2004). ...
The Rouyn-Noranda mining district of Quebec contains 20 Cu-Zn (±Au ±Ag) volcanogenic massive sulfide (VMS) deposits, including the giant and gold-rich Quemont and Horne deposits. Mineralized epigenetic veins are also present, but their origin and relative timing remain enigmatic. The nature and extent of their alteration signatures and the effect of their superposition on district-scale alteration patterns is unknown. The VMS-related quartz-sulfide Cu-Zn-Ag veins have δ18Oquartz values of 8.5 ± 0.8‰, reflecting δ18Ofluid compositions of –0.4 to 3.1‰ (250°–350°C) that are typical of Archean seawater. They are associated with a proximal Fe-rich chlorite alteration and marginal spotted sericite-chlorite alteration with whole-rock δ18O values of 2.9 to 5.9‰ and are interpreted to have formed within the structurally controlled discordant upflow zones of a VMS hydrothermal system. Younger gold-bearing quartz-carbonate veins were emplaced along mechanical anisotropies created by mafic dikes during north-south compression and the formation of regional E-trending faults, folds, and cleavage. They are characterized by δ18Oquartz values of 11.3 ± 0.8‰, reflecting δ18Ofluid compositions of 2.4 to 5.9‰ (250°–350°C), typical of a metamorphic fluid, possibly mixed with a lower δ18O upper crustal fluid. They are associated with ankerite, calcite, muscovite, chlorite, albite, and quartz ± hematite alteration with whole-rock δ18O values of 5.8 to 10.3‰. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon ages for two tonalite intrusions constrain the maximum age of the Cu-Zn-Ag veins to 2697.6 ± 0.7 Ma and the minimum age to 2695.3 ± 1.0 Ma, which is also the maximum age of the gold quartz-carbonate veins. Superposition of alteration related to the gold quartz-carbonate veins on previously chlorite- and sericite-altered rocks has resulted in mixed alteration signals with whole-rock δ18O values of ~6 to 8‰ that have perturbed and masked regional alteration patterns related to older VMS mineralization, such as those found in the Quemont and Horne deposits. These results indicate that defining alteration vectors in camps that have superimposed hydrothermal systems requires full consideration of the hydrothermal history of the camp, and if such constraints are lacking, whole-rock δ18O values should not be used as a stand-alone exploration method.
... The description of the deformation zones is a terminological morass. In this study, we describe the deformation zones following Blenkinsop et al. (2020). ...
Orogenic gold deposits are generally thought to represent one perhaps protracted event. However, recent research on orogenic gold deposits increasingly offers evidence for some deposits forming through multiple and clearly discreet hydrothermal episodes. The giant Zaozigou orogenic Au-Sb deposit in the Triassic to Cretaceous West Qinling Orogen, central China, includes both steeply dipping and gently dipping orebodies. The two distinct mineralization styles provide a valuable setting for investigating a multiple mineralization model by integrating structural analysis within a robust geochronological framework. Through fieldwork and geochronology, we define a progression of major tectonic events in the area of the Zaozigou deposit. The deposit is hosted within a well-bedded sequence of Early Triassic metasedimentary rocks of the South Qinling Terrane. Pre-mineralization E-W shortening (D1) during subduction of the Mianlue oceanic slab include folding with resulting axial planes striking N-S, emplacement of Triassic ENE-striking and WNW-striking dacite dikes accompanied by Middle Triassic greenschist facies metamorphism. Late Triassic gold-stibnite quartz vein and disseminated mineralization formed along ENE-striking and steeply dipping D2 brittle to ductile sinistral faults. Their orientations suggest a link to the regional NNE-SSW maximum principal stress coinciding with transpression caused by the Late Triassic collision between the South China Block and South Qinling Terrane. Overprinting Early Cretaceous quartz-stibnite veins developed along gently dipping (20° to 40°) brittle D3 normal fault zones, which exhibit a NE-SW minimum principal stress. This younger deformation event is interpreted to be related to the Early Cretaceous tectonic transition from shortening to extension of the West Qinling Orogen. Therefore, the Zaozigou deposit reveals a model of multiple orogenic gold mineralizing events, with migration of hydrothermal fluids during discrete deformation episodes and the resulting formation of a single composite deposit formed along overprinting structures at separate times of orogenesis.
... These interiors of the TTG-like complexes deform more brittlely than the surrounding sedimentary and volcanic rocks. They host therefore fluid-channel structures and trap zones, such as local bends in shear zones, related dilational zones, damages zones and brittle fracturing networks in more rigid parts of the intrusion (e.g., Robert and Brown, 1986;Blenkinsop et al., 2020;or Cox, 2020). Such mineralized systems were observed in the West African Carton, for example at the Chirano gold deposit in Ghana (Allibone et al., 2004), or at the Edikan gold deposits also in Ghana (Tourigny et al., 2018). ...
... Although the authors are unanimous in considering the role played by the shear zones of the Central Domain in channeling the flow of hydrothermal fluids to form the various Au-lode deposits, aspects concerning its kinematic history, as well as the distribution and occurrence have been neglected so far. This history is particularly relevant in structurally controlled hydrothermal gold mineralizations since they usually show a close relationship with the kinematic evolution of shear and fault zones (Sayab et al., 2018;Blenkinsop et al., 2020). ...
... The main aspect of these studies has been to demonstrate that, in general, the high-strain zones have involved simultaneous and variable ratios of pure and simple shear components during their deformation history (Frassi et al., 2009;Thigpen et al., 2010;Ponmanee et al., 2016;Fossen and Cavalcante, 2017;Tiwari et al., 2020). In gold-bearing shear zones has been shown that the kinematic flow and the formation of hydrothermal gold mineralizations have a close and very particular relationship (e.g., Mamtani, 2013;Kassem et al., 2016;Blenkinsop et al., 2020). ...
... More than simply that, the regime of kinematic flow along this segment seems to have been one of the conditioning factors for creating a structural environment favorable to the emplacement of gold-bearing veins. Indeed, the relative contributions of pure and simple shear deformation may result in potential sites of permeability creation and mineralization (Blenkinsop et al., 2020). Therefore, the partitioning of kinematic flow into domains dominated by simple shear has contributed to the channeling of fluid flows within the shear zone on ongoing deformation. ...
... Entire thin-section scans were made using an Epson Perfection Pro scanner in plane-polarized and cross-polarized light. We use our microscopic observations to search for evidence for grain-scale brittle, crystal-plastic, diffusive mass transfer, and alteration-related deformation (c.f., Rutter, 1986;Blenkinsop et al., 2020;Wang, 2021). Systematic X-ray diffraction (XRD) analyses were done to determine whole-rock mineralogy and to constrain rock compositions, possible depth ranges, and fluid-rock interactions in the fault-related rocks. ...
... This is consistent with other analyses of fault-related rocks that formed at 2-4 km depth in the San Andreas Fault system (Chester and Logan, 1986;Evans, 1998, 2000;Schleicher et al., 2009Schleicher et al., , 2012Holdsworth et al., 2011;Bradbury et al., 2015;Forand et al., 2018;Studnicky, 2021), the San Gabriel Fault (Anderson et al., 1983;Chester et al., 1993;Evans and Chester, 1995;Chester and Chester, 1998), and other faults (Bruhn et al., 1994;Gratier et al., 2003;Faulkner et al., 2003;Wibberley and Shimamoto, 2003;Marone and Saffer, 2007;Wibberley et al., 2008;Mitchell and Faulkner, 2009;Rutter et al., 2012;Boulton et al., 2017). These distributed fault-and shear-zone zones are produced by complex interactions of deformation, alteration, and mineralization within these zones (Blenkinsop et al., 2020). ...
Quantifying shallow fault zone structure and characteristics is critical for accurately modeling the complex mechanical behavior of earthquakes as energy moves within faults from depth. We examine macro- to microstructures, mineralogy, and properties from drill core analyses of fault-related rocks in the steeply plunging ALT-B2 geotechnical borehole (total depth of 493 m) across the San Gabriel Fault zone, California. We use macroscopic drill core and outcrop-sample analyses, core-based damage estimates, optical microscopy, and X-ray diffraction mineralogic analyses to determine the fault zone structure, deformation mechanisms, and alteration patterns of exhumed deformed rocks formed in a section of the fault that slipped 5-12 million years ago, with evidence for some Quaternary slip. The fault consists of two principal slip zones composed of cohesive cataclasite, ultracataclasite, and intact clay-rich, highly foliated gouge within upper and lower damage zones 60 m and 50 m thick. The upper 6.5 m thick principal slip zone separates Mendenhall Gneiss and Josephine Granodiorite, and a lower 11 m thick principal slip is enclosed within the Josephine Granodiorite. Microstructures record overprinted brittle fractures, cohesive cataclasites, veins, sheared clay-rich rocks, and folded foliated and carbonate-rich horizons in the damage zones. Carbonate veins are common in the lower fault zone, and alteration and mineralization assemblages consist of clays, epidote, calcite, zeolites, and chloritic minerals. These data show that shallow portions of the fault experienced fluid-rock interactions that led to alteration, mineralization, and brittle and semi-brittle deformation that led to the formation of damage zones and narrow principal slip zones that are continuous down-dip and along strike.
... Therefore, the rheological contrast between the gneiss and the schist seem to play and important role in the location of the veins at the deposit scale. A somewhat similar case of structural (rheological) control was described at the Renco gold deposit in Zimbabwe, also hosted in amphibolite facies metamorphic rocks, whose mineralization is mostly hosted in meter-wide competent lithons (Blenkinsop et al., 2020). ...
... The differences in gold grades and styles of mineralization can be explained by syn-tectonic (D 2 ) fluid flow, the different metamorphic grade (amphibolite versus mid-to lower-greenschist) and ductility of wall rocks that prevented the formation of larger, brittle, high-permeability structures. Cox et al., 2001;Sibson, 2004;Goldfarb et al., 2005;Deng et al., 2015;Vearncombe and Zelic, 2015;Groves et al., 2018;Blenkinsop et al., 2020). As a result, the relationships between mineralization, alteration and controlling structures are commonly well preserved, which allows for the detailed reconstruction of fluid pathways and mineralizing pro- ...
We report the characteristics and controls of low-grade gold-sulfide disseminations in the Twin Hills prospects, the Central Zone of the Damara Belt in Namibia, that combines to a large (>12 km strike length) zone of mineralization. The host rocks are subvertical, tightly folded and transposed, amphibolite-facies metaturbidites (cordierite-biotite metapelites and quartz-biotite metapsammites) that form the subvertical limb of a regional-scale syncline. Sulfide and gold grains are finely dispersed in the host rocks or form networks of quartz-sulfide veinlets. Zones of economic-grade gold mineralization are associated with fine-scale quartz-sulfide (pyrrhotite > arsenopyrite >> pyrite) vein stockworks. Morphology and deformational textures of the mineralized vein networks suggest their formation during flexural-slip folding and the progressive transposition of the metaturbidites into the regional, ENE trending steep foliation. The more competent metapsammites promoted fracturing while ductile strain during flexural-slip was localized into the schistose metapelites. As a result, economic-grade mineralization is best developed in well-bedded, compositionally heterogeneous parts of the metaturbidites that experienced pronounced strain partitioning. Metapelite-dominated packages, in contrast, show mainly disseminated sulfide mineralization, fewer and variably transposed vein networks and only sub-economic gold grades. The association of disseminated and vein-type mineralization suggests that pervasive fluid flow was channelized within the lithologically heterogeneous packages that provided fracture permeabilities and hydraulic gradients for more focused fluid flow. Higher gold grades correspond to subtle (5-15°) deflections of bedding and the regional foliation that may relate to dilational jog geometries. On a prospect-scale, occurrence of economic-grade gold mineralization coincides to the inflection and change of the vergence of regional-scale first-order folds. The style of mineralization shares similarities with turbidite-hosted orogenic gold deposits. The differences in gold grades and styles of mineralization can be explained by syn-tectonic (D2) fluid flow, the different metamorphic grade (amphibolite versus mid- to lower greenschist) and ductility of wall rocks that prevented the formation of larger, brittle, high-permeability structures.
... Structural geology is recognised as a critical element for most forms of mineralisation (Sillitoe, 2010;Blenkinsop et al., 2020) including Fe ore (section 3.1). This is supported by most MPM studies that include a structural element, even if just a fault trace representation. ...
The past two decades have seen a rapid adoption of artificial intelligence methods applied to mineral exploration. More recently, the easier acquisition of some types of data has inspired a broad literature that has examined many machine learning and modelling techniques that combine exploration criteria, or ‘features’, to generate predictions for mineral prospectivity. Central to the design of prospectivity models is a ‘mineral system’, a conceptual model describing the key geological elements that control the timing and location of economic mineralisation. The mineral systems model defines what constitutes a training set, which features are representative of geological evidence of mineralisation, how features are engineered and what modelling methods are used. Mineral systems are knowledge-driven conceptual models, thus all parameter choices are subject to human biases and opinion, and alternative models are possible. However, the effect of alternative mineral systems models on prospectivity is rarely compared despite the potential to heavily influence final predictions. In this study, we focus on the effect of conceptual uncertainty on Fe ore prospectivity models in the Hamersley region, Western Australia. Four important considerations are tested. (1) Five different supergene and hypogene conceptual mineral systems models guide the inputs for five forest-based classification prospectivity models model. (2) To represent conceptual uncertainty, the predictions are then combined for prospectivity model comparison. (3) Representation of three-dimensional objects as two-dimensional features are tested to address commonly ignored thickness of geological units. (4) The training dataset is composed of known economic mineralisation sites (deposits) as ‘positive’ examples, and exploration drilling data providing ‘negative’ sampling locations. Each of the spatial predictions are assessed using independent performance metrics common to AI-based classification methods and subjected to geological plausibility testing. We find that different conceptual mineral systems produce significantly different spatial predictions, thus conceptual uncertainty must be recognised. A benefit to recognising and modelling different conceptual models is that robust and geologically plausible predictions can be made that may guide mineral discovery.
... Orogenic gold deposits are the principal sources of gold and are characterized by high grades and large tonnages (Weatherley and Henley, 2013). They occur not only in coeval compressional to transpressional environments but also in strike-slip extensional settings (Chen and Fu, 1992;Groves et al., 1998Groves et al., , 2003Goldfarb et al., 2001;Chen, 2006Chen, , 2013Blenkinsop et al., 2020). These deposits genetically accepted as being associated with structural deformation, which improves fluid migration and focuses fluid flow on places favourable for gold deposition (Groves et al., 2018). ...
... Along with the tectonic transition from compression to sinistral strike-slip motion, this process led to sinistral ductile shear deformation on related A-type folds and low-angle stretching lineations. Although the fluids for orogenic gold deposits are suggested to be deeply sourced and widespread over the entire orogenic belt (Groves et al., 2018), the permeabilities of crustal rocks are too low to generate ore formation on realistic timescales unless rocks experience deformation (Blenkinsop et al., 2020). Hence, deformation of >393 Ma provided favourable places for the migration of ore fluids and precipitation of the transported elements, and deep-seated metamorphic ore fluids migrated upwards along the Sanjiashan ductile shear zone and its subsidiary faults to levels with lower pressures to form the Qingbaishan gold orebody (Fig. 10). ...
... Generally, orogenic-type gold deposits are accepted to have formed in compressional to transpressional environments in accretionary or collisional orogens (Chen and Fu, 1992;Goldfarb et al., 2001;Groves et al., 2003;Chen, 2006Chen, , 2013. In addition, many examples show how strike-slip shearing at a variety of scales may be important for the genesis of such deposits (Blenkinsop et al., 2020). Strike-slip deformation in the Beishan orogen took place during the Early Devonian, as recorded by sinistral motion along Sanjiashan faults ( Fig. 4B-F), and after the end of the Carboniferous, as recorded by dextral strike-slip shear zones (Coleman, 1989;Windley et al., 1990;Chen et al., 2005a). ...
The Beishan orogen is an economically important gold mineralization belt that hosts more than 20 gold deposits. Most Au orebodies occur within large-scale fault zones, indicating a correlation between structural evolution and gold mineralization. Previous studies have demonstrated that Au mineralization generally developed in the Permian–Triassic; however, pre-Permian gold mineralization and its temporal relationship with tectonic evolution remain poorly understood. The Qingbaishan deposit, located in the Beishan orogen, NW China, is hosted by the Sanjiashan shear zone. A detailed field-based structural analysis revealed that the Sanjiashan shear zone has thrust and sinistral strike-slip characteristics, such as asymmetrical folds and S-C fabrics. The muscovite ⁴⁰Ar/³⁹Ar age from auriferous quartz shows that the Qingbaishan gold system formed around 399.7 ± 1.6 Ma, consistent with the time of Sanjiashan sinistral ductile shearing in the Beishan orogen. The carbon and oxygen isotope compositions of auriferous quartz suggest that the host rocks within the Precambrian Gudongjin Group would have been a significant source of ore metals and that the low δ¹⁸O values in quartz resulted from fluid reactions with ¹⁸O-poor host rocks. The Qingbaishan Au deposit is concluded to be a strike-slip-dominated orogenic-type system related to continental collision between the Tarim and Kazakhstan–Ili plates.
By integrating the age data obtained from this study with previous geochronological results, two episodes of gold mineralization in Beishan are distinguished: an early episode around 399 Ma, when sinistral strike-slip zone-related orogenic gold deposits formed in a syncollisional setting, and a late episode around 298–231 Ma, when dextral strike-slip deformation produced deposits in a postcollisional extensional setting.
... Faults and fractures are products of brittle deformation, and their combined influence not only governs the direction of hydrothermal fluid flow within geological media but also determines the final geometry and extent of the resultant hydrothermal ore deposit (e.g., Hodgson, 1989;Sibson, 1992;Sibson, 1996;Roberts et al., 1999;Stowell et al., 1999;Cox et al., 2001;Gaboury et al., 2001;Lafrance, 2004;Austin and Blenkinsop, 2009;Yang et al., 2013;Micklethwaite et al., 2015;Taillefer et al., 2017). Thus, analysis of fault-fracture networks and their controls on mineralization is important for better defining targets for mineral exploration and constraining genetic models ore genesis (e.g., Caine et al., 1996;Brogi, 2008;Rowland and Simmons, 2012;Blenkinsop et al., 2020). ...
... Generally, in the case of hydrothermal Au-Ag deposits formed by the concentrated flow of large volumes of fluid, understanding the relationships in the conduits that control fluid transport has important implications for mineralization and thus mineral exploration (Caine et al., 1996;Cox, 1999;Cox et al., 2001;Stephens et al., 2004;Tripp and Vearncombe, 2004). Common examples of conduits for hydrothermal fluids include faults, fractures, folds, schistosity, and bedding planes (Cox et al., 2001;Blenkinsop et al., 2020). Fluids can be evenly distributed across an entire structural pathway, or localized within specific structures within damage zones due to differences in strain (e.g., Cox et al., 2001). ...
Gasado Island, on the southwestern Korean Peninsula, comprises c. 50 Ma volcanic rocks that are cut by faults and fractures hosting low-sulfidation epithermal Au-Ag mineralization. In this study, we examined the relationship between the fault-fracture networks and auriferous vein systems to better understand the role of brittle structures in controlling hydrothermal fluid flow. Geometrical and fractal analyses were performed to express and quantitatively compare the vein geometries and thickness population. The results were as follows: (1) The geometrical analysis revealed a strong relationship between Au-Ag-bearing quartz veins and NE-SW-striking, oblique sinistral-normal faults, indicating that these structures are a key control on mineralization. (2) Box-counting fractal analysis applied to veins hosted by fault zone demonstrated that the D-values (fractal dimensions) are directly proportional to vein density – indicating that damage zones control vein density. (3) The linear traverse line analysis yielded cumulative frequency plots of vein thicknesses that showed obvious changes in the slope, which are reflected in the variable D-values. The cause of this slope variability is interpreted to be the presence of hybrid veins that fill secondary fault planes, which disturbs the original linear relationship shown by cumulative thickness distribution data. This study shows that vein density and physical properties are strongly controlled by the types, or existence, of fault damage zones. Understanding fault zone architecture may assist with the prediction of locations that concentrate mineralizing fluids and may benefit the initial stage of mineral exploration.
