Development of fluid conduits in the auriferous shear zones of the Hutti Gold Mine, India: evidence for spatially and temporally heterogeneous fluid flow

Abstract. This study focuses on physiochemical processes occurring in a brittle-ductile shear zone at both fluid-present and fluid-limited conditions. In the studied shear zone (Wyangala, SE Australia), a coarse-grained two-feldsparquartz-biotite granite is transformed into a medium-grained orthogneiss at the shear zone margins and a fine-grained quartz-muscovite phyllonite in the central parts.The orthogneiss displays cataclasis of feldspar and crystalplastic deformation of quartz. Quartz accommodates most of the deformation and is extensively recrystallized, showing distinct crystallographic preferred orientation (CPO). Feldspar-to-muscovite, biotite-to-muscovite and albitization reactions occur locally at porphyroclasts' fracture surfaces and margins. However, the bulk rock composition shows very little change in respect to the wall rock composition. In contrast, in the shear zone centre quartz occurs as large, weakly deformed porphyroclasts in sizes similar to that in the wall rock, suggesting that it has undergone little deformation. Feldspars and biotite are almost completely reacted to muscovite, which is arranged in a fine-grained interconnected matrix. Muscovite-rich layers contain significant amounts of fine-grained intermixed quartz with random CPO. These domains are interpreted to have accommodated most of the strain. Bulk rock chemistry data show a significant increase in SiO 2 and depletion in NaO content compared to the wall rock composition.We suggest that the high-and low-strain microstructures in the shear zone represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. Instead, we propose that the microstructural and mineralogical changes in the shear zone centre arise from a local metasomatic alteration around a brittle precursor. When the weaker fine-grained microstructure is established, the further flow is controlled by transient porosity created at (i) grain boundaries in fine-grained areas deforming by grain boundary sliding (GBS) and (ii) transient dilatancy sites at porphyroclast-matrix boundaries. Here a growth of secondary quartz occurs from incoming fluid, resulting in significant changes in bulk composition and eventually rheological hardening due to the precipitation-related increase in the mode and grain size of quartz. In contrast, within the shear zone margins the amount of fluid influx and associated reactions is limited; here deformation mainly proceeds by dynamic recrystallization of the igneous quartz grains.The studied shear zone exemplifies the role of syndeformational fluids and fluid-induced reactions on the dominance of deformation processes and subsequent contrasting rheological behaviour at micron to metre scale.

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“…The mineral abbreviations used in the following sections follow the recommendations of Kretz (1983).…”

Section: Sample Selection and Preparationmentioning

confidence: 99%

“…Sibson, 1982;Scholz, 2007), and is a major source and transport region for ore-forming fluids (e.g. Kolb et al, 2004). However, it is also the leastunderstood part of the continental crust, where the rheological strength estimates and assumptions of rock deformation mechanisms vary widely.…”

Section: Introductionmentioning

confidence: 99%

Strain localization in brittle–ductile shear zones: fluid-abundant vs. fluid-limited conditions (an example from Wyangala area, Australia)

Spruženiece

Piazolo

2015

Solid Earth

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“…Algoma-type BIF occurred in the KolareRamagirieHuttieMaski greenstone belts in the Dharwar Craton, which also contains a large number of greenstone belt type Au deposits (e.g., Karnataka; Kolar) and graphite schists (Kolb et al, 2004;Turchenko et al, 2009;Shi et al, 2010). In the SargureHolenarsipureNuggihalli schist belts, maficeultramafic duniteeharzburgiteegabbro-anorthosite intrusions contain podiform chromite bodies (e.g., Aladahalli).…”

Section: Precambrian Metallogenesis Of the Indmentioning

confidence: 99%

Correlations between the North China Craton and the Indian Shield: Constraints from regional metallogeny

Chen

et al. 2015

Geoscience Frontiers

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a b s t r a c tThe correlation between the North China Craton (NCC) and the Indian Shield (IND) has been a hot topic in recent years. On the basis of ore deposit databases, the NCC and IND have shown broad similarity in metallogenesis from the middle Archaean to the Mesoproterozoic. The two blocks both have three major metallogenic systems: (1) the Archaean BIF metallogenic system; (2) the Paleoproterozoic Cu-Pb-Zn metallogenic system; and (3) the Mesoproterozoic Fe-Pb-Zn system. In the north margin of the NCC and the west margin of the IND, the Archaean BIF-Au-Cu-Pb-Zn deposits had the same petrogenesis and host rocks, the Paleoproterozoic Cu-Pb-Zn deposits were controlled by active belts, and the Mesoproterozoic Fe-Pb-Zn deposits were mainly related to multi-stage rifting. Matching regional mineralization patterns and geological features has established the continental assembly referred to as "NCWI", an acronym for the north margin of the NCC (NC) and the west margin of the IND (WI) during the middle Archaean to the Mesoproterozoic. In this assembly, the available geological and metallogenic data from the Eastern Block and active belts of NC fit those from the Dharwar craton and the AravallieDelhi eVindhyan belt of WI, respectively. Moreover, the depositional model and environment of Paleoproterozoic metasedimentary manganese deposits in NCWI implied that the assembly may be located at low latitudes, where the conditions were favorable for dissolving ice and precipitating manganese deposits.Ó 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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“…Pressure cycling as a result of seismic activity may be indicated by high-salinity and low-density fluid inclusions (Jin et al 2008;Srivastava and Sahay 2003). Fault-failure during seismic events creates enhanced fracture permeability and fracture volume that acts as sink for fluids and triggers mineral deposition (Kolb et al 2004;Petit et al 1999;Sibson et al 1988). Post-failure discharge causes drainage of 'geopressured' fluids (Sibson et al 1988) and pressure drop towards or even to hydrostatic values, if the fault rupture reached the surface (Herrington and Wilkinson 1993;Sibson 2001).…”

Section: Fluid Sources and Migrationmentioning

confidence: 99%

Fluid evolution at the Variscan front in the vicinity of the Aachen thrust

Синдерн

Meyer

Lögering

et al. 2011

Int J Earth Sci (Geol Rundsch)

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Quartz-carbonate-chlorite veins were studied in borehole samples of the RWTH-1 well in Aachen. Veins formed in Devonian rocks in the footwall of the Aachen thrust during Variscan deformation and associated fluid flow. Primary fluid inclusions indicate subsolvus unmixing of a homogenous H 2 O-CO 2 -CH 4 -(N 2 )-Na-(K)-Cl fluid into a H 2 O-Na-(K)-Cl solution and a vapour-rich CO 2 -(H 2 O, CH 4 , N 2 ) fluid. The aqueous end-member composition resembles that of metamorphic fluids of the Variscan front zone with salinities ranging from 4 to 7% NaCl equiv. and maximum homogenisation temperatures of close to 400°C. Pressure estimates indicate a burial depth between 4,500 and 8,000 m at geothermal gradients between 50 and 75°C/26 MPa, but pressure decrease to sublithostatic conditions is also indicated, probably as a consequence of fracture opening during episodic seismic activity. A second fluid system, mainly preserved in pseudo-secondary and secondary fluid inclusions, is characterised by fluid temperatures between 200 and 250°C and salinities of \5% NaCl equiv. Bulk stable isotope analyses of fluids released from vein quartz, calcite, and dolomite by decrepitation yielded dD H2O values from -89 to -113 %, d 13 C CH4 from -26.9 to -28.9% (VPDB) and d 13 C CO2 from -12.8 to -23.3% (VPDB). The low dD and d 13 C range of the fluids is considered to be due to interaction with cracked hydrocarbons. The second fluid influx caused partial isotope exchange and disequilibrium. It is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the Stavelot-Venn massif. The metamorphic fluid was focused along major thrust faults of the Variscan front zone such as the Aachen thrust. A second fluid influx was introduced from formation waters in the footwall of the Aachen thrust as a consequence of progressive deformation. Mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics.

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Development of fluid conduits in the auriferous shear zones of the Hutti Gold Mine, India: evidence for spatially and temporally heterogeneous fluid flow

Cited by 79 publications

References 23 publications

Strain localization in brittle–ductile shear zones: fluid-abundant vs. fluid-limited conditions (an example from Wyangala area, Australia)

Strain localization in brittle–ductile shear zones: fluid-abundant vs. fluid-limited conditions (an example from Wyangala area, Australia)

Correlations between the North China Craton and the Indian Shield: Constraints from regional metallogeny

Fluid evolution at the Variscan front in the vicinity of the Aachen thrust

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