Die Genese der Goldlagerstätte Hira Buddini, Südindien

The Hira Buddini Gold Mine is situated in the Hutti-Maski Greenstone Belt of the Indian Dharwar Craton. Hydrothermal gold mineralization is hosted by a narrow ENE- trending steep dipping reverse shear zone at the lithological contact of metabasalt,metadacite and metagabbro. The host rocks are interpreted to have been formed in a sub-seafloor environment of an island arc, which subsequently underwent deformation and metamorphism. A prograde metamorphic evolution of the host rocks is indicated by geothermobarometry on zoned amphibole-plagioclase pairs. A regional foliation developed during intense horizontal shortening at peak metamorphic conditions at P = 400 ± 100 MPa and T = 610° ± 40°C. A first stage of hydrothermal gold mineralization occurred at slightly retrograde P-T conditions (P < 400 MPa, T = 500 - 550°C) during the development of a brittle-ductile shear zone. Sigmoidal extension veins, extensional shear veins and shear veins formed during this stage. Gold mineralization is confined to the hydrothermally altered wall rocks, and to the selvages of quartz-calcite bearing sigmoidal extension veins. Within the host rocks, different alteration zones are developed, which reflect the transition between a wallrock-controlled and a fluid-controlled alteration style.Mineral assemblages, thermodynamic modelling and geochemistry reflect gradients in XCO2, potassium-, calcium- and sulphur- concentration between the different alteration zones. The ore mineral assemblage magnetite + pyrite suggest the presence of a relatively oxidizing hydrothermal fluid, which might be of magmatic origin. An increase in sulphur fugacity towards the inner proximal alteration zone is indicated by the replacement of ilmenite by pyrite and the absence of magnetite. Wall rock sulphidation is identified as the most likely cause for gold precipitation. Boron isotopic studies on tourmaline indicate mixing of a magmatic and a metamorphic fluid within the shear zone system (Krienitz et al., 2008). A second stage of hydrothermal gold mineralization formed under greenschist facies conditions at p almost equal 200 MPa and T not less than 350°C. Within the reactivated, locally gold bearing veins, coexisting low salinity H2O-NaCl and CO2 ± CH4 fluid inclusions indicate phase separation. Furthermore, variable salinities of aqueous fluid inclusions between 0 - 38 wt. -% NaCl eq. are interpreted to be the result of fluid mixing after phase separation has occurred. The boron isotopy of tourmaline indicates the involvement of a magmatic fluid during the second stage of gold mineralization (Krienitz et al., 2008).

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2009

Author dc:creator

• Hellmann, André

Contributors dc:contributor

• Meyer, Franz Michael

• info:eu-repo/classification/ddc/550
• Goldlagerstätte
• Archaikum
• Inselbogen
• Metamorphose
• Flüssigkeitseinschluss
• Scherzone
• Turmalin
• Geowissenschaften
• orogene Goldlagerstätte
• hydrothermale Alteration
• Flüssigkeitseinschlüsse
• orogenic gold deposit
• archean
• island arc
• metamorphism
• hydrothermal alteration
• fluid inclusions
• phase separation
• fluid mixing
• shear zone
• tourmaline

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112694%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A50139