GU Report 6 - Geochronology of gold deposits in the western Lachlan Fold Belt, Victoria: A review
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Product description:A variety of geochronological methods have been applied to the western Lachlan Fold Belt, Victoria, over the past decade, to constrain the timing of regional metamorphism, deformation, magmatism, and gold mineralisation. Techniques employed include in-situ SHRIMP U-Pb zircon, Re-Os sulphide and 40Ar/39Ar whole-rock/amphibole/mica/pyrite laser probe or furnace step-heating methods. A review of the available literature suggests that multiple deformation events (Delamarian and Lachlan Orogenies) affected the western Stawell Zone (~500 to 440 Ma), whereas metamorphism in the Bendigo Zone may be restricted to ~440 Ma, with the Melbourne Zone exhibiting younger deformation ages of ~410 Ma. Ages for granitic intrusions in this region range from ~410 Ma to ~370 Ma. ‘Orogenic’ gold deposits in the Stawell and Bendigo Zones have reported mineralisation ages in the range of ~455 to ~410 Ma. So-called ‘intrusion-related’, polymetallic and Au-Sb-As deposits yielded younger mineralisation ages in the range of ~420 to ~360 Ma. Critical assessment of the available age data indicates that, while the timing of granite emplacement and some gold mineralisation events are relatively well-constrained (e.g. Bendigo), the timing of deformation and some gold deposition events is more uncertain. It is also clear that many 40Ar/39Ar results are adversely affected by poor sample selection, inadequate sample characterization and, in some cases, inappropriate analytical protocols. In addition, some 40Ar/39Ar results have been ‘over-interpreted’ or even misinterpreted. It is recommended that future studies employ a wider range of dating methods including U-Pb monazite geochronometry and other techniques such as fluid inclusion noble gas and halogen geochemistry to better constrain the timing and origin of gold mineralisation in Victoria. Download The downloadable version of this report is supplied in PDF format. Bibliographic reference Fu, B., Fairmaid, A.M. & Pillips, D., 2007. Geochronology of gold deposits in the western Lachlan Fold Belt, Victoria: A review. GeoScience Victoria Gold Undercover Report 6. Department of Primary Industries. Related products:
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