The new UWA Research Repository can be accessed at the following link: http://research-repository.uwa.edu.au. Please update your favourites accordingly
Refine your search
Brief view Table view Full view
Sort by:
Record 1 of 1 1

SFX
Complex Object
 
The nature, origin and timing of gold mi The nature, origin and timing of gold mi... - Complex Object ()
Title
The nature, origin and timing of gold mineralisation in proterozoic rocks of the Peak Hill district, Western Australia / S.E. Thornett
Author
Year
1995
Abstract
The gold mines at Peak Hill lie within a group of deposits in the western part of the Proterozoic Nabberu Basin, which rests unconformably upon the northern margin of the Yilgarn Craton. The Peak Hill deposits are hosted by mafic and pelitic schist which appears to overlie the southwestern projection of the Marymia Dome. The main objectives of this study were to establish the controls on gold mineralisation, in particular the structural setting, timing, nature and physical conditions of emplacement of the ore-forming fluids. Three deposits, at Peak Hill - Fiveways, Mount Pleasant and Jubilee were studied and compared. All of these deposits lie in different stratigraphic positions in rocks of the Peak Hill Metamorphic Suite. Gold occurs mainly in pelitic schist, in close proximity to bodies of mafic schist or metadolerite, and commonly shows an intimate relationship with graphitic schist. The host rocks are highly deformed, with evidence of early thrusting and layer-pardllel fabric development (Sl). Three later phases of folding are recognised; the earliest is manifested in asymmetric recumbent folds, with the two younger fold generations producing interference folds which define the Peak Hill Dome. D4 folds and associated shear zones are identified as the principal structures controlling gold mineralisation, but earlier (D1) shear zones also appear to be mineralised. In the vicinity of the three deposits studied, regional metamorphism has reached amphibolite facies conditions, with geothermometry on prograde assemblages giving temperatures of 535 to 620°C. Phengite geobarometry, on corresponding assemblages, indicates high minimum pressures of 6.5 to 7 kbar. Intense retrograde alteration accompanies gold mineralisation in D4 shear zones and folds, and comprises hydrous alteration assemblages rich in Fe, K, S, CO2 and possibly Na. Alteration assemblages contain
Fe-chlorite, biotite, white-mica, albite, garnet, pyrite, carbonate, tourmaline and fluorite.
Thermometric evidence from the Fe-chlorite and low-albite indicates crystallisation temperatures of between 250 to 375°C. The deposition temperature of much of the gold is also inferred to lie within this range. Higher temperatures (530 to 620°C) obtained from apparently retrograde garnet-biotite grain pairs in strongly altered rocks, may signify an extended history of shear zone development and alteration (possibly D1), and perhaps mineralisation. Fluid inclusion petrography on gold mineralised quartz veins indicates that the hydrothermal fluid associated with mineralisation was H2O rich and moderately saline, with some CO2 and possibly minor CH4. Thirty to fifty percent of the fluid inclusions are vapour-rich, suggesting that mineralised fluids were trapped in a relatively lowpressure environment where phase separation was common. Lead-isotope data, from galena and lead tellurides which are intimately associated with gold mineralisation, suggest that the Peak Hill mineralisation is broadly synchronous with other Glengarry and Nabberu deposits at 1.9 - 1.8 Ga. Data from Nathans and Labouchere, in the west of the Glengarry Fold Belt, indicate that the lead is derived from the underlying Archaean Yilgam basement of the Murchison Province. However, results from Peak Hill and the Marymia Mine suggest that lead in these two deposits has the same, non-Yilgarn, source. Although Peak Hill is geographical close to the deposits of the western Glengarry Fold Belt, and shares some geological characteristics, the leadisotope data suggest that the Peak Hill gold mineralisation is more closely related to the deposits of the Marymia Dome. This is consistent with structural and geological indications that the Marymia Dome is the basement beneath the Peak Hill Metamv;phic Suite.
Identifier
http://repository.uwa.edu.au:80/R/-?func=dbin-jump-full&object_id=34947&silo_library=GEN01
Subject
Department/School
Type
Thesis (M.Sc.)--University of Western Australia, 1995
Persistent URL
http://repository.uwa.edu.au:80/R/-?func=dbin-jump-full&object_id=34947&silo_library=GEN01
Related collections
> Theses