40 Ar/ 39 Ar and U-Pb geochronology of the Goonumbla porphyry Cu-Au deposits, New South Wales, Australia

Abstract

The 4øAr/39Ar technique of K-Ar dating has been used to determine the age of hydrothermal sericite associated with mineralization in the Goonumbla porphyry copper-gold deposits, Lachlan fold belt, New South Wales, Australia. The 4øAr/a9Ar age spectra from Goonumbla hydrothermal sericite indicate that vein and groundmass (potassic and phyllic) alteration were broadly contemporaneous at 439.2 q-1.2 Ma (la). The 4øAr/a9Ar dates obtained from hydrothermal alkali feldspar are considerably younger than those from coeval hydrothermal sericite. U-Pb dating of magmatic zircons by ion microprobe yields an age of 438.5 _ 3.6 Ma (la) for the Nelungaloo Volcanics which underlie the mineralized Goonumbla sequence, providing a maximum age for mineralization and suggesting that the two successions are largely coeval.The 4øAr/39Ar age spectra obtained in this investigation from fine-grained sericite illustrate the amenability of this hydrothermal phase to dating by the 4øAr/3OAr technique and suggest that there is considerable potential for application of this dating method to Phanerozoic ore deposits. The close agreement in ages between the 4øAr/a9Ar and U-Pb results gives confidence in the application of both dating techniques to altered Paleozoic rocks.

Magmatic characteristics and geochronology of Ordovician igneous rocks from the Cadia – Neville region, New South Wales: implications for tectonic evolution

“…The ca 439 Ma age for magmatism and alteration near Cadia is similar to that recorded at Goonumbla, near Parkes in the Junee -Narromine Volcanic Belt, where other ages include a 438 + 3.6 Ma U -Pb SHRIMP zircon age for a monzodiorite (Perkins et al 1990) and 439.2 + 1.2 Ma (Perkins et al 1990) and 440 + 1.1 Ma (Perkins et al 1995) The coarsely porphyritic and equigranular holocrystalline intrusions dated by radiogenic isotope techniques in the Cadia -Neville -Carcoar region (Figure 4) have shoshonitic geochemical affinities. However, the intrusions dated by Perkins et al (1992) from the Junction Reefs -Burnt Yards -Mandurama region have high-K calc-alkaline affinities (P. Blevin pers.…”

Direct Associations Between Potassic Igneous Rocks and Gold-Copper Deposits in Volcanic Arcs

“…Hydrothermal sericite associated with mineralization yields an 40 Ar/ 39 Ar step-heating age of 439.2 ± 1.2 Ma (Perkins et al 1990a). Uranium-Pb dating by ion microprobe on magmatic zircons from diorites near the Goonumbla deposits yields an age of 438 ± 3.5 Ma (Perkins et al 1990b).…”

“…Data from Richards (1990a) setting, formed from high salinity fluids (Heithersay et al 1990;Heithersay and Walshe 1995;Wilson et al 2003), and were coeval with high-K igneous rocks (e.g. Perkins et al 1990a). Many Cretaceous to Cenozoic epithermal (e.g.…”

“…• The Ordovician Northparkes (Goonumbla) copper-gold deposit, New South Wales, Australia (Jones 1985;Heithersay 1986;Heithersay et al 1990;Perkins et al 1990aPerkins et al , b, 1992Müller et al 1994;Heithersay and Walshe 1995;Blevin 2002;Lickfold et al 2003;Harris and Holcombe 2014).…”

Complex volcanic facies architecture of the Forest Reefs Volcanics near Cadia, New South Wales, associated with prolonged arc-related volcanism

“…The more evolved trachyandesites and coeval dioritic, monzonitic and syenitic intrusions were associated with the final subaerial evolution of the volcano, which included a large caldera. However, biostratigraphic and radiogenic age determinations (Perkins et al 1990(Perkins et al , 1992Packham et al 1999; suggested that the two episodes of shoshonitic volcanism were separated by between 15 and 20 million years. In addition, evidence from recent mapping and drillcore logging suggests that the Forest Reefs Volcanics include the products of at least two intrabasinal shoshonitic volcanic centres intercalated with a volcaniclastic apron, and that deposition and volcanism were entirely submarine.…”