Zircon U–Pb dating of Early Palaeozoic monzonitic intrusives from the Goonumbla area, New South Wales

Abstract

Zircon U–Pb ages measured on four small intrusions into the succession of Ordovician volcanic rocks that hosts Northparkes Cu–Au mine northwest of Parkes, New South Wales, place limits on the age of the volcanic sequence. The basal Nelungaloo Volcanics are constrained by a cross‐cutting monzodiorite to be ≥484.3 ± 2.9 Ma (Early Ordovician). Similarly, the overlying basal Goonumbla Volcanics are constrained by another cross‐cutting monzodiorite to be ≥450.8 ± 4.2 Ma (Middle Ordovician). A later generation of monzonites intruded into the middle and upper Goonumbla Volcanics yield ages of 439.1 ± 4.5 and 438.9 ± 4.7 Ma (Siluro‐Ordovician). These various ages are consistent with the ages of fossiliferous sediments within the volcanic sequence, and indicate that both the intrusive and volcanic rocks span an appreciable period of time—neither are the product of a single magmatic episode. Intrusion of the youngest monzonites and mineralisation was virtually contemporaneous.

Early Oligocene partial melting in the Main Central Thrust Zone (Arun valley, eastern Nepal Himalaya)

“…The zircon rims have low Th/U (0.01-0.02) and are extremely rich in U with concentrations up to 8900 ppm. Such high concentrations are known to produce a matrix effect (Butera et al, 2004), which has been documented to be significant above ~2500 ppm of U and leads to ages ~3% older for each 1000 ppm of U (Butera et al 2004, Hermann et al 2006 andRubatto unpublished data). When such matrix correction is applied to analyses with more than 2500 ppm of U, the clustering of the ages improve but remains poor around 27-29 Ma with scatter above analytical uncertainty.…”

120 to 0 Ma tectonic evolution of the southwest Pacific and analogous geological evolution of the 600 to 220 Ma Tasman Fold Belt System

“…Arc-type lavas as old as 480 Ma are recorded from the Ordovician volcanic Parkes-Narromine belt (Butera et al 2001), which trends southward into northeastern Victoria around the headwaters of the Murray River. A detailed discussion of the subsequent SiluroDevonian tectonic development of the Lachlan Fold Belt is beyond the scope of this paper.…”

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

“…Porphyry copper-gold mineralization is typically hosted by quartz-monzonite intrusions (Müller et al 1994;Heithersay and Walshe 1995). Uranium-Pb zircon dating of the intrusions has established that they do not represent a single magmatic episode, but three distinct episodes at about 482, 450 and 440 Ma, respectively (Butera et al 2001;Blevin 2002). Empirical studies suggest a direct relationship between increasing mineral deposit size and the degree of K-enrichment in the related igneous progenitor in the Lachlan Fold Belt (Blevin 2002;Holliday et al 2002).…”