Endeavour 26 North; a porphyry copper-gold deposit in the Late Ordovician, shoshonitic Goonumbla volcanic complex, New South Wales, Australia

Abstract

Endeavour 26 North is the largest of 12 pipelike porphyry Cu-Au deposits found near Parkes in central- west New South Wales, within the Late Ordovician Goonumbla Volcanic Complex. The dominant volcanic rocks of the complex, the Goonumbla Volcanics, are latitic flows and volcanic breccias which are overlain by the trachytic Wombin Volcanics. The volcanic rocks are characterized by high K 2 O and high K 2 O/Na 2 O ratios, which are typical of the shoshonite association, as well as an enrichment in large ion lithophile elements and a low concentration of high field strength elements. The Nelungaloo Volcanics form an Early Ordovician, nonshoshonitic volcanic substrate to the complex which initially developed in a submarine and subsequently subaerial setting. The 87 Sr/ 66 Sr, epsilon Nd , and Pb isotope data indicate the magmas were derived from mantle sources. The shoshonitic magmas may be products of high-pressure fractionation in the subcontinental lithosphere. The porphyry deposits are associated with a gravity low which is taken to reflect a subvolcanic chamber beneath the center of the complex. All deposits are located within a pronounced circular feature in the aeromagnetic data that is interpreted as the margin of a collapsed caldera. Dioritic to monzonitic stocks, which in part define the caldera rim, represent a resurgent phase of magmatism. The Endeavour 31 stock which was part of this phase is ringed by six porphyry Cu-Au deposits, including Endeavour 26 North. The deposits are centered on fingerlike quartz monzonite porphyries which cut the Endeavour 31 stock at depth. Geochemical anomalies of Cu and Zn in the bedrock define the size of the alteration system associated with the stock. In part the distribution of the Cu-Au deposits is controlled by the Endeavour lineament. In comparison to most other volcanic and intrusive rocks of the Goonumbla Volcanic Complex, the Endeavour..