Neighbouring orogenic gold deposits may be the products of unrelated mineralizing events

Abstract

Models for exploration targeting are often developed by assessing known gold deposits in a region, and targeting similar geological features such as geochemical anomalies, favourable host rocks or structural settings with the assumption that they represented the footprint of the mineralizing event. Belvedere and Paulsens are gold deposits with similar characteristics located in the Wyloo Inlier in the north Capricorn Orogen, Western Australia. Gold at both deposits is hosted in quartz–carbonate–sulfide veins within mafic intrusive rock. Prior to this study they were thought to have formed during the same hydrothermal mineralizing event. At Belvedere, in situ baddeleyite geochronology yields a weighted mean 207Pb∗/206Pb∗ crystallization age of 2082 ± 30 Ma for the Belvedere dolerite which hosts the ore body. Xenotime intergrown with ore-stage alteration minerals, and encased in arsenopyrite, yielded a 207Pb∗/206Pb∗ date of 1681 ± 9 Ma, interpreted to represent the timing of hydrothermal activity related to gold mineralization at the Belvedere deposit. Despite the similarities between the two deposits, our results indicate that they underwent different geological histories with primary gold mineralization at Paulsens occurring at c. 2400 Ma, pre-dating both the Belvedere dolerite and mineralization within the dolerite. Furthermore, field relationships show that the suite of dolerite dykes to which the Belvedere dolerite belongs, crosscut gold mineralization at Paulsens. The in situ U–Pb geochronology techniques employed here, combined with field relationships, have led to a better understanding on age constraints of gold deposition in the Wyloo Inlier and challenges the assumption that orogenic deposits in a given region probably formed during a single mineralizing event.