Regional geophysics of the Alberton-Mangana goldfield, Northeast Tasmania

Abstract

Reconnaissance gravity and high-resolution aeromagnetic data, acquired in 1993 as part of the Tasmanian Government NETGOLD project, were used to investigate the regional structural setting of the area and the distribution of gold mineralisation. Gold mineralisation in northeast Tasmania occurs both close to, and remote from, outcropping granitoids. The total recorded gold production is in excess of 50 tonnes. In the Alberton-Mangana Goldfield the distribution of mineralised sites defines a prominent NNW trending regional lineament which passes through the corridor of Mathinna Group rocks separating the Scottsdale and Blue Tier Batholiths. Mineralisation occurs primarily within discrete quartz-sulphide veins hosted by the metasediments. The Mathinna Group rocks are variably magnetic and the majority of the granitoids are effectively non-magnetic. NE-trending magnetic lineaments mark faults which truncate subtle NNW-trending anomalies attributed to lithological variations in the Mathinna Group. There is no consistent relationship between NE-trending faults and mineralised sites but dextral movement on these structures may have been important in dilation and mineralisation of pre-existing ENE-trending fractures. Broad ovoid magnetic anomalies in areas of Mathinna Group outcrop result from large scale alteration systems probably related to underlying granodioritic intrusives. The economic potential of these systems has not been tested. The residual Bouguer gravity field is characterised by strongly negative anomalies in areas of granite outcrop. Modelling suggests that the entire Alberton-Mangana area is underlain by low density granite with the thickness of Mathinna Group rocks increasing from less than 1 km at Alberton in the north to in excess of 3 km in the south near Mangana.