Exploring the Solomon Islands with airborne geophysics

Abstract

The Island of Guadalcanal occurs as an 's' shape with each end twisted along the en echelon chain of the Solomon Islands primary fractured arc. The regional geology of Guadalcanal consists broadly of Mesozoic gabbroic and ultrabasic basement with Tertiary intrusives and sedimentary cover, and Quaternary volcanics. Helicopter borne magnetic and radiometric surveying was completed to delineate known gold-copper porphyry and epithermal style mineralisation events as well as locating structurally favourable sites for the emplacement and control of mineralisation. Porphyry prospects in the mountainous southern weather coast are coincident with magnetic features that correlate with IP anomalies. An intense amplitude magnetic anomaly on the southern side of Mount Turipukumahi is interpreted as an intrusive in the contact between gabbro and Kavo greywacke beds where magnetite rich skarn is likely to exist. A post volcanic event at the Sutakiki prospect is apparent as an outer halo of magnetite and potassium destruction 2km in diameter. The event is also coincident with a circular topographic depression with magnetic ring dykes occurring within. The topographic depression and ring dykes suggest it is a remnant of a collapsed strato-volcano, which is the possible control for present gold mineralisation. Controlling mechanisms for widespread mineralisation near the Gold Ridge deposit appears related to a 10 km-diameter partially collapsed strato-volcano that is evident from both the digital terrain model and Radarsat images. An inner 5km-diameter halo of potassium anomalies is directly coincident with anomalous surface gold and copper sampling results. Other volcano occurrences evident from the Radarsat and magnetic data indicate the presence of a magmatic arc. Hot springs are located along the proposed arc, which appears to be a control of most of the mineralisation that exists on the island.