Browns Dome FALCON Airborne Gravity Gradiometry Survey Central Tanami Final Report

Abstract

A regional gravity data acquisition programme is proposed for co-funding, covering 500km2 of the Browns Dome area. Northern Star Resources (NSR) seeks to develop gold +/-REE exploration targets on the margins of the Browns Dome, in the Tanami Province, while improving the regional geological understanding. The Browns Dome area remains one of the most poorly understood parts of a poorly understood mineral province. Historic age dating provided Neo-Archaean dates for high grade metamorphic rocks present on the southern margin of the dome however recent age dating and reassessment of the Archaean date suggests at least two phases of Lower Proterozoic granite intruded the amphibolite to granulite metamorphic grade rocks. The age of these rocks is still unknown though they have been attributed to the Twigg Formation, the lowest part of the Tanami Group. It is this group of rocks that hosts all the economic gold mineralisation discovered in the Tanami. Gold mineralisation is spatially related to the contact with orogenic granite intrusions around the Tanami Mine and DBS mining area. In the western sector of the Tanami a biotite grade contact metamorphic facies are spatially associated with gold mineralisation and granite intrusions. By establishing equivalent spatial zonation patterns, it is hoped that a similar target zonation approach can be applied to the Browns Dome area. Seven kilometres west of the Browns Dome project area Northern Minerals Limited (ASX: NTU) is focussed on the development of heavy rare earths project the element dysprosium. Mining has begun at this project. NSR is focussed on the discovery of gold in the Tanami. As part of a budgeted reconnaissance exploration programme to be completed independently by NSR, a cofunded detailed gravity survey is recommended to assist in mapping out the southern margin of the dome. The gravity data should separate out the lower density intrusive rocks which, coupled with recently acquired potential field data should provide a solid basis for mapping the granite intrusions. The denser country rocks which are apparent on the southern margin of the dome should be mapped out by the detailed survey and any major faults should be evident. NSR has successfully used very close-spaced gravity survey grids around the Groundrush deposit and found that it is possible to image shallow, dense features like gabbroic intrusive rocks. This is an innovative use of this kind of data, previously gravity surveying has been considered a broad-brush tool. It will be very interesting to try and map out the dense stratigraphy around the dome using this technique which is far cheaper than aerial surveying. Combining new high-density gravity, AEM (current surveys funded by GA http://www.ga.gov.au/eftf/minerals/nawa/ausaem) and magnetic data, NSR should be able to generate high quality gold exploration targets. The products of the data inversions that NSR will create would further valueadd the datasets.