ARTICLE Geological and structural controls on gold mineralization in the Tanami District, Northern Territory Andrew J. Tunks & David R. Cooke Received: 1 January 2006 / Accepted: 5 September 2006 / Published online: 11 November 2006 # Springer-Verlag 2006 Abstract Gold mineralization in the Tanami district is hosted within moderately northwest dipping turbiditic sedimentary and basaltic volcanic rocks of the Paleoprote- rozoic Mt. Charles Formation. The gold occurs within a complex sinistral wrench-fault array and associated veins and alteration haloes. The main mineralized faults have a northerly trend and dip steeply east. Subsidiary structures trend at 030° and 070° and dip towards the southeast. Paleostress calculations based on fault striation populations and geometry (strike and dip) of faults indicate that at the time of the mineralizing event, σ 1 was sub-horizontal and SE–NW directed with σ 2 subvertical. Structural studies indicate that the mineralization occurred after the regional folding event and synchronous with the emplacement of felsic dykes into the mine sequence. Gold veins in the Tanami district are interpreted to be part of an outer thermal aureole gold system that formed during the emplacement of granitoids in the nearby ∼1,815 to ∼1,799 Ma Frankenia and/or Coomarie domes. Economic gold mineralization occurred late in the paragenetic history of the district. Gold is hosted by quartz-carbonate veins within shear zones, and also in the surrounding sericite- quartz- pyrite ± carbonate- altered wallrocks. Gold-mineralized veins precipitated at depths of 3 to 6 km from high temperature (∼300°C), low salinity (∼5 wt% NaCl equivalent) fluids with low CO 2 contents. Barren quartz, dolomite and calcite veins that occur in pre- and post-mineralization thrust faults formed from high salinity (∼20 wt% NaCl equivalent), low temperature (∼120–150°C) basinal brines. Pyrite in the gold mineralized veins and alteration halos has lower δ 34 S values (6.8 to 12.5‰) than local diagenetic pyrite (17.8 to 19.2‰) or pyrite in pre-mineralization thrust faults (31.7 to 37.1‰). The mineralizing fluids are inferred to have contained a well-homogenized mixture of magmatic and sedimentary-derived sulfur. Keywords Proterozoic . Tanami . Granite . Gold mineralization . Thermal aureole Introduction The Tanami goldfield, located 650 km northwest of Alice Springs, is one of several significant gold districts in the Paleoproterozoic Tanami region of the Northern Territory. This area has become one of the major gold provinces of Northern Australia. Historically, investigations into the geology of the region have been neglected because of deep weathering, lack of exposure, and remoteness. The Tanami region grades, without clear boundary, into the Arunta inlier to the southeast and is separated from the Halls Creek inlier and the King Leopold Mobile zone to the west by the overlying sedimentary units of the Middle Proterozoic Birrindudu Basin (Plumb 1990; Fig. 1). Gold was originally discovered at Tanami in 1904, and the area has been worked intermittently since then. Large- scale, open-cut mining commenced in 1987 within mining lease 153 (MLS153) and was undertaken first by the Tanami Joint Venture and then by Zapopan N.L. until Miner Deposita (2007) 42:107–126 DOI 10.1007/s00126-006-0097-z Editorial handling: D. Huston D. R. Cooke (*) CODES ARC Centre of Excellence in Ore Deposits, University of Tasmania, Private Bag 79, Hobart, Tasmania 7001, Australia e-mail: d.cooke@utas.edu.au Present address: A. J. Tunks A-Cap Resources Ltd., Suite 5.10, Level 5, 737 Burwood Rd, Hawthorn, Victoria 3122, Australia