Paleoproterozoic stratigraphy and gold mineralisation in the Granites-Tanami Orogen, North Australian Craton

Abstract

The Granites-Tanami Orogen (GTO) is a significant auriferous province located in the poorly exposed southwestern part of the North Australian Craton. The stratigraphic succession of the Paleoproterozoic Tanami Group in the orogen is hard to define conclusively, owing to the general lack of outcrop, and is best understood by studying orientated diamond drill holes, such as those at the Dead Bullock Soak and Tanami goldfields, and the Groundrush and Coyote gold deposits. The group is broadly a succession of turbiditic sedimentary rocks included in the Killi Killi Formation conformably overlying shale, mafic volcanic units associated with abundant dolerite and diorite sills, and chert nodules and bands in the Stubbins and Dead Bullock formations. The Mount Charles Formation, previously inferred to be younger than the Killi Killi Formation, is lithologically similar to the Stubbins Formation and also overlain by the Killi Killi Formation. Based on whole-rock and trace-element geochemistry, geochronology, lithostratigraphy and the principles of superposition, the ca 1864 Ma Stubbins, Dead Bullock and Mount Charles formations are here correlated and assigned to the Dead Bullock Formation of the Tanami Group. The deposition of the now extended Dead Bullock Formation was in a back-arc basin setting to the east of the Halls Creek Orogen. Deposition in the basin changed with the introduction of sand-dominated turbiditic successions forming the Killi Killi Formation before ca 1850 Ma when collisional tectonics between the GTO and Halls Creek Orogen resulted in the development of northerly trending isoclinal (F_GTO1) folds and associated layer-parallel faults. A second (D_GTO2) major collisional event followed at ca 1795 Ma, which is associated with orogenic lode-gold deposits at Callie, Groundrush, Old Pirate and Coyote, and the intrusion-hosted Buccaneer gold deposit in the GTO. This was a period in the history of the GTO when granitic rocks were emplaced shortly before or synchronously with gold mineralisation at ca 1795 Ma.

花岗岩 - Tanami造山带（ GTO）是一个重要的含金区，地处出露不佳的北澳大利亚克拉通西南部分。该造山带内古元古代Tanami群的地层层序很难有结论性的界定，这是由于露头普遍缺乏，只有通过研究为目的的金刚石钻孔才取得最佳了解，例如Dead Bullock Soak 金矿和Tanami金矿，以及Groundrush和Coyote金矿。Tanami群是一个浊积岩地层序列，包括Killi Killi组，整合地上覆于Stubbin组合Dead Bullock组的页岩、具有丰富的辉绿岩和闪长岩的镁铁质火山岩和燧石结核和燧石带之上。Mount Charles组先前曾被推断为比Killi Killi组更年轻，其岩性与Stubbins组相似，上覆地层为Killi Killi组。基于全岩和微量元素地球化学、年代学、岩石地层学和叠加原理，年代大约为1864Ma的Stubbins组、Dead Bullock组和Mount Charles组在此被归并为Tanami群的Dead Bullock组。扩展了的Dead Bullock组沉积于Halls Creek造山带东侧的弧后盆地环境。盆地内的沉积作用随着砂为主的浊流序列的开始而产生变化，在约1850Ma形成Killi Killi组。当时 GTO和Halls Creek造山带之间的碰撞导致偏北走向的等斜（ FGTO1 ）褶皱和相关平行断层。在约1795Ma，第二个（ DGTO2 ）主要碰撞事件随之发生，这与Callie、Groundrush、Old Pirate及Coyote的造山脉金矿床相关，也与GTO中的侵入带中的Buccaneer金矿相关。在GTO的这段历史中，在金矿化作用之前不久或与此同时（约1795Ma），花岗岩石侵位。

KEY WORDS:

• Paleoproterozoic
• Granites-Tanami Orogen
• orogenic and intrusive-related gold
• Dead Bullock Soak goldfield
• Tanami goldfield
• Groundrush
• Old Pirate
• Coyote
• Buccaneer

ACKNOWLEDGEMENTS

We gratefully acknowledge AMIRA International and the industry sponsors, including AusAid and the ARC Linkage Project LP110100667, for their support of the WAXI project (P934A), and this is contribution 244 from the ARC Centre of Excellence for Core to Crust Fluid Systems (<http://www.ccfs.mq.edu.au>). We are also appreciative of the contribution of the various Geological Surveys and Departments of Mines in West Africa as sponsors in kind of WAXI. Finally, we wish to recognise our WAXI research colleagues from the various Institutions from around the world. This manuscript has benefited by the comments made by W. Witt, D. Huston and L. Vandenberg.

Notes

¹ The nomenclature of the GTO used here is a modification of that established by Blake et al. (1979).

² These are SHRIMP U–Pb zircon geochronological data collected by the authors, and are included in an unpublished manuscript.