A structural examination of the Telfer gold-copper deposit and surrounding region, northwest Western Australia: the role of polyphase orogenic deformation in ore-deposit development and implications for exploration

Hewson, Simon Andrew John (1996) A structural examination of the Telfer gold-copper deposit and surrounding region, northwest Western Australia: the role of polyphase orogenic deformation in ore-deposit development and implications for exploration. PhD thesis, James Cook University.

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Abstract

The Telfer Au (+Cu) deposit is one of Australia's premier gold-producers, currently accounting for approximately 400,000oz. per year. It's discovery in 1972 heralded the recognition of the Proterozoic Paterson Province, in which it is located, as a polymetallic terrane with the potential for significant gold and base-metal mineralisation. The Paterson Province represents a small exposure (= 36 000km²) of the large NW -SE trending Paterson Orogen, a continental-scale orogenic belt that passes across northern Western Australia and into central Australia. Rocks in the Paterson Province have recorded a protracted Proterozoic history for this orogenic belt, which includes continent-continent collision at ~1250Ma (Watrara Orogeny) and late-Proterozoic collisional tectonism (the Paterson Orogeny) between 700 and 600Ma. The latter generated considerable mineralisation in middle- to late-Proterozoic metasedimentary rocks of the Paterson Province.

Late-Proterozoic mineralisation in the Paterson Province is well developed in the NE region where numerous syn- and post-tectonic granitoids, gabbros and dolerites intruded the metasedimentary sequence. However, mineral exploration in this region is commonly hindered by extensive Phanerozoic and Tertiary cover that precludes observation of much of the Proterozoic sequence. Additionally, the province lies within the Great Sandy Desert, and is thus covered by extensive aeolian sand deposits. The large amount of younger cover has resulted in relatively small scattered "windows" that expose the mineralised Proterozoic rock sequence. The NE region of the Paterson Province provides one of the best exposures of this sequence and hosts the Telfer deposit.

Sampling of gossanous and stratabound quartz veining in the Telfer Dome (a regional antiformal fold) in 1972 by geologists from both Day Dawn Minerals and Newmont Pty Ltd identified gold enriched horizons within the pelitic sedimentary sequence (Telfer Formation) exposed in the dome. Subsequent drilling of these horizons confirmed an initial resource of 1 Million ounces of gold and mining activity commenced in 1975. During the early 1980's mining concentrated on one particular reef that outcropped in Main Dome, a sub-dome of the Telfer Dome. This reef, the Middle Vale Reef (MVR) exhibited strong secondary enrichment of gold and has historically comprised a significant resource in the Telfer deposit (Dimo, 1990). During the middle to late 1980's a shift to high-volume low-grade mining was facilitated by the ongoing success of dump leach extraction of gold from rocks previously too low-grade to be milled. This incresased throughput caused production to expand to the second subdome (West Dome) as the E-Reefs were mined, and helped to make Telfer one of the top four gold producers in Australia during the late 1980's.

More recently, deep diamond drilling in Main Dome (commenced in 1992) has led to the discovery of approximately ten to twelve new reefs at depth in the dome. Underground mining, which had commenced in 1990, has been extended through an exploration decline 10 the upper of these newly discovered reefs (MIO and M30). This decline is currently being extended to reach the deepest reef, the 130, at approximately 1 100m below the present ground surface. This should occur by the end of 1997. Another consequence of the deep drilling has been the further confirmation of an epigenetic genesis for the Telfer deposit. and particularly the identification of mineralisation in units other than the Telfer Formation.

Initial research on the stratabound reefs in the Telfer deposit suggested that they had formed through syngenetic exhalative processes (Tyrwhitt, 1979; Turner, 1982). A variation on this, whereby the MVR was considered to have formed as an evaporite horizon that was subsequently replaced by quartzsulphide assemblages, was proposed by Royle (1985). However, the expansion of mining and deep drilling within the deposit provided increasing evidence for an epigenetic origin. This came both through structural observations and geochemical fluid-inclusion studies that indicated the reefs were locally discordant, had associated stockwork veining in both the foot- and hanging-walls, contained magmatic elements in the ore-assemblage and that the ore-fluids were of variable salinity and temperature (Goellnicht, 1987). These observations led to an epigenetic model whereby magmatic fluids from the regional granitoids had mixed with cooler connate/formational waters, and had precipitated in structurally controlled, and compositionally favourable, sites within the Telfer Dome (Goellnicht, 1987; Goellnicht et al., 1989). Subsequent research downgraded the role of the granites, suggesting that they acted more as heat sources to convectively circulate connate/contact-metamorphic fluids that scavenge elements from the sedimentary sequence (Hall & Berry, 1989; Rowins. 1994).

The changing ideas on the genesis of the Telfer mineralisation are reflected in the changing focus of mineral exploration in the Telfer region and the Paterson Province. Initial exploration, utilising the syngenetic exhalative model, concentrated on locating further outcropping Telfer Formation. The inferred variable thickness of exhalative lenses was considered to have assisted the formation of the regional domal antiforms (Turner, 1982), and consequently those domes that exposed the Telfer Formation were targeted. However, recognition of an epigenetic genesis has focussed exploration activity towards targeting favourable host structures, such as regional folds and other ore-fluid traps. The change in exploration strategy means that a greater reliance is now placed on the structural geological setting of mineralisation in the Paterson Province. This study represents the first formal examination whereby the structural geological setting of mineralisation in the Telfer Mine is integrated with the regional- and orogenic-scale tectonic development of the Paterson Province.

Item ID: 27718
Item Type: Thesis (PhD)
Keywords: Telfer mine; Great Sandy Desert, W.A.; Proterozoic Paterson Province; gold deposits; geological history; geological composition; exploration activity
Date Deposited: 26 Jun 2013 02:27
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 51%
04 EARTH SCIENCES > 0403 Geology > 040312 Structural Geology @ 49%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840199 Mineral Exploration not elsewhere classified @ 49%
84 MINERAL RESOURCES (excl. Energy Resources) > 8402 Primary Mining and Extraction Processes of Mineral Resources > 840299 Primary Mining and Extraction of Mineral Resources not elsewhere classified @ 51%
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