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Toongi, Dubbo Zirconia Project |
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New South Wales, NSW, Australia |
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Zr REE Nb Ta U
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Toongi zirconium, niobium, tantalum and rare earth deposit, the basis of the Dubbo Zirconia Project (DZP), is located 30 km south of Dubbo in central western New South Wales, Australia, ~400 km north-west of Sydney.
The deposit is hosted by the Toongi trachyte intrusive, exposed as an oval shaped Jurassic aged volcanic mass that has an ~900 m east-west axis and is ~600 m north-south, covering an area of ~36 ha, and has an indeterminate depth extent.
The Toongi trachyte is one of a number of alkaline bodies which form part of a relatively extensive alkaline volcanic complex in the Dubbo region, composed of both intrusive and extrusive trachytic rocks, which in turn are related to the major Eastern Australian alkaline igneous event. It intrudes into and overlies a flat lying sequence of interbedded sandstone and siltstone of the Triassic Napperby Formation.
The Napperby Formation in the Toongi-Dubbo area represents a south-western embayment of the Permo-Triassic Gunnedah Basin, and rests unconformably on Silurian and Devonian rocks of the Lachlan Fold Belt. This basement includes mixed sedimentary and igneous rocks, including acid volcanic suites of the Silurian Toongi Group mainly to the west, while to the south and east the dominant rocks are mixed sedimentary and igneous rocks of the Devonian Hyandra Creek and Gregra Groups, as well as Devonian granitoids of the Yoevil Batholith and slightly older mafic to intermediate intrusive rocks.
The trachytic complex in the Toongi-Dubbo district is interpreted to represent a 210 to 185 Ma volcanic complex that commenced with basaltic sheet flows overlain by a 10 to 25 km diameter trachytic lava and tuff cone, culminating in late trachytic domes and finally the mineralised intrusive phase at ~184 Ma (Alkane Resources, 2011).
The northern, western and southern margins of the intrusive trachytic mass are marked by a narrow zone of silicified and chalcedonic quartz-veined trachyte, interpreted to represent an intensely silicified and veined chilled margin. This siliceous zone is generally quite narrow, usually <5 m thick. This outer zone commonly has lower grades and lower metallurgical recoveries. Narrow, 2 to 3 m thick basalt dykes cross-cut the ore body. The Napperby Formation is also intruded by basalt and trachyte sills thought to be of similar age to the Toongi trachyte.
Weathering of the ore body is limited to a 15 m depth, although minor oxidation is observed to as deep as 40 m below the surface, while there is some evidence that the depth of oxidation is greater in the eastern portions of the mass.
Drilling indicates that the Toongi trachyte is not a volcanic plug as initially interpreted, but rather a volcanic sill or flow. A further (Railway Prospect) trachyte development 4 km to the north of the main Toongi intrusion occurs as a broadly sub-horizontal mineralised flow which unconformably overlies Napperby Formation sediments. This ~55 to 65 m thick volcanic package appears to gradually thicken to the east where it is >84 m thick.
The Toongi trachyte is dominantly composed of K-feldspar, albite and aegerine microphenocrysts set in a very fine grained groundmass of similar composition. Limited mineralogical and textural variations, such as vesiculation and coarser grain sizes, have been identified and are associated with minor grade variations, but overall the intrusive contains highly elevated grades, both laterally and vertically, of zirconium, niobium, tantalum, hafnium, yttrium and other rare earth elements (REE's) distributed uniformly both laterally and vertically.
Mineralogical (SEM) studies indicate that ore minerals generally have extremely rare compositions and are very fine grained, being <100µm in size (most <20µm). Unnamed calcium and REE-rich zircono-silicates (similar to eudialyite or armstrongite) are the dominant ore minerals of zirconium and yttrium while natroniobite (NaNbO3) and calcian bastnasite are the major source of niobium and LREE's respectively. All these minerals are soluble in sulphuric acid and only very minor amounts of refractory zircon and a refractory niobium mineral (possibly columbite) have been detected. The orebody also contains low level uranium and thorium values, and would be classified as weakly radioactive.
More than 120, largely vertical, reverse circulation and a few diamond drill holes have been completed on a staggered 100 x 50 m grid, mostly to a maximum depth of 55 m, but including some that are deeper, confirming the continuity of ore grades to 100 m depth.
Identified mineral resources are (Alkane Resources, 2011):
Measured Resources from surface to a depth of 55 m (340 mRL) - 35.7 Mt @ 1.96% ZrO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.04% HfO2,
0.14% Y2O3, 0.75% other REO for 0.9% Total REO + 0.014% U3O8,
Inferred Resources from a depth of 55 to 100 m (295 mRL) - 37.5 Mt @ 1.96% ZrO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.04% HfO2,
0.14% Y2O3, 0.75% other REO for 0.9% Total REO + 0.014% U3O8,
TOTAL RESOURCE - 73.2 Mt @ 1.96% ZrO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.04% HfO2, 0.14% Y2O3, 0.75% other REO, 0.014% U3O8
Estimated ore reserves are (Alkane Resources, 2012):
Proved reserves - 8.07 Mt @ 1.91% ZrO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.04% HfO2, 0.14% Y2O3, 0.75% other REO,
Probable reserves - 27.86 Mt @ 1.93% ZrO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.04% HfO2, 0.14% Y2O3, 0.75% other REO,
TOTAL RESERVES - 35.93 Mt @ 1.93% ZrO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.04% HfO2, 0.14% Y2O3 and 0.75% other REO.
This summary is largely drawn from releases available from the Alkane Resources website.
The most recent source geological information used to prepare this decription was dated: 2012.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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