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Pajingo, Vera-Nancy, Scott, Cindy, Steph, Camembert, Lynne |
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Queensland, Qld, Australia |
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Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Pajingo mine has been largely based on the Vera-Nancy group of adularia-sericite, low sulphidation, high grade gold-silver orebodies, located some 150 km SSW of the city of Townsville and 53 km south of Charters Towers, in north Queensland, Australia. Other veins include Scott, Cindy, Steph, Camembert and Lynne, which with Vera and Nancy, which are in the centre of the trend, are distributed over a NW-SE strike length of ~6.5 km. These deposits form a zoone that is exposed to the north and plunges gently to the SE where they are concealed at depths of ~200 m.
Gold was originally discovered by Battle Mountain Gold Company in the Pajingo Goldfield in 1983. Mining commenced on the Scott Lode in 1987 as an open pit operation. In 1991 Battle Mountain entered into a joint venture with Normandy Mining Limited. Following the discovery of the small Cindy orebody in the late 1982, the Vera and Nancy lodes were discovered in 1995. Underground mining commencing in 1996. In 2001, Newmont acquired Battle Mountain Gold and in 2002 after also taking ownership of Normandy controlled 100% of the operation. In 2007, North Queensland Metals and Heemskirk Consolidated purchased Pajingo from Newmont. In 2010, Conquest Mining Limited acquired 100% of Pajingo via its takeover of North Queensland Metals and purchase of the Heemskirk Consolidated share of the operation. In November 2011, Evolution Mining Limited was formed through the amalgamation of a number of operations including Conquest Mining and Pajingo. In August 2016, The Pajingo mines were acquired by Minjar Gold, a wholly owned subsidiary of Jinan Hi-Tech Development Co. Ltd, which is a listed company on the Shanghai Stock Exchange. Gold production has continued throughout since 1996, with new deposits having been delineated within the mineralised system that occupies a circle of ~7 km radius defining an area of around 150 sq km. The larger Vera-Nancy line of deposits were discovered in 1994-95 and mining commenced in 1997, with high grade gold having subsequently been delineated over a strike length of about 3 km and to depths of more than 400 m.
The Pajingo mineralisation is in the northern portion of the Drummond Basin which was filled by Late Devonian to Carboniferous, largely continental, sediments and volcanics, comprising lower arenites, passing up into andesites, terrestrial sediments and felsic tuffs. It overlies the Ordovician to Devonian Lolworth-Ravenswood Batholith and lower Palaeozoic volcano-sedimentary packages to the north which host the Charters Towers, Ravenswood and Mount Leyshon gold deposits.
The immediate host sequence, the Vera-Nancy Volcanics, are composed of massive, variably porphyritic andesitic lava, porphyritic andesitic lithic tuffs (fine ash to bomb size), lesser amygdaloidal lava, volcanic breccia and local epiclastic volcaniclastics of probable 350 Ma age. These volcanics have been weathered to an average depth of 70 m. The surface expression of veins is often as low ridges of silicified, brecciated, moderately to strongly quartz-veined andesite which persists to depths of as much as 200 m before classic epithermal veins are intersected.
The vein field at Pajingo, which occupies an area of some 140 square kilometres, corresponds to a zone of thickening of the andesite, interpreted as representing a main volcanic centre. Numerous epithermal quartz-veins are hosted by NW, NE and E-W trending structures, which are mostly steeply dipping and from a few cms to occasionally 20 m in thickness. They are normally enclosed by an envelope of silicification that may be up to 50 m thick.
Rheology contrasts of enveloping host rocks are important for vein development, with the maximum dilation occurring below a massive andesite horizon in the footwall of Vera, which is juxtaposed against the porphyritic andesite forming the footwall lithology. Volcaniclastic andesite is a relatively poor host to mineralisation, although these units are strongly altered, suggesting they are permeable, but poor in focussing fluids. Sinters are found locally in spatial association with known mineralisation at Lynne and Camembert. At Lynne, the overlying Moonlight mineralisation comprises higher grade stringer veins which propagate through sinter with significant alteration beneath and above these horizons. These relationships suggest mineralisation continued after the sinter was formed (Osborne and Chambers, 2017).
The Vera-Nancy series of lodes occur as shoots within a structure which is up to 7 km in length, strikes north-west, dips at 55 to 85°SW, and hosts other high grade shoots beyond Vera and Nancy. This structure is interpreted to be a strike-slip fault with the individual shoots such as Vera and Vera North developed in dilational jogs. Most economic shoots have strike lengths of 150 to 500 m and extend down dip for 100 to 400 m and are 1 to 10 m thick. Gaps exist between shoots where quartz development is limited, although the host faults generally persist.
Propylitisation, characterised by dark green chlorite, extends for up to 80 m outwards from the veins, grading to strong phyllic alteration dominated by silica-pyrite adjacent to the veins. Moderate to strong hematite dusting occurs on the outer margin of the phyllic zone, overprinted by the silica-pyrite. The silica is a grey translucent chalcedony with fine grained pyrite accounting for up to 40% of the rock mass. Some minor argillic alteration (illite-smectite and kaolinite-dickite) is also included within the phyllic zone (Porter, 1990).
Osborne and Chambers (2017) describe the alteration halo as follows, from proximal to distal:
• Inner proximal zone - moderate to strong silica-pyrite alteration comprising pyrite ±silica ±kaolinite ±illite;
• Outer proximal zone - transitional silica-illite alteration comprising illite-smectite ±pyrite;
• Medial zone - comprising hematite ±interlayered illite-smectite ±smectite;
• Distal zone - chlorite alteration comprising chlorite ±calcite.
Alteration halos are asymmetric, extending for several tens of centimetres along lithological boundaries into the hanging wall, whilst in the footwall of veins the haloes are spatially restricted and tend to parallel mineralisation. However, as stated above in more permeable hosts these haloes may be more extensive.
Gold is present as fine grains (5 to 150 microns) and electrum in quartz and chalcedony veins enveloped by a halo of silicification and brecciation that is often strongly pyritic.
Production from the original Scott Lode amounted to 1.35 Mt @ 8.86 g/t Au, 29.4 g/t Ag.
The declared resource at Vera-Nancy prior to mining in 1997 was 1.68 Mt @ 14.1 g/t Au, 10.8 g/t Ag at Vera plus
0.8 Mt @ 12.0 g/t Au, 15.6 g/t Ag at Nancy.
The remaining reserve at Pajingo at the start of 2003 was 2.7 Mt @ 11.0 g/t Au, while the production in 2002 was 0.656 Mt @ 12.6 g/t Au.
Production from 1996 to the end of 2021 has totalled ~105 tonnes of recovered gold (Minjar Gold website, 2022).
Remaining Ore Reserves and Mineral Resources as of 2011 were (Evolution Mining Pajingo Fact Sheet, 2011):
Mineral Resources - 4.84 Mt @ 5.8 g/t Au containing 28 tonnes of gold;
Ore Reserves - 0.77 Mt @ 6.2 g/t Au containing 4.8 t of gold.
Remaining Ore Reserves and Mineral Resources as at 31 December 2012 (Evolution Mining Annual Report, 2012) were:
Mineral Resources, open pit - 0.231 Mt @ 3.6 g/t Au containing 0.8 tonnes of gold;
Mineral Resources, underground - 5.16 Mt @ 5.3 g/t Au containing 27.2 tonnes of gold;
Ore Reserves, open pit - 0.214 Mt @ 3.3 g/t Au containing 0.8 tonnes of gold;
Ore Reserves, underground - 0.904 Mt @ 5.06 g/t Au containing 27.2 tonnes of gold.
Remaining Ore Reserves and Mineral Resources as at 31 December 2015 (Evolution Mining Annual Report, 2016) were:
Mineral Resources - 2.54 Mt @ 7.04 g/t Au containing 17.9 tonnes of gold;
Ore Reserves - 0.55 Mt @ 5.97 g/t Au containing 3.3 t of gold.
NOTE: Mineral Resources are inclusive of Ore Reserves.
As Minjar Gold is not listed on the ASX, and Shanghai Stock Exchange reporting rules do not require resources/reserves to be published, no estimates are available post 2016. It is producing ~2.4 tonnes of gold per annum as of 2021 (Minjar Gold website, 2022)
The most recent source geological information used to prepare this decription was dated: 2017.
Record last updated: 9/6/2022
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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Selected References:
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Anonymous 1998 - Vera-Nancy (incl. Pajingo): in Register of Australian Mining 1997/98 p 198
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Anonymous 1998 - Normandy Mining Limited: in Extracts from the Normandy Mining Limited 1997 Annual Report pp 12-15, 26-28
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Anonymous 1998 - Normandy Mining Limited: in Extracts from the Normandy Mining Limited 1997 Annual Report pp 12-14, 17, 26-28.
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Bobis R E, Jaireth S, Morrison G W 1995 - The anatomy of a Carboniferous epithermal ore shoot at Pajingo, Queensland: setting, zoning, alteration, and fluid conditions: in Econ. Geol. v90 pp 1776-1798
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Cornwell J and Tredinnick I, 1993 - Geology and geochemistry and mining of the Pajingo epithermal vein system: in 17th International Geochemical Exploration Symposium (IGES), May 1995, Townsville, Qld pp 54-68
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Evans, R.C. and Jones, B.H., 1997 - The discovery and evaluation of the Vera-Nancy deposit, North Queensland: in World Gold 97 Conference, Singapore, 1-3 September 1997, AusIMM Pub., Melbourne, Ser. no. 2/97, pp. 233-237.
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Osborne, D.J. and Chambers, C.D., 2017 - Pajingo gold deposit: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The Australasian Institute of Mining and Metallurgy Mono 32 pp 717-720.
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Parks, J. and Robertson, I.D.M., 2003 - Pajingo epithermal gold deposit, NE Queensland: in CRC LEME 2003 www.crcleme.org.au/RegExpOre/MtLeyshon.pdf pp. 1-4
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Porter R R G 1990 - Pajingo gold deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1483-1487
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Richards D R, Elliott G J, Jones B H 1998 - Vera North and Nancy gold deposits, Pajingo: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 685-690
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White, N.C., Leake, M.J., McCaughey, S.N. andd Parris, B.W., 1995 - Epithermal gold deposits of the southwest Pacific: in J. of Geochemical Exploration v.54, pp. 87-136.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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