pmd CRC GOLD MINERALISATION IN IN THE TASMAN FOLD BELT SYSTEM, NORTHEASTERN QUEENSLAND, AUSTRALIA

Transcription

1 pmd CRC GOLD MINERALISATION IN IN THE TASMAN FOLD BELT SYSTEM, NORTHEASTERN QUEENSLAND, AUSTRALIA G.S. G.S. Teale Teale 1, 1, I.M.A. I.M.A. Vos Vos 2, 2, F.P. F.P. Bierlein Teale 1 Teale && Associates Associates Pty Pty Ltd, Ltd, PO PO Box Box 740, 740, North North Adelaide Adelaide SA SA 5006, 5006, Australia Australia 2 pmd*crc, 2 pmd*crc, School School of of Geosciences, Geosciences, Monash Monash University, University, VIC VIC 3800, 3800, Australia Australia

2 Tasminides in * Eastern Australia Major lode gold deposits Queensland 1 2 edge of Precambrian craton Hodgkinson - Broken River Fold Belt Thomson Fold Belt 3 Major Lode Gold Deposits 1. Charters Towers 2. Ravenswood 3. Gympie 4. Hillgrove 5. Hill End 6. Walhalla 7. Bendigo 8. Ballarat 9. Stawell 10. Beaconsfield South Australia New South Wales 4 New England Orogen 5 Delamerian Victoria Lachlan Orogen Bierlein & Crowe (2000) Tasmania km

3 Central Victoria Central Victorian Goldfields have produced 2500 tonnes of gold. Deposits occur in quartz-rich turbidites of Cambro- Ordovician (Bendigo-Ballarat Zone) to Early Devonian (Melbourne Zone) age. Metamorphic grade ranges from zeolite to greenschist facies. The role of carbonaceous sediments is possibly important but debated Gold mineralisation is metamorphic related (orogenic) and pre-dates intrusive activity by as much as 80Ma.

4 Location Qld Cairns Innisfail 146 E Camel Creek Big Rush Area North East Queensland 19 S Greenvale Camel Creek Ingham CORAL SEA 19 S N Townsville Big Rush 0 100km 146 E Charters Towers 118 G Teale 2004

5 Broken River Province Production of approximately 3 tonnes of gold with little alluvial gold present. Deposits and prospects occur in a sequence that ranges from Ordovician to Carboniferous. Metamorphic grade ranges from sub-greenschist to greenschist. The role of carbonaceous sediments was important.

6 Gold mineralisation is orogenic and pre-dates Permo- Carboniferous intrusive activity (eg mineralisation can be contact metamorphosed). Pyrite, arsenopyrite, stibnite and trace to rare gold, aurostibite, chalcopyrite, berthierite, tetrahedrite, boulangerite, galena and sphalerite. Dominant gangue phases in high grade reefs are quartz, carbonate and lesser white mica and chlorite.

7 Camel Creek Mine Camel Creek Area North East Queensland Camel Camel Creek Homestead Creek Blue Gold Beatrice Jacko, Jacko Extended Red Gold Mt Jimmy Dora Creek Ryeburn Homestead AP Gold Spartan Dead Horse Golden Cup Kangaroo Hills Homestead N Mt Lyall 115 G Teale 2004

8 Reserve drilling at the Blue Gold prospect, Amanda Bel Goldfield, 1988

9 4000 N Black Bull N 3000 N Pit M 0 metres N 1000 N Central Pit South Pit Camel Creek Area North East Queensland Mining Zones 116 G Teale 2004

10 Melange in South Pit, Camel Creek Mine

11 Transposed and boudinaged greywacke beds in carbonaceous shales, Camel Creek Mine

12 480 RL 1040 E 1060 E 1080 E 1100 E GA68 RT g/t GA48 Orebody Outline 460 RL RT 188 RT g/t 2.5 g/t RT g/t 7.5g/t 3.5g/t 0.42 g/t 2.03 g/t 440 RL Camel Creek Mine Central Pit Section 1970N (looking grid north) 0 10m 2.9 g/t 117 G Teale 2004

13 Free gold associated with sphalerite in massive stibnite 0.12 mm

14 Gold developing after aurostibite and enclosing quartz gangue 0.12 mm

15 Closer view of previous slide. Aurostibite is being replaced by gold + stibnite ± native antimony mm

16 Gold in textural equilibrium with stibnite. Stibnite adjacent to the gold grain contains 0.7% Au mm

17 Fluid Inclusion Study The simple two phase liquid-vapour nature of the inclusions and the absence of gaseous phases like carbon dioxide or methane suggest that water was the main fluid constituent. No evidence of boiling which could be related to ore deposition was recorded. Fluid salinities between 2 and 5 wt% NaCl equivalent. Homogenisation temperatures suggest minimum fluid trapping temperatures between 160ºC and 300ºC. The inclusions are typical of orogenic gold deposits (lower T end) and have similar salinities, pressures and compositions.

18 Homogenisation T Amanda Bel Goldfield Th (Deg C) Camel Creek Golden Cup Red Gold Frequency

19 Location Qld Cairns Innisfail 146 E Camel Creek Big Rush Area North East Queensland 19 S Greenvale Camel Creek Ingham CORAL SEA 19 S N Townsville Big Rush 0 100km 146 E Charters Towers 118 G Teale 2004

20 Central Pit area at Big Rush during a pit blast.

21 BR RL 480 RL Orebody Outline BR g/t 1.07 g/t 1.51 g/t 1.07g/t 1.08 g/t 1.44 g/t 1.04 g/t 1.45 g/t 1.73 g/t 470 RL 460 RL 0.74g/t 0 10m 0.5 g/t 1.06 g/t Big Rush Mine SOUTH PIT Section N E 0.32 g/t E E E 113 G Teale 2004

22 460RL Level plan showing high grade mineralisation and enclosing arsenopyrite-rich halo

23 South North 500 RL 400 RL Grade Control values greater than 5g/t 19.9g/t 11.3g/t incl. 45g/t 8.9g/t 15.8g/t 12.89g/t incl. 44.1g/t 32.9g/t 10.9g/t 17g/t 11.42g/t 11g/t 6.22g/t 6.64g/t 7.57g/t 5.14g/t 5.96g/t 22.08g/t 12.95g/t incl. 43.6g/t 12.54g/t Final Pit Outline 51.6g/t incl g/t 6.48g/t incl. 41.1g/t 18.8g/t g/t 0 50 m Big Rush Mine Central Pit - Longitudinal Section Intercepts > 5g/t Au 118 G Teale 2004

24 Controls on Mineralisation, Big Rush Deposit 1. Presence of highly carbonaceous (including graphite), pyritic and calcareous shales. 2. Presence of tuffaceous sandstones intercalated with carbonaceous shales. These act as conduits for mineralising fluids. 3. Structural control on mineralisation of strong axial planar cleavage (020º-030º) developed in tight parasitic folds in black shales (axial planar reefs and veins, disrupted saddles) and/or open folds in greywacke/sandstone units (saddle reefs, 3-dimensional quartz-sulphide stockworks).

25 4. Slightly oblique shears and fault structures cutting the main mineralised package. 5. Plunge variation of folds on the local scale in conjunction with a mild warping of the fold structure. 6. Intersection of subtle 110º structures with the main Big Rush trend appears to cause blow-outs in the mineralisation.

26 Wallrock Alteration Development of ankerite, sericite, quartz and arsenopyrite in carbonaceous shales. This alteration domain can contain 0.5ppm to 1ppm gold. Forms a significant proportion of oxidised heap leach ore. Arsenopyrite scorodite (FeAsO 4.2H 2 O) hydrated iron oxides; gold released and is amenable to cyanide leaching.

27 Mineral Chemistry Wide range of chlorite and carbonate compositions from deposit to deposit and within each deposit. Gold generally contains ~10% Ag. Arsenopyrite can contain from below detection gold to 1.5% gold. Stibnite can contain up to 0.7% gold.

28 Any questions?