Interpretation of Multi Element Geochemistry in the Charters Towers Region

Transcription

1 Interpretation of Multi Element Geochemistry in the Charters Towers Region Gregg Morrison & Simon Beams & Terra Search Project Team

2 CT MM geochem: Introduction Terra Search/GSQ Explorer 3 database is a comprehensive geochem data set Used extensively by all players in C.T. region Augmented by company data for this project thanks to Resolute/Carpentaria/MIM; Mt Leyshon G.M./ Normandy; Ramelius; Mantle Mining; Liontown Resources; Denjim; Piccadilly G.M. Used to classify metallogenic camps And to model metal zones for selected deposits as exploration templates

3 CT MM geochem: Terra Search Database expansion Charters Towers Block Start of Project June ,000 seds (blue) 132,000 soils (red) 31,000 rock chip (green) 11,000 drill holes (black) May 2015 Data set to manipulate has grown to 181,000 soils 42,000 rock chip 16,600 drill holes

4 CT MM geochem : Au in soils reflects sampling strategy K O S, Far Fanning Charters Towers NW WMC, MLGM

5 CT MM geochem: Bismuth in 8257 (Ravenswood) Rishton Mt Wright Ravenswood Mt Canton Bi is a good indicator of magmatic systems Distinguishes well P C porphyry gold from E.Dev. orogenic Silurian plutonic Cu Mo also have Bi enriched Can also be enriched in Cu rich VMS Bullseye Camp Oven 3 Sisters

6 Metallogenic classification using ME data average granod enrich Ag As Au Ba Bi Cu Mo Pb Sb Sn Te W Zn Au Ag Pb Bi(As Cu) +/ Te Zn 46 element ICP data languishes IOGAS and Leapfrog interpretation used more for rock type Use typical hydrothermal metals for class & zoning CLASSIFICATION METHODOLOGY Based on 11 metal set Au Ag As Sb Pb Zn Cu Bi Te Mo W Select metals & sort (use Clark to eliminate BLD values) Average metals for population. Normalise to background List relative enrichment in orders of magnitude Scheme based on ~100 examples from Charters Towers region

7 CT ME geochem: Classification using multi metal data Porphyry level IRGS have AU PM BI TE (polymetallic ) Bi dominant in felsic and Te dominant in mafic intrusive systems Plutonic Cu has Cu Mo Bi +/ peripheral As Pb Zn Orogenic Gold have Au basemetals +/ As Te (no Bi) Epithermals tend to be Au As dominated Element Class Deposit Type Core Age Example AU PM BI felsic IRGS Mo W Bi CARB PERM Mt Wright AU PM BI TE intermediate IRGS Cu Mo CARB PERM Mt Leyshon AU PM TE BI int mafic IRGS Cu Mo, Cu Au CARB PERM Mt Remarkable AU AS BI TE+/-BM mafic porphyry IRGS Cu Au LCARB, DEV? Ravenswood AU AS TE BI mafic plutonic IRGS? Au? CARB, DEV? Mt Clearview CU MO plutonic IRCS Cu Mo, Mo SIL Titov AU BM +/- AS, TE orogenic intrusion hosted EDEV Charters Towers AU +/- TE AS BM epithermal ECARB, PERM Pajingo AS=As+/ Sb; AU=Au+/ Ag; BM=Cu+Zn+Pb; PM= Cu+Pb+Zn+As+/ Sb

8 CT ME geochem: Interpretation of ME calculation Previous example Quartz veins shear zone sericite alteration porphyry dikes Au basemetal in complex comb quartz veins Au Ag Pb Bi (As Cu) +/ Te Zn Class AU PM BI TE porphyry level Bi +/ Te Intermediate IRGS Ag Pb As distal basemetal As zone at surface potential deeper in Cu proximal zone

9 CT ME geochem: Classical porphyry zoning patterns Ideal pattern: Ca F peripheral Hg Sb As distal AS Pb Zn Ag distal BM Cu Bi Au proximal BM Cu Mo Te Core Varies by igneous source Mafic Cu Au core e.g. Plateau Interm. Cu Mo core e.g. Mt Leyshon Felsic Mo W Bi core e.g. Mt Wright Best Au progressively more distal mafic to felsic Cu Au core Plateau Au Bi Te Cu proximal BM Mt Leyshon Zn Cu Pb Bi Au distal BM Kidston

10 KIDSTON Pipe Metal Zoning Confined in pipe Overall zoning on a Thermal gradient Au only above sill With Pb-Zn-Cu Deep Mo-W-Bi Classify: IAMX Exposed distal BM Core Mo-W- Bi

11 CT ME geochem: metal zoning method. With two or three dimensional data sets and a few hundred data points It is possible to build a metal zoning model Do Z score(standard deviation) test on each element to make all elements equal Plot the Z scores in plan or section and manually look for spatial overlap of metal concentrations Combine and average Z scores for multiple elements to define zones Or do a PCA on the Z scores to define element clusters Contour zones or display in Leapfrog

12 CT ME geochem: Three Sisters metal zoning Data source & collaboration Carpentaria Gold

13 Ravenswood District: Ravenswood Town metal zoning Centred on Area 4 Fault in Sarsfield pit With the deepest mineralisation Zoning of key metals up & out Mushroom shape from to central feeder and dispersion in re activated structures Zoning reflects declining temperature Consistent with alteration zones best ore shallow central Ore by fluid decompression At structure intersection

14 CT ME geochem: Mt Leyshon metal zoning confined 3600 me 3700 me 3800 me 3900 me 4000 me 4100 me 4200 me GR and DL MPBX 6200 mn 5600 mn 5700 mn 5800 mn 5900 mn 6000 mn 6100 mn GR and DL MPBX MLBX Au > 0.4 ppm Cu > 500 ppm Pb > 500 ppm Zn > 1000 ppm MLBX MPBX MP PYRITE K FELDSPAR DIKES TS MLD508 MLD507 MLD506 MLD509A MPBX Mine Fault 6200 mn 6100 mn 6000 mn 5900 mn 5800 mn 5700 mn 3700 me 3800 me 3900 me MHBX 4000 me 4100 me 4200 me

15 IRGS NQ Mt Wright soil and rock metal zoning Zn Ag Pb Pb Zn 3km diameter soil anomaly Zn, Bi, Au only 5ppb on hill 1km tall system, well zoned Au 0.1ppm at surface, Best Au ore m below

16 3 element Z score plot Mt Wright Pb Zn Ag (0.1 Au) Zn Ag Au(lo grade) Au Bi Cu (ore) inner Au Cu (ore)

17 MM data interpretation: Metal Zoning in IRGS model Overall metal association distinguishes crustal levels of systems As Sb typical epithermal Basemetals typical porphyry level Bi Te without basemetals plutonic

18 Conclusion Plenty of scope for interpreting ME data Sort rock types & alteration Classify hydrothermal systems Zoning models Most direct in system vector for Au