RATIO ANALYSIS IN LITHOGEOCHEMISTRY: QUANTIFYING ALTERATION AND INTEGRATING RESULTS INTO EXPLORATION EFFORTS. Elura GER - Discrimination Diagram

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1 RATIO ANALYSIS IN LITHOGEOCHEMISTRY: QUANTIFYING ALTERATION AND INTEGRATING RESULTS INTO EXPLORATION EFFORTS Y Index/Z Index Altered! Elura GER - Discrimination Diagram Muscovite, Ankerite Weathering 'Protolith' Siderite or non Ca carbonates Pyrite Altered Shale Altered Sandstone Weathered Altered Shale Weathered Altered Sandstone Background Shale Background Sandstone Weathered Background Shale Weathered Background Sandsto Background Weathered Chlr, Calc, Alb Goethite, Hematite, Kaolinite X Index/Z Index 1

2 PRESENTATION OUTLINE RATIONALE FOR LITHOGEOCHEMISTRY PEARCE ELEMENT RATIOS (PER) Examples Use in Exploration GENERAL ELEMENT RATIOS (GER) Examples Use in Exploration CONCLUSIONS 2

3 Alteration Haloes - Idealised Model WEATHERED ROCK WEATHERED CRYPTIC HALO WEATHERED VISIBLE HALO FRESH ROCK ORE DEPOSIT VISIBLE ALTERATION HALO CRYPTIC ALTERATION HALO FAULT - FLUID CARRIER Cryptic Alteration - Those mineral and elemental changes resulting from fluid-rock interactions related to a mineralising event.. In particular that alteration which is not visible to the naked eye. You may also like to include alteration which is very difficult to quantify with the naked eye, despite its presence being readily detectable Fresh and Weathered 3

4 WHY STUDY CRYPTIC LITHOGEOCHEMICAL ALTERATION? MORE EXTENSIVE THAN VISIBLE ALTERATION A SYSTEMATIC METHOD TO TRACK ALTERATION- RELATED MINERALOGICAL CHANGES IS NEEDED (RATHER THAN SUBJECTIVE ESTIMATES) - MORE RIGOROUS AND INFORMATIVE PATHFINDER ELEMENTS AND OTHER EXPLORATION RESULTS CAN BE OVERLAIN ON RATIO DIAGRAMS - MORE LAYERS = LESS RISK Extensive - greater footprint to target Using the ratio methods, can accurately model mineral changes - no statistical assumptions It is possible to calculate alteration strength or completeness - depending on the reactions involved. Combine with other pathfinders or key indicators to maximise potential of Discovery. 4

5 RATIO ANALYSIS SOLVES TWO BIG PROBLEMS CLOSURE AN ARTEFACT INDUCED IN DATA BY THE SUMMATION OF COMPONENTS TO 100% PRE-EXISTING LITHOGEOCHEMICAL TRENDS CHEMICAL VARIATIONS IN THE HOST ROCK WHICH EXISTED PRIOR TO THE ORE FORMING EVENT. THESE CAN BE GREATER IN MAGNITUDE THAN VARIATION DUE TO ALTERATION. 5

6 EXAMPLE PER DIAGRAM Calcium and Carbonate Controls PER DIAGAMS Calcite Effect Calcite 0.6 Ank/Dolo Effect Siderite Effect Ca/Zr 0.4 Ankerite, Dolomite Siderite C/Zr Minerals as Vectors Conserved Denominator Molar Values 6

7 CASE STUDY EXAMPLES: LOCATIONS AND SUMMARY Elura: Devonian Turbidite Host, Vertical Pods Crosscut Stratigraphy 8.5%Zn, 5.3%Pb, and 69ppm Ag Century: Proterozoic Shales and Siltstones (Shelf), Faulted or Erosional Truncations, Stratiform but Mildly Transgressive 10.2%Zn, 1.5%Pb, 36ppm Ag Elura Pods have a NNW trend to them 700m long. 7 Pods, with northern 5 400m below surface Elura main and second pod are exposed to the weathering profile Deposit possibly located at the tip of a blind thrust Dilational Model and Fluid Mixing Models proposed for Ore Formation Metal Carrying Solutions likely deep basinal.. Reduced acd???, possibly basement influence CSA Siltstone Bland - Lower Greenschist Metamorphism, good for lack of interfering metaomatism Half of the resource currently mined Century - large resource, no natural terminations, no equivalent of the ore sequence with 8 kilometres of the deposit. H4s shelf sediments - Proterozoic. Overlain by Cambrian Carbonate Low Fe Sphalerite, Sulphides parallel sediment layering, but mineralisation as a whole shallowly transgresses stratigraphy. Thermochemical Sulphate Reduction Model Theory of Oxidised near neutral brines. Weathering variable, certainly not the extensive preservation as at Cobar 7

8 ELURA 8

9 Elura: Calcium vs Carbonate Carbon Altered Shales Altered Sandstones Background Shales Background Sandstones Calcite Control Ca/Ti Ankerite Control C/Ti Note background altered and shale-sandstone split. No C addition to sands, but C addition in shales. Minor Ca loss, but not much. 9

10 Elura: Potassium and Aluminium Controls Altered Shales Altered Sandstones Background Shales Background Sandstones Muscovite Control 1 Illite Control 10 K/Ti Chlorite (Al - Na)/Ti (Sandstones only Adjusted) Split by lithology/lithotype and altered/background Shales muscovite Sandstones two paths - two resulting chemistries. 10

11 MAKING IT EXPLORATION-FRIENDLY 11

12 MAKING THE RATIOS USEFUL TWO BROAD WAYS TO DO THIS.. PLOT VALUES IN A SPATIAL SENSE COMBINE VALUES IN CHEMICAL SPACE TO VIEW MULTIPLE ALTERATION INDICATORS IN ONE PLOT 12

13 Targets Background Zone of Interest Area Approximately 20x10km North by East 13

14 0.36 Combination PER Diagram - Sb Overlay Muscovite 0.32 K/Al (Al-Na for Sandstones) Priority Exploration Targets Background Illite Sb: <= 1 Sb: (1,5] Sb: (5,10] Sb: > 10 Ankerite/Dolomite Calcite Ca/C Combined Method - best samples lie in the ellipse - Carb, K and Sb indicators. Chloritic sands should be monitored on this diagram, may plot outside the ellipse. 14

15 RQ mode PCA used to combine PER scores with trace element pathfinder responses. Good way to combine a lot of variables into one plot.. Should be used with caution, as assumptions need to be made during construction. 15

16 THINGS TO KEEP IN MIND SLOPES ON PER DIAGRAMS CAN BE USED TO QUANTIFY ALTERATION ONCE QUANTIFIED, THE MINERALOGICALLY AND CHEMICALLY CONSTRAINED ALTERATION NUMBER CAN BE PLOTTED LIKE ANY OTHER RAW ANALYSIS Except that it is far more informative! No closure effects and background has been removed! RESULTS CAN BE MADE SIMPLE ENOUGH FOR EXPLORATION TO USE! 16

17 EXAMPLE GER DIAGRAM Potassic and Structural Water Controls 1.0 K-Feldspar GER DIAGAMS Biotite K/Al 0.4 Goethite (vector) Muscovite 0.2 Albite, Anorthite Kaolinte Chlorite (4,0) OH/Al Minerals as Vectors Conserved Denominator Molar Values 17

18 Elura GER DIAGRAM Potassium, Structural Water and Aluminium Controls Altered Shales Altered Sandstones Background Shales Background Sandstones Muscovite 1 Biotite (2,1) Goethite K/AL Illite Albite, Andesite Kaolinite Chlorite (4,0) OH/AL 18

19 CENTURY Photo Courtesy of PASMINCO 19

20 20

21 Bit blurry because of new statistica format.. Sorry :/ Diagram used to show how elemental pathfinders can be overlain on the complicated GER diagrams 21

22 IMPORTANT POINTS GERs CAN BE USED AS A TEMPLATE TO PLOT TRACES, ISOTOPE RESULTS ETC ONTO USING GERs AS A TEMPLATE GIVES GOOD MINERALOGICAL CONTROL ON INTERPRETATIONS GERs OFTEN HARDER TO REDUCE TO A SINGLE NUMBER - LACK OF SIMPLE SLOPES HOWEVER IT IS POSSIBLE TO ZONE GER DIAGRAMS AND CODE SPATIAL PLOTS BY THESE ZONES 22

23 CONCLUSIONS RATIO ANALYSIS, ie PER, GER, ARE EXCELLENT TOOLS FOR INDENTIFYING AND QUANTIFYING ALTERATION PER, GER RESULTS CAN BE COMBINED WITH OTHER GEOCHEMICAL AND SPATIAL INFORMATION - EASY TO INCORPORATE INTO EXPLORATION EFFORTS PER AND GER DIAGRAMS AVOID CLOSURE, MODEL MINERALOGY AND CAN ACCOUNT FOR BACKGROUND VARIATION - THEY SHOULD BECOME THE STANDARD DATA ANALYSIS METHOD IN LITHOGEOCHEMISTRY 23

24 THANK YOU! Special Thanks to: UC AEG/IGES CRC LEME CRCLEME Cooperative Research Centre for Landscape Environments and Mineral Exploration CRCLEME 24

25 CLOSURE EXAMPLE! Extensive Moles in Original and Altered Samples Intensive Mole % in Original and Altered Samples Note how there are differences between concentration values, and the absolute values. Moles Mole % Original Sample Altered Sample A B C D E Element Original Sample Altered Sample A B C D E Elements 25