Exploration Geochemistry: Updating Its Contribution to Mineral Resource Development. L. Graham Closs Colorado School of Mines.

Transcription

1 Exploration Geochemistry: Updating Its Contribution to Mineral Resource Development. L. Graham Closs Colorado School of Mines May 22, 2012

2 Geochemistry in the Exploration Process

3 Means of Contributing to Mineral Resource Development

4 Improving GX Contribution Breakthrough Approach ( Silver Bullet ) Continuous Improvement Approach Revisiting Underutilized Concepts and Technologies

5 Exploration versus Science Exploration uses science but is not science since it s aims are fundamentally different. Science strives for understanding, whereas exploration strives solely for discovery, with or without understanding, by whatever means. MEANS versus Ends! after Muessig (1979, 2011)

6 Fit For Purpose (FFP) the degree to which data produced by a measurement process enables a user to make technically and administratively correct decisions for a stated purpose Thompson and Ramsey, 1995.

7 Exploration Geochemistry Survey Components Planning and Design Field and Laboratory Sampling Chemical Analysis Data Interpretation

8 Components of Exploration Geochemistry Surveys Each part of the sequence depends on proper execution of the previous component of the geochemical program. Evaluate the weakest link in the sequence. Lavin, 1981 If you fail to pay appropriate attention to one of these components, you jeopardize the whole program.

9 Planning and Design Critical Issues Targeting Suggested approaches: Conceptual Models - examples from the tropics Orientation Surveys - objectives / strategies

10 Surficial Conceptual Models What they are: an effort to develop idealized models for the systematic description of exploration geochemical data which adequately describe, in easily understood form, the principles and mechanisms of formation of anomalies which govern the use of exploration geochemistry.

11 Regional Regolith Mapping in Lateritic Terrain (CSIRO RED System) Regolith Mapping

12 Regolith, Landforms and Sample Media Anand and Butt, 2010

13 Contrasting Exploration Approaches Based Upon Regolith Mapping RESIDUAL AREAS Complete Profile EROSIONAL AREAS Truncated Profile Exposed 1. Laterite 2. Derived lag or coarse soil 3. Open-spaced sampling Exposed 1. Gossan 2. Ferruginous lag or coarse soil 3. Closed-spaced drilling Covered 1. Stratigraphic drilling 2. Define buried laterite areas 3. Open-spaced drilling 4. ID and sample residual laterite Covered 1. Drilling 2. Good regolith logging 3. Sub-horizontal supergene Au Smith et al, 1992 CSIRO

14 Surficial Conceptual Models Terrain Surface Dispersion Models Currently Available 1. Canadian Cordillera & Canadian Shield Norden (Scandinavia) Basin and Range (SW US / N Mexico) Tropical rain forests Deeply weathered terrain (Australia) Tropical terrain Periglacial deep weathering Tropical and subtropical terrains Arctic and temperate terrains Australian Continent 2005 Models vs Modeling: the process is ongoing!

15 Sampling What? - Back to conceptual models How? - Back to orientation surveys

16 Conceptual Model Tropical Rain Forest

17 Major Pedo-Morphological Units Tropical Rain Forest

18 Does the exploration approach provide thorough assessment of the area?

19 Orientation Surveys: A pilot investigation to establish optimum routine field, analytical and interpretative procedures to confidently recognize true anomalies. Conducted before routine survey work is initiated Orientation Survey Needs Types of Orientation Survey clear understanding of target type(s) knowledge of surficial environment sample type(s) available - optimize sample collection procedures sample interval, orientation and density field observations required sample size requirements sample fraction(s) for analysis analytical methods selection geochemical suite for analysis data format for interpretation etc. public data review case histories consultants traditional - field & laboratory combination approach

20 Chemical Analysis Chemical analysis update total vs partial Current / special situations Field Portable Analysis (FPXRF) Fit-For-Purpose Concept QA / QC: Components / Regulatory requirements

21 Which Selective Extraction? Enzyme Leach Leach Sodium Pyrophosphate Ammonium Acetate Cold Hydroxylamine HCl Hot Hydroxyamine HCl Ammonium Oxylate Bioleach SGH MMI Cyanide Target Material Amorphous MnOx Organic matter Carbonates Amorphous Mn oxides Amorphous Fe + Mn oxides Amorphous Fe + Magnetite Metals from cell membranes Soil Gas Hydrocarbons Weakly sorbed cations Au (also Ag, Cu + others)

22 Current Common Options Total Digestion Mapping 4 Acid digestion General Partial Digestion Exploration Aqua Regia update Partial Extraction Options Special problems

23 Matching Dispersion, Sampling & Analysis Targeting Process (from Cohen, 1993)

24 Analytical Data Quality Fit For Purpose

25 Field Portable Exploration Geochemistry What do we mean by field portable? Goal: real-time, onsite measurement of geochemical parameters of interest for immediate decision making by professionals and next stage exploration program planning and implementation Characteristics: small, lightweight, rugged, easy to operate (field personnel), easy to transport, safe to operate, computer - processable data capture, multimedia analysis capability, and cost effective

26 FPXRF Applications (What is it you really want to sample?)

27 Stream Sediment Homogenized Sample Variability (field standard) Sample Variability Instrument Variability Arsenic 120 seconds 9 Points on a sample bag Minimum 14.3 ppm Maximum 41.8 ppm Mean 28.1 ppm Median 24.7 ppm Std. Dev. 8.0 ppm Error 8.4 ppm Arsenic seconds 10 Analyses same point Minimum 21.5 ppm Maximum 29.6 ppm Mean 26.5 ppm Median 26.4 ppm Std. Dev ppm Error 7.8 ppm.

28 Common Element Interferences 50 Peak Height (counts per second) FeKa FeKb CoKa No CoKb ZnKa ZnKb PbLa AsKa No AsKb No SeKa PbLb SeKb Energy Level (KeV)

29 Geochemist as QP NI has numerous sections that deal with laboratories and quality control protocols. Some of these include: details regarding sample preparation, assaying and analytical procedures used and whether the laboratories are certified by a standards association and the particulars of any certification. a summary description of the type of analytical or testing procedures utilized, sample size, the name and location of each analytical or testing laboratory used, the certification of each laboratory and any relationship of the laboratory to the issuer.

30 Data Interpretation and Implementation Conceptual and Technological Contributions Conceptual catchment basin analysis framework Statistical population analysis Spatial / Visualization Improvements mapping deposit geochemical signatures 3-D geochemical mapping

31 Catchment Basin Analysis Representation of GX results within catchment basins. Requires delineating basins based upon stream order. Classification exercise.

32 Evaluation Population Analysis >200 populations represent processes isolate individual populations determine their spatial relationships evaluate primary and secondary processes by spatial and multielement relationships

33 Map Interpretation Geology + Sample Locations

34 Summary Improving GX Contribution Breakthrough Approach Silver Bullet Continuous Improvement Approach Fit For Purpose Revisiting Underutilized Concepts and Technologies Surficial Conceptual Models/ Orientations Surveys