Maximising the value of NVCL HyLogger data: Understanding automated mineralogical interpretations Belinda Smith, Mark Berman, Ralph Bottrill, Tania Dhu, Suraj Gopalakrishnan, Georgina Gordon, David Green, Jon Huntington, Alan Mauger NORTHERN TERRITORY GEOLOGICAL SURVEY
Introduction • Aims – Understanding what the HyLogging NVCL is – New to HyLogging – understanding what it is and what it is telling you – HyLogger User – understanding the different levels of processing – Increase understanding of the methods and processes behind the mineral outputs from TSG. NORTHERN TERRITORY GEOLOGICAL SURVEY
National Virtual Core Library (NVCL) • AuScope NVCL initiative – started 1 in 2007 Material – Australia-wide drillcore Infrastructure 4 Access Infrastructure database comprising high- resolution imagery and mineralogical data from Technology Human spectroscopic scanning Infrastructure 2 – facilitate geoscience research Infrastructure – data available to the public via 3 a web-based delivery system NORTHERN TERRITORY GEOLOGICAL SURVEY
AuScope Portal http://portal.auscope.org/portal/gmap.html NORTHERN TERRITORY GEOLOGICAL SURVEY
HyLogging basics • Produces images of the core • Produces reflectance spectra (matched to minerals) • Improves objectivity of core logging • Enhances geological understanding • Sampling every 8mm x 8mm width for whole length of core Multiple data streams • Wallara 1 (1668m / 349 integrated in TSG software core trays) = 218,125 spectra NORTHERN TERRITORY GEOLOGICAL SURVEY
Automated Mineralogical Interpretation • Voluminous data with 100,000s spectra in a single drillhole • Hundreds of drillholes; thousands of metres nationwide • Automate the mineral matching with; – TSA (The Spectral Assistant). Refine with; – Restricting minerals in TSA (uTSA) – Creating domains in TSA (dTSA) – Using CLS with domains NORTHERN TERRITORY GEOLOGICAL SURVEY
Mineralogical Interpretation of HyLogger Data (XRD, petrography, SEM) External Validation CLS Recommended for TIR spectra Steps are not sequential Constrained Least processing (non-unique spectra) Squares Good for basement / seds drillholes Domaining (dTSA) Creating and using scalars TSA – User Matches (uTSA) uTSA +/- scalars Manual restriction of unlikely minerals Minerals match across whole hole sTSA The Spectral Assistant (TSA) – System Matches ALL DATASETS Algorithm matching to whole spectral library NORTHERN TERRITORY GEOLOGICAL SURVEY
TSA mineral matching • ‘Unmixes’ spectral response into mineral mixes of 2 (SWIR) or 3 (TIR) using an algorithm • Only matches to minerals in the library • If a mineral isn’t active in that wavelength range, you won’t see it • If there’s more than 2 - 3 (SWIR) or 3 -4 (TIR) minerals per spectrometer you won’t see them • It is NOT an assay! You get a indication of minerals present, NOT an absolute quantifiable modal value. • Nonetheless valuable as nothing else is as fast. NORTHERN TERRITORY GEOLOGICAL SURVEY
Strengths of TSA Mineral Outputs • Automated process which can handle (simple) mineral mixtures very quickly • Detailed: mineral match output for each spectrum (8mm*18mm) • Results returned as mineral names (rather than wavelengths) so outputs easily understood by geoscientists • Summary overviews can show bulk mineral changes in the entire drilled length NORTHERN TERRITORY GEOLOGICAL SURVEY
Detailed TSA outputs NORTHERN TERRITORY GEOLOGICAL SURVEY
TSA results…. sTSA Summary epidote SYSTEM TSA has ‘unsupervised/ unedited’ watermark. talc Mathematical fit; no geology used. Black shales, dolomitic quartz sandstones dolostones metamorphosed basement NORTHERN TERRITORY GEOLOGICAL SURVEY
TSA results…. uTSA Summary USER (uTSA) – has been refined to epidote still present dolomite exclude unlikely chlorite calcite minerals when spectral matching. BUT sediments amphibole show epidote, calcite talc phlogopite phlogopite gone (can’t exclude because they’re quartz in basement). NORTHERN TERRITORY GEOLOGICAL SURVEY
TSA results…. uTSA Summary DOMAINED Results have epidote still here been DOMAINED; no phlogopite, dolomite calcite chlorite epidote in sediments but epidote gone is in basement. calcite amphibole talc, phlogopite removed quartz NORTHERN TERRITORY GEOLOGICAL SURVEY
TSG SOFTWARE – mineral matching (TSA) SWIR & TIR results black = spectrum blue = modelled spectrum Well-crystalline kaolinite 100% SRSS = 146 black = Petermann Sandstone; from LA05DD01 spectrum Quartz 100% blue = Does not see modelled kaolinite feature Appears to be a well-sorted sandstone spectrum TSA SWIR response of wx kaolinite only TSA TIR response of quartz only black = SWIR can’t ‘see’ quartz spectrum 93% quartz, 6% kaolinite green = modelled spectrum CLS has quartz AND kaolinite NORTHERN TERRITORY GEOLOGICAL SURVEY
TIR Spectra Mixing TIR TSA non-uniqueness Result SWIR TSA says.. • FeMg Chlorite • Phengitic mica Slide courtesy Andy Green, OTBC Pty Ltd
CLS vs. TSA in the TIR • TSA can’t effectively look at as many mixtures in the TIR (n=3). CLS can return 6 – 7 mixtures • TSA has difficulty with non-unique spectra • TSA concentrates on getting the best fit over the whole spectrum and may miss small features (think kaolinite in Petermann Sandstone) • CLS has to use a manually selected Restricted Mineral Set (optional in TSA) NORTHERN TERRITORY GEOLOGICAL SURVEY
HyLogging vs. other mineralogy outputs: XRD / EDAX / Petrography • HyLogger returns voluminous whole-of-drillhole measurements vs. individual point sampling done with hand-held devices • HyLog FIRST, destructive sampling SECOND (when wanting to compare mineral results from two techniques) • HyLogger weakness is quantifiable mineralogy • Mineralogy validation ongoing; many Surveys have in- house XRD facilities NORTHERN TERRITORY GEOLOGICAL SURVEY
TSA Mineral Mix Proportions • Relatively semi-quantitative – May depend on absorption co-efficient – Linear surface measurement (not whole core) – Does not deal well with complex mixtures – Proportions are RELATIVE…. If a dominant mineral is inactive in that wavelength range, then it won’t be returned as a mineral match from that spectrometer – If a mineral is < 15% of the mineral mix, it won’t be listed (default) NORTHERN TERRITORY GEOLOGICAL SURVEY
Factors influencing confidence levels of automated mineral modelling • Core quality (look at imagery) • Complexity of mineral assemblage • Degree of processing External Validation • Incorporating scalars into the CLS Combined Least Squares processing workflow Domaining (dTSA) Creating and using scalars • Domaining TSA – User Matches (uTSA) Manual restriction of unlikely minerals • External validation The Spectral Assistant (TSA) – System Matches Algorithm matching to whole spectral library NORTHERN TERRITORY GEOLOGICAL SURVEY
HyLogger Data – ‘fit for purpose’? • Good for voluminous whole-of-drillhole data External • Good for mineral matches of 2 – 3 Validation minerals CLS • Good for stratigraphic Combined Least Squares boundaries/correlations; alteration haloes Domaining (dTSA) • Increased level of processing (restricted mineral matching of algorithm using Creating and using scalars context and common sense) gives TSA – User Matches (uTSA) Manual restriction of unlikely minerals increased confidence in the results Minerals match across whole hole • Need to learn to recognise what is likely, The Spectral Assistant (TSA) – System Matches Algorithm matching to whole spectral library what is real; what needs validation with external techniques NORTHERN TERRITORY GEOLOGICAL SURVEY
Validate the mineral response • Use of scalars • Look at the imagery (core quality) • Look at the spectral fit to the algorithm • Validate using complementary techniques (XRD, petrography, etc) • Use your geological knowledge: – ‘am I likely to see that mineral in that geological environment?’ – is that mineral responsive in that wavelength range? (think quartz/ feldspars not showing in SWIR) – is that mineral in the TSA library? NORTHERN TERRITORY GEOLOGICAL SURVEY
Conclusions • HyLogging is a valuable technique • Automated mineralogical interpretation methods are essential to deal with the volume of data • Understanding the methods and processes behind the mineral outputs will assist geoscientists in applying NVCL HyLogger data to their specific problems with confidence • Next speakers can show examples of applying HyLogger data NORTHERN TERRITORY GEOLOGICAL SURVEY
Acknowledgements • Andy Green (OTBC Pty Ltd) has contributed to much of this work, particularly CLS and TSA modelling work. NORTHERN TERRITORY GEOLOGICAL SURVEY
NORTHERN TERRITORY GEOLOGICAL SURVEY
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