Hecker, C.A.

van der Meer, F.D.

van Ruitenbeek, F.J.A.

English

University of Twente Research Information

Airborne mineralogic cross section through a porphyry copper – epithermal – skarn system  Dr. Christoph Hecker, Department of Earth Systems Analysis, University of Twente; Dr. Frank van Ruitenbeek, Department of Earth Systems Analysis, University of Twente; Prof. John Dilles, College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA; Dr. Dean Riley, The Aerospace Corporation, Chantilly, VA, USA; currently with Booz Allen Hamilton Inc.; Prof. Freek van der Meer, Department of Earth Systems Analysis, University of Twente;  Porphyry-Cu and epithermal alteration are two alteration facies of the same system but at different depths. Where the porphyry system meets neighbouring sediments, Cu-skarn alteration is produced. As fluids circulate through the system towards the surface, changes in fluid chemistry, temperature and pressure create distinct zones with variable mineral assemblages. Most of these minerals are infrared active and can be measured from hyperspectral imagery. Traditional, ground-based studies to map individual minerals or alteration zones are based on point observations and are not ideal for distinguishing patterns.  In this study we use hyperspectral imagery from the ProSpecTIR (visible to short-wave infrared) and SEBASS (thermal infrared) sensors to map patterns of mineral distributions over the Yerington Batholith in Nevada, USA. We use the minimum wavelength mapping technique to highlight mineralogic patterns of the dominating mineral assemblages, and use the complementarity of the two wavelength bands to map alteration zones and fluid pathways exposed at the surface. Preliminary results show that hard classification based only on the dominating mineral is resulting in a lot of speckles but that the intermediate results shows mineral distribution patterns that are directly and simply interpretable by experienced field geologists.  AIRBORNE MINERALOGIC CROSS SECTION THROUGH A PORPHYRY COPPER –EPITHERMAL – SKARN SYSTEMC. HECKER,F.J.A. VAN RUITENBEEKJ. DILLESD. RILEYF.D. VAN DER MEERGENERALIZED PORPHYRY-CU ALTERATION MODEL2 Source: Sillitoe, 2010STUDY AREA: YERINGTON BATHOLITH, NEVADA3cross section from 1 to 6 km paleodepthGEOLOGIC OVERVIEW YERINGTON (ANN-MASON)Source: Hecker (2012) PhD 8cross section from 1 to 6 km paleodepthGEOLOGIC OVERVIEW YERINGTON (ANN-MASON)Source: Hecker (2012) PhD 8AIRBORNE IMAGING SPECTROSCOPY DATAData courtesy Aero.org and SpecTIRVNIR-SWIR ProSpecTIR sensor128 bands LWIR SEBASS sensor9 No SWIR features for non OH-bearing Silicates => TIR emissivity spectra neededSWIR – TIR COMPLEMENTARITYVIS - SWIR LWIRTECHNIQUES USED Minimum Wavelength Mapping=> Dominant minerals in SWIR & TIR LWIR Lab analysis on field samples=> determine thresholds for classification Decision tree classification=> combine step 1 and 2 into SWIR&TIR mineral assemblages8WAVELENGTH OF LOCAL MINIMA9123wav. depth1 2.205 μm 0.372 2.165 μm 0.283 2.386 μm 0.09Continuum removedDominant absorption features:INTERPOLATION10Second order fiton 3 points:f(w) = ax2 + bx + cwmin= -b / 2adepth = 1 - f(wmin)Shifts in the order of 1 nm can be detected.Source: van Ruitenbeek et al (2014)Planetary and space science, 101, pp.108-117WAVELENGTH & DEPTH11Identification of feature AbundanceWavelength Depth2000 nm                                  2500 nm     0%                                       20%HSV FUSION OF WAVELENGTH & DEPTH12buddingtonitealunitewhite micascalciteFused image Legend MineralsWavelength mapping on ProspecTIR-VS  between 2.1-2.4µmDAAAABCBAA: Skarn and HornfelsEpidote, amphibole,carbonateB: Porphyry regimeActinolite, chlorite,epidote, sericiteBA10Wavelength mapping on SEBASS between 8.05-11.65µmDAAAABCA: Skarn and HornfelsGarnet and carbonate B: Porphyry regimePlagioclase and quartzBA11COMBINED MINWAV INTERPRETATIONSWIR LWIR12 Min Wavelength Mapping Works for LWIR too! Highlight minerals and compositions Intuitive; great for overview, across flightline but ignoring spectral details AcknowledgementsThe Aerospace Corporation for the SEBASS and Prospectir data collection as part of an Internal Research and Development Grant awarded to Dean Riley when he was that The Aerospace Corporation. CONCLUSIONS15AIRBORNE MINERALOGIC CROSS SECTION THROUGH A PORPHYRY COPPER –EPITHERMAL – SKARN SYSTEMC. HECKER,F.J.A. VAN RUITENBEEKJ. DILLESD. RILEYF.D. VAN DER MEERc.a.hecker@utwente.nlAIRBORNE HYPERSPECTRAL IMAGINGYERINGTON TIR COLOUR COMPOSITE  RGB = (11.1, 9.64, 9.06)TailingsCu-SkarnEpithermal Auadvanced argillicPorphyry CuK-alteration

Airborne mineralogic cross section through a porphyry copper-epithermal-skarn system

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