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TitleCustomizing spectral libraries for effective mineral exploration
 
AuthorPercival, J BORCID logo; Bosman, S A; Potter, E GORCID logo; Peter, JORCID logo; Laudadio, A B; Abraham, A C; Shiley, D A; Sherry, C
SourceSession: Role of Clay Minerals in the Quest for Mineral Resources 16th International Clay Conference (ICC); International Clay Conference, Field Excursion Guidebook vol. 7, 2017, 1 pages
LinksAbstract - Résumé
Image
Year2017
Alt SeriesEarth Sciences Sector, Contribution Series 20160358
PublisherInternational Clay Conference
MeetingInternational Clay Conference (ICC); Granada; ES; July 17-21 2017
Documentbook
Lang.English
Mediapaper; on-line; digital
File formatpdf
Subjectsmineralogy; miscellaneous; clay analyses; clay mineralogy; clay minerals; x-ray fluorescence; spectroscopic analyses; sampling techniques; sampling methods; infrared spectral analyses
ProgramTargeted Geoscience Initiative (TGI-4) Uranium Ore Systems
AbstractExplorationists require rapid analytical results to make cost-effective decisions during drilling operations. Progress over the last few decades in field instrumentation has facilitated acquisition of in situ, non-destructive, rapid, semi-quantitative to quantitative chemical analyses, provided that calibration, interferences and matrix effects are well considered. Handheld X-ray fluorescence spectroscopy (XRF) has become more precise in detecting elements of interest in exploration programs and Laser-Induced Breakdown Spectroscopy (LIBS) is now capable of being used in the field due to recent changes to make it portable. However, for certain deposit types, alteration mineralogy may be a stronger indicator of proximity to mineralization. This is especially important in volcanogenic massive sulfide (VMS), epithermal gold (high or low sulphidation), Iron Oxide-Copper-Gold (IOCG), sedimentary exhalative (SEDEX), Mississippi Valley-type (MVT) and unconformity uranium deposits. Changes in clay mineralogy provide information on genetic and/or alteration history, and may reflect different source rocks, fluids, or depths of formation. In epithermal gold deposits, the high sulphidation processes give rise to alunite, a characteristic indicator mineral. In the uranium-rich Athabasca Basin (AB), Canada, clay mineral alteration can guide the location of more detailed geophysical surveys, surface sampling and ultimately, drilling operations, as a project advances. Clay mineralogical changes from diagenetic dickite to hydrothermal illite are commonly observed associated with uranium deposits in the eastern part of the AB. In contrast, mineralogical changes are less extensive and more subtle in deposits in the western part of the AB and deposits hosted in basement rocks.

For rapid mineral identification, both portable X-ray diffractometry (XRD) and infrared (IR) spectrometry are effective techniques. However, XRD requires some sample preparation whereas IR does not, other than ensuring a dry surface. Today, handheld IR spectrometers are equipped with on-board spectral libraries which enable rapid qualitative analysis of major minerals, and this permits the facile recognition of key alteration minerals. Spectral libraries can be general or customized for specific mineral deposit environments. To create a library, careful collection of spectra in a controlled environment on pure specimens of key alteration minerals is required. The spectrometer system is validated prior to use using a wavelength standard to assure consistency across all reference samples. In this study, spectra were collected using a Spectralon® white reference puck as a relative reference and then were mathematically transformed to absolute reflectance format to account for the reflectance characteristics of the Spectralon® panel. The spectrum of each new example is then compared to other examples of this mineral to assure that only the most representative spectra are added to the library. This comparison process requires many examples of each mineral to characterize that species. To this end, we participated in collecting spectra on a variety of standards using the ¿Kodama clay collection¿ (a suite of carefully analysed samples donated to the GSC following Dr. H. Kodama¿s retirement) that were incorporated into the National Mineral Collection [1]. The spectra collected were evaluated using a variety of spectral plotting software and after validating each new example they were incorporated into the on-board library of the handheld ASD-HALO near-infrared mineral identification instrument. Currently, collection of spectra is underway for rare earth element-bearing minerals, typical of carbonatite and alkali intrusive deposits, housed in the National Mineral Collection. This talk will examine the utility of alteration minerals in exploration programs and how field portable instruments can provide essential rapid, non-destructive, qualitative to quantitative information.
Summary(Plain Language Summary, not published)
This paper discusses the optimal conditions to collect visible-near infrared-shortwave infrared (VIS-NIR-SWIR) spectra from selected minerals housed in the National Mineral Collection. On-board spectral libraries in handheld, mineralogical identification instruments can provide a rapid analysis of minerals in hand specimens or outcrops. Alteration and indicator minerals typify a variety of ore deposits and can vector to mineralization. The focus will be on examples from the Athabasca basin - uranium exploration. Current application on rare earth element-, niobium- and/or uranium- and thorium-bearing minerals, representing deposits for critical metals, will also be presented.
GEOSCAN ID299741

 
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