ALBERT

Description: We have investigated the application of ground, laboratory, and airborne optical remote sensing methods for the detection of hydrothermal alteration zones associated with the Izok Lake volcanogenic massive sulfide (VMS) deposit in Nunavut, Canada. This bimodal-felsic Zn-Cu-Pb-Ag deposit is located above the tree line in a subarctic environment where lichens are the dominant cryptogamic species coating the rocks. The immediate host rhyolitic rocks have been hydrothermally altered and contain biotite, chlorite, and white micas as dominant alteration minerals. These minerals have spectral Al-OH and Fe-OH absorption features in the short-wave infrared wavelength region that display wavelength shifts, which are documented to be due to chemical compositional changes. Our ground spectrometer measurements indicate that there is a systematic trend in the Fe-OH absorption feature wavelength position of biotite/chlorite with increasing distance from the VMS deposit: the average Fe-OH absorption feature wavelength position of the proximal areas (398–3,146 m from mineralization) is observed at 2,254 nm, and that of the distal areas (5,782–6,812 m) at 2,251 nm. Moreover, the proximal areas have an average Al-OH absorption feature wavelength position at 2,203 nm, in contrast with the average wavelength position at 2,201 nm in the distal areas, implying a spectral shift of 2 nm. These findings indicate that hydrothermal alteration zones can be detected by hyperspectral remote sensing, despite the presence of abundant lichen cover. However, the airborne results discussed in this study required the screening out of more than 99% of the pixels in the area.

Description: Short-wave infrared (SWIR, 1.90–2.36 μ m) and long-wave infrared (LWIR, 8.1–11.1 μ m) hyperspectral images collected using the SisuROCK system were used to develop an automated methodology for generating kimberlite dilution maps. Smoothed and denoised images from two Snap Lake (Northwest Territories, Canada) kimberlite drill cores were processed, and SWIR and LWIR spectral endmembers were extracted from the images with each mineralogical endmember assigned to one of four compositional groups: undiluted kimberlite, microdiluted kimberlite, micro- and macrodiluted kimberlite, and crustal rocks. These endmembers were used to classify the SWIR and LWIR images, and the results were validated using linescan data, drill core logs, petrology reports, and the results of X-ray diffraction, Raman spectroscopy, and Micro-Fourier Transform Infrared (FTIR) spectroscopy. This study demonstrates that hyperspectral imagery can be used to generate dilution maps for hypabyssal kimberlites that far supersede other current techniques in terms of spatial resolution.

Description: Ore grade is one of the primary variables controlling the economic recovery of bitumen from oil sands reservoirs, hence there is a need for fast and reliable quantification of total bitumen content (TBC). This is typically achieved through laboratory-based Dean-Stark analyses of drill core samples. However, this method is time and labor intensive and destructive to the core sample. Hyperspectral imaging is a remote sensing technique that can be defined as reflectance spectroscopy with a spatial context, where high-resolution digital imagery (~1 mm/pixel [0.04 in./pixel]) is acquired and reflectance measurements are collected in each pixel of the image. This study compares two hyperspectral models for the determination of TBC from imagery of both fresh and dry core samples. For three out of four suites of fresh core, TBC was predicted within ±1.5 wt. % of the Dean-Stark data with both spectral models achieving correlations of $${R}^{2} 〉 0.97$$ . For a fourth fresh core and the dry core, larger margins of error were found because of some instances of overestimation. Surface roughness because of uneven oil distribution and small-scale fracturing is a potential source of error in some of the spectral TBC results, particularly for the dry core. Producing results within minutes with the additional benefit of being nondestructive to the core sample, hyperspectral imaging shows great potential to become a viable alternative method for bitumen content determination in oil sands.

Description: An understanding of the mineralogy and petrogenesis of rare earth element deposits has significant implications for their economic viability. Lanthanide-bearing compounds are known to produce sharp absorption features in the visible to short-wave infrared region (VIS-SWIR), however, a significant knowledge gap exists between the fields of hyperspectral reflectance spectroscopy and rare earth element mineralogy. Reflectance spectra were collected from four bastnäsite samples, two parisite samples, and one synchysite sample from the visible into the short-wave infrared. These REE fluorocarbonate mineral samples were characterized via scanning electron microscopy and electron probe microanalysis. Sharp absorptions of REE-bearing minerals are mostly the result of 4 f -4 f intraconfigurational electron transitions and for the light REE-enriched fluorocarbonates, the bulk of the features can be ascribed to Nd 3+ , Pr 3+ , Sm 3+ , and Eu 3+ . The lanthanide-related spectral responses of the REE fluorocarbonates are consistent across the group, supporting the notion that the REE cation site is very similar in each of these minerals. Carbonate-related spectral responses differed between these minerals, supporting the notion that the crystallographic sites for the carbonate radical differ between bastnäsite, synchysite, and parisite. Exploitable spectral differences include a distinct absorption band at 2243 nm that separates bastnäsite from synchysite and parisite. Similarly, for bastnäsite a dominantly Pr 3+ -related absorption band located is at 1968 nm, while in synchysite and parisite it occurs at 1961 nm.

Description: Short-wave infrared (SWIR) field and laboratory spectra were used to identify and characterize hydrothermal alteration mineral chemical variability in host rocks proximal to the Izok Lake Zn-Cu-Pb-Ag volcanogenic massive sulfide (VMS) deposit in Nunavut, Canada. The deposit is hosted within a sequence of predominantly felsic pyroclastic rocks of Archean age that are regionally metamorphosed to amphibolite facies. These rocks are characterized by the muscovite-biotite-sillimanite and chlorite-biotite-cordierite mineral suite. Proximal to the deposit, white micas are Al rich to potassic muscovite, and the biotite and chlorite are Mg rich. In areas that are immediately outboard of the proximal alteration zones, rocks are altered to Al-poor muscovite and intermediate to Fe-rich biotite and chlorite. Outboard of this, distal areas are characterized by potassic muscovite and Mg-rich biotite and chlorite. The white micas and biotite/chlorite group minerals display considerable variation in their Al-OH and Fe-OH absorption feature wavelength positions. The variations in muscovite and biotite/chlorite compositions (as determined by the Al-OH and Fe-OH absorption feature wavelength positions) broadly correlate with changes in hydrothermal alteration intensity, as measured by the Ishikawa and chlorite-carbonate-pyrite alteration indices. Our findings suggest that the large-scale alteration intensity trends of the Izok Lake study area can be elucidated using the spectral properties of the hydrothermal alteration minerals.

Description: Quartz is an anisotropic mineral, and each mid-infrared (7–15 μm) reflectance spectrum collected from an individual quartz crystal is strongly influenced by its orientation. As a result, quartz reflectance spectra contain features that systematically change with orientation. In this study, the trough at 8.63 μm was used to derive crystal orientation information from quartz reflectance spectra collected using a high spatial resolution spectrometer with a 100 x 100 μm spot size. The intensity of this trough was quantified using two band ratios (Ref 8.48 / Ref 8.63 and Ref 9.01 / Ref 8.63 ), and band ratio Ref 8.48 / Ref 8.63 was used to infer the orientation of quartz crystals in an Archean granite sample to characterize any fabric.

Description: Baffin Island (Nunavut, Canada) is located in the remote arctic where geological exposure is high, terrain is expansive, and field seasons are short. Metacarbonates in the Lake Harbour Group, southern Baffin Island, are considered to be prospective for sapphire (corundum), lapis lazuli (lazurite), and spinel gem deposits. This research is an investigation of the hyperspectral signature of rocks from the Beluga sapphire occurrence near Kimmirut, Nunavut. Thirty-five rock and thin section offcut samples from the Beluga corundum occurrence were studied in a laboratory setting using high spatial resolution imaging spectroscopy in the shortwave infrared region (SWIR, ~975 to 2500 nm). Analysis of hyperspectral imagery successfully reproduced mineralogical and textural information relevant to gem mineralization previously assessed through thin section petrography and scanning electron microscopy. Scapolite, phlogopite, and muscovite from these rocks are shown to have distinct spectral responses from the host marble that is dominated by calcite. Furthermore, spectrally distinct prehnite and zeolite, both locally associated with corundum mineralization, are readily distinguishable. From the perspective of regional exploration, the small footprint of colored gemstone deposits in combination with their unique mineralogical makeup, unusual settings, and unfamiliarity to most geoscientists has resulted in very few discoveries in this remote but otherwise fertile area. These factors, in combination with the unique spectral responses observed from hand samples and thin section offcuts, provide a positive case for mapping and exploration of gem corundum targets by high spatial resolution hyperspectral imaging as part of regional surveys.

Description: The paleoenvironments represented by the middle McMurray Formation have been actively debated within the last few decades. Highly detailed core studies have investigated the ichnology of the middle McMurray to gain insight on the paleodepositional conditions of these sediments. However, oil saturation makes diagnostic sedimentary and biogenic features difficult to see in core surfaces. Following on earlier published research, shortwave infrared (SWIR) hyperspectral imagery is collected, analyzed and compared to a previously studied McMurray Formation core. The method is tested on one well to be applied to the future studies. SWIR imagery significantly enhances the visibility of physical and biological sedimentary structures, especially within coarse-grained, bitumen-saturated intervals. The new observations provide support for interpretations derived from the direct study of the core and, in some cases, provide new observations that refine the core interpretation. Specifically, based on additional trace-fossil observations, lithosome L1 (high- and low-angle cross-stratified sandstone) is interpreted to represent bioturbation consistent with the middle estuary rather than the inner estuary. Deposition of lithosomes L2a (sandstone-dominated IHS) and L2b (equally interbedded sandstone and mudstone IHS) likely occurred in the middle estuary instead of inner to middle estuary. Interpretation of depositional locale is not changed for L2c, whereas L2d (mudstone-dominated burrowed IHS) is now interpreted to be deposited in the middle estuary instead of the previously suggested inner-middle estuary.

Description: Reflectance spectroscopy in the visible to short-wave infrared regions (500 to 2500 nm) was carried out using natural samples of the rare earth element (REE) phosphate minerals monazite, xenotime, and britholite. Samples were characterized by scanning electron microscopy and electron microprobe analysis. Absorption band positions were recorded with their probable origins, and spectral variability among the samples is discussed. Spectral features of these minerals are driven primarily by 4 f -4 f intraconfigurational electronic transitions of trivalent lanthanides. The distinct REE distributions of monazite, xenotime, and britholite drive their bulk spectral patterns, which in turn are sufficiently distinct to enable spectral classification. Spectral variability of some specific REE-related absorptions are interpreted to be driven by differences of the coordination polyhedra for the lanthanide cations between the crystal structures. Spectra of these minerals were also compared against carbonatite-hosted REE bearing fluorapatite. The work presented here strengthens the growing foundation for the interpretation of reflectance spectra of these REE phosphate minerals and enables exploitation of the observed features by the remote sensing community for detection, identification, and quantification of REE phosphate minerals. This is especially relevant for hyperspectral imaging spectroscopy with high spatial resolution, where the spectral response of a pixel becomes increasingly dominated by mineralogy.