ALBERT

Description: A successful method of mineral exploration in glaciated terrain is the use of indicator minerals recovered from carefully selected glacial sediments, and subsequently traced back to their bedrock source. The successful application of indicator mineral methods relies on efficient and effective recovery as well as the correct identification of a wide variety of indicator minerals. The Geological Survey of Canada (GSC) has developed protocols for ongoing and future research projects to achieve the highest quality for reporting indicator mineral data. Such protocols include the use of field duplicate samples, blank samples, and base material spiked with known numbers, morphologies, species, and sizes of indicator minerals. Field duplicate samples serve to estimate sediment heterogeneity. Spiked samples are used to monitor the accuracy of the sample processing and mineral identification methods for recovering specific minerals. Blank samples serve to detect potential carry-over contamination. In certain instances, a specific sample processing order is essential and should be communicated to the commercial processing laboratory. Ore-rich samples collected near known mineralization are to be processed last, to reduce chances of carry-over contamination. Repeated indicator mineral counts should be carried out on at least 10% of the heavy mineral concentrates to measure reproducibility (precision) of the mineral counts. All indicator mineral data, original laboratory reports, heavy mineral concentrates, unmounted picked grains, and grain mounts are now archived at the GSC, using specific guidelines.

Description: Iron oxides are minerals resistant to chemical alteration and mechanical abrasion, and which have ferromagnetic properties and a range of chemical compositions. These characteristics are useful as indicator minerals in exploration, for example using till in glaciated terrains. Iron oxide proportions, grain size, and chemical composition of till samples collected near the Sue-Dianne Cu-Au-Ag IOCG deposit in the Great Bear magmatic zone (Northwest Territories, Canada) and magmatic Ni-Cu deposits in the Thompson Nickel Belt (Manitoba, Canada) show that subsamples containing c. 100 grains from the 0.25–1.0 mm grain size ferromagnetic fraction yield a representative mineralogical and compositional range of oxide grains from a till sample. Subsamples with less than 100 grains yield statistically less representative data. The 1–2 mm grain size fraction typically contains too few iron oxide grains and thus using this fraction is not statistically representative. The composition of iron oxides from eight till and five bedrock samples was determined along transects up- and down-ice of the Cu-Au-Ag Sue-Dianne IOCG deposit. At, and immediately down-ice of, the deposit, hematite is the principal oxide and shows dominant BIF and IOCG chemical signatures in the Ca+Al+Mn v. Ti+V discriminant diagram. Up-ice and farther down-ice of the deposit, magnetite and titanomagnetite are the dominant oxides and magnetite shows dominant Kiruna and IOCG signatures. The composition of iron oxides from six till samples along a north–south transect and 11 till samples from a 180 km-long east–west transect, along the older and younger directions of ice-flow, respectively, was determined in the Thompson Nickel Belt (Manitoba, Canada). The proportion of magnetite in till with the signature of Ni-Cu deposits increases for at least 1 km south of the Pipe Ni-Cu deposit along the direction of the older southward ice flow, whereas the glacial dispersal of magnetite with a chemical signature typical of Ni-Cu deposits was limited during the younger westerly ice flow.

Description: In this study, results by direct portable XRF (‘pXRF’) on unsieved till samples were compared with those by established laboratory methods (aqua regia or fusion ICP-MS and ICP-ES) on the 〈0.063-mm fraction to determine if the application of direct pXRF in the field would serve as an acceptable guide for immediate follow-up work. Four test sites in Canada were chosen: the Halfmile Lake Cu-Pb-Zn VMS deposit; the intrusion-hosted W-Mo Sisson deposit; a Pb-Zn Mississippi Valley–type (MVT) deposit in the Pine Point district; and the Triple B kimberlite. Unsieved till samples from the GSC archive collection were used for this study and included samples from background areas, immediately overlying, and at various distances down-ice of each deposit. Ziploc® and Whirl-Pak® bags that were used to contain the samples in the field were tested for their properties of X-ray attenuation and contamination. In general, the performance of pXRF in the four test areas was very good where concentrations of elements of interest (indicator or pathfinder elements) were substantially above detection limits by this technique (in the low ppm range for many elements). The following elements, shown to be useful indicator elements (important constituents of the ore/commodity) or pathfinder elements (those associated with the commodity elements) by the established methodology, showed similar patterns by pXRF on the unsieved material: Zn, Cu, Pb, and As at Halfmile Lake; W, Mo, Cu, Zn, Pb, and As at the Sisson deposit; Zn, Pb, and Fe at Pine Point; and Ca, Sr, Cr, and Ni at Triple B. Pathfinder elements whose concentrations were too low for determination by pXRF include: Ag and Sb at Halfmile Lake; Ag and Cd at Sisson; Cd, S, and Se at Pine Point; and Co, Mg, P, U, and Th at Triple B. The high background for Bi by pXRF, equivalent to c . 50 ppm, and its noisy signal precluded its use at Halfmile Lake and Sisson. Elements which tended to show poor precision (three analyses each sample) by pXRF in some samples due to sample heterogeneity include Sn, V, and W. Mercury was erroneously reported for the majority of samples in the low ppm range by pXRF whereas its concentration in fact was in the low ppb range. Several Pb-, Zn- ( c . 1% Pb, Zn) and Fe-rich (up to 16% Fe) samples demonstrated spectral interferences by: Pb on As, Th and Se; Zn on Cu; and Fe on Co. Results for six till samples analysed in Ziploc® and Whirl-Pak® bags showed that Ziploc® absorbs fewer low-energy photons and hence is preferable for determining light elements such as Si, K and Ca. Supplementary material: Four data-sets are available at http://www.geolsoc.org.uk/SUP18897

Description: In this study, results by direct portable XRF (‘pXRF’) on unsieved till samples were compared with those by established laboratory methods (aqua regia or fusion ICP-MS and ICP-ES) on the 〈0.063-mm fraction to determine if the application of direct pXRF in the field would serve as an acceptable guide for immediate follow-up work. Four test sites in Canada were chosen: the Halfmile Lake Cu-Pb-Zn VMS deposit; the intrusion-hosted W-Mo Sisson deposit; a Pb-Zn Mississippi Valley–type (MVT) deposit in the Pine Point district; and the Triple B kimberlite. Unsieved till samples from the GSC archive collection were used for this study and included samples from background areas, immediately overlying, and at various distances down-ice of each deposit. Ziploc® and Whirl-Pak® bags that were used to contain the samples in the field were tested for their properties of X-ray attenuation and contamination. In general, the performance of pXRF in the four test areas was very good where concentrations of elements of interest (indicator or pathfinder elements) were substantially above detection limits by this technique (in the low ppm range for many elements). The following elements, shown to be useful indicator elements (important constituents of the ore/commodity) or pathfinder elements (those associated with the commodity elements) by the established methodology, showed similar patterns by pXRF on the unsieved material: Zn, Cu, Pb, and As at Halfmile Lake; W, Mo, Cu, Zn, Pb, and As at the Sisson deposit; Zn, Pb, and Fe at Pine Point; and Ca, Sr, Cr, and Ni at Triple B. Pathfinder elements whose concentrations were too low for determination by pXRF include: Ag and Sb at Halfmile Lake; Ag and Cd at Sisson; Cd, S, and Se at Pine Point; and Co, Mg, P, U, and Th at Triple B. The high background for Bi by pXRF, equivalent to c . 50 ppm, and its noisy signal precluded its use at Halfmile Lake and Sisson. Elements which tended to show poor precision (three analyses each sample) by pXRF in some samples due to sample heterogeneity include Sn, V, and W. Mercury was erroneously reported for the majority of samples in the low ppm range by pXRF whereas its concentration in fact was in the low ppb range. Several Pb-, Zn- ( c . 1% Pb, Zn) and Fe-rich (up to 16% Fe) samples demonstrated spectral interferences by: Pb on As, Th and Se; Zn on Cu; and Fe on Co. Results for six till samples analysed in Ziploc® and Whirl-Pak® bags showed that Ziploc® absorbs fewer low-energy photons and hence is preferable for determining light elements such as Si, K and Ca. Supplementary material: Four data-sets are available at http://www.geolsoc.org.uk/SUP18897

Description: The relationship between cathodoluminescence (CL) response and chemical composition of scheelite from a variety of ore-deposit settings ( e.g ., orogenic Au, skarn, porphyry-related, greisens, VMS) was investigated using SEM-EDS, CL imaging, and LA-ICP-MS techniques. Our detailed study concentrates on five samples of scheelite from a range of ore-deposit settings, including orogenic Au, skarn, VMS, and greisen deposits, but draws on a yet unpublished data base of more than 39 deposits world-wide. Results indicate that the scheelite zonation patterns observed under CL can be useful in discriminating between scheelite arising from differing mineralized environments. Scheelite from orogenic Au deposits exhibits a homogenous CL response in contrast to that from proximal intrusion-related systems, such as porphyries, skarns, and greisens that show a strong oscillatory zonation, with individual zones ranging from 〈1 μm to 〉300 μm in width. Results from LA-ICP-MS analyses show significant chemical variations in scheelite with respect to Mo, Sr, As, and REE + Y. Maps generated from CL imaging and LA-ICP-MS data reveal a strong negative correlation between the intensity of the CL response in scheelite and Mo content. While enrichments of Sr, As, and REE + Y are noted, none exhibit a correlatable effect with CL response. Furthermore, the qualitative Mo and W X-ray maps produced via SEM-EDS correlate with the corresponding LA-ICP-MS maps of the scheelite grain, successively delineating the zonation patterns observed under CL. This work also demonstrates that the combination of CL and LA-ICP-MS mapping is a powerful tool in the discussion of observed CL textures, elemental relationships, mineral growth history, and paragenesis.

Description: An indicator mineral and geochemical case study was carried out around the Sisson W–Mo deposit to test modern indicator mineral and analytical methods and document glacial and fluvial dispersal from a significant W–Mo source. Indicator minerals in the 0.25 – 2.0 mm non-ferromagnetic heavy mineral fraction of till and stream sediments include the primary ore minerals scheelite, wolframite and molybdenite, as well as chalcopyrite, joseite, native Bi, bismutite, bismuthinite, galena, sphalerite, arsenopyrite, pyrrhotite and pyrite. Indicator minerals in c. 12 – 14 kg samples define glacial dispersal of at least 10 km down ice (SE) of the deposit and fluvial dispersal at least 4 km downstream. The presence of very coarse (0.5 – 2.0 mm) indicator minerals in till and stream sediments marks proximity (〈1 km) to the mineralized source. Indicator elements for the deposit in the 〈0.063 mm fraction of till, the 〈0.177 mm fraction of stream sediments, and in stream water include W and Mo, and various combinations of pathfinder elements Ag, As, Bi, Cd, Cu, In, Pb, Te and Zn. This list of elements is more extensive than previously identified for the Sisson deposit or other studies around W mineralization in glaciated terrain. The study demonstrates that indicator mineral methods, so well known for diamond and gold exploration, have a broader application that includes W–Mo exploration.

Description: The Broken Hammer Cu–Ni–PGE–Au footwall deposit in the North Range of the Sudbury Structure in Canada consists of a shallow surface zone of vein-hosted and vein stockwork-hosted mineralization within Sudbury breccia developed in the quartz monzonite Levack Gneiss Complex. The surface of the deposit consists of a 2–120 cm wide chalcopyrite vein and numerous smaller veins dominated by chalcopyrite–magnetite–millerite with trace gold, platinum group minerals, tellurides, bismuthides and selenides. The Laurentide Ice Sheet flowed southward across the region depositing a sandy till that contains abundant sperrylite (hundreds of grains), chalcopyrite, pyrite and gold in the heavy mineral fraction down-ice of mineralization. Mineral liberation analysis of the