Appendix 1
Drill cores stored at the Geological Survey of Sweden (SGU) in Malå or at the Boliden Mineral core archive in Boliden (Sweden) were sampled as follows: (i) 57 samples from the Upper Sandstone and Lower Sandstone orebodies at Laisvall (including 4 samples with steeply-dipping galena-sphalerite-calcite veinlets); (ii) eight samples from the sandstone orebody at Vassbo, (iii) one sample of shale with pyrite at the base of the Grammajukku Formation at the contact with the underlying Upper Sandstone at Laisvall, and (iv) one sample of pyrite-rich grey shale in the Alum Shale Formation at Vassbo. At Laisvall, the samples were selected in profiles at proximal and distal positions relative to the Nadok fault and Central Malm fault systems, which have been interpreted as feeder systems for mineralization (Saintilan et al. 2015a).After petrographic investigations, aliquots of these samples were utilized for determination of the sulfur isotope composition of sulfidesand barite, and strontium isotope composition of barite.An additionalseparate of phosphorite pellets in the phosphorite conglomerate at Laisvall (Fig. 2a) was obtained from drill core samples using a microdrill and processed for strontium isotope analyses.
In addition, thirteen drill core samples and one outcrop sample were taken from the stratigraphy at Laisvall for organic geochemistry analyses: (i) Eleven shale samples from the Grammajukku and Alum Shale Formations; (ii) two mineralized sandstone samples from the Upper and Lower Sandstones; and (iii) one barren Lower Sandstone sample from outcrops located ~ 5 km to the southeast of the mined area. The shale samples are representative of the stratigraphy upward from the base of the Grammajukku Formation to the uppermost autochthonous part of the Alum Shale Formation at Laisvall. The uppermost sample of black organic-rich shale (ASF 11) was sampled at the top of a few centimeter-thick limestone horizon within the Alum Shale Formation (cf. Thickpenny 1984). Shale sample ASF4 was split in three subsamples (ASF4-0, ASF4-1 and ASF4-2). These samples correspond to the first meter of organic-rich shale in the autochthonous part of the Alum Shale Formation at Laisvall, above the contact with the Grammajukku Formation.Hydrocarbons were extracted from ASF4-1 and ASF4-2, and from the three sandstone samples.
Thin sections of all samples were studied using transmitted and reflected light microscopy and a Cl8200 MK5-optical cathodoluminescence microscope with a cold cathode that was mounted on a petrographical microscope. The beam conditions were set at 15 kV and 50 to 60 mA with an unfocused beam of approximately 1 cm in an observation chamber with a residual pressure of 80 mTorr. Samples were not coated. Twenty representative thin sections were mounted on an aluminum stub with double-sided conductive carbon tape. A c. 25 nm thin coating of carbon was deposited on the samples by low vacuum sputter prior to imaging with a Jeol JSM 7001F Scanning Electron Microscope (SEM, Section of Earth and Environmental Sciences, University of Geneva, Switzerland). Investigation of solid black inclusions in barite, calcite and fluorite, and dark fluid inclusions in sphalerite in three samples from Laisvall was carried out by Raman spectrometry at the University of Geneva using a LABRAM confocal Raman microspectrometer with a 532.8-nm He-Ne laser coupled to a B40 Olympus microscope with a 50× objective. Barite and sphalerite fragments from these samples were then mounted on an aluminum stub and coated with gold (c. 10 nm) before investigation using SEM on back-scattered electron mode (BSE) and energy-dispersive X-ray analysis (EDX).
Three representative thin sections were selected for QEMSCAN® imagery and analysis: (i) a sample from the Upper Sandstone orebody in which phosphorous- and/or REE-bearing minerals were investigated in detail; and (ii) two samples from the Lower Sandstone orebody at Laisvall and the sandstone orebody at Vassbo in which the distribution of the cementing phases (quartz, calcite, barite, Pb-Zn sulfides) and their relationships were studied. Automated bulk-rock mineral analysis and textural imaging of the studied samples were performed using an FEI QEMSCAN® Quanta 650F facility at the Section of Earth and Environmental Sciences, University of Geneva, Switzerland. The system is equipped with two Bruker QUANTAX light-element energy dispersive X-ray spectrometers. Analyses were conducted at high vacuum, accelerating voltage of 25 kV, and probe current of 10 nA on carbon-coated samples. FieldImage operating mode (Pirrie et al. 2004) was used for analyses. X-ray spectra acquisition time was 10 ms per pixel, using a point-spacing of 5 µm. Up to 285 individual fields were measured in each sample, with 1500 pixels per field. Data processing was performed using the iDiscover software package. The final products consist of high-quality spatially resolved and fully quantified mineralogical maps enabling basic image analysis, including particle size and shape distribution, mineral assemblages and mineral proportion definitions.
For sulfur isotope studies, all samples were crushed using a hydraulic press and sieved. Following heavy liquid separation of the 315 to 125 µm size fractions, the heavy mineral fractions were handpicked under a binocular microscope to obtain sulfide (galena, sphalerite and pyrite) and barite aliquots. All aliquots (n=163 and 25 duplicates) were subsequently powdered using an agate mortar and pestle, and analyzed for the stable sulfur isotope composition by elemental analysis and isotope ratio mass spectrometry (EA-IRMS) at the Institute of Earth Surface Dynamics, University of Lausanne, Switzerland. The EA-IRMS analyses were done using a Carlo Erba 1108 elemental analyzer connected to a Thermo Fisher Delta V stable isotope ratio mass spectrometer that was operated in the continuous He flow mode. The stable isotope composition of sulfur is reported in the delta (δ) notation as the per mil (‰) deviation of the isotope ratio (34S/32S) relative to the VCDT standard. The precision of the EA-IRMS analyses, evaluated by replicate measurements of laboratory standards (barite, sphalerite, and pyrite) and international reference materials (sphalerite, silver sulfide) is better than ±0.2‰ (1σ).
For strontium isotope studies, barite and phosporite pellet aliquots were digested with HCl 6M in screw-sealed Teflon vials on a hot plate at 140°C for several hours. The solutions were centrifuged and the supernatant was recovered and transferred to Teflon vials, where it was dried down on a hot plate. The residue was re-dissolved in a few drops of 14 M HNO3 and dried down again, before Sr separation from the matrix using a Sr-Spec resin. The Sr separate was re-dissolved in 5 ml of ~2% HNO3 solutions and ratios were measured using a Thermo Neptune PLUS Multi-Collector ICP-MS in static mode. The 88Sr/86Sr (8.375209) ratio was used to monitor internal fractionation during the run. Interferences at masses 84 (84Kr), 86 (86Kr) and 87 (87Rb) were also corrected in-run by monitoring 83Kr and 85Rb. The SRM987 standard was used to check external reproducibility, which on the long-term (more than 100 measurements during one year) was ±10 ppm. The internally corrected 87Sr/86Sr values were further corrected for external fractionation. A87Sr/86Sr ratio of 0.721269 ± 1.4x10-5 is reported as 0.721269 ± 14.
The samples for organic geochemical analyses were prepared and analyzed in the Stable Isotope and Organic Geochemistry Laboratories at the University of Lausanne (Switzerland) using procedures described previously (Spangenberg and Herlec 2006; Spangenberg et al. 2014). To remove the weathered material and any contamination from packing and handling, the rocks were cut in slabs with a water-cooled saw. The slabs were cleaned with deionized water (>18MΩ resistance), analytical grade acetone and dried at 50°C for 24 hours. The cleaned slabs were crushed in a thoroughly cleaned hydraulic press and powdered to <125 µm by short grinding periods in an agate ring grinder mill. The powders were stored in pre-annealed (at 450°C for four hours) aluminum disposable canisters and aluminum foil sheets prior to organic geochemical analyses. Total bitumen (extractable organic matter, EOM) was obtained from an aliquot (100 to 200 g) of the powdered samples by refluxing with dichloromethane (DCM) for six days, with a change of solvent after the first two days. The DCM fractions were combined, gently evaporated to 1 mL, and passed through an activated copper column to remove elemental sulfur. The solvent was passively evaporated to near dryness, and extracts with 0.5 mL DCM stored in 2 mL vials at +4 °C until required for analyses. The extracts were separated into two fractions (aliphatic and aromatic hydrocarbons) using silica/alumina gel liquid chromatography.
Chemical characterization of the aliphatic hydrocarbons was performed by gas chromatography‒mass spectrometry (GC‒MS), using an Agilent Technologies gas chromatograph HP 6890 coupled to a HP 5973 quadrupole mass selective detector (MSD) with HP-5MS fused-silica capillary column (60 m length, 0.25 mm internal diameter, coated with 0.10 μm 5%-diphenyl–95% dimethyl-polysiloxane as stationary phase) and helium as carrier gas. An aliquot normalized to the extracted aliquot size was introduced in a splitless injector at 280 °C. After an initial period of 7 min at 70 °C, the column was heated to 280 °C at 5 °C/min followed by an isothermal period of 20 min. The MSD was operated in the electron impact mode at 70 eV, with a source temperature of 250 °C, an emission current of 1 mA, multiple-ion detection with a mass range from 50 to 700 a.m.u, and a scan rate of 1.5 scans/sec (resolution of 6.15 scans/a.m.u.). Compound identifications were made by comparison with synthetic standards, GC retention times, interpretation of mass spectrometric fragmentation patterns and literature mass spectra. The absence of measurable recovered bitumen in two procedure blanks indicates that no detectable laboratory contaminations were introduced into the samples.
Carbon and nitrogen stable isotope analyses of the total organic carbon were performed on the eleven shale samples. The powdered samples were acidified (1M HCl) for removal of inorganic carbon, rinsed thoroughly with deionized water, filtered, dried overnight, and stored in pre-annealed beakers. The solid residues were mostly kerogen with some residual silicate fraction, and aliquotswere submitted to carbon and nitrogen isotope analyses by EA-IRMS. The C and N isotope compositions are reported in the delta (δ) notation as the per mil (‰) deviation of the (13C/12C) and (15N/14N) isotope ratios relative to the VPDB and N2 in AIR standards, respectively. The reproducibility of the EA-IRMS measurements for C and N is better than ±0.1‰ and ±0.3‰ (1σ), respectively. The TOC (wt.% C) and total organic nitrogen (TON, wt.% N) of each sample was determined by integration of the corresponding EA-IRMS measurement of the carbon and nitrogen isotope composition.