A Lithogeochemical Study of the Metal Contents of the Upper Cretaceous Oil Shales in the Pasquia Hills, East-Central Saskatchewan Murray C. Rogers 1 Information from this publication may be used if credit is given. It is recommended that reference to this publication be made in the following form: Rogers, M.C. (2016): A lithogeochemical study of the metal contents of the Upper Cretaceous oil shales in the Pasquia Hills, east-central Saskatchewan; in Summary of Investigations 2016, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2016-4.2, Paper A-1, 17p. This paper is associated with the following publication: Rogers, M.C. (2016): Geochemical analyses of drillhole core from Cretaceous Upper Colorado Group oil shale in east-central Saskatchewan (NTS 63E/03, /04); Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, Data File 41. Abstract The results of a multi-element geochemical study are reported from the selective sampling of core from five drillholes that intersected Cretaceous oil shales on the northwest flank of the Pasquia Hills in east-central Saskatchewan. Black shales, particularly organic-rich shales, commonly have anomalous—and in some cases potentially economic—metal contents. Upper Cretaceous oil shales of the Niobrara (First White Speckled Shale) and Favel (Second White Specks) formations occur at shallow depth, in subcrop and as local outcrop, in the Pasquia Hills, and extend in subcrop and at depth through central Saskatchewan. Although the oil shales in the Pasquia Hills have been extensively drilled and tested for their kerogen (oil) potential since the 1960s, there is no public record that they have been examined in any detail for their metal contents. The core from several recent drillholes from this region is stored in Regina at the Subsurface Geological Laboratory of the Ministry of the Economy. Five of these holes from the northwest flank of the Pasquia Hills were selected for sampling. The oil shale sections in these holes average about 30 m in thickness. Four representative one-metre chip samples of the core were taken from each hole, approximately equidistant through each core section. The samples were then sent for multi-element analysis by inductively coupled plasma–optical emission spectroscopy (ICP-OES) and fire assay (Au, Pt, Pd)–ICP-OES. The United States Geological Survey’s (USGS) standard for metalliferous black shales was used as a basis to interpret the results of the multi-element analyses. The gold values (with one exception) are highly anomalous, with 19 of the 20 samples exceeding the USGS standard of 5.6 ppb. The arithmetic mean (average) value for all 20 samples was 45 ppb (eight times (8X) greater than the USGS standard) and the high value was 129 ppb (23X). Based on the albeit limited number of drillholes and samples, the mean gold values display a general westward increase, with the highest mean value of 103 ppb Au in the most western drillhole. A hydrothermal source to the west is inferred for the anomalous gold. Other metalliferous elements include Ag, Zn, Se, P2O5, Sr and V. Based on the clearly anomalous but unspectacular level of values and the consistent distribution of these metals both within the individual drillholes and between the drillholes, their source has been attributed to absorption of metals by organic matter from seawater and further concentration in minerals during diagenesis in the reduced, anoxic sediments. Keywords: oil shale, Upper Cretaceous, metals, geochemistry, gold, Pasquia Hills, east-central Saskatchewan 1. Introduction The purpose of this lithogeochemical study was to determine the metal contents of the Upper Cretaceous oil shales on a portion of the northwest flank of the Pasquia Hills area of east-central Saskatchewan (Figure 1). Macauley (1984) defines oil shale as an organic-rich, fine-grained, dark brown to black sedimentary rock that contains kerogen from which liquid hydrocarbons can be extracted by heating. Black shales, particularly organic-rich shales, often have anomalous, and in some cases potentially economic, metal contents. 1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 1000-2103 11th Avenue, Regina, SK S4P 3Z8 Although the Saskatchewan Ministry of the Economy has exercised all reasonable care in the compilation, interpretation and production of this product, it is not possible to ensure total accuracy, and all persons who rely on the information contained herein do so at their own risk. The Saskatchewan Ministry of the Economy and the Government of Saskatchewan do not accept liability for any errors, omissions or inaccuracies that may be included in, or derived from, this product. Saskatchewan Geological Survey 1 Summary of Investigations 2016, Volume 2 Figure 1 – Location of the project area on the northwest flank of the Pasquia Hills, east-central Saskatchewan (geological and urban municipality base map is from the Geological Atlas of Saskatchewan, Saskatchewan Ministry of the Economy website) showing the regional subcrop of the oil shale formations (Kws) and estimated projection of the Tabbernor Fault Zone (TFZ). The Pasquia Hills form the northwestern extent of the Manitoba Escarpment. The area to the east of the town of Arborfield (Figure 2) was selected for this study because the oil shales are near the surface here and, since the 1960s, have been the focus of a number of drill programs because of their kerogen content. The core from several drillholes from recent programs is available for examination and study at the Saskatchewan Ministry of the Economy’s Subsurface Geological Laboratory (SGL) in Regina. Five of these drillholes (Figure 2) from a Questerre Energy Corporation (Questerre) drill program on the northwest flank of the Pasquia Hills in 2012 were selected for core sampling and multi-element analysis. The oil shales in this area, which generally contain ≥5% total organic carbon (TOC), have average cored sections of about 30 m. Figure 2 – Locations of the five Questerre Arborfield drillholes selected for the core sampling program, with the local interpreted geology noted (base map is from the Geological Atlas of Saskatchewan, Saskatchewan Ministry of the Economy website). Locations of other drillholes with core available at the SGL are also indicated (green dots) but not labelled. The complete geochemical results, as well as information on the drillhole and sample locations, are tabulated in Data File 41, a separate publication associated with this paper. Saskatchewan Geological Survey 2 Summary of Investigations 2016, Volume 2 2. Deposit Model for Metalliferous Black Shales Pyritic black shales occur throughout the world and are potential sources of a wide variety of metals that may include Ni, Mo, As, Zn, Pb, Cu, Cd, Co, Cr, U, V, Se, Ag, Au, platinum group elements (PGE), rare metals, and rare earth elements (REE)+(Y,Sc) in addition to oil and industrial minerals. They typically have high organic carbon contents, to which the metal contents are commonly correlated. The stratabound to stratiform mineralization tends to be very large, low grade and regionally extensive, but with rare, notable high-grade exceptions such as in southern China. The black shales are commonly related to periods of widespread oceanic anoxia. Deposits and districts that have been and are being mined include Talvivaara, Finland; Yangtze Platform, southern China; and the Alum Shale, Sweden. There are two principal genetic theories for their formation: 1) hydrothermal metal exhalation along basin margin faults with the deposition of metals in reduced, anoxic sediments; and 2) absorption of metals from seawater onto organic matter, followed by concentration in sulphides and other minerals in anoxic sediments during diagenesis under euxinic conditions. a) World Examples The Talvivaara Ni-Cu-Zn deposit in Finland is a Precambrian example of mineralized, metamorphosed, sulphidic black shale (Loukola-Ruskeeniemi and Heino, 1996). It is hosted by the Paleoproterozoic Kainuu schist belt, which consists mainly of metasedimentary rocks with discontinuous serpentinites. The orebody, which is mined by open pit and bio-heap-leach methods, contains 300 million tonnes grading 0.26% Ni, 0.14% Cu and 0.53% Zn, with 100 ppm Mo, 630 ppm V and 7% organic C. The deposit is up to 330 m thick, although this has been modified by tectonic thickening. Dominant sulphides, comprising pyrrhotite and pyrite with minor chalcopyrite, sphalerite, alabandite and pentlandite, occur as fine disseminations, and as coarser grains in quartz-sulphide veins. Loukola-Ruskeeniemi and Heino (1996) attribute the mineralization to hydrothermal activity in a rift environment with deposition in organic-rich anoxic sediments. Early Cambrian, black shale–hosted Mo-Ni and V mineralization of the Yangtze Platform, China occurs as a thin (a few centimetres) sulphide horizon with a strike length of about 1600 km (Lehmann et al., 2016). Mining occurs intermittently along this extent. The mineralization consists of Mo (~4%) and Ni (~2%), with about 600 ppm V and highly anomalous Zn, As, Se, Au, Ag, PGE and U. Metal enrichment is attributed to an environment of high biological activity, a very low clastic sediment accumulation rate, and a low rate of organic matter deposition in a stratified oxic- suboxic-euxinic basin, with the bottom water/sediment interface scavenging metals under euxinic conditions. The Alum Shale in Sweden has been mined periodically for centuries for alum [KAl(SO4)2-12H2O], oil and uranium (Large, 2012). It is a Cambrian to Lower Ordovician, organic-rich, pyritic shale unit that is 20 to 60 m thick, within black shales that are over 200 m thick. At the Viken project, an NI 43-101–compliant Inferred Mineral Resource of 3.019 billion tonnes grading 172 ppm U3O8, 335 ppm Ni, 120 ppm Cu and 421 ppm Zn has been defined (Continental Precious Minerals Inc., 2014). The deposit was also reported to contain significant concentrations of molybdenum and vanadium. The Nick property in Yukon bears similarities to the southern China deposits (Hulbert et al., 1992).