Sedimentology and Provenance of the Wood Mountain Formation and Derived Glacial and Glaciofluvial Sediments – Context for Kimberlite Indicator Mineral Anomalies
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Preliminary Investigation: Sedimentology and Provenance of the Wood Mountain Formation and Derived Glacial and Glaciofluvial Sediments – Context for Kimberlite Indicator Mineral Anomalies Lynn Kelley and Gary Yeo Kelley, L. and Yeo, G. (2004): Preliminary investigation: Sedimentology and provenance of the Wood Mountain Formation and derived glacial and glaciofluvial sediments – context for kimberlite indicator mineral anomalies; in Summary of Investigations 2004, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2004-4.2, CD-ROM, Paper A-12, 10p. Abstract Garnet, diopside, and chromite with chemistries inferred to indicate mantle affinity are geochemical pathfinders exploited in prospecting for diamond. In southern Saskatchewan, these minerals are found in high abundances in gravel, sand, and poorly-consolidated conglomerate of the Wood Mountain Formation, and overlying tills and glaciofluvial deposits. Several campaigns have been mounted to explore for a potential kimberlitic source for these pathfinder minerals, but no satisfactory explanation for their presence has been put forward. This project is intended to provide geological context for the occurrences of kimberlite indicator minerals found in the Wood Mountain area, by examining the transport history and provenance of the strata containing them. This note summarizes preliminary observations on sediment transport data and sediment provenance from seven locations. Grain size analysis, detailed provenance studies, and analysis for kimberlite indicator minerals and detrital gold are pending, and will be reported upon in a future communication. Keywords: Wood Mountain, kimberlite indicator, sediment provenance, paleocurrent. 1. Introduction a) Exploration History Southern Saskatchewan has been explored for diamond since at least 1963, when a De Beers affiliate discovered kimberlite indicator minerals in the Frenchman River Valley (Lehnert-Thiel et al., 1992). Kimberlite indicator mineral surveys carried out by various public agencies (Simpson, 1991; Gent, 1992; Swanson and Gent, 1993; Thorleifson and Garrett, 1993; Millard and Drever, 1994; Thorleifson et al., 1994; Millard and Day, 1996) confirmed the presence of indicator minerals in gravel, sand and poorly-consolidated conglomerate of the Wood Mountain Formation, and tills and glaciofluvial deposits of local provenance in southern Saskatchewan. The 1988 discovery by Monopros (then the Canadian exploration arm of De Beers) of the Sturgeon Lake kimberlite block, northeast of Prince Albert, was followed by an unprecedented staking rush. In addition to the central Saskatchewan staking activity that led to the discovery of the Fort à la Corne kimberlite field, Monopros, Cameco, and Better Resources staked ground in the southern part of the province. Better Resources confirmed some of the indicator mineral anomalies and flew a 5730 line-km aeromagnetic survey in search of local kimberlite sources (SIR Assessment Files 72-0005; 72G3-NE-0001; 72G6-SW-0001; 72H5-SW-0009; and 72J-0002). The company recognized several magnetic features as potential kimberlite targets, but failed to drill test any of them and most of the ground lapsed. Pure Gold Resources staked a large tract of ground in 1998, again confirmed some of the indicator mineral anomalies, and flew 16 152 km of aeromag (SIR Assessment File 72G-0001). Again, potential targets were not drill tested. Madison Exploration recently launched an exploration program in southern Saskatchewan centred on a northeast-trending linear magnetic anomaly near Scout Lake. The anomaly was identified from the Better Resources magnetic survey, but Better Resources was focused on circular structures as targets indicative of the classic kimberlite “pipe,” and ignored this linear feature. Madison has completed a Mobile Metal Ions survey over the anomaly, and plans further exploration, including drilling, in the fall of 2004. b) Previous Work Peridotitic garnet, G-10 garnet, chrome diopside, and chromite have been recorded in the Wood Mountain area (Figure 1). Peridotitic garnet abundances of 25 to more than 50 grains per sample are reported in six samples that form a northwest trend beginning just north of the village of Rockglen. Most of these samples also contain multiple grains of chrome diopside; two samples on this trend, and another just to the southwest, contain single grains of high-chromium chromite. Another cluster of samples with high abundances of peridotitic garnets and chrome diopside were collected northeast of the West Block of Grasslands National Park. One sample in this cluster Saskatchewan Geological Survey 1 Summary of Investigations 2004, Volume 2 Saskatchewan Geological Survey 2 Summary Peridotitic Garnet Eclogitic Garnet High-chrome Chromite 50 to 346 grains S# 0# 10 to 12 grains S# 19 to 26 grains S# S# 10 to 14 grains 25 to 49 grains 0# 5 to 9 grains S# S# 10 to 24 grains 5 to 9 grains 0# 1 to 4 grains # 1 to 4 grains S# 5 to 9 grains Saskatchewan # 1 to 4 grains G10 Garnet Chrome Diopside N KIM samples, non anomalous 0# 3 or 4 grains ]' 3 to 6 grains Wood Mountain Study Area 0# 2 grains Y# 2 grains Wood Mountain Fm. 0# 1 grain Y# 1 grain a N# N N#N % N N N N N N N ## N %N La0N# fleche N N N#### N N N N N N Y#0#N N N Cadillac Assiniboia N 0#N# n N S#N % N NOgema N N N N### N N N % ## N N 0#N## N S#N N## N## N 0#N N#S S# ## N N# N S#N S#N N N N## N N N# S#N S#N N# NN N N ### N S#N S# N### N % #Y# N# S#NNN N# N N S S# N S#YN #### N N# ### N 0# S#N S#N N N# Val Marie NNN Y#N YS#N S#Y#NS Wood#N S# S#YN S#NN N % S#N ## S #NSY#N S# 0#NS S#S N## S#N S#N #N ofInvestigations 2004,Volume2 NNN##### Mtn. S 0N# YS#N S#N S#N S#N S#N N# N S#N N#### N ]'S#0N S#S#NN S#N S#N S#N % N NN# N N # 0N#N S# N## NN N S#N # ### N S# N S#N N Y#N N NN # Rockglen ## N N N### N S0#N N## N S#N N S#NNN#N# N# N N## # N N # NN NN N S0#N N N N N N S# Grasslands 0 30 60 90 kilometres National Park Figure 1 - Kimberlite indicator mineral (KIM) anomalies in the Wood Mountain area. Base map from Slimmon (2002). contains a single grain of high chromium chromite. Samples containing G-10 garnets and eclogitic garnets occur throughout the area, but form no discernible pattern. The anomalous results occur more or less across the outcrop belt of the late Miocene Wood Mountain Formation, and include results from both the poorly consolidated Wood Mountain conglomerate and overlying glacioclastic sediments. The Wood Mountain Formation (and its stratigraphic equivalent in Montana, the Flaxville Formation) is one of a series of Tertiary fluvial conglomerates in southern Saskatchewan. Paleographic reconstructions by Vonhof (1969), Whitaker (1980), and Leckie and Cheel (1989) suggested that the coarse siliciclastic deposits of the Wood Mountain Formation were formed by eastward transport of coarse gravels from the Eocene-Miocene Cypress Hills Formation and northward fluvial transport of sediment derived from the Belt Supergroup and the various Cenozoic intrusive and extrusive rocks of the Montana Alkaline Province (Hearn, 1989). Kjarsgaard (1995) compared compositional data for garnet and clinopyroxene from southern Saskatchewan tills with similar data for garnet and clinopyroxene derived from Montana Alkaline Province igneous rocks and found significant overlap. One interpretation is that the rocks of the Montana Alkaline Province, eroded and transported north and east by streams, might be the source of the kimberlite indicator minerals found in the Wood Mountain Formation. Overlying tills in the Wood Mountain vicinity inherited abundant indicator minerals from the latter. Kimberlites have been documented in at least two locations in the Montana Alkaline Province: the Williams Kimberlite of the Missouri Breaks diatremes is about 200 km southwest of the Wood Mountain area, and the recently discovered Homestead Kimberlite is in the Grassrange intrusion field, about 300 km to the southwest (Ellsworth, 2000; Doden et al., 2001). Hearn (1999) described peridotitic xenoliths in aillikitic rocks at Froze-to- Death Butte, Johnson Ranch, Gold Butte, and other locations in the Porcupine Dome, about 300 km south- southwest of the Wood Mountain area. Xenolithic (contained in peridotite xenoliths) and xenocrystic (liberated from xenoliths and in contact with matrix) garnets of G-9 composition were relatively common, but no G-10 or eclogitic garnets were found. Clinopyroxene containing greater than 1.5% Cr2O3 and chromite with Cr2O3 content in the 52 to 59% range were also noted. Swanson and Gent (1993) advocated a local source for kimberlite indicator minerals in the Wood Mountain area. They noted that the abundance of kimberlite indicator minerals in till was highly variable and that there was little correlation between abundance of indicator minerals in tills and the relative proportion of locally-derived sediment (quartzite and chert cobbles) in the till. They described garnet grain surfaces from Wood Mountain area samples that showed virtually no abrasion due to sedimentary transport and in some instances also had kelyphitic rims or orange- peel textures. Furthermore, the senior author has observed euhedral prismatic bright green clinopyroxenes in tills between the two blocks of Grasslands National Park. These observations are at odds with the concept of fluvial transport from source rocks hundreds of kilometres away. Laboratory abrasion studies carried out on kimberlite indicator minerals by Atkinson (1989) and McCandless (1990) suggest that preservation of euhedral shapes or primary surface textures would be unlikely beyond a few tens of kilometres of fluvial transport. Indicator minerals may have been transported to the Wood Mountain area in lithic boulders or cobbles and the indicator minerals liberated locally.