Preliminary Observations on the Geology and Mineralogy of the Rapid Creek Formation, Blow River and Davidson Mountains Map Area (NTS 117A/8 and NTS117 A/9), Yukon
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Preliminary observations on the geology and mineralogy of the Rapid Creek Formation, Blow River and Davidson Mountains map area (NTS 117A/8 and NTS117 A/9), Yukon Heidi Tomes Department of Earth Sciences, University of Toronto, Toronto, ON Kimberly Tait and Ian Nicklin Royal Ontario Museum, Toronto, ON Ronald Peterson Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, ON Robert Beckett Peterborough, Ontario Tomes, H., Tait, K., Nicklin, I., Peterson, R., and Beckett, R., 2013. Preliminary observations on the geology and mineralogy of the Rapid Creek Formation, Blow River and Davidson Mountains map area (NTS 117A/8 and NTS117A/9), Yukon. In: Yukon Exploration and Geology 2012, K.E. MacFarlane, M.G. Nordling, and P.J. Sack (eds.), Yukon Geological Survey, p. 147-161. ABSTRACT The Rapid Creek Formation, exposed at Big Fish River and Rapid Creek, in the Richardson Mountains of Yukon is well known for its rare phosphate minerals. Mapping, geochemical sampling, and collection of phosphate minerals and nodules from this formation occurred over a three week field program in the summer of 2012. The Rapid Creek Formation is a phosphorite-rich ironstone facies composed of alternating beds of phosphate and siderite-rich mudstones and shale. Secondary minerals collected from crosscutting mineralized veins in this area include unusual apatite, augelite, arrojadite group minerals, dypingite, lazulite, and garyansellite-kryzhanovskite. Phosphate nodules with satterlyite, wolfeite, vivianite-barićite, wicksite, and arrojadite-group minerals have been identified and collected for study. [email protected] YUKON EXPLORATION AND GEOLOGY 2012 147 Yukon GeoloGical ReseaRch INTRODUCTION of 2012, the authors completed a three week, preliminary mapping and geochemical sampling field program of Phosphate minerals were first discovered in the Rapid the Rapid Creek Formation at Big Fish River, Yukon and Creek area when Campbell (1962) identified lazulite, collected specimens from both Rapid Creek and Big MgAl (PO ) (OH) , in samples collected by B. Cameron, 2 4 2 2 Fish River. A preliminary study of the geological setting but this early discovery was not followed up on. In the and mineralization observed during this field program is 1970s, F.G. Young, a geologist with the Geological presented here. Survey of Canada noted this occurrence which drew the attention of Welcome North Mines (Young, 1972; Young and Robertson, 1984). Subsequently Al Kulan, prospector GEOLOGICAL SETTING and Director of Welcome North Mines, found large well- The phosphatic ironstone deposit at Rapid Creek and crystallized specimens of lazulite and other phosphate Big Fish River lies within the Richardson Mountains minerals while staking claims in the area (Young and in northeast Yukon (Fig. 1; Young et al., 1976). The Robertson, 1984; Robinson et al., 1992). The incredible sediments were deposited as part of an Aptian-Albian quality of the crystals of rare phosphates such as wardite, flysch sequence in the Blow trough, a structural depression NaAl (PO ) (OH) ·2H O, arrojadite-group minerals, and 3 4 2 4 2 about 50 km wide that runs approximately north-south lazulite (now recognized as Yukon’s official gemstone) (Young and Robertson, 1984; Robinson et al., 1992). The prompted numerous collecting trips to the area by Royal sequence was bordered by the Cache Creek High to the Ontario Museum mineralogists throughout the 1970s east, where the Richardson Mountains are now located, (Robinson et al., 1992). There have been fifteen new and uplift to the west (Young and Robertson, 1984; minerals discovered from this region, including barićite Robinson et al., 1992). The combination of subsidence of (Sturman and Mandarino, 1976), gormanite (Sturman the Blow trough and erosion due to the uplift to the west et al., 1981a), marićite (Sturman et al., 1977), nahpoite resulted in the formation of a thick sequence of turbidite (Coleman and Robertson, 1981), satterlyite (Mandarino sandstone, conglomerate, mudstone, and shale which et al., 1978), and wicksite (Sturman et al., 1981b). More thins towards the eastern structural high and grades into recently, previously collected samples from this locality the Rapid Creek Formation (Young and Robertson, 1984; have been studied with modern instruments resulting in Robinson et al., 1992). The flyschoid sequence was buried the description of bobdownsite (Tait et al., 2011), and by approximately 1500 to 3000 m of sediment during the new arrojadite group end members (Tomes, in progress). Late Cretaceous and Early Tertiary, and was later affected Many studies in the 1970s and 1980s described these by the onset of Tertiary Laramide deformation, which new minerals but only studies by Robertson (1980, caused faulting, compression, uplift, and erosion to occur, 1982), Young and Robertson (1984) and Yeo (1992) have bringing the Albian portion of the sequence to the present considered the geological setting of these minerals. day surface (Young and Robertson, 1984). The Rapid Creek Formation is unusual in a number of respects: (1) the formation conditions for phosphorites RAPID CREEK FORMATION and siderite-rich ironstones are not complementary to The strata studied here have been called various names one another; (2) primary mineralogy in most phosphorite such as the Aptian-Albian flysch division (Young et al., consists of carbonate-rich fluorapatite (commonly known 1976), the upper Aptian to lower Albian flysch (Jeletzky, as francolite), Ca (PO CO ) (F,O); however, at Big Fish 5 4, 3 3 1971), the Albian flyschoid phase (Young, 1973; Norris River the principal mineralogy consists of microcrystalline and Yorath, 1981), and the Aptian-Albian flysch sequence secondary phosphate minerals with an unknown Ca-Fe-Mg (Young, 1972). Yeo (1992) notes that Robertson (1980, phosphate origin (Robertson, 1980, 1982). (3) The 1982) proposed the name the Rapid Creek Formation but geological environment that allowed these assemblages of disputes this title commenting that at least three units of rare phosphates to form is unique; the sedimentary rocks formation rank are described within this by Norris (1981, host several mineral species previously known only from 1983) and Young (1977). Yeo (1992) describes a Rapid igneous and more highly metamorphosed environments. Creek group that includes three map units from Norris The current study has set out to elucidate the relationships (1981) Ksr, Krr, and Kbr and informally calls the unit of between the host ironstone and the unusual secondary interest the Blow River Formation. However, Yeo (1992) phosphate minerals found at this locality. In the summer overlooks the description by Young and Robertson (1984) 148 YUKON EXPLORATION AND GEOLOGY 2012 Tomes eT al. – GeoloGY & MineRaloGY of Rapid cReek foRMation, RichaRdson Mountains 136°50'0"W 136°40'0"W 136°30'0"W M M M M M M M M M M M M M M 0 2.5 5 68°35'0"N Yukon km 68°35'0"N No r t h F w est reek y r T e apid C o t R rr M i i rr t o e M T r ies ukon Y 68°30'0"N 68°30'0"N er iv F ish R Big F F M M F M M M M M M M M M M M M M M F F 68°25'0"N M M M M M M M M M M M M M M M 68°25'0"N M M M M M M M M M M M M M M 136°50'0"W 136°40'0"W 136°30'0"W 136°20'0"W Legend QUATERNARY QUATERNARY: Hummocky or ridged moraine in area of Laurentide glaciation UPPER CRETACEOUS AND LOWER TERTIARY FISH RIVER GROUP: Moose Channel Formation: lower part: sandstone, conglomeritic, lithic; alluvial and deltaic TENT ISLAND FORMATION: upper member: mudstone and sandstone; marine; includes Cuesta Creek Member BOUNDARY CREEK FORMATION: mudstone, bituminous, bentonitic, ironstone concretions; marine LOWER CRETACEOUS Kbr: RAPID CREEK FORMATION: sandstone, conglomerate and shale; flyschoid Krr: RAT RIVER FORMATION: interbedded units of sandstone and shale; marine UNDIVIDED: shale, siltstone, sandstone and coal; marine and nonmarine; includes Mount Goodenough Formation McGUIRE FORMATION: shale, siltstone and very fine grained argillaceous bioturbated sandstone; ironstone concretions in lower beds; marine MARTIN CREEK FORMATION: sandstone, coal, and shale; marine and nonmarine JURASSIC AND LOWER CRETACEOUS KINGAK FORMATION: dark grey siltstone and shale; marine PORCUPINE RIVER FORMATION: siltstone and fine to very fine grained sandstone; marine and nonmarine HUSKY FORMATION: shale, siltstone and ironstone; marine Symbols geological boundary............................................................................................................... syncline (defined, approximate)............................................................................................. F anticline (defined, approximate)............................................................................................. M fault, extention (solid cicle indicates downthrow side; defined, approximate)....................... Figure 1. General geology map showing the location of the Kbr unit from Norris (1981) which is equivalent to the Rapid Creek Formation. The study areas along Big Fish River and Rapid Creek from the 2012 field season are indicated by black squares. Inset shows general location of study area in Yukon. Modified from Norris (1981). YUKON EXPLORATION AND GEOLOGY 2012 149 Yukon GeoloGical ReseaRch which formally names the ironstone facies previously The sedimentology of the Rapid Creek Formation is of known as the Bedded ironstone and shale unit (Young, interest due to the unique composition of phosphate 1972, 1973, 1977; Young et al. 1976) of the Aptian-Albian grains within some of the ironstone facies (Robertson, flysch division as the Rapid Creek Formation. According 1980, 1982; Young and Robertson, 1984). The phosphate to the outcrop map in Young and Robertson (1984) the grains within the coarser grained sediments consist of 2+ 3+ Rapid Creek Formation is equivalent to, at minimum, parts arrojadite-group minerals, satterlyite, (Fe ,Mg,Fe )2(PO4)- 2+ 3+ of the Kbr formation from Norris (1981). Here the unit (OH,O), and gormanite, (Fe ,Mg)3(Al,Fe )4 (PO4)4- is called the Rapid Creek Formation based on the formal (OH)6·2H2O, the latter two of which were first described name and description published by Young and Robertson from this formation (Robertson, 1980, 1982; Young and (1984).