Uranium Deposits Uranium is a very dense metal which can be used as an abundant source of concentrated energy. It occurs in most rocks in concentrations of 2 to 4 parts per million and is as common in the earth's crust as tin, tungsten and molybdenum. . There are three main types of uranium deposits including 1.unconformity-type deposits, 2. paleoplacer deposits and 3. sandstone-type (roll front) deposits (Figure 1). Sandstone-type deposits are abundant in sedimentary rocks of the Colorado Plateau and found on the Navajo Nation. This type of uranium deposit is easier and cheaper to mine than the other types because the uranium is found near the surface of the Earth. These deposits formed when oxidized groundwater that had leached uranium from surface rocks flowed down into aquifers, where it was reduced to precipitate uraninite, the primary ore mineral of uranium. In some deposits, like those found on the Navajo Nation, reduction took place along curved zones know as roll-fronts, which represent the transition from oxidized to reduced conditions in the aquifer.
Sandstone Unconformity Paleoplacer Figure 1 Geologic setting of important types of uranium deposits. Note that each type of deposit is shown in host rocks of the most common age. Figure courtesy of Kesler, S.E., 1994, Mineral Resources, Economics and the Environment : Macmillan, New York, 394 p.
Unconformity Uranium Deposits The unconformity-type deposits are the world’s main source of uranium. These deposits form at or near the contact between an overlying sandstone and underlying metamorphic rocks, often metamorphosed shales. The orebodies have lens – or pod – like shapes, and most often occur along fractures in sandstone or in basement rocks. The host rocks often have disseminated uranium minerals and show hydrothermal alterations, which may indicate that the deposits formed after the rocks. The mineralized bodies may carry minor amounts of sulphide minerals like pyrite, arsenopyrite, galena and sphalerite, as wall as nickel-cobalt arsenides.
Because this type of deposit is a relatively recent discovery – the first uranium deposits in Saskatchewan and northern Australia were found in the late 1960s and early 1970s – geologists are still trading theories about their origin. A model that has gained favor in recent years suggests that fluids with dissolved uranium and other metals, moving through the sandstone, encountered the basement rocks, where chemical conditions were ideal to cause the metals to precipitate from solution.
Uranium Minerals The major primary ore mineral is uraninite (basically UO2) or pitchblende (U2O5.UO3, better known as U3O8), though a range of other uranium minerals is found in particular deposits. These include carnotite (uranium potassium vanadate), the davidite-brannerite-absite type uranium titanates, and the euxenite-fergusonite-samarskite group(niobates of uranium and rare earths). Brannerite is particularly important as it occurs as up to 30% of the mineralisation at Olympic Dam and over 20% at Valhalla near Mount Isa, but does not dissolve readily in sulfuric acid and so is largely not recovered. Research is being undertaken to improve the recovery of this, which has significant implications for the quantum of Australian recoverable low-cost resources of uranium.
鈾主要的礦石為 • 瀝青鈾礦 (Pitch blende, U3O8) • 方鈾礦 (Uraninite, UO2) • 鈾石 [Coffinite, ] • 釩酸鉀鈾礦 (Carnotite, K2U2V2O12．3H2O)
The uranium mineralization takes the form of carnotite (K2(UO2) 2 (VO4) 2-1-3H2O), a secondary uranium mineral. Carnotite occurs in small patches and lenses around grains and pebbles, or finely disseminated. Several discontinuous, tabular mineralized bodies of economic interest occur over an area measuring 15 km by 0.5 km. Mineralization occur in a zone above and below the water table. Thickness of the mineralized zones varies from less than 1 m to 15 m, but may locally exceed 30 m. The total historical resource for Langer Heinrich is 22.2 Mt at 0.1% U3O8. Carnotite: a yellow secondary uranium mineral
A large variety of secondary uranium minerals is known, many are brilliantly coloured and fluorescent. The commonest are gummite (a general term like limonite for mixtures of various secondary hydrated uranium oxides with impurities); hydrated uranium phosphates of the phosphuranylite type, including autunite (with calcium), saleeite (magnesian) and torbernite (with copper); and hydrated uranium silicates such as coffinite, uranophane (with calcium) and sklodowskite (magnesian).
Geology of Uranium Deposits • Uranium occurs in a number of different igneous, • hydrothermal and sedimentary geological environments. • Most of Australia's uranium resources are in two kinds of • orebodies, unconformity-related and breccia complex, • while sedimentary deposits are less significant than • overseas. Most Canadian deposits are unconformity- • related. • Uranium deposits world-wide can be grouped into 10 major categories of deposit types based on the geological setting of the deposits (OECD/NEA & IAEA, 2000). Australian uranium deposits can be grouped into 6 of these categories, with some mineralisation in two further ones:
1. Unconformity-related deposits - Unconformity-related deposits arise from geological changes occurring close to major unconformities. Below the unconformity, the metasedimentary rocks which host the mineralisation are usually faulted and brecciated. The overlying younger Proterozoic sandstones are usually undeformed. Unconformity-related deposits constitute approximately 33% of the World Outside Centrally Planned Economies Area (WOCA)'s uranium resources and they include some of the largest and richest deposits. Minerals are uraninite and pitchblende. The main deposits occur in Canada (the Athabasca Basin, Saskatchewan and Thelon Basin, Northwest Territories); and Australia (the Alligator Rivers region in the Pine Creek Geosyncline, Northern Territories and Rudall River area, W Australia).
T -Thelon Canadian Paleo-Mesoproterozoic basins (red) within the Canadian Shield have potential for or contain known unconformity-associated U deposits..
Alligator Rivers Region Rudall River Region Olympic Dam
Unconformity-related deposits constitute a major proportion (20%) of Australia's total uranium resources, and much of Australia's total production since 1980 has been mined from two of these deposits - Nabarlek (now mined out) and Ranger 1 & 3. Other major deposits in the Alligator Rivers region are Jabiluka, Koongarra and Ranger 68. Today, all of Canada's uranium production is from unconformity-related deposits - Key Lake, Cluff Lake, Rabbit Lake (all now depleted), and McClean Lake and McArthur River deposits. Other large, exceptionally high grade unconformity-related deposits currently being developed include Cigar Lake (averaging almost 20% U3O8, some zones over 50% U3O8).
The deposits in the Athabasca Basin occur below, across and immediately above the unconformity, with the highest grade deposits situated at or just above the unconformity (e.g. Cigar Lake and McArthur River). In the Alligator Rivers region, the known deposits are below the unconformity and like their Canadian counterparts, are generally much lower grade. Uranium exploration in the Alligator Rivers region and Arnhem Land has been restricted since the late 1970s because of political and environmental factors. Much of the Alligator Rivers region and Arnhem Land have only been subjected to first pass exploration designed to detect outcropping deposits and extensions of known deposits, e.g. Jabiluka 2 was found by drilling along strike from Jabiluka 1.
Kombolgie S.S.= 1650 Ma Kombolgie unconformity
2. Breccia complex deposits - The Olympic Dam deposit is one of the world's largest deposits of uranium, and accounts for about 66% of Australia’s reserves plus resources. The deposit occurs in a hematite-rich granite breccia complex in the Gawler Craton. It is overlain by approximately 300 metres of flat-lying sedimentary rocks of the Stuart Shelf geological province. The central core of the complex is barren hematite-quartz breccia, with several localised diatreme structures, flanked to the east and west by zones of intermingled hematite-rich breccias and granitic breccias. These zones are approximately one kilometre wide and extend almost 5 km in a northwest-southeast direction. Virtually all the economic copper-uranium mineralisation is hosted by these hematite-rich breccias. This broad zone is surrounded by granitic breccias extending up to 3 km beyond the outer limits of the hematite-rich breccias.
Figure 1. Distribution of Australia's initial in-ground uranium resources (t U3O8), by type of deposit. (Source of data: OZMIN 2005).
The deposit contains iron, copper, uranium, gold, silver, rare earth elements (mainly lanthanum and cerium) and fluorine. Only copper, uranium, gold, and silver are recovered. Uranium grades average from 0.08 to 0.04% U3O8, the higher-grade mineralisation being pitchblende. Copper grades average 2.7% for proved reserves, 2.0% for probable reserves, and 1.1% for indicated resources. Gold grades vary between 0.3-1.0 g/t. Details of the origin of the deposit are still uncertain. However the principal mechanisms which formed the breccia complex are considered to have been hydraulic fracturing, tectonic faulting, chemical corrosion, and gravity collapse. Much of the brecciation occurred in near surface eruptive environment of a crater complex during eruptionscaused by boiling and explosive interaction of water (from lake, sea or groundwater) with magma.
3. Sandstone deposits - Sandstone uranium deposits occur in medium to coarse-grained sandstones deposited in a continental fluvial or marginal marine sedimentary environment. Impermeable shale/mudstone units are interbedded in the sedimentary sequence and often occur immediately above and below the mineralised sandstone. Uranium precipitated under reducing conditions caused by a variety of reducing agents within the sandstone including: carbonaceous material (detrital plant debris, amorphous humate, marine algae), sulphides (pyrite, H2S), hydrocarbons (petroleum), and interbedded basic volcanics with abundant ferro-magnesian minerals (e.g. chlorite).
Sandstone deposits constitute about 18% of world uranium resources. Orebodies of this type are commonly low to medium grade (0.05 - 0.4% U3O8) and individual orebodies are small to medium in size (ranging up to a maximum of 50 000 t U3O8). The main primary uranium minerals are uraninite and coffinite. Conventional mining/milling operations of sandstone deposits have been progressively undercut by cheaper in situ leach mining methods. The United States has large resources in sandstone deposits in the Western Cordillera region, and most of its uranium production has been from these deposits, recently by in situ leach (ISL) mining. The Powder River Basin in Wyoming, the Colorado Plateau and the Gulf Coast Plain in south Texas are major sandstone uranium provinces.
Other large sandstone deposits occur in Niger, Kazakhstan, Uzbekistan, Gabon(Franceville Basin), and South Africa (Karoo Basin). Kazakhstan has reported substantial reserves in sandstone deposits with average grades ranging from 0.02 to 0.07% U. Sandstone deposits represent only about 7% of Australia's total resources of uranium. Within the Frome Embayment, six uranium deposits are known, the largest being Beverley, Honeymoon, East Kalkaroo and Billaroo West-Gould Dam, all amenable to ISL mining methods. Other deposits are Manyingee, Oobagooma, and Mulga Rock in WA and Angela, NT. At Mulga Rock uranium mineralisation is in peat layers interbedded with sand and clay within a buried palaeochannel.
4. Surficial deposits - Surficial uranium deposits are broadly defined as young (Tertiary to Recent) near-surface uranium concentrations in sediments or soils. These deposits usually have secondary cementing minerals including calcite, gypsum, dolomite, ferric oxide, and halite. Uranium deposits in calcrete are the largest of the surficial deposits. Uranium mineralisation is in fine-grained surficial sand and clay, cemented by calcium and magnesium carbonates. Surficial deposits comprise about 4% of world uranium resources. Calcrete deposits represent 5% of Australia’s total reserves and resources of uranium. They formed where uranium-rich granites were deeply weathered in a semi-arid to arid climate. The Yeelirrie deposit in WA is by far the world's largest surficial deposit. Other significant deposits in WA include Lake Way, Centipede, Thatcher Soak, and Lake Maitland.
Yeelirrie Figure 3. Australian uranium deposits in relation to occurrences of felsic igneous rocks known to have at least 10 ppm uranium.
In WA, the calcrete uranium deposits occur in valley-fill sediments along Tertiary drainage channels, and in playa lake sediments. These deposits overlie Archaean granite and greenstone basement of the northern portion of the Yilgarn Craton. The uranium mineralisation is carnotite (hydrated potassium uranium vanadium oxide). Calcrete uranium deposits also occur in the Central Namib Desert of Namibia. Calcrete = caliche = opaque, reddish-brown to white calcareous material of secondary accumulation (in place), commonly found in layers on the surface of stony soil of arid and semiarid regions, but also occurring as a subsoil deposit in subhumid climates. It is composed largely of crusts or succession of crusts of soluble calcium salts in addition to impurities such as gravel, sand, silt and clay.
5. Volcanic deposits - uranium deposits of this type occur in acid volcanic rocks and are related to faults and shear zones within the volcanics. Uranium is commonly associated with molybdenum and fluorine. These deposits make up only a small proportion of the world’s uranium resources. Significant resources of this type occur in China, Kazakhstan, Russian Federation and Mexico. In Australia, volcanic deposits are quantitatively very minor - Ben Lomond and Maureen in Qld are the most significant deposits.
6. Intrusive deposits - included in this type are those associated with intrusive rocks including granite, pegmatite, and monzonites. Major world deposits include Rossing (Namibia), Ilimaussaq (Greenland) and Palabora (South Africa). In Australia, the main ones are Radium Hill (SA) which was mined from 1954-62 (mineralisation was mostly davidite) and the large bodies of low grade mineralisation at Crocker Well and Mount Victoria in the Olary Province, SA. Davidite: A dark-brown uraniferous, iron-titanate mineral. It is a primary mineral in high-temperature hydrothermal lodes, occurs in pegmatites and basic igneous rocks.
7. Metasomatite deposits - these occur in structurally-deformed rocks that were already altered by metasomatic processes, usually associated with the introduction of sodium, potassium or calcium into these rocks. Major examples of this type include Espinharas deposit (Brazil) and the Zheltye Vody deposit (Ukraine). Valhalla and Skal near Mount Isa are Australian examples. 8. Metamorphic deposits - In Australia the largest of this type was Mary Kathleen uranium/rare earth deposit, 60km east of Mount Isa, Qld, which was mined 1958-63 and 1976-82. The orebody occurs in a zone of calcium-rich alteration within Proterozoic metamorphic rocks.
9. Quartz-pebble conglomerate deposits - these deposits make up approximately 13% of the world's uranium resources. Where uranium is recovered as a by-product of gold mining, the grade may be as low as 0.01% U3O8. In deposits mined exclusively for uranium, average grades range as high as 0.15% U3O8. Individual deposits range in size from 6000-170 000 t contained U3O8. Major examples are the Elliot Lake deposits in Canada and the Witwatersrand gold-uranium deposits in South Africa. The mining operations in the Elliot Lake area have closed in recent years because these deposits are uneconomic under current uranium market conditions. No such economic deposits are known in Australia, although quartz-pebble conglomerate containing low-grade uraninite and gold mineralisation exists in several Archaean-Palaeoproterozoic basins in Western Australia. These are similar in lithology and age to the Witwatersrand conglomerates, being formed before there was any oxygen in the atmosphere.
10. Vein deposits - Vein deposits constitute about 9% of world uranium resources. Major deposits include Jachymov (Czech Republic) and Shinkolobwe (Zaire). The Olympic Dam deposit is the largest U resource in the world but it is also the lowest in grade and essentially a one-of-a-kind Cu deposit from which U is won as a by-product along with REE, gold, silver and many other commodities. The present annual production capacity of this underground deposit is limited to 4,500 t U from ore grading close to 1.6% Cu, 0.06 % U, 0.6 g/t Au and 6 g/t Ag. Plans are to increase it to the level of 6,500 t U. This tonnage must be viewed in the context of the world production of 36,112 t U in year 2000, and the demand of 64, 014 t U for the world's 438 commercial nuclear reactors (NEA-IAEA, 2001). Other very large but low-grade U resources of the world include the volcanogenic Streltsovka caldera in Russia with 250,000 t U, sandstone types in Kazakhstan and Niger with multiples of 100,000 t U, and the historic Erzgebirge vein type district with over 200,000 t U.
Unconformity Associated Uranium Deposits in Canada by C.W. Jefferson, D.J. Thomas2, S.S. Gandhi1, P. Ramaekers3, G. Delaney4, D. Brisbin2, C. Cutts5, P. Portella5, and R.A. Olson6 1 Geological Survey of Canada, 601 Booth Street, Ottawa K1A 0E82 Cameco Corporation, 2121 - 11th Street West, Saskatoon, SK S7M 1J33 MF Resources, 832 Parkwood Dr. SE, Calgary, AB T2J 2W74 Saskatchewan Industry and Resources, 2101 Scarth Street, Regina SK S4P 3V75 AREVA subsidiary COGEMA Resources Inc., P.O. Box 9204, 817 - 45th St. W., Saskatoon, SK S7K 3X56 Alberta Geological Survey, Energy Utilities Board, 4th Fl., Twin Atria, 4999-98 Ave., Edmonton AB T6B 2X3
Abstract This paper reviews the attributes and context of unconformity-associated uranium (U) deposits. In these, pods, veins and semi-massive replacements of uraninite are overlain by quartz dissolution / clay - dravite - quartz alteration halos and located near unconformitiesbetween Paleo- to Mesoproterozoic siliciclastic basins and metamorphic basement. In major producing basins (e.g. Athabasca, Kombolgie) the 1-2 km, flat-lying, and apparently un-metamorphosed, mainly fluvial strata include red to pale tan quartzose conglomerate, arenite and mudstone deposited from ~1730 to <1540 Ma and pervasively altered. Below the basal unconformity, red hematitic and bleached clay-altered regolith grades down through chloritic altered to fresh basement gneiss.
The highly metamorphosed, interleaved Archean to Paleoproterozoic granitoid and supracrustal basement gneiss includes graphitic metapelite that preferentially hosts shear zones and ore deposits. A variety of deposit shapes, sizes and compositions ranges from monometallic U and generally basement-hosted moderately dipping veins, to U-dominated polymetallic sub-horizontal uraninite lenses just above or straddling the unconformity, including variable Ni, Co, As, Pb >> Au, Pt, Cu, REE and Fe. Athabasca U deposits record one or two primary hydrothermal alteration and ore-forming events~1500-1600 and 1460-1350 Ma with U remobilization ~1176, 900 and 300 Ma.
Definition Unconformity-associated uranium (U) deposits comprise massive pods, veins and/or disseminations of uraninite spatially associated with unconformities between Proterozoic siliciclastic basins and metamorphic basement. The siliciclastic basins (Figure 1) are relatively flat-lying, un-metamorphosed, late Paleoproterozoic to Mesoproterozoic, fluvial red-bed strata. The underlying basement rocks comprise tectonically interleaved Paleoproterozoic metasedimentary and Archean to Proterozoic granitoid rocks. Uranium as uraninite (commonly in the form of pitchblende) is the sole commodity in the monometallic sub-type and principle commodity in the polymetallic sub-type that includes variable amounts of Ni, Co, As and traces of Au, Pt, Cu and other elements. Some deposits include both sub-types and transitional types, with the monometallic tending to be basement-hosted, and the polymetallic generally hosted by basal siliciclastic strata and paleo-weathered basement at the unconformity.
T -Thelon Canadian Paleo-Mesoproterozoic basins (red) within the Canadian Shield have potential for or contain known unconformity-associated U deposits..
Figure 3:Relationships of the Athabasca Basin to major tectonic elements of the northwestern Canadian Shield.
Grade, Tonnage and Value Statistics Global Unconformity-Associated And Other Uranium Resources Global context and consideration of all U deposit types are important for those engaged in production, exploration and outreach in the Canadian nuclear energy industry, because social-political aspects of the nuclear energy industry strongly affect its viability around the world. World U resources are contained in some ten different deposit types, with the major types in decreasing order of world resources as follows: Mesoproterozoic unconformity associated (>33% in Australia and Canada), the one giant Olympic Dam Mesoproterozoic breccia complex deposit in Australia (>31%), sandstone hosted (18%, mostly in the USA, Kazhakstan and Niger), surficial deposits (4% mainly in Australia), large tonnage but low grade resources in early Paleoproterozoic conglomeratic deposits, and small percentages in volcanic, metasomatic, metamorphic, granite-hosted and vein-type deposits (World Uranium Mining, 2004).
The Olympic Dam deposit is the largest U resource in the world but it is also the lowest in grade and essentially a one-of-a-kind Cu deposit from which U is won as a by-product along with REE, gold, silver and many other commodities. The present annual production capacity of this underground deposit is limited to 4,500 t U from ore grading close to 1.6% Cu, 0.06 % U, 0.6 g/t Au and 6 g/t Ag. Plans are to increase it to the level of 6,500 t U. This tonnage must be viewed in the context of the world production of 36,112 t U in year 2000, and the demand of 64, 014 t U for the world's 438 commercial nuclear reactors (NEA-IAEA, 2001). Other very large but low-grade U resources of the world include the volcanogenic Streltsovka caldera in Russia with 250,000 t U, sandstone types in Kazakhstan and Niger with multiples of 100,000 t U, and the historic Erzgebirge vein type district with over 200,000 t U.
Geological Attributes Continental scale (geotectonic environment) The continental-scale geotectonic environment of significant unconformity-associated U deposits is, in simple terms, at the base of flat lying, thin (less than 5 km) fluviatile strata resting on peneplaned tectonometamorphic complexes in the interiors of large cratons. Cross sections of the Athabasca Basin illustrate these relationships (Figs. 4, 5). The influence of plate or plume tectonics on the origins, diagenesis and mineralization processes of interior Proterozoic basins are considered enigmatic (Ross, 2000). Peneplaned and deeply paleo-weathered basement, and continental sedimentation, implies prolonged stable cratonic environments that persisted before and during the mineralization. This long-held view is modified in light of recent tectonostratigraphic analysis by Ramaekers and Catuneanu (2004) and Ramaekers et al. (2005a), and seismic insights into the deep basement (Hajnal et al., 2005). These provide reasonable and testable modern plate-tectonic hypotheses for the origin of the Athabasca Basin, as follows.
Figure 4: Regional geology of the Athabasca Basin region in northern Saskatchewan and Alberta.
Figure 5: Lithostratigraphic cross section of the Athabasca Basin. MF are members of Manitou Falls Formation; MFw is Warnes Member. Line of section is shown as NW-SE in Figure 4. Structural cross section shown as W-E in Figure 4.
Ramaekers et al. (2005a) deduce that the Athabasca and Thelon repositories of fluvial strata developed accommodation space and subsequent hydrothermal processes by a combination of escape tectonics driven by far field stresses, high heat flow resulting from intrusion of deep mafic magmas (possibly the regional "bright reflector" of Hajnal et al., 1997, 2005; Macdougall and Heaman, 2002) and/or subsidence possibly caused by mantle phase changes associated with relict descending shallow-subduction slabs. The escape tectonic framework (i.e. crustal wedges being squeezed out laterally by converging cratons) is based on evidence of very subtle transtensional to transpressive Mesoproterozoic tectonism, marked by brittle reactivation of a network of regional to secondary and tertiary Paleoproterozoic fault zones in the 1.9 Ga Taltson and 1.8 Ga Trans-Hudson orogens that accommodated ductile transpression during convergence of the Slave, Rae and Superior provinces (e.g. Hoffman, 1988).
Time and space distribution of unconformity-associated uranium districts • Unconformity-associated U deposits in the Athabasca and Thelon basins are constrained in age by recent detrital and diagenetic geochronology of stratigraphic sequences above the unconformity, linked with existing geochronology of the deposits. Rainbird et al. (2005) estimate that sedimentation began in the Athabasca Basin at about 1740-1730 Ma, considering metamorphic ages on titanite as young as 1750 Ma in basement rocks (Orrell, et al., 1999). The Barrensland Group of Thelon Basin also has a maximum age of 1750-1720 Ma (Miller, et al., 1989; Rainbird, et al., 2003a) based on ages of early diagenetic phosphatic material in basal strata.
The upper ages of these two groups are weakly constrained. Rainbird et al. (2005) have dated internal tuffaceous units in the third sequence of the Athabasca Group (Wolverine Point Formation) at 1644±13Ma (U-Pb), close to previous approximate U-Pb dates of >1650-1700 Ma on diagenetic fluorapatite in Fair Point and Wolverine Point formations by Cumming et al. (1987). Sequence 4 is capped by organic-rich shale of the Douglas Formation that appears to be about 100 Ma younger (Creaser and Stasiuk, 2005) and carbonate (Carswell Formation) whose upper age is unconstrained. Uranium deposits could have formed before either of these times, and the fluorapatite ages of >1650-1700 Ma suggest a basin-wide diagenetic/hydrothermal event at about that time. Available geochronology of Athabasca U deposits records one or two main hydrothermal ore-related events within the basin at circa 1500 and 1350 Ma that were overprinted by further alteration and U remobilization events at approximately 1176 Ma, 900 Ma and 300 Ma (Hoeve and Quirt 1984; Cumming and Krstic 1992; Fayek et al., 2002a). This implies that the U deposits began to form while sediment was still accumulating in the Athabasca Basin, after early diagenesis and during late, high-temperature diagenesis with a remarkable time span of at least 100 Ma, and possibly more than 200 Ma.
Figure 11: Simplified mineral paragenesis of the Paleo- to Mesoproterozoic Athabasca, Thelon and Kombolgie basins. The ages of primary uraninite, U1 (~1500-1600) and U1' (~1350-1400) might both be primary. Depositional ages in the Athabasca Group are Zv: U-Pb on volcanic zircon in Wolverine Point Formation, and Os-Re: primary organic matter in Douglas Formation.