Sedimentary Nickel, Zinc, and Platinum-group-element Mineralization in Devonian Black Shales at the Nick Property, Yukon, Canada: A New Deposit Type

Abstract A thin layer of stratiform Ni-Zn-PGE sulfide mineralization of sedimentary-diagenetic origin was deposited during the Middle to Upper Devonian in the euxinic "Nick basin". The mineralized unit (>3 cm thick), which seems to have been developed over the entire sedimentary basin of > 80 km2, consists of pyrite, vaesite (NiS^, and sphalerite. The average grade of the mineralization is about 5.3% Ni, 0.73% Zn, =770 ppb (PGE + Au), and up to 61 ppm Re. Anomalous Se, As, Mo, P, Ba and U are present. A minimum of 0.90 x 106 tonnes of Ni were deposited in the basin (based on a bed thickness of 3 cm) during the Devonian. The unique metal association, extensive lateral distribution, persistent metal grade, mineralogical makeup, and stratigraphic control demonstrate that this is a new deposit type and a new geological environment for Ni and PGE+Au. The sulfide layer occurs at the base of a Phosphatic Chert Member which is underlain by a distinctive marker unit consisting of concretionary limestone structures. The limestone spheroids may represent a vent-specific carbonate fades developed adjacent to faults that emanated nutrient-rich hydrothermal discharges just prior to the main mineralizing event. The suite of elements associated with the Nick mineralization suggests that the ore-forming metals were originally bound to organic matter derived from decaying marine organisms. Discharge of hot brines bearing organic-matter-bound metals took place along numerous conduits within basin faults that are now manifest as bitumen veins. Our syndiagenetic model proposes that these fluids were discharged laterally from the conduits into the unconsolidated bottom sediment (ooze). The introduction of this metalliferous fluid, rich in organic matter, stimulated biological activity and bacterial reduction of its contained SO4 to sulfide. Hot, dense, laterally migrating hydrothermal fluid precipitated thin sulfide-rich laminae within bottom sediment. Published thermodynamic studies suggest that the diagnostic vaesite-pyrite assemblage crystallized at approximately 138°C. The l?*S values range from -14.7 % to -10.0 %o and are up to 34 %o lighter than locally surrounding sulfides and age-equivalent mineralized strata elsewhere in the Selwyn Basin. The 513C values of calcite in the footwall of the mineralized unit (-12 %t> to -6 %o) are isotopically much lighter than regional values. The lighter isotopic character is attributed to the hydrothermal discharge of fluids enriched in organic compounds. Although geochemical profiles of the lower Earn Group sediments that host the Nick mineralization reveal that these black shales are not distinctive, the unusual Ni, Zn, PGE, U, Ba, and P elemental associations and their anomalous concentrations in stream sediments can be used to explore for this deposit type.
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Summary: The three traditional types of Variscan vein Pb-Zn-(Ag) mineralization recognized in the Bohemian massif from historic paragenetic studies are confirmed by modern metallogenic studies. Stable C, S, and O isotope data, as well as Pb and Sr isotopic ratios of the deposits, indicate a 4 predominantly crustal origin of the constituents in all three types. Although the data also suggest differences in temperature and pressure of formation, and the oxidation conditions and nature of the hydrotherma...
Publication: Exploration & Mining Geology
Author(s): J.H. BERNARD, K. ZAK
Issue: 1
Volume: 1
Year: 1992
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Summary: Giant, sediment-hosted lead-zinc deposits in northern Australia formed during development of Mid-Proterozoic extensional basins that overlie Lower Proterozoic basement. The basement in the Mount Isa area, exposed by folding and faulting, contains fractionated, high-heat-producing granites. These granites generate heat at a rate of about 6/iWm-3, probably sufficient to form giant lead-zinc deposits either by (a) driving episodic convection of saline basement and basin fluids for periods of...
Publication: Exploration & Mining Geology
Author(s): M. SOLOMON, C.A. HEINRICH
Issue: 1
Volume: 1
Year: 1992
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Summary: Auriferous, bedding-parallel veins occur in zones of carbonaceous, argillaceous and sulfidic turbidites in the Lower to Middle Cambrian sandy flysch of the Goldenville Formation. The S^S values for vein and wall-rock arsenopyrite and pyrrhotite, and for regional pyrite and pyrrhotite, are highly positive. The values are similar to those from Cambro-Ordovician sediment-hosted deposits of other types, and display trends that increase upward in the stratigraphic sequence. The similarity in...
Publication: Exploration & Mining Geology
Author(s): ALAN L. SANGSTER
Issue: 1
Volume: 1
Year: 1992
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Summary: The Urkut rhodochrosite deposit and Branisko Mn showings (rancieite, manganiferous calcite), located in Lower Jurassic marine sedimentary rocks with black shale, were studied by organic-geochernical methods. Both depositional localities were affected by the Lower Jurassic Toarcian anoxic event. Urkiit shales are rich in organic matter (av. 2.94 wt^o total organic carbon), the composition of which indicates derivation mainly from marine sources, with some terrigenous component. The shales...
Publication: Exploration & Mining Geology
Author(s): MARTA POLGARI, BOHUMIL MOLAK, EVA SUROVA
Issue: 1
Volume: 1
Year: 1992
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Summary: Unusually rich molybdenum ores (cutoff grade = 4.1% Mo) hosted by Lower Cambrian black shales have been mined since 1985 near Zunyi in the province of Guizhou in China. Similar ores were once worked for Mo and Ni near Dayong in the province of Hunan. In both mining areas, mineralization occurs in Lower Cambrian black shale (Niutitang Formation and strati-graphic equivalents) as a single sulfide bed or lens with exposed thicknesses up to 15 cm and reported thicknesses up to 35 cm. In addition...
Publication: Exploration & Mining Geology
Author(s): RAYMOND M. COVENEY JR., JAMES B. MUROWCHICK, R.I. GRAUCH, CHEN NANSHENG
Issue: 1
Volume: 1
Year: 1992
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Summary: The lower and the upper parts of the Doushantuo Formation, Hubei Province, China, contain silicate-type K-rich beds (illite and feldspar), and intraclastic phosphorites, as well as Ag-V and V deposits in a "Black Shale Series". The K-rich beds formed in an anoxic basin whereas the phosphorites formed in a more oxic and higher energy depositional environment. The Black Shale Series occurs in the lower and upper parts of the Doushantuo Formation; that in the upper part consists of black illite...
Publication: Exploration & Mining Geology
Author(s): FAN DELIAN, YE JIE, LUI TIEBING
Issue: 1
Volume: 1
Year: 1992
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Summary: Thick westward prograding clastic wedges were deposited along the margin of ancestral North America from Mid-Proterozoic to Mid-Paleozoic time. Periodic rifting and tectonic subsidence resulted in the formation of starved sub-basins along this otherwise passive continental margin. These sub-basins host important sedimentary exhalative barite-zinc-lead-silver deposits. In northeastern British Columbia, a thick succession of Paleozoic basinal facies clastic rocks is preserved within the...
Publication: Exploration & Mining Geology
Author(s): D.G. MACINTYRE
Issue: 1
Volume: 1
Year: 1992
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