Summary:
The Project Gibellini consists of the Gibellini, Louie Hill and Bisoni–McKay vanadium deposits.
Deposit Types
The vanadium deposits that occur on the Property are examples of the “USGS Shale-Hosted Vanadium” deposit type of Kelley et al. (2017). Vanadium-rich metalliferous black shales occur primarily in late Proterozoic and Phanerozoic marine successions. The term shale is used broadly to include a range of carbonaceous rocks that include marls and mudstones. These fine-grained sedimentary rocks were deposited in inland seas and on continental margins. They typically contain high concentrations of organic matter, reduced sulfur, and a suite of metals including copper, molybdenum, nickel, platinum group elements (PGEs), silver, uranium, vanadium, and zinc.
The vanadium mineralization of the Gibellini, Louie Hill, and Bisoni–McKay areas is hosted in sedimentary rocks. Oxidation of the primary organic and reduced sulfide material in portions of the deposit resulted in the presence of secondary vanadium oxide minerals. The depth and intensity of oxidation is variable across the deposits and accounts for the three primary stratiform facies recognized on the project: oxide, transitional, and reduced. Mineralization is tabular, conformable with bedding, and remarkably continuous in grade and thickness between drill holes.
The mineralization at the Gibellini manganese–nickel mine forms a pipe-like structure hosted in limestone, is primarily enriched in manganese, zinc, and nickel, and may be hydrothermal or sedimentary in origin, or a combination of the two.
Gibellini
The Gibellini deposit occurs within organic-rich siliceous mudstone, siltstone, and chert of the Gibellini facies of the Devonian Age Woodruff Formation.
In general, the beds strike north–northwest and dip from 15–50° to the west. The siltstone/shale unit that hosts the vanadium Mineral Resource estimate is from 175 ft to over 300 ft thick and overlies gray mudstone of the Bisoni facies. The shale has been oxidized to various hues of yellow and orange up to a depth of 100 ft.
Alteration (oxidation) of the rocks is classified as one of three oxide codes: oxidized, transitional, and reduced. Vanadium grade changes across these boundaries. The transitional zone reports the highest average grades and RMP geologists interpreted this zone to have been upgraded by supergene processes.
Louie Hill
The Louie Hill deposit lies approximately 500 m south of the Gibellini deposit, being separated from the latter by a prominent drainage. Mineralization at Louie Hill is hosted by organic-rich siliceous mudstone, siltstone, and chert of the Gibellini facies of the Devonian Woodruff Formation and probably represents a dissected piece of the same allochthonous fault wedge containing the Gibellini deposit.
Mineralized beds cropping out on Louie Hill are often contorted and shattered but in general strike in a north–south direction, and dip to the west at 0–40°.
Rocks underlying the Louie Hill Deposit consist of mudstone, siltstone, and fine-grained sandstone probably of Mississippian age (Webb and/or Chainman Formations). Oxidation of the mineralized rocks has produced light-colored material with local red and yellow bands of concentrated vanadium minerals.
Bisoni–McKay
The Bisoni–McKay deposits occur approximately eight miles south of the Gibellini deposit. Vanadium mineralization at Bisoni–McKay is hosted by the Gibellini facies of the Devonian Woodruff Formation. The exposed Woodruff rocks are composed of carbonaceous shale, mudstone, siltstone and minor limey shale and sandstone. The Bisoni facies of the Woodruff Formation underlies the Gibellini facies and consists of gray dolomitic or argillaceous mudstone and siltstone with less carbonaceous material. Devonian Devils Gate Limestone and Mississippian Webb Formation rocks are also mapped in the area.
The Woodruff and underlying Devils Gate Limestone contact relationship is mapped as a fault, which may be a slide block plane. Prior to Tertiary faulting, the Devils Gate Limestone, the overlying Woodruff Formation, and the Webb Formation appear to have been folded as a unit as exemplified by the north-trending fold and an accompanying fault that extends along the west side of the North A area. The fold may be due to drag along the north–south fault trend.
The Gibellini facies and the greater Woodruff Formation are typically preserved and exposed in down-dropped fault blocks. The Woodruff Formation is juxtaposed with the older, massive outcrops of Devils Gate Limestone on the east and west in the North A and South B areas. In the northwestern part of the North A area, a northwest trending concealed fault has juxtaposed the Devils Gate limestone against the Webb Formation rocks that has resulted in placing the Woodruff rocks in fault contact with the younger Webb Formation rocks.
The thickness of the Woodruff Formation is uncertain because complete sections have not been drilled, but it is likely to be between 300–400 ft.
Mineralization and Alteration
Vanadium mineralization at Gibellini, Louie Hill, and Bisoni–McKay is hosted in siltstone/shale sedimentary rocks. Mineralization is tabular, conformable with bedding, and remarkably continuous in grade and thickness between drill holes.
Alteration of the rocks is limited to oxidation and is classified as one of the three oxide codes: 1 = oxidized, 2 = transitional, and 3 = reduced. Vanadium grades change across these boundaries. In general, the transitional zone reports the highest average grades, the oxide zone reports the next highest average grades, and the reduced zone reports the lowest average grades. At Bisoni–McKay, the oxide zone has the lowest grades, the transition zone is much thinner than at Gibellini, and may or may not be higher in vanadium grade than the reduced zone.
In the oxidized zone, complex vanadium oxides occur in fractures in the sedimentary rocks including metahewettite (CaV6O16·H2O), bokite (KAl3Fe6V26O76·30H2O), schoderite (Al2PO4VO4·8H2O), and metaschoderite (Al2PO4VO4·6-8H2O). In the reduced sediments, vanadium occurs in organic material (kerogen) made up of fine grained, flaky, and stringy organism fragments less than 15 µm in size (Bohlke et al., 1981).
Other workers found vanadium mineralization to occur within manganese modules (psilomene family) in the shale (Assad and Laguiton, 1973). X-ray diffraction (XRD) mineral identification by SGS Lakefield Research in Ontario, Canada (SGS Lakefield) reported the occurrence of the vanadium mineral fernandinite (CaV8O20·H2O) (SGS Lakefield, 2007). Other minerals reported to occur at Gibellini are marcasite, sphalerite, pyrite, and molybdenite (Desborough et al., 1984).