The Gibellini vanadium deposit occurs within an allocthonous
fault wedge of organic-rich siliceous mudstone, siltstone,
and chert, which forms a northwest trending prominent ridge.
These rocks are described by Noranda as thin bedded shales,
very fissile and highly folded, distorted and fractured
(Condon, 1975). In general, the beds strike north-northwest
and dip from 15 to 50° to the west. Outcrops of the
shale are scarce except for along road cuts and trenches.
The black shale unit which hosts the vanadium resource is
from 175 to over 300 feet thick and overlies gray mudstone.
The shale has been oxidized to various hues of yellow and
orange up to a depth of 100 feet.
In the oxidized zone, complex vanadium oxides occur in fractures
in the sedimentary rocks including metahewettite (CaV6
O16 —H2O),
bokite (KAl3 Fe6
V26 O76 —30H2O),
schoderite, and metaschoderite (Al (PO4)
(VO4)—6-8H2O).
In the unoxidized sediments, vanadium occurs in organic
material (kerogen) made up of fine grained, flaky, and stringy
organism fragments less than 15 microns 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). XRD mineralogy work by SGS Lakefield
Research in Ontario, Canada reported the occurrence of the
vanadium mineral fernandinite (CaV8
O20 -– H2O)
(SGS, 2007). Other minerals reported to occur at Gibellini
are marcasite, sphalerite, pyrite, and molybdenite (Desborough
and others, 1984).
The top 100 to 120 feet of the Gibellini vanadium deposit
is oxidized, producing various orange, pink, and purple
vanadium oxide minerals. Vandadium grades in the oxide zone
are generally higher than in the unoxidized zone but lower
than in the transition zone. Below the oxidized zone is
the transition zone (mixed oxidized and unoxidized rocks),
which typically contains the highest grades in the deposit.
An unoxidized zone underlies the transition zone and typically
is lower in vanadium grade than the oxide and transition
zones.
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