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Department of Geology, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5A3
Institute for Geothermal Sciences, Kyoto University, Noguchibaru, Beppa, Oita, Japan 874-0903
Corresponding author: e-mail,
dlentz{at}unb.ca
The Hunt Mo skarn deposit is one of the best examples of a late tectonic, granitic pegmatite-related, skarn system in the Grenville province. An Re-Os age of 1069 ± 11 Ma was obtained from a molybdenite crystal (6.4 ppm Re) hosted in proximal skarn (sample 50O) consistent with a contact metasomatic origin related to the granitic body. Although less evolved than other Grenvillian pegmatites, the Condon Lake granitic pegmatite is a low-temperature, A-type intrusion, with moderate redox characteristics. In contrast to many Mo-bearing skarns in the region, this deposit has low U, Th, REE, F, and P contents. The reduced marginal magnesian skarn is well zoned geochemically, mineralogically, and texturally from the contact outward into the dominant graphite-bearing calc-silicate-calcite-dolomite marble, which is locally intercalated with clinopyroxenite, orthoamphibolite, and pyroxene-biotite quartzofeldspathic gneiss. A narrow zone of endoskarn (<1 m; scapolite-K feldspar-Ca clinopyroxene) and wider, zoned exoskarn (<10 m; scapolite-Ca clinopyroxene (proximal), Ca clinopyroxene-phlogopite, Ca clinopyroxene-tremolite-phlogopite, tremolite-phlogopite (distal), marble), which hosts the bulk of the primary molybdenite (± pyrrhotite) and minor secondary pyrite-pyrrhotite-molybdenite veins. In addition to the obvious Si, Fe, Ti, Mn, S, and Mo addition, Cu, Zn, Y, Nb, and Zr are also slightly enriched. The high f(H2O)/f(HF) ratios (138,000–204,000) and moderate f(H2O)/f(HCl) ratios (2,200–1,000) at the Hunt deposit contrast with the lower fugacity ratios from other Mo-bearing U-Th-REE skarns in the region, indicating that Mo transport and deposition is principally related to a hydroxide complex.
The calc-silicate phase equilibria used to describe the zonation sequence
have been reinterpreted using quartz-undersaturated (silica) activities; this
shifts the calc-silicate-forming reaction boundaries to very low X(CO2)
(<0.005), consistent with decarbonation reactions induced via dissolved
silica infiltration. The modeled fluid/rock in the skarn based on dissolved
molybdenum is greater than 20. The carbon and oxygen isotopes of calcite are
consistent with infiltrative metasomatic skarns from the pegmatite and a
dominantly igneous source for the sulfur (
34S
= 2–9
). Overall, the deposition of Mo is probably facilitated by a reaction
with carbonate (increase in Ca(OH)2, CaCl2 resulting in
complex destabilization), a decrease in fO2
triggering an increase H2S/SO2, S in the host rocks (fS2),
and a slight decrease in temperature (650°–500°C).
This article has been cited by other articles:
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  D. R. LENTZ and R. A. CREASER Re-Os Model Age Constraints on the Genesis of the Moss Molybdenite Pegmatite-Aplite Deposit, Southwestern Grenville Province, Quyon, Quebec, Canada Exploration and Mining Geology, January 1, 2005; 14(1-4): 95 - 103. [Abstract] [Full Text] [PDF]
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 A. Karimzadeh Somarin Geochemical effects of endoskarn formation in the Mazraeh Cu-Fe skarn deposit in northwestern Iran Geochemistry: Exploration, Environment, Analysis, November 1, 2004; 4(4): 307 - 315. [Abstract] [Full Text] [PDF]
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