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Exploration and Mining Geology; January 2006; v. 15; no. 1-2; p. 101-121; DOI: 10.2113/gsemg.15.1-2.101
© 2006 Canadian Institute of Mining, Metallurgy & Petroleum
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A Fluid Inclusion and Stable Isotopic Investigation of the Boston Lode-Gold Deposit, Hope Bay Volcanic Belt, Nunavut

J.U. STEMLER1, J.P. RICHARDS1,{dagger} and K. MUEHLENBACHS1

Dept. of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3.

Correspondence: {dagger} Corresponding Author.

The Boston deposit is a recently discovered Archean lode-gold deposit located approximately 700 km northeast of Yellowknife, in the southern portion of the Hope Bay volcanic belt. Primary H2O-CO2-NaCl fluid inclusions associated with gold mineralization at Boston are of low salinity (4.6 ± 1.4 eq. wt.% NaCl, n = 182) and contain pure CO2. Homogenization temperatures of liquid-phase inclusions average 270° ± 33°C (n = 141), but some fluid inclusion assemblages contain coexisting liquid- and vapor-phase inclusions that homogenize near critical conditions, suggesting phase separation. In these groups, liquid-phase inclusions homogenized at 299° ± 25°C (n = 24), and vapor-phase inclusions homogenized at 338° ± 28°C (n = 18). These temperatures overlap within error, and a median temperature of ~320°C is taken as representative of trapping conditions within the veins. An approximate pressure of 2–3 kbar was estimated from fluid inclusion isochores at this temperature.

Stable isotopic compositions of carbonate minerals from the mineralized zones range from –4.7{per thousand} to –3.1{per thousand} in {delta}13C, and from 11.2{per thousand} to 12.8{per thousand} in {delta}18O; quartz ranges from {delta}18O = 12.8{per thousand} to 14.9{per thousand}; and pyrite ranges from {delta}34S = 2.1{per thousand} to 3.5{per thousand}. The {delta}18OH2O, {delta}13CCO2, and {delta}34SH2S values of the fluid calculated from these minerals at 320°C are 6{per thousand}–9{per thousand}, –2.4{per thousand} ± 0.6{per thousand}, and 1.5{per thousand} ± 0.5{per thousand}, respectively, and are intermediate between metamorphic and magmatic compositions. A unique source for the fluids cannot, therefore, be constrained from these data.

Petrographic and geochemical data for the Boston deposit are consistent with data from other Archean lode-gold deposits worldwide, implying that the Boston deposit formed in a similar environment and from similar types of fluids. These results suggest that the Hope Bay volcanic belt may represent a major new mesothermal gold belt in this part of Nunavut.

Key Words: Fluid inclusions • Stable isotopes • Hope Bay volcanic belt • Nunavut • Lode-gold deposit






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