GEOCHEMICAL CHARACTERIZATION OF VEIN-HOSTED GOLD MINERALIZATION IN THE MONEY KNOB DEPOSIT, LIVENGOOD, ALASKA

The Money Knob deposit in Livengood, Alaska is an ~10km² area of substantial gold mineralization within the Tintina gold belt. With a 2011 resource estimation of >10 million ounces at a 0.5g/ton cutoff, Money Knob is poised to join the ranks of other significant Tintina gold belt deposits, such as Donlin Creek, Ft. Knox, and Pogo. Gold mineralization at Money Knob is described as intrusion-related, with the majority of extractable gold being microscopic inclusions within associated sulfides. These sulfides are disseminated in felsic to intermediate dikes and more concentrated in quartz (qtz) rich veins. These features often follow fault zones and cross cut the stratigraphic units of the country rock.

Previous work has shown that the gold is strongly correlated with the concentration of two sulfides in particular: arsenopyrite (asp) and stibnite (stib). This study sampled several sets of veins containing asp and/or stib, which were designated to one of three categories: qtz-asp, quartz-stib, and quartz-asp-stib. To test the statistical relationship of these vein categories to gold grade, Pearson’s correlation coefficient was calculated for each using ICPMS elemental analyses. Results for each category were as follows: qtz-asp=0.77, qtz-stib=0.55, qtz-asp-stib (using Sb)=0.65, qtz-asp-stib (using As)=0.76. These results indicate that gold is most strongly associated with asp, but is also associated with the presence of stib.

Additionally, sulfur isotope analyses were used to explore the geochemical character of the vein sets. Using sphalerite-pyrite and sphalerite-stibnite pairs, sulfur isotope ratios gave preliminary vein equilibrium temperatures which ranged from 244 to 307°C. Preliminary mean δ³⁴S values for qtz-asp and qtz-asp-stib were -4.51 and -5.15, respectively. These temperatures and isotopic ratios are consistent with other intrusion-related gold veins.