Thermal and chemical profiling of the Bald Mountain district, White Pine County, Nevada

Apatite fission track and stable isotope analysis are two methods that can be used
to guide exploration for hydrothermal systems. Both have been applied to the Bald
Mountain district, Nevada. Results from forty-four apatite fission track analysis indicate
three ages of thermal activity. The oldest group of ages (nineteen samples) ranges
from 61 Ma to greater than 120 Ma; samples in this group probably represent partially
reset grains in old rocks and are probably geologically meaningless. The second
group (six samples) yields Eocene ages which range from ~34 Ma to ~51 Ma, with
three samples near ~40 Ma. The third group (seventeen samples) yields Miocene ages
which cluster around ~23 Ma. Rocks with Eocene and Miocene ages are spatially
associated with the fossil hydrothermal activity or are along the Bida trend, whereas
rocks with the older ages are found distal to the Bida trend. Results of analysis of 102
carbonate samples for oxygen and carbon isotopes indicate six areas of water-rock
interaction. The δ18O value of unaltered carbonate rock is +25 per mil or greater,
whereas lower values are indicative of areas of meteoric water-rock interaction. Samples
with values ranging from 5–20 per mil are considered to have experienced significant
water-rock interaction. Samples having such low values coincide with areas of
known mineralization and include the 1 South Pit, Rat Pit, LBM Deposit, Horseshoe
Pit, Casino Pit, and the Top Pit. Possibly because of the interplay of multiple
processes, carbon isotopes do not appear to show a recognizable pattern.