Genetic Links Between the Development of Multi-Generational Extensional Basins Across the Basin and Range Province and the Formation of Low-Sulfidation Epithermal Deposits

The Basin and Range Province is one of the largest extensional provinces in the
world and host to over 50 known low-sulfidation epithermal deposits. The low-sulfidation
deposits primarily occur in three distinct age groups: Mid-Miocene, Late-
Miocene, and Pliocene. These periods not only correspond to low-sulfidation mineralization
episodes but also correspond to episodes of increased extension rates across
the Basin and Range. The relationships between active tectonism and low-sulfidation
epithermal mineralization in this region are commonly difficult to correlate directly
at the deposit-scale. When recognized, this relationship can effectively help predict
when and where deposits were likely to have formed during a respective chronostratigraphic
period.
Research on the structural development of the Northern Nevada Rift and its related
epithermal deposits has determined that discrete stages of basin development
directly affected how the strain was partitioned both vertically and laterally across
the rift. The localization of strain formed and maintained structural permeability
through an evolving basin architecture. This basin architecture directly influenced the
permeability of structural pathways for ascending hydrothermal fluids. The focused
strain is manifested by growth faults, which ruptured at the paleosurface, resulting
in basin subsidence. Further, research indicates that near-surface processes involving
fault rupture are temporally related to magmatism and hydrothermal activity. This
evidence suggests that fault-enhanced permeability and concomitantly-reduced shear
strength of fault-bounded wall rocks sustained the repeated exploitation, by ore fluids
and magmas, of specific structures within a basin’s architecture. The record of basin
development in the Northern Nevada Rift supports this hypothesis, with discrete architectural
stages directly corresponding to the time and space formation of numerous
low-sulfidation deposits.
Lessons learned from the Northern Nevada Rift can be utilized to develop new
models for understanding the structural evolution of known and unknown epithermal
deposits of a distinct age group. A comparison of structural geometries and basin
histories of well-known deposits such as Sleeper (~16.1 Ma), Comstock Lode (~14.1
Ma), Midas (~15.4 Ma), Aurora (~10.5 Ma), (Talapoosa (~10 Ma), Patterson District
(~5.5), Wind Mountain (~2), and Cahuilla (~2 Ma) reveals striking similarities to the
Northern Nevada Rift. Are these similarities coincidental, or are they features reflecting
similar processes leading to deposit formation? If the latter, then how can the relationships
between structural development and hydrothermal activity be recognized
and used to ascertain the prospectivity of an epithermal target?
Key Words: growth fault, fault inheritance, bonanza deposit, vertical accretion