T186 Structural and Tectonic Controls on Gold Mineralization from the Roots of Mountain Belts to Hot Springs

Tuesday, 21 October 2014
8:00 AM - 12:00 PM
302/303

STRUCTURAL AND LITHOLOGICAL CONTROLS ON FLUID FLOW IN CARLIN-TYPE GOLD DEPOSITS IN NEVADA: INSIGHTS FROM STABLE ISOTOPES

Paper number: T186-7
Program: Technical Sessions
Time: 9:25 AM – 9:40 AM

Authors

Abstract

The distribution of gold and related hydrothermal alteration around Carlin-type gold deposits in Nevada reflects complex structural and lithological controls on hydrothermal fluid flow. The vast majority of Carlin-type gold deposits in Nevada are hosted in carbonate host rocks. Stable isotopes of carbon and oxygen can be used to identify former zones of hydrothermal fluid flow in Carlin-type gold deposits, as the fluid causes the isotopic characteristics of the carbonate host rocks to change; hydrothermally altered carbonate host rock becoming relatively depleted in 18O. Analyses of carbon and oxygen isotope ratios from carbonate host rock from within, above and below gold-bearing rocks from the Betze-Post, Pipeline and Long Canyon gold deposits (comprising around 5,000 stable isotope analyses) in Nevada reveal complex patterns of stable isotope alteration, inferred to reflect the fluid pathways utilized by hydrothermal fluids which caused gold mineralization.

Around the Betze-Post deposit, isotopic alteration is found up to 3 km from known mineralization, but is discontinuous laterally and vertically, with the most significant isotopic alteration coincident with both significant gold deposits and subvertical faults. At the Pipeline deposit, significant isotopic alteration occurs within the ore zone, but very little alteration is found beneath the deposits, inferring that fluids migrated laterally into the deposits. Around the Long Canyon deposit, isotopic alteration is largely restricted to damage zones immediately within and above the main zones of gold mineralization, and is consistent with the model put forward by Smith et al (2013) with hydrothermal fluid migrating laterally along boudin necks and fractures.

Together, the data highlight the complex nature of hydrothermal fluid pathways controlling Carlin-type gold deposits in Nevada, with several deposits appearing to be related to subhorizontal, rather than subvertical, hydrothermal fluid flow.

References: M.T. Smith, D. Rhys, K. Ross, C. Lee and J.N. Gray. 2013. Economic Geology v. 108 p. 1119-1145