Evidence of boiling and epithermal vein mineralization in Carlin-type deposits on the Getchell trend, Nevada

Boiling in northeast (NE)-trending faults during Eocene gold mineralization at the Getchell and Twin Creeks deposits is indicated by cogenetic liquid-rich and vapor-rich fluid inclusions. Both primary and secondary fluid inclusions in orpiment record similar evidence of boiling. However, banding in paragenetically younger calcite indicates that boiling was episodic in addition to being localized to NE-trending faults. The presence of CO2-rich secondary fluid inclusions in fluorite from the Getchell mine is an artifact of boiling and a depth of <= 980m is representative of the Late-stage in these Carlin-type deposits. An similar to 0.5m wide crystalline white-quartz vein in the DZ Fault, Twin Creeks mine contains cogenetic liquid-rich and vapor-rich fluid inclusions. Intergrown with the quartz is 42 Ma adularia and native gold that occurs both as disseminations within and along boundaries between quartz grains. This vein extends beyond the DZ Fault and cuts massive brown jasperoid of the HGO ore zone. The contrasting styles of mineralization (e.g., low-sulfidation epithermal versus Carlin type), crosscutting relationship, and precise adularia age provides an important constraint on the age of Carlin-type gold mineralization at the Twin Creeks mine.