Form of Gold and its Relation to the Hydrothermal History of Carlin-type Deposits

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Kesler et al 0207273 This proposal requests funding for a comprehensive study of the form of gold and its relation to the hydrothermal history of Carlin-type deposits. Most studies of these deposits have focused on macro-scale (geologic) observations with limited attention to micro-scale features. They have left a fragmented picture of the form of gold in Carlin-type deposits and how it relates to the origin and age of the deposits. The study will combine state-of-the-art high-resolution, transmission electron microscopy (HRTEM) and xray absorption, near edge structure (XANES) with more traditional surface ion mass spectrometry (SIMS) analyses to provide comprehensive mineralogical information. Work will focus on the Twin Creeks, Betze-Post-Screamer, and Meikle Carlin-type deposits, all of which have been well studied geologically. By combining observations from the atomic scale to the deposit scale, we will provide better control on mechanisms of gold transport and deposition in these deposits and on their hydrothermal history and age. Our main objectives will be to determine whether structurally bound gold in arsenian pyrite, the main host for gold in these deposits, is present as interlayers of arsenopyrite/marcasite in pyrite, and how they relate to nano-scale gold particles observed in reconnaissance studies of these deposits. This information is important because structurally bound gold might have been deposited from solutions that were not saturated with respect to native gold, thus allowing them to collect gold more efficiently during their formation. We will also evaluate whether arsenian pyrite-hosted gold and small particles of native gold are coeval or were deposited at different times. This information is needed to relate gold to the appropriate stage of mineralization and evaluate the possibility that Carlin-type deposits in Nevada were formed by several, spatially overlapping, gold-depositing events. Deposition from unsaturated solutions and formation by multiple events could also help explain why these deposits are so large. Finally, our work will relate the deposits to their geologic and tectonic setting, which is essential to exploration for ore to serve the next generation.