12 Mining in the Rocky Mountain and Cordilleran Regions and Beyond: Risks and Opportunities

Thursday, 13 May 2021
8:30 AM - 10:30 AM
Mackay School of Earth Sciences & Engineering Room

THE COVE DEPOSIT AND THE ORIGIN OF CARLIN-STYLE DEPOSITS

Paper number: 12-2
Program: Theme Sessions
Time: 8:50 AM – 9:10 AM

Authors

Abstract

Carlin-style gold deposition is the leading gold source in Nevada. Despite its significance, the fine-grained nature of Carlin-style mineralization and lack of associated quartz veins make it difficult to ascertain a genesis for the gold. A magmatic origin model is gaining traction but is criticized as it fails to explain the lack of zoning or high-temperature mineralization in Carlin-type deposits. The Cove deposit, located in Lander County and owned by Premier Gold Inc., grades from deep base metal vein type (BMVT) mineralization to Carlin-style mineralization. Both formed between 39.2 and 34.3 Ma. This transition provides an opportunity to investigate the origin of Carlin-style mineralization. This research uses fluid inclusions and base metal veins to increase our understanding of how Carlin-style systems form. Additionally, carbonate isotopes have been proposed as a vector for Carlin-style deposits to evaluate the extent of fluid-rock interactions. Current work tests the viability of this vector at Cove.

The fluid inclusion petrography and cathodoluminescence imaging show primary fluid inclusions in quartz cogenetic to sulfides in BMVT veins. This allows the next steps of microthermometry and analyzing inclusions in BMVT veins for a “Carlin-style” signature— such as Au, As, Tl, and Sb enrichments—to evaluate the potential for BMVT systems to evolve into Carlin-style systems. This research also found evidence of phase separation in BMVT veins at Cove that may indicate higher temperatures of formation than previously considered. An emerging class of veins in porphyry systems— “E-veins” —share mineralogical similarities to base metal veins at Cove. These similarities, coupled with previously obtained δ34S values, indicate magmatic influence at Cove. This leads to a discussion of how “E-veins” can be identified outside of porphyry systems. Early results from carbonate isotopes show depleted δ18O values in Au bearing samples relative to barren ones and decreasing δ18O values with depth, likely correlating with increased fluid-rock interactions. These results support that carbonate isotopes are a potentially effective vector into cryptic alteration halos. This research examines magmatic links to Carlin-style mineralization and evaluates carbonate isotopes as an exploration vector.

Geological Society of America Abstracts with Programs. Vol. 53, No. 4

doi: 10.1130/abs/2021CD-363240

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