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Geologic framework of the Northern Great Basin

 

 

 

Tectonic setting of mineral deposits in the northern Great Basin

Statement of Problem: The northern Great Basin is one of the world’s most prolific gold-producing regions, with most production from Carlin-type deposits along the Carlin trend in north-central Nevada. How these deposits formed is still hotly debated even after decades of study. Most recent models suggest that magmatism played an essential role, begging the question why—when so much of the Great Basin was the locus of intense Eocene to Oligocene volcanism—are Carlin-type deposits apparently concentrated in only one place? Is this a function of unusual magmatism in this area, favorable post-mineral preservation, or something else? With respect to post-mineral preservation, the USGS Mineral and Environmental Resources Program, notes that “Areas of cover are practically the only remaining areas for the identification of new mineral resources within the U.S. Cover includes pre-, syn-, and post-mineralization rocks, colluvium/alluvium and water that conceal a mineral resource from recognition at the surface of the earth.” The goal of this task is to advance our understanding of the temporal and spatial relationship of magmatism to mineral deposit formation in the Great Basin, and combine this information with new structural data (see Task 1) to help the Mineral and Environmental Resources Program with their upcoming assessment of the potential for undiscovered deposits beneath structural or stratigraphic cover. Specific problems include improving correlation of ash-flow tuff units and source calderas in central Nevada, understanding the geologic and petrologic evolution of the Caetano caldera and its relationship to major gold deposits, and understanding the magmatic history and post-eruption structural history of the nested Oligocene caldera complex in the Stillwater Range (also part of Task 1).

Objectives: Two objectives of this task are to complete a 1:75,000 scale geologic map and cross-sections of the Caetano caldera south of Battle Mountain, Nevada, and to complete a 1:50,000 scale map of the southern Stillwater Range, Nevada (also an objective of Task 1). The Eocene Caetano caldera is one of the best-exposed calderas in the world, and one of the most informative for the study of caldera magmatism and the process of caldera formation. The southern Stillwater Range also exposes an unusually complete crustal section through a caldera complex, similar in some respects to Caetano but different in important ways, notably the absence of massive nearby Carlin-type gold deposits. Together with geologic mapping, a related objective of this task is to understand the evolution of these large magmatic systems, and more generally the relationship of mid-Tertiary magmatism to mineralization in the northern Great Basin.

   

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