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Climate-induced geochemical and morphological evolution of placer gold deposits at Rich Hill, Arizona, USA

2016; Geological Society of America; Volume: 129; Issue: 1-2 Linguagem: Inglês

10.1130/b31522.1

1943-2674

Erik Melchiorre, George D. Kamenov, Chelsea Sheets-Harris, A. V. Andronikov, W. Britt Leatham, Jeff Yahn, D. S. Lauretta,

Geological formations and processes

Research Article| January 01, 2017 Climate-induced geochemical and morphological evolution of placer gold deposits at Rich Hill, Arizona, USA Erik B. Melchiorre; Erik B. Melchiorre † 1Department of Geology, California State University, 5500 University Parkway, San Bernardino, California 92407, USA †emelch@csusb.edu Search for other works by this author on: GSW Google Scholar George D. Kamenov; George D. Kamenov 2Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA Search for other works by this author on: GSW Google Scholar Chelsea Sheets-Harris; Chelsea Sheets-Harris 1Department of Geology, California State University, 5500 University Parkway, San Bernardino, California 92407, USA Search for other works by this author on: GSW Google Scholar Alexandre Andronikov; Alexandre Andronikov 3Department of Geosciences, University of Arizona, Tucson, Arizona 85721-0092, USA Search for other works by this author on: GSW Google Scholar W. Britt Leatham; W. Britt Leatham 1Department of Geology, California State University, 5500 University Parkway, San Bernardino, California 92407, USA Search for other works by this author on: GSW Google Scholar Jeff Yahn; Jeff Yahn 4J.W. Mining, Wickenburg, Arizona 85390, USA Search for other works by this author on: GSW Google Scholar Dante S. Lauretta Dante S. Lauretta 5Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721-0092, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Erik B. Melchiorre † 1Department of Geology, California State University, 5500 University Parkway, San Bernardino, California 92407, USA George D. Kamenov 2Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA Chelsea Sheets-Harris 1Department of Geology, California State University, 5500 University Parkway, San Bernardino, California 92407, USA Alexandre Andronikov 3Department of Geosciences, University of Arizona, Tucson, Arizona 85721-0092, USA W. Britt Leatham 1Department of Geology, California State University, 5500 University Parkway, San Bernardino, California 92407, USA Jeff Yahn 4J.W. Mining, Wickenburg, Arizona 85390, USA Dante S. Lauretta 5Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721-0092, USA †emelch@csusb.edu Publisher: Geological Society of America Received: 24 Feb 2016 Revision Received: 28 Jul 2016 Accepted: 10 Aug 2016 First Online: 02 Jun 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2016 Geological Society of America GSA Bulletin (2017) 129 (1-2): 193–202. https://doi.org/10.1130/B31522.1 Article history Received: 24 Feb 2016 Revision Received: 28 Jul 2016 Accepted: 10 Aug 2016 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Erik B. Melchiorre, George D. Kamenov, Chelsea Sheets-Harris, Alexandre Andronikov, W. Britt Leatham, Jeff Yahn, Dante S. Lauretta; Climate-induced geochemical and morphological evolution of placer gold deposits at Rich Hill, Arizona, USA. GSA Bulletin 2017;; 129 (1-2): 193–202. doi: https://doi.org/10.1130/B31522.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Placer gold deposits can serve as a wet/dry paleoclimate indicator because they preserve a record of physical and chemical modification. We hypothesized that such a record would be present across the four main placer units at Rich Hill, Arizona, USA. The oldest placer unit, a paleo-erosional surface on a modern topographic high, records moderate precipitation and erosion with modest transport distance following 25–22 Ma unroofing of the lode gold source. By 17–5 Ma, high-angle Basin and Range faulting produced a shallow basin that preserved three additional placer units. The oldest is a thin gold-rich gravel within bedrock gravity traps, suggestive of a steep gradient and abundant nonseasonal precipitation. The middle unit has well-rounded gold nuggets with deep chemical weathering that record abundant nonseasonal precipitation, but with a less steep gradient and significant fluvial sediment deposition. The uppermost unit is a pulse placer unit deposited by a series of landslides and debris flows during a period of lower, seasonal precipitation. During this dry period, and continuing to the present, microbial communities may have been established within the seasonally wet bedrock traps of the lowermost placer unit. This resulted in biological modification of placer gold chemistry and production of Mn-Ba–oxide biomats, which have coated and cemented both placer gold and sediments. This record of physical and chemical change within a sequence of placer gold units is consistent with known Arizona paleoclimate conditions, and it demonstrates the potential utility of this technique for paleoenvironmental reconstructions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.