Remobilized Geochemical Anomalies Related to Deep Gold Zones, Carlin Trend, Nevada

Cluer, J. Kelly

doi:10.2113/econgeo.107.7.1343

Cited by 4 publications

(3 citation statements)

References 9 publications

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“…Table A2). Given the lack of any mineralogic evidence for hydrothermal alteration, we interpret the high Tl to result from postmineralization mobilization from surrounding ore. High concentrations of Au, As, Sb, Hg, Tl, and S in clay-filled fractures in middle Miocene sedimentary deposits above the Carlin trend demonstrate this process (Cluer, 2012). A least altered low-SiO2 rhyolite (H09-1) dike from outcrop has plagioclase only weakly (Grant, 1986;Hofstra and Cline, 2000).…”

Section: Alteration and Mineralization Of Cortez Rhyolitesmentioning

confidence: 95%

Timing of Rhyolite Intrusion and Carlin-Type Gold Mineralization at the Cortez Hills Carlin-Type Deposit, Nevada, USA

Henry

John

Leonardson³

et al. 2023

Economic Geology

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Carlin-type gold deposits (CTDs) of Nevada are the largest producers of gold in the United States, a leader in world gold production. Although much has been resolved about the characteristics and origin of CTDs in Nevada, major questions remain, especially about (1) the role of magmatism, whether only a source of heat or also metals, (2) whether CTDs only formed in the Eocene, and (3) whether pre-Eocene metal concentrations contributed to Eocene deposits. These issues are exemplified by the CTDs of the Cortez region, the second largest concentration of these deposits after the Carlin trend. Carlin-type deposits are notoriously difficult to date because they rarely generate dateable minerals. An age can be inferred from crosscutting relationships with dated dikes and other intrusions, which we have done for the giant Cortez Hills CTD. What we term “Cortez rhyolites” consist of two petrographic-geochemical groups of siliceous dikes: (1) quartz-sanidine-plagioclase-biotite-phyric, high-SiO2 rhyolites emplaced at 35.7 Ma based on numerous 40Ar/39Ar dates and (2) plagioclase-biotite-quartz ± hornblende-phyric, low-SiO2 rhyolites, which probably were emplaced at the same time but possibly as early as ~36.2 Ma. The dikes form a NNW-trending belt that is ~6–10 km wide × 40 km long and centered on the Cortez Hills deposit, and they require an underlying felsic pluton that fed the dikes. Whether these dikes pre- or postdated mineralization has been long debated. We show that dike emplacement spanned the time of mineralization. Many of both high- and low-SiO2 dikes are altered and mineralized, although none constitute ore. In altered-mineralized dikes, plagioclase has been replaced by kaolinite and calcite, and biotite by smectite, calcite, and marcasite. Sanidine is unaltered except in a few samples that are completely altered to quartz and kaolinite. Sulfides present in mineralized dikes are marcasite, pyrite, arsenopyrite, and As-Sb–bearing pyrite. Mineralized dikes are moderately enriched in characteristic Carlin-type elements (Au, Hg, Sb, Tl, As, and S), as well as elements found in some CTDs (Ag, Bi, Cu, Mo), and variably depleted in MgO, CaO, Na2O, K2O, MnO, Rb, Sr, and Ba. In contrast, some high-SiO2 rhyolites are unaltered and cut high-grade ore, which shows that they are post-ore. Both mineralized and post-ore dikes have indistinguishable sanidine 40Ar/39Ar dates. These characteristics, along with published interpretations that other giant CTDs formed in a few tens of thousands of years, indicate the Cortez Hills CTD formed at 35.7 Ma. All Cortez-area CTDs are in or adjacent to the Cortez rhyolite dike swarm, which suggests that the felsic pluton that fed the dikes was the hydrothermal heat source. Minor differences in alteration and geochemistry between dikes and typical Paleozoic sedimentary rock-hosted ore probably reflect low permeability and low reactivity of the predominantly quartzofeldspathic dikes. Despite widespread pre-35.7 Ma mineralization in the Cortez region, including deposits near several CTDs, we find no evidence that older deposits or Paleozoic basinal rocks contributed metals to Cortez-area CTDs. Combining our new information about the age of Cortez Hills with published and our dates on other CTDs demonstrates that CTD formation coincided with the southwestern migration of magmatism across Nevada, supporting a genetic relationship to Eocene magmatism. CTDs are best developed where deep-seated (~6–8 km), probably granitic plutons, expressed in deposits only as dikes, established large, convective hydrothermal systems.

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Section: Alteration and Mineralization Of Cortez Rhyolitesmentioning

confidence: 95%

Timing of Rhyolite Intrusion and Carlin-Type Gold Mineralization at the Cortez Hills Carlin-Type Deposit, Nevada, USA

Henry

John

Leonardson³

et al. 2023

Economic Geology

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“…Detailed studies of ore-stage arsenian pyrite show that trace element and sulfur isotope zoning formed from temporally discrete ore fluids fed by separate structures (Barker et al, 2009;Longo et al, 2009;Muntean et al, 2009). Recent research also focused on enlarging the target for Carlin-type gold deposits by looking for zoning patterns surrounding Carlin-type gold deposits, including lithogeochemistry (Patterson and Muntean, 2011) and halos of depleted δ 18 O in carbonate oxygen isotopes (Barker et al, 2013;Hickey et al, 2014a;Vaughan et al, 2016), as well as signatures in transported alluvial and sedimentary cover and groundwater (Muntean and Taufen, 2011;Cluer, 2012). In chapter 2, Muntean (2018) presents a mineral systems approach to exploring for Carlintype gold deposits in Nevada.…”

Section: Overview Of the Volumementioning

confidence: 99%

Diversity in Carlin-Style Gold Deposits

Muntean¹

2018

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Reviews in Economic Geology is a series publication of the Society of Economic Geologists designed to accompany the Society's Short Course series. Like the Short Courses, each volume provides comprehensive updates on various applied and academic topics for practicing economic geologists and geochemists in exploration, development, research, and teaching. Volumes are produced in conjunction with each new Short Course, first serving as a textbook for that course and subsequently made available to SEG members and others at a modest cost.

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“…By collecting ore or rock samples, the association can be inferred through the stoichiometry of ore-forming minerals [31][32][33][34][35]. Such investigations on a certain type of mineral deposit have been summarized as exploration geochemical models and have been used in turn to find potential deposits of that type in other areas [31,[36][37][38]. Characteristic zonation of mineralization-related minerals/elements is a widely used tool for locating buried mineralization [39,40].…”

Section: Introductionmentioning

confidence: 99%

Quantifying the Distribution Characteristics of Geochemical Elements and Identifying Their Associations in Southwestern Fujian Province, China

Wang

2020

Minerals

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The distribution of geochemical elements in the surficial media is the end product of geochemical dispersion under complex geological conditions. This study explored the frequency and spatial distribution characteristics of geochemical elements and their associations. It quantifies the frequency distribution via mean, variance, skewness and kurtosis, followed by measuring the spatial distribution characteristics (i.e., spatial autocorrelation, heterogeneity and self-similarity) via semivariogram, q-statistic and multifractal spectrum, and further identify the elemental associations based on these distribution parameters using hierarchical clustering. A criterion was defined to identify the importance of parameters in the clustering procedure. A case study processing a geochemical dataset of stream sediment samples collected in southwestern Fujian province of China was carried out to illustrate and validate the procedure. The results indicate that studies of the frequency and spatial distribution characteristics of geochemical elements can enhance the knowledge of geochemical dispersions. The associations identified based on the frequency and spatial distribution parameters are different from those obtained by conventional cluster analysis. Spatial distribution characteristics cannot be neglected when investigating the distribution patterns of geochemical elements and their associations. The findings can enhance the knowledge of the geochemical dispersion in the study area and might benefit the following-up mineral exploration.

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Remobilized Geochemical Anomalies Related to Deep Gold Zones, Carlin Trend, Nevada

Cited by 4 publications

References 9 publications

Timing of Rhyolite Intrusion and Carlin-Type Gold Mineralization at the Cortez Hills Carlin-Type Deposit, Nevada, USA

Timing of Rhyolite Intrusion and Carlin-Type Gold Mineralization at the Cortez Hills Carlin-Type Deposit, Nevada, USA

Diversity in Carlin-Style Gold Deposits

Quantifying the Distribution Characteristics of Geochemical Elements and Identifying Their Associations in Southwestern Fujian Province, China

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