Chapter 36: Carlin-Type Gold Deposits in Nevada: Geologic Characteristics, Critical Processes, and Exploration

2020 ◽  
pp. 775-795
Author(s):  
John L. Muntean
Keyword(s):  
Late Eocene ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Passive Margin ◽  
Future Research ◽  
Time Interval ◽  
High Angle ◽  
Rock Interaction ◽  
Critical Components ◽  
Carlin Type Gold Deposits

Abstract Carlin-type gold deposits in Nevada account for ~5% of worldwide annual gold production, typically about ~135 metric tons (t) (~4.5 Moz) per year. They are hydrothermal epigenetic replacement bodies hosted predominantly in carbonate-bearing sedimentary rocks. They are known for their “invisible” gold that occurs in the crystal structure of pyrite. Over 95% of the production from these deposits is from four clusters of deposits, which include the Carlin trend and the Cortez, Getchell, and Jerritt Canyon camps. Despite differences in the local geologic settings, the characteristics of the deposits are very similar in the four clusters. Shared characteristics include: (1) alteration characterized by carbonate dissolution, silicate argillization, and silicification; (2) ore formation characterized by auriferous arsensian pyrite, typically as rims on preore pyrite, followed by late open-space deposition of orpiment, realgar, stibnite, and other minerals; (3) Ag/Au ratios of <1 in ore; (4) an As-Hg-Sb-Tl geochemical signature; (5) low temperatures (~160°–240°C) and salinities of ore fluids (~1–6 wt % NaCl equiv) and fairly shallow depths of formation (<~2–3 km); and (6) lack of mineral and elemental zoning around ore. The four clusters share regional geologic controls related to formation as follows: (1) along the rifted margin of a craton, (2) within the slope facies of a passive margin sequence dominated by carbonates, (3) in the lower plate of a regional thrust fault, and (4) during a narrow time interval in the late Eocene (~42–34 Ma). The geometries and ore controls of the deposits in the four clusters are also very similar. At the deposit scale, ore and hydrothermal alteration are commonly associated with high-angle faults and preore low-angle contractional structures, including thrust faults and folds. The high-angle faults acted as fluid pathways for upwelling ore fluids, which were then diverted into lower angle favorable strata and contractional structures, where fluid-rock interaction led to replacement of carbonate and formation of ore. Rheologic contrasts between lithologies were also critical in diverting fluids into wall rocks. Common rheologic contrasts include contacts between thin- and thick-bedded lithologic units and the margins of contact metamorphic aureoles associated with Mesozoic intrusions. The similarities suggest common processes. Four critical processes are apparent: (1) development of source(s) for gold and other critical components of the ore fluids, (2) formation of fluid pathways, (3) water-rock interaction and gold deposition, and (4) a tectonic trigger, which was renewal of magmatism and a change from contraction to extension in the late Eocene. Consensus exists on these processes, except for the source of gold and other components of the ore fluid, with most models calling upon either a magmatic-hydrothermal source or a crustal source, where metals were scavenged by either meteoric or metamorphic fluids. Future research should focus on Carlin-style deposits in Nevada that exhibit epithermal characteristics and deposits that appear to have a clear genetic association with magmatic-hydrothermal systems associated with upper crustal intrusions. Rather than discrete types of ore deposits, there may be continua between Carlin-type gold deposits, epithermal deposits, and distal disseminated deposits, with the four large camps representing an end member.

CALCITE U-Pb DATING UNRAVELS THE AGE AND HYDROTHERMAL HISTORY OF THE GIANT SHUIYINDONG CARLIN-TYPE GOLD DEPOSIT IN THE GOLDEN TRIANGLE, SOUTH CHINA

2021 ◽  
Vol 116 (6) ◽  
pp. 1253-1265
Author(s):  
Xiao-Ye Jin ◽  
Jian-Xin Zhao ◽  
Yue-Xing Feng ◽  
Albert H. Hofstra ◽  
Xiao-Dong Deng ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Early Cretaceous ◽  
South China ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Late Triassic ◽  
Gold Deposition ◽  
Golden Triangle ◽  
Icp Ms ◽  
Carlin Type Gold Deposits

Abstract The ages of Carlin-type gold deposits in the Golden Triangle of South China have long been questioned due to the general lack of minerals unequivocally linked to gold deposition that can be precisely dated using conventional radiogenic isotope techniques. Recent advances in U-Pb methods show that calcite can be used to constrain the ages of hydrothermal processes, but few studies have been applied to ore deposits. Herein, we show that this approach can be used to constrain the timing of hydrothermal activity that generated and overprinted the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle. Three stages of calcite (Cal-1, Cal-2, and Cal-3) have been recognized in this deposit based on crosscutting relationships, cathodoluminescence colors, and chemical (U, Pb, and rare earth element [REE]) and isotope (C, O, Sr) compositions. Cal-1 is texturally associated with ore-stage jasperoid and disseminated Au-bearing arsenian pyrite in hydrothermally altered carbonate rocks, which suggests it is synmineralization. Cal-2 fills open spaces and has a distinct orange cathodoluminescence, suggesting that it precipitated during a second fluid pulse. Cal-1 and Cal-2 have similar carbonate rock-buffered chemical and isotopic compositions. Cal-3 occurs in veins that often contain realgar and/or orpiment and are chemically (low U, Pb, and REE) and isotopically (higher δ13C, lower δ18O and Sri values) distinct from Cal-1 and Cal-2, suggesting that it formed from a third fluid. U-Pb isotope analyses, by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for U-rich Cal-1 and Cal-2 and by LA-multicollector (MC)-ICP-MS for U-poor Cal-3, yield well-defined age constraints of 204.3 to 202.6, 191.9, and 139.3 to 137.1 Ma for Cal-1, Cal-2, and Cal-3, respectively. These new ages suggest that the Shuiyindong gold deposit formed in the late Triassic and was overprinted by hydrothermal events in the early Jurassic and early Cretaceous. Given the association of Cal-3 with orpiment and realgar, and previous geochronologic studies of several other major gold deposits in the Golden Triangle, we infer that the latest stage of calcite may be associated with an early Cretaceous regional gold metallogenic event. Combined with existing isotopic ages in the region, these new ages lead us to propose that Carlin-type gold deposits in the Golden Triangle formed during two metallogenic episodes in extensional settings, associated with the late Triassic Indochina orogeny and early Cretaceous paleo-Pacific plate subduction. This study shows that the calcite U-Pb method can be used to constrain the timing of Carlin-type gold deposits and successive hydrothermal events.

Burial Diagenesis of the Eocene Sobrarbe Delta (Ainsa Basin, Spain) Inferred From Dolomitic Concretions

2015 ◽  
Vol 85 (9) ◽  
pp. 1037-1057 ◽  
Author(s):  
Guilhem Hoareau ◽  
Francis Odonne ◽  
Daniel Garcia ◽  
Elie-Jean Debroas ◽  
Christophe Monnin ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Isotope Composition ◽  
Active Tectonics ◽  
Foreland Basin ◽  
Late Eocene ◽  
Passive Margin ◽  
Burial Diagenesis ◽  
The South ◽  
Rock Interaction ◽  
Fracture Development

Abstract:  Little attention has been focused on the burial diagenesis of deltas deposited on active foreland-basin margins, where tectonics is likely to strongly impact fluid–rock interactions. A petrographic, geochemical, and microthermometric study of several fractured dolomite concretions and enclosing prodelta marls provides insights into the evolution of burial diagenesis in the Eocene Sobrarbe deltaic complex (Ainsa Basin, Spain), and more generally, on the paleohydrology of the South Pyrenean foreland basin. Shallow burial diagenesis was controlled by microbial activity in marine-derived porewaters. Microbial sulfate reduction was first responsible for the formation of pyrite and early calcite, followed by the growth of dolomite concretions during methanogenesis. Subsequent diagenesis was limited to temperatures and depth of less than approximately 75°C and 2 km, respectively. Diagenesis was recorded in porous bioturbation traces and septarian fractures found inside dolomite concretions, as well as in tectonic shear fractures. Neomorphic tabular barite, found only in the bioturbation traces, is interpreted to have formed early in marine-derived porewaters. Septarian fractures were then filled by Fe-rich calcite and centimeter-size celestine. Stable isotopes indicate that calcite probably formed in meteoric-derived waters coming from the overlying fluvial delta plain. The sulfur isotope composition of celestine is compatible with precipitation in waters of mixed parentage, but the exact origin of dissolved sulfate remains poorly constrained. In tectonic fractures, celestine precipitated coevally with calcite displaying evidence of strong fluid–rock interaction. Dissolved sulfate may have migrated to the fractures during active tectonics from the late Eocene to the Oligocene. The paragenesis and the proposed paleohydrologic model are similar to those previously described for other deltaic systems deposited in active foreland basins, including the South Pyrenean foreland basin. These features point to common diagenetic processes in syntectonic foreland-basin deltas, involving both meteoric and marine fluid sources. Similar to passive margin settings, early diagenesis appears to be controlled mainly by relative variations of sea level, whereas during further burial, the development of permeable tectonic fractures is likely to facilitate the influx of basinal or continental waters into fine slope deposits, impacting the diagenetic record. These results emphasize the importance of fracture development in the fluid-flow regime of syntectonic foreland-basin deltas. They demonstrate the necessity to take this parameter into account in fluid-flow modeling of foreland-basin margins.

Chapter 16: Giant Carlin-Type Gold Deposits of the Cortez District, Lander and Eureka Counties, Nevada

2020 ◽  
pp. 335-353
Author(s):  
Mark A. Bradley ◽  
L. Page Anderson ◽  
Nathan Eck ◽  
Kevin D. Creel
Keyword(s):  
Great Basin ◽  
Genetic Model ◽  
Gold Mineralization ◽  
Late Eocene ◽  
Gold Deposits ◽  
Gold Deposition ◽  
Lower Paleozoic ◽  
Fine Grained ◽  
Siliciclastic Rocks ◽  
Carlin Type Gold Deposits

Abstract The Cortez district is in one of the four major Carlin-type gold deposit trends in the Great Basin province of Nevada and contains three giant (>10 Moz) gold orebodies: Pipeline, Cortez Hills, and Goldrush, including the recently discovered Fourmile extension of the Goldrush deposit. The district has produced >21 Moz (653 t) of gold and contains an additional 26 Moz (809 t) in reserves and resources. The Carlin-type deposits occur in two large structural windows (Gold Acres and Cortez) of Ordovician through Devonian shelf- and slope-facies carbonate rocks exposed through deformed, time-equivalent lower Paleozoic siliciclastic rocks of the overlying Roberts Mountains thrust plate. Juxtaposition of these contrasting Paleozoic strata occurred during the late Paleozoic Antler orogeny along the Roberts Mountains thrust. Both upper and lower plate sequences were further deformed by Mesozoic compressional events. Regional extension, commencing in the Eocene, opened high- and low-angle structural conduits for mineralizing solutions and resulted in gold deposition in reactive carbonate units in structural traps, including antiforms and fault-propagated folds. The Pipeline and Cortez Hills deposits are located adjacent to the Cretaceous Gold Acres and Jurassic Mill Canyon granodioritic stocks, respectively; although these stocks are genetically unrelated to the later Carlin-type mineralization event, their thermal metamorphic aureoles may have influenced ground preparation for later gold deposition. Widespread decarbonatization, argillization, and silicification of the carbonate host rocks accompanied gold mineralization, with gold precipitated within As-rich rims on fine-grained pyrite. Pipeline and Cortez Hills also display deep supergene oxidation of the hypogene sulfide mineralization. Carlin-type mineralization in the district is believed to have been initiated in the late Eocene (>35 Ma) based on the age of late- to postmineral rhyolite dikes at Cortez Hills. The Carlin-type gold deposits in the district share common structural, stratigraphic, alteration, and ore mineralogic characteristics that reflect common modes of orebody formation. Ore-forming fluids were channeled along both low-angle structures (Pipeline, Goldrush/Fourmile) and high-angle features (Cortez Hills), and gold mineralization was deposited in Late Ordovician through Devonian limestone, limy mudstone, and calcareous siltstone. The Carlin-type gold fluids are interpreted to be low-salinity (2–3 wt % NaCl equiv), low-temperature (220°–270°C), and weakly acidic, analogous to those in other Carlin-type gold deposits in the Great Basin. The observed characteristics of the Cortez Carlin-type gold deposits are consistent with the recently proposed deep magmatic genetic model. Although the deposits occur over a wide geographic area in the district, it is possible that they initially formed in greater proximity to each other and were then spatially separated during Miocene and post-Miocene regional extension.

scholarly journals Prospects for identifying strategic metals deposits in the Russian Arctic

2017 ◽  
pp. 59-74
Author(s):  
A.L. Galyamov ◽  
◽  
A.V. Volkov ◽  
K.V. Lobanov ◽  
K.Y. Murashov ◽  
...  
Keyword(s):  
Relative Number ◽  
Spatial Relations ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Passive Margin ◽  
Russian Arctic ◽  
Volcanic Arcs ◽  
Passive Margins ◽  
Geodynamic Environment ◽  
Proterozoic Basement

Mineral deposits are important in the economy of the Russian Arctic. In addition to the petroleum and gas, the resources of PGE minerals and gold, nickel and titanium are more than 10% of global significance. Meanwhile, the most arctic territory is out of availability of detailed geological and geophysical data due to severe climatic situation. The spatial relations of ore deposits and ore-bearing sequences of different geodynamic settings at Russia territory show that the geological sequences of three basic types of geodynamic environment contain an overwhelming number (over 70%) deposits: archaean-proterozoic basement, passive continental margin, volcanic arcs of active margins. There are two groups of ore types. The first are the types (i.e. BIF) are specific to definite sedimentary or igneous rocks, the second (i.e. gold veins etc.) are due to superimposed geotectonic processes. The complex metallogeny may be found in the subductional and accretional terrains, where the blocks of different geodynamic formation are combined. In these areas ores, previously deposited, might been transformed under the later processes until the regeneration and development of new type ores. The convergence of passive margins also might had caused the changes of geodynamic environments and led to form the vertical and lateral facies with metallogenic features combined. In Arctic regions, despite the similar ratio formation areas, the relative number of discovered and evaluated ore deposits is low in areas of active margin, including volcanic arcs and collision. This is especially true for deposits of lead and zinc, ferrous and rare metals. The significant lack of gold deposits is evident. In the areas of passive margin facies the most hidden deposits are of rare and ferrous metals, as well as lead, zinc and gold.

Application of high resolution airborne geophysics to epithermal gold exploration in Northeast Queensland and Coromandel, New Zealand

1989 ◽  
Vol 20 (2) ◽  
pp. 99 ◽  
Author(s):  
S.S. Webster ◽  
R.W. Henley
Keyword(s):  
High Resolution ◽  
Regional Scale ◽  
Cost Effective ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Magnetic Data ◽  
Mapping Technique ◽  
Epithermal Gold ◽  
Airborne Geophysics ◽  
Airborne Geophysical Data

High resolution airborne geophysical data over broad areas have been found to optimize exploration for epithermal gold deposits in differing geological environments.Genetic exploration models may be tested in favourable sites by the recognition of geophysical signatures. These signatures reflect structural, lithological and alteration patterns arising from controls on ore deposits and can be applied at regional or detailed scales, using the same data set.At regional scale (e.g. 1:100,000) the magnetic data reflect the regional tectonics and divide the area into domains for the application of appropriate genetic models. At prospect scale (e.g. 1:25,000) the radiometric data allow the extrapolation of poorly outcropping geology to provide a cost-effective mapping technique. The magnetic data can be used to supplement this interpretation or can be used to target deeper sources for direct investigation by drilling.

scholarly journals Commentary to 18F-GP1, a Novel PET Tracer Designed for High-Sensitivity, Low-Background Detection of Thrombi: Imaging Activated Platelets in Clots—Are We Getting There?

2018 ◽  
Vol 17 ◽  
pp. 153601211774905
Author(s):  
Andrew W. Stephens ◽  
Norman Koglin ◽  
Ludger M. Dinkelborg
Keyword(s):  
Thrombus Formation ◽  
High Sensitivity ◽  
Current Status ◽  
Future Research ◽  
Current Standard ◽  
Heart Attacks ◽  
Activated Platelets ◽  
Pet Tracer ◽  
Causes Of Mortality ◽  
Critical Components

Thrombus formation can lead to heart attacks, stroke and pulmonary embolism, which are major causes of mortality. Current standard diagnostic imaging methods detect anatomic abnormalities such as vascular flow impairment but have limitations. By using a targeted molecular imaging approach critical components of a pathology can be selectively visualized and exploited for an improved diagnosis and patient management. The GPIIb/IIIa receptor is abundantly and specifically exposed on activated platelets and is the key receptor in thrombus formation. This commentary describes the current status of GPIIb/IIIa-based PET imaging approaches with a focus on the recently published preclinical data of the small-molecule PET tracer 18F-GP1. Areas of future research and potential clinical applications are discussed that may lead to an improved detection of critical thromboembolic events and an optimization of available antithrombotic therapies by tracking activated platelets.

scholarly journals U–Pb dating of middle Eocene–Pliocene multiple tectonic pulses in the Alpine foreland

Solid Earth ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 2539-2551
Author(s):  
Luca Smeraglia ◽  
Nathan Looser ◽  
Olivier Fabbri ◽  
Flavien Choulet ◽  
Marcel Guillong ◽  
...  
Keyword(s):  
Middle Eocene ◽  
Regional Scale ◽  
Earthquake Hazard ◽  
Late Eocene ◽  
Passive Margin ◽  
Tectonic Activity ◽  
Thrust Belt ◽  
Fold And Thrust Belt ◽  
Earthquake Hazard Assessment ◽  
Alpine Foreland

Abstract. Foreland fold-and-thrust belts (FTBs) record long-lived tectono-sedimentary activity, from passive margin sedimentation, flexuring, and further evolution into wedge accretion ahead of an advancing orogen. Therefore, dating fault activity is fundamental for plate movement reconstruction, resource exploration, and earthquake hazard assessment. Here, we report U–Pb ages of syn-tectonic calcite mineralizations from four thrusts and three tear faults sampled at the regional scale across the Jura fold-and-thrust belt in the northwestern Alpine foreland (eastern France). Three regional tectonic phases are recognized in the middle Eocene–Pliocene interval: (1) pre-orogenic faulting at 48.4±1.5 and 44.7±2.6 Ma associated with the far-field effect of the Alpine or Pyrenean compression, (2) syn-orogenic thrusting at 11.4±1.1, 10.6±0.5, 9.7±1.4, 9.6±0.3, and 7.5±1.1 Ma associated with the formation of the Jura fold-and-thrust belt with possible in-sequence thrust propagation, and (3) syn-orogenic tear faulting at 10.5±0.4, 9.1±6.5, 5.7±4.7, and at 4.8±1.7 Ma including the reactivation of a pre-orogenic fault at 3.9±2.9 Ma. Previously unknown faulting events at 48.4±1.5 and 44.7±2.6 Ma predate the reported late Eocene age for tectonic activity onset in the Alpine foreland by ∼10 Myr. In addition, we date the previously inferred reactivation of pre-orogenic strike-slip faults as tear faults during Jura imbrication. The U–Pb ages document a minimal time frame for the evolution of the Jura FTB wedge by possible in-sequence thrust imbrication above the low-friction basal decollement consisting of evaporites.

scholarly journals Reticulate Nummulites (N. fabianii Linage) and Age of the Pellatispira-Beds of the Drazinda Formation, Sulaiman Range, Pakistan

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Ozcan E
Keyword(s):  
Mediterranean Region ◽  
Late Eocene ◽  
Test Surface ◽  
Time Interval ◽  
Late Oligocene ◽  
Shallow Marine ◽  
Western Tethys ◽  
Two Samples ◽  
Evolutionary Scheme ◽  
Weak Surface

The Eocene shallow marine Pellatispira-beds in the upper part of the Drazinda Formation represent the latest phase of Cenozoic Tethyan marine deposition in the Sulaiman Range, West Pakistan. The unit consists of stratigraphically important taxa as Heterostegina,Silvestriella, Pellatispira, a new Baculogypsina (possibly ancestral to modern Baculogypsina) and reticulate Nummulites implying a latest middle to late Eocene (late Bartonian-Priabonian) age. A more precise age of the unit requires the biometric study of reticulate Nummulites, the evolutionary scheme of which is better known from the peri-Mediterranean region in the Tethys. This group, which was subdivided into a series of successive chrono-species based on the biometry of inner cross-diameter of proloculus and changes in the types of granulation/reticulation on the test surface in the late Eocene-late Oligocene interval, appears to have a significant biostratigraphic potential for a high-resolution biostratigraphy in the peri-Mediterranean region (Western Tethys). The reticulate Nummulites in two samples from Rakhi Nala and Zinda Pir, ZP22 and RNB10, were studied and compared with those from the peri-Mediterranean region. The isolated specimens have a weak surface granulation externally, a distinct small umbonal granule (pile) and typical reticulation. The samples ZP22 and RNB10 from Zinda Pir and and Rakhi Nala sections have an average inner cross diameter of proloculus of 152.0 and 153.0 μm respectively. The reticulate Nummulites in both samples are assigned to N. hormoensis, a chrono-species characteristic for the shallow benthic zone (SBZ 18), referable to latest Bartonian-early Priabonian time interval. Since Heterostegina in peri-Mediterranean region and in Pakistan belongs to different lineages, a correlation of N. hormoensis in the studied samples with the wellestablished evolutionary scheme of Heterostegina reticulata and H.armenica lineages from the Western Tethys was not possible.

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