scholarly journals Ar–Ar dating for hydrothermal quartz from the 2.4 Ga Ongeluk Formation, South Africa: implications for seafloor hydrothermal circulation

2018 ◽  
Vol 5 (9) ◽  
pp. 180260
Author(s):  
Takuya Saito ◽  
Hua-Ning Qiu ◽  
Takazo Shibuya ◽  
Yi-Bing Li ◽  
Kouki Kitajima ◽  
...  
Keyword(s):  
South Africa ◽  
Fluid Inclusion ◽  
Fluid Inclusions ◽  
Hydrothermal System ◽  
Magmatic Fluid ◽  
Crustal Fluid ◽  
Hydrothermal Quartz ◽  
Argon Isotopes ◽  
Stepwise Crushing ◽  
Binary Mixing

Fluid inclusions in hydrothermal quartz in the 2.4 Ga Ongeluk Formation, South Africa, are expected to partially retain a component of the ancient seawater. To constrain the origin of the fluid and the quartz precipitation age, we conducted Ar–Ar dating for the quartz via a stepwise crushing method. The obtained argon isotopes show two or three endmembers with one or two binary mixing lines as the crushing proceeds, suggesting that the isotopic compositions of these endmembers correspond to fluid inclusions of each generation, earlier generated smaller 40 Ar- and K-rich inclusions, moderate 40 Ar- and 38 Ar Cl (neutron-induced 38 Ar from Cl)-rich inclusions and later generated larger atmospheric-rich inclusions. The K-rich inclusions show significantly different 40 Ar/ 38 Ar Cl values compared to the 38 Ar Cl -rich inclusions, indicating that it is difficult to constrain the quartz formation age using only fluid inclusions containing excess 40 Ar. The highest obtained 40 Ar/ 36 Ar value from the fluid inclusions is consistent with an expected value of the Ongeluk plume source, suggesting that the quartz precipitation was driven by Ongeluk volcanism. Considering the fluid inclusion generations and their compositions, the hydrothermal system was composed of crustal fluid and magmatic fluid without seawater before the beginning of a small amount of seawater input to the hydrothermal system.

PIXE and microthermometric analyses of fluid inclusions in hydrothermal quartz from the 2.2Ga Ongeluk Formation, South Africa: Implications for ancient seawater salinity

2016 ◽  
Vol 286 ◽  
pp. 337-351 ◽  
Author(s):  
Takuya Saito ◽  
Takazo Shibuya ◽  
Tsuyoshi Komiya ◽  
Kouki Kitajima ◽  
Shinji Yamamoto ◽  
...  
Keyword(s):  
South Africa ◽  
Fluid Inclusions ◽  
Hydrothermal Quartz ◽  
Seawater Salinity

scholarly journals Nitrogen Isotopic Composition and Density of the Archean Atmosphere

Science ◽  
2013 ◽  
Vol 342 (6154) ◽  
pp. 101-104 ◽  
Author(s):  
Bernard Marty ◽  
Laurent Zimmermann ◽  
Magali Pujol ◽  
Ray Burgess ◽  
Pascal Philippot
Keyword(s):  
Isotopic Composition ◽  
Partial Pressure ◽  
Significant Role ◽  
Fluid Inclusions ◽  
Environmental Conditions ◽  
Thermal Budget ◽  
Hydrothermal Quartz ◽  
Nitrogen Isotopic Composition ◽  
Argon Isotopes

Understanding the atmosphere’s composition during the Archean eon is fundamental to unraveling ancient environmental conditions. We show from the analysis of nitrogen and argon isotopes in fluid inclusions trapped in 3.0- to 3.5-billion-year-old hydrothermal quartz that the partial pressureof N2of the Archean atmosphere was lower than 1.1 bar, possibly as low as 0.5 bar, and had a nitrogen isotopic composition comparable to the present-day one. These results imply that dinitrogen did not play a significant role in the thermal budget of the ancient Earth and that the Archean partial pressure of CO2was probably lower than 0.7 bar.

scholarly journals Fluid Inclusion Characteristics of the Kışladağ Porphyry Au Deposit, Western Turkey

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 64 ◽  
Author(s):  
Nurullah Hanilçi ◽  
Gülcan Bozkaya ◽  
David A. Banks ◽  
Ömer Bozkaya ◽  
Vsevolod Prokofiev ◽  
...  
Keyword(s):  
Fluid Inclusion ◽  
Fluid Inclusions ◽  
Meteoric Water ◽  
High Salinity ◽  
Gold Mineralization ◽  
Magmatic Fluid ◽  
Salinity Range ◽  
Western Turkey ◽  
Magmatic Complex ◽  
Low Salinity

The deposit occurs in a mid-Miocene monzonite magmatic complex represented by three different intrusions, namely Intrusion 1 (INT#1), Intrusion 2 (INT#2, INT #2A), and Intrusion 3 (INT#3). Gold mineralization is hosted in all intrusions, but INT#1 is the best mineralized body followed by INT#2. SEM-CL imaging has identified two different veins (V1 and V2) and four distinct generations of quartz formation in the different intrusions. These are: (i) CL-light gray, mosaic-equigranular quartz (Q1), (ii) CL-gray or CL-bright quartz (Q2) that dissolved and was overgrown on Q1, (iii) CL-dark and CL-gray growth zoned quartz (Q3), and (iv) CL-dark or CL-gray micro-fracture quartz fillings (Q4). Fluid inclusion studies show that the gold-hosted early phase Q1 quartz of V1 and V2 veins in INT#1 and INT#2 was precipitated at high temperatures (between 424 and 594 °C). The coexisting and similar ranges of Th values of vapor-rich (low salinity, from 1% to 7% NaCl equiv.) and halite-bearing (high salinity: >30% NaCl) fluid inclusions in Q1 indicates that the magmatic fluid had separated into vapor and high salinity liquid along the appropriate isotherm. Fluid inclusions in Q2 quartz in INT#1 and INT#2 were trapped at lower temperatures between 303 and 380 °C and had lower salinities between 3% and 20% NaCl equiv. The zoned Q3 quartz accompanied by pyrite in V2 veins of both INT#2 and INT#3 precipitated at temperatures between 310 and 373 °C with a salinity range from 5.4% to 10% NaCl eq. The latest generation of fracture filling Q4 quartz, cuts the earlier generations with fluid inclusion Th temperature range from 257 to 333 °C and salinity range from 3% to 12.5% NaCl equiv. The low salinity and low formation temperature of Q4 may be due to the mixing of meteoric water with the hydrothermal system, or late-stage epithermal overprinting. The separation of the magmatic fluid into vapor and aqueous saline pairs in the Q1 quartz of the V1 vein of the INT#1 and INT#2 and CO2-poor fluids indicates the shallow formation of the Kışladağ porphyry gold deposit.

Paragenesis of an Orogenic Gold Deposit: New Insights on Mineralizing Processes at the Grass Valley District, California

2020 ◽  
Author(s):  
Ryan D. Taylor ◽  
Thomas Monecke ◽  
T. James Reynolds ◽  
Jochen Monecke
Keyword(s):  
Fluid Inclusion ◽  
Fluid Inclusions ◽  
Hydrothermal System ◽  
Pressure Fluctuations ◽  
Hydrothermal Fluids ◽  
Orogenic Gold ◽  
The North ◽  
Primary Fluid ◽  
Growth Zones ◽  
East West

Abstract The Grass Valley orogenic gold district in the Sierra Nevada foothills province, central California, is the largest historical gold producer of the North American Cordillera. Gold mineralization is associated with shallowly dipping north-south veins hosted by the 160 Ma Grass Valley granodiorite to the southwest of the Grass Valley fault and steeply dipping east-west veins in accreted oceanic rocks to the northeast of this major fault. Quartz veins from both vein types show well-preserved primary textural relationships. Using a combination of petrographic and microanalytical techniques, the paragenetic sequence of minerals within the veins and the compositions of ore minerals were determined to constrain the mechanisms of quartz vein formation and gold deposition. The veins are composed of early quartz that formed through cooling of hydrothermal fluids derived from a geopressured reservoir at depth. The early quartz shows growth zoning in optical cathodoluminescence and contains abundant growth bands of primary inclusions. The primary inclusion assemblages and myriads of crosscutting secondary fluid inclusions have been affected by postentrapment modification, suggesting that early quartz formation was postdated by pronounced pressure fluctuations. These pressure fluctuations, presumably involving changes from lithostatic to hydrostatic conditions, may be related to fault failure of the host structure as predicted by the fault-valve model. Fluid flow associated with pressure cycling took place along microfractures and grain boundaries resulting in extensive recrystallization of the early quartz. Deposition of pyrite, arsenopyrite, and first-generation gold from these hydrothermal fluids causing recrystallization of the early quartz occurred as a result of wall-rock sulfidation. The gold forms invisible gold in the compositionally zoned pyrite or micron-sized inclusions within pyrite growth zones. The latest growth zones in euhedral quartz crystals that formed in association with this stage of the paragenesis contain very rare primary fluid inclusions that have not been affected by postentrapment modification. The hydrothermal system transitioned entirely to hydrostatic conditions immediately after formation of the latest quartz, explaining the preservation of the primary fluid inclusions. The formation of minor quartz in open spaces was followed by the deposition of second-generation native gold and telluride minerals that are commonly associated with base metal sulfides. Ore formation at this stage of the paragenesis is attributed to the rapid decompression of hydrothermal fluids escaping from the geopressured part of the crust into the overlying hydrostatic realm. There is no fluid inclusion evidence that this pressure drop resulted in fluid immiscibility of the hydrothermal fluids. Fluid inclusion evidence suggests that the north-south veins formed at a paleodepth of ~8 km, whereas the east-west veins appear to have formed at ~10 to 11 km below surface, confirming previous inferences that the NE-dipping Grass Valley reverse fault accommodated a large displacement. The findings of the study at Grass Valley have significant implications for the model for orogenic gold deposits, as the reconstruction of the paragenetic relationships provides evidence for the occurrence of two discrete events of gold introduction that occurred at different conditions during the evolution of the hydrothermal system.

Quartz precipitation and fluid inclusion characteristics in sub-seafloor hydrothermal systems associated with volcanogenic massive sulfide deposits

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
Matthew Steele-MacInnis ◽  
Liang Han ◽  
Robert Lowell ◽  
J. Rimstidt ◽  
Robert Bodnar
Keyword(s):  
Fluid Inclusion ◽  
Fluid Inclusions ◽  
Hydrothermal System ◽  
Massive Sulfide ◽  
Hydrothermal Systems ◽  
Fluid Immiscibility ◽  
Quartz Dissolution ◽  
Vms Deposits ◽  
Quartz Solubility ◽  
Dissolution And Precipitation

AbstractResults of a numerical modeling study of quartz dissolution and precipitation in a sub-seafloor hydrothermal system have been used to predict where in the system quartz could be deposited and potentially trap fluid inclusions. The spatial distribution of zones of quartz dissolution and precipitation is complex, owing to the fact that quartz solubility depends on many inter-related factors, including temperature, fluid salinity and fluid immiscibility, and is further complicated by the fact that quartz exhibits both prograde and retrograde solubility behavior, depending on the fluid temperature and salinity. Using the PVTX properties of H2O-NaCl, the petrographic and microthermometric properties of fluid inclusions trapped at various locations within the hydrothermal system have been predicted. Vapor-rich inclusions are trapped as a result of the retrograde temperature-dependence of quartz solubility as the convecting fluid is heated in the vicinity of the magmatic heat source. Coexisting liquid-rich and vapor-rich inclusions are also trapped in this region when quartz precipitates as a result of fluid immiscibility that lowers the overall bulk quartz solubility in the system. Fluid inclusions trapped in the shallow subsurface near the seafloor vents and in the underlying stockwork are liquid-rich with homogenization temperatures of 200–400°C and salinities close to that of seawater. Volcanogenic massive sulfide (VMS) deposits represent the uplifted and partially eroded remnants of fossil submarine hydrothermal systems, and the relationship between fluid-inclusion properties and location within the hydrothermal system described here can be used in exploration for VMS deposits to infer the direction towards potential massive sulfide ore.

The source and significance of argon isotopes in fluid inclusions from areas of mineralization

1986 ◽  
Vol 79 (3-4) ◽  
pp. 303-318 ◽  
Author(s):  
S. Kelley ◽  
G. Turner ◽  
A.W. Butterfield ◽  
T.J. Shepherd
Keyword(s):  
Fluid Inclusions ◽  
Argon Isotopes

Formation of emeralds at pegmatite-ultramafic contacts based on fluid inclusions in Kianjavato emerald, Mananjary deposits, Madagascar

2006 ◽  
Vol 70 (2) ◽  
pp. 141-158 ◽  
Author(s):  
Ye. Vapnik ◽  
I. Moroz ◽  
M. Roth ◽  
I. Eliezri
Keyword(s):  
Fluid Inclusion ◽  
Fluid Inclusions ◽  
East Coast ◽  
Fluid Inclusion Data ◽  
Pan African ◽  
Probe Analysis ◽  
Raman Probe

AbstractKianjavato emerald (Mananjary deposits, East coast of Madagascar) was formed during metasomatic processes at the contact between pegmatites and hornblendites. The metasomatic exchange was related to a Pan-African tectonometamorphic event.Fluid inclusions in the Kianjavato emerald and quartz were studied by means of microthermometry and Raman probe analysis. Three main types of inclusions were revealed: CO2-rich, CH4-rich and aqueous-rich, with a salinity of ∼2 wt.% NaCl equiv. The inclusions occurred along the same primary and pseudosecondary trails and were considered to be formed simultaneously. Based on fluid-inclusion data, the conditions of emerald growth were 250°C < T < 450°C and P = 1.5 kbar.The fluid inclusion data for Kianjavato emerald were compared to the data for another Madagascar emerald, Ianapera. The latter is of similar age, but its genesis was determined by a shearing event. Our fluid inclusion data suggested that shearing was also important as a mechanism of introducing CO2-rich fluid for the genesis of the Kianjavato emerald.

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