Stable-isotope, fluid-inclusion, and mineralogical studies relating to the genesis of amethyst, Thunder Bay Amethyst Mine, Ontario

1993 ◽  
Vol 30 (9) ◽  
pp. 1955-1969 ◽  
Author(s):  
J. R. McArthur ◽  
E. A. Jennings ◽  
S. A. Kissin ◽  
R. L. Sherlock
Keyword(s):  
Fluid Inclusion ◽  
Meteoric Water ◽  
Stable Condition ◽  
Hydrothermal Solution ◽  
Wall Rock ◽  
Near Surface ◽  
Vein System ◽  
Thunder Bay ◽  
Quartz Monzonite ◽  
Homogenization Temperatures

The Thunder Bay Amethyst Mine exploits a vein system in which the main zoned sequence consists of chalcedony, colorless quartz, and three to four stages of amethyst. The main sequence surrounds fragments of a brecciated earlier sequence containing chalcedony, colorless quartz, and prasiolite, which appears to be thermally bleached amethyst. The vein system occupies a fault in Archean granodiorite and is associated with a narrow zone of chloritic and hematite alteration overprinted by weak argillic alteration. Fragments of Proterozoic (1339 Ma) Sibley Group rocks occur in the vein system, indicating the former presence of a shallow cover during deposition of quartz and limiting the maximum age of the deposit. These downfallen fragments and the abundance of vugs indicate near-surface formation of the deposit.Main-stage fluid-inclusion homogenization temperatures are in the range from 91.2 to 40.9 °C (mean 68.4 °C) in amethyst, whereas in colorless quartz homogenization temperatures range from 146.5 to 114.7 °C (mean 132.1 °C). Eutectic temperatures fall in three ranges with means of −50.9, −48.7, and −43.9 °C, which are related to paragenetic position and indicate an NaCl–CaCl2–H2O system, with possible additional components in later inclusions. Salinities in amethyst-hosted inclusions decrease in the growth direction from 22.9 to 15.3 equiv.wt% NaCl.Trace sulfide and other mineral inclusions indicate a trend of decreasing Eh and pH from an initially rather oxidized (sulfate stable) to a reduced (sulfide stable) condition during deposition. Sulfur isotopic composition in pyrite and chalcopyrite ranges from δ34S = −0.4 to −1.4‰ and is similar to values obtained from lead–zinc–barite in other vein deposits surrounding the Sibley depositional basin. Oxygen isotopes in quartz range from δ18O = +12.7 to +17.1‰, corresponding to δ18O(H2O) = −2.1 to −12.8‰ using fluid-inclusion temperatures. Fresh quartz monzonite wall rock (δ18O = +11.82‰) and altered quartz monzonite (δ18O = +11.01‰) do not seem to have undergone significant isotopic exchange with the hydrothermal solution, and the trend of isotopic change does not account for the trend of δ18O(H2O) determined in quartz. Rather, mixing of local meteoric water with a basinal brine appears to explain the observed trend.The amethyst deposits are believed to have been formed by basinal brines expelled from Sibley Group sediments. The brines dissolved silica by alteration processes accompanying their passage through granitic basement rocks in basin marginal faults. Amethyst was deposited on mixing with meteoric water. The temperature interval for amethyst formation appears to be restricted to less than ~90 °C. Temperatures causing thermal bleaching of amethyst are as low as 145 °C, and possibly 115 °C, as indicated by these results. This low range of temperature is not in agreement with bench-type experiments indicating bleaching at hundreds of degrees Celsius.

scholarly journals Fluid Inclusion and Oxygen Isotope Constraints on the Origin and Hydrothermal Evolution of the Haisugou Porphyry Mo Deposit in the Northern Xilamulun District, NE China

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-19 ◽  
Author(s):  
Qihai Shu ◽  
Yong Lai
Keyword(s):  
Fluid Inclusion ◽  
Meteoric Water ◽  
Early Time ◽  
Low Oxygen ◽  
Potassic Alteration ◽  
Low Salinity ◽  
Oxygen Isotopic ◽  
Homogenization Temperatures ◽  
Porphyry Mo Deposit ◽  
Positive Correlations

The Haisugou porphyry Mo deposit is located in the northern Xilamulun district, northeastern China. Based on alteration and mineralization styles and crosscutting relationships, the hydrothermal evolution in Haisugou can be divided into three stages: an early potassic alteration stage with no significant metal deposition, a synmineralization sericite-chlorite alteration stage with extensive Mo precipitation, and a postmineralization stage characterized by barren quartz and minor calcite and fluorite. The coexistence of high-salinity brine inclusions with low-salinity inclusions both in potassic alteration stage (~440°C) and locally in the early time of mineralization stage (380–320°C) indicates the occurrence of fluid boiling. The positive correlations between the homogenization temperatures and the salinities of the fluids and the low oxygen isotopic compositions (δ18Ofluid < 3‰) of the syn- to postmineralization quartz together suggest the mixing of magmatic fluids with meteoric water, which dominated the whole mineralization process. The early boiling fluids were not responsible for ore precipitation, whereas the mixing with meteoric water, which resulted in temperature decrease and dilution that significantly reduced the metal solubility, should have played the major role in Mo mineralization. Combined fluid inclusion microthermometry and chlorite geothermometer results reveal that ore deposition mainly occurred between 350 and 290°C in Haisugou.

Hydrothermal zircon and baddeleyite in Val-d'Or Archean mesothermal gold deposits: characteristics, compositions, and fluid-inclusion properties, with implications fortiming of primary gold mineralization

1993 ◽  
Vol 30 (12) ◽  
pp. 2334-2351 ◽  
Author(s):  
Robert Kerrich ◽  
Robert King
Keyword(s):  
Fluid Inclusion ◽  
Gold Mineralization ◽  
Wall Rock ◽  
Gold Deposits ◽  
Southern Volcanic Zone ◽  
Primary Fluid ◽  
Inheritance Model ◽  
Homogenization Temperatures ◽  
Host Rocks

Zircon and baddeleyite occur within quartz–tourmaline veins at four gold deposits in the Val-d'Or district of the Archean Abitibi Southern Volcanic Zone. Host rocks have experienced intense metasomatic enrichment of Zr, Hf, Y, and rare earth elements. The zircons contain primary inclusions of quartz, tourmaline, pyrite, albite, K-mica, scheelite, and gold, and gold occurs in primary fluid inclusions in zircons. Magmatic zircons in host rocks do not have this suite of inclusions; consequently a wall-rock inheritance model for the vein zircons is implausible. Compositionally, the zircons feature pronounced interzone and intergrain variations of Hf, Y, Yb, Th, and U, and sporadic anomalous Ce contents of ~ 1100 ppm, distinct from magmatic counterparts. Two principal types of primary fluid inclusion occur in the vein zircons. Type 1 H2O–CO2 inclusions have low salinities, variable quantities of CO2 and homogenization temperatures of 260–380 °C, and type 2 CO2 rich inclusions contain minor H2O and CH4. The vein zircons coprecipitated at 260–380 °C and ~ 2 kbar (1 kbar = 100 MPa) with coexisting minerals of undisputed hydrothermal origin, such as vein quartz and gold. In the Superior Province, mesothermal gold deposits are related in space and time to translithospheric structures that mark the diachronous accretion of allochthonous subprovinces from north to south between ~ 2710 and 2680 Ma. Consequently, vein zircon ages of ~ 2680 Ma record the primary mineralizing event, whereas aberrantly young ages for rutile, titanite, scheelite, and micas in the same vein systems, that scatter over 2630–2579 Ma, reveal the age of secondary remobilization events.

scholarly journals Multiphase Calcite Cementation and Fluids Evolution of a Deeply Buried Carbonate Reservoir in the Upper Ordovician Lianglitag Formation, Tahe Oilfield, Tarim Basin, NW China

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-19 ◽  
Author(s):  
Jiaqing Liu ◽  
Zhong Li ◽  
Lijuan Cheng ◽  
Jiawei Li
Keyword(s):  
Fluid Inclusion ◽  
Tarim Basin ◽  
Meteoric Water ◽  
Oil And Gas ◽  
Isotope Analysis ◽  
Carbonate Reservoir ◽  
Upper Ordovician ◽  
Nw China ◽  
Tahe Oilfield ◽  
Homogenization Temperatures

Oil and gas have been found in the Upper Ordovician Lianglitag Formation carbonates in the Tahe Oilfield, Tarim Basin, NW China. This study documents the origin of diagenetic fluids by using a combination of petrology, SIMS, fluid inclusion, and radiogenic isotope analysis. Six stages of calcite cements were revealed. C1-C2 formed in marine to early burial environments. C3 has relatively low δ18OVPDB values (−8.45‰ to −6.50‰) and likely has a meteoric origin. Meteoric water probably fluxed into aquifers during the Early Paleozoic and Late Paleozoic uplift. C4 has δ18OVPDB values typically 3‰ higher than those of C3, and probably formed during shallow burial. C5 displays relatively negative δ18OVPDB values (−8.26‰ to −5.12‰), and the moderate-to-high fluid-inclusion temperatures imply that it precipitated in burial environments. C6 shows homogenization temperatures (up to 200°C) higher than the maximum burial and much lower salinities (<10.61 wt% NaCl), which may suggest that the fluid was deeply recycled meteoric water. The average 87Sr/86Sr ratios of fracture- and vug-filling calcite cements are much higher, indicative of incorporation of radiogenic Sr. Caves and fractures constitute the dominant reservoir spaces. A corresponding diagenesis-related reservoir evolution model was established that favors exploration and prediction.

scholarly journals Precious Metal Enrichment at the Myra Falls VMS Deposit, British Columbia, Canada

Geosciences ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 422
Author(s):  
Daniel Marshall ◽  
Carol-Anne Nicol ◽  
Robert Greene ◽  
Rick Sawyer ◽  
Armond Stansell ◽  
...  
Keyword(s):  
Fluid Inclusion ◽  
Precious Metal ◽  
Metal Enrichment ◽  
Sea Floor ◽  
North West ◽  
Low Salinity ◽  
Volcanogenic Massive Sulphide ◽  
Igneous Fluids ◽  
Homogenization Temperatures ◽  
Water Depths

Gold, present as electrum, in the Battle Gap, Ridge North-West, HW, and Price deposits at the Myra Falls mine, occurs in late veinlets cutting the earlier volcanogenic massive sulphide (VMS) lithologies. The ore mineral assemblage containing the electrum comprises dominantly galena, tennantite, bornite, sphalerite, chalcopyrite, pyrite, and rarely stromeyerite, and is defined as an Au-Zn-Pb-As-Sb association. The gangue is comprised of barite, quartz, and minor feldspathic volcanogenic sedimentary rocks and clay, comprised predominantly of kaolinite with subordinate illite. The deposition of gold as electrum in the baritic upper portions of the sulphide lenses occurs at relatively shallow water depths beneath the sea floor. Primary, pseudosecondary, and secondary fluid inclusions, petrographically related to gold, show boiling fluid inclusion assemblages in the range of 123 to 173 °C, with compositions and eutectic melt temperatures consistent with seawater at approximately 3.2 wt % NaCl equivalent. The fluid inclusion homogenization temperatures are consistent with boiling seawater corresponding to water depths ranging from 15 to 125 m. Slightly more dilute brines corresponding to salinities of approximately 1 wt % NaCl indicate that there is input from very low-salinity brines, which could represent a transition from subaqueous VMS to epithermal-like conditions for precious metal enrichment, mixing with re-condensed vapor, or very low-salinity igneous fluids.

Clumped isotope geothermometry of an Ordovician carbonate mound, Hudson Bay Basin

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-102
Author(s):  
Josué J. Jautzy ◽  
Martine M. Savard ◽  
Denis Lavoie ◽  
Omid H. Ardakani ◽  
Ryan S. Dhillon ◽  
...  
Keyword(s):  
Fluid Inclusion ◽  
Oil And Gas ◽  
Fission Track ◽  
Hudson Bay ◽  
Apatite Fission Track ◽  
Burial Diagenesis ◽  
Carbonate Mound ◽  
History Of ◽  
Homogenization Temperatures ◽  
Clumped Isotope

The Hudson Bay sedimentary basin was overlooked geologically until two decades ago. Recent efforts to understand the palaeogeothermal history of this basin have led to the evaluation of fluid inclusion microthermometry, apatite fission track, organic matter reflectance and Rock–Eval analyses. Although apatite fission track and organic maturity indicators tend to show relatively low maximum burial temperatures (60–80°C), evidence of potential oil slicks on the sea surface and oil and gas shows in offshore wells have been reported across Hudson Bay. Fluid inclusion microthermometry in a carbonate mound sequence suggests homogenization temperatures of 118 ± 25 and 93 ± 10°C for recrystallized synsedimentary marine calcite and late pore-filling burial calcite, respectively. This sequence provides an interesting geological framework to test the application of clumped isotope thermometry against independent geothermometers. Here, we present clumped isotope data acquired on the late calcite cements and diagenetically altered early marine phases. The integration of clumped isotopic data with other thermal indicators allows the reconstruction and refinement of the thermal–diagenetic history of these carbonates by confirming an episode of heating, probably of hydrothermal origin and prior to normal burial diagenesis, that reset both fluid inclusions and the clumped isotope indicators without recrystallization.

Genesis of the Pb–Zn deposit at Sant’Antonio di Val D’Aspra, Southern Tuscany (Italy): disparity between geo-petrographic data and fluid inclusion microthermometry

1990 ◽  
Vol 54 (375) ◽  
pp. 289-294 ◽  
Author(s):  
M. Giamello ◽  
F. Riccobono ◽  
G. Sabatini
Keyword(s):  
Fluid Inclusion ◽  
Carbonate Rocks ◽  
Fluid Inclusion Study ◽  
Mississippi Valley ◽  
Ore Minerals ◽  
Inclusion Study ◽  
History Of ◽  
Homogenization Temperatures ◽  
The One ◽  
Internal Sediments

AbstractThe Pb–Zn deposit at Sant'Antonio di Val d'Aspra in the Farma Valley (Southern Tuscany) is hosted by Lower Moscovian carbonate rocks and shows many characters commonly found in Mississippi Valley type (MVT) deposits. Ore minerals (essentially sphalerite and galena) are closely confined to dolomitized portions of an only partly preserved black limestone. Mineralized carbonate rocks appear to have been eroded before the deposition of the overlying Upper Moscovian (Late Podolskian) shales. The diffuse presence of structures frequently found in internal sediments of karstic cavities indicates that supergene mechanisms have played an important role in the history of the deposit. A fluid inclusion study carried out on ore and gangue minerals revealed the presence of two different types of inclusions. The homogenization temperatures ranged from 120°C to 225°C but the most frequently found values were around 170°C. Salinity ranged from moderately low values up to 20 eq. wt. % NaCl. Lead isotopic composition rules out any relationship between the Sant'Antonio mineralization and Tertiary hydrothermal base metal occurrences in the same area. When all the data are taken together, a contrast is evident between geo-petrographic and isotopic data on the one hand, and fluid-inclusion microthermometry on the other.

Uraninite-albite veins from the Mistamisk Valley of the Labrador Trough, Quebec

1981 ◽  
Vol 44 (336) ◽  
pp. 471-483 ◽  
Author(s):  
L. Kish ◽  
M. Cuney
Keyword(s):  
Aqueous Solution ◽  
Fluid Inclusion ◽  
Gas Phase ◽  
Hydrothermal Solution ◽  
Hydrothermal Solutions ◽  
Fluid Inclusion Data ◽  
Vein Formation ◽  
Lower Proterozoic ◽  
Temperature And Pressure ◽  
First Time

AbstractThe uraninite-albite veins of the Mistamisk area occur in the argillite member of the Dunphy Formation, which is near the base of the slightly meta-morphosed Lower Proterozoic sequence of the central Labrador Trough. The vein minerals are albite, uraninite, dolomite, and chlorite, and minor quantities of quartz, tellurides, sulphides, gold, and organic material. Pitchblende and calcite are related to late remobilization.The veins were deposited in fractures by hydrothermal solutions, and metasomatism caused albitization of wall rocks. Fluid inclusions have an unusual composition, described here for the first time in connection with soda-metasomatism; the aqueous solution of the inclusions is oversaturated in NaCl and contains Ca2+ and Mg2+, and the gas phase mostly consists of N2, CO and CO2. The presence of hematite and absence of hydrocarbons indicates that the vein-forming solution was oxidizing.The temperature and pressure of vein formation, estimated from fluid inclusion data, was 300°–350° and 2.5 kbar respectively consistent with the composition of the phengite which is a common metamorphic mineral of the host rock. Vein emplacement occurred in the waning stages of the Hudsonian Orogeny, the hydrothermal solution possibly originating by metamorphism of sodic schists of the Mistamisk area, which are possibly of evaporitic origin.

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