Hydrothermal alteration, veining, and fluid-inclusion characteristics of the Kalzas wolframite deposit, Yukon

1989 ◽  
Vol 26 (10) ◽  
pp. 2106-2115 ◽  
Author(s):  
J. V. Gregory Lynch
Keyword(s):  
Hydrothermal Alteration ◽  
Sedimentary Rocks ◽  
Hydrothermal Activity ◽  
Contact Metamorphism ◽  
Quartz Veins ◽  
The Core ◽  
Outer Periphery ◽  
Windermere Supergroup ◽  
Homogenization Temperatures ◽  
Host Rocks

Kalzas is a sheeted vein and stockwork wolframite deposit, crosscutting continental margin sedimentary rocks of the Proterozoic Windermere Supergroup in central Yukon. Mineralization is synchronous with Cretaceous post-tectonic granites of the Selwyn Plutonic Suite.Parallel sets of planar quartz veins contain coarse euhedral wolframite and are generally oriented perpendicular to southeast-plunging fold axes. Widespread alteration of the host rocks and intense stockwork veining surround the veins. Alteration and mineralization show a distinct concentric zonation across a 2.5 km long southeast-trending oval. The core zone is characterized by orthoclase contained within quartz–tourmaline–wolframite veins. Minor phases include apatite, molybdenite, bismuthinite, pyrite, chalcopyrite, and pyrrhotite. Host rocks are prevasively tourmalinized and sericitized. Hydrothermal alteration here at the core of the system overprints early biotitization of the host rocks. The biotitization appears to have been the result of earlier contact metamorphism from a hidden pluton situated beneath the deposit that converted the chloritic groundmass of the metasediments to biotite. At the fringe of wolframite mineralization, cassiterite occurs with quartz, muscovite, and tourmaline, whereas orthoclase is distinctly lacking. The outer periphery of the concentrically zoned sequence features pervasive sericitization, disseminated pyrite, and the disappearance of tourmaline. Here, quartz veins are barren except for minor galena.Three main stages mark the mineralogical evolution of the deposit: (1) early biotitization of the chloritic host rocks in the core area; (2) quartz-dominated veining with internally complex timing relations, hydrothermal alteration, and zoning; and (3) carbonate veining and replacement of wolframite by scheelite.Fluid inclusions within quartz are dominated by H2O and contain variable amounts of CO2 as well as minor CH4 and NaCl. The CO2 content ranges from approximately 0 to 6 mol%. The fluids are generally dilute but locally contain as much as 7 wt.% NaCl equivalent. Homogenization temperatures are variable: for quartz, 160–340 °C; for cassiterite, 280–350 °C; and for apatite, 220–360 °C. Minimum hydrothermal pressures at the time of mineralization are estimated to have been in the range 300–600 bar (1 bar = 100 kPa). Fluctuations in pressure with cooling appear to have resulted in CO2 immiscibility and the formation of late-stage carbonates at the termination of hydrothermal activity.

scholarly journals Amethyst occurrences in Tertiary volcanic rocks of Greece: mineralogical and genetic implications

2013 ◽  
Vol 47 (1) ◽  
pp. 477 ◽  
Author(s):  
P. Voudouris ◽  
I. Psimis ◽  
C. Mavrogonatos ◽  
C. Kanellopoulos ◽  
M. Kati ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Hydrothermal Activity ◽  
Hydrothermal Fluids ◽  
Calc Alkaline ◽  
Northern Greece ◽  
Volcanic Arc ◽  
Quartz Veins ◽  
High Sulfidation ◽  
Host Rocks ◽  
Of Greece

Epithermal-altered volcanic rocks in Greece host gem-quality amethyst veins in association with various silicates, carbonates, oxides, sulfides and halides. Host rocks are Oligocene to recent calc-alkaline to shoshonitic lavas and pyroclastics of intermediate- to acid composition. The amethyst-bearing veins occur in the periphery of porphyry-type and/or high-sulfidation epithermal mineralized centers in northern Greece (e.g. Sapes, Kirki, Kornofolia/Soufli, Lesvos island) and on Milos island in the active Aegean Volcanic Arc. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), argillic, propylitic and zeolitic types. Precipitation of amethyst in the northern Greece occurrences, took place during the final stages of the magmatic-hydrothermal activity from near-neutral to alkaline fluids, as indicated by the presence of gangue adularia, calcite, smectite, chlorite, sericite, pyrite, zeolites (laumontite, heulandite, clinoptilolite), analcime and minor amounts of barite, halite, epidote and fluorite in the quartz veins. Amethyst at Milos Island (Chondro Vouno and Kalogries-Vani areas), is accompanied by barite, smectite and lepidocrocite. Colloform-crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Fluid inclusion- and mineralogical data suggest that the studied amethyst were formed at: 174-246 °C (Sapes area), 100-175 °C (Kirki and Kornofolia areas) and 223-234°C (Lesvos island). The amethyst formation requires oxidizing conditions and is probably the result of mixing between meteoric or seawater with upwelling hydrothermal fluids. The involvement of seawater in the studied mineralization is supported by the presence of halite and abundant barite in the veins. Finally, the studied amethyst deposits should be evaluated as potential gemstone sources in Greece.

Gold mineralisation at Eqi, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 129-140 ◽  
Author(s):  
Henrik Stendal ◽  
Christian Knudsen ◽  
Mogens Marker ◽  
Bjørn Thomassen
Keyword(s):  
Hydrothermal Alteration ◽  
Hydrothermal Activity ◽  
Gold Deposits ◽  
Volcanic Complex ◽  
Igneous Complex ◽  
Original Series ◽  
West Greenland ◽  
Quartz Veins ◽  
North East ◽  
Altered Zone

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stendal, H., Knudsen, C., Marker, M., & Thomassen, B. (1999). Gold mineralisation at Eqi, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 129-140. https://doi.org/10.34194/ggub.v181.5121 _______________ Gold mineralisation at Eqi, north-east Disko Bugt, West Greenland, is hosted in Archaean (c. 2800 Ma old) supracrustal rocks; the latter are divided by a thrust into a lower volcanic unit and an upper sedimentary and volcaniclastic unit. The lower volcanic unit comprises three parts: a basal pillowed greenstone sequence, an acid volcanic complex, and an upper mafic igneous complex. Intensive hydrothermal activity resulted in extensive carbonatisation and sericitisation, which is most intense just above a system of acid feeder dykes within the basal greenstone sequence. Primary enrichment in gold took place during pervasive hydrothermal alteration, and the gold is mainly located in carbonate-altered rocks. Remobilisation of gold occurred during formation of later quartz veins in the altered zone; these quartz veins have gold contents of up to 60 ppm. The geological setting, geochemistry and formation of the gold mineralisation at Eqi is similar to many Archaean gold deposits in the Abitibi belt of Canada.

CHARACTERIZATION OF PALEOPROTEROZOIC STRUCTURES, AURIFEROUS QUARTZ VEINS, AND HOST ROCKS, FISHER PROPERTY, SEABEE GOLD OPERATION, SASKATCHEWAN, CANADA

2019 ◽  
Author(s):  
Courtney Carol Onstad ◽  
◽  
Kevin M. Ansdell ◽  
Camille A. Partin ◽  
Anders Carlson
Keyword(s):  
Quartz Veins ◽  
Host Rocks

Shale gas leakage in lower Ecca shales during contact metamorphism by dolerite sill intrusions in the Karoo Basin, South Africa

2021 ◽  
Author(s):  
V. Nengovhela ◽  
B. Linol ◽  
L. Bezuidenhout ◽  
T. Dhansay ◽  
T Muedi ◽  
...  
Keyword(s):  
South Africa ◽  
Grain Boundaries ◽  
Shale Gas ◽  
Elevated Temperatures ◽  
Contact Metamorphism ◽  
Microscopy Imaging ◽  
Gas Leakage ◽  
Karoo Basin ◽  
Maximum Temperatures ◽  
Host Rocks

Abstract Contact metamorphism along widespread dolerite sills and dykes, emplaced at 182 to 183 Ma through the sedimentary host rocks of the Karoo Basin, triggered devolatilization of carbon-rich shales of the Lower Ecca Group. Hornfel samples collected from drill cores that intersect dolerite sills were analyzed for mineral phase equilibria, chemistry and porosity to characterize thermal aureoles at various distances from sill intrusions. Andalusite-chiastolite and cordierite porphyroblasts with biotite and muscovite occur within 10 to 20 m of many intrusive contacts. These metamorphic minerals crystallized when host shales attained maximum temperatures ranging between 450 and 600°C. Scanning electron microscopy imaging confirms that the hornfels are compact and that their metamorphic minerals limit porosity along grain boundaries. In few cases intra-mineral porosity occurs within individual crystals such as calcite, andalusite and cordierite. Disequilibrium metamorphic textures such as irregular grain boundaries, and inclusions in andalusite and cordierite reveal that the elevated temperatures were too short-lived to accomplish complete (re)crystallization. Thermal modeling results are consistent with the observed metamorphic mineral assemblages. Gas leakage calculations along a 7 m and a 47 m thick dolerite sill that intrude toward the top of the Whitehill Formation suggest that methane volumes ranging between 8 to 15 Tcf were generated during the sill emplacement. Methane was likely released into the atmosphere through hydrothermal vent complexes that are well preserved in the western Karoo Basin. If such loss was widespread across the entire basin, the implications for paleo-climate change and preserved shale gas reserves in the Karoo Basin of South Africa would be significant.

scholarly journals Genesis of the Longmendian Ag–Pb–Zn Deposit in Henan (Central China): Constraints from Fluid Inclusions and H–C–O–S–Pb Isotopes

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Xinglin Chen ◽  
Yongjun Shao ◽  
Chunkit Lai ◽  
Cheng Wang
Keyword(s):  
Fluid Inclusions ◽  
Central China ◽  
Granitic Magma ◽  
Two Phase ◽  
Quartz Veins ◽  
The North ◽  
Granitic Magmatism ◽  
Polymetallic Sulfides ◽  
Homogenization Temperatures ◽  
Stage 1

The Longmendian Ag–Pb–Zn deposit is located in the southern margin of the North China Craton, and the mineralization occurs mainly in quartz veins, altered gneissic wallrocks, and minor fault breccias in the Taihua Group. Based on vein crosscutting relations, mineral assemblages, and paragenesis, the mineralization can be divided into three stages: (1) quartz–pyrite, (2) quartz–polymetallic sulfides, and (3) quartz–carbonate–polymetallic sulfides. Wallrock alteration can be divided into three zones, i.e., chlorite–sericite, quartz–carbonate–sericite, and silicate. Fluid inclusions in all Stage 1 to 3 quartz are dominated by vapor-liquid two-phase aqueous type (W-type). Petrographic and microthermometric analyses of the fluid inclusions indicate that the homogenization temperatures of Stages 1, 2, and 3 are 198–332°C, 132–260°C, and 97–166°C, with salinities of 4.0–13.3, 1.1–13.1, and 1.9–7.6 wt% NaCleqv, respectively. The vapor comprises primarily H2O, with some CO2, H2, CO, N2, and CH4. The liquid phase contains Ca2+, Na+, K+, SO42−, Cl−, and F−. The sulfides have δ34S=–1.42 to +2.35‰ and 208Pb/204Pb=37.771 to 38.795, 207Pb/204Pb=15.388 to 15.686, and 206Pb/204Pb=17.660 to 18.101. The H–C–O–S–Pb isotope compositions indicate that the ore-forming materials may have been derived from the Taihua Group and the granitic magma. The fluid boiling and cooling and mixing with meteoric water may have been critical for the Ag–Pb–Zn ore precipitation. Geological and geochemical characteristics of the Longmendian deposit indicate that the deposit is best classified as medium- to low-temperature intermediate-sulfidation (LS/IS) epithermal-type, related to Cretaceous crustal-extension-related granitic magmatism.

scholarly journals HERMIONE, EVOLUTION OF ATe-BEARING EPITHERMAL MINERALIZATION, ARGOLIS, HELLAS

2007 ◽  
Vol 40 (2) ◽  
pp. 996 ◽  
Author(s):  
S. Tombros ◽  
K. St. Seymour
Keyword(s):  
Sedimentary Rocks ◽  
Ore Deposits ◽  
Stage I ◽  
Stage Ii ◽  
Quartz Veins ◽  
Minor Contribution ◽  
Epithermal Mineralization ◽  
Ore Bodies ◽  
Calcite Veins ◽  
Sandstone Formation

The Cu-Te-bearing pyrite deposits of Hermione, Argolis are hosted in Miocenic ophiolites. The ophiolites are overlain by a shale-sandstone formation with intercalations of limestones and manganiferous sedimentary rocks. The ore deposits form irregular lenticular or stratiform ore bodies, and veins. These ore bodies are related to volcanic activity in an arc-related rift at the margins of a palaeocontinent. Late N- to NNE-trending, sinistral, milky quartz-pyrite-calcite veins cut the host ophiolites. Alteration haloes of quartz-calcite, albite-sericitechlorite, and chalcedony-epidote-clay minerals are developed in the lavas as concentric shells, or as envelops that parallel the quartz veins. The telluriumbearing mineralization is developed in two successive stages, characterized by the assemblages: pyrite-(pyrrhotite)-magnetite-chalcopyrite-sphalerite (Stage I) and galena-sphalerite-freibergite-marcasite-chalcocite (Stage II), followed by a supergene stage. The cobaltiferous pyrite-chalcopyrite geothermometer defined two ranges of last-equilibration temperatures: 220° to 250°Cfor Stage I, and 120° to 195°Cfor Stage II. The calculated δ18 Ο and SD compositions of the mineralizing fluids, at 200° and 250°C, reflect the dominance of a magmatic component. The calculated δ SH2S fluid values reveal a magmatic source for the sulphur, with minor contribution from submarine sediments, whereas tellurium is proposed to be derived from a mafic-ultramafic source.

scholarly journals Mineralogical and Fluid Inclusions Study of Epithermal Type Veins Intruding the Volcanic Rocks of the Kornofolia Area, Evros, NE Greece.

2019 ◽  
Vol 55 (1) ◽  
pp. 202
Author(s):  
Foteini Aravani ◽  
Lambrini Papadopoulou ◽  
Vasileios Melfos ◽  
Triantafillos Soldatos ◽  
Triantafillia Zorba ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Fluid Inclusion ◽  
Hydrothermal Alteration ◽  
Fluid Inclusions ◽  
Volcanic Rocks ◽  
The Other ◽  
Calc Alkaline ◽  
Ft Ir ◽  
Host Rocks

The volcanic rocks of Kornofolia area, Evros, host a number of epithermal-type veins. The host rocks are Oligocene calc-alkaline andesites to rhyo-dacites. The andesites form hydrothermal breccias and show hydrothermal alteration. The veins comprise mainly silica polymorphs such as quartz, chalcedony and three types of opal (milky white, transparent and green). Amethyst also forms in veins at the same area. Apart from the silica polymorphs, the veins are accompanied by calcite and zeolites. The main aim of this study is the characterization of the silica polymorphs. Using FT-IR analyses, variations in the crystal structure of the three opals were recognized. The green opal is found to be more amorphous than the other two types. Fluid-inclusion measurements were performed in calcite and were compared with amethyst from previous studies. The Th is between 121-175 °C and the Te between -22.9 and -22.4 °C. The salinities range from 0.9 to 4.5 wt % NaCl equiv.

Miocene to Messinian deformation and hydrothermal activity in a pre-Alpine basement massif of the French western Alps: new U-Th-Pb and argon ages from the Lauzière massif

2010 ◽  
Vol 181 (3) ◽  
pp. 227-241 ◽  
Author(s):  
Dominique Gasquet ◽  
Jean-Michel Bertrand ◽  
Jean-Louis Paquette ◽  
Jérémie Lehmann ◽  
Gueorgui Ratzov ◽  
...  
Keyword(s):  
Late Miocene ◽  
Shear Zones ◽  
Hydrothermal Activity ◽  
Western Alps ◽  
Strike Slip ◽  
Quartz Veins ◽  
The North ◽  
Slip Regime ◽  
Tectonically Active ◽  
Dextral Strike Slip

Abstract U-Pb and Th-Pb dating of monazite from hydrothermal quartz veins (“Alpine veins”) from the Lauzière massif (North Belledonne) together with Ar/Ar ages of adularias from the same veins constrain the age of the last tectono-metamorphic events that affected the External Crystalline Massifs (ECM). Ages obtained are surprisingly young. The study of the structural context of the veins combined with our chronological data, allow us to propose a tectonic scenario of the northern ECM for the 15-5 Ma period, which was poorly documented so far. The quartz veins are of two types: (i) the oldest are poorly mineralized (chlorite and epidote), flat-lying veins. The quartz fibres (= extension direction) are near vertical and seem to be associated with a subvertical dissolution schistosity superimposed upon an early Alpine deformation underlined by “mini-biotite”. They bear a sub-horizontal stretching lineation; (ii) the youngest veins are very rich in various minerals (anatase, rutile, phénacite, meneghinite, beryl, synchysite, ….). They are almost vertical. Their “en echelon” geometry as well as the horizontal attitude of their quartz fibres show a dextral strike-slip regime. Two groups of Th-Pb ages have been obtained: 11 to 10 Ma and 7 to 5 Ma. They were obtained from the most recent veins (vertical veins) sampled in different areas of the massif. The ca. 10 Ma ages are related to veins in the Lauzière granite and its metamorphic country-rocks at about 2 km from the eastern contact of the massif, while the ages of ca. 5 Ma correspond to veins occurring in mylonites along this contact. Adularias provided Ar/Ar ages at ca. 7 Ma. By contrast, a monazite from a vein of the Pelvoux massif (Plan du Lac) yielded a Th-Pb age of 17.6 Ma but in a different structural setting. Except fission track ages, there are very little ages of this range published in the recent literature on the Alps. The latter concern always gold mineralized veins (NE Mont Blanc and SW Lepontine dome). The last compressive tectonic regime dated between 15 and 12 Ma is coeval with (i) the late “Roselend thrust” event, which is recorded in the Mont Blanc by shear-zones with vertical lineation, (ii) the last movements in the basal mylonites of the Swiss Nappes, (iii) the horizontal Alpine veins from the Mont Blanc and Belledonne massifs (with vertical quartz fibres), which are similar to the early veins of the Lauzière. On the contrary, the vertical veins of the Lauzière, dated between 11 and 5 Ma, correspond to a dextral strike slip regime. This suggests that most of the strike-slip tectonics along the ECM took place during two stages (ca. 10 Ma and ca. 7-5 Ma) and not only at 18 Ma as had been proposed previously. Our ages are consistent with the late Miocene-Pliocene overlap of the Digne thrust to the South and to part of the normal movement along the Simplon fault to the North. Thus, all the external crystalline massifs were tectonically active during the late Miocene. This suggests that tectonic events in the external alpine belt may have contributed to some extent to the geodynamical causes of the Messinian crisis.

An Overview of the ULU Gold Deposit, High Lake Volcanic Belt, Nunavut, Canada

2004 ◽  
Vol 13 (1-4) ◽  
pp. 15-23
Author(s):  
E. FLOOD ◽  
P. KLEESPIES ◽  
M. TANSEY ◽  
H. MUNTANION ◽  
R. CARPENTER
Keyword(s):  
Mineral Assemblage ◽  
Spatial Association ◽  
Sedimentary Rocks ◽  
Volcanic Belt ◽  
Wall Rock ◽  
Potassium Feldspar ◽  
Lode Gold ◽  
The Core ◽  
Flood Zone ◽  
Alteration Minerals

Abstract BHP Minerals discovered the Archean lode gold ULU deposit on the western margin of the High Lake Volcanic Belt in 1989. The greenschist to amphibolite facies mafic volcanic and sedimentary rocks on the property are folded into a 5 km-long anticline. There is a close spatial association of Au-As zones to the trace of this F2 ULU anticline. The largest of these auriferous zones, the Flood zone, is localized at the core of the fold. The southeast-trending Flood zone consists of several anastomosing lenses that have been traced for 435 m on surface. Overall, it dips steeply (70° to 80°) to the southwest and has been intersected to depths below 600 m. The hosting high-iron tholeitic basalt displays a lower amphibolite mineral assemblage of ferrohornblende + plagioclase + ilmenite with accessory quartz and epidote. Alteration minerals include biotite, chlorite, hornblende, actinolite-tremolite, and potassium feldspar (microcline) with minor calcite, epidote, tourmaline, and titanite. The highest gold values occur where brecciated basaltic wall-rock clasts are replaced by acicular arsenopyrite + quartz + K-feldspar. BHP Minerals completed 54,783 m of both exploration and resource development drilling before selling the ULU property to Echo Bay Mines in 1995. Development of ULU as a satellite deposit to Echo Bay’s Lupin mine began in 1996. A -15% ramp was extended to the 155-meter level, and 16,011 m of underground drilling were completed before the decline in gold prices forced a suspension of activities at ULU in August 1997. The current owners, Wolfden Resources Inc., drilled 18,569 m in 2004 to increase confidence in the resource blocks. Following this drill program, a revised resource calculated by an independent consultant determined that the ULU deposit contains an inferred/indicated mineral resource of 1,130,000 t grading 11.34 g/t gold (373,748 oz) to the 360-m level. The portal was re-opened in 2005 and a prefeasibility study is underway.

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