共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Hernández M. Jébrak P. Higueras R. Oyarzun D. Morata J. Munhá 《Mineralium Deposita》1999,34(5-6):539-548
The Almadén district is the largest mercury concentration in the world, with a total content of about 250 000 t of mercury,
nearly one third of the known total mercury resources of the Earth. Mercury has been exploited since the Celtic and Roman
times, with peak production during the Renaissance and between 1939–1945. The district is hosted by a Paleozoic synclinorium
overlying Precambrian rocks. The Paleozoic sequence comprises epicontinental quartz arenite rocks, including black shales
and quartzites. Diatremes, alkaline lavas of different composition, and late tholeiitic diabases account for the Ordovician
to Devonian magmatism. The tectonic setting of this complex suite corresponds to the intraplate type. The mercury deposits
of Almadén can be classified into two main types: type 1, early stratiform type ores characterized by cinnabar deposition
on the lower Silurian quartzites (Criadero quartzite; e.g. the Almadén and El Entredicho deposits), and type 2, late discordant
orebodies (e.g. Las Cuevas), largely hosted or related to diatremes (the `frailesca rocks') of alkaline basaltic composition.
In type 1 cinnabar was deposited during diagenesis, in relation to hydrothermal circulation driven by magmatic activity. Type
2 include a variety of deposits having in common the discordant character of the orebodies (e.g. veins, stockworks, massive
replacements), and their wide dispersion along the stratigraphic column, i.e. from Lower Silurian (e.g. Nueva Concepción)
to Upper Devonian (e.g. Corchuelo).
Received: 23 October 1998 / Accepted: 4 January 1999 相似文献
2.
Andreas G. Mueller Gregory C. Hall Alexander A. Nemchin Darren O’Brien 《Mineralium Deposita》2008,43(8):873-889
The Pueblo Viejo deposit (production to 1996: 166 t Au, 760 t Ag) is located in the Dominican Republic on the Caribbean island
of Hispaniola and ranks as one of the largest high-sulfidation/acid-sulfate epithermal deposits (reserves in 2007: 635 t Au,
3,648 t Ag). One of the advanced argillic ore bodies is cut by an inter-mineral andesite porphyry dike, which is altered to
a retrograde chlorite–illite assemblage but overprinted by late-stage quartz–pyrite–sphalerite veins and associated low-grade
Au, Ag, Zn, Cd, Hg, In, As, Se, and Te mineralization. The precise TIMS U–Pb age (109.6 ± 0.6 Ma) of the youngest zircon population
in this dike confirms that the deposit is part of the Early Cretaceous Los Ranchos intra-oceanic island arc. Intrusion-related
gold–sulfide mineralization took place during late andesite–dacite volcanism within a thick pile (>200 m) of carbonaceous
sand- and siltstones deposited in a restricted marine basin. The high-level deposit was shielded from erosion after burial
under a late Albian (109–100 Ma) ophiolite complex (8 km thick), which was in turn covered by the volcano-sedimentary successions
(>4 km) of a Late Cretaceous–Early Tertiary calc-akaline magmatic arc. Estimates of stratigraphic thickness and published
alunite, illite, and feldspar K-Ar ages and closure temperatures (alunite 270 ± 20°C, illite 260 ± 30°C, K-feldspar 150°C)
indicate a burial depth of about 12 km at 80 Ma. During peak burial metamorphism (300°C and 300 MPa), the alteration assemblage
kaolinite + quartz in the deposit dehydrated to pyrophyllite. Temperature–time relations imply that the Los Ranchos terrane
then cooled at a rate of 3–4°C/Ma during slow uplift and erosion. 相似文献
3.
J. Götze M. Plötze Th. Götte R. D. Neuser D. K. Richter 《Mineralogy and Petrology》2002,76(3-4):195-212
Summary ?Sheet silicates of the serpentine–kaolin-group (serpentine, kaolinite, dickite, nacrite, halloysite), the talc–pyrophyllite-group
(talc, pyrophyllite), the smectite-group (montmorillonite), and illite (as a mineral of the mica-group) were investigated
to obtain information concerning their cathodoluminescence behaviour. The study included analyses by cathodoluminescence (CL
microscopy and spectroscopy), electron paramagnetic resonance (EPR), X-Ray diffraction (XRD), scanning electron microscopy
(SEM) and trace element analysis.
In general, all dioctahedral clay minerals exhibit a visible CL. Kaolinite, dickite, nacrite and pyrophyllite have a characteristic
deep blue CL, whereas halloysite emission is in the greenish-blue region. On the contrary, the trioctahedral minerals (serpentine,
talc) and illite do not show visible CL.
The characteristic blue CL is caused by an intense emission band around 400 nm (double peak with two maxima at 375 and 410 nm).
EPR measurements indicate that this blue emission can be related to radiation induced defect centres (RID), which occur as
electron holes trapped on apical oxygens (Si–O centre) or located at the Al–O–Al group (Al substituting Si in the tetrahedron).
Additional CL emission bands were detected at 580 nm in halloysite and kaolinite, and between 700 and 800 nm in kaolinite,
dickite, nacrite and pyrophyllite.
Time-resolved spectral CL measurements show typical luminescence kinetics for the different clay minerals, which enable differentiation
between the various dioctahedral minerals (e.g. kaolinite and dickite), even in thin section.
Received December 3, 2001; revised version accepted February 27, 2002 相似文献
4.
The Las Cuevas mercury deposit is located in the northern part of the Almadén district, Ciudad Real, Spain. It displays characteristic epigenetic features. A reinterpretation of the geological context of the deposit and a detailed structural analysis indicate that the host rocks at Las Cuevas belong to the same stratigraphic units that host the old Almadén mine, but that they experienced a different tectonic evolution. Two types of ore are distinguished at Las Cuevas: (1) hydraulic breccias in a black quartzite, identical to the San Francisco horizon of the Almadén mine. This ore has been interpreted as syngenetic and is associated with an alkaline explosive volcanic event; and (2) a stockwork composed of horizontal subcritical tension cracks which developed along the contact between black shales and volcanic rocks in the hinge of a drag fold, and which is associated with advanced argillic alteration. Mobilization of mercury from type 1 to type 2 ore was related to a local inversion of the stress field associated with an increase of permeability by self-sealing, which probably occurred during uplift. Las Cuevas is representative of a whole class of mercury deposits hosted within basement rocks. 相似文献
5.
Andreas Dietrich Ronald Gutierrez Eric P. Nelson Paul W. Layer 《Mineralium Deposita》2012,47(3):233-249
The San José district is located in the northwest part of the Deseado massif and hosts a number of epithermal Ag–Au quartz
veins of intermediate sulfidation style, including the Huevos Verdes vein system. Veins are hosted by andesitic rocks of the
Bajo Pobre Formation and locally by rhyodacitic pyroclastic rocks of the Chon Aike Formation. New 40Ar/39Ar constraints on the age of host rocks and mineralization define Late Jurassic ages of 151.3 ± 0.7 Ma to 144.7 ± 0.1 Ma for
volcanic rocks of the Bajo Pobre Formation and of 147.6 ± 1.1 Ma for the Chon Aike Formation. Illite ages of the Huevos Verdes
vein system of 140.8 ± 0.2 and 140.5 ± 0.3 Ma are 4 m.y. younger than the volcanic host rock unit. These age dates are among
the youngest reported for Jurassic volcanism in the Deseado massif and correlate well with the regional context of magmatic
and hydrothermal activity. The Huevos Verdes vein system has a strike length of 2,000 m, with several ore shoots along strike.
The vein consists of a pre-ore stage and three main ore stages. Early barren quartz and chalcedony are followed by a mottled
quartz stage of coarse saccharoidal quartz with irregular streaks and discontinuous bands of sulfide-rich material. The banded
quartz–sulfide stage consists of sulfide-rich bands alternating with bands of quartz and bands of chlorite ± illite. Late-stage
sulfide-rich veinlets are associated with kaolinite gangue. Ore minerals are argentite and electrum, together with pyrite,
sphalerite, galena, chalcopyrite, minor bornite, covellite, and ruby silver. Wall rock alteration is characterized by narrow
(< 3 m) halos of illite and illite/smectite next to veins, grading outward into propylitic alteration. Gangue minerals are
dominantly massive quartz intergrown with minor to accessory adularia. Epidote, illite, illite/smectite, and, preferentially
at deeper levels, Fe-chlorite gangue indicate near-neutral pH hydrothermal fluids at temperatures of >220°C. Kaolinite occurring
with the late sulfide-rich veinlet stage indicates pH < 4 and a temperature of <200°C. The Huevos Verdes system has an overall
strike of 325°, dipping on average 65° NE. The orientations of individual ore shoots are controlled by vein strike and intersecting
north-northwest-striking faults. We propose a structural model for the time of mineralization of the San José district, consisting
of a conjugate shear pair of sinistral north-northwest- and dextral west-northwest-striking faults that correspond to R and R′ in the Riedel shear model and that are related to master faults (M) of north-northeast-strike. Veins of 315° strike can
be interpreted as nearly pure extensional fractures (T). Variations in vein strike predict an induced sinistral shear component
for strike directions of >315°, whereas strike directions of <315° are predicted with an induced dextral strike–slip movement.
The components of the structural model appear to be present on a regional scale and are not restricted to the San José district. 相似文献
6.
Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps) 总被引:52,自引:2,他引:50
Gerhard Vavra Rolf Schmid Dieter Gebauer 《Contributions to Mineralogy and Petrology》1999,134(4):380-404
Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone
(IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments
in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons
in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic
variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite
facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types
in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the
leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived
event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite
(300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in
the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic
(anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the
adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation
of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration
and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled
alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during
extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at
210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower
Jurassic.
Received: 7 July 1998 / Accepted: 4 November 1998 相似文献
7.
Mineralogical and chemical variations in hypogene and supergene kaolin deposits in a mobile fold belt the Central Andes of northwestern Peru 总被引:1,自引:0,他引:1
In western Peru kaolin-alunite deposits occur in Lower Cretaceous and Tertiary clastic, volcaniclastic and volcanic, mostly
rhyolitic, rocks. Alunites from␣hypogene kaolin deposits yield K /Ar ages of 11.5 ±␣0.7␣Ma and 13.3 ± 0.4 Ma. In addition
to kaolin and alunite, the following minerals are present: white mica, smectite, barite, pyrophyllite, tridymite, cristobalite,
α- and β-quartz, chamosite, gibbsite, and aluminum-phosphate-sulphate minerals (APS). APS mineralizations with REE-bearing
svanbergite and florencite originate from supergene alteration. Woodhouseite, goyazite, crandallite and pure svanbergite develop
in hypogene and supergene kaolin deposits. The distinction between hypogene and supergene kaolinization can be made using
various element ratios in kaolin (P vs. S, Zr vs. Ti, Cr + Nb vs. Ti + Fe, and Ce + Y + La vs. Ba + Sr). S,␣Ba, and Sr are
considerably enriched in kaolin during hydrothermal alteration, whereas Cr, Nb, Ti and lanthanide elements are concentrated
mainly during weathering. Au and Ag become enriched during hypogene kaolinization (advanced argillitization). Kaolinization
is associated with the evolution of the Central Andes as follows: (1) during the Lower Cretaceous kaolinization characterizes
phases of relative tectonic quiescence during mountain building and took place in a miogeosynclinal back-arc basin. The kaolin-bearing
sediments were laid down in flood plain to delta plain environments; (2) in the magmatic arc/back-arc basin (eugeosyncline)
kaolinization was mainly associated with uplift and peneplanation; (3) in the magmatic arc proper, late Miocene kaolinization
of volcanic and volcaniclastic rocks has many features in common with the high sulphidation epithermal Au deposits.
Received: 11 August 1995 / Accepted: 8 May 1996 相似文献
8.
Several precious metal-bearing, low sulfidation epithermal veins occur in the rolling topography of the Osilo area, northern
Sardinia. The Sa Pala de Sa Fae and the Sa Pedra Bianca veins were subject to intense diamond drilling exploration in the
mid 1990 s. The veins extend for 1–3 km, dip steeply, and range from 1 to 10 m in width. High K-calc-alkaline volcanic deposits
containing plagioclase phenocrysts (along with lesser pyroxene, amphibole, magnetite, olivine and sanidine) form the main
host rocks. Gold grades in drill intersections range from <0.1 to <20 ppm, with silver-gold ratios of around 4 to 7. Mineralogical
studies show a systematic distribution of three hydrothermal mineral assemblages. At distances >50 m from the vein, the assemblage
albite + Fe-chlorite + illite + pyrite (± montmorillonite ± calcite ± K-feldspar) prevails regionally, and its formation is
attributed to minor metasomatism of the country rock involving the addition of water, carbon dioxide and hydrogen sulfide.
At distances <10 m from the vein, the assemblage quartz + K-feldspar + pyrite ± illite dominates, forming an alteration envelope
that cross cuts regional alteration. Quartz and K-feldspar increase in abundance towards the vein. Quartz is the main vein
mineral, and it displays a range of morphologies and textures including crustiform colloform banding, quartz pseudomorphs
of platy calcite, breccias and coarse euhedral crystals. Electrum and argentite which are the main gold and silver minerals
deposited during the early stages of vein mineralization with rhomb-shaped crystals of K-feldspar (adularia). Pyrite, plus
lesser marcasite, arsenopyrite, stibnite and sphalerite, are the other sulfide phases in veins. Kaolinite ± halloysite ± jarosite
form a late assemblage overprinting earlier hydrothermal alteration. It is mostly restricted to shallow depths of a few meters,
except near veins. Most of this assemblage likely formed from weathering and oxidation of sulfides. Microthermometric measurements
were made on quartz-hosted, two-phase (liquid + vapor) inclusions, containing ∼75% liquid; mean homogenization temperatures
(∼750 measurements) range from 220 to 250 °C, and ice-melting temperatures (∼550 measurements) range from 0.0 to −2.3 °C.
The presence of co-existing vapor-rich and liquid rich inclusions, with quartz pseudomorphs of platy calcite, indicate that
boiling conditions existed. Slight vapor-bubble expansion of a few fluid inclusions subjected to crushing experiments indicates
inclusion fluids contained variable but low concentrations of dissolved gas. This study shows that gold-silver mineralization
formed in subvertical channels from ascending solutions at 250 °C at around 300 to 450 m below the paleo-water table in a
typical low-sulfidation epithermal environment. Hydrothermal solutions that produced vein mineralization and related alteration
were dilute (<4.1 equivalent wt.% NaCl and <4 wt.% CO2), near neutral pH, reduced and, at times, boiling.
Received: 19 May 1998 / Accepted: 8 March 1999 相似文献
9.
Bohdan Kříbek Karel Žák Petr Dobeš Jaromír Leichmann Marta Pudilová Miloš René Bohdan Scharm Marta Scharmová Antonín Hájek Daniel Holeczy Ulrich F. Hein Bernd Lehmann 《Mineralium Deposita》2009,44(1):99-128
Three major mineralization events are recorded at the Rožná uranium deposit (total mine production of 23,000 t U, average
grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium
quartz-carbonate-sulfide mineralization. (1) K–Ar ages for white mica from wall rock alteration of the pre-uranium mineralization
style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root
and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of
low-salinity aqueous inclusions, together with H2O-CO2-CH4, CO2-CH4, and pure CH4 inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a
reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into
the pre-ore, ore, and post-ore substages. K–Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma
and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early
Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx
of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions
is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these
fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C.
During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of
the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K–Ar ages of illite from ore substage
alteration range from 277.2 ± 5.5 to 264.0 ± 4.3 Ma and roughly correspond with the results of chemical U–Pb dating of authigenic
monazite (268 ± 50 Ma). The uranium ore deposition was accompanied by large-scale decomposition of biotite and pre-ore chlorite
to Fe-rich illite and iron hydrooxides. Therefore, it is proposed that the deposition of uranium ore was mostly in response
to the reduction of the ore-bearing fluid by interaction with ferrous iron-bearing silicates (biotite and pre-ore chlorite).
The Th data on primary, mostly aqueous, inclusions trapped in carbonates of the ore substage range between 152°C and 174°C
and total salinity ranges over a relatively wide interval of 3.1 to 23.1 wt% NaCl eq. Gradual reduction of the fluid system
during the post-ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite. Chlorite
thermometry yielded temperatures of 150°C to 170°C. Solid bitumens that post-date uranium mineralization indicate radiolytic
polymerization of gaseous and liquid hydrocarbons and their derivatives. The origin of the organic compounds can be related
to the diagenetic and catagenetic transformation of organic matter in Upper Stephanian and Permian sediments. (3) K–Ar ages
on illite from post-uranium quartz-carbonate-sulfide mineralization range from 233.7 ± 4.7 to 227.5 ± 4.6 Ma and are consistent
with the early Tethys-Central Atlantic rifting and tectonic reactivation of the Variscan structures of the Bohemian Massif.
A minor part of the late Variscan uranium mineralization was remobilized during this hydrothermal event. 相似文献
10.
Mineralisation at the Zarshuran, NW Iran, occurs on the flank of an inlier of Precambrian rocks hosted in black silty calcareous
and carbonaceous shale with interbedded dolomite and limestone varying in thickness from 5 to 60 m and extending along strike
for approximately 5–6 km. Two major, steeply dipping sets of faults with distinct trends occur in the Zarshuran: (1) northwest
(310–325) and (2) southwest (255–265). The main arsenic mineralisation occurs at the intersection of these faults. The mineral
assemblage includes micron to angstrom-size gold, orpiment, realgar, stibnite, getchellite, cinnabar, thallium minerals, barite,
Au-As-bearing pyrite, base metal sulphides and sulphosalts. Hydrothermal alteration features are developed in black shale
and limestone around the mineralisation Types of alteration include: (1) decalcification, (2) silicification, (3) argillisation,
(4) dolomitisation, (5) oxidation and acid leaching and (6) supergene alteration. The early stage of mineralisation involved
removal of carbonates from the host rocks, followed by quartz precipitation. The main stage includes massive silicification
associated with argillic alteration. In the late stage veining became more dominant and the main arsenic ore was deposited
along fault cross cuts and gouge. These characteristics are typical of Carlin-type sediment-hosted disseminated gold deposits.
The early stage of mineralisation contains only two-phase aqueous fluid inclusions. The main stage has two groups of three-phase
CO2-bearing inclusions with minor CH4 ± N2, associated with high temperature, two-phase aqueous inclusions. During the late stage, fluids exhibit a wide range in composition,
salinity and temperature, and CH4 becomes the dominant carbonic fluid with minor CO2 associated with a variety of two-phase aqueous fluid inclusions. The characteristics of fluids at the Zarshuran imply the
presence of at least two separate fluids during mineralisation. The intersections of coexisting carbonic and aqueous inclusion
isochores, together with stratigraphic and mineral stability evidence, indicate that mineralisation occurred at 945 ± 445
bar and 243 ± 59 °C, implying a depth for mineralisation of at least 3.8 ± 1.8 km (assuming a lithostatic pressure gradient).
Fluid density fluctuations and the inferred depth of formation suggest that the mineralisation occurred at the transition
between overpressured and normally pressured regimes. Geochronologic studies utilising K/Ar and Ar/Ar techniques on hydrothermal
argillic alteration (whole rock and separated clay size fractions) and on volcanic rocks, indicates that mineralisation at
Zarshuran formed at 14.2 ± 0.4 Ma, and was contemporaneous with nearby Miocene volcanic activity, 13.7 ± 2.9 Ma. It is proposed
that mineralisation was the result of the infiltration of hydrothermal fluids containing a magmatic gas component, and that
it was localised in the Zarshuran Unit because of the redox boundary that it provided and/or because it lay between an overpressured
region at depth and a zone of circulating, hydrostatically pressured fluids above.
Received: 10 December 1997 / Accepted: 5 March 1999 相似文献
11.
EL H. Talbi J. Honnorez N. Clauer F. Gauthier-Lafaye P. Stille 《Contributions to Mineralogy and Petrology》1999,137(3):246-266
Petrological and chemical variations, as well as oxygen and strontium isotopic data are presented for metagabbros from the
Romanche and Vema fracture zones. These rocks were affected by several types and degrees of alterations ranging from slight
hydrothermal alteration to complete amphibolitization. Five major kinds of alteration processes ranging from late-magmatic
deuteric alteration (stage I) to low temperature (<150 °C) alteration (stage V) were identified. Water-rock interactions between
300 and 650 °C are the most dominant interactions resulting in the most prevailing secondary mineralogical assemblages which
characterize the amphibolite and/or greenschist facies (amphibole ± plagioclase ± epidote ± titanite ± chlorite ± prehnite).
Hydrothermal alteration of these gabbroic rocks results in isotopic exchanges between rocks and seawater-derived fluids. These
exchanges lead to decrease of gabbroic δ18O toward values as low as +3.9‰, and larger Sr isotopic variations than other oceanic gabbroic rocks (87Sr/86Sr ratios shift to 0.7029–0.7051). Calculation of a chemical budget indicates that metagabbros are hydrated and enriched in
Fe and probably in Mg and Cl, while Si, Ca and Ti are released to the hydrothermal fluids. In addition to metamorphic recrystallization
and geochemical transformation, hydrothermal alteration of oceanic gabbros contributes to the control of the global ocean
geochemistry.
Received: 8 March 1999 / Accepted: 12 July 1999 相似文献
12.
Verónica Oliveros Dania Tristá-Aguilera Gilbert Féraud Diego Morata Luis Aguirre Shoji Kojima Fernando Ferraris 《Mineralium Deposita》2008,43(1):61-78
The Michilla mining district comprises one of the most important stratabound and breccia-style copper deposits of the Coastal
Cordillera of northern Chile, hosted by the Middle Jurassic volcanic rocks of the La Negra Formation. 40Ar/39Ar analyses carried out on igneous and alteration minerals from volcanic and plutonic rocks in the district allow a chronological
sequence of several magmatic and alteration events of the district to be established. The first event was the extrusion of
a thick lava series of the La Negra Formation, dated at 159.9 ± 1.0 Ma (2σ) from the upper part of the series. A contemporaneous intrusion is dated at 159.6 ± 1.1 Ma, and later intrusive events are
dated at 145.5 ± 2.8 and 137.4 ± 1.1 Ma, respectively. Analyzed alteration minerals such as adularia, sericite, and actinolite
apparently give valid 40Ar/39Ar plateau and miniplateau ages. They indicate the occurrence of several alteration events at ca. 160–163, 154–157, 143–148,
and 135–137 Ma. The first alteration event, being partly contemporaneous with volcanic and plutonic rocks, was probably produced
in a high thermal gradient environment. The later events may be related either to a regional low-grade hydrothermal alteration/metamorphism
process or to plutonic intrusions. The Cu mineralization of the Michilla district is robustly bracketed between 163.6 ± 1.9
and 137.4 ± 1.1 Ma, corresponding to dating of actinolite coexisting with early-stage chalcocite and a postmineralization
barren dyke, respectively. More precisely, the association of small intrusives (a dated stock from the Michilla district)
with Cu mineralization in the region strongly suggests that the main Michilla ore deposit is related to a magmatic/hydrothermal
event that occurred between 157.4 ± 3.6 and 163.5 ± 1.9 Ma, contemporaneous or shortly after the extrusion of the volcanic
sequence. This age is in agreement with the Re–Os age of 159 ± 16 Ma obtained from the mineralization itself (Tristá-Aguilera
et al., Miner Depos, 41:99–105,2006). 相似文献
13.
Advanced argillic (AA) alteration is developed over a vertical interval of 500 m, above (and enclosing) Late Devonian quartz
monzodiorite intrusions that accompany porphyry-style Cu–Au mineralization at the Hugo Dummett deposit. The AA alteration
is mainly in basaltic rocks and locally extends into the overlying dacitic ash-flow tuff for about 100 m. The AA zone overprints
porphyry-style quartz veins associated with quartz monzodiorite intrusions, but at least partly precedes high-grade porphyry-style
bornite mineralization. Mineralogically, it consists of andalusite, corundum, residual quartz, titanium oxides, diaspore,
alunite, aluminum phosphate-sulfate (APS) minerals, zunyite, pyrophyllite, topaz, kaolinite, and dickite, as well as anhydrite
and gypsum, but is dominated by residual quartz and pyrophyllite. Alteration zonation is not apparent, except for an alunite-bearing
zone that occurs approximately at the limit of strong quartz veining. Whole-rock geochemistry shows that the AA alteration
removes most major elements except Si, Al, Ti, and P, and removes the trace elements Sc, Cs, and Rb. V, Zr, Hf, Nb, Ta, U,
and Th are relatively immobile, whilst light REEs (La to Nd), Sr, Ba, and Ga can be enriched. Middle REEs (Sm to Gd) are moderately
depleted; Y and heavy REEs (Tb to Lu) are strongly depleted except in two unusual samples where middle to heavy REEs are enriched. 相似文献
14.
The nature, origin and physicochemical controls of hydrothermal Mo-Bi mineralization in the Cadillac deposit, Quebec, Canada 总被引:2,自引:0,他引:2
Mo-Bi mineralization occurs in subvertical and subhorizontal quartz-muscovite-± K-feldspar veins surrounded by early albitic
and later K-feldspathic alteration halos in monzogranite of the Archean Preissac pluton, Abitibi region, Québec, Canada. Molybdenite
is intergrown with muscovite in the veins or associated with K-feldspar in the alteration halos. Mineralized veins contain
five main types of fluid inclusions: aqueous liquid and liquid-vapor inclusions, aqueous carbonic liquid-liquid-vapor inclusions,
carbonic liquid and vapor inclusions, halite-bearing aqueous liquid and liquid-vapor inclusions, trapped mineral-bearing aqueous
liquid and liquid-vapor inclusions. The carbonic solid in frozen carbonic and aqueous-carbonic inclusions melts in most cases
at −56.7 ± 0.1 °C indicating that the carbonic fluid consists largely of CO2. All aqueous inclusion types and the aqueous phase in carbonic inclusions have low initial melting temperatures (≥70 °C),
requiring the presence of salts other than NaCl. Leachate analyses show that the bulk fluid contains variable proportions
of Na, K, Ca, Cl, and traces of Mg and Li. The following solids were identified in the fluid inclusions by SEM-EDS analysis:
halite, calcite, muscovite, millerite (NiS), barite and antarcticite (CaCl2 · 6H2O). All are interpreted to be trapped phases except halite which is a daughter mineral, and antarcticite which formed during
sample preparation (freezing). Aqueous inclusions homogenize to liquid at temperatures between 75 °C and 400 °C; the mode
is 375 °C. Aqueous-carbonic inclusions homogenize to liquid or vapor between 210 °C and 400 °C. Halite-bearing aqueous inclusions
homogenize by halite dissolution at approximately 170 °C. Aqueous inclusions containing trapped solids exhibit liquid-vapor
homogenization at temperatures similar to those of halite-bearing aqueous inclusions. Temperatures of vein formation, based
on oxygen isotopic fractionation between quartz and muscovite, range from 342 °C to 584 °C. The corresponding oxygen isotope
composition of the aqueous fluid in equilibrium with these minerals ranges from 1.2 to 5.5 per mil with a mean of 3.9 per
mil, suggesting that the liquid had a significant meteoric component. Isochores for aqueous fluid inclusions intersect the
modal isotopic isotherm of 425 °C at pressures between 590 and 1900 bar. A model is proposed in which molybdenite was deposited
owing to decreasing temperature and/or pressure from CO2-bearing, moderate to high salinity fluids of mixed magmatic-meteoric origin that were in equilibrium with K-feldspar and
muscovite. These fluids resulted from the degassing of a monzogranitic magma and evolved through interaction with volcanic
(komatiitic) and sedimentary country rocks.
Received: 6 February 1997 / Accepted: 28 January 1998 相似文献
15.
Oxygen isotope systematics of emerald: relevance for its origin and geological significance 总被引:2,自引:0,他引:2
G. Giuliani C. France-Lanord P. Coget D. Schwarz A. Cheilletz Y. Branquet D. Giard A. Martin-Izard P. Alexandrov D. H. Piat 《Mineralium Deposita》1998,33(5):513-519
Oxygen isotopic composition of emerald from 62 occurrences and deposits in the world reveals a wide range in δ18O (SMOW) between +6.2 and +24.7‰. The δ18O-values for each deposit are restricted and can be used to determine the origin of emerald from the world's most important
producers. The δ18O-value of emerald appears to be a fingerprint of its origin, especially for gems of exceptional quality from Colombia (eastern
emerald zone, δ18O = +16.8 ± 0.1‰; western emerald zone, δ18O = +21.2 ± 0.5‰), Afghanistan (δ18O = +13.5 ± 0.1‰), Pakistan (Swat-Mingora districts, δ18O = +15.7 ± 0.1‰), Brazil (Santa Terezinha de Goiás, δ18O = +12.2 ± 0.1‰; Quadrilatero Ferrifero, δ18O = +6.9 ± 0.4‰) and Zimbabwe (Sandawana, δ18O = +7.5 ± 0.5‰). Furthermore, the 18O-composition of emerald appears to be a good marker of its geological environment because the data suggest that host-rock-buffering
of fluid δ18O is considerable during fluid-rock interaction.
Received: 29 January 1998 / Accepted: 25 March 1998 相似文献
16.
Synchronous deformation and hydrothermal activity in the shear zone hosted high-sulphidation Au-Cu deposit at Peak Hill, NSW, Australia 总被引:1,自引:0,他引:1
A. Allibone 《Mineralium Deposita》1998,33(5):495-512
Altered and mineralised rocks at Peak Hill, are confined to a 300–500 m wide, north-south striking, steeply dipping, shear
zone that is flanked by the Mingelo Volcanics along its western side, and Cotton Formation siltstones along its eastern side.
This shear zone is defined by extensive zones of cataclasite and strongly foliated micaceous schists in marked contrast to
the largely undeformed nature of the adjacent rocks. Advanced argillic assemblages (quartz-kaolinite-pyrite ± alunite ± illite)
occur throughout the core of the Peak Hill deposit. Propylitic assemblages, including albite, quartz, interlayered chlorite-smectite,
illite and ankerite, and a narrow discontinuous zone of argillic (quartz-illite-pyrite) alteration are developed in the Mingelo
Volcanics along the western side of the deposit. Propylitic, argillic and advanced argillic assemblages are overprinted by
an internally zoned phase of phyllosilicate alteration that grades inwards from a peripheral sericite-clay-chlorite assemblage,
through phyllic assemblages (muscovite/illite-pyrite ± paragonite) to a pyrophyllite-pyrite ± diaspore ± andalusite altered
core. Au-Cu mineralisation is hosted by barite-pyrite veins that cut the advanced argillic assemblage, but pre-date the phyllosilicate-dominated
alteration. Native Au (lacking Ag), calaverite, Te-rich tennantite-tetrahedrite (goldfieldite), chalcopyrite, covellite and chalcocite occur in the barite-pyrite veins. No ore-bearing minerals were detected in any of
the alteration assemblages. The total gold content of the Peak Hill deposit is currently 720 K ounces and this includes 100 K
ounces of unmined reserves. Within the shear zone phyllosilicate minerals are developed in strain shadows and partly define
the stretching lineation associated with dip-slip movement. The zonation within the phyllosilicate assemblages mimics the
geometry of bends in the shear zone and minor internal structures. These textures indicate that the phyllosilicate alteration
developed synchronous with movement on the shear zone. Earlier advanced argillic alteration and mineralisation are developed
in rocks derived from both sides of the shear zone. Hydrothermal activity associated with the earlier advanced argillic alteration
was therefore either synchronous with juxtaposition of these distinct rock units, or occurred during a later phase of movement
on the shear zone. Cross-cutting fibrous textures in the auriferous barite-pyrite veins indicate that repeated fracturing
of the advanced argillic altered rocks accompanied development of successive generations of auriferous veins. Concentrations
of auriferous veins are localised in steeply plunging shoots that are oriented parallel to the stretching lineation in the
shear zone. These features all indicate movement on the host shear zone accompanied each phase of hydrothermal activity in
the Peak Hill deposit. The location, alteration zonation and distribution of mineralised veins within the deposit are intimately
controlled by deformation on the host shear zone synchronous with hydrothermal activity. The development of high-sulphidation
hydrothermal systems synchronous with deformation along brittle-ductile shear zones is a predictable consequence of intrusive
activity during deformation in areas characterised by a high geothermal gradient. The close relationship between tectonism
and hydrothermal activity indicates that these deposits are likely to be located in the vicinity of regional-scale shear zones.
Deposits are likely to be aligned parallel to the regional-scale structural “grain” and restricted to areas of conspicuous
deformation as is the case at Peak Hill (and Temora, NSW). Aluminous alteration zones concentrated in the vicinity of regional-scale
structures in the Carolina Slate Belt may be a further example of this style of hydrothermal activity.
Received: 30 September 1996 / Accepted: 28 August 1997 相似文献
17.
The uranium- /fission-xenon systems in eleven samples selected from three occurrences in the Schwarz- wald were investigated
(Menzenschwand, Wittichen, Müllenbach). Relationships between mineralogical properties, Xe release profiles and Xe-Xe age
spectra provide criteria for sample suitability for U-Xe and Xe-Xe dating and interpretation of the Xe-Xe age spectra. U leaching
from pitchblendes was demonstrated for three of the Wittichen samples, indicating also disturbed U-Pb relations. The results
show that the U-Xe isotopic system is a valuable geochronological tool for studying uranium minerals. In samples of two deposits,
fission Xe was well preserved and allowed us to determine Xe-Xe plateau ages: 301 ± 11, 304 ± 9 and 279 ± 10 Ma for Menzenschwand
and 244 ± 9 Ma for Wittichen pitchblendes. These ages show the closure times of the U-Xe isotope systems and most probably
correspond to the formation of these pitchblendes. They are in accord with published U-Pb data. Four other samples of these
two deposits had very irregular spectra. An attempt was made to interpret integrated Xe-Xe ages (U-Xe ages) in these samples
in terms of alteration events. Little fission Xe was found in material from Müllenbach. There is a large time gap between
the formation of the hosting granites and the U-ore depositions (about 30 and 90 Ma, respectively) in Menzenschwand and Wittichen.
Received: 10 November 1998 / Accepted: 19 August 1999 相似文献
18.
Friedrich Lucassen Sven Lewerenz Gerhard Franz José Viramonte Klaus Mezger 《Contributions to Mineralogy and Petrology》1999,134(4):325-341
Crustal xenoliths from basanitic dikes and necks that intruded into continental sediments of the Cretaceous Salta Rift at
Quebrada de Las Conchas, Provincia Salta, Argentina were investigated to get information about the age and the chemical composition
of the lower crust. Most of the xenoliths have a granitoid composition with quartz-plagioclase-garnet-rutile ± K-feldspar
as major minerals. The exceedingly rare mafic xenoliths consist of plagioclase-clinopyroxene-garnet ± hornblende. All xenoliths
show a well equilibrated granoblastic fabric and the minerals are compositionally unzoned. Thermobarometric calculations indicate
equilibration of the mafic xenoliths in the granulite facies at temperatures of ca. 900 °C and pressures of ca. 10 kbar. The
Sm-Nd mineral isochron ages are 95.1 ± 10.4 Ma, 91.5 ± 13.0 Ma, 89.0 ± 4.2 Ma (granitoid xenoliths), and 110.7 ± 23.6 Ma (mafic
xenolith). These ages are in agreement with the age of basanitic volcanism (ca. 130–100 and 80–75 Ma) and are interpreted
as minimum ages of metamorphism. Lower crustal temperature at the time given by the isochrons was above the closure temperature
of the Sm-Nd system (>600–700 °C). The Sm-Nd and Rb-Sr isotopic signatures (147Sm/144Nd = 0.1225–0.1608; 143Nd/144Ndt
0 = 0.512000–0.512324; 87Rb/86Sr = 0.099–0.172; 87Sr/86Srt
0 = 0.708188–0.7143161) and common lead isotopic signatures (206Pb/204Pb = 18.43–18.48; 207Pb/204Pb = 15.62–15.70; 208Pb/204Pb = 38.22 –38.97) of the granitoid xenoliths are indistinguishable from the isotopic composition of the Early Paleozoic metamorphic
basement from NW Argentina, apart from the lower 208Pb/204Pb ratio of the basement. The Sm-Nd depleted mantle model ages of ca. 1.8 Ga from granitoid xenoliths and Early Paleozoic
basement point to a similar Proterozoic protolith. Time constraints, the well equilibrated granulite fabric, P-T conditions and lack of chemical zoning of minerals point to a high temperature in a crust of nearly normal thickness at ca.
90 Ma and to a prominent thermal anomaly in the lithosphere. The composition of the xenoliths is similar to the composition
of the Early Paleozoic basement in the Andes of NW Argentina and northern Chile. A thick mafic lower crust seems unlikely
considering low abundance of mafic xenoliths and the predominance of granitoid xenoliths.
Received: 21 July 1998 / Accepted: 27 October 1998 相似文献
19.
Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile 总被引:1,自引:0,他引:1
J. Carrillo-Rosúa S. Morales-Ruano D. Morata A. J. Boyce M. Belmar A. E. Fallick P. Fenoll Hach-Alí 《Mineralogy and Petrology》2008,92(3-4):341-360
Summary The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous
andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E
fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are
pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As
+ Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs
interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up
to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid
inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.%
NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ18O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest
the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed
for the formation of the El Dorado deposit.
Author’s present address: J. Carrillo-Rosúa, Dpto. de Didáctica de las Ciencias Experimentales, Universidad de Granada, Campus de Cartuja, 18071, Granada, Spain 相似文献
20.
Ian S. Buick Robert Frei Ian Cartwright 《Contributions to Mineralogy and Petrology》1999,135(2-3):244-254
Lower Calcsilicate Unit metasediments and underlying migmatitic Napperby Gneiss metagranite at Conical Hill in the Reynolds
Range, central Australia, underwent regional high-grade (∼680 to 720 °C), low-pressure/high-temperature metamorphism at 1594 ±
6 Ma. The Lower Calcsilicate Unit is extensively quartz veined and epidotised, and discordant grandite garnet + epidote quartz
veins may be traced over tens of metres depth into pegmatites that pooled at the Lower Calcsilicate Unit-Napperby Gneiss contact.
The quartz veins were probably precipitated by water-rich fluids that exsolved from partial melts derived from the Napperby
Gneiss during cooling from the peak of regional metamorphism to the wet granite solidus. Pb stepwise leaching (PbSL) on garnet
from three discordant quartz veins yielded comparable single mineral isochrons of 1566 ± 32 Ma, 1576 ± 3 Ma and 1577 ± 5 Ma,
which are interpreted as the age of garnet growth in the veins. These dates are in good agreement with previous Sensitive
High Resolution Ion Microprobe (SHRIMP) ages of zircon and monazite formed during high-temperature retrogression (1586 ± 5
to 1568 ± 4 Ma) elsewhere in the Reynolds Range. The relatively small age difference between peak metamorphism and retrograde
veining suggests that partial melting and melt crystallisation controlled fluid recycling in the high-grade rocks. However,
PbSL experiments on epidote intergrown with, and partially replacing, garnet in two of the veins yielded isochrons of 1454 ± 34
and 1469 ± 26 Ma. The ∼100–120 Ma age difference between intergrown garnet and late epidote from the same vein suggests that
the vein systems may have experienced multiple episodes of fluid flow.
Received: 24 April 1998 / Accepted: 17 December 1998 相似文献