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1.
The Palaeoproterozoic Kristineberg VMS deposit, Skellefte district, northern Sweden, part I: geology
Hans Årebäck Timothy J. Barrett Stig Abrahamsson Pia Fagerström 《Mineralium Deposita》2005,40(4):351-367
The Kristineberg volcanic-hosted massive sulphide (VMS) deposit, located in the westernmost part of the Palaeoproterozoic
Skellefte district, northern Sweden, has yielded 22.4 Mt of ore, grading 1.0% Cu, 3.64% Zn, 0.24% Pb, 1.24 g/t Au, 36 g/t
Ag and 25.9% S, since the mine opened in 1941, and is the largest past and present VMS mine in the district. The deposit is
hosted in a thick pile of felsic to intermediate and minor mafic metavolcanic rocks of the Skellefte Group, which forms the
lowest stratigraphic unit in the district and hosts more than 85 known massive sulphide deposits. The Kristineberg deposit
is situated lower in the Skellefte Group than most other deposits. It comprises three main ore zones: (1) massive sulphide
lenses of the A-ore (historically the main ore), having a strike length of about 1,400 m, and extending from surface to about
1,200 m depth, (2) massive sulphide lenses of the B-ore, situated 100–150 m structurally above the A-ore, and extending from
surface to about 1,000 m depth, (3) the recently discovered Einarsson zone, which occurs in the vicinity of the B-ore at about
1,000 m depth, and consists mainly of Au–Cu-rich veins and heavily disseminated sulphides, together with massive sulphide
lenses. On a regional scale the Kristineberg deposit is flanked by two major felsic rock units: massive rhyolite A to the
south and the mine porphyry to the north. The three main ore zones lie within a schistose, deformed and metamorphosed package
of hydrothermally altered, dominantly felsic volcanic rocks, which contain varying proportions of quartz, muscovite, chlorite,
phlogopite, pyrite, cordierite and andalusite. The strongest alteration occurs within 5–10 m of the ore lenses. Stratigraphic
younging within the mine area is uncertain as primary bedding and volcanic textures are absent due to strong alteration, and
tectonic folding and shearing. In the vicinity of the ore lenses, hydrothermal alteration has produced both Mg-rich assemblages
(Mg-chlorite, cordierite, phlogopite and locally talc) and quartz–muscovite–andalusite assemblages. Both types of assemblages
commonly contain disseminated pyrite. The sequence of volcanic and ore-forming events at Kristineberg is poorly constrained,
as the ages of the massive rhyolite and mine porphyry are unknown, and younging indicators are absent apart from local metal
zoning in the A-ores. Regional structural trends, however, suggest that the sequence youngs to the south. The A- and B-ores
are interpreted to have formed as synvolcanic sulphide sheets that were originally separated by some 100–150 m of volcanic
rocks. The Einarsson zone, which is developed close to the 1,000 m level, is interpreted to have resulted in part from folding
and dislocation of the B-ore sulphide sheet, and in part from remobilisation of sulphides into small Zn-rich massive sulphide
lenses and late Au–Cu-rich veins. However, the abundance of strongly altered, andalusite-bearing rocks in the Einarsson zone,
coupled with the occurrence of Au–Cu-rich disseminated sulphides in these rocks, suggests that some of the mineralisation
was synvolcanic and formed from strongly acidic hydrothermal fluids.
Editorial handling: P. Weihed 相似文献
2.
A multi-element geochemical study of the wall rocks of intermediate to felsic volcanic-hosted massive sulfide deposits was carried out to identify pathfinder elements which significantly enlarge the size of exploration targets. Drill core samples from the Crandon massive sulfide deposit in Wisconsin, and outcrop samples from the United Verde and Iron King deposits in Arizona, and from the Captains Flat, Mt. Costigan, and Wiseman Creek deposits in New South Wales, Australia were analyzed. Because anomalously high fluorine values have been described in several volcanic-hosted ore systems, fluorine was included in the study.All of the above deposits have patterns of fluorine enrichment around ore. Drill core samples from two noneconomic prospects within ten miles of the Crandon deposit contain background to only weakly anomalous fluorine values.At the large Crandon deposit (> 50 million tons of zinc, copper ore), fluorine enrichment extends approximately 320 m into the footwall rocks and at least 220 m into the hanging wall rocks. At the large United Verde deposit (> 50 million tons of copper, zinc ore), fluorine enrichment is recognizable in the footwall rocks at least 650 m from the ore. At the smaller Iron King deposit (five million tons production of zinc, lead, copper ore), fluorine enrichment extends for a distance of approximately 60 m into the footwall rocks. At the small deposits in New South Wales (< five million tons production of zinc, lead, copper ore), fluorine enrichment is easily recognizable, but with the samples collected, the limits of the anomalous patterns cannot be defined.Fluorine occurs in some hydrothermal systems unassociated with mineralization and is therefore not a specific signature of ore-forming processes. From the work completed, many massive sulfide deposits in volcanic rocks occur in hydrothermal systems which contain fluorine. On the basis of the data presented, if anomalously high fluorine values do exist in an exploration search area, the chances of finding a massive sulfide ore deposit are improved.Genetic models for volcanic-hosted massive sulfide ore deposits have concentrated on rock textures, alteration mineralogy, and geochemistry of the ore metals. From the data presented, fluorine should be considered as a component of massive sulfide systems in intermediate to felsic volcanic rocks, and should be considered as a possible complexing agent for the ore metals. 相似文献
3.
W. Vivallo 《Mineralium Deposita》1985,20(1):33-42
The Early Proterozoic sulfide deposit at Garpenberg is located in the metallogenetic province of central Sweden. It is a strata-bound massive sulfide deposit contained in a supracrustal sequence of mainly acid metavolcanic rocks. Stratiform Zn-Pb-Cu mineralization is underlain by Cu-bearing stockwork ore and an extensive alteration zone. The sulfide ores and their altered wall rocks were formed by subseafloor hydrothermal activity. The alteration pattern observed in the wall rocks of this deposit is consistent with a hydrothermal system where the fluid consists mainly of seawater and a high water/rock mass ratio predominates. The hydrothermal activity caused the destruction of the primary mineralogy, mainly feldspars, and a general redistribution of the chemical elements in the altered wall rocks which were principally depleted in Ca, Na and Eu and enriched in Mg. Eu was redeposited with the ore metals near or at the seafloor and Ca was deposited as limestone. Most of the major and trace elements show large mobility during the alteration; only Ti, Zr, Y and REE (excluding Eu) behaved as relatively immobile elements. 相似文献
4.
The Archean Murchison greenstone belt, Limpopo Province, South Africa, represents a rifted epicontinental arc sequence containing
the largest volcanic-hosted massive sulfide (VMS) district in Southern Africa. The so-called Cu–Zn line is host to 12 deposits
of massive sulfide mineralization including: Maranda J, LCZ, Romotshidi, Mon Desir, Solomons, and Mashawa with a total tonnage
of three million metric tons of very high grade Zn, subordinate Cu, and variable Pb and Au ore. The deposits developed during
initial phases of highly evolved felsic volcanism between 2,974.8 ± 3.6 and 2,963.2 ± 6.4 Ma and are closely associated with
quartz porphyritic rhyolite domes. Elevated heat supply ensured regional hydrothermal convection along the entire rift. Recurrent
volcanism resulted in frequent disruption of hydrothermal discharge and relative short-lived episodes of hydrothermal activity,
probably responsible for the small size of the deposits. Stable thermal conditions led to the development of mature hydrothermal
vent fields from focused fluid discharge and sulfide precipitation within thin layers of felsic volcaniclastic rocks. Two
main ore suites occur in the massive sulfide deposits of the “Cu–Zn line”: (1) a low-temperature venting, polymetallic assemblage
of Zn, Pb, Sb, As, Cd, Te, Bi, Sn, ±In, ±Au, ±Mo occurring in the pyrite- and sphalerite-dominated ore types and (2) a higher
temperature suite of Cu, Ag, Au, Se, In, Co, Ni is associated with chalcopyrite-bearing ores. Sphalerite ore, mineralogy,
and geochemical composition attest to hydrothermal activity at relatively low temperatures of ≤250 °C for the entire rift,
with short-lived pulses of higher temperature upflow, reflected by proportions of Zn-rich versus Cu-rich deposits. Major-
and trace-metal composition of the deposits and Pb isotope signatures reflect the highly evolved felsic source rock composition.
Geological setting, host rock composition, and metallogenesis share many similarities not only with Archean VMS districts
in Canada and Australia but also with recent arc–back-arc systems on the modern seafloor where fragments of continental crust
and areas of elevated heat flow are involved in petrogenetic and associated metallogenic processes. 相似文献
5.
The Kristineberg massive sulfide deposit is hosted by metamorphosed volcanic and subvolcanic rocks of the Palaeoproterozoic
Skellefte Group. The deposit consists of: (1) two main massive sulfide horizons, the A-ores and B-ores, which dip steeply
southwards and are separated by 100–150 m; and (2) the Einarsson Zone, a complex interval of Cu–Au-rich ‘stockwork‘ sulfides
and small massive sulfide lenses in altered and deformed rocks near the 1,000 m level. The Einarsson Zone occurs some 20–100 m
south of the B-ores. There are no definite younging indicators in the mine sequence. In many areas of the mine, the original
host rocks are impossible to identify petrographically due to the abundance of secondary minerals such as quartz, chlorite,
muscovite, cordierite, andalusite, phlogopite, pyrite and talc, combined with variably schistose fabrics. Application of immobile-element
methods to 600 recent whole-rock chemical analyses has, however, allowed the original rock types to be identified and correlated.
Rhyolite X lies immediately north of the A-ore, while andesitic to dacitic to rhyodacitic rocks make up the 100–150 m interval
between the A-ore and B-ore, and massive rhyolite A lies immediately south of the B-ore. The felsic rocks are mostly of calc-alkaline
affinity, excluding rhyolite X, which is transitional. The mine porphyry, which lies north of the A-ore and forms the marginal
phase of the synvolcanic Viterliden Intrusive Complex, is compositionally similar to dacite and rhyodacite. Mass changes calculated
for all rock types indicate that most of the volcanic rocks in the mine area are strongly depleted in Na and Ca, and have
gained variable amounts of Mg and Fe, whereas Si changes range from negative to positive. Gains in Fe and changes in Si are
largest within 5–10 m of the massive sulfide lenses. Cordierite-bearing schists of andesitic to felsic compositions that lie
between massive sulfide lenses A and B are not as altered. The Einarsson Zone commonly shows large gains in Fe and Mg, while
Si shows large gains to large losses. Immobile-element ratios indicate that very different secondary assemblages in the mine,
e.g. andalusite–quartz–muscovite and cordierite–chlorite–talc, can be produced from the same precursor volcanic unit, e.g.,
rhyolite. Conversely, the same secondary mineral assemblage can be produced from different rocks, e.g. weakly altered andesite
and strongly altered rhyolite. The common presence of cordierite + andalusite in the mine area, without anthophyllite, is
unusual in the alteration systems of volcanic-hosted massive sulfide deposits, and is proposed to have formed by the metamorphic
reaction of the synvolcanic alteration minerals kaolinite and chlorite to produce cordierite. Where kaolinite was in excess
of chlorite, andalusite was also formed. We propose that highly acidic alteration fluids locally produced high-Al minerals
such as kaolinite that either overprinted, or occurred in place of, a more typical sericite–chlorite–quartz alteration assemblage
that otherwise formed near the massive sulfide lenses. Application of lithogeochemical methods to the altered, deformed and
metamorphosed Kristineberg rocks has identified specific volcanic contacts with massive sulfide potential, and quantified
the effects of synvolcanic hydrothermal alteration. Such an approach can increase the effectiveness of mineral exploration
in metamorphosed terrains. 相似文献
6.
H. Albert Gilg Maria Boni Giuseppina Balassone Cameron R. Allen David Banks Farid Moore 《Mineralium Deposita》2006,41(1):1-16
The Angouran Zn-(Pb–Ag) deposit, Zanjan Province, NW Iran, is located within the central Sanandaj-Sirjan Zone of the Zagros orogenic belt. The deposit has proven and estimated resources of 4.7 Mt of sulfide ore at 27.7% Zn, 2.4% Pb, and 110 g/t Ag, and 14.6 Mt of oxidized carbonate ores at 22% Zn and 4.6% Pb. It is hosted by a metamorphic core complex that is unconformably overlain by a Neogene volcanic and evaporite-bearing marine to continental sedimentary sequence. The sulfide orebody, precursor to the significant nonsulfide ores, is located at the crest of an open anticline at the contact between Neoproterozoic to Cambrian footwall micaschists and hanging wall marbles. 40Ar–39Ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid Mid-Miocene exhumation of the metamorphic basement (∼20 Ma) and yield an upper age constraint for mineralization. The fine-grained sulfide ore is massive, replacive, often brecciated, clearly postmetamorphic and dominated by Fe-poor sphalerite, with minor galena, pyrite, anhydrite, quartz, muscovite, dolomite, and rare calcite. Sphalerite contains Na–Ca–Cl brine inclusions (23–25 mass% total dissolved solids) with homogenization temperatures of 180–70°C. Fluid inclusion chemistry (Na–K–Li–Ca–Mg–Cl–Br), ore geochemistry, S, and Pb isotope data suggest that the Angouran sulfide ore formed by the interaction of modified, strongly evaporated Miocene seawater and the lithotypes of an exhumed metamorphic core complex. Minor contributions of metals from Miocene igneous rocks cannot be excluded. Mineralization occurred in a collisional intra-arc setting with high heat flow, probably during the transition from an extensional to a compressional regime. The Angouran deposit may represent a new type of low-temperature carbonate-hosted Zn–Pb ore that is distinct from Mississippi Valley type and sedimentary-exhalative deposits.Editorial handling: B. Lehmann 相似文献
7.
Nikolaos Skarpelis 《Resource Geology》2020,70(4):311-335
Massive Zn‐Pb‐Ag sulfide mineralization appears conformable with felsic volcanism, developed in an Upper Jurassic volcanic arc to the Southwest (SW) of the Serbo‐Macedonian continent in Northern Greece. The host volcanic sequence of the mineralization comprises mylonitized rhyolitic to rhyodacitic lavas, pyroclastics, quartz‐feldspar porphyries, and cherty tuffs. A “white mica—quartz—pyrite” mineral assemblage characterizes the volcanic rocks in the footwall and hanging‐wall of massive sulfide ore layers, formed as a result of greenschist‐grade regional metamorphism on “clay‐quartz‐pyrite” hydrothermal alteration haloes. Massive ore lenses are usually underlain by deformed Cu‐pyrite and quartz‐pyrite stockworks. Most of the sulfide ore bodies have proximal‐type features. Ductile deformation and regional metamorphism have transformed many of the stockwork structures. The mineralization is characterized by high Zn, Pb, and Ag contents, while Cu and critical metals are low. Primary depositional textures, for example, layering, clastic pyrite, colloform, and atoll textures were identified. The overall textural features of the mineralization indicate it has undergone mechanical deformation. The most prominent features of the effects of metamorphism, folding and shearing, are modification of the ore body morphology toward flattened and boudinage structures and transformation of the ore textures toward the dominance of planar fabrics. Sulfur isotope analyses of sulfides along with textural observations are consistent with a dual source of sulfide sulfur. Sulfur isotope values for sphalerite, non‐colloform pyrite, galena, and chalcopyrite fall in a limited range from ?1.6 to +4.8‰ (mean δ34S + 2‰), indicating a hydrothermal source derived from the reduction of coeval seawater sulfate in the convective system. Pyrites with colloform and atoll textures are characterized by a 34S depletion, indicating a bacterial reduction of coeval seawater sulfate. The morphology of ore beds, the mineralogy, sulfide textures, and ore chemistry along with the petrology and tectonic setting of the host rocks can be attributed to typical of a bimodal‐felsic metallogenesis. Although similar in many respects to classic Kuroko‐type volcanogenic massive sulfide mineralization, it has some atypical features, like the absence of barite ore, which is possibly a result of significant temporal depletion in sulfate due to bacterial reduction, a conclusion supported by the widespread occurrence of colloidal and atoll textures of pyrite. 相似文献
8.
Abstract: Tizapa volcanogenic massive sulfide (VMS) deposit is hosted in greenschist facies metamorphic rocks; footwall is green schist of felsic to mafic metavolcanic rocks and hanging wall is graphite schist of metasedmentary pelitic rock. Pb-Pb dating of ore samples indicates 103. 4Ma to 156. 3Ma for the age of mineralization (JICA/MMAJ, 1991). 相似文献
9.
C. Trepka-Bloch 《Mineralium Deposita》1985,20(1):23-29
The Näsliden and Rävliden deposits in the Skellefte field consist of stratiform massive sulfide ores associated with submarine volcanic and clastic rocks. The ores are pretectonic. Consequently, the orebodies are considered to have formed syngenetically with deposition of the host rocks. Banding and interlayering with host sediments are common features. Cu : Zn and Zn : Pb ratios of the ores show stratigraphically and laterally defined trends. Cu : Pb : Zn ratios correspond with those found in other deposits of volcanogenic origin. Nonstratiform breccia Cu mineralizations occur directly under the massive stratiform ores in the footwall rocks where hydrothermal alteration is strongest. Ore formation took place intermittently resulting in clusters of ore systems occurring at slightly different stratigraphical levels within each deposit. 相似文献
10.
Ahmed G. Abd Allah 《Arabian Journal of Geosciences》2012,5(2):217-231
Volcanic-hosted (Cu–Zn–Pb) massive sulfide mineralizations are described from four prospects in the Eastern Desert: Helgate,
Maaqal, Derhib, and Abu Gurdi. Helgate and Maaqal prospects are hosted in island arc volcanics in a well-defined stratigraphic
level. Massive sulfides form veins and lenses. Although these veins and lenses are locally deformed, sulfides from Helgate
and Maaqal prospects show primary depositional features. They form layers and colloidal textures. Sphalerite, pyrite, chalcopyrite,
and galena are the major sulfides. Gangue minerals are represented by chlorite, quartz, and calcite. The sulfide mineralizations
at Helgate and Maaqal are Zn-dominated. Derhib and Abu Gurdi prospects occur as disseminations, small massive lenses, and
veins along shear zones in talc tremolite rocks at the contact between metavolcanics and metasedimentary rocks. The host rocks
at Derhib and Abu Gurdi are metamorphosed to lower amphibolite facies as revealed by silicate mineral assemblage and chemistry.
Chalcopyrite, pyrite, sphalerite, and galena are the major sulfide minerals while pyrrhotite is less common. Recrystallization,
retexturing and remobilization of sulfide minerals are reflecting postdepositional metamorphic and structural modifications.
Electrum and Ag–Pb–Bi tellurides are common accessories. Gangue minerals comprise amphiboles of actinolite and actinolitic
hornblende composition, talc, and chlorite. The ores at Derhib and Abu Gurdi are Cu–Zn and Zn-dominated, respectively. The
distinct geological, petrographical, and geochemical differences between sulfide mineralizations at Helgate–Maaqal on one
hand and Derhib and Abu Gurdi on the other hand suggest two genetic types of sulfide mineralizations; Helgate–Maaqal prospects
(type 1) are similar to the Archean analogs from Canada (Noranda type), while Derhib and Abu Gurdi (type 2) show similarity
to ophiolite-associated deposits similar to those described from Cyprus, Oman, and Finland. In genetic type 1, ore minerals
were deposited on the seafloor; the role of postdepositional hydrothermal activity is limited. In genetic type 2, base metals
were part of the ultramafic rocks and were later redistributed and mobilized during deformation to be deposited along shear
zones. The dominance and diversity of tellurides in genetic type 2 highlight the role of metamorphic–hydrothermal fluids. 相似文献
11.
对马元铅锌矿白云石-硫化物型和重晶石-硫化物型矿石中的热液矿物白云石和重晶石的同位素和稀土元素地球化学特征对比研究表明,白云石的δ~(13)CPDB为-2.51×10-3~0.93×10-3,δ18OSMOW为17.55×10~(-3)~23.24×10~(-3),说明成矿流体中碳、氧来源于震旦系碳酸盐岩的溶解;锶同位素组成(0.711 46)表明Sr来源以壳源锶为主,可能与富放射性锶的上覆碎屑岩或下伏基底变质火山岩有关;稀土元素具有明显的正Eu异常(δEu平均为1.415),表明白云石-硫化物型矿化流体具有盆地中循环热卤水特点。重晶石的硫同位素(平均为33×10~(-3))具有富重硫且分布均一的特点,暗示硫可能来源于富集重硫的单一海相硫酸盐;Sr同位素(0.709 18~0.709 71)特征表明其来源以海水锶为主,有少量壳源锶加入;稀土元素具有明显负Ce异常(δCe平均为0.255)和正Eu异常(δEu平均为1.43),表明重晶石--硫化物型矿化有关的流体可能是海水(或大气降水)与盆地循环热流体混合的结果。白云石--硫化物型矿石和重晶石-硫化物型矿石的沉淀可能是盆地中循环热卤水与海水(或大气降水)两种端元组分以不同比例混合的结果。 相似文献
12.
The Ansil Cu–Au volcanogenic massive sulfide deposit is located within an Archean-age cauldron infill sequence that contains
the well-known Noranda base metal mining district. The deposit is unusual in that 17% of the massive pyrrhotite–chalcopyrite
orebody is replaced by semi-massive to massive magnetite. Temporally associated with the magnetite formation are several calc-silicate
mineral assemblages within the massive sulfide lens and the underlying sulfide stockwork vein system. Coarse-grained andradite–hedenbergite
and ferroactinolite–ilvaite alteration facies formed in the immediate footwall to the massive magnetite–sulfide lens, whereas
an epidote–albite–pyrite-rich mineral assemblage overprints the margins of the chlorite-rich stockwork zone. The epidote-rich
facies is in turn overprinted by a retrograde chlorite–magnetite–calcite mineral assemblage, and the andradite–hedenbergite
is overprinted first by ferroactinolite–ilvaite, followed by semi-massive to massive magnetite. The footwall sulfide- and
magnetite-rich alteration facies are truncated by a late phase of the Flavrian synvolcanic tonalite–trondhjemite complex.
Early phases of this intrusive complex are affected to varying degrees by calc-silicate-rich mineral assemblages that are
commonly confined to miarolitic cavities, pipe vesicles and veins. The vein trends parallel the orientation of synvolcanic
faults that controlled volcanism and hydrothermal fluid migration in the overlying cauldron succession. The magnetite-rich
calc-silicate alteration facies are compositionally similar to those of volcanic-hosted Ca–Fe-rich skarn systems typical of
oceanic arc terranes. Tonalite–trondhjemite phases of the Flavrian complex intruded to within 400 m of the base of the earlier-formed
Ansil deposit. The low-Al trondhjemites generated relatively oxidized, acidic, Ca–Fe-rich magmatic–hydrothermal fluids either
through interaction with convecting seawater, or by assimilation of previously altered rocks. These fluids migrated upsection
along synvolcanic faults that controlled the formation of the original volcanogenic massive sulfide deposit. This is one of
the few documented examples of intense metasomatism of a VMS orebody by magmatic–hydrothermal fluids exsolved from a relatively
primitive composite sub-seafloor intrusion.
Received: 15 April 1999 / Accepted: 20 January 2000 相似文献
13.
Gossan Hill is an Archean (∼3.0 Ga) Cu–Zn–magnetite-rich volcanic-hosted massive sulfide (VHMS) deposit in the Yilgarn Craton
of Western Australia. Massive sulfide and magnetite occur within a layered succession of tuffaceous, felsic volcaniclastic
rocks of the Golden Grove Formation. The Gossan Hill deposit consists of two stratigraphically separate ore zones that are
stratabound and interconnected by sulfide veins. Thickly developed massive sulfide and stockwork zones in the north of the
deposit are interpreted to represent a feeder zone. The deposit is broadly zoned from a Cu–Fe-rich lower ore zone, upwards
through Cu–Zn to Zn–Ag–Au–Pb enrichment in the upper ore zone. New sulfur isotope studies at the Gossan Hill deposit indicate
that the variation is wider than previously reported, with sulfide δ34S values varying between −1.6 and 7.8‰ with an average of 2.1 ± 1.4‰ (1σ error). Sulfur isotope values have a broad systematic
stratigraphic increase of approximately 1.2‰ from the base to the top of the deposit. This variation in sulfur isotope values
is significant in view of typical narrow ranges for Archean VHMS deposits. Copper-rich sulfides in the lower ore zone have
a narrower range (δ34S values of −1.6 to 3.4‰, average ∼1.6 ± 0.9‰) than sulfides in the upper ore zone. The lower ore zone is interpreted to have
formed from a relatively uniform reduced sulfur source dominated by leached igneous rock sulfur and minor magmatic sulfur.
Towards the upper Zn-rich ore zone, an overall increase in δ34S values is accompanied by a wider range of δ34S values, with the greatest variation occurring in massive pyrite at the southern margin of the upper ore zone (−1.0 to 7.8‰).
The higher average δ34S values (2.8 ± 2.1‰) and their wider range are explained by mixing of hydrothermal fluids containing leached igneous rock
sulfur with Archean seawater (δ34S values of 2 to 3‰) near the paleoseafloor. The widest range of δ34S values at the southern margin of the deposit occurs away from the feeder zone and is attributed to greater seawater mixing
away from the central upflow zone.
Received: 10 June 1999 / Accepted: 28 December 1999 相似文献
14.
The Niujiaotang Cd-rich zinc deposit,Duyun, Guizhou province,southwest China: ore genesis and mechanisms of cadmium concentration 总被引：3，自引：0，他引：3
The Niujiaotang zinc deposit in southeastern Guizhou, China, is a Mississippi Valley-type Zn deposit within Early Cambrian carbonate rocks. Sphalerite is enriched in cadmium (average 1.4 wt.% Cd), which occurs mostly as isomorphous impurities in the sphalerite lattice. Discrete cadmium minerals (greenockite and otavite) are rare and are found almost exclusively in the oxidation zone of the deposit, probably formed as secondary minerals during weathering–leaching processes. Geochemical data show that the sulfides are enriched in heavy sulfur, with δ34S ranging from +10.0‰ to +32.8‰ (mean +22.5‰). The consistent Pb isotopic compositions in different sulfide minerals are similar to that of Cambrian strata. The ore lead probably came from U- and Th-rich upper crustal rocks, such as the Lower Cambrian Wuxun Formation. The ore fluid is of low-temperature (101°C to 142°C) type, with a Na–Ca–Mg–Cl-dominant composition, and is interpreted as oil-field brine. The data indicate that the metals were mainly derived from the Early Cambrian strata (Qingxudong and Wuxun Formations), whereas sulfur is sourced from sulfate in Cambrian strata or oil-field brines of the Majiang petroleum paleoreservoir. The genetic model for the deposit invokes an Early Cambrian shallow-sea environment on the Yangtze Platform. Zinc and Cd in seawater were concentrated in abundant algae via unknown biological mechanisms, resulting in large amounts of Zn- and Cd-rich algal ooliths. During the Ordovician, concurrent with destruction of the Majiang petroleum paleoreservoir, oil-field brines migrated from the center of the basin to the margin leaching metals from the Cambrian strata. In the Niujiaotang area, preexisting Zn and Cd, particularly in the Qingxudong and Wuxun Formation, were further mobilized by hot brines rising along the Zaolou fault system, forming stratiform and generally conformable Zn–Cd orebodies in reactive carbonate lithologies. 相似文献
15.
The Ashele Deposit: A Recently Discovered Volcanogenic Massive Sulfide Cu-Zn Deposit in Xinjiang, China 总被引：1，自引：0，他引：1
Abstract: The Ashele Cu-Zn deposit is a recently discovered volcanogenic massive sulfide deposit in Xinjiang, Northwestern China. It is the largest Cu-Zn deposit in this type of deposits in China, which were formed in the early period of later Palaeozoic Era. This deposit is hosted within a suit of bimodal submarine volcanic rocks of the Ashele Formation of Lower-Middle Devonian System formed in an environment of paleocontinental margin rift setting. Lensoid orebodies occur between spilitic rocks developed at footwall and quartz-keratophyric tuff at hanging wall. Zonation of metal elements in the Ashele mine is one of typical volcanic-related exhalative Cu-Zn sulfide deposits in the world. Black ores enriched in Pb, Zn and Ag occurs on the top of the No. 1 orebody in the Ashele deposit, yellow ores enriched in Cu in the middle part, and the chalcopyritization stringer below the massive sulfide ores. Zonation of ore-structure in the No. 1 orebody is also apparent and corresponds to the zoning of elements, i. e. lamellar and/or banded sulfide-sulfate ores on the top, massive sulfide ores in the middle, and stockwork veinlets associated with altered breccia pipe on the bottom. Four epochs of mineralization in the Ashele deposit has been recognized. The first period of syngenetic-exhalative deposition of sulfides is the main epoch of mineralization, and the ores deposited subsequently subjected to thermo-metamorphism at the second epoch, superimposed by hydrothermal mineralization at the third epoch, and weathered or oxidized at the fourth epoch.
More than 100 categories of minerals have been recognized in the Ashele mine, but only pyrite, chalcopyrite, sphalerite, tetrahedrite, galena, barite, quartz, chlorite, sericite, and calcite are dominant, making up various types of ores, and alteration pipes or horizons. Studies of ore petrology suggest that the massive ores were volcanogenic and deposited by exhalative process. 相似文献
More than 100 categories of minerals have been recognized in the Ashele mine, but only pyrite, chalcopyrite, sphalerite, tetrahedrite, galena, barite, quartz, chlorite, sericite, and calcite are dominant, making up various types of ores, and alteration pipes or horizons. Studies of ore petrology suggest that the massive ores were volcanogenic and deposited by exhalative process. 相似文献
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湖南沃溪金-锑-钨矿床成因的稀土元素地球化学证据 总被引：11，自引：0，他引：11
沃溪金-锑-钨矿床的稀土元素地球化学组成良好地反映了成矿作用的条件和过程,并为示踪矿床成因提供了有用的信息.以流体包裹体为代表的成矿溶液,以较高的稀土总量、显著的轻稀土富集和缺乏明显的铕异常为特征,代表了一种通过在碎屑沉积物柱中循环而萃取矿质的演化的海水热液.矿石相对于成矿流体(母液)富集重稀土而轻微亏损铕,反映了矿石沉淀过程中来自于海水的稀土元素掺合.同一矿层内由下往上,重稀土相对富集的程度逐渐增大而稀土总量则逐渐降低,表明随着热液化学沉淀作用的进行,海水掺合的影响逐渐增强.矿石的稀土元素组成,无论在分布模式还是在轻重稀土之间的分馏程度上,均与其他许多 Sedex型多金属矿床十分相似,暗示了这些矿床具有相似的成因机制.稀土元素地球化学特征支持矿床同生沉积成因的观点. 相似文献
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本文采用四极等离子质谱仪(ICP-MS)方法测定了可可塔勒铅锌矿矿物流体包裹体的稀土元素含量。研究表明,成矿流体稀土元素配分模式均为轻稀土富集,Eu具有明显正异常。矿石硫化物流体包裹体稀土特征具有3种稀土配分模式,即平滑右倾型、平坦型、倒“V”字型,矿体下盘围岩的稀土总量明显高于上盘围岩的稀土总量,具有明显的Eu的负异常,成矿流体具有多来源、成矿具有多阶段叠加特点,具有双淋滤模式特征。 相似文献
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The Navachab gold deposit in the Damara belt of central Namibia is hosted by a near-vertical sequence of amphibolite facies
shelf-type metasediments, including marble, calc-silicate rock, and biotite schist. Petrologic and geochemical data were collected
in the ore, alteration halos, and the wall rock to evaluate transport of elements and interaction between the wall rock and
the mineralizing fluid. The semi-massive sulfide lenses and quartz–sulfide veins are characterized by a complex polymetallic
ore assemblage, comprising pyrrhotite, chalcopyrite, sphalerite, and arsenopyrite, native bismuth, gold, bismuthinite, and
bismuth tellurides. Mass balance calculations indicate the addition of up to several orders of magnitude of Au, Bi, As, Ag,
and Cu. The mineralized zones also record up to eightfold higher Mn and Fe concentrations. The semi-massive sulfide lenses
are situated in the banded calc-silicate rock. Petrologic and textural data indicate that they represent hydraulic breccias
that contain up to 50 vol.% ore minerals, and that are dominated by a high-temperature (T) alteration assemblage of garnet–clinopyroxene–K-feldspar–quartz.
The quartz–sulfide veins crosscut all lithological units. Their thickness and mineralogy is strongly controlled by the composition
and rheological behavior of the wall rocks. In the biotite schist and calc-silicate rock, they are up to several decimeters
thick and quartz-rich, whereas in the marble, the same veins are only a few millimeters thick and dominated by sulfides. The
associated alteration halos comprise (1) an actinolite–quartz alteration in the biotite schist, (2) a garnet–clinopyroxene–K-feldspar–quartz
alteration in the marble and calc-silicate rock, and (3) a garnet–biotite alteration that is recorded in all rock types except
the marble. The hydrothermal overprint was associated with large-scale carbonate dissolution and a dramatic increase in CO2 in the ore fluid. Decarbonation of wall rocks, as well as a low REE content of the ore fluid resulted in the mobilization
of the REE, and the decoupling of the LREE from the HREE. The alteration halos not only parallel the mineralized zones, but
may also follow up single layers away from the mineralization. Alteration is far more pronounced facing upward, indicating
that the rocks were steep when veining occurred. The petrologic and geochemical data indicate that the actinolite–quartz–
and garnet–clinopyroxene–K-feldspar–quartz alterations formed in equilibrium with a fluid (super-) saturated in Si, and were
mainly controlled by the composition of the wall rocks. In contrast, the garnet–biotite alteration formed by interaction with
a fluid undersaturated in Si, and was mainly controlled by the fluid composition. This points to major differences in fluid–rock
ratios and changes in fluid composition during alteration. The alteration systematics and geometry of the hydrothermal vein
system are consistent with cyclic fluctuations in fluid pressure during fault valve action.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献