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1.
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
2.
The Hongtoushan volcanogenic massive sulfide (VMS) deposit is the largest Archean Cu–Zn deposit in China, located in the Qingyuan greenstone belt on the northern margin of the North China Craton. The Cu–Zn mineralization was stratigraphically controlled by the interbeds (~ 100 m in thickness) of mafic–felsic volcanic sets and overlain by banded iron layers. However, the relationship between VMS deposits and associated volcanics has not been examined. This study ultimately clarifies the times and sources of the volcanics and mineralization. Based on in situ zircon U–Pb and O isotope on VMS-hosting mafic, felsic volcanic rocks, banded and massive sulfide ores and postmineralization pegmatite vein, we considered that there were two main formation stages for the Qingyuan Cu–Zn deposits; one was exhalative-hydrothermal sedimentation and another was further Cu–Zn enriched by later hydrothermal processes. The timing of the first stage occurred at 2571 ± 6 Ma based on the magmatic zircons in the VMS-hosting mafic volcanic rocks, from which the inherited zircons also indicate the existence of 2.65–3.12 Ga ancient supercrustal rocks in the Qingyuan district. A modern mantle-like δ18Ozircon value of 5.5 ± 0.1‰ (2SD) for this volcanism was well preserved in the inherited core domains of ore samples. It suggests that the mafic volcanics was most likely sourced from partial melting of juvenile crust, e.g., TTG granites. A large-scale metamorphic or hydrothermal event is documented by the recrystallized zircons in sulfide ores. The timing is tightly constrained by the hydrothermal zircon U–Pb ages. They are 2508 ± 4 Ma for the banded ore, 2507 ± 4 Ma for the massive ore and 2508 ± 2 Ma for the postmineralization pegmatite vein. These indistinguishable ages indicate that the 2507 Ma hydrothermal systems played a significant role in the upgrading of the VMS Cu–Zn orebodies. The weighted δ18O values of hydrothermal zircons show a successively increasing trend from 6.0 ± 0.1‰ (2σ) for the banded ore, 6.6 ± 0.2‰ (2σ) for the massive ore to 7.3 ± 0.2‰ (2σ) for the later pegmatite vein. This variation might be induced by gradual inputting of the δ18O-rich oceanic crust and/or oceanic sediment during the hydrothermal cycling system. Considering its modern mantle-like oxygen isotope composition of 2571 Ma volcanism, a submarine volcanic hydrothermal system involving mantle plumes is a preferred setting for the Neoarchean VMS Cu–Zn deposits in the Qingyuan greenstone belt. 相似文献
3.
The 3.09 to 2.97 Ga Murchison Greenstone Belt is an important metallotect in the northern Kaapvaal Craton (South Africa), hosting several precious and base metal deposits. Central to the metallotect is the Antimony Line, striking ENE for over 35?km, which hosts a series of structurally controlled Sb–Au deposits. To the north of the Antimony Line, hosted within felsic volcanic rocks, is the Copper–Zinc Line where a series of small, ca. 2.97 Ga Cu–Zn volcanogenic massive sulfide (VMS)-type deposits occur. New data are provided for the Malati Pump gold mine, located at the eastern end of the Antimony Line. Crystallizations of a granodiorite in the Malati Pump Mine and of the Baderoukwe granodiorite are dated at 2,964?±?7 and 2,970?±?7?Ma, respectively (zircon U–Pb), while pyrite associated with gold mineralization yielded a Pb–Pb age of 2,967?±?48?Ma. Therefore, granodiorite emplacement, sulfide mineral deposition and gold mineralization all happened at ca. 2.97?Ga. It is, thus, suggested that the major styles of orogenic Au–Sb and the Cu–Zn VMS mineralization in the Murchison Greenstone Belt are contemporaneous and that the formation of meso- to epithermal Au–Sb mineralization at fairly shallow levels was accompanied by submarine extrusion of felsic volcanic rocks to form associated Cu–Zn VMS mineralization. 相似文献
4.
The Paleoproterozoic Ruttan Cu–Zn volcanogenic massive-sulfide (VMS) deposit is a large, relatively low grade, bimodal-siliciclastic
type deposit in the Rusty Lake volcanic belt of northern Manitoba. The deposit contained over 82.8 million tonnes of massive
sulfide, of which 55.7 million tonnes were mined from 1973 to 2002. The deposit consists of a series of moderately to steeply
dipping, south-facing lenses that extend along strike at the surface for 1.1 km and to a depth of 1.0 km. These lenses occur
within a steeply dipping, bimodal volcanic, volcaniclastic and siliciclastic sequence. In the immediate mine area, transitional
calc-alkalic to high-silica (tholeiitic), felsic, and intermediate volcanic/volcaniclastic rocks of the Mine Sequence are
host to, and intercalated with, the massive-sulfide lenses. Transitional tholeiitic to calc-alkalic basalt and andesite are
present in the footwall sequence, approximately 500 m down-section from the ore horizon. The overlying rocks are predominantly
fine-grained volcaniclastics and siliciclastics, but include polyfragmental agglomerate that contains mafic bombs and scoriaceous
felsic fragments. Syn-depositional felsic and mafic dikes, sills, and apophyses are ubiquitous throughout the Mine Sequence,
including the ore lenses, indicating continued, near-vent magmatism, and volcanism during ore formation. Fabrics in altered
hostrocks have consistent, down-plunge stretching lineations to the SSE that suggest the deposit has been elongated by a factor
of ~1.2–1.5; otherwise, the deposit is remarkably undeformed. Syn- and post-depositional faults in the mine area have relatively
minor displacements up to tens of meters. Proximal (within 200 m) footwall rocks exhibit moderate to strong chloritization,
characterized by the upper greenschist to lower amphibolite facies assemblages that include cordierite–almandine–andalusite–sillimanite–biotite ± staurolite ± anthophyllite ± talc,
and local silicification. The proximal hanging wall rocks are characterized by sericite ± gahnite alteration, which is restricted
to within approximately 75 m of the uppermost lenses. Additional gangue minerals are anhydrite and carbonate minerals (siderite,
dolomite, ankerite, and calcite), as well as chlorite, sericite, biotite, talc, and quartz. Carbonate (excluding siderite),
potassium feldspar, silicification and epidotization are common distal alteration zones in the footwall to the Mine Sequence
several kilometers to the northeast. There are three principal groups of massive sulfide lenses; the East lenses, the West
lenses, and the Western Anomaly lenses to the far west. In general, Cu is relatively enriched at the stratigraphic base and
in the center of the deposit, whereas Zn is enriched upsection and at the outer margins. Some of the Zn-rich ore exhibits
primary mineralogical layering. Parts of the West and Western Anomaly lenses show two layers with Cu-rich bases and Zn-rich
tops. The massive sulfide is typically 10–40-m thick; one area along the margin of the main lenses is over 130-m thick and
may represent deposition adjacent to a syn-depositional fault. The main sulfide phases are pyrite, pyrrhotite, chalcopyrite,
sphalerite, and galena, with tetrahedrite as the most abundant trace phase. Gahnite is ubiquitous in the chlorite-rich assemblages
adjacent to the ore lenses. The average base, precious and trace metal contents estimated from Cu and Zn concentrates, and
from millhead grades and recoveries. Metals easily transported as chloride and bisulfide complexes in hydrothermal fluids
including: Pb, Ag, In, Cu, Cd, Au, and Zn are enriched by 1.5–2.5 orders of magnitude in comparison to the bulk continental
crust. Other elements such as Sn, Mo, and As are at near-crustal concentrations, whereas Mn, Ga, and Co are significantly
depleted in comparison to the crust. Calculated metal concentrations in the average hydrothermal fluid based on the average
metal contents are comparable to, or higher than those measured at sediment covered ridge hydrothermal systems, which precipitate
much of their metal budget in the subsurface. Average rare earth element contents for the sulfide are light rare earth element
enriched (LaN/YbN=22) and range from 0.45 to 0.02x chondritic values, with a moderate negative Eu anomaly (Eu*=0.51). Metal and trace element
contents in the Ruttan exhalite horizon, and in proximal (within 1–2 km) exhalites along strike from the 0.6 million tonne
Dar-2 Cu–Zn deposit 12 km south of Ruttan, have positive Eu anomalies, whereas negative Eu anomalies are present at distance.
The positive Eu anomalies reflect high temperature paleoseafloor hydrothermal venting and precipitation of Eu2+-enriched clays and possibly carbonates, and indicate proximity to base-metal deposits. Silver and lead are also enriched
in the exhalites near the deposits, whereas Mn is enriched at ~1–3 km along strike, but not consistently.
Editorial handling: B. Gemmel
An erratum to this article is available at . 相似文献
5.
Kalin Kouzmanov Robert Moritz Albrecht von Quadt Massimo Chiaradia Irena Peytcheva Denis Fontignie Claire Ramboz Kamen Bogdanov 《Mineralium Deposita》2009,44(6):611-646
Vlaykov Vruh–Elshitsa represents the best example of paired porphyry Cu and epithermal Cu–Au deposits within the Late Cretaceous
Apuseni–Banat–Timok–Srednogorie magmatic and metallogenic belt of Eastern Europe. The two deposits are part of the NW trending
Panagyurishte magmato-tectonic corridor of central Bulgaria. The deposits were formed along the SW flank of the Elshitsa volcano-intrusive
complex and are spatially associated with N110-120-trending hypabyssal and subvolcanic bodies of granodioritic composition.
At Elshitsa, more than ten lenticular to columnar massive ore bodies are discordant with respect to the host rock and are
structurally controlled. A particular feature of the mineralization is the overprinting of an early stage high-sulfidation
mineral assemblage (pyrite ± enargite ± covellite ± goldfieldite) by an intermediate-sulfidation paragenesis with a characteristic
Cu–Bi–Te–Pb–Zn signature forming the main economic parts of the ore bodies. The two stages of mineralization produced two
compositionally different types of ores—massive pyrite and copper–pyrite bodies. Vlaykov Vruh shares features with typical
porphyry Cu systems. Their common geological and structural setting, ore-forming processes, and paragenesis, as well as the
observed alteration and geochemical lateral and vertical zonation, allow us to interpret the Elshitsa and Vlaykov Vruh deposits
as the deep part of a high-sulfidation epithermal system and its spatially and genetically related porphyry Cu counterpart,
respectively. The magmatic–hydrothermal system at Vlaykov Vruh–Elshitsa produced much smaller deposits than similar complexes
in the northern part of the Panagyurishte district (Chelopech, Elatsite, Assarel). Magma chemistry and isotopic signature
are some of the main differences between the northern and southern parts of the district. Major and trace element geochemistry
of the Elshitsa magmatic complex are indicative for the medium- to high-K calc-alkaline character of the magmas. 87Sr/86Sr(i) ratios of igneous rocks in the range of 0.70464 to 0.70612 and 143Nd/144Nd(i) ratios in the range of 0.51241 to 0.51255 indicate mixed crustal–mantle components of the magmas dominated by mantellic signatures.
The epsilon Hf composition of magmatic zircons (+6.2 to +9.6) also suggests mixed mantellic–crustal sources of the magmas.
However, Pb isotopic signatures of whole rocks (206Pb/204Pb = 18.13–18.64, 207Pb/204Pb = 15.58–15.64, and 208Pb/204Pb = 37.69–38.56) along with common inheritance component detected in magmatic zircons also imply assimilation processes of
pre-Variscan and Variscan basement at various scales. U–Pb zircon and rutile dating allowed determination of the timing of
porphyry ore formation at Vlaykov Vruh (85.6 ± 0.9 Ma), which immediately followed the crystallization of the subvolcanic
dacitic bodies at Elshitsa (86.11 ± 0.23 Ma) and the Elshitsa granite (86.62 ± 0.02 Ma). Strontium isotope analyses of hydrothermal
sulfates and carbonates (87Sr/86Sr = 0.70581–0.70729) suggest large-scale interaction between mineralizing fluids and basement lithologies at Elshitsa–Vlaykov
Vruh. Lead isotope compositions of hydrothermal sulfides (206Pb/204Pb = 18.432–18.534, 207Pb/204Pb = 15.608–15.647, and 208Pb/204Pb = 37.497–38.630) allow attribution of ore-formation in the porphyry and epithermal deposits in the Southern Panagyurishte
district to a single metallogenic event with a common source of metals. 相似文献
6.
The Meso-Cenozoic geodynamic evolution of the eastern Pontides orogenic belt provides a key to evaluate the volcanogenic massive sulfide (VMS) deposits associated with convergent margin tectonics in a Cordilleran-type orogenic belt. Here we present new geological, geochemical and zircon U–Pb geochronological data, and attempt to characterize the metallogeny through a comprehensive overview of the important VMS mineralizations in the belt. The VMS deposits in the northern part of the eastern Pontides orogenic belt occur in two different stratigraphic horizons consisting mainly of felsic volcanic rocks within the late Cretaceous sequence. SHRIMP zircon U–Pb analyses from ore-bearing dacites yield weighted mean 206Pb/238U ages ranging between 91.1 ± 1.3 and 82.6 ± 1 Ma. The felsic rocks of first and second horizons reveal geochemical characteristics of subduction-related calc-alkaline and shoshonitic magmas, respectively, in continental arcs and represent the immature and mature stages of a late Cretaceous magmatic arc. The nature of the late Cretaceous magmatism in the northern part of the eastern Pontides orogenic belt and the various lithological associations including volcaniclastics, mudstones and sedimentary facies indicate a rift-related environment where dacitic volcanism was predominant. The eastern Pontides VMS deposits are located within the caldera-like depressions and are closely associated with dome-like structures of felsic magmas, with their distribution controlled by fracture systems. Based on a detailed analyses of the geological, geophysical and geodynamic information, we propose that the VMS deposits were generated either in intra arc or near arc region of the eastern Pontides orogenic belt during the southward subduction of the Tethys oceanic lithosphere. 相似文献
7.
现代海底热液成矿作用研究现状及发展方向 总被引：15，自引：0，他引：15
现代海底热水成矿作用研究的重大进展表现在两个方面：（１）大批活动的和窒息的热液活动区和硫化物矿床在洋脊、岛弧、弧后盆地及板内火山活动中心等海底环境相继发现。在沉积物饥饿洋脊，矿床规模较小，Ｃｕ－Ｚｎ为主，沉积物覆盖洋脊，矿床规模巨大，Ｐｂ－Ｚｎ为主。弧后扩张或弧间裂陷盆地，形成Ｐｂ－Ｚｎ→Ｚｎ－Ｐｂ－Ｃｕ→Ｃｕ－Ｚｎ矿床谱系。岛弧环境硫化物矿床不具规模，板内火山活动中心以氧化物－硫化物矿化为特色。（２）现代海底热水成矿作用观察和研究为古代ＶＭＳ矿床成因研究提供了重要信息，对现有成矿理论产生重要影响。现代成矿观念强调：①海底成矿作用虽可产生于不同环境，但均与张裂断陷事件密切相关。矿床规模和分布特点受张裂速率制约；②成矿物质主体来源于热水循环的火山－沉积岩和下伏基底物质；③硫化物堆积发生于丘堤－烟囱联合构成的机构和结壳下部，通过开放空间的硫化物充填和先成矿石淋滤迁移来实现。④热液流体呈双扩散对流循环。现代海底热水成矿作用的未来研究方向可概括为强度方向和广度方向。广度研究将加大力度去发现新的矿床，强度研究将采用地球物理方法并配以必要的钻探，深入揭示矿床的三维结构和热液体系及成矿机制。 相似文献
8.
Constraints on gold and copper ore grades in porphyry-style Cu–Au ± Mo deposits are re-examined, with particular emphasis
on published fluid pressure and formation depth as indicated by fluid inclusion data and geological reconstruction. Defining
an arbitrary subdivision at a molar Cu/Au ratio of 4.0 × 104, copper–gold deposits have a shallower average depth of formation (2.1 km) compared with the average depth of copper–molybdenum
deposits (3.7 km), based on assumed lithostatic fluid pressure from microthermometry. The correlation of Cu/Au ratio with
depth is primarily influenced by the variations of total Au grade. Despite local mineralogical controls within some ore deposits,
the overall Cu/Au ratio of the deposits does not show a significant correlation with the predominant type of Cu–Fe sulfide,
i.e., chalcopyrite or bornite. Primary magma source probably contributes to metal endowment on the province scale and in some
individual deposits, but does not explain the broad correlation of metal ratios with the pressure of ore formation. By comparison
with published experimental and fluid analytical data, the observed correlation of the Cu/Au ratio with fluid pressure can
be explained by dominant transport of Cu and Au in a buoyant S-rich vapor, coexisting with minor brine in two-phase magmatic
hydrothermal systems. At relatively shallow depth (approximately <3 km), the solubility of both metals decreases rapidly with
decreasing density of the ascending vapor plume, forcing both Cu and Au to be coprecipitated. In contrast, magmatic vapor
cooling at deeper levels (approximately >3 km) and greater confining pressure is likely to precipitate copper ± molybdenum
only, while sulfur-complexed gold remains dissolved in the relatively dense vapor. Upon cooling, this vapor may ultimately
contract to a low-salinity epithermal liquid, which can contribute to the formation of epithermal gold deposits several kilometers
above the Au-poor porphyry Cu–(Mo) deposit. These findings and interpretations imply that petrographic inspection of fluid
inclusion density may be used as an exploration indicator. Low-pressure brine + vapor systems are favorable for coprecipitation
of both metals, leading to Au-rich porphyry–copper–gold deposits. Epithermal gold deposits may be associated with such shallow
systems, but are likely to derive their ore-forming components from a deeper source, which may include a deeply hidden porphyry–copper
± molybdenum deposit. Exposed high-pressure brine + vapor systems, or stockwork veins containing a single type of intermediate-density
inclusions, are more likely to be prospective for porphyry–copper ± molybdenum deposits. 相似文献
9.
Abstract. The Takara volcanogenic massive sulfide (VMS) deposit occurs in Miocene formation of the Misaka Mountain, the South Fossa Magna region, central Japan. The tectonic setting of the Misaka Mountain is reconstructed to be a part of the paleo Izu-Ogasawara arc which collided with the Honshu arc and to form accreted body in the present position. The Takara deposit, therefore, is considered to have formed in the paleo Izu-Ogasawara arc.
The ores from the Takara deposit are classified into pyrite-type ore, chalcopyrite-type ore, and sphalerite-type ore on the basis of chemical composition and their mineral assemblages. Some pyrite-type ores are characterized by their high Au content. The Au content is hardly recognized in the chalcopyrite-type and sphalerite-type ores.
The ores from the Takara deposit have intermediate bulk chemical composition between those from the Besshi-type deposits and the Kuroko-type deposits that are two representative VMS deposits. However, the bulk chemical composition is closer to that from the Kuroko-type deposits. And moreover, chemical composition of tetrahedrite-tennantite series minerals (tetrahedrite) is similar to that from the Kuroko-type deposits. The bulk chemical composition (Cu, Zn, Co, Pb, and As contents) of ores is affected by the chemical composition of volcanic rocks associated with VMS deposits. 相似文献
The ores from the Takara deposit are classified into pyrite-type ore, chalcopyrite-type ore, and sphalerite-type ore on the basis of chemical composition and their mineral assemblages. Some pyrite-type ores are characterized by their high Au content. The Au content is hardly recognized in the chalcopyrite-type and sphalerite-type ores.
The ores from the Takara deposit have intermediate bulk chemical composition between those from the Besshi-type deposits and the Kuroko-type deposits that are two representative VMS deposits. However, the bulk chemical composition is closer to that from the Kuroko-type deposits. And moreover, chemical composition of tetrahedrite-tennantite series minerals (tetrahedrite) is similar to that from the Kuroko-type deposits. The bulk chemical composition (Cu, Zn, Co, Pb, and As contents) of ores is affected by the chemical composition of volcanic rocks associated with VMS deposits. 相似文献
10.
鲁春VMS 锌铅铜多金属矿床产于金沙江构造带内鲁春-红坡牛场伸展裂谷盆地中,是三江地区典型的火山成因块状硫化物矿床,其含矿层位为双峰式火山岩系中的流纹质火山--沉积岩系。通过研究该矿床的主成矿元素、双峰式火山岩和矿石的稀土元素特征,对其成矿金属来源、赋矿火山岩及构造环境进行研究表明,鲁春多金属矿床属Zn --Pb --Cu 型火山成因块状硫化物矿床,形成于碰撞造山后在薄陆壳( 陆缘弧) 基底上伸展而成的裂谷盆地环境; 矿石的主成矿元素含量特征w ( Zn) /w ( Pb + Zn) 均值为0. 64,与日本黑矿和四川呷村矿床较为接近; ΣREE 为( 15. 99 ～ 144. 43) × 10 － 6,平均73. 99 × 10 － 6,LREE/ HREE 为3. 59 ～ 11. 40,平均6. 30,呈典型的LREE 富集型; δEu 为0. 13 ～ 0. 46,平均0. 28,Eu 负异常明显,与矿区流纹岩极为相似。矿体与流纹岩空间上的密切关系以及地球化学特征的一致性表明,成矿金属元素源自下伏的长英质岩系。 相似文献
11.
We have analyzed the chemical composition and boron isotope composition of tourmaline from tourmalinites, granite and a quartz-tourmaline
vein from the Deri ore zone and from a pegmatitic band in the Rampura-Agucha ore body. These two Proterozoic massive sulfide
deposits occur in the Aravalli-Delhi orogenic belt, Rajasthan, northwest India. Tourmaline from stratiform tourmalinites closely
associated with the massive sulfides in the Deri deposit have preserved their original chemical compositions despite regional
and thermal metamorphism in the area. These tourmalines have low Fe/(Fe + Mg) ratios (0.19–0.30; mean 0.26) that suggest formation
close to the sediment-sea water interface. The δ11B values (−15.5 and −16.4‰) are compatible with boron derived from leaching of argillaceous sediments and/or felsic volcanics
underlying the original massive sulfide deposit during its formation. Boron isotope compositions measured in tourmaline from
a post-ore granite and quartz-tourmaline vein in the Deri deposit indicate that boron in these tourmalines was derived from
the tourmalinites produced during ore formation. The boron isotope systematics of a coarse brown tourmaline crystal from a
pegmatitic band on the hanging wall contact of the Rampura-Agucha deposit indicate that 45 ± 25% of the boron within the original
tourmaline was lost during upper amphibolite facies regional metamorphism.
Received: 3 April 1996 / Accepted: 11 April 1996 相似文献
12.
Tobias E. Bauer Pietari Skyttä Tobias Hermansson Rodney L. Allen Pär Weihed 《Mineralium Deposita》2014,49(5):555-573
The Skellefte district in northern Sweden is host to abundant volcanogenic massive sulphide (VMS) deposits comprising pyritic, massive, semi-massive and disseminated Zn–Cu–Au ± Pb ores surrounded by disseminated pyrite and with or without stockwork mineralisation. The VMS deposits are associated with Palaeoproterozoic upper crustal extension (D1) that resulted in the development of normal faults and related transfer faults. The VMS ores formed as sub-seafloor replacement in both felsic volcaniclastic and sedimentary rocks and partly as exhalative deposits within the uppermost part of the volcanic stratigraphy. Subsequently, the district was subjected to deformation (D2) during crustal shortening. Comparing the distribution of VMS deposits with the regional fault pattern reveals a close spatial relationship of VMS deposits to the faults that formed during crustal extension (D1) utilising the syn-extensional faults as fluid conduits. Analysing the shape and orientation of VMS ore bodies shows how their deformation pattern mimics those of the hosting structures and results from the overprinting D2 deformation. Furthermore, regional structural transitions are imitated in the deformation patterns of the ore bodies. Plotting the aspect ratios of VMS ore bodies and the comparison with undeformed equivalents in the Hokuroko district, Japan allow an estimation of apparent strain and show correlation with the D2 deformation intensity of the certain structural domains. A comparison of the size of VMS deposits with their location shows that the smallest deposits are not related to known high-strain zones and the largest deposits are associated with regional-scale high-strain zones. The comparison of distribution and size with the pattern of high-strain zones provides an important tool for regional-scale mineral exploration in the Skellefte district, whereas the analysis of ore body shape and orientation can aid near-mine exploration activities. 相似文献
13.
Patrick Mercier-Langevin Vicky McNicoll Rodney L. Allen James H. S. Blight Benoît Dubé 《Mineralium Deposita》2013,48(4):485-504
The Boliden deposit (8.3 Mt at 15.9 g/t Au) is interpreted to have been formed between ca. 1894 and 1891 Ma, based on two new U–Pb ID-TIMS ages: a maximum age of 1893.9?+?2.0/?1.9 Ma obtained from an altered quartz and feldspar porphyritic rhyolite in the deposit footwall in the volcanic Skellefte group and a minimum age of 1890.8?±?1 Ma obtained from a felsic mass-flow deposit in the lowermost part of the volcano-sedimentary Vargfors group, which forms the stratigraphic hanging wall to the deposit. These ages are in agreement with the alteration and mineralization being formed at or near the sea floor in the volcanogenic massive sulfide environment. These two ages and the geologic relationships imply that: (1) volcanism and hydrothermal activity in the Skellefte group were initiated earlier than 1.89 Ga which was previously considered to be the onset of volcanism in the Skellefte group; (2) the volcano-sedimentary succession of the Vargfors group is perhaps as old as 1892 Ma in the eastern part of the Skellefte district; and (3) an early (synvolcanic) deformation event in the Skellefte group is evidenced by the unconformity between the ≤1893.9?+?2.0/?1.9 Ma Skellefte group upper volcanic rocks and the ≤1890.8?±?1 Ma Vargfors sedimentary and volcanic rocks in the Boliden domain. Differential block tilting, uplift, and subsidence controlled by synvolcanic faults in an extensional environment is likely, perhaps explaining some hybrid VMS-epithermal characteristics shown by the VMS deposits of the district. 相似文献
14.
The Géant Dormant gold mine is a sulfide-rich quartz vein gold deposit hosted by a volcano-sedimentary sequence and an associated
felsic endogenous dome and dikes. The auriferous quartz-sulfide veins were preceded by two synvolcanic gold-bearing mineralizing
events: early sulfidic seafloor-related and later disseminated pyrite in the felsic dome. This deposit differs from classical
Archean auriferous quartz vein deposits by the low carbonate and high sulfide contents of the veins and by their formation
prior to ductile penetrative deformation. The δ18O values of quartz associated with seafloor-related auriferous sulfides average 11.9 ± 0.6‰ (n = 3). The seafloor hydrothermal fluids had a δ18O value of 3.2‰ calculated at 250 °C. The oxygen isotope composition of quartz and chlorite from veins average 12.5 ± 0.3‰
(n = 20) and 5.9 ± 1.1‰ (n = 4) respectively. Assuming oxygen isotope equilibrium between quartz and chlorite, the veins formed at a temperature of
∼275 °C, which is consistent with the calculated temperature of 269 ± 10 °C from chlorite chemistry. The gold-bearing fluids
had a δ18O value of 4.7‰ calculated at 275 °C. The δ34S values of sulfides from the three gold events range from 0.6 to 2.8‰ (n = 32) and are close to magmatic values. Sulfur isotope geothermometry constrains the sulfide precipitation in the gold-bearing
veins at a temperature of ∼350 °C. The similarity of the isotope data, the calculated δ18O of the mineralizing fluids and the likely seawater fluid source suggest that the three mineralizing events are genetically
related to a volcanogenic hydrothermal system. The high value of the auriferous fluids (δ18O = 4.7‰) is attributed to a significant magmatic fluid contribution to the evolved seawater-dominated convective hydrothermal
system. The two-stage filling of veins at increasing temperature from quartz-chlorite (275 °C) to sulfides (350 °C) may reflect
the progressive maturation of volcanogenic hydrothermal systems. These results, together with field and geochemical data,
suggest that formation of gold-rich volcanogenic systems require specific conditions that comprise a magmatic fluid contribution
and gold from arc-related felsic rocks, coeval with the mineralizing events. This study shows that some auriferous quartz-vein
orebodies in Archean terranes are formed in volcanogenic rather than mesothermal systems.
Received: 12 December 1998 / Accepted: 5 July 1999 相似文献
15.
16.
Ana M. Dreher Roberto P. Xavier Bruce E. Taylor Sérgio L. Martini 《Mineralium Deposita》2008,43(2):161-184
The Igarapé Bahia Cu–Au deposit in the Carajás Province, Brazil, is hosted by steeply dipping metavolcano-sedimentary rocks
of the Igarapé Bahia Group. This group consists of a low greenschist grade unit of the Archean (∼2,750 Ma) Itacaiúnas Supergroup,
in which other important Cu–Au and iron ore deposits of the Carajás region are also hosted. The orebody at Igarapé Bahia is
a fragmental rock unit situated between chloritized basalt, with associated hyaloclastite, banded iron formation (BIF), and
chert in the footwall and mainly coarse- to fine-grained turbidites in the hanging wall. The fragmental rock unit is a nearly
concordant, 2 km long and 30–250 m thick orebody made up of heterolithic, usually matrix-supported rocks composed mainly of
coarse basalt, BIF, and chert clasts derived from the footwall unit. Mineralization is confined to the fine-grained matrix
and comprises disseminated to massive chalcopyrite accompanied by magnetite, gold, U- and light rare earth element (LREE)-minerals,
and minor other sulfides like bornite, molybdenite, cobaltite, digenite, and pyrite. Gangue minerals include siderite, chlorite,
amphibole, tourmaline, quartz, stilpnomelane, epidote, and apatite. A less important mineralization style at Igarapé Bahia
is represented by late quartz–chalcopyrite–calcite veins that crosscut all rocks in the deposit area. Fluid inclusions trapped
in a quartz cavity in the ore unit indicate that saline aqueous fluids (5 to 45 wt% NaCl + CaCl2 equiv), together with carbonic (CO2 ± CH4) and low-salinity aqueous carbonic (6 wt% NaCl equiv) fluids, were involved in the mineralization process. Carbonates from
the fragmental layer have δ13C values from −6.7 to −13.4 per mil that indicate their origin from organic and possibly also from magmatic carbon. The δ34S values for chalcopyrite range from −1.1 to 5.6 per mil with an outlier at −10.8 per mil, implying that most sulfur is magmatic
or leached from magmatic rocks, whereas a limited contribution of reduced and oxydized sulfur is also evident. Oxygen isotopic
ratios in magnetite, quartz, and siderite yield calculated temperatures of ∼400°C and δ18O-enriched compositions (5 to 16.5 per mil) for the ore-forming fluids that suggest a magmatic input and/or an interaction
with 18O-rich, probably sedimentary rocks. The late veins of the Igarapé Bahia deposit area were formed from saline aqueous fluids
(2 to 60 wt% NaCl + CaCl2 equiv) with δ18Ofluid compositions around 0 per mil that indicate contribution from meteoric fluids. With respect to geological features, Igarapé
Bahia bears similarity with syngenetic, volcanic-hosted massive sulfide (VHMS)-type deposits, as indicated by the volcano-sedimentary
geological context, stratabound character, and association with submarine volcanic flows, hyaloclastite, and exhalative beds
such as BIF and chert. On the other hand, the highly saline ore fluids and the mineral assemblage, dominated by magnetite
and chalcopyrite, with associated gold, U- and LREE-minerals and scarce pyrite, indicate that Igarapé Bahia belongs to the
Fe oxide Cu–Au (IOCG) group of deposits. The available geochronologic data used to attest syngenetic or epigenetic origins
for the mineralization are either imprecise or may not represent the main mineralization episode but a later, superimposed
event. The C, S, and O isotopic results obtained in this study do not clearly discriminate between fluid sources. However,
recent B isotope data obtained on tourmaline from the matrix of the fragmental rock ore unit (Xavier, Wiedenbeck, Dreher,
Rhede, Monteiro, Araújo, Chemical and boron isotopic composition of tourmaline from Archean and Paleoproterozoic Cu–Au deposits in the Carajás Mineral
Province, 1° Simpósio Brasileiro de Metalogenia, Gramado, Brazil, extended abstracts, CD-ROM, 2005) provide strong evidence of the
involvement of a marine evaporitic source in the hydrothermal system of Igarapé Bahia. Evaporite-derived fluids may explain
the high salinities and the low reduced sulfur mineral paragenesis observed in the deposit. Evaporite-derived fluids also
exclude a significant participation of magmatic or mantle-derived fluids, reinforcing the role of nonmagmatic brines in the
genesis of Igarapé Bahia. Considering this aspect and the geological features, the possibility that the deposit was generated
by a hydrothermal submarine system whose elevated salinity was acquired by leaching of ancient evaporite beds should be evaluated. 相似文献
17.
Robert R. Seal II Robert A. Ayuso Nora K. Foley Sandra H. B. Clark 《Mineralium Deposita》2001,36(2):137-148
The Barite Hill gold deposit, at the southwestern end of the Carolina slate belt in the southeastern United States, is one
of four gold deposits in the region that have a combined yield of 110 metric tons of gold over the past 10 years. At Barite
Hill, production has dominantly come from oxidized ores. Sulfur isotope data from hypogene portions of the Barite Hill gold
deposit vary systematically with pyrite–barite associations and provide insights into both the pre-metamorphic Late Proterozoic
hydrothermal and the Paleozoic regional metamorphic histories of the deposit. The δ34S values of massive barite cluster tightly between 25.0 and 28.0‰, which closely match the published values for Late Proterozoic
seawater and thus support a seafloor hydrothermal origin. The δ34S values of massive sulfide range from 1.0 to 5.3‰ and fall within the range of values observed for modern and ancient seafloor
hydrothermal sulfide deposits. In contrast, δ34S values for finer-grained, intergrown pyrite (5.1–6.8‰) and barite (21.0–23.9‰) are higher and lower than their massive counterparts,
respectively. Calculated sulfur isotope temperatures for the latter barite–pyrite pairs (Δ=15.9–17.1‰) range from 332–355 °C
and probably reflect post-depositional equilibration at greenschist-facies regional metamorphic conditions. Thus, pyrite and
barite occurring separately from one another provide pre-metamorphic information about the hydrothermal origin of the deposit,
whereas pyrite and barite occurring together equilibrated to record the metamorphic conditions. Preliminary fluid inclusion
data from sphalerite are consistent with a modified seawater source for the mineralizing fluids, but data from quartz and
barite may reflect later metamorphic and (or) more recent meteoric water input. Lead isotope values from pyrites range for
206Pb/204Pb from 18.005–18.294, for 207Pb/204Pb from 15.567–15.645, and for 208Pb/204Pb from 37.555–38.015. The data indicate derivation of the ore leads from the country rocks, which themselves show evidence
for contributions from relatively unradiogenic, mantle-like lead, and more evolved or crustal lead. Geological relationships,
and stable and radiogenic isotopic data, suggest that the Barite Hill gold deposit formed on the Late Proterozoic seafloor
through exhalative hydrothermal processes similar to those that were responsible for the massive sulfide deposits of the Kuroko
district, Japan. On the basis of similarities with other gold-rich massive sulfide deposits and modern seafloor hydrothermal
systems, the gold at Barite Hill was probably introduced as an integral part of the formation of the massive sulfide deposit.
Received: 17 August 1998 / Accepted: 12 October 2000 相似文献
18.
Y.-H. Sung C. L. Ciobanu A. Pring J. Brügger W. Skinner N. J. Cook M. Nugus 《Mineralogy and Petrology》2007,90(3-4):249-270
Summary The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic
belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglüshan
Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8
± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These
data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower
Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts
developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated
study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic
framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime
of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and
lithospheric thinning in East China. 相似文献
19.
Four of the major plutons in the vicinity of the Candelaria mine (470 Mt at 0.95% Cu, 0.22 g/t Au, 3.1 g/t Ag) and a dike–sill system exposed in the Candelaria open pit have been dated with the U–Pb zircon method. The new geochronological data indicate that dacite magmatism around 123 Ma preceded the crystallization of hornblende diorite (Khd) at 118 ± 1 Ma, quartz–monzonite porphyry (Kqm) at 116.3 ± 0.4 Ma, monzodiorite (Kmd) at 115.5 ± 0.4 Ma, and tonalite (Kt) at 110.7 ± 0.4 Ma. The new ages of the plutons are consistent with field relationships regarding the relative timing of emplacement. Plutonism temporally overlaps with the iron oxide Cu–Au mineralization (Re–Os molybdenite ages at ∼115 Ma) and silicate alteration (ages mainly from 114 to 116 and 110 to 112 Ma) in the Candelaria–Punta del Cobre district. The dated dacite porphyry and hornblende diorite intrusions preceded the ore formation. A genetic link of the metallic mineralization with the quartz–monzonite porphyry and/or the monzodiorite is likely. Both of these metaluminous, shoshonitic (high-K) intrusions could have provided energy and contributed fluids, metals, and sulfur to the hydrothermal system that caused the iron oxide Cu–Au mineralization. The age of the tonalite at 110.7 Ma falls in the same range as the late alteration at 110 to 112 Ma. Tonalite emplacement may have sustained existing or driven newly developed hydrothermal cells that caused this late alteration or modified 40Ar/39Ar and K/Ar systematic in some areas. 相似文献
20.
Modern seafloor hydrothermal systems provide important insights into the formation and discovery of ancient volcanic-hosted massive sulfide (VHMS) deposits. In 2010, Integrated Ocean Drilling Program (IODP) Expedition 331 drilled five sites in the Iheya North hydrothermal field in the middle Okinawa Trough back-arc basin, Japan. Hydrothermal alteration and sulfide mineralization is hosted in a geologically complex, mixed sequence of coarse pumiceous volcaniclastic and fine hemipelagic sediments, overlying a dacitic to rhyolitic volcanic substrate. At site C0016, located adjacent to the foot of the actively venting North Big Chimney massive sulfide mound, massive sphalerite-(pyrite-chalcopyrite ± galena)-rich sulfides were intersected (to 30.2% Zn, 12.3% Pb, 2.68% Cu, 33.1 ppm Ag and 0.07 ppm Au) that strongly resemble the black ore of the Miocene-age Kuroko deposits of Japan. Sulfide mineralization shows clear evidence of formation through a combination of surface detrital and subsurface chemical processes, with at least some sphalerite precipitating into void space in the rock. Volcanic rocks beneath massive sulfides exhibit quartz-muscovite/illite and quartz-Mg-chlorite alteration reminiscent of VHMS proximal footwall alteration associated with Kuroko-type deposits, characterized by increasing MgO, Fe/Zn and Cu/Zn with depth. Recovered felsic footwall rocks are of FII to FIII affinity with well-developed negative Eu anomalies, consistent with VHMS-hosting felsic rocks in Phanerozoic ensialic arc/back-arc settings worldwide.Site C0013, ∼100 m east of North Big Chimney, represents a likely location of recent high temperature discharge, preserved as surficial coarse-grained sulfidic sediments (43.2% Zn, 4.4% Pb, 5.4% Cu, 42 ppm Ag and 0.02 ppm Au) containing high concentrations of As, Cd, Mo, Sb, and W. Near surface hydrothermal alteration is dominated by kaolinite and muscovite with locally abundant native sulfur, indicative of acidic hydrothermal fluids. Alteration grades to Mg-chlorite dominated assemblages at depths of >5 mbsf (metres below sea floor). Late coarse-grained anhydrite veining overprints earlier alteration and is interpreted to have precipitated from down welling seawater as hydrothermal activity waned. At site C0014, ∼350 m farther east, hydrothermal assemblages are characterized by illite/montmorillonite, with Mg-chlorite present at depths below ∼30 mbsf. Recovered lithologies from distal, recharge site C0017 are unaltered, with low MgO, Fe2O3 and base metal concentrations.Mineralization and alteration assemblages are consistent with the Iheya North system representing a modern analogue for Kuroko-type VHMS mineralization. Fluid flow is focussed laterally along pumiceous volcaniclastic strata (compartmentalized between impermeable hemipelagic sediments), and vertically along faults. The abundance of Fe-poor sphalerite and Mg-rich chlorite (clinochlore/penninite) is consistent with the lower Fe budget, temperature and higher oxidation state of felsic volcanic-hosted hydrothermal systems worldwide compared to Mid Ocean Ridge black smoker systems. 相似文献