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1.
Recent exploration in the vicinity of the giant (>90 Mt) Navan orebody has resulted in the discovery of ore-grade mineralisation to the southwest of the deposit, much of which occurs within the Upper Pale Beds, a horizon that is only weakly mineralised above the main orebody. Within this new U lens, mineralisation preferentially occurs within bioclastic carbonate grainstones and calcareous quartz sandstones, and is dominated by sulphide replacement of the carbonate component of the host sequence. Much of the replacive mineralisation is spatially associated with hydrothermal cavities, which are filled by a variable mixture of brecciated replacement sulphide minerals, space-filling sulphide and gangue cements, and internal sediments. Mineralisation also occurs within veins and dissolution seams, and as disseminated sulphide minerals. Massive mineralisation is typically a complex, chaotic, combination of replacement, cavity, and fracture-filling sulphides. Fluid inclusion analyses of ore-stage saddle dolomite indicate temperatures at the time of sulphide precipitation of ~90–150 °C, with a maximum of 175 °C. These temperatures are lower than those typically proposed for Irish-type deposits.  相似文献   

2.
The Oyu Tolgoi cluster of seven porphyry Cu-Au-Mo deposits in southern Mongolia,define a narrow,linear,12 km long,almost continuously mineralised trend,which contains in excess of 42 Mt of Cu and1850 t of Au,and is among the largest high grade porphyry Cu-Au deposits in the world.These deposits lie within the Gurvansayhan island-arc terrane,a fault bounded segment of the broader Silurian to Carboniferous Kazakh-Mongol arc,located towards the southern margin of the Central Asian Orogenic Belt,a collage of magmatic arcs that were periodically active from the late Neoproterozoic to PermoTriassic,extending from the Urals Mountains to the Pacific Ocean.Mineralisation at Oyu Tolgoi is associated with multiple,overlapping,intrusions of late Devonian(~372 to 370 Ma) quartzmonzodiorite intruding Devonian(or older) juvenile,probably intra-oceanic arc-related,basaltic lavas and lesser volcaniclastic rocks,unconformably overlain by late Devonian(~370 Ma) basaltic to dacitic pyroclastic and volcano sedimentary rocks.These quartz-monzodiorite intrusions range from earlymineral porphyritic dykes,to larger,linear,syn-,late- and post-mineral dykes and stocks.Ore was deposited within syn-mineral quartz-monzodiorites,but is dominantly hosted by augite basalts and to a lesser degree by overlying dacitic pyroclastic rocks.Following ore deposition,an allochthonous plate of older Devonian(or pre-Devonian) rocks was overthrust and a post-ore biotite granodiorite intruded at~365 Ma.Mineralisation is characterised by varying,telescoped stages of intrusion and alteration.Early A-type quartz veined dykes were followed by Cu-Au mineralisation associated with potassic alteration,mainly K-feldspar in quartz-monzodiorite and biotite-magnetite in basaltic hosts.Downward reflux of cooled,late-magmatic hydrothermal fluid resulted in intense quartz-sericite retrograde alteration in the upper parts of the main syn-mineral intrusions,and an equivalent chlorite-muscovite/illite-hematite assemblage in basaltic host rocks.Uplift,facilitated by syn-mineral longitudinal faulting,brought sections of the porphyry deposit to shallower depths,to be overprinted and upgraded by late stage,shallower,advanced argillic alteration and high sulphidation mineralisation.Key controls on the location,size and grade of the deposit cluster include(i) a long-lived,narrow faulted corridor;(ii) multiple pulses of overlapping intrusion within the same structure;and(iii) enclosing reactive,mafic dominated wall rocks,focussing ore.  相似文献   

3.
The Otavi Mountain Land is a base metal sulphide ore province in northern Namibia where deposits are hosted by platform carbonates of the Otavi Group in a foreland fold-and-thrust belt on the northern edge of the Pan-African Damara Belt. Deposits have been classified as the Berg Aukas- or Tsumeb-types, based on differences in ore association, stratigraphic position and geochemistry of ores and gangue carbonates. Mineralisation at these deposits is accompanied by carbonate alteration in the form of dolomite and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Based on cathodoluminescence imaging, trace and rare earth element (REE), O and C isotope, and fluid inclusion data, a series of carbonate generations, constituting wall rock alteration around the Tsumeb and Kombat (Tsumeb-type) and Berg Aukas (Berg Aukas-type) deposits, was established. Similar data obtained on the recently discovered Khusib Springs deposit indicate a strong affinity to Tsumeb-type deposits. Tsumeb-type deposits are distinguished from Berg Aukas-type deposits by having trace element and REE concentrations that are significantly higher in the alteration products compared to the carbonate host rocks. Only around Tsumeb-type deposits a relative enrichment in light REE is noted for the hydrothermal carbonate generations that are cogenetic with the main stage of mineralisation. Microthermometric results from fluid inclusions in carbonate alteration phases and associated quartz indicate relatively high salinity (17–23 wt% NaCl equivalent) for the main mineralising and subsequent sulphide remobilisation stages at the deposits investigated. Estimated mineralisation temperatures are significantly higher for Tsumeb-type deposits (370–405 °C) with early sulphide remobilisation in Tsumeb at 275 °C, whereas they are lower at Berg Aukas (up to 255 °C). Fluid inclusion leachate analysis suggests that most of the observed salinity can be ascribed to dissolved, predominantly Ca- and Mg-carbonates and chlorides with subordinate NaCl. Na-Cl-Br leachate systematics indicate a derivation of the fluid salinity from the interaction with evaporitic rocks en route. Tsumeb-type mineralisation is interpreted to be derived from fluids expelled during Pan-African orogeny in the more intensely deformed internal zones of the Damara Belt further south. When the high salinity fluids reached the carbonate platform after having scavenged high concentrations of base metals, base metal sulphide precipitation occurred in zones of high porosity, provided by karst features in the carbonate sequence. Results obtained for the Berg Aukas-type deposits emphasise their derivation from basinal brines, similar to Mississippi Valley-type deposits, and confirm that mineralisation of the Berg Aukas- and Tsumeb-types are both spatially and temporally distinct. Received: 5 May 1999 / Accepted: 10 November 1999  相似文献   

4.
The Archaean lode gold deposits in the Mt. York District, Pilbara Block, Western Australia are hosted in banded iron formation (Main Hill/Breccia Hill prospect) of the ca. 3.33 Ga Gorge Creek Group and in amphibolites (Zakanaka prospect) of the ca. 3.46 Ga Warrawoona Group. Gold mineralisation at the Main Hill/Breccia Hill prospect is associated with breccias comprising quartz clasts in a quartz-pyrrhotite matrix, and quartz-amphibole veins, with löllingite being the major host for gold. Minimum temperatures for gold mineralisation at the prospect are constrained as 455°C to 550°C by arsenopyrite thermometry. Gold mineralisation at the Zakanaka prospect is spatially associated with quartzclinopyroxene-calcite-microcline-calcic-amphibole veins and biotite altered wallrock adjacent to the veins. Temperatures for vein emplacement are estimated as 480°C to 570°C using both plagioclase-amphibole thermometry and mineral equilibria with respect to T and XCO2. The timing of gold mineralisation relative to the peak of metamorphism is constrained by mineral textures and the relative temperatures of hydrothermal alteration and metamorphism. Gold mineralisation at both deposits was broadly synchronous with the peak of regional amphibolite facies metamorphism, which reached temperatures of 520°C to 640°C based on amphibole-plagioclase and garnet-biotite thermometry. In this respect, the deposits are similar to other well documented syn-amphibolite facies lode gold deposits from the Archaean Southern Cross greenstone belt in the Yilgarn Block, and represent the deeper section of a crustal continuum of lode gold deposits that includes mesothermal deposits such as those at Kalgoorlie at higher crustal levels.  相似文献   

5.
Gold deposits in the Syama and Tabakoroni goldfields in southern Mali occur along a north-northeast trending mineralised litho-structural corridor that trends for approximately 40 km. The deposits are interpreted to have formed during a craton-wide metallogenic event during the Eburnean orogeny. In the Syama goldfield, gold mineralisation in 9 deposits is hosted in the hanging-wall of the Syama-Bananso Shear Zone in basalt, greywacke, argillite, lamprophyre, and black shale. Gold is currently mined primarily from the oxidised-weathered zone of the ore bodies. In the Syama deposit, mineralisation hosted in altered basalt is associated with an intense ankerite–quartz–pyrite stockwork vein systems, whereas disseminated style mineralisation is also present in greywackes. In contrast, the Tellem deposit is hosted in quartz–porphyry rocks.In the Tabakoroni goldfield, gold mineralisation is hosted in quartz veins in tertiary splay shears of the Syama-Bananso Shear Zone. The Tabakoroni orebody is associated with quartz, carbonate and graphite (stylolite) veins, with pyrite and lesser amounts of arsenopyrite. There are four main styles of gold mineralisation including silica-sulphide lodes in carbonaceous fault zones, stylolitic quartz reefs in fault zones, quartz–Fe–carbonate–sulphide lodes in mafic volcanics, and quartz–sulphide stockwork veins in silicified sediments and porphyry dykes. The several deposit styles in the goldfield thus present a number of potential exploration targets spatially associated with the regional Syama-Bananso Shear Zone and generally classified as orogenic shear-hosted gold deposits.  相似文献   

6.
Antimony-rich vein mineralisation is widespread in the German part of the Variscan orogenic belt. Mineralogical investigation of a representative suite of these deposits, coupled with fluid inclusion characterisation and microthermometry, permits a reconstruction of their genetic evolution. Two structural settings host antimony mineralisation: the cores or flanks of anticlinal zones and major lithological contrasts. Channelled migration of geothermal fluids through permeable rock sequences and later stagnation of fluids in cap-rock situations inside the anticlinal zones led to mineral deposition. The mineralising event is interpreted as relating to input of deep-sourced fluids during late-orogenic exhumation at the transitional stage between collision tectonics and the late-Variscan extensional regime. Fluid inclusion data, chlorite geothermometry and the presence of meneghinite as a characteristic Pb-Sb-sulfosalt mineral in a number of vein systems allows constraints on model P-T conditions at the onset of mineralisation to be made. These are as high as 390 to 440?°C at 0.6–1.0?kbar for the Saarsegen, Apollo and Schöne Freundschaft deposits, with lower temperatures of 320–340?°C being obtained for the Spes deposit. The fluid inclusion data indicate drastic fluid cooling during the mineralising event; minimum temperatures of approximately 150–220?°C are obtained for all deposits at the end of vein quartz formation, which coincided with deposition of stibnite and most of the Pb-Sb sulfosalts. Besides the formation of extensional quartz-stibnite-Pb-sulfosalt veins, the mineralising, low-salinity NaCl-KCl-rich high-temperature tectonic brines have overprinted sulfide assemblages within earlier siderite-(Cu)-Pb-Zn veins. This has led to replacement reaction textures and remobilisation of sulfide components within the vein systems. In contrast with the earlier siderite-(Cu)-Pb-Zn veins, neither the quartz-stibnite-sulfosalt nor the (Cu)-Pb-Sb sulfosalt assemblages were affected by Variscan deformation. Rather, they display characteristic extensional features crosscutting all earlier structures and can thus be assigned to a later phase of mineralisation. Fluid composition characteristics and structural criteria indicate formation in the latest part of the Variscan mineralisation cycle; a post-Variscan genesis being rejected on grounds of conspicuously diverging fluid characteristics. A comparison of antimony deposits in the Rheinisches Schiefergebirge with other late-orogenic deposits elsewhere in the European Variscan belt indicates a significant number of shared features, enabling them to be placed into a common model related to the onset of late-Variscan brittle extensional tectonics.  相似文献   

7.
The Archaean lode-gold deposits at Norseman, Western Australia, consist of auriferous quartz veins in dextral-reverse ductile-brittle shear zones within tholeiitic metabasalts of upper-greenschist to amphibolite facies metamorphic grade. Three types of deposits (Northern, Central, Southern) are delineated on the basis of their spatial distribution, veining style, alteration mineraloty and metamorphic grade of host rocks. Northern deposits, hosted in upper-greenschist to lower-amphibolite facies rocks, comprise massive to laminated quartz veins with selvedges of quartz-chlorite-calcite-biotite-plagioclase assemblages. Central deposits, hosted in lower-amphibolite facies rocks, consist of laminated to massive quartz veins with selvedges of quartz-actinolite-biotite-plagioclasecalcite assemblages. Southern deposits, hosted in middleamphibolite facies metabasalts, consist of banded quartz-diopside-calcite-microcline-zoisite veins. All deposits exhibit variable ductile deformation of veins and contiguous alteration haloes, consistent with a syn-deformational genesis at high temperatures. From Northern to Southern deposits, the alteration assemblages are indicative of higher temperatures of formation, and there are progressively greater degrees of dynamically recovered textures in alteration and gangue minerals. These observations imply that a thermal variation of gold-related hydrothermal alteration exists within the Norseman Terrane over a distance of 40 km, with TNorthern<TCentral<TSouthern This thermal zonation is corroborated by T−XCO 2 phase relations between vein selvedge assemblages, which signify formation temperatures of approximately 420°–475°C, 470°–495°C and >500°C for Northern, Central and Southern deposits, respectively. The sum of structural, petrographic and mineral chemistry data indicates that the alteration assemblages formed in high-temperature, open hydrothermal systems and have not been subsequently metamorphosed. The thermal differences between the deposit groups may reflect (1) a temperature gradient, at relatively constant P, corresponding to the proximity of the deposits to regional granitoid complexes, or (2) formation of the deposits at progressively deeper crustal levels from north to south. In either case the deposits represent a continuum of gold deposition from upper-greenschist to amphibolite facies, now exposed in an oblique section through the Archaean crust at Norseman.  相似文献   

8.
蒙古国欧玉陶勒盖铜(金)矿床物探找矿技术分析   总被引：2，自引：0，他引：2  
欧玉陶勒盖铜金矿是21世纪初由加拿大Ivanhoe Mines公司探明的世界级斑岩型铜金矿床, 矿体规模大、埋藏深, 被掩没在蒙古国南部茫茫戈壁沙漠中, 找矿难度极大。物探方法技术(激电、高精度磁测和电磁法)在矿床勘查评价中起到了重要作用, 研究其有效性, 总结该矿床的综合方法找矿经验, 可为掩盖区寻找隐伏斑岩铜多金属矿床提供借鉴。  相似文献   

9.
A gold-bearing quartz vein system has been identified in Archaean basement rocks at Sortekap in the Kangerlussuaq region of east Greenland, 35 km north–northeast of the Skaergaard Intrusion. This constitutes the first recorded occurrence of Au mineralisation in the metamorphic basement rocks of east Greenland. The mineralisation can be classified as orogenic style, quartz vein-hosted Au mineralisation. Two vein types have been identified based on their alteration styles and the presence of Au mineralisation. Mineralised type 1 veins occur within sheared supracrustal units and are hosted by garnet-bearing amphibolites, with associated felsic and ultramafic intrusions. Gold is present as native Au and Au-rich electrum together with arsenopyrite and minor pyrite and chalcopyrite in thin alteration selvages in the immediate wall rocks. The alteration assemblage of actinolite-clinozoisite-muscovite-titanite-scheelite-arsenopyrite-pyrite is considered to be a greenschist facies assemblage. The timing of mineralisation is therefore interpreted as being later and separate event to the peak amphibolite facies metamorphism of the host rocks. Type 2 quartz veins are barren of mineralisation, lack significant alteration of the wall rocks and are considered to be later stage. Fluid inclusion microthermometry of the quartz reveals three separate fluids, including a high temperature (T h ?=?300–350 °C), H2O–CO2–CH4 fluid present only in type 1 veins that in interpreted to be responsible for the main stage of Au deposition and sulphidic wall rock alteration. It is likely that the carbonic fluids were actually trapped at temperatures closer to 400 °C. Two other fluids were identified within both vein types, which comprise low temperature (100–200 °C) brines, with salinities of 13–25 wt%?eq. NaCl and at least one generation of low salinity aqueous fluids. The sources and timings of the secondary fluids are currently equivocal but they may be related to the emplacement of Paleogene mafic intrusions. The identification of this occurrence of orogenic-style Au mineralisation has implications for exploration in the underexplored area of east Greenland between 62 and 69°?N, where other, similar supracrustal units are known to be present.  相似文献   

10.
The Mallery Lake area contains pristine examples of ancient precious metal-bearing low-sulfidation epithermal deposits. The deposits are hosted by rhyolitic flows of the Early Proterozoic Pitz Formation, but are themselves apparently of Middle Proterozoic age. Gold mineralization occurs in stockwork quartz veins that cut the rhyolites, and highest gold grades (up to 24 g/t over 30 cm) occur in the Chalcedonic Stockwork Zone. Quartz veining occurs in two main types: barren A veins, characterized by fine- to coarse-grained comb quartz, with fluorite, calcite, and/or adularia; and mineralized B veins, characterized by banded chalcedonic silica and fine-grained quartz, locally intergrown with fine-grained gold or electrum. A third type of quartz vein (C), which crosscuts B veins at one locality, is characterized by microcrystalline quartz intergrown with fine-grained hematite and rare electrum. Fluid inclusions in the veins occur in two distinct assemblages. Assemblage 1 inclusions represent a moderate temperature (Th=150 to 220 °C), low salinity (~1 eq. wt% NaCl, with trace CO2), locally boiling fluid; this fluid type is found in both A and B veins and is thought to have been responsible for Au-Ag transport and deposition. Assemblage 2 inclusions represent a lower temperature (Th=90 to 150 °C), high salinity calcic brine (23 to 31 wt% CaCl2-NaCl), which occurs as primary inclusions only in the barren A veins. Assemblage 1 and 2 inclusions occur in alternating quartz growth bands in the A-type veins, where they appear to represent alternating fluxes of dilute fluid and local saline groundwater. No workable primary fluid inclusions were observed in the C veins. The A-vein quartz yields '18O values from 8.3 to 14.5‰ (average=10.9ǃ.7‰ [1C], n=30), whereas '18O values for B-vein quartz range from 11.2 to 14.0‰ (average=13.0ǂ.9‰, n=12). Calculated '18OH2O values for the dilute mineralizing fluid from B veins range from -2.6 to 0.2‰ (average=-0.8ǂ.9‰, n=12) and are consistent with a dominantly meteoric origin. No values could be calculated for the brine, however, because all A-vein quartz samples contain mixed fluid inclusion populations. However, the fact that A-vein quartz samples extend to lower '18O values than the B veins suggests that the brine had a lighter isotopic signature relative to the dilute fluid. Hydrogen isotopic ratios of fluid inclusion waters extracted from eleven quartz samples of both vein types range from 'DFI=-56 to -134‰, but show no particular correlation with vein type. In most respects, the mineralogical and fluid characteristics of the Mallery Lake system are comparable to those of Phanerozoic low-sulfidation deposits, and although the presence of high salinity brines is unusual in such deposits, it is not unknown (e.g., Creede, Colorado). In addition, one of the few other examples of well-preserved, Precambrian, low-sulfidation epithermal deposits, from the Central Pilbara tectonic zone, Australia, contains a similarly bimodal fluid assemblage. The significance of these saline brines is not clear, but from this study we infer that they were not directly involved with Au-Ag transport or deposition.  相似文献   

11.
Quartz from granites, greisens and quartz veins from a 1596 m long vertical section through the Cínovec/Zinnwald Li-Sn-W deposit (Czech Republic) was studied using cathodoluminescence (CL) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP MS). The trace contents of Al, Ti, Li and the Ge/Ti and Al/Ti values in quartz reflect the degree of fractionation of parental melt from which primary quartz crystallized. From the biotite granite to the younger zinnwaldite granite, quartz is characterized by increasing contents of Al (from 136–176 to 240–280 ppm) and decreasing Ti (from 16–54 to 6–14 ppm), while the contents of Li and Ge are similar (15–36 and 0.8–1.7 ppm, respectively). Quartz of the greisen stage and vein stage is poor in all measured elements (26–59 ppm Al, 0.5–1.6 ppm Ti, 2–13 ppm Li, 0.8–1.6 ppm Ge). The youngest low-temperature quartz forming thin coatings in vugs in greisen and veins differs in its extreme enrichment in Al (>1000 ppm) and Li (∼100 ppm) and very low Ti (<1 ppm). Within the greisen, remnants of primary magmatic quartz should be distinguished from metasomatic greisen-stage quartz in their higher intensity of CL and relatively higher Ti contents. A part of primary magmatic quartz may by secondarily purified via infiltration of hydrothermal fluids and dissolution–reprecipitation processes. Such quartz parallels newly formed greisen-stage quartz in its chemical and CL properties; the share of greisen-stage quartz may by therefore overestimated.  相似文献   

12.
The Tasiast gold deposits are hosted within Mesoarchean rocks of the Aouéouat greenstone belt, Mauritania. The Tasiast Mine consists of two deposits hosted within distinctly different rock types, both situated within the hanging wall of the west-vergent Tasiast thrust. The Piment deposits are hosted within metasedimentary rocks including metaturbidites and banded iron formation where the main mineral association consists of magnetite-quartz-pyrrhotite ± actinolite ± garnet ± biotite. Gold is associated with silica flooding and sulphide replacement of magnetite in the turbidites and in the banded iron formation units. The West Branch deposit is hosted within meta-igneous rocks, mainly diorites and quartz diorites that lie stratigraphically below host rocks of the Piment deposits. Most of the gold mineralisation at West Branch is hosted by quartz–carbonate veins within the sheared and hydrothermally altered meta-diorites that constitute the Greenschist Zone. At Tasiast, gold mineralisation has been defined over a strike length > 10 km and to vertical depths of 740 m. All of the significant mineralised bodies defined to date dip moderately to steeply (45° to 70°) to the east and have a south–southeasterly plunge. Gold deposits on the Tasiast trend are associated with second order shear zones that are splays cutting the hanging wall block of the Tasiast thrust. An age of 2839 ± 36 Ma obtained from the hydrothermal overgrowth on zircons from a quartz vein is interpreted to represent the age of mineralisation.  相似文献   

13.
A newly discovered, extensive sphalerite-bearing breccia (~7.5 wt.% Zn) is hosted in dolomitised Carboniferous limestones overlying Ordovician–Silurian metasedimentary rocks on the Isle of Man. Although base metal sulphide deposits have been mined historically on the island, they are nearly all quartz vein deposits in the metamorphic basement. This study investigates the origin of the unusual sphalerite breccia and its relationship to basement-hosted deposits, through a combination of petrographic, cathodoluminescence, fluid inclusion, stable isotope and hydrogeologic modelling techniques. Breccia mineralisation comprises four stages, marked by episodes of structural deformation and abrupt changes in fluid temperature and chemistry. In stage I, high-temperature (T h > 300°C), high-salinity (20–45 wt.% equiv. NaCl) fluid of likely basement origin deposited a discontinuous quartz vein. This vein was subsequently dismembered during a major brecciation event. Stages II–IV are dominated by open-space filling sphalerite, quartz and dolomite, respectively. Fluid inclusions in these minerals record temperatures of ~105–180°C and salinities of ~15–20 wt.% equiv. NaCl. The δ34S values of sphalerite (6.5–6.9‰ Vienna-Canyon Diablo troilite) are nearly identical to those of ore sulphides from mines in the Lower Palaeozoic metamorphic rocks. The δ18O values for quartz and dolomite indicate two main fluid sources in the breccia’s hydrothermal system, local Carboniferous-hosted brines (~0.5–6.0‰ Vienna standard mean ocean water) and basement-involved fluids (~5.5–11.5‰). Ore sulphide deposition in the breccia is compatible with the introduction and cooling of a hot, basement-derived fluid that interacted with local sedimentary brines.  相似文献   

14.
The Falun gold quartz vein mineralization is located ca 230 km NW of Stockholm, Sweden, within the Early Proterozoic volcano-sedimentary sequence of Bergslagen. The mineralization consists of a system with subparallel quartz veins that crosscut the alteration zone to the Falun massive sulphide deposit. Early barren and late gold-bearing quartz veins follow tectonic structures postdating the formation of the massive sulphide ore. Both generations of veins are epigenetic to the massive sulphide ore and were formed by hydrothermal processes. Fluid inclusion study of the gold-bearing quartz veins indicates a low-moderately saline fluid (0.3 to 17.4 equiv wt% NaCl). Heterogeneous trapping is indicated by coexisting inclusions showing a variable CO2 content from 100% CO2 ± CH4 to 100% aqueous fluid. Temperatures of total homogenization also show a wide spread from 116–350°C with a slightly bimodal distribution with peaks at ca 180°C and 280°C. MeasuredδD values — 69 to — 63%0 (SMOW), of inclusion fluid and calculatedδ 18O values of hydrothermal fluids — 7.5 to — 1.4%0 (SMOW), strongly suggest a meteoric origin for the fluids. The quite consistentδD values and the range inδ 18O values indicate that major water-rock interaction led to the evolution inδ18O of the hydrothermal fluids.  相似文献   

15.
Trace elements (Al, K, Ti, Fe), growth and deformation pattern in quartz of the multiple deformed Carcoar, Barry and Sunset Hills granites were investigated by electron micro probe and cathodoluminescence. Zoned quartz phenocrysts with high Ti concentrations (>70 ppm) that show blue cathodoluminescence originated from the early stage of magma crystallisation. Multiple deformation of quartz causes the redistribution of Al and K in the quartz lattice, which results in the accumulation of these elements in submicroscopic inclusions (<0.5 µm) of muscovite-like composition. In contrast, structural Ti in quartz is mostly kept in the lattice. Common halos of defect-poor, secondary quartz around fluid inclusions result from re-equilibration of fluid inclusions because of differences between fluid pressure and lithostatic pressure, e.g. during uplift (isothermal decompression) and/or !/#-transition of quartz. During healing, defect-poor secondary quartz grows at the cost of the host quartz and releases or replaces defect centres. The results of micro-structural investigations combined with Al-in-hornblende thermobarometry allow the reconstruction of regional processes. Carcoar and Barry granodiorites and Sunset Hills granite were intruded in the Late Ordovician-Early Silurian at depths of 4-8.6 and 10-12 km, respectively. In contrast to the continuous crystallisation of the granodiorite magmas, the magma of the Sunset Hills granite ascended in a stepwise fashion, causing multiple quartz nucleation. The two granodiorites were multiple, post-magmatically deformed, first, during Early Devonian under more brittle conditions at temperatures of 350-400 °C, whereas the Sunset Hills granite experienced more ductile deformation at temperatures of around 550 °C.  相似文献   

16.
中亚成矿域斑岩铜金成矿的地质环境问题   总被引：1，自引：0，他引：1  
薛春纪  赵晓波  莫宣学 《岩石学报》2016,32(5):1249-1261
中亚成矿域在蒙古、乌兹别克斯坦、吉尔吉斯斯坦和哈萨克斯坦产有Oyu Tolgoi、Almalyk、Andash-Taldy Bulak、Aktogai、Kounrad等众多巨型和世界级斑岩铜金矿床,中国新疆北部斑岩铜金找矿持续重大突破令人期待。中亚成矿域大规模斑岩铜金成矿于什么地质环境?新疆北部、尤其天山斑岩铜金地质找矿持续突破的前景怎样?都是颇受关注的重大地质和找矿问题。通过广泛深入文献调研和重要矿集区实地调查研究表明,中亚构造成矿域在古亚洲洋壳俯冲增生、陆陆碰撞和后碰撞伸展等不同时期地质环境中,虽然均有斑岩铜金成矿作用发生,但古亚洲洋俯冲形成不同时期的增生岛弧是中亚斑岩铜金最为重要的成矿地质环境,大规模斑岩铜金成矿出现在洋盆演化末期、或即将关闭时的成熟岛弧环境。为什么中亚重要斑岩铜金矿床多形成于年长的成熟岛弧是值得探索的重要科学问题。新疆北部、尤其天山不同时期的岛弧发育完整,岛弧岩浆作用强烈而漫长,斑岩铜金成矿条件优越,大型-超大型铜金矿地质找矿潜力巨大,有望持续发现重要斑岩铜金矿床。  相似文献   

17.
近二十年来,蒙古南戈壁成矿带在寻找大宗金属矿产方面取得丰硕成果,发现了欧玉陶勒盖和查干苏布尔加等与古亚洲洋晚泥盆世岛弧演化有关的大型斑岩型矿床。研究表明:1)欧玉陶勒盖—查干苏布尔加地区在法门期弧岩浆与矿化作用之后,经历了短暂的抬升和剥蚀过程,随后被石炭纪火山-沉积岩所覆盖。两个矿床皆被埋藏于法门期(D_3)—杜内期(C_1)不整合面之下;2)矿床现今出露于石炭纪—二叠纪岩体包围的"天窗"中,矿体能否保存与其上覆岩层遭受的剥蚀程度有关;3)近EW向展布的蒙古南戈壁成矿带在欧玉陶勒盖—查干苏布尔加地区受三叠纪—早白垩世准巴彦断裂左旋走滑运动的影响,局部转变为NE走向,向东可延伸至中国境内东乌旗一带。因此,在中国内蒙古东乌旗地区开展的找矿勘查工作应重点关注法门期(D_3)—杜内期(C_1)不整合之下的晚泥盆世侵入体及其围岩,并在成矿远景区进行相应的区域构造解析研究。  相似文献   

18.
The molybdenite and scheelite mineralisation in the Native Dog Pluton at Monkey Gully near Yea is hosted within an I-type (post-orogenic) pluton, which shows extensive fractionation and magma mixing, and was emplaced in an extensional environment. The pluton comprises four principal rock types: tonalite, granodiorite, dacite and leucogranite. Emplacement of the pluton was in an extensional northwest to southeast paleostress field. Early extensional quartz veins, related to cooling, are overprinted by both dacitic dykes and late-stage quartz sheeted veins. The late-stage veins host the molybdenum and tungsten mineralisation in the deposit. 206Pb/238U zircon ages of 356 ±14 Ma and 375 ± 22 Ma place pluton formation and mineralisation at the onset of the Kanimblan Orogeny and later than other major molybdenum deposits in Victoria. Key factors governing the source for the granite and its associated mineralisation are: (1) the presence of a highly fractionated and sulfur-rich leucogranite; and (2) the pluton's location in a regional jog overlying the Selwyn basement block. Finally, a model is developed to explain the differences between this Melbourne Zone molybdenum and tungsten deposit compared with other metallogenic porphyry deposits.  相似文献   

19.
杨波  赵元艺 《地质通报》2017,36(1):90-111
南蒙古欧玉陶勒盖矿床是世界上已知最大的斑岩型铜金矿床之一,处在中古生代哈萨克-蒙古岩浆弧内,是中国"一带一路"项目中中国企业"走出去"的重要方向之一。铜金储量高、矿床品位好、矿化范围广、矿体规模巨大,属世界级超大型斑岩型铜(金)矿床,开发潜力巨大。在收集大量资料的基础上,通过整理和分析,建立成因模型,并划分出北Heruga区域、Javkhlant区域、西Hugo深部区域、西Hugo深部区域、Ulaan Khud北部矿点5个找矿远景区。欧玉陶勒盖矿床所在成矿带沿哈萨克-蒙古岩浆弧向两端延伸,向西经新疆土屋铜矿延伸至哈萨克斯坦境内的科翁腊德和阿克脱盖斑岩铜矿,向东延伸至中国境内多宝山、铜山地区。  相似文献   

20.
Porphyry Cu-Mo-Au mineralisation with associated potassic and phyllic alteration, an advanced argillic alteration cap and epithermal quartz-sulphide-gold-anhydrite veins, are telescoped within a vertical interval of 400-800 m on the northeastern margin of the Thames district, New Zealand. The geological setting is Jurassic greywacke basement overlain by Late Miocene andesitic-dacitic rocks that are extensively altered to propylitic and argillic assemblages. The porphyry Cu-Mo-Au mineralisation is hosted in a dacite porphyry stock and surrounding intrusion breccia. Relicts of a core zone of potassic K-feldspar-magnetite-biotite alteration are overprinted by phyllic quartz-sericite-pyrite or intermediate argillic chlorite-sericite alteration assemblages. Some copper occurs in quartz-magnetite-chlorite-pyrite-chalcopyrite veinlets in the core zone, but the bulk of the copper and the molybdenum are associated with the phyllic alteration as disseminated chalcopyrite and as molybdenite-sericite-carbonate veinlets. The advanced argillic cap has a quartz-alunite-dickite core, which is enveloped by an extensive pyrophyllite-diaspore-dickite-kaolinite assemblage that overlaps with the upper part of the phyllic alteration zone. Later quartz-sphalerite-galena-pyrite-chalcopyrite-gold-anhydrite-carbonate veins occur within and around the margins of the porphyry intrusion, and are associated with widespread illite-carbonate (argillic) alteration. Multiphase fluid inclusions in quartz stockwork veins associated with the potassic alteration trapped a highly saline (50-84 wt% NaCl equiv.) magmatic fluid at high temperatures (450 to >600 °C). These hypersaline brines were probably trapped at a pressure of about 300 bar, corresponding to a depth of 1.2 km under lithostatic conditions. This shallow depth is consistent with textures of the host dacite porphyry and reconstruction of the volcanic stratigraphy. Liquid-rich fluid inclusions in the quartz stockwork veins and quartz phenocrysts trapped a lower salinity (3-20 wt% NaCl equiv.), moderate temperature (300-400 °C) fluid that may have caused the phyllic alteration. Fluid inclusions in the quartz-sphalerite-galena-pyrite-chalcopyrite-gold-anhydrite-carbonate veins trapped dilute (1-3 wt% NaCl equiv.) fluids at 250 to 320 °C, at a minimum depth of 1.0 km under hydrostatic conditions. Oxygen isotopic compositions of the fluids that deposited the quartz stockwork veins fall within the 6 to 10‰ range of magmatic waters, whereas the quartz-sulphide-gold-anhydrite veins have lower '18Owater values (-0.6 to 0.5‰), reflecting a local meteoric water (-6‰) influence. A '18O versus 'D plot shows a trend from magmatic water in the quartz stockwork veins to a near meteoric water composition in kaolinite from the advanced argillic alteration. Data points for pyrophyllite and the quartz-sulphide-gold-anhydrite veins lie about midway between the magmatic and meteoric water end-member compositions. The spatial association between porphyry Cu-Mo-Au mineralisation, advanced argillic alteration and quartz-sulphide-gold-anhydrite veins suggests that they are all genetically part of the same hydrothermal system. This is consistent with K-Ar dates of 11.6-10.7 Ma for the intrusive porphyry, for alunite in the advanced argillic alteration, and for sericite selvages from quartz-gold veins in the Thames district.  相似文献   

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