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1.
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   

2.
Gold mineralization associated with quartz reefs is related to the structural history of the Early Devonian, Walhalla Group. These reefs are situated in the Walhalla Synclinorium, developed during the Middle to Late Devonian Tabberabberan Orogeny. A pervasive north‐south‐trending axial planar cleavage and two styles of folding were produced during regional east‐west compression. The first are upright, open to close folds with sub‐horizontal fold axes. The second are plunging inclined, close to tight folds with fold axes that plunge steeply to the north and south. An extensional event is associated with the emplacement of the Woods Point Dyke swarm and a set of normal faults that offset all earlier structures. High‐angle reverse faults, which post‐date the folding and the emplacement of the dykes, were utilized as conduits for hydrothermal fluids and preferentially localize mineralization to laminated quartz veins. En echelon vein arrays formed during initial stages of reverse faulting became deformed during prolonged shearing to produce ptygmatic veins. Laminated quartz veins within high‐angle reverse faults contain arsenopyrite and pyrite in vein margins and gold in fractures that cross‐cut continuous quartz crystals. Gold, galena, chalcopyrite and sphalerite may also be deposited adjacent to and within fractured arsenopyrite and pyrite. Late‐stage, cross faults developed in a regime of north‐south compression and post‐date the laminated quartz veins and mineralization.  相似文献   

3.
The eastern Lachlan Orogen in southeastern Australia is noted for its major porphyry–epithermal–skarn copper–gold deposits of late Ordovician age. Whilst many small quartz vein-hosted or orogenic lode-type gold deposits are known in the region, the discovery of the Wyoming gold deposits has demonstrated the potential for significant lode-type mineralisation hosted within the same Ordovician volcanic stratigraphy. Outcrop in the Wyoming area is limited, with the Ordovician sequence largely obscured by clay-rich cover of probable Quaternary to Cretaceous age with depths up to 50 m. Regional aeromagnetic data define a north–south trending linear belt interpreted to represent the Ordovician andesitic volcanic rock sequence within probable Ordo-Silurian pelitic metasedimentary rocks. Drilling through the cover sequence in 2001 to follow up the trend of historically reported mineralisation discovered extensive alteration and gold mineralisation within an andesitic feldspar porphyry intrusion and adjacent volcaniclastic sandstones and siltstones. Subsequent detailed resource definition drilling has identified a substantial mineralised body associated with sericite–carbonate–albite–quartz–(±chlorite ± pyrite ± arsenopyrite) alteration. The Wyoming deposits appear to have formed as the result of a rheological contrast between the porphyry host and the surrounding volcaniclastic rocks, with the porphyry showing brittle fracture and the metasedimentary rocks ductile deformation. The mineralisation at Wyoming bears many petrological and structural similarities to orogenic lode-style gold deposits. Although the timing of alteration and mineralisation in the Wyoming deposits remain problematic, a relationship with possible early to middle Devonian deformation is considered likely.  相似文献   

4.
Recent high‐resolution aeromagnetic data have delineated an extensive swarm of undeformed northeast‐trending dolerite dykes in the southeastern Yilgarn Craton, known previously only from isolated exposures in surface mining operations. Owing to parallelism of the dykes to the Fraser Mobile Belt, the eastern segment of the Albany‐Fraser Orogen, the swarm is referred to here as the Fraser Dyke Swarm. Ion‐microprobe dating of baddeleyite from a granophyric segregation in the centre of one dyke yields a mean 207Pb/206Pb age of 1212 ± 10 Ma (95% confidence limits). The location of the Fraser Dyke Swarm, adjacent and parallel to the Fraser Mobile Belt, suggests that the dykes may have been emplaced into lines of weakness that originated during tectonic loading and downwards flexure of the craton margin. This is the first evidence of ca 1210 Ma mafic dykes and associated crustal‐scale extension in the southeast Yilgarn Craton, although the age is similar to those reported recently for dolerite and quartz diorite dykes in the central and southern part of the craton, suggesting that a genetic relationship may exist between intrusions in the two areas.  相似文献   

5.
《Journal of Structural Geology》2004,26(6-7):1025-1041
Intrusion-related gold deposits at the Clear Creek, Scheelite Dome and Dublin Gulch properties of the Tombstone Gold Belt (TGB), Yukon Territory have dominantly E-striking, steeply dipping, auriferous quartz extension veins within intrusions. In adjacent metasedimentary rocks gold is hosted in subvertical NW- to NNW-striking sinistral faults as veins and breccias, in E-striking extension veins and locally in E- to ENE-striking fault veins. These structural relationships indicate low magnitude, broadly E–W-directed shortening and N–S extension during stock emplacement and gold mineralisation at ∼92 Ma.The lack of any deviation or deflection of the extension vein orientations in the country rocks, with respect to their orientation within the stocks, indicates consistent stress trajectories in both rock types. These TGB deposits formed at 5–8 km depth, where mean and differential stresses may be greater in magnitude than in shallower porphyry environments. Many porphyry systems feature magmatic-related stresses that dominated the local stress field, with more variable vein orientations the result. Conversely, orogenic gold systems usually exhibit strong dimensionality in vein orientations. Fault-hosted mineralisation in metasedimentary rocks of the TGB deposits in this study is comparable in geometry, but generally smaller in size than in many orogenic gold systems. Intrusion-related systems of the TGB exhibit intermediate structural styles of mineralisation that provide a useful bridge in understanding the diversity of mechanically controlled structural styles in otherwise mostly unrelated gold deposit types.  相似文献   

6.
New 40Ar/39Ar geochronological data support, and significantly expand upon, preliminary age data that were interpreted to suggest an episodic and diachronous emplacement of gold across the western Lachlan fold belt, Australia. These geochronological data indicate that mineralisation in the central Victorian gold province occurred in response to episodic, eastward progressing deformation, metamorphism and exhumation associated with the formation of the western Lachlan fold belt. Initial gold formation throughout the Stawell and the Bendigo structural zones can be constrained to a broad interval of time between 455 and 435 Ma, with remobilisation of metals into new structures and/or new pulses of mineralisation occurring between 420 and 400 Ma, and again between 380 and 370 Ma, linked to episodic variations in the regional stress-field and during intrusion of felsic dykes and plutons. This separation of ages is incompatible with the view that gold emplacement in the western Lachlan fold belt was the result of a single, orogen-wide event during the Devonian. A distinct phase of gold mineralisation, characterised by elevated Cu, Mo, Sb or W, is associated with both Late Silurian to Early Devonian (~420 to 400 Ma) and Middle to Late Devonian (~380 to 370 Ma) magmatism, when crustal thickening and shortening during the ongoing consolidation of the western Lachlan Fold Belt led to extensive melt development in the lower crust and resulted in widespread magmatism throughout central Victoria. These ~420 to 400 Ma and ~380 to 370 Ma occurrences, best exemplified by the Wonga deposit in the Stawell structural zone and many of the Woods Point deposits in the Melbourne structural zone, but also evidenced by occurrences at Fosterville and Maldon in the Bendigo structural zone, clearly formed synchronous with, or post-date, the emplacement of plutons and dykes, and thus are spatially (if not genetically) related to melt generation at depth. This later, magmatic-associated and polymetallic type of gold mineralisation is economically subordinate to the earlier, metamorphic-associated type of gold deposition in the Stawell and Bendigo structural zones, but tends to be the dominant style in the Melbourne Zone. These new geochronological constraints, together with zircon U-Pb data from felsic intrusive rocks of known relationship to gold mineralisation, demonstrate that initial hydrothermal alteration associated with gold emplacement in the western Lachlan fold belt was metamorphic-related, predating the emplacement of granite plutons by as much as 80 million years. This timing differs from other important orogenic gold districts where gold deposition is closely associated spatially with felsic magmatism. The early introduction of metamorphically derived fluids well before magmatism may reflect variations in the timing of peak metamorphic conditions at different crustal levels in an accretionary prism undergoing simultaneous deformation and erosion. Consequently, no genetic link exists between the main phase(s) of gold mineralisation and magmatism in the central Victorian gold province. With the exception of formation of a minor magmatism-related and geochemically-distinct mineralisation style at about 420 to 400 Ma, and again at about 380 to 370 Ma, the apparent spatial relationship between gold mineralisation and felsic intrusions is merely the result of melts and fluids being channelised along the same structures.  相似文献   

7.
The West African craton is known for its structurally hosted Au deposits in Ghana, Burkina Faso, Côte d'Ivoire, Mali and Niger. The Essakane goldfield in northeast Burkina Faso has produced 1 606,000 oz of gold since 2010 from the Essakane Main Zone. The Essakane goldfield is made up of several exploration and artisanal sites that include; Essakane Main Zone, Gossey, Falagountou, Sokadie, Tin Zoubratan, Essakane North and South, Korizéna, Bom Kodjélé, Tin Taradat, Tassiri, Gaigou, and Takabangou. Gold mineralisation in sheeted and stockworks quartz–carbonate and tourmaline veins occurs with pyrite, arsenopyrite, and traces of pyrrhotite, galena and hematite. It is hosted in sheared, folded and contact metamorphosed volcanic, volcanoclastic and sedimentary Birimian Supergroup sequences. The maximum age of gold mineralisation in the Essakane goldfield is syn-deformational and formed during the Eburnean Orogeny (D2) at 2130–1980 Ma.  相似文献   

8.
The Hillgrove gold–antimony deposit is hosted in late Palaeozoic, biotite-grade metasedimentary rocks and Permo-Carboniferous granitoid intrusions of the New England Orogen. Mineralisation occurred at a range of structural levels during rapid uplift in the orogen at 255–245 Ma. Hydrothermal fluids were controlled by extensional faults in a regional-scale sinistral strike-slip fault system. Principal faults in this system were developed in, and possibly evolved from, mylonite zones which were active during Late Permian tectonics. Earliest mineralisation formed scheelite-bearing quartz veins, and these were followed by auriferous arsenopyrite–pyrite–quartz–carbonate veins with minor base metal sulphides. This latter type was accompanied by sericitisation and carbonation of the host rock, with addition of sulphur, arsenic and gold, in zones up to 20 m from veins. Quartz–stibnite veins with electrum, gold, aurostibite, and arsenopyrite form a prominent and economically important hydrothermal type, with little wall-rock alteration but extensive hydrothermal breccia formation and local open-space filling textures. Below a mining depth of 300–500 m, this type passes over a short distance downwards into stibnite-poor gold-bearing veins. Late-stage carbonate–stibnite veins with gold and silver sulphosalts cut all earlier veins, and have open-space filling textures. Aspects of the Hillgrove deposit have similarities to many other orogenic gold deposits in the SW Pacific which have been formed at different structural levels. Hillgrove is distinctive in having evidence for mineralisation at this wide range of structural levels in the one deposit, formed progressively during syn-orogenic uplift. Editorial handling: N. White  相似文献   

9.
Gold Deposits in Beishan Mountain, Northwestern China   总被引：2，自引：0，他引：2  
Abstract. The Beishan Mountain spans three provinces ‐ Gansu, Xinjiang and Inner Mongolia, having an area of 120,000 km2 Tectonically, it transverses three different tectonic units, i.e. Siberia, Kazakhstan and Tarim plates, and is composed of nine ter‐rains with widely exposed Precambrian and Paleozoic strata, complex structures, intensive magmatic activities and widespread ore deposits. It is not only a main part of Tianshan‐Yinshan‐Great Hinggan metallogenic belt in China, but also a key to under‐stand the evolution of central‐Asian orogenic system. At present, more than 100 gold deposits and prospects have been discovered, explored and mined, among which Nanjinshan, Mazhuangshan, Liushashan, Jinwozi, Zhaobishan and Xiaoxigong are the most important ones. Based on the host rocks and the geological features, all these gold occurrences can be subdivided into three groups (or types): (1) hosted by Carboniferous or Permian volcanic or subvolcanic rocks; (2) hosted by or related to plutonic intrusions; and (3) hosted by Precambrian metamorphic rocks. The first group includes the Mazhuangshan gold deposit, which occurs in Hercynian quartz por‐phyry and rhyolite porphyry as gold‐bearing quartz veins. The second group is composed of the Liushashan, Nanjinshan Zhaobishan and Jinwozi gold deposits. Gold mineralization at these four deposits occurs within Hercynian granitoids intrusion: or late Paleozoic sedimentary rocks as quartz veins, veinlets and altered rocks. The Xiaoxigong gold deposit belongs to the third group, and is hosted by Precambrian schist, amphibolite and migmatite as quartz veins and altered rocks. Isotopic age dating data, geological and geochemical evidence suggest that most of the groups 1 and 2 gold deposits were generated during the emplacement of the Hercynian or partly Indosinian intrusions. These intrusions may provide both heat and metals for groups 1 and 2 deposits. In contrast, although the formation is closely related to the Hercynian magma‐tism, the ore‐forming materials of the group 3 deposits may not only come from the intrusions, but also from the Precambrian metamorphic rocks.  相似文献   

10.
The Woods Point dyke swarm comprises hundreds of narrow, subparallel igneous dykes and dozens of pipe-shaped dyke bulges within strongly deformed early Palaeozoic turbidites of the Melbourne trough. Porpylitic alteration accompanied dyke emplacement and was followed by microfracturing induced by high fluid pressures, involving CO2 of magmatic origin, as the dykes solidified. Further stress caused through-going faults having ladder and other patterns. Isotopic studies suggest that metamorphically or geothermally-derived solutions filled the faults and other fractures with quartz and carbonate and altered immediately adjacent dyke rock. However earlier-formed vein and wall rock carbonates retained their magmatic isotopic composition. Fluid inclusions indicate vein deposition began at approximately 400°C with salinities up to 9 weight percent NaCl. Nine sulfide minerals and gold were deposited in the veins after ankerite, sericite and albite, while quartz deposition continued through all stages. Sulfur isotopic determinations indicate the vein sulfur could not have been derived from adjacent sedimentary rocks, nor exclusively from the dykes. Metamorphic waters of marine origin is a viable source for sulfur. Saline and CO2-rich alkaline solutions reacted with the dyke wall rocks and probably evolved chemically prior to deposition of gold. Vug carbonates deposited by meteoric water that leached vein carbonates mark the end of vein formation.Present Adress: 631 Station Street, North Carlton 3054, Victoria, Australia  相似文献   

11.
New 40Ar/39Ar data from sedimentary rock-hosted orogenic gold deposits in northeastern Tasmania constrain most ore formation to between 395 Ma and 385 Ma. These 385–395 Ma ages for the formation of orogenic gold agree well with an inferred Early to Middle Devonian timing for peak deformation and folding across much of northeastern Tasmania. Data from micas within alteration halos in some deposits give dates of ~420–430 Ma; these dates confirm the occurrence of an earlier Silurian phase of deformation and suggest that at least some of the mineralisation was possibly generated during this event. Gold mineralisation hosted by Middle Devonian post-tectonic granites may be genetically related to magmatism following orogeny, but these deposits formed virtually synchronously with peak deformation-related systems. Early to Middle Devonian deformation in northeastern Tasmania also reactivated older structures in western Tasmania, and the formation of quartz vein-hosted gold mineralisation there. Based on geological, structural, tectonic and metallogenetic similarities, northeastern Tasmania is interpreted as a lateral equivalent of the turbidite-dominated fold-thrust belt of the western Lachlan Orogen. However, unlike Victoria, where the sedimentary rock sequence developed on oceanic crust, northeastern Tasmania was probably underlain by thinned Proterozoic crust, either as part of a promontory along the Gondwana margin or as a microcontinental fragment. This may have protected the Palaeozoic succession from large-scale, pre-Devonian orogeny, with collision not beginning until the Middle Devonian. These variations in the structural and tectonic evolution, and the timing of deformation and ore formation can explain the difference in contained gold, and the distribution and number of major orogenic gold deposits within the Palaeozoic of northeastern Tasmania.Electronic supplementary material Supplementary material is available for this article at  相似文献   

12.
The Hillgrove mineral field, in the southern part of the New England Orogen of northeastern New South Wales, Australia, contains numerous mesothermal Au---Sb vein systems. Calc-alkaline (shoshonitic) lamprophyre (CAL) dykes are also associated with mineralisation with dilational lode structures acting as conduits for dyke intrusion, which has occurred before and after major quartz-stibnite veining. Dykes include minette and vogesite compositions and were emplaced in the late Permian (247–255 Ma), at the same time as regionally extensive I-type magmatism in the New England Orogen. Least-altered dykes are enriched in Mg, K, Ba, Rb, Sr, Zr, Th, Cr and Ni relative to I-type intrusives although chemical affinities are evident between lamprophyres and the more mafic members of the high-K Moonbi Plutonic Suite.

Hillgrove lamprophyres are commonly enriched in Sb, As, Hg, Au, W and Bi with respect to average CAL compositions. Evidence indicates this is most likely due to contamination of magma during intrusion through mineralised structures, rather than a primary magmatic feature. Partially resorbed xenocrystic stibnite occurs in dykes which have intruded lode structures, probably facilitated by the low melting point of stibnite (550°C) and its incorporation into the magma. Carbon and oxygen isotopic data from carbonates in least-altered, post-lode lamprophyres are indistinguishable from carbonate in altered dykes and veins, implying that hydrothermal interaction continued after dyke intrusion. Although it is unlikely that lamprophyre dykes have been a direct source for mineralisation at Hillgrove, the close temporal and spatial relation of dykes, mesothermal Au---Sb veins and I-type intrusions are interpreted to be manifestations of the post-collisional setting and influx of mantle-derived heat and partial melts into the New England Orogen during the late Permian.  相似文献   


13.
The Hodgkinson and Broken River provinces of the Mossman Orogen in north Queensland host numerous orogenic gold deposits and still remain under-explored. This paper discusses regional metallogenic controls and results of a probabilistic quantitative assessment of undiscovered gold potential in the region. Significant orogenic gold deposits in the region occur only within relatively small well-endowed metallogenic zones, likely to be controlled by the eastern margin of the Paleoproterozoic continental crust underlying the western Mossman Orogen. Three distinct styles of primary orogenic gold deposits are present in the area: gold–quartz veins, refractory gold associated with quartz–pyrite–arsenopyrite veins and stockworks and stibnite–quartz±gold veins. Refractory gold deposits are estimated to have the highest potential for significant undiscovered resources in the region. The Hodgkinson Province is estimated to host between one and ten significant undiscovered refractory gold ore fields, with a 50 % probability of at least 20 t of total contained gold and a 90 % probability of at least 1 t. The Broken River Province is estimated to host up to five significant undiscovered refractory gold ore fields, with a 50 % probability of at least 12 t of contained gold.  相似文献   

14.
Stratiform quartz-sulphide-gold veins, locally termed reefs are hosted within the Proterozoic Transvaal Sequence sedimentary succession, in the Sabie-Pilgrim's Rest goldfield, eastern Transvaal. These deposits have produced about 180 tonnes of gold and share many characteristics with those of Telfer, Western Australia. Detailed examination of the Elandshoogte Mine shows that gold deposition occurred in two stages, both linked to bedding-parallel thrust faulting within the sedimentary pile. Deformation being concentrated within incompetent shale beds, interlayered within more competent units. The majority of gold was introduced in the second stage of mineralisation and occurs within fractures in early-formed sulphide minerals. Deposition of competent quartz veins accompanying early sulphide and gold mineralisation resulted in a change in deformation style within the reef zone, from early shearing in shales to later duplex faulting of the quartz-reef. Fluids accompanying faulting are implied to have transported gold, and a magmatic source of mineralisation is suggested.  相似文献   

15.
The 43 t (1.4 Moz) of gold in the Woodcutters goldfield 50 km north of Kalgoorlie has wide geological significance in terms of gold in Archaean granite, as well as its local commercial and exploration significance. Woodcutters is already one of the largest Archaean gold systems in granite, and is unusual in being so far laterally from the nearest greenstone belt. Gold in the Federal zone, one of the deposits making up the Woodcutters goldfield, is hosted in hornblende‐biotite granodiorite,6 km from the mapped contact with greenstone. In Federal open pit, the granodiorite is coarse‐grained in the northern half, and a fine‐grained granodiorite in the south, with both hosting gold. These two types of granodiorite are rather similar in both mineralogy and geochemistry. There is also a subordinate fine‐grained monzodiorite. The Federal gold mineralisation is in a northwest‐striking, northeast‐dipping (315° strike/60°E dip) shear zone in the Scotia granite. Variation in grainsize of the host rocks might have affected the style of deformation with more brittle fabrics in the coarse‐grained phase and more ductile fabrics prominent in the fine‐grained granodiorite. Hydrothermal alteration is extensively developed around the Federal deposit and is a useful vector towards gold mineralisation. Distal epidote alteration surrounds a proximal muscovite‐biotite alteration zone that contains quartz‐sulfide veins. The alteration shares some of the common alteration characteristics of Archaean greenstone‐hosted gold, but differs in that carbonate‐chlorite alteration is only weakly developed. This difference is readily explained in terms of host‐rock composition and lower concentrations of Fe, Mg and Ca in the granite compared with greenstone. Fluid‐inclusion studies demonstrate that the fluids associated with the hydrothermal alteration at Woodcutters shared the common characteristics of fluids in Archaean greenstone gold, namely low‐salinity and dominant H2O–CO2. Fluid inclusions with moderate salinity were found in one fresh sample away from mineralisation, and are inferred to represent possible magmatic fluid. There is no evidence of a granite‐derived fluid being responsible for gold mineralisation. The granodiorite host rock had cooled, crystallised and had at least started to undergo deformation prior to gold introduction. The distribution of gold mineralisation in the Woodcutters goldfield has the style, shape and orientation comparable with greenstone‐hosted gold deposits in the same region. The northwest trend, the quartz veining and simple pyrite mineralogy are all features common to other greenstone‐hosted gold deposits near Kalgoorlie such as Mt Pleasant. The alteration fluid appears to have penetrated the granite on the scale of many hundreds of metres, causing large‐scale alteration. Woodcutters gold mineralisation resulted from the same metamorphic fluid processes that led to formation of greenstone gold deposits. In this metamorphic model, granitic rocks are predicted to be less‐favourable gold hosts than mafic rocks for two reasons. Granitic rocks do not generally fracture during regional deformation in such a way as to create large‐scale dilation. Furthermore, with less iron and no carbon, granitic rocks have lower potential to precipitate gold from solution by wall‐rock reaction. The metamorphic model predicts that those granite types with higher Fe should host better gold deposits, all other factors being equal. Accordingly, tonalite‐trondhjemite and hornblende‐bearing granodiorite should provide better environments for major gold deposits compared with monzogranite, and granite sensu stricto, as borne out by Woodcutters, but mafic rocks should be better hosts than any of these felsic to intermediate rocks.  相似文献   

16.
在综述了脉岩与热液型脉状金矿关系的基础上，认为中基性脉岩、煌斑岩脉不仅在空间上与脉状金矿相伴生，形成时间祁近，而且在物源和成因上有着密切的关联。脉岩是脉状金矿床成因系列的组成部分。据此提出中基性岩浆在某种动力作用下，诱导上覆花岗质岩石（包括古老变质岩）熔融，并发生混染，在地壳脉动作用下，脉岩与含矿流体多期次多阶段侵位，在相应的部位形成脉岩与矿脉共存的金矿区带。  相似文献   

17.
Gold mineralisation in the White River area, 80 km south of the highly productive Klondike alluvial goldfield, is hosted in amphibolite facies gneisses in the same Permian metamorphic pile as the basement for the Klondike goldfield. Hydrothermal fluid which introduced the gold was controlled by fracture systems associated with middle Cretaceous to early Tertiary extensional faults. Gold deposition occurred where highly fractured and chemically reactive rocks allowed intense water–rock interaction and hydrothermal alteration, with only minor development of quartz veins. Felsic gneisses were sericitised with recrystallisation of hematite and minor arsenic mobility, and extensively pyritised zones contain gold and minor arsenic (ca 10 ppm). Graphitic quartzites (up to 5 wt.% carbon) caused chemical reduction of mineralising fluids, with associated recrystallisation of metamorphic minerals (graphite, pyrrhotite, pyrite, chalcopyrite) in host rocks and veins, and introduction of arsenic (up to 1 wt.%) to form arsenopyrite in veins and disseminated through host rock. Veins have little or no hydrothermal quartz, and up to 19 wt.% carbon as graphite. Late-stage oxidation of arsenopyrite in some graphitic veins has formed pharmacosiderite. Gold is closely associated with disseminated and vein sulphides in these two rock types, with grades of up to 3 ppm on the metre scale. Other rock types in the White River basement rocks, including biotite gneiss, hornblende gneiss, pyroxenite, and serpentinite, have not developed through-going fracture systems because of their individual mineralogical and rheological characteristics, and hence have been little hydrothermally altered themselves, have little hydrothermal gold, and have restricted flow of fluids through the rock mass. Some small post-metamorphic quartz veins (metre scale) have been intensely fractured and contain abundant gold on fractures (up to 40 ppm), but these are volumetrically minor. The style of gold mineralisation in the White River area is younger than, and distinctly different from, that of the Klondike area. Some of the mineralised zones in the White River area resemble, mineralogically and geochemically, nearby coeval igneous-hosted gold deposits, but this resemblance is superficial only. The White River mineralisation is an entirely new style of Yukon gold deposit, in which host rocks control the mineralogy and geochemistry of disseminated gold, without quartz veins.  相似文献   

18.
We report results of metallogenic, structural, petrological, and fluid-inclusion studies that characterise the nature of gold mineralisation in the Amanda Bel Goldfield, the most significant gold producer in the Palaeozoic Broken River Province of northeastern Queensland, Australia. Gold–antimony–arsenic and gold–arsenic deposits in the Amanda Bel Goldfield occur along distinctive northeastern trends, suggesting a strong structural control for their development during several phases of deformation in the Devonian to Carboniferous. Field evidence, as well as petrographic, scanning electron microscope and fluid-inclusion analysis of mineralised samples, indicate the presence of two main stages of gold genesis. These are distinguished by the coarse grained versus invisible nature of gold particles and their association with particular sulfide phases. A third stage of gold deposition is attributed to introduction of antimony±gold-rich ore fluids. Fluid-inclusion studies record minimum trapping temperatures between 140 and 380°C, and salinities of up to 6.5 wt% NaCl equivalent for the two main gold-forming stages. Our analyses further indicate that mineralising solutions for the earlier of the two main gold-forming stages were slightly more saline, and that the ore-hosting veins formed at higher temperatures. The style of gold mineralisation in the Amanda Bel Goldfield is compatible with orogenic gold deposits that form primarily during compressional and transpressional deformation along convergent plate margins in accretionary and collisional orogens. The increased understanding gained from our studies on the origin and nature of the deposits aids predictive mineral discovery elsewhere in the Broken River Province, and also in analogous terranes throughout the Tasman Fold Belt System of eastern Australia.  相似文献   

19.
The largest gold district in China is the Jiaodong Peninsula, where three types of gold deposits are recognized: quartz vein, fracture-altered and breccia types. The first two developed along a group of NE-trending faults and are hosted by granitic intrusions, dated at 160 to 150 Ma (biotite granite) and 130 to 126 Ma (granodiorite), and by metamorphic rocks of the Precambrian crystalline basement. The breccia-type gold system is mainly located around the northern margin of the Jiaolai Cretaceous basin, where mineralisation is controlled by both detachment fractures and NE-trending faults. This study is based on stable isotope determinations from ten gold deposits, including Linglong, Jiaojia, Sanshandao, Cangshang, Wang'ershan, Dayigezhuang, Denggezhuang, Pengjiakuang, Fayunkuang and Dazhuangzi, as well as the Linglong Jurassic biotite granite, Guojialing Cretaceous granodiorite and Archean gneiss. The stable isotope systematics reflect the style of the three types of gold deposits, but also show that they belong to the same metallogenic system, in which the hydrothermal fluids were derived from a mantle fluid reservoir and mixed with crustal fluids. The ore-forming age is later than both the Jurassic biotite granite and Cretaceous granodiotite, but overlaps with the 121 to 114 Ma ages of lamprophyre and diabase dykes. The hydrothermal fluids that were responsible for both gold mineralisation and the retrograde alteration of the diabase and lamprophyre dykes are similar, and represent a CO2 and potassium-rich system. This fluid system is interpreted to be the consequence of Cretaceous lithospheric thinning, asthenospheric upwelling and mantle degassing in Eastern China.  相似文献   

20.
The Bagassi gold deposits are situated on the West African craton and hosted in Palaeoproterozoic rocks of the Houndé greenstone belt, southwest Burkina Faso. High-grade gold mineralisation is hosted in quartz–gold ± pyrite veins-lodes (V1A), in dilational zones and narrow shears in the Bagassi granitoid, and forms the majority of the resource–reserve portfolio in the Bagassi exploration permits, with gold grades of 18–21 g/t. Shear hosted gold-pyrite mineralisation in quartz veins in dilational jogs (V1B) occurs along narrow discontinuous shear zones that trend north-northwest in Birimian-aged metabasaltic units, and forms a secondary gold resource. Gold mineralisation is restricted to formation in the late Eburnean Orogeny and formed during a change from east-west to transcurrent compression and shearing. The Bagassi deposits demonstrate that granitoids emplaced prior to onset of the Eburnean Orogeny represent viable gold mineralisation in host rocks that are increasingly seen to be associated with significant gold resources.  相似文献   

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