Статті в журналах з теми "Breccia intrusions"

AbstractThe Rum Igneous Centre comprises two early marginal felsic complexes (the Northern Marginal Zone and the Southern Mountains Zone), along with the later central ultrabasic–basic layered intrusions. These marginal complexes represent the remnants of near-surface to eruptive felsic magmatism associated with caldera collapse, examples of which are rare in the North Atlantic Igneous Province. Rock units include intra-caldera collapse breccias, rhyolitic ignimbrite deposits and shallow-level felsic intrusions, as well the enigmatic ‘Am Màm intrusion breccia’. The latter comprises a dacitic matrix enclosing lobate basaltic inclusions (~1–15 cm) and a variety of clasts, ranging from millimetres to tens of metres in diameter. These clasts comprise Lewisian gneiss, Torridonian sandstone and coarse gabbro. Detailed re-mapping of the Am Màm intrusion breccia has shown its timing of emplacement as syn-caldera, rather than pre-caldera as previously thought. Textural analysis of entrained clasts and adjacent, uplifted country rocks has revealed their thermal metamorphism by early mafic intrusions at greater depth than their present structural position. These findings provide a window into the evolution of the early mafic magmas responsible for driving felsic magmatism on Rum. Our data help constrain some of the physical parameters of this early magma–crust interaction and place it within the geochemical evolution of the Rum Centre.

Sudbury breccias are commonly attributed to meteoritic impact at about 1.85 Ga in the vicinity of the Sudbury Igneous Complex. In the Whitefish Falls area, about 75 km southwest of Sudbury, similar breccias are widely developed in argillites of the ~2.3 Ga Gowganda Formation. There is abundant evidence of "soft sediment" deformation of the Huronian sediments in the form of complex "fault" contacts, clastic dyke intrusions, and chaotic folding. These movements appear to have been penecontemporaneous with intrusion of highly irregular diabase bodies, which are interpreted as being older than the ~2.2 Ga Nipissing diabase. Complex shapes of diabase bodies and highly irregular contact relationships between diabase and argillites, including intrusions of sediment veins into diabase, support intrusion of the diabase into incompletely consolidated sediments. These data, together with chemical evidence of mixing of diabase, argillite, and other materials in the breccia bodies, suggest that the breccias at Whitefish Falls may have formed as a result of interaction between hot mafic magma and semiconsolidated, water-rich mud, more than 350 Ma prior to formation of the Sudbury Igneous Complex and attendant phenomena that are presumed to be impact related.

The Honningsvåg Intrusive Suite consists of several layered mafic/ultramafic intrusions and a transgressive body of igneous breccia that appears to represent a magma conduit. It is emplaced into a Silurian, flysch-type sedimentary sequence that is thermally metamorphosed to spotted slate, cordierite–andalusite or pyroxene hornfels and agmatitic migmatite. Folds and flattened reduction spots in the hornfelses suggest that emplacement took place after Caledonian deformation and development of a slaty cleavage. Tectonic rotation subsequent to emplacement has led to exposure of the Honningsvåg Intrusive Suite in a natural cross-section corresponding to ∼10 km of crustal depth. Basaltic magma was initially emplaced as a several-kilometre-tall pipe that crystallized to form Intrusion 1. A second magma chamber was initiated alongside this pipe and subsequently expanded laterally into a sill-like magma body as batches of olivine-saturated basalt were added. A later magma chamber, represented by Intrusion 4, developed largely within the cumulates forming the upper part of Intrusion 2 and appears to have been accompanied by opening of a broad inclined feeder into which blocks and slabs of older cumulates collapsed. The resulting igneous breccias of Intrusion 3 are chaotic and largely clast-dominated in the lower part of the conduit, but enclosed slabs are matrix supported and orientated parallel to an originally subhorizontal banding in the feldspathic peridotite matrix in the upper part. The core of the breccia body has a troctolite matrix and contains blocks of older breccia, suggesting re-opening of the conduit, either during the crystallization of Intrusion 4 or possibly during the development of chambers represented by the younger layered intrusions. The cumulates in Intrusion 4 subsided sufficiently to invert marginal parts of the Layered Series before a further magma chamber was initiated in its roof rocks. The last major magma chamber opened alongside Intrusion 5 and extended upwards as a pipe or broad dyke to the highest structural levels exposed. Cross-cutting relationships show that the Honningsvåg magma chambers were not active simultaneously but were emplaced sequentially, generally at successively higher structural levels. Olivine tholeiite magma initially pooled in a crustal zone where it had neutral buoyancy. Subsequent chambers are suggested to have been initiated by emplacement of magma along the density discontinuities that existed above and around crystallized intrusions and their associated hornfelses. Chambers evolved by fractional crystallization, assimilation of country rocks and periodic replenishment. The abandonment of magma chambers may have resulted from the expulsion of low-density residual melts.

ABSTRACTPipe-shaped breccia bodies associated with diorite intrusions are composed mainly of angular clasts of local schists with a few transported clasts of quartzite. Plate shaped fragments are commonly oriented to define planar fabrics in the breccias. These features indicate the operation of gas fluidisation within the pipes and both entrainment and expanded bed conditions are inferred. The fabrics result from the collapse of the fluidised suspensions as the gas flow declined. Dilational fracture patterns in the country rock comparable with the stress release patterns found around mine shafts can be matched with the fractures required to produce the angular schist clasts. It is concluded that fracturing and the introduction of fragments into the fluidised breccia system was a continuous process and that the pipe diameter increased progressively with time. Microdiorite sheets and related stock like bodies of diorite cut and metamorphose the breccias. Compaction, hornfelsing and hydrothermal alteration also contributed to breccia formation.

Pseudotachylyte bodies were recently identified within and adjacent to the Early Proterozoic East Bull Lake and Shakespeare–Dunlop intrusions, located approximately 25–40 km west-southwest of the western margin of the Sudbury Igneous Complex. These breccia-like bodies locally form extensive vein networks and are preferentially developed along the contact between the intrusions and older Archean granitoid rocks. The pseudotachylyte veins comprise variable proportions of locally derived rock fragments and an aphanitic to fine-grained crystalline matrix that commonly displays flow textures. The veins appear to have formed by intense cataclasis and (or) frictional melting. These occurrences are very similar in appearance to Sudbury Breccia dykes that are observed at a radial distance of up to 80 km from the Sudbury Igneous Complex. Sudbury Breccia is widely believed to have formed as a result of the Sudbury event—a cataclysmic explosion that occurred at 1.85 Ga. The location of the pseudotachylyte veins described herein may coincide with one of the concentric bands of relatively intense Sudbury Breccia development observed to the north of the Sudbury Igneous Complex.

A field study combined with a laboratory study and 3D modeling have been performed in order to decipher the genesis of the Salau deposit W-Au mineralization (Pyrenees, France), one of the most important for tungsten in Europe. Results show the existence of two superimposed ore types, emplaced ca. 10 km depth and within decreasing temperature conditions: a calcic silicates skarn with rare scheelite and disseminated sulphides followed by a mineralized breccia with massive sulphides (pyrrhotite and chalcopyrite dominant), coarse-grained scheelite and gold, representing the main part of the ore mined in the past. This breccia is localized in ductile-brittle shear-zones which crosscut the granodiorite. U/Pb dating on zircon, apatite and scheelite, previously realized, confirmed this polyphase evolution. These two types of mineralization, linked to the emplacement of two successive intrusions as confirmed by sulphur isotopic analysis, granodioritic then leucogranitic, can be classified as belonging to the Intrusion-Related Gold Deposit type (IRGD). The emplacement of the high-grade gold and scheelite breccia was initiated by the progressive localization of the regional deformation in the Axial Zone of the Pyrenees during the Permian within E-W dextral-reverse faults.

Abstract Previous studies in Gondang Subdistricthave identified underground mud reservoirnear a rock intrusion, while another study near Gondang Subdistrict has identified deep fault structures. This study will identify the distribution and characteristics of possible geological features in the area using magnetotelluric (MT) method to further describe the relationship between the geological features related to local geology. MT data measurements were conducted on 7 stations alonga north-south line, then modelled in 2D using nonlinear conjugate gradient algorithm. The model was used to describe the subsurface resistivity distribution and to identify the geological features. The results show 5 resistive zones (20–1250 Ω⋅m) and 4 conductive zones (≤10 Ω⋅m). The former consist of 4 vertical zones, 1 vertical zone deeper than 5 km, and 1 horizontal zone near the surface. 2 conductive zones surround a resistive zone, while 2 others stretch below the horizontal resistive zone. The vertical resistive zones are interpreted as andesite intrusions, and the horizontal one as volcanic breccia. The conductive zones are interpreted consisting of tuff and marl with possible saline water content. 3 vertical intrusions are thought to have the same source, and all vertical intrusions are suspected to co-occurr with the Pandan Volcano intrusion.

Recent identification of hydrothermally altered rocks and breccia in the underexplored Montresor belt of Paleoproterozoic metasedimentary rocks suggests the possible presence of undiscovered mineralization. This study examines potential field data from the region with the goal of identifying subsurface features that could be associated with or serve as vectors to mineralization (subsurface alteration zones, faulting and (or) igneous intrusions). Gravity data were used to model regional and local geological features using known geology and physical properties from the study area and environs as constraints, and documents dense intrusive bodies underlying the Paleoproterozoic sequences. Maps of transformed apparent magnetic susceptibility values outline corridors of weak magnetization that correspond to observed zones of non-magnetic breccia and epidote–hematite–quartz alteration. Imputing the apparent susceptibility and rock property information into a magnetic forward model defines the geometry of this alteration zone, which is best explained as a northerly dipping non-magnetic or demagnetized, metasomatized intrusive sheet. The presence of previously undocumented igneous intrusions, their association with demagnetized hydrothermal breccia, and the continuity of the demagnetized zone suggests additional prospective areas within the region. This geological–geophysical framework for the nature and geometry of the Montresor belt and its surrounds highlights the importance of integrated modelling for areas with limited data.

Abstract The Richat structure (Sahara, Mauritania) appears as a large dome at least 40 km in diameter within a Late Proterozoic to Ordovician sequence. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks. Several hypotheses have been presented to explain the spectacular Richat structure and breccia, but their origin remains enigmatic. The breccia body is lenticular in shape and irregularly thins at its extremities to only a few meters. The breccia was created during karst dissolution and collapse. Internal sediments fill the centimeter- to meter-scale cavities. Alkaline enrichment and the presence of Cretaceous automorphous neoformed K-feldspar demonstrate the hydrothermal origin of these internal sediments and their contemporaneity with magmatism. A model is proposed in which doming and the production of hydrothermal fluids were instrumental in creating a favorable setting for dissolution. The circular Richat structure and its breccia core thus represent the superficial expression of a Cretaceous alkaline complex with an exceptionally well preserved hydrothermal karst infilling at its summit.

Abstract The Productora Cu-Au-Mo deposit is hosted by a Cretaceous hydrothermal breccia complex in the Coastal Cordillera of northern Chile. The current resource, which includes the neighboring Alice Cu-Mo porphyry deposit, is estimated at 236.6 Mt grading 0.48% Cu, 0.10 g/t Au, and 135 ppm Mo. Local wall rocks consist of a thick sequence of broadly coeval rhyolite to rhyodacite lapilli tuffs (128.7 ± 1.3 Ma; U-Pbzircon) and two major intrusions: the Cachiyuyito tonalite and Ruta Cinco granodiorite batholith (92.0 ± 1.0 Ma; U-Pbzircon). Previous studies at Productora concluded the deposit had strong affinities with the iron oxide copper-gold (IOCG) clan and likened the deposit to Candelaria. Based on new information, we document the deposit geology in detail and propose a new genetic model and alternative classification as a magmatic-hydrothermal breccia complex with closer affinities to porphyry systems. Hydrothermal and tectonic breccias, veins, and alteration assemblages at Productora define five paragenetic stages: stage 1 quartz-pyrite–cemented breccias associated with muscovite alteration, stage 2 chaotic matrix-supported tectonic-hydrothermal breccia with kaolinite-muscovite-pyrite alteration, stage 3 tourmaline-pyrite-chalcopyrite ± magnetite ± biotite-cemented breccias and associated K-feldspar ± albite alteration, stage 4 chalcopyrite ± pyrite ± muscovite, illite, epidote, and chlorite veins, and stage 5 calcite veins. The Productora hydrothermal system crosscuts earlier-formed sodic-calcic alteration and magnetite-apatite mineralization associated with the Cachiyuyito stock. Main-stage mineralization at Productora was associated with formation of the stage 3 hydrothermal breccia. Chalcopyrite is the dominant hypogene Cu mineral and occurs predominantly as breccia cement and synbreccia veins with pyrite. The Alice Cu-Mo porphyry deposit is characterized by disseminated chalcopyrite and quartz-pyrite-chalcopyrite ± molybdenite vein stockworks hosted by a granodiorite porphyry stock. Alice is spatially associated with the Silica Ridge lithocap, which is characterized by massive, fine-grained, quartz-altered rock above domains of alunite, pyrophyllite, and dickite. Rhenium-Os dating of molybdenite indicates that main-stage mineralization at Productora occurred at 130.1 ± 0.6 Ma, and at 124.1 ± 0.6 Ma in the Alice porphyry. Chalcopyrite and pyrite from Productora have δ34Ssulfide values from –8.5 to +2.2‰, consistent with a magmatic sulfur source and fluids evolving under oxidizing conditions. No significant input from evaporite- or seawater-sourced fluids was detected. Stage 3 tourmalines have average initial Sr of 0.70397, consistent with an igneous-derived Sr source. The Productora magmatic-hydrothermal breccia complex formed as a result of explosive volatile fluid release from a hydrous intrusive complex. Metal-bearing fluids were of magmatic affinity and evolved under oxidizing conditions. Despite sharing many similarities with the Andean IOCG clan (strong structural control, regional sodic-calcic alteration, locally anomalous U), fluid evolution at the Productora Cu-Au-Mo deposit is more consistent with that of a porphyry-related magmatic hydrothermal breccia (sulfur-rich, acid alteration assemblages and relatively low magnetite contents, <5 vol %). The Productora camp is an excellent example of the close spatial association of Mesozoic magnetite-apatite, porphyry, and magmatic-hydrothermal breccia mineralization styles, a relationship seen throughout the Coastal Cordillera of northern Chile.

The eight classical Monteregian hills are monadnocks on the St. Lawrence Lowlands and adjacent Appalachian foothills in a swath that sweeps 80 km eastward from Montréal. Gravity anomalies suggest the presence of about 200 km3 of mafic and ultramafic Monteregian rocks at depth. Mounts Royal, Saint-Bruno, and Rougemont are interpreted to be pluglike intrusions atop large laccoliths that were fed by magma that spread laterally along the buried Precambrian–Paleozoic unconformity. Mounts Saint-Hilaire, Saint-Grégoire, and Yamaska lie at higher stratigraphic levels in flat-lying sedimentary host rocks. These six intrusions filled the lower parts of breccia pipes formed by the explosive upward escape of volatiles. Late-stage settling of the cooling intrusions dragged downward an encircling collar of baked host rocks. The two easternmost hills (Brome and Shefford) are interpreted to be thin intrusive sheets emplaced along Appalachian thrusts. Stepwise emplacement of magma in the thick cover rocks in the east promoted contamination and may account for the presence of quartz-bearing felsic rocks. Igneous rocks along the deeply buried unconformity in the east and felsic rocks, all undetectable by gravity, could add substantially to the total volume of the Monteregians. The absence of Monteregian intrusives west of Montréal (apart from Oka) is explained by the removal through erosion of Paleozoic cover rocks. The Monteregian intrusives developed only in cover rocks; feeders in the Precambrian basement are possibly small and may be covered by Quaternary deposits. Monteregian magmatism was a major event, out of all proportion to the small intrusions presently exposed, and may have emplaced as much as 1000 km3 of igneous rock.

Several deposits of low-sulfide Pt–Pd ores have been discovered in recent decades in the Paleoproterozoic Fedorova–Pana Layered Complex located in the Kola Region (Murmansk Oblast) of Russia. The deposits are divided into two types: reef-style, associated with the layered central portions of intrusions, and contact-style, localized in the lower parts of intrusions near the contact with the Archean basement. The Kievey and the North Kamennik deposits represent the first ore type and are confined to the North PGE Reef located 600–800 m above the base of the West Pana Intrusion. The reef is associated with a horizon of cyclically interlayered orthopyroxenite, gabbronorite and anorthosite. The average contents of Au, Pt and Pd in the Kievey ore are 0.15, 0.53 and 3.32 ppm, respectively. The North Kamennik deposit has similar contents of noble metals. The Fedorova Tundra deposit belongs to the second ore type and has been explored in two sites in the lower part of the Fedorova intrusion. Mineralization is mainly associated mainly with taxitic or varied-textured gabbronorites, forming a matrix of intrusive breccia with fragments of barren orthopyroxenite. The ores contain an average of 0.08 ppm Au, 0.29 ppm Pt and 1.20 ppm Pd. In terms of PGE resources, the Fedorova Tundra is the largest deposit in Europe, hosting more than 300 tons of noble metals.

AbstractThe Triassic Lashly Formation occurs to the east of Mount Brooke at Coombs Hills. Previously established informal members B, C, and D of the Lashly Formation are now identified at Coombs Hills. Lashly Formation member D passes up into a poorly exposed interval of silicic shard-bearing fine-grained sandstone and tuff, which is correlated with the Jurassic Shafer Peak Formation of north Victoria Land and Hanson Formation of the Beardmore Glacier region. Lashly Formation members C and D are intruded by three phreatic explosion pipes, resulting from emplacement of Ferrar Dolerite intrusions at depth and associated explosive steam generation. These pipes, ranging up to 180 m in horizontal dimension, comprise sedimentary clasts in a sand matrix, most of which was locally derived. Pipe margins are mainly ill defined and adjacent country rock is commonly disaggregated or shattered, although retaining stratigraphic order. Locally, thin basalt intrusions have interacted with coal beds.

Abstract The Cipatujah area is part of the Southern Mountains of West Java which has diverse and unevenly distributed lithology. The lithology that dominates the Cipatujah and surrounding areas originate from the volcanic activities such as lava, volcanic breccias, tuffs, and intrusions. While the sedimentary rocks that compose them are limestone and sandstone rocks. The lithology that dominates the southern region is carbonate sedimentary rocks, which are represented by sandstone units. In the northern part, the lithologies are dominated by deposition results volcanic activity consists of various materials originating from andesitic lava units that extend to the east of the research area, while the volcanic breccia deposited from north to the west of the research area. There is a tuff unit layer above the volcanic breccia to the south. In the eastern area deposited carbonate rock units that form the karst landscape. Lithology characterization and determination of rock units in the Cipatujah area were carried out using image processing techniques from color composite bands from Landsat-8 (OLI) data. Geological analysis using SWIR-2 (7), SWIR-1 (6), and blue (2) composite bands and lithology using near-infrared (5) composites SWIR-1 (6), and SWIR-2 (7) bands. Then the analysis results are examined with geological data from the mapping that has been done before. Approach to band composite analysis by verifying geological data taken directly to help improve the identification and validation of better and more measured lithological distribution.

Batur paleovolcano is located in Wediombo Beach area, Gunungkidul Regency, Yogyakarta and is being part of Wuni Formation. Several volcanic products including lava flow, autoclastic breccia and volcanic breccia can be found associated with diorite intrusions. This research is aimed to characterize geological, mineralogical andgeochemical variations of igneous rocks from Batur paleovolcano to understand its petrogenesis. Detailed geological mapping with scale of 1:12,500 is conducted to identify geological aspects and delineate igneous rocks distributions. Igneous rocks and selected wall rocks samples were prepared for laboratory analysis including 8 samples for petrography and 5 samples for ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) analysis. Several geochemical data from previous study are also added to investigate the geochemical variations. Geological condition of the research area consists of four rock units including colluvial deposit, limestone, andesite lava and diorite intrusion. Geological structures found are normal fault and shear joint where the main stress direction is north–south. Petrography analysis showed that igneous rocks in this research area consist of diorite intrusion and andesite lava with phorphyritic texture. Plagioclase become the most abundant minerals found both as phenocryst phase and groundmass. Hornblende only occur as phenocryst phase in minor amounts as accesory mineral. Major elementsgeochemistry analysis showed the rocks are characterized by intermediate silica with low alkali content. They are can be categorized as calc-alkaline series. However, some samples are fall into tholeiitic series. Major elements variation and textural study also indicate the magma is experienced differentiation process by fractional crystallization mechanism. This study suggests that igneous rocks from Batur paleovolcano is formed by two phases of formation. Earlier phase is the formation of andesite lava in island arc tholeiitic tectonic setting then at the later phase is formation of diorite intrusion in the calc-alkaline basalts tectonic setting.

ABSTRACTThe area lies within a ∼15 km-wide compartment of polyphase-deformed Dalradian (Neoproterozoic) rocks, bounded by the NE-trending Tyndrum and Ericht–Laidon transcurrent faults. Sinistral movement on these faults caused a periclinal structure, the Orchy Dome, to develop from flat-lying Dalradian rocks. This dome controlled the spatial distribution of lamprophyre intrusions and explosion breccia pipes, before being cross-cut by a network of near-vertical faults. Some of these faults are host to giant, segmented, quartz-breccia veins up to 5 km long and 19 m thick, formed by cyclic injection of over-pressured Si-rich fluid into newly-formed faults. The quartz-breccia bodies consist of a plexus of quartz veins with cockade and vuggy textures, indicative of open-space, high-level crystallisation. The faults comprise a NE-trending set of mineralised veins, including the Cononish Au–Ag deposit, and two pairs of conjugate [NW- and NE-trending] and [NNW- and NNE-trending], generally non-mineralised, faults. Their geometry is that predicted by the Coulomb model for Riedel R and R′ shear fractures, modified by variations in pore fluid pressure. They were active c. 430–425 Ma ago, coincident with emplacement of the Lochaber Batholith, whose buried extension, together with the mantle, probably provided the bulk of the fluid needed to form the veins.

This paper provides a comprehensive synthesis of virtually all units and events of Early and Middle Proterozoic age in the Yukon, spanning ~1 Ga. Early and Middle Proterozoic time was dominated by a series of extensional-basin-forming events punctuated by orogenesis, magmatism, and hydrothermal activity. Basinal deposits include the Wernecke Supergroup (>1.71 Ga), Pinguicula Group (~1.38 Ga), and Mackenzie Mountains Supergroup (1.00–0.78 Ga). Igneous rocks include the Bonnet Plume River Intrusions (1.71 Ga), Slab volcanics (≥1.6 Ga), Hart River sills and volcanics (1.38 Ga), and Bear River (Mackenzie) dykes (1.27 Ga). A voluminous hydrothermal event generated the widespread Wernecke breccias at 1.60 Ga. The Racklan orogeny deformed the Wernecke Supergroup prior to emplacement of the Wernecke Breccia. The Corn Creek orogeny deformed Mackenzie Mountains Supergroup and older rocks prior to deposition of the Windermere Supergroup (<0.78 Ga). Long intervals with scanty rock records extended for as much as 300 Ma and appear to represent periods of crustal stability and subaerial conditions. By the time of Windermere rifting (<0.78 Ga), the supracrust of northwestern Laurentia was a mature, largely denuded orogenic belt with a composite sedimentary–metamorphic–igneous character. New isotopic data include Nd depleted mantle model ages for the Wernecke Supergroup (2.28–2.69 Ga) and Wernecke Breccia (2.36–2.96 Ga), a U–Pb zircon age for a Hart River sill 1381.9+5.3-3.7 (Ma), detrital U–Pb zircon ages from the basal Pinguicula Group (1841–3078 Ma), detrital muscovite ages from the Mackenzie Mountains Supergroup (1037–2473 Ma), and muscovite 40Ar/39Ar cooling ages from the Wernecke Supergroup (788 ± 8 and 980 ± 4 Ma).

Tue Kærven Syenite Complex is recognized as the earliest intrusive body in the Kangerdlugssuaq region associated with the opening of the proto-Atlantic Ocean in the Lower Tertiary. Earlier investigations of the geology of the Kærven Syenite Complex have interpreted the intrusion as a single igneous body, emplaced subsequent to the Kærven Gabbro and in turn cut by the Kangerdlugssuaq intrusion. Preliminary sampling on Kærven in 1977 revealed a relatively large range of rock types in the complex (syenite - alkali feldspar syenite - alkali feldspar granite). Tue field work conducted in 1986 has verified these findings and enabled the distinction of 8 intrusive events within the complex. Further, a preliminary geological map has been produced. An igneous breccia separates the complex from the earlier Kærven Gabbro along parts of the eastern and southern margins. The central part of the Kærven Syenite Complex include an hitherto unrecognized slice of Precambrian basement gneisses with numerous approximately N-S trending basaltic dykes. This is multiply intruded by syenite. Most notably in the eastern part of the complex, intimate associations of brecciated and remobilized basement gneiss and melts of syenitic through monzonitic to tonalitic composi­tions are found. The form of the intrusive bodies are more or less dyke-shaped and N-S trending. Toere is a general stratigraphic younging to the SW, which is matched by the tater adjacent Kangerdlugssuaq intrusion. Tue intrusive sequence and trend of the intrusions are thought to be closely related to an extentional tectonic regime present in this part of the fjord for a considerable period onwards from the earliest Tertiary magmatic activity in the area.

Abstract The Saint-Gilles breccias, on the western flank of Piton des Neiges volcano, are clearly identified as debris avalanche deposits. A petrographic, textural and structural analysis of the breccias and inter-bedded autochthonous lava flows enables us to distinguish at least four successive flank slides. The oldest deposit sampled the hydrothermally-altered inner parts of the volcano, and has a large volume. Failure was favored by the presence of a deep intensely-weathered layer. The younger deposits are from superficial sources, as their products are rarely hydrothermalized and are more vesicular. The breccia formation, and especially the progressive breaking up occurring during the debris avalanche displacement, indicates the existence of high speed transport. In the Cap La Houssaye coastal area, abrasion and striation of the underlying lava formation, as well as the packing features observed in the breccia, are considered to be deceleration structures. Introduction Huge landslides of volcano flanks, whether or not initiated by magmatic intrusions, have been recognized as catastrophic events since the 1980 Mount St Helens eruption. On oceanic shield volcanoes, the contribution of failure to the edifice-building process was proposed by Moore [1964] and suggested elsewhere for Hawaii [Lipman et al., 1985 ; Moore et al., 1989], Reunion island [Lénat et al., 1989], Etna [McGuire et al., 1991], and Canarias [Carracedo, 1994, 1996 ; Marty et al., 1996]. This contribution is particularly obvious in island volcanoes showing a U-shaped caldera open to the ocean. Several mechanisms inherent to the causes of failure have been proposed, such as dyke intrusion [McGuire et al., 1990 ; Iverson, 1995 ; Voight and Elsworth, 1997], caldera collapse [Marty et al., 1997], or volcanic spreading [Borgia et al., 1992 ; van Wyk de Vries and Francis, 1997]. Invariably, other factors have been proposed as favorable to volcanic destabilization, such as the probable occurrence of deep low-cohesion layers due to the existence of pyroclastic or hyaloclastic layers [Duffield et al., 1982 ; Siebert, 1984] or an old basement. Gravity spreading models are now frequently proposed to explain the destruction of volcanic edifices [Borgia et al., 1992 ; Merle and Borgia, 1996 ; van Wyk de Vries and Borgia, 1996 ; van Wyk de Vries and Francis, 1997], most of them taking into account basal or intra-volcanic weakness zones. We propose that in such a scenario, density heterogeneity should be an important factor governing the slow evolution of the volcanic pile. Clague and Denlinger [1994] proposed a olivine-rich ductile basal layer that influences the stability of volcano flanks. On Reunion island, a large volcanic landslide has been proposed to explain the peculiar morphology of Piton de la Fournaise-Grand Brûlé [Vincent and Kieffer, 1978]. Bathymetric surveys [Bachèlery and Montagionni, 1983 ; Lénat et al., 1989, 1990 ; Cochonnat et al., 1990 ; Lénat and Labazuy, 1990 ; Labazuy, 1991 ; Bachèlery, 1995 ; Ollier et al., 1998] have confirmed the offshore occurrence of debris avalanche deposits. Similar deposits are also known to exist along the western, northern and southwestern submarine flanks of the Piton des Neiges volcano. Unlike other deposits showing inland prolongation, “Saint-Gilles breccias” displays a well-preserved and non-weathered texture and structure. Because of striking analogies between the “Saint-Gilles breccias” and, for example, the Cantal stratovolcano debris avalanche deposits [Cantagrel, 1995], we conclude that these formations are the products of repeated avalanches during the Piton des Neiges basaltic period [Bachèlery et al., 1996]. We propose an interpretation of their origin, emplacement mechanism and their role in the evolutionary process of the western flank of Piton des Neiges. Volcano-structural setting Mechanical instability of oceanic volcanic edifices generates huge flank landslides, with lateral and mainly submarine transport of sub-aerial materials. These landslides participate in the building of the lower submarine slopes of the volcano. Geophysical surveys have detected low cohesion materials in most offshore Reunion island areas [Malengrau et al., 1999 ; de Voogd et al., 1999 ; Lénat et al., 2001] showing that these materials have largely contributed to the construction of offshore Reunion Island. Such deposits are also found in the inner part (“Cirques”) of Piton des Neiges [Maillot, 1999]. On the other hand, electric and electromagnetic soundings have revealed a deep extending conductor within the Piton de la Fournaise volcanic pile [Courteaud et al., 1997 ; Lenat et al., 2000]. Interpretations about the nature and origin of this conductor depend on its location. In the central caldera zone, as revealed by SP positive anomalies [Malengrau et al., 1994 ; Zlotnicki et al., 1994], the hydrothermal and magmatic complex is probably responsible for the observed low resistivities. Along the flanks, such a hypothesis may not be realistic. Courteaud [1996] suggests the occurrence of a deep argilized layer of volcano-detritic origin. In any case, the hydrothermal complex with high fluid pressures and secondary minerals appears as a potential weak zone that may contribute to the volcano’s instability [Lopez and Williams, 1993 ; Frank, 1995]. Chronology and stratigraphy Extent of the debris avalanche deposits The various breccias found at the western end of Reunion island, on the Piton des Neiges volcano flank, cover a 16 km2 area between Cap Marianne and Saint-Gilles (fig. 1). They are overlain upwards (&gt; 250 to 300 m) by trachyandesitic (mugearite) lava flows of Piton des Neiges differentiated series [Billard, 1974]. Some restricted breccia outcrops in deep valleys from Bernica to the north up to l’Hermitage to the south indicate the existence of larger extension of the debris avalanche deposits. Furthermore, breccias with similar “Saint-Gilles” facies appear down the Maïdo cliff to Mafate “Cirque” at an altitude 1300 m, beneath 600 m of mugearite and some olivine basalt flows. Unpublished electromagnetic data (CSAMT soundings) confirm the inland continuity of the “Saint-Gilles breccias” up to the Maïdo along the Piton des Neiges western flank, hidden by mugearitic flows. Available bathymetric surveys offshore Saint Paul – Saint Gilles areas show the obvious underwater prolongation of “Saint-Gilles breccias” : a shallow depth (&lt; 100 m) plateau followed by a slope with hummocky surface down to 2 500 m depth [Bachèlery et al., 1996 and fig. 2]. From this data, the total surface of “Saint-Gilles” debris avalanche deposits is estimated as more than 500 km2. Chronology A coastal cliff, from Ravine Bernica to Boucan Canot, provides the best outcrop of the northern part of “Saint-Gilles breccias”, with a clear inter-bedding of breccia units and lava formations (photo 1and fig. 3). – The lower breccia unit (Br I), of unknown thickness, has a remarkable friable aspect and a grayish color. – The first autochthonous lava formation (L1) consists in thin pahoehoe olivine basalt flows filling large valleys dug into “Br I”. The top of this formation is striated by the overlying “Br II” unit (photo 2). – Breccia unit “Br II” is interbedded between L1 and L2 olivine basalts. More compact and massive, “Br II” is characterized by a reddish matrix and dark blocks, with many curved fracture surfaces. – On “Br II” or directly on L1, picritic basalt flows L2 are found, filling narrow valleys. – Breccia unit “Br III” lies on “Br II” with a striking sheared contact plane visible along the main road (photo 3). It is a typical debris avalanche deposit with large imbricate blocks within a fine-grained beige matrix. – Once again, basaltic flows of lava formation L3 fill a valley dug into “Br III” near Petite Anse river. – Breccia unit “Br IV” rests on L3 at Petite Anse, but its contact with “Br III” elsewhere is not clear. The facies of this unit is very similar to the “Br III”. All the breccia units are covered by basaltic and trachyandesitic flows from the end of the Piton des Neiges basaltic series, and differentiated series. In the Saint-Gilles river, two formations are superposed : picritic basalts (L4) have flowed on the “Br IV” breccia unit, latter aphyric trachy-andesitic (mugearite) flows (L6) overlapped L4 and the breccia landforms, reaching in places the coastal area. To the north, at Plateau Caillou, plagioclase-phyric basalt flows (L5) are found between mugearite and breccias. Elsewhere on Piton des Neiges, such flows are symptomatic of the transition from the basaltic series to the differentiated series [Billard, 1974]. The occurrence of autochthonous basaltic formations L1 to L3, inter-bedded with “Saint-Gilles breccias”, enables us to distinguish at least four superposed breccia units. Although the emplacement age of the lower “Br I” is not known precisely, it is overlain and therefore older than Cap Marianne pahoehoe lavas (L1) dated at 0.452 Ma [Mc Dougall, 1971]. On the other hand, the upper breccia units are younger than the pahoehoe olivine basalt at Cap la Houssaye dated at 0,435 Ma but older than L5 plagioclasic basalts dated at 0.35 Ma. Geological description of the “breccia sequence” In the synthetic lithologic log (fig. 4) of the Saint-Gilles area, autochthonous lava formations are clearly broken into four separate breccia units. Lava formations. – L1 formation consists of numerous thin pahoehoe olivine-rich to aphyric basaltic flows. Both L2 and L3 formations are characterized by a few thicker (decametric) olivine (frequently picritic) basalt flows. Breccia units. – All breccia units display common characteristics such as the universal association of two facies (photo 4) : (i) a matrix – sandy to silty – facies containing a non-sorted mixture of non-stratified heterogeneous materials ranging from granular size to blocky elements, (ii) coherent large blocks and large pieces (‘block’ facies) of various lithology such as lava flow, scorias, pyroclastics or other breccias ; blocks displaying frequent “jigsaw” features. The lower breccia unit “Br 1” (fig. 4) has a more compact but very heterogeneous aspect, with a chaotic distribution of blocks in a less-developed matrix. This unit is characterized by a deep hydrothermal alteration with a lot of zeolites, chlorite, clays, calcite and oxides. The upper breccia units, “Br II” to “Br IV” (fig. 4) are less heterogeneous than “Br I” because their matrix facies are more voluminous and because the matrix clearly separates the bigger blocks. In both facies, a great diversity of fresh lithologic types such as picritic basalt, olivine-phyric basalt, plagioclase-phyric basalt and aphyric more or less vesicular basalts, gabbro, dunite are found, with no or only few slightly zeolitised blocks. Plurimetric to metric blocks are severely fractured, disintegrated into millimetric to decimetric angular pieces. The frequent polygenic aspect is due to block juxtaposition or imbrication. The abundant matrix is composed of crushed rocks and mineral elements, fine-grained (&lt; mm), showing frequent fluidity and bedding marks (photo 5). The very heterogeneous composition of the matrix is confirmed at a microscopic scale. On the contrary, cores of blocks appear as jigsaw-puzzle-like monolithologic pieces of various basaltic rocks. At their edges, disintegration leads to progressive mixing with neighboring blocks that feed the matrix. Discussion Originality of “Saint-Gilles breccias” “Saint-Gilles breccias” constitute one of the few cases [see also Cantagrel et al., 1999] of debris avalanche deposit outcroppings on the sub-aerial part of an oceanic shield volcano. The main part of the deposit is suspected to be offshore. Their hummocky surface in delineating parallel ridges can be compared to the one described offshore the Grand Brûlé area, east of Piton de la Fournaise [Bachèlery et al., 1996]. “Saint-Gilles breccias” were deposited after several Piton des Neiges flank slide events that were separated by basaltic flows. Repeated debris avalanches have also been proposed to explain Piton de la Fournaise offshore deposits [Lenat et al., 1990 ; Labazuy, 1991]. The occurrence of autochthonous interbedded lava formations is essential to interpret the thick piling up of slide material along Reunion volcano flanks as deposits of repeated avalanches at the same place, instead of as being the products of a single huge event. Many structural and textural features noticed in the upper breccia units reveal crucial information on the emplacement mechanism of debris avalanches. For instance, brecciated blocks are typical of progressive break-up during transport processes. Blocks can simply be fractured, or they can be so severely disintegrated that stretching and mixing with other blocks and matrix formation are observed. The observation of such phenomena implies the existence of numerous percussive events between rocks, as well as internal vibrations in the debris avalanche and therefore the existence of high-speed transport. Lava formations L1 underlying upper breccia units are truncated and strongly striated in a seaward direction (photo 2), parallel to the breccia morphological ridges. In the same way, internal contact surfaces between upper breccia units are shear planes underlain by cataclastic layers and lenses (photo 3). Such structures are interpreted as due to drastic deceleration effects of avalanches reaching a topographic leveling out in the coastal area. This concords with the occurrence of sub-vertical contact areas between the blocks and the matrix. These injections of matrix between the blocks are generated bottom-up from the shear plane at the moment of the sudden deceleration of the avalanche. Other fracture planes that are in accordance with the morphology of ridges, are found in “Br III” unit (see fig. 5). They are interpreted as the result of packing effects. Origin of flank failures Although the source area of breccia formations has not yet been clearly identified, it has to be in the central part of Piton des Neiges as seen in the western cliff of “cirque de Mafate”. Furthermore, “Br I” deeply weathered materials evidently come from the hydrothermalized core of the volcano. Though the “Br I” thickness is not known, the volume involved may be considerable and a part of this volume must constitute the main body of Saint-Gilles offshore deposits. The upper breccias units “Br II” to “Br IV” display very similar textures and lithologies, with dominant non-altered basaltic rocks from the “Phase II” building stage of Piton des Neiges [Billard, 1974]. These units are very thin in the coastal area of Cap La Houssaye (see fig. 2) despite a proximal facies (meaning a deposit in the transport zone nearer than the main deposit zone). They obviously originate from shallow flank slides of restricted extent. We suggest that the upper Saint-Gilles deposits are due to repeated events that produced thin high-speed debris avalanches. Emplacement modalities The morphology of “Saint-Gilles breccias”, or submarine deposits offshore Grand Brûlé (east of Piton de la Fournaise volcano), are typical of sliding movements along shallow depth shear planes (several hundred meters up to two kilometers) within the volcanic pile. But several levels of decollement are suggested by seismic refraction and reflection profiles offshore La Reunion, the deepest corresponding to the top of the preexisting oceanic sediments [de Voogt et al., 1999]. Until now, in Reunion Island, only shallow failures affecting the upper parts of volcanic edifices, with deposits on the lower slopes, have been positively identified. Conditions that trigger giant flank landslides affecting oceanic shields remain poorly understood but we can reasonably speculate that weak hydrothermally-altered layers in the inner part of the volcano favor these gravity-driven processes related to repeated dike injections. The “Saint-Gilles breccia” sequence is considered as a multiphase lateral collapse structure whose first event (“Br I”) was apparently the most voluminous. The corresponding deposit displays frequent hydrothermally-altered material symptomatic of originating from the Piton des Neiges core. Within Piton des Neiges, the low cohesive weathered layer is quite extensive [Nativel, 1978 ; Rançon, 1982] possibly reaching down the volcano flanks [Courteaud et al., 1997]. The interpretative scheme that we propose (fig. 6) in our evaluation of the conditions for the emplacement of Saint-Gilles sequence, takes into account the existence of such a mechanical discontinuity within the volcanic pile. We propose that the massive landslide failure of the west flank of Piton des Neiges volcano that produced the “Br I” breccia, provided efficient channels for younger Piton des Neiges lavas to reach the western and southwestern coastline. Morphological features, as well as radiometric data [Mc Dougall, 1971 ; Gillot and Nativel, 1982] and magnetic surveys [Lénat et al., 2001], yield evidence for preferential accumulation of lava during the last 0.5 m.y. (corresponding mainly to the differentiated series) in this part of the volcano. The relative asymmetry of Piton des Neiges was acquired by rift migration in response to the first huge landslide that produced the “Br I” unit of “Saint-Gilles breccia”, in the manner described by Lipman et al. [1990] for Mauna Loa volcano in Hawaii. The later repetition of flank collapses is consistent with similar structures on other oceanic islands. Since the first lateral collapse, the Piton des Neiges edifice was probably characterized by the existence of an asymmetrical steeper western flank where the old zeolite-rich “Br I” deposits possibly act as a detachment surface for later successive landslides which may have occurred recurrently over a short time interval.

The need for alternative energy other than fossil energy is felt to be increasingly urgent for the fulfillment of domestic electrical energy. In meeting the demand for electricity, the government needs to investigate alternative geothermal energy, to find out the potential for geothermal energy to provide electricity. The realization of this policy is that the government conducts an integrated geothermal investigation to find prospective geothermal areas that can be developed as electric power. Nokilalaki District, Sigi Regency, Central Sulawesi Province is one area that has geothermal potential in Indonesia. The Kadidia geothermal area, Sigi Regency, Central Sulawesi Province is one of the volcanic geothermal fields that have good potential and needs to be investigated further, especially on geological conditions that affect the presence of geothermal energy. The research method used is the method of analyzing the results of field observations. From the observations, it can be concluded that the geomorphology of the research area is divided into Tongoa hills, Nokilalaki Granite Intrusions, Kamamora Hills, and Kadidia Alluvial Plains. The stratigraphy of the study area from old to young consists of Breccia, Sandstone, Granite Intrusion A, Granite Intrusion B, Granite Intrusion C, and Alluvial Plain. The geological structure of the study area consists of the Kamamora sinistral shear fault and the Kadidia dextral shear fault. The geological history of the study area begins in the early Miocene which is the beginning of the movement of the Palu - Koro fault.

Abstract Pandan volcano is one of the dormant Quaternary volcanoes in East Java characterized by several volcanic centers which extend to the northern part. This study is aimed to identify the volcanic rocks and intrusions of Jari - Krondonan area, Bojonegoro as well as determine their petrology and mineralogical characteristics. Geological observation was conducted to obtain primary data and to collect samples. Thin section of samples was prepared to analyze the petrographic aspects. Field observation shows several volcanic hills at Mount Jati, Mount Puru, Mount Watu, and Mount Lawang sites. Based on field mapping, lithologies of the research area are andesitic lava and intrusion with columnar joint or sheeting joint structure, surrounded by andesitic breccia. Andesite characterized by porphyritic texture with visible phenocrysts and volcanic glass groundmass. Samples from Mount Lawang and Mount Watu are composed of plagioclase and hornblende as main minerals. Samples from Mount Jati and Mount Puru are composed of plagioclase and pyroxene. Quartz, sanidine, and olivine present as accessory minerals. Plagioclase and pyroxene occasionally formed glomerocryst and poikilitic texture, which play an important role in the fractionation and crystal settling processes. Sieve and regular zoning in plagioclase suggest magma mixing. Gabbro and metamorphic xenoliths found in Mount Lawang and Mount Watu indicates an interaction with country rock during magma rising.

The gold-sulfide deposit Southern Ashaly is localized in carbonaceous terrigenous formation (black shale strata) of the middle carboniferous (Bukon suite, which is the ore-hosting for super large deposit Bakyrchik). The Southern Ashaly is at the exploration stage and according to preliminary estimates of the expected resources belongs to a large deposit in scale. Ore gold mineralization of such level as Southern Ashaly in southwestern Kalba is found for the first time and gives hope for the discovery of such objects in the Boko Vassilyevskoye ore field. Ore-hosting at the field Southern Ashaly is carbonaceous terrigenous formation of the middle carboniferous, with no visible signs of volcanic formations. But, it was revealed, at microscopic research by us, paragenetic relation of the gold mineralization with small intrusions of plagiogranites and zones of plagiogranite porphyry dykes and found volcano-sedimentary rocks (aleuritic tuffsandstone, tuff breccia) which have undergone hydrothermal-metasomatic changes. The vein-disseminated gold-sulfide mineralization is associated with beresitizated plagiogranites and plagigranite-porphyries and hydrothermally altered tuff sandstones, tuff breccia and carbonaceous shales. Southern Ashaly unlike Bakyrchik deposit which contains invisible gold in sulfides, all the gold is concentrated in the pyrite mainly in the form of micro-sized (1-5 µm or less) in arsenopyrite is noted rarely.

A comparative description of two sulfide copper-nickel deposits confined to the middle massifs is given: Aguablanca (Iberian Massif, Spain) and Shanuch (Kamchatka Massif, Russia). It was shown that both deposits are spatially and genetically related to small intrusions and dikes of mostly basic composition. Ore bodies are funnel-shaped, lenticular, stock-shaped, and vein-like, and are spread to significant depths. Both deposits contain rich sulfide copper-nickel ores as well as relatively poor; the ore texture is predominantly breccia or massive, seldom disseminated. Ore mineral composition includes pyrrhotite, pentlandite, and chalcopyrite with an insignificant admixture of minerals of the platinum group elements and gold. The ore bodies were topped with an "iron hat", which was the main sign of copper-nickel mineralization at depth.

The Paleoproterozoic East Arm Basin of Canada hosts polymetallic vein, iron oxide–apatite (IOA), and potential iron oxide–copper–gold (IOCG) mineral occurrences, mainly associated with a belt of ca. 1.87 Ga intermediate-composition sills termed the Compton intrusions. Advances in our knowledge of the East Arm Basin and of IOA and IOCG deposits within the broader context of iron oxide and alkali-calcic alteration systems enables a new regional analysis of this mineralization and facilitates comparison of these mineral occurrences and host rocks to the nearby Great Bear magmatic zone IOCG districts. The Compton intrusions and co-magmatic Pearson Formation volcanic rocks are comparable in age and composition to intrusive plus volcanic rocks of the Great Bear magmatic zone that host IOA–IOCG mineralization. Taking into account fault displacements, emplacement of Compton intrusions and Pearson Formation volcanic rocks are also consistent with the architecture of modern arcs, supporting a direct relationship with the Great Bear subduction zone. Trace element patterns of uraninite contained in IOA occurrences of the East Arm Basin are also similar to the patterns of uraninite from the Great Bear magmatic zone occurrences, consistent with both regions having experienced similar iron oxide and alkali-calcic alteration and mineralization. Our new results indicate that exploration for IOA, IOCG, and affiliated deposits in the East Arm Basin should focus on delineating increased potassic-iron alteration types and fault/breccia zones associated with these systems through field mapping and application of geochemical, radiometric, magnetic, and gravity surveys.

Abstract Surface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/39Ar total gas age of 40.64 ± 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with quartz-alunite replacement of rhyolite, ~750 m southwest of the collapse zone over the block cave of the porphyry copper deposit, are distinctly younger, at 38.12 ± 0.66 and 38.04 ± 0.22 Ma (averages of duplicate analyses, with ±2σ errors). Previously reported U/Pb ages of zircons from 15 Eocene-age diorite, granodiorite, and granite porphyry intrusions have weighted mean ages that range from about 44 to 41 Ma, with peak magmatic flux interpreted at 44 to 43 Ma. Porphyry copper ores in the El Salvador district formed at about the same time as porphyry intrusions, with intrusive centers that migrated in a south-southwest direction, from the small deposits at Cerro Pelado (~44.2 Ma), to Old Camp (~43.6 Ma) and M Gulch-Copper Hill (~43.5–43.1 Ma), to the main ore deposit at Turquoise Gulch (~42 Ma). The granodiorite porphyry intrusions at Turquoise Gulch are associated with ~80% of the known copper ore of the district; they record waning stages of magmatism at 42.5 to 42.0 Ma, followed by weakly altered latite dikes at 41.6 Ma. Molybdenite in quartz veins returned Re-Os ages of 41.8 to 41.2 Ma. The two alunite samples from our study with coincident dates of ~38 Ma provide evidence for magmatic-hydrothermal activity younger than any recognized to date, consistent with the alteration overprint of quartz-alunite on older muscovite after erosion. This younger activity must have been associated with a blind intrusion, likely located south of the Turquoise Gulch deposit, based on the distribution of alteration minerals, and offset from the zoning associated with the Turquoise Gulch center. Stable isotope values (δ34S, δ18O, δD) of the ~38 Ma alunite indicate a high-temperature hypogene origin, consistent with formation in a lithocap environment that typically is located at shallow levels over and on the shoulders of porphyry copper deposits. Both observations—alteration overprint and markedly younger age of alunite—indicate the potential for porphyry copper mineralization south of Granite Gulch, as much as 1,000 m below the level of the coeval outcropping quartz-alunite replacement, perhaps near ~2,000-m elevation; this is hundreds of meters deeper than the known copper ore of Turquoise Gulch.

Two methods of both the singular value decomposition (SVD) and the Bi-dimensional empirical mode decomposition (BEMD) were applied in extraction of gravity anomalies associated with gold mineralization in Tongshi gold field, respectively in this paper. Conclusions drawn by the comparison study are as follows: (a) The ore-controlling factor in the Tongshi gold field illustrated in the images obtained from the original gravity data by the two methods is the same that the Tongshi intrusions with a negative circular gravity anomaly and the ring contact metasomatic mineralization zone around the Tongshi intrusions with the positive gravity anomaly. (b) The two methods reveal the same spatial relationship between the ore-controlling factor and various gold mineralizations that the skarn and porphyry types of gold deposits are located within the complex pluton and the Carlin and Crypto-breccia types of gold deposits located within the contact metasomatic mineralization zone. (c) The image produced by BEMD not only reflects the structural features of the ore-controlling factor (Tongshi complex pluton), but also does the distributions of the other geological units in the Tongshi gold field such as the Mesozoic volcanic sedimentary basin in NW orientation with obvious negative gravity anomaly and the conceal metamorphic base swell in NW orientation with the positive gravity anomaly located between the Tongshi intrusions and the Mesozoic volcanic sedimentary basin. The image produced by SVD might depict in more detail the inner structure of the Tongshi intrusions and the ring contact metasomatic zone than that produced by BEMD. The higher gravity anomaly areas in island shape within the ring contact metasomatic zone may be caused by the skarn bodies with iron-copper-gold mineralization. (d) Under the constraints of the ore-forming geological setting, the results obtained from the original gravity data by combination of the two methods can depict the relationships between the ore-controlling factors and the gold mineralizations more exactly than the alternative methods.

The Archean Côté Gold Au(–Cu) deposit is the first large gold deposit discovered in the Swayze greenstone belt of the Abitibi Subprovince. The deposit is a low-grade, large-tonnage type with a combined indicated and inferred resource of 8.65 M oz Au (245.2 t Au). The deposit is hosted by the Chester intrusive complex (CIC), a multiphase, subvolcanic intrusion composed of low-Al tonalite, diorite, and quartz diorite, plus magmatic and hydrothermal breccia bodies. The age of the tonalite and dioritic phases is constrained at 2741–2739 ± 1 Ma using high-precision isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb zircon geochronology. Although these phases are co-temporal and co-spatial, they appear to be petrogenetically unrelated. The CIC was emplaced into mafic metavolcanic rocks of the Arbutus Formation whose geochemistry reflects a back-arc environment. The tonalite of the CIC is coeval and co-genetic with the felsic to intermediate metavolcanic rocks of the Yeo Formation. Emplacement of the CIC into a shallow crustal level is inferred based on the incorporation of screens and inclusions of the Yeo Formation and is supported by the presence of textures in tonalite and dioritic rocks (e.g., granophyres, miarolitic cavities, and pegmatites), as well as Al-in-hornblende geobarometry results of ≤1.3 ± 0.6 kbars (1 kbar = 100 MPa). The CIC is petrologically similar to other subvolcanic, low-Al tonalite–trondhjemite–diorite intrusions that underlie volcanogenic massive sulphide (VMS)-type deposits and which themselves may contain syn-intrusion mineralization. Several geochemically unrelated dykes and deformation events crosscut and postdate the CIC.

Abstract An intermediate-composition hydroclastic breccia deposit is exposed in the upper reaches of a deep glacial valley at Ruapehu volcano, New Zealand, indicating an ancient accumulation of water existed near the current summit area. Lobate intrusions within the deposit have variably fluidal and brecciated margins, and are inferred to have been intruded while the deposit was wet and unconsolidated. The tectonic setting, elevation of Ruapehu, and glacial evidence suggest that the deposit-forming eruption took place in meltwater produced from an ancient glacier. The breccia-lobe complex is inferred to have been emplaced at &gt; 154 ± 12 ka, during the penultimate glacial period (190–130 ka) when Ruapehu’s glaciers were more extensive than today. This age is based on overlying radiometrically dated lava flows, and by correlation with a well-constrained geochemical stratigraphy for Ruapehu. Field relations indicate that the glacier was at least 150 m thick, and ubiquitous quench textures and jigsaw-fit fracturing suggest that the clastic deposit was formed from non-explosive fragmentation of lava in standing water. Such features are unusual for the high flanks of a volcanic edifice where steep topography typically hinders accumulation of water or thick ice, and hence the formation and retention of hydroclastic material. Although not well-constrained for this time, the vent configuration at Ruapehu is inferred to have contributed to an irregular edifice morphology, allowing thick ice to locally accumulate and meltwater to be trapped.

The Djarkadougou gold prospect is located on the Birimian greenstone belt of the Houndé exploration permit held by the company Orezone Inc. The permit is at 275 km far from the capital Ouagadougou south- western Burkina Faso, West Africa. This area is based on sheared and metamorphosed greenschist facies rocks. Metamorphism locally reaches to the amphibolite facies around intrusions. There are two major lithological units whose interface is marked by a NW-SE trending shear corridor: an unit of andesite-basaltic rocks of andesitic breccias in the East and volcaniclastic and sedimentary unit composed flows, tuffs and felsic to mafic breccia, interbedded volcano-sedimentary rocks. All this together is intruded by plutonic rocks, and various felsic to mafic dykes. These rocks have undergone ductile to brittle heterogeneous deformations and hydrothermal alteration sericite ±carbonate ±quartz±sulphide within deformation corridors. The rocks of the East and West domains affected by three phases of brittle-ductile deformation (D1, D2, and D3) and the meteoric alteration is systematic in superficial facies of Djarakadougou core drilling.Geochemical analysis shows a tholeiitic to calc-alkaline volcanic serie characteristic a bimodal volcanism. The spectra of normalized REE chondrites are generally flat and constant reminding those of N-MORB basalt. The chemical compositions of andesite and basalt are deferred on several discrimination diagrams especially Th / Yb - Nb / Yb and 2 Nb - Zr / 4 - Y show that andesites and basalts of the prospect are issued in geotectonic setting of volcanism preponderant arc.

ABSTRACT The mafic-ultramafic Samapleu deposits of the Yacouba complex, which host nickel, copper sulfides, and platinum-group minerals, are located in the Biankouma-Silipou region, western Ivory Coast. These intrusions originate from the mantle and would have been established during the Proterozoic (2.09 Ga) around 22 km deep within the Archean granulites (3.6–2.7 Ga) which at least partially contaminated them. Platinum-group and sulfide minerals from the Samapleu deposits were studied using optical microscopy, scanning electron microscopy, the electronic microprobe, X-ray fluorescence, fire assay, and a Thermo Fisher Scientific Delta S isotope ratio mass spectrometer system. The sulfide mineralization (mainly pyrrhotite, pentlandite, chalcopyrite ± pyrite) is mainly disseminated with, in places, semi-massive to massive sulfide veins. It is especially abundant in pyroxenite horizons with net or breccia textures. The isotopic ratios of sulfur measured from the sulfides (an average of 0.1‰), the R factor (between 1500 and 10,000), and the Cu/Pd ratios indicate a mantle source. Thus, the sulfides would have formed from sulfide liquids produced by immiscibility from the silicate mantle magma under mafic-ultramafic intrusion emplacement conditions and with possible geochemical modification of the magmas by assimilation of the surrounding continental crust. The platinum-group minerals (michenerite, merenskyite, moncheite, Co-rich gersdorffite, irarsite, and hollingworthite) are mainly associated with the sulfide phases. The nature of the platinum-group minerals is indicative of the probable role of late-magmatic hydrothermal fluids during the mineralizing process.

Abstract In 2013, a diamond drill program tested an extensive advanced argillic alteration lithocap within the Hu’u project on eastern Sumbawa Island, Indonesia. A very large and blind copper-gold deposit (Onto) was discovered, in which copper occurs largely as disseminated covellite with pyrite, and as pyrite-covellite veinlets in a tabular block measuring at least 1.5 × 1 km, with a vertical thickness of ≥1 km. Copper and gold are spatially related with a series of coalesced porphyry stocks that intrude a polymictic diatreme breccia capped by a sequence of intramaar laminated siltstones, volcaniclastic and pyroclastic rocks, and overlain by andesite flows and domes. The porphyry intrusions were emplaced at shallow depth (≤1.3 km), with A-B–type quartz veinlet stockworks developed over a vertical interval of 300 to 400 m between ~100 and 500 m below sea level (bsl), 600 to 1,000 m below the present surface, which is at 400 to 600 m above sea level. In the area drilled at Onto, the diatreme breccia, all porphyry intrusions and, to a lesser extent, the surrounding older andesite sequence have all been overprinted by intense subhorizontal advanced argillic alteration, zoned downward from illite-smectite, quartz-dickite to quartz-alunite and quartz-pyrophyllite ± diaspore alteration. The alteration package includes two particularly well-developed zones of residual quartz with vuggy texture in subhorizontal zones at shallow depth, the upper one is still porous but the lower horizon, ~100 m thick, is largely silicified and is located at or near the top of the quartz-alunite alteration. Mineralization starts below the lowermost silicic horizon with more than 90% of the current resource in quartz-pyrophyllite-alunite and quartz-alunite alteration. Mineralization is dominated by a high-sulfidation assemblage of covellite-pyrite ± native sulfur largely in open-space fillings and replacements, but also as discrete pyrite-covellite and covellite only veins down to at least 1 km. Although the greatest amount of copper occurs as paragenetically late covellite deposited during formation of the advanced argillic alteration, approximately 60% of resource at 0.3% Cu cutoff still occurs within the porphyry stocks, indicating the porphyry stocks are a fundamental control on mineralization. There is considerable remobilization and dispersion of copper and, to a lesser extent, gold into the surrounding pre-mineral breccia and the late intermineral intrusions from the two earliest porphyry phases, resulting in quite consistent copper and gold grades throughout the currently delineated mineral resource. The very high sulfidation state of the mineralization is thought to be a consequence of the metal-bearing ore fluids cooling in the advanced argillic-altered host rocks in the absence of a rock buffer. Early chalcopyrite-bornite ± pyrite mineralization with potassic ± chloritic and sericitic alteration is only preserved on the margins of the system and more rarely at depth in a few holes 600 m bsl (~1,100 m below surface) but makes up only a small proportion (~8%) of the current resource. The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 ± 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 ± 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 ± 0.02 and 0.35 ± 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 ± 0.22 to 0.284 ± 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 ± 0.064 to 0.038 ± 0.018 Ma.

The Buchans Group, central Newfoundland, represents an Ordovician continental bimodal calc-alkaline arc sequence that hosts numerous volcanogenic massive sulfide (VMS) occurrences, including both in situ and mechanically transported sulfide breccia–conglomerate orebodies. Diverse lithic clasts associated with transported deposits include rounded granitoid clasts. Earlier workers have suggested that Buchans Group VMS-hosting felsic extrusive units, small granodiorite intrusions (e.g., Wiley’s Brook), and granitoid cobbles associated with transported ore represent co-genetic products of the same magmatic system. The granitoid cobbles and small granodiorite intrusions are geochemically similar and closely resemble Buchans Group felsic volcanic units. U–Pb zircon age determinations show a (i) 466.7 ± 0.5 Ma crystallization age for the Wiley’s Brook granodiorite (WBG), (ii) 464 ± 4 Ma crystallization age for a granitoid cobble, and (iii) 466 ± 4 Ma maximum deposition age for a conglomerate–sandstone sequence associated with transported ore. Thus, Buchans Group felsic plutonic rocks are within experimental error of felsic volcanism and VMS deposition. Furthermore, εNd (T) (T, time of crystallization) values of four granitoid cobbles (–1.95 to –4.0) overlap values obtained from Buchans Group felsic volcanic units. Our results are compatible with plutonic and volcanic rocks being related through fractional crystallization or partial melting processes but do not support a petrogenetic link between VMS deposition and exposed felsic plutons. Comparisons to modern arc analogues favour exhumation of plutonic rocks by extension along caldera or rift walls and (or) subaerial erosion. Enigmatic rounding of Buchans granitoid clasts was likely accomplished in a subaerial or shallow marine environment, and the clasts transported into a VMS-active basin by mass flows.

The Kışladağ porphyry Au deposit occurs in a middle Miocene magmatic complex comprising three different intrusions and magmatic-hydrothermal brecciation related to the multiphase effects of the different intrusions. Tourmaline occurrences are common throughout the deposit, mostly as an outer alteration rim around the veins with lesser amounts disseminated in the intrusions, and are associated with every phase of mineralization. Tourmaline mineralization has developed as a tourmaline-rich matrix in brecciated zones and tourmaline-quartz and/or tourmaline-sulfide veinlets within the different intrusive rocks. Tourmaline was identified in the tourmaline-bearing breccia zone (TBZ) and intrusive rocks that had undergone potassic, phyllic, and advanced argillic alteration. The tourmaline is present as two morphological varieties, aggregates of fine crystals (rosettes, fan-shaped) and larger isolated crystals and their aggregates. Four tourmaline generations (tourmaline I to IV) have different compositions and substitutions. Tourmaline I in TBZ and INT#1 is distinguished by the highest Fetot and enriched in Fe3+. Tourmalines II and III occur as fine aggregates, accompanied by the formation of isolated crystals and are characterized by lower Fetot and Fe3+. Tourmaline IV is characterized by the lowest Fetot, enriched in Cl, and has the highest proportion of X-site vacancy among all the tourmalines. Tourmaline I may be attributed to the potassic stage in INT#1 and early tourmaline in TBZ. Tourmalines II and III from INT#1 and the TBZ could be referred to the phyllic stage. The low Fe content in tourmaline is caused by the simultaneous deposition of sulfide minerals. Tourmaline IV from the TBZ and tourmaline II from INT#3 are distinguished by the high X-site vacancy proportion up to the formation of X-site vacant species as well as enriched in Cl; they can be attributed to the argillic stage of the hydrothermal process. The textural and especially chemical data of the tourmaline from the Kışladağ Au deposit provide information on the physico-chemical conditions during the porphyry to epithermal transition and subsequent epithermal overprinting.

Independence volcano is a major volcanic complex in the lower part of the Absaroka Volcanic Supergroup (AVS) of Montana and Wyoming. Recently reported Rb–Sr mineral dates from the complex give apparent ages of 91 and 84 Ma, whereas field relationships and the physical and compositional similarity of the rocks with other dated parts of the AVS indicate an Early to Middle Eocene age for eruption and deposition. To resolve the conflict between age assignments based on stratigraphic correlations and Rb–Sr dates, we report new paleomagnetic data and 40Ar/39Ar dates for Independence volcano. Paleomagnetic data for the stock and an andesite plug that cuts the stock are well grouped, of reverse polarity, and yield a virtual geomagnetic pole that is essentially identical to Late Cretaceous and Tertiary reference poles. The reverse polarity indicates that the magnetization of these rocks is probably younger than the Cretaceous normal superchron, or less than about 83.5 Ma. Hornblende from a volcanic breccia near the base of the volcanic pile gives a 40Ar/39Ar age of 51.57 Ma, whereas biotites from a dacite sill and a granodiorite stock that forms the core of the volcano give dates that range from 49.96 to 48.50 Ma. These dates record the age of eruption and intrusion of these rocks and clearly show that the age of Independence volcano is Early to Middle Eocene, consistent with stratigraphic relations. We suggest that the Rb–Sr mineral dates from the Independence stock and related intrusions are unreliable.

The dyke of the Papôa volcanic breccia cross-cutting the Lower Jurassic sequence of the Lusitanian Basin (West Iberia) contains granitic xenoliths. In this study, for the first time, U-Th-Pb zircon analysis of two xenoliths yielded 298±4Ma for biotite granite and of 292±2Ma for two-mica granite, indicating that the pre-Mesozoic basement of the Lusitanian Basin includes Permian intrusions. These ages are close within the margin of error of the age of the Late Carboniferous granites of the Berlengas isle that with the Late Devonian high-grade metamorphic rocks of the Farilhões isles, located northwest of the study area, which form the pre-Mesozoic basement of the Lusitanian Basin. These new geochronological findings enable it to be established that Permo-Carboniferous magmatism lasted at least 13Ma, in this region of the Appalachian-Variscan belt. Furthermore, a comparison with available data from Paleozoic tectonic units of the Appalachian-Variscan belt located both in the Iberian Massif and outside it enables the suggestion to be made that the Lusitanian Basin (Peniche) most probably rests on the South Portuguese Zone, which may also be correlated with the Rhenohercynian Zone present in southwest England, and the Meguma terrane of Nova Scotia.

The Nicola Group at Hedley, British Columbia, is a late Carnian to late Norian (Late Triassic) sequence of calcareous sedimentary and arc-related volcaniclastic rocks. It was deposited on a tectonically active paleoslope that marked either the rifted eastern margin of the shallow-marine Nicola basin or the faulted edge of an intrabasinal platform. The lower part of the Nicola Group comprises a succession of four essentially coeval sedimentary facies. From east to west across the district, these are informally named the thin (approx. 200 m), shallow-marine, limestone-dominant French Mine formation; the thicker, calcareous siltstone-dominant Hedley and Chuchuwayha formations in the central part of the district; and the thick (up to 2200 m), deeper water and argillite-dominant Stemwinder formation. These facies are all blanketed by the Whistle formation, a 1200 m thick unit of basaltic tuff and tuffaceous sediment whose base is marked by a gravity-slide megabreccia, the Copperfield breccia. The Nicola arc at Hedley was associated with two plutonic episodes. Oldest are the Hedley intrusions, which are related to economic Au skarns, including the Nickel Plate deposit, which has produced over 71 t of gold from 13.4 Mt of ore. The Hedley intrusions are similar in composition (quartz gabbro to quartz diorite) and overall metaluminous chemistry to other island-arc-generated plutons related to many Cu and Fe skarns in British Columbia, although they are less evolved. They also differ in having lower Fe2O3/FeO ratios (avg. 0.23), indicating a reduced oxidation state, and higher Ba/La and Sc/Nb ratios. A slightly younger plutonic episode produced the 193 Ma (Early Jurassic) Bromley batholith and the 194 Ma Mount Riordan stock; the latter is associated with the Mount Riordan (Crystal Peak) industrial garnet skarn. Gold skarns are preferentially developed in areas where the Hedley intrusions cut the Hedley and French Mine formations. The Au skarn ore is marked by anomalous As, Bi, Te, and Co values, and by high pyrrhotite/pyrite and pyroxene/garnet ratios. It is distinct from the ore of Fe, Cu, Mo, Pb–Zn, W, and Sn skarns by its very low Cu/Au, Zn/Au, and Ag/Au ratios (avg. 97, 18, and 12, respectively).

The texture and variety of types of breccia bodies of the ore section of the Svoboda at the Malmyzhskoye deposit have been studied and described: a large one — the complex structure of eruptive (hydrothermal-magmatic) breccias and a relatively small — the columnar body of phreatic breccias. Eruptive breccias are intra-ore with respect to gold-copper mineralization. The detrital part in them is represented mainly by metasomatically altered intrusive rocks of the 1st phase of introduction and sedimentary formations of the cretaceous Largasinsky suite. Breccia cementing material is potassium feldspar-quartz-chlorite-sericite mass, which is an intensively metasomatically altered rock of the 2nd intrusive phase of intrusion. Ore mineralization in breccias has a veindisseminated texture and is part of the clastic part of breccias and is also superimposed on the already formed breccia bodies in the process of their metasomatic alternation. Phreatic breccias formed at the final stages of the development of the porphyry system. They are distinguished by low copper and gold contents and sharp secant contacts with the rocks surrounding them. The composition of the debris is generally similar to eruptive breccia, cement is quartz-sericite-epidote-chlorite. The position of ore mineralization is similar to that in eruptive breccias, but it is manifested to a much lesser extent. According to the proposed genetic model, the formation of the body of eruptive breccias occurred as a result of fluidization of rocks located in the arches of the intrusive body, followed by the introduction of significant volumes of magmatic melt. Subsequently, when rising, the fluids interacted with the cold near-surface waters, which caused the formation of phreatic breccias. The studied features of breccia formations are in a good agreement with the classical model of copper-porphyry deposits of the world.

This paper presents the field descriptions and microscopic observations of a tectonic breccia in the basement gneiss of the Cabo Frio and Arraial do Cabo areas, State of Rio de Janeiro, Brazil, and its intrusive contact with the Early Cretaceous mafic dyke. At the sea cliff close to the Ilha do Japonês, there is an excellent contact outcrop between them. The tectonic breccia zone is 10 to 20m wide and has N30ºE direction. The breccia clasts are angular and characterized by auto-brecciation texture, and composed of breccia with similar aspect of the host tectonic breccia. The matrix is firmly consolidated by hydrothermalism and following silicification. The mafic dyke is 7 to 10m wide and of N45ºE direction. Along the contact, the dyke chilled margin featured by fine-grained basalt and prismatic joints can be observed. At the Conchas Beach and Arraial do Cabo city, there are four outcrops demonstrating the mafic dyke intrusion into the consolidated tectonic breccias. These outcrops prove that the tectonic breccias are older than the Early Cretaceous tholeiitic dykes. The fault breccias could have been formed during the brittle-phase tectonism of the last stage of the Pan-African Orogeny by hydrothermalism without magmatic activities, namely tectonic hydrothermalism. The existence of the clasts constituent of the breccia that are composed of breccia suggests that the fault movement and following hydrothermalism occurred repeatedly.

Abstract The Nova-Bollinger Ni-Cu sulfide deposit is associated with a small chonolith (tube-shaped) intrusion emplaced at lower crustal depths into granulite facies migmatite gneisses. The deposit comprises disseminated and net-textured ores within the intrusions and a high proportion of massive, semimassive, and breccia exocontact ores within the underlying country rocks. Internally disposed endocontact ores show typical magmatic textures including conventional net texture, leopard net texture characterized by the presence of centimeter-sized clots of olivine and intercumulus phases, and globular ores. Some of the globular ores show an association of sulfide blebs with clinopyroxene-carbonate intergrowths that may represent infilling of original CO2-rich vapor bubbles. The exocontact ores have an assemblage of textures indicative of emplacement into hot, soft country rocks at a large-scale melting-infiltration front. Characteristic features range from hard-walled extensional vein arrays to complex infiltrations of disseminated sulfide within chaotically folded paragneiss. Sulfide infiltration was accompanied by partial melting of the country rock, producing felsic leucosomes, some of them strongly enriched in garnet, mainly occupying vein walls and interpreted as the result of counterflow of displaced silicate partial melt. Coarse-grained pentlandite-chalcopyrite-pyrrhotite loop textures are characteristic of all ore types, down to the scale of the infiltrating sulfides within the gneisses, and are regarded as diagnostically magmatic textures generated by sulfide liquid fractionation and growth of high-temperature pentlandite by peritectic reaction between fractionated sulfide melt and early crystallized monosulfide solid solution. The highly distinctive features of the Nova-Bollinger ores are a consequence of their emplacement in the mid to lower crust under peak granulite facies conditions. Under these unusual conditions the timescales for cooling between the silicate solidus and sulfide solidus temperatures were of the order of millions of years, being controlled by the temperature-time path for the exhumation of the orogen as a whole. Sulfides solidified over a time period three orders of magnitude greater than the thousand-year timescale for the solidification of the host silicate magmas. Furthermore, timescales for deformation matched those for cooling and solidification, allowing the country rocks to undergo deformation during ore emplacement. Fluctuating strain rates during and after initial emplacement of the carrier magmas into the host intrusion caused episodes of brittle extension, allowing unusually efficient penetration of partially molten sulfide into heterogeneous, partially molten silicate country rock, resulting in an unusually extensive thermomechanical aureole compared with other mafic intrusion-hosted nickel systems globally.

AbstractQuartz veins and vein-breccias in a greywacke-shale sequence of ?Carboniferous-Triassic age were previously regarded as mesothermal silicified fault breccias, and related to an adjacent Eocene granodiorite pluton. New mapping of vein assemblages and textures, and their structural and cross-cutting relationships, demonstrates that the steeply dipping, sheeted, epithermal-textured vein array was hydraulic in origin and possibly Cretaceous in age. The main vein and breccia swarm trends for 14 km NNE along-strike and 2 km across-strike, cutting large irregular areas of silicified and brecciated sandstone, and patchy areas of pyritic, propylitic and K-feldspar alteration. Angular vein fabrics and hydraulic disruption textures indicate wedging by hydrothermal solutions, hydraulic rupture, brecciation and fragment transport, followed by open-space precipitation, in veins generally < 15 cm thick and breccias up to a few metres thick. Hydrothermal quartz, chlorite, calcite and chalcedony predominate, with variable amounts of chalcopyrite, galena, sphalerite and pyrite. Epidote, arsenopyrite, K-feldspar and andradite garnet are conspicuous in places. Breccias were pre-and syn-mineralization, whereas mineral precipitation was pre-, syn- and post-breccia formation. Hydrothermal activity was simultaneous with extensional faulting, striking NNE, and accompanied by intrusion of dacitic dykes. There followed conjugate shearing on east- and ESE-striking faults, intrusion of high-level tonalite stocks, and several phases of basaltic andesite dyke intrusion. These hypabyssal rocks were probably coeval with the Antarctic Peninsula Volcanic Group dominating Livingston Island, dated between 130 and 75 Ma. Minor copper and iron sulphide-bearing veins occur in adjacent volcanic and hypabyssal intrusive rocks. The Hurd Peninsula veins may, therefore, form part of a volcanic-epithermal hydrothermal system (adularia-sericite-quartz type), of Cretaceous age, rather than a porphyry-related system of Eocene age.

Rocks of the Bravo Lake Formation on Turtle Back Island and Pillow Island off the western coast of central Baffin Island, Nunavut, represent a well-exposed example of the mafic volcanic and intrusive sequences commonly preserved near the base of Paleoproterozoic intracratonic basins in the Archean Rae and Hearne provinces of the Canadian Shield. The Bravo Lake Formation is composed of relatively undeformed amygdaloidal pillowed flows, radial columnar and tortoise-shell jointed pillows, hydroclastic breccia, extensional partially sheeted dyke swarms, laminated mafic sediments, massive and fragmental flows, and layered and megacrystic intrusions. Volcanic structures and textures imply emplacement in a low-energy shallow (<2 km depth) submarine environment. High-temperature submarine hydrothermal alteration of the Bravo Lake Formation mobilized Ba and Rb and was subsequently followed by dry closed system prograde amphibolite-facies regional metamorphism. Selected immobile trace element and rare-earth element (REE) compositions characterize these rocks as alkali basalt, minor tholeiitic basalt, and minor fractionated intermediate rocks that display significant light REE enrichment and high field-strength element concentrations suggestive of within-plate basalts. The stratigraphic setting, volcanic and intrusive structures, and chemical compositions suggest formation during local strike-slip-related rifting, rather than a mantle plume environment. The Bravo Lake Formation and its correlatives in other Paleoproterozoic intracratonic basins indicate that crustal thinning and the resultant local rifting of continental crust was widespread throughout the Rae and Hearne provinces of the Canadian Shield during the Paleoproterozoic.

Abstract Precambrian iron oxide copper-gold (IOCG) deposits are generally encountered with multistage hydrothermal overprints and hence have complex isotopic records. Precise dating of ore-forming and overprinting events and assessment of time-resolved metal sources are fundamental for understanding ore genesis. Here, we quantify the evolution history by integrating in situ U-Pb dating of texturally constrained allanite and Sm-Nd isotope data of ores and major rare earth element (REE) minerals in the breccia-hosted Lanniping Fe-Cu deposit in Kangdian region, southwestern China. The economically mineralized breccia in Lanniping Fe-Cu deposit is characterized by pervasive and texturally destructive replacement of polymictic clasts, including host metasedimentary packages, the intruded dolerite, and pre-ore halokinetic breccia. Ore minerals in cements are mainly composed of magnetite, chalcopyrite, bornite, and variable amounts of REE-rich minerals (e.g., apatite and allanite/epidote). Two types of allanite were identified in ores. Type I prismatic allanite texturally intergrown with magnetite has a SHRIMP U-Pb age of 1728 ± 20 Ma (1σ), which matches a zircon U-Pb age of 1713 ± 14 Ma (2σ) for the dolerite clasts and provides the direct age constraint on the Fe-Cu mineralization event. Type II anhedral allanite shows complex zoning and is spatially associated with, but texturally later than, magnetite, apatite, and chalcopyrite. This type of allanite yields significantly younger SHRIMP dates of 1015 ± 33 (1σ) and 800 ± 16 Ma (1σ) for cores and rims, respectively, which correspond to discrete regional magmatic events and hence record hydrothermal overprint/remobilization events of ore minerals in the deposit. Integrated Sm-Nd isotope compositions of type I allanite, apatite, and whole ores generally align along the reference Sm-Nd isochron of 1728 Ma, further confirming the primary ore formation at ~1.7 Ga. Corresponding εNd(1728 Ma) values ranging from –2.8 to 0.3 are significantly higher than those of the host metasedimentary rocks (–9.5 to –6.2) but comparable to those of contemporaneous igneous intrusions (–0.3 to 5.3) in the region, demonstrating that REE components of the primary ores were dominantly sourced from rocks of mantle-derived affinity. Both cores and rims of the younger type II allanite grains have Nd isotope compositions consistent with the unique time-evolved line of the ~1.7 Ga ores, implying that REEs incorporated into type II allanite were ultimately sourced from the primary ores in this deposit. The combined texture, chemical, U-Pb, and Sm-Nd isotope data thus demonstrate that REE remobilization was localized during post-ore hydrothermal overprint with negligible external inputs of REEs to the primary ores in the Lanniping deposit. In this contribution, we not only date primary ore formation but also recognize several younger allanite generations that record internal metal redistributions in response to post-ore tectonothermal events. Our study highlights the potential of ore-associated REE minerals such as allanite for resolving the age of multiple stages of hydrothermal events in complex ore deposits by ion probe, provided that careful examination of textural and paragenetic relationship of ores is conducted. Our finding of these younger allanite generations also exemplifies the significance of evaluation on time-resolved metal input for better characterizing the evolution history of the IOCG deposits.

The Annieopsquotch Complex is an ophiolite that forms the Annieopsquotch Mountains of southwest Newfoundland. It contains rocks of the critical zone, gabbro zone (2.3 km thick), sheeted dyke zone (1.5 km thick), and pillow lava zone of a typical ophiolite. The zones trend northeast, face and dip southeast at approximately 50–70°, and are offset by faults.Cumulate rocks of the critical zone preserve graded layers, trough structures, and slump folds and locally are metamorphosed and deformed. The gabbro zone contains many textural varieties of gabbro, pegmatitic pods, layering, trondhjemite pods, and amphibolite near the base. It passes through a transition zone to a sheeted dyke zone that extends the full strike length of the ophiolite. Dykes trend northwest and are aphyric or plagioclase-phyric diabase. The pillow lava zone, besides pillow basalt, contains minor pillow breccia, hyaloclastite, and chert.The Annieopsquotch Complex is faulted against an Ordovician tonalite terrane to the northwest across the Lloyds River Fault and against the Victoria Lake Group to the southeast. It is cut by dykes and sills correlated with both these units. The complex is cut by two Late Ordovician gabbro–diorite intrusions and a granite of presumed Devonian age and is unconformably overlain by Early Silurian terrestrial sedimentary and volcanic rocks.Major-, trace-element, and clinopyroxene chemistry of the complex and other ophiolitic fragments between Buchans and King George IV Lake is typical of N-type MORB. These likely constituted one allochthon of Iapetus Ocean or marginal basin crust emplaced over the Ordovician continental margin of North America during the Taconic Orogeny.

AbstractThe Southern Mountains Zone of the Rum Central Complex lies inside a major ring fault and comprises an intricate association of country-rock outcrops, breccias and rhyodacite. The breccias and rhyodacite were long thought to be products of subterranean explosion and intrusion, respectively. Here, we report new observations that support re-interpretation of these units as mass movement deposits and ignimbrites. The most abundant breccias (Coire Dubh-type) consist mainly of country-rock clasts <1 m in diameter in a sand or silt matrix. Internally bedded and graded, and interlayered with sandstones and lithic tuffs, these breccias are interpreted as debris flow and stream flow deposits. Rhyodacite sheets show gradational or sharp, concordant contacts with Coire Dubh-type breccias, and display graded basal lithic tuffs and graded fiamme swarms. These sheets are interpreted as moderately to densely welded rhyodacite ignimbrites (25–100 m thick). A steep body of fragmented (fiamme-bearing) rhyodacite with intrusive non-fragmented contacts is interpreted as an ignimbrite vent system. The rhyodacite and breccia succession is over 200 m thick and unconformably overlies a structurally uplifted Precambrian basement, within which there is also evidence of later subsidence. Outcrops of potential caldera-collapse ‘megabreccia’ are more structurally consistent than previously thought, and are re-interpreted here as coherent segments of Precambrian country rock (caldera floor). The Southern Mountains Zone breccias and rhyodacites respectively reflect sedimentary and pyroclastic processes acting in response to a complex tectonic interplay of intrusion-related uplift and caldera subsidence.

Abstract Low-sulfide platinum group element (PGE) mineralization of the Norilsk-type intrusions is located within the Upper Gabbroic Series, which comprises rocks heterogeneous in texture and composition. The highest grade of 10 to 50 g/t PGEs is confined primarily to chromitiferous taxitic gabbrodolerite, which forms irregular lens- and vein-like bodies that interfinger with contact gabbrodolerite, intrusion breccia, leucogabbro, and gabbrodolerite variably enriched in olivine, from olivine free up to picritic compositions. The abundant amygdules and pegmatoidal textures in Upper Gabbroic Series taxitic rocks, as well as the high enrichment of halogen in minerals (e.g., ≤4.6 wt % Cl in apatite), indicate a higher volatile content of the local magma compared to the magma that precipitated the Main Series. The observed diversity in spinel compositions, which evolve from chromite to Cr magnetite as well as toward hercynite, titanomagnetite, and ulvöspinel, is also indicative of crystallization from a fluid-saturated mush that subsequently reacted, to varying degrees, with contaminated trapped melt and immiscible fluid. The high PGE/S ratio is a primary feature of this mineralization style, albeit the ratio partly increased during sulfide replacement and resorption. The PGE tenor of bulk sulfides calculated as ΣPGE (g/t) in 100% sulfides exceeds 160 and may reach up to 1,400 to 2,500 in low-S ores (0.2–3 wt % S), whereas the value does not exceed 42 in the Talnakh disseminated ore and ranges from 35 to 120 in the Norilsk disseminated ore (1–10 wt % S). Several PGE peaks in the vertical sections correlate well with Cu, Ni, S, and Cr peaks, as well as with observed elevated proportion of amygdules. Low-sulfide ores are composed of two primary sulfide assemblages of pyrrhotite + pentlandite + chalcopyrite and pentlandite + pyrrhotite. The primary sulfides are depleted in the heavier 34S isotope relative to sulfides of the corresponded main orebodies (e.g., mean δ34S = 8.9‰ versus δ34S = 12.3‰, respectively, in the Kharaelakh intrusion). A secondary pyrite + millerite + chalcopyrite assemblage has isotope composition enriched in 34S by 2 to 6‰ δ34S with respect to primary sulfides. The directly measured PGE content in sulfides (e.g., 11–2,274 g/t Pd in pentlandite and 0.10–33.3 g/t Rh in pyrrhotite) is within the range of the typical Norilsk-type magmatic sulfide compositions. The textural setting and diversity of platinum group minerals (PGMs) favor the hypothesis of fluid-controlled crystallization. However, the distinct PGM assemblages in Norilsk 1 and Talnakh-Kharaelakh low-sulfide ores are comparable with those of the corresponding presumably magmatic disseminated and massive orebodies. The most remarkable characteristic is the widespread Pt-Fe alloys in Norilsk 1 and their absence in Talnakh-Kharaelakh, which is interpreted to reflect better preservation of the high-temperature PGMs in Norilsk 1 in contrast to their substantial replacement in more oxidized fluid-enriched environments in Talnakh-Kharaelakh.

AbstractThe large Zijinshan high-sulfidation epithermal Cu-Au deposit, together with the adjacent Luoboling porphyry Cu-Mo deposit, constitutes a major porphyry-epithermal ore district in South China. Current debate centers on whether the Zijinshan and the adjacent Luoboling deposits are cogenetic or represent separate ore-forming events, which is a question of importance for exploration in the district. In this contribution, the magmatichydrothermal history of the relationship between Zijinshan and Luoboling is reconstructed based on new alunite 40Ar/39Ar ages from Zijinshan and zircon U-Pb ages of ore-related intrusions from both deposits. This study has been complemented by S isotope analysis on the dated alunite to assess their origin.Three types of coexisting alunite and sulfide assemblages exist at Zijinshan, namely, (1) alunite-quartz-covellite cemented breccias; (2) alunite-digenite veins and (3) banded alunite-pyrite veins. Their field occurrences and S isotope features suggest a magmatic-hydrothermal origin for alunite-quartz-covellite cemented breccias and alunite-digenite veins, whereas the origin of alunite-pyrite veins is likely to be related to magmatic steam. Given the intimate textural coexistence between sulfides and alunite, four undisturbed 40Ar/39Ar plateau ages obtained from alunite-quartz-covellite cemented breccia and alunite-digenite vein-type alunite define the timing of Zijinshan high-sulfidation mineralization from 102.86 ± 0.61 to 101.19 ± 0.60 Ma. These agree with bracketing zircon U-Pb ages of pre-ore dacite porphyry at 104.8 ± 0.9 Ma and 104.7 ± 0.5 Ma and a zircon U-Pb age of a post-ore granite porphyry dike at 99.5 ± 0.7 Ma. Combined with their field occurrences, the four alunite ages may imply episodic hydrothermal pulses and a possible time span of over 500 k.y. for the overall high-sulfidation mineralization. Two alunite samples from alunite-pyrite veins yield a slightly disturbed 40Ar/39Ar plateau age at 101.67 ± 0.61 Ma and an apparently undisturbed age at 99.91 ± 0.59 Ma, probably reflecting partial or complete thermal resetting related to the coeval granite porphyry dikes. At Luoboling, zircon U-Pb analysis yields an age of 133.6 ± 1.1 Ma for a dark, ore vein-bearing quartz-diorite porphyry sample and confirms the petrographic observation that they are xenoliths of early wall rocks for the porphyry mineralization. A granodiorite porphyry sample with abundant A-veins is interpreted as an intermineral porphyry phase, dated at 106.5 ± 1.4 Ma. This age is interpreted as the upper limit for porphyry Cu-Mo mineralization and agrees well with previously reported molybdenite Re-Os and biotite 40Ar/39Ar ages, which collectively suggest porphyry Cu-Mo mineralization and potassic alteration at Luoboling were formed within the interval between ca. 106 and 104 Ma.Taken together, the age of the Zijinshan high-sulfidation mineralization is substantially younger than the porphyry mineralization at Luoboling, and we conclude that there is no direct genetic link between the two deposits. However, the Zijinshan Cu-Au deposit is temporally associated with the deep porphyritic granodiorite, which gives zircon U-Pb ages from 102.1 ± 0.8 to 101.8 ± 0.5 Ma, overlapping with the alunite 40Ar/39Ar ages for the high-sulfidation mineralization. This finding has important implications for the ongoing exploration for the two mineralization types in the ore district and elsewhere.

The North Spirit Lake greenstone belt in the Sachigo Subprovince of the Superior Province comprises parts of three sequences of volcanic and sedimentary rocks; the main (youngest) is separated from the older sequences by an unconformity to disconformity. The belt is bounded by large granitoid batholiths and was metamorphosed under greenschist to, locally, hornblende–cordierite facies. U–Pb zircon dating was performed on volcanic, sedimentary, and plutonic rocks in order to establish an absolute chronology for the evolution of the area.A tuff breccia in the lowermost supracrustal sequence is dated at 3023 ± 2 Ma. Zircons from a tuff in the middle sequence show complex U–Pb relationships; although they do not allow a precise age determination, the data suggest that the tuff formed sometime between 2950 and 2800 Ma ago. Zircons from a quartz arenite, also in the middle sequence, yield a simple data pattern and define an age of [Formula: see text], suggesting derivation of the sediment from a uniform source of this age. A zircon analysis from a tonalitic clast in a conglomerate at the base of the upper sequence yields a minimum age of 2975 Ma. The clast may have had the same origin as the zircons in the quartz arenite. Another tonalitic clast from the same conglomerate yields a slightly older age of 3001 ± 3 Ma. No remnant of these tonalites can be recognized in the field, suggesting that they have been largely removed during subsequent erosional processes.Two subvolcanic intrusions from the upper sequence yield zircon ages of 2743 ± 2 and 2731 ± 2 Ma, respectively. A crystal tuff, also in the upper sequence, contains two generations of zircons: newly formed magmatic zircons, which date the extrusion of the tuff at 2735 ± 10 Ma, and older grains with a minimum age of 2862 Ma, which represent inherited zircons. This tuff was thus generated at least in part by anatectic melting of >2862 Ma crust.A quartz diorite from MacDowell Lake in the adjacent Berens River Subprovince yields an age of 2744 ± 2 Ma. A mafic inclusion in the quartz diorite contains amoeboidal, strongly fractured zircons, which point to an intercept age of about 2727 Ma. This age could either reflect a metamorphic event or represent a geologically meaningless mixed age.

Gajah Volcano and Ijo Volcano are two tertiary volcanoes located in the Kulon Progo Dome area, Yogyakarta. Gajah Volcano is located in the middle of the Kulon Progo Dome which is the oldest in the complex and belongs to Early Oligocene volcanism period (± 29 mya). On the other hand, Ijo Volcano is a product of younger volcanism period, occurred in the Late Oligocene (± 25 mya). The tectonic deformation occurred during the Late Oligocene-Early Miocene led to the formation of geological structures like faults and joints, which also serve as pathway for acid-intermediate intrusion rocks. The intrusions are associated with hydrothermal alteration and ore mineralization in both volcanoes. There has been no research comparing the characteristics of hydrothermal deposits that formed on Gajah Volcano and Ijo Volcano. This will be the main objective of this research. The research was carried out at two mineralization prospect locations representing each volcano, namely the Kaligono area (Gajah Volcano) and the Hargorojo area (Ijo Volcano). The results were obtained from geological and alteration mapping as well as representative rocks/veins sampling...Petrology,..petrography, mineragra- phy, and XRD analyzes conducted on altered rock and vein samples from the two prospects indicated some differences. Kaligono prospect area (Gajah Volcano) consists various of alteration types ie. phylic (quartz-sericite-illite-pyrite),..propylitic..(chlorite-calcite-pyrite±epi- dote±actinolite), and argillic (illite-smectite-kaolinite±quartz). The mineralized veins found on Gajah Volcano show vein swarm, brecciated, stockwork, and massive vein structure with massive vein textures. The veins in Kaligono show NE-SW and NW-SE trends and hosted by Andesite, Dacite, and Andesite Lava. Gangue minerals that are found in the vein samples are quartz, illite, iron oxide, pyrite, and carbonate minerals. The ore minerals consist of magnetite, chalcopyrite, and sphalerite. Meanwhile in Hargorojo prospect area (Ijo Volcano), the types of alteration found including phylic (quartz-sericite-pyrite),..propylitic..(pyrite-calcite±ch- lorite), and argillic (illite-smectite-kaolinite-quartz). The mineralized veins found on Ijo Volcano have a massive vein structure, brecciation, and stockwork with comb, drussy, and massive vein textures. The veins have NNE-SSW and E-W trend and hosted by Andesite and Dacite. The gangue minerals are carbonate minerals, oxide minerals, pyrite, barite, quartz and chalcedony. The ore minerals include chalcopyrite, silver, galena, and sphalerite. Based on the vein characteristics of Kaligono prospect, such as a complex stockwork structure, hydrothermal breccia, and massive vein texture, which contain high temperature hydrothermal minerals, ie. epidote, actinolite, and magnetite, maybe indicate this deposit is controlled by deep..structure..related..to..the..porphyry miner alization. Whereas in the Hargorojo prospect shows the typical textures of shallow epithermal system (open space filling), such as comb and drussy, which contain lower temperature hydrothermal minerals, such as chalcedony, silver, and galena. Based on textural and mineralogical characteristics, Kaligono prospect suggests that the alteration and mineralization takes place deeper or closer to the magmatic source. On the other hand, Hargorojo prospect suggests the alteration and mineralization process relatively far from the source.

The metasedimentary and magmatic terranes in the southern part of the Ouessant Island (Western Brittany, France) are the offshore prolongation of the Léon Variscan metamorphic domain. They mainly consist of micaschists and subordinate amphibolitic lenses (meta-pillow lavas and volcaniclastic successions) cut by a swarm of trondhjemite sills, together with a large porphyritic monzogranite body, newly dated at 336 Ma, and later syeno-leucogranitic intrusions. A large spectrum of fluidal peperites, including spectacular “fiamme”-bearing breccias, is observable at the contact between metasediments and most of the intrusives. The coexistence of amphibolitized basalts, adakitic trondhjemites, and peraluminous granites in the inferred South Ouessant basin is assigned to a variety of deep subcontemporaneous processes, including asthenospheric partial melting, high-pressure fractionation in lithospheric reservoirs (or partial remelting of deep crystallized mafic intrusions), and continental crust melting. Implications of these new results are discussed in the Visean basinal framework of the Armorican Massif, formed at an early stage of the Variscan orogeny.