Автор(ы):Claudinei Gouveia de Oliveira, Edison Tazava
Издание:PGS Publishing, Linden Park, 2002 г., 10 стр.
Язык(и)Английский
The Igarape Bahia Au-Cu(-REE-U) deposit, Carajas mineral province, northern Brazil

The Igarape Bahia Au-Cu-(REE-U) deposit is located in the Carajas Mineral Province - Northern Brazil - and is hosted by an Archaean low-grade metamorphosed volcanosedimentary sequence characterized by metavolcanic rocks of the footwall and metavolcanoclastic/metasedimentary rocks of the hangwall. An intense hydrothermal alteration occurred in this sequence, promoting intense chloritization, Fe-metasomatism, Cu-sulphidation (chalcopyrite and bornite), carbonatization, silicification, tourmalinization and biotitization.

ТематикаПолезные ископаемые
Автор(ы):Anselmo D.V.Soares, Celio F.Barreira, Marcos Giovanni S.Dos Santos, Petronila C.Ronze
Издание:PGS Publishing, Linden Park, 2002 г., 12 стр.
Язык(и)Английский
Alemao copper-gold (U-REE) deposits, Carajas, Brazil

The Alemao copper-gold deposit is located within the Carajas Mineral Province of Northern Brazil and was discovered in 1996 by DOCEGEO using geophysical and geological techniques. Alemao is hosted by the Igarape Bahia Group, which comprises two lithological and stratigraphic domains: a lower metavolcanic unit composed of metavolcanic rocks and acid to intermediate volcanoclastics; and an upper clastic-chemical metasedimentary unit with volcanoclastic rocks. The Alemao ore body is covered by a 250 metres thick unconfonnable siliciclastic unit referred as the Aguas Claras Formation. The ore body, which is 500 metres in length and 50 to 200 metres wide, strikes NE-SW and dips steeply to the NW, being emplaced along the contact between the two stratigraphic domains of the Igarape Bahia Group. In the ore zone, the hydrothermal paragenesis is marked by ferric minerals (magnetite-hematite), sulphides (chalcopyrite, pyrite), chlorite, carbonate (siderite, calcite, ankerite) and biotite, with minor quartz, tourmaline, fluorite, apatite, uraninite, gold and silver. Sericite and albite are rare. The mineralisation is represented by hydrothermal breccias and "hydrothermalites" classified into two types: (1) the BMS type, composed of massive bands of magnetite and chalcopyrite and by polymitic breccias with a matrix comprising magnetite, chalcopyrite, siderite, chlorite, biotite and amphiboles; (2) the BCLS type breccia which comprises brecciated hydrothermalised volcanic rocks with chalcopyrite, bornite, pyrite, chlorite, siderite, ankerite, tourmaline and molybdenite in the matrix, as well as dissemination in the rock. The geochemical association of Fe-Cu-Au-U-REE in iron rich, heterolithic, hydrothermal breccias at the Alemao Cu-Au Deposit, as well as its possible association with an extensional tectonic setting, suggests a correlation with Olympic Dam type mineralization. The total estimated ore resources based on a krigging method is 170 Mt @ 1.5% Cu and 0.8g/tAu.

ТематикаПолезные ископаемые
МеткиAlemao deposit, Carajas, Copper, Gold
Автор(ы):Richard A.Leveille, Robert Marschik, Walter Martin
Издание:PGS Publishing, Linden Park, 2002 г., 12 стр.
Язык(и)Английский
La Candelaria and the Punta del Cobre district, Chile: early cretaceous iron-oxide Cu-Au(-Zn-Ag) mineralization

La Candelaria is the largest of the iron oxide Cu-Au(-Zn-Ag) deposits in the Punta del Cobre belt, which also hosts the Punta del Cobre district, sensu strictu. The Punta del Cobre belt lies within an Early Cretaceous continental volcanic arc/marine back-arc basin terrane. The volcanic arc and marine carbonate back-arc sequences are intruded by Early Cretaceous granitoid plutons that form part of the Chilean Coastal Batholith. The deposits of the Punta del Cobre belt occur along the eastern margin of the batholith within (e.g., La Candelaria) or just outside the contact metamorphic aureole (e.g., the Punta del Cobre district). Andesitic volcanic and volcaniclastic host rocks are intensely altered by biotite-quartz-magnetite. This style of alteration extends much further to the east of the intrusive contact than the metamorphic mineral associations in the overlying rocks that are clearly zoned outboard. Local areas of intense calcic amphibole veining that overprints all rock types occur within the contact metamorphic aureole.

ТематикаПолезные ископаемые
МеткиArgentum, Copper, Gold, Iron-oxide, La Cendelaria, Punta del Cobre, Zink
Автор(ы):Roger G.Skirrow
Издание:PGS Publishing, Linden Park, 2002 г., 12 стр.
Язык(и)Английский
Gold-copper-bismuth deposits of the Tennant creek district, Australia: a reappraisal of diverse high-grade systems

Gold-copper-bismuth deposits of the Tennant Creek district, Northern Territory, Australia, are distinctive as some of the highest grade deposits within the Fe-oxide Cu-Au global family. They are unified by an association with epigenetic magnetite ± hematite - rich 'ironstones' that are hosted by a sequence -I860 Ma, low metamorphic grade, Fe-oxide rich greywacke, siltstone and shale. While many of the high grade gold orebodies are dominated by magnetite - chlorite ± minor hematite, muscovite and pyrite, there are significant variations representing a spectrum of styles from reduced (pyrrhotite-bearing) Cu-Au-Bi deposits to oxidised hematitic Au-Bi(Cu) deposits. Shear-hosted Au-Cu mineralisation outside ironstones further adds to the diversity of styles present in the district. Ironstones predated syn- to late-deformational ~1825-1830 Ma introduction of Au, Cu and Bi in ~-300-350°C, acidic, low-moderate salinity or hypersaline fluids, which were in places carbonic and nitrogenous. The very wide range of oxidation-reduction conditions during ore deposition across the district is interpreted as the product of both reduced (magnetite ± pyrrhotite stable, H2S > S04=) and oxidised (hematite stable, S04= > H2S) fluids reacting with ironstones and/or mixing. Oxygen and hydrogen isotope data point to an hybrid ore fluid source with input of evolved surficial or formation waters, whereas Sm-Nd reconnaissance data and sulfur isotope compositions are consistent with contributions from igneous sources.

ТематикаПолезные ископаемые
МеткиBismuth, Copper, Gold, Gold-copper-bismuth deposit, Tennant creek
Автор(ы):Geordie Mark, Nick H.S.Oliver, Patrick J.Williams, Richard A.Crookes, Rick K.Valenta
Издание:PGS Publishing, Linden Park, 2002 г., 13 стр.
Язык(и)Английский
The evolution of the Ernest Henry Fe-oxide-(-Cu-Au) hydrothermal system

The >1510-1500 Ma Ernest Henry Fe-oxide-Cu-Au orebody is a hydrothermal deposit hosted in K-feldspar altered ca 1740 Ma plagioclase phyric volcanic rocks in the Cloncurry district, Mount Isa Inlier. Mineralization occurred late in a post-peak metamorphic hydrothermal system, and the ore is mainly hosted in an infill-supported hydrothermal breccia that grades to crackle veining at the margins. The orebody has a > 1km down dip extension, and is structurally-controlled between two shear zones that trend NE-SW and dip -35° to the SE. The ore is mainly composed of subrounded clasts separated by a fine- to medium-grained infill composed of magnetite, calcite, pyrite, biotite, K-feldspar, chalcopyrite, hematite, garnet, barite, fluorite, quartz and molybdenite.

ТематикаПолезные ископаемые
МеткиCopper, Ernest Henry ore body, Fe-oxide systems, Gold, iron oxide-Cu-Au
Автор(ы):Lachlan J.Reynolds
Издание:PGS Publishing, Linden Park, 2002 г., 12 стр.
Язык(и)Английский
Geology of the Olympic Dam Cu-U-Au-Ag-REE deposit

The -1590 Ma Olympic Dam Cu-U-Au-Ag-REE deposit is located in the Stuart Shelf geological province of South Australia, on the eastern margin of the Gawler Craton. The deposit is hosted by the Olympic Dam Breccia Complex, a large hydrothermal breccia system wholly contained within the Roxby Downs Granite, a Proterozoic age granitoid inteipreted to be part of the Hiltaba Suite. Initial hydrothermal activity within the Olympic Dam Breccia Complex was probably localised by structures in a dextral fault jog environment. Subsequent development of the complex involved repetitive and overprinting physical, chemical and volcanic brecciation mechanisms, resulting in a highly variable array of irregularly shaped and distributed breccia zones with widely differing and gradational lithologies. A complex pattern of hydrothermal alteration dominated by hematite and sericite, with lesser chlorite, siderite and quartz is associated with the breccia zones. Mineralisation within the deposit is intimately associated with iron-oxide alteration of the granitoid, which dominantly occurs as hematite, with lesser magnetite at depth and on the periphery of the breccia complex. The principal copper minerals within the deposit show a broad lateral and vertical, hypogene zonation pattern grading from chalcopyrite on the margins to bornite, then chalcocite adjacent to a central barren core. Gold and silver are mainly associated with the copper sulfides, while uranium dominantly occurs in pitchblende disseminated throughout the hematitic breccia zones. Overall, mineralisation grade generally correlates with the degree of hematite alteration and is largely dependent on copper sulfide tenor. Minor brittle faulting post-dates breccia development and appears to have exploited existing anisotropies within the complex. Late-stage fault movements are associated with barite-fluorite vein arrays which overprint the orebody. The deposit formed in a high level volcanic environment, venting to the surface and possibly forming a composite phreatomagmatic eruption crater, which has subsequently been completely eroded. Mafic and felsic dykes intruded the breccia complex, locally producing diatreme structures. Tectonism, hydrothermal activity, dyke intrusion, brecciation, alteration and mineralisation within the system were broadly concurrent and interdependent. Hydrothermal fluids and metals have a dominantly magmatic source, probably associated with the Middle Proterozoic volcano-plutonic event correlated with the Gawler Range Volcanics and Hiltaba Suite intrusives.

ТематикаПолезные ископаемые
МеткиCopper, Gold, Olympic Dam, REE, Stuart Shelf, Uranium
Автор(ы):Peter J.Pollard
Издание:PGS Publishing, Linden Park, 2002 г., 15 стр.
Язык(и)Английский
Evidence of magmatic fluid and metal source for Fe-oxide Cu-Au mineralization

Fe-oxide-Cu-Au deposits typically formed in continental arc and intracratonic tectonic settings, predominantly in the Proterozoic, but also during the Phanerozoic. The lack of reported evaporitic sequences in several major Fe-oxide-Cu-Au districts including the Gawler Craton and Stuart Shelf, Tennant Creek, Great Bear Magmatic Zone, and Carajas districts suggests that the presence of evaporites is not a prerequisite for the formation of these deposits.

Fluid inclusion studies of Fe-oxide-Cu-Au deposits typically indicate the presence of coexisting hypersaline and C02-rich fluid inclusions that may have originated by unmixing of an original H,0-C02-salts fluid. At the Lightning Creek prospect in the Cloncurry district, these fluid types were generated during crystallization of granitic sills that are associated with a major magnetite-rich vein system. Stable isotope data from Lightning Creek and a number of Cu-Au deposits in the Cloncurry district and elsewhere are compatible with formation of these deposits principally from magmatic-hydrothermal fluids. Syn- to post-mineralization Na-Ca-rich fluids are present in many deposits, and may represent meteoric and/or connate fluids that mixed with the hypersaline magmatic fluids during or after mineralization.

ТематикаПолезные ископаемые
МеткиCopper, Cu-Au mineralization, Fe-oxide, Gold, Magmatic fluid, Metal source
Автор(ы):Murray W.Hitzman
Издание:PGS Publishing, Linden Park, 2002 г., 17 стр.
Язык(и)Английский
Iron oxide-Cu-Au deposits: what, where, when and why

Abstract - The magnetite-apatite deposits ("Kiruna-type") and the iron oxide-Cu-Au deposits form end members of a continuum. In general the magnetite-apatite deposits form prior to the copper-bearing deposits in a particular district. While the magnetite-apatite deposits display remarkably similar styles of alteration and mineralization from district to district and throughout geologic time, the iron oxide-Cu-Au deposits are much more diverse. Deposits of this family are found in post-Archean rocks from the Early Proterozoic to the Pliocene. There appear to be three "end member" tectonic environments that account for the vast majority of these deposits: (A) intra-continental orogenic collapse; (B) intra-continental anorogenic magmatism; and (C) extension along a subduction-related continental margin. All of these environments have significant igneous activity probably related to mantle underplating, high heat flow, and source rocks (subaerial basalts, sediments, and/or magmas) that are relatively oxidized; many districts contain(ed) evaporites. While some of the magnetite-apatite deposits appear to be directly related to specific intrusions, iron oxide-Cu-Au deposits do not appear to have a direct spatial association with specific intrusions. Iron oxide-Cu-Au deposits are localized along high- to low-angle faults which are generally splays off major, crustal-scale faults. Iron oxide-Cu-Au deposits appear to have formed by: 1) significant cooling of a fluid similar to that responsible for precipitation of magnetite-apatite; 2) interaction of a fluid similar to that causing precipitation of magnetite-apatite with a cooler, copper-, gold-, and relatively sulfate-rich fluid of meteoric or "basinal" derivation; or 3) a fluid unrelated to that responsible for the magnetite-apatite systems but which is also oxidized and saline, though probably cooler and sulfate-bearing. The variability of potential ore fluids, together with the diverse rock types in which these deposits are located, results in the wide variety of deposit styles and mineralogies.

ТематикаПолезные ископаемые
МеткиApatite, Copper, Gold, iron oxide-Cu-Au, Iron-oxide, Kiruna-type, Magnetit
Автор(ы):T.Michael Porter
Издание:PGS Publishing, Linden Park, 2002 г., 3 стр.
Язык(и)Английский
Hydrothermal iron-oxidecopper-gold and related ore deposits

Abstract: Following the discovery of the giant Olympic Dam ore deposit in 1975, a realisation developed that there was an important class of mineral deposits not previously appreciated. It became apparent that this class, the Iron Oxide Copper-Gold deposits, included not only Olympic Dam, but also a number of other known deposits. It also became apparent that this was a class that could produce large, high grade prizes, of the order of 0.25 to 1 billion tonnes of around +1% Cu and 0.5 g/t Au. As a consequence this class has been one of the major targets of the exploration industry over the last decade, resulting in the discovery of further giant orebodies in Australia such as Ernest Henry, and Candelaria, Salobo, Sossego and others in South America.

This class of deposit however, does not represent a single style or a common genetic model, but rather a family of loosely related ores that share a pool of common characteristics. The principal feature they have in common is the abundance of iron oxides that accompany the ore and the intensity of the associated alteration, particularly albitisation and Fe metasomatism. The iron oxides are present as either magnetite or hematite and almost invariably precede the emplacement of the other economic minerals. These deposits are found throughout geologic time, around the globe and in settings from intra-cratonic, to continental margins above subduction zones.

There is a differences of opinion both on the processes involved in their formation, matched by the diversity in styles of mineralisation within the class, as well as which deposits should be included within the family.

The aim of this volume is to bring together a wide range of knowledge, experience and opinion from around the globe to assist in understanding this economically and geologically important family of deposits.

ТематикаПолезные ископаемые
Издание:PGS Publishing, Linden Park, 2005 г., 257 стр., ISBN: 0-9580574-3-5
Язык(и)Английский
Super porphyry copper and gold deposits. Volume 2

Porphyry-style Cu-Au/Mo deposits are among the most sought after targets for both base and precious metal exploration in the world today. Of particular interest are the "super porphyry" copper and or gold deposits, because of their size, grade and ability to support large scale, long life, profitable operations.

The term "super porphyry" is interpreted loosely in this publication, relating in general to the largest deposits in any established porphyry province. For a discussion of the accepted terminology and size classification of large porphyry-style deposits, see the introduction section of Richards, (2005) in this publication.

ТематикаПолезные ископаемые
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