Platina em complexos ultramáficos zonados

Platina em complexos ultramáficos zonados

ALASKAN-TYPE Pt+/-Os+/-Rh+/-Ir by Graham T. Nixon British Columbia Geological Survey

Ref: ultramáfica, alaska, magnetita, cromita, platina, ósmio, irídio
Nixon, G. T. (1996): Alakan-type Pt+/-Os+/-Rh+/-Ir, in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T, Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 113-116.

IDENTIFICATION

SYNONYMS: Zoned ultramafic, Uralian-type, Alaskan-type.
COMMODITIES (BYPRODUCTS): Pt (Ir, Os, Rh, magnetite).
EXAMPLES (British Columbia - Canada/International): Tulameen Complex and associated placers; magnetite plus trace platinum group elements (PGE) -Lodestone Mountain (092HSE034), Tanglewood Hill (092HSE035); chromite - Grasshopper Mountain (092HNE011); olivine - Grasshopper Mountain Olivine (092HNE189); Red Mountain, Goodnews Bay (Alaska, USA), Tin Cup Peak (Oregon, USA), Ural Mountains and Aldan Shield (Russia), Fifield district (NSW, Australia).

GEOLOGICAL CHARACTERISTICS

CAPSULE DESCRIPTION: Ultramafic intrusive complexes, commonly zoned, forming sills, stocks or intrusive bodies with poorly known external geometry. Subeconomic platinum group elements in lode occurrences are associated with: 1) thin (centimetre-scale), disrupted chromitite layers , 2) thick (metre-scale) concentrations of cumulus magnetite or 3) clinopyroxenite. Economic placer deposits appear to be derived predominantly from chromitite- hosted PGE occurrences.
TECTONIC SETTINGS: Traditionally subdivided into orogenic (unstable) and platformal (stable) environments. In British Columbia, Alaskan-type complexes were emplaced during an episode of Cordillera-wide, subduction-related arc magmatism followed by an episode of orogenic compression.
DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Zoned to crudely layered ultramafic- mafic intrusive complexes with rarely preserved (or poorly documented) metamorphic aureoles. Intrusive margins are commonly faulted. Traditionally viewed as deep-seated cumulates diapirically re-emplaced at high levels in the crust. In British Columbia, at least, most intrusions appear to represent cumulate deposition in upper crustal (subvolcanic?) magma chambers and the diapiric re-emplacement model lacks definitive supporting evidence.
AGE OF MINERALIZATION: Precambrian to late Mesozoic; most Alaskan-type complexes in British Columbia appear to be mid-Triassic to late Early Jurassic in age.
HOST/ASSOCIATED ROCK TYPES: Predominantly dunite, wehrlite, olivine clinopyroxenite, clinopyroxenite, hornblende clinopyroxenite, clinopyroxene hornblendite, hornblende- and/or clinopyroxene-bearing gabbro/diorite. Minor lithologies include chromitite, magnetitite, olivine-hornblende clinopyroxenite, and hornblendite. Associated feldspar-bearing lithologies include gabbro/diorite, monzonite, monzodiorite and minor alkali-feldspar syenite and hornblende- feldspar ± quartz ± biotite pegmatite.
DEPOSIT FORM: Lode occurrences of PGEs are primarily controlled by magmatic cumulate stratigraphy:

• 1) chromitites are restricted to dunites where they form thin discontinuous layers or schlieren, pods and nodular masses seldom more than a metre in length;
  2) magnetitites and concentrations of cumulus magnetite form well bedded, locally continuous layers up to six m thick intercalated with hornblende clinopyroxenite;
  3) lenses and vein-like bodies of relatively coarse-grained or "pegmatoid", biotite and magnetite-poor, PGE-bearing clinopyroxenites are enclosed by finer grained, biotite and magnetite-rich, PGE-poor clinopyroxenites.

TEXTURE/STRUCTURE: Cumulus and intercumulus textures are most common; poikilitic textures may predominate locally, especially in hornblende-bearing lithologies. Comparatively rare macroscopic layering. Euhedral to subhedral chromite concentrations form networks around olivine or discrete wispy or thin layers in dunite. Chromitites typically form schlieren and nodular masses due to syndepositional remobilization. Magnetite-rich accumulations usually form thin to thick bedded layers in hornblende clinopyroxenite. Tectonic deformation, commonly in the form of ductile shear fabrics, is locally superimposed on magmatic textures, and is especially prevalent at intrusive contacts.
ORE MINERALOGY (Principal and subordinate): Three types of PGE mineral (PGM) associations are recognized in lode occurrences: 1) chromitite-PGM association, principally chromite and Pt-Fe(-Cu-Ni) alloys (e.g. tetraferroplatinum, isoferroplatinum, rare native platinum, tulameenite) and minor Os-Ir and Pt-Ir alloys, Rh-Ir sulpharsenides (hollingworthite-irarsite series), sperrylite (PtAs2), geversite (PtSb2), and laurite (RuS2); 2) magnetitite-PGM association (not well documented), principally magnetite (Ti-V-rich in certain cases) and Pt-Fe and Os-Ir alloys, and rare cooperite (PtS); 3) clinopyroxenite-PGM association (known from a single locality - Fifield, NSW, Australia), principally Pt-Fe alloys (isoferroplatinum-tetraferroplatinum), erlichmanite (OsS2), cooperite, and sperrylite-geversite. Minor amounts of base metal sulphides (chalcopyrite, pentlandite, pyrrhotite, pyrite, bornite, violarite, bravoite, millerite, heazlewoodite) generally accompany the PGM in all three associations.
GANGUE MINERALOGY (Principal and subordinate): The principal gangue minerals include olivine, chrome spinel, clinopyroxene, and hornblende in ultramafic rocks; hornblende, clinopyroxene and plagioclase in gabbroic/dioritic rocks; and hornblende, quartz (rare) and alkali feldspar in leucocratic differentiates. Orthopyroxene is characteristically absent as a cumulus phase but may form very rare intercumulus grains. Accessory magnetite and apatite are generally common, and locally abundant in hornblende clinopyroxenite; sphene and zircon occur in felsic differentiates; phlogopite-biotite is particularly widespread as an accessory phase in British Columbia.
ALTERATION MINERALOGY: Secondary PGM are minor and closely associated with the primary PGM alloys. Remobilization of PGE is believed to be extremely limited and may be commonly related to postmagmatic serpentinizaton processes acting during regional metamorphism and deformation.
WEATHERING: It has been argued by some that the PGE found in placer occurrences may owe their origin to the hydromorphic dispersion and precipitation of PGE during normal weathering processes. The debate continues, but it is clear from a variety of textural, mineralogical and isotopic (Re-Os) data that the common placer PGE occurrences are the products of mechanical degradation of magmatic lode occurrences and not surficial remobilization processes.
ORE CONTROLS: The PGM appear to be restricted to chromitite, magnetite-rich or clinopyroxenite layers which formed by primary magmatic crystallization processes. The chromite is typically associated with dunite whereas the magnetite is found with clinopyroxenite.
GENETIC MODEL: The origin of the PGE in Alaskan-type deposits is magmatic with very limited low-temperature remobilization. A low sulphidation, relatively high oxidation magmatic environment (subduction-related?) appears to be an important genetic control. The chromitites in dunite and, to a much lesser extent, the magnetite-rich layers in clinopyroxenite, appear to be the ultimate source of the placer PGE.
ASSOCIATED DEPOSIT TYPES: Placer deposits (C01, C02) are extremely important since they have been the only significant economically recoverable source of PGE associated with Alaskan-type complexes. Some lode deposits have been worked in Russia but their documentation is extremely poor.
COMMENTS: All of the world's most important Alaskan-derived placers appear to be related to concentrations of PGE in chromitites. Gold in these placers appears to have been derived from a separate source. Magnetite accumulations in clinopyroxenites of the Tulameen Complex have been explored for magnetite. EXPLORATION GUIDES
GEOCHEMICAL SIGNATURE: Primarily Pt, with subsidiary Os, Rh and Ir; other elements such as Cu, Ni, and Cr may be locally important. Geochemical pathfinder elements for PGE, such as As and Sb, may also be important.
GEOPHYSICAL SIGNATURE: Primarily magnetic; gravity may be important.
OTHER EXPLORATION GUIDES: Stream sediment sampling of heavy mineral concentrates for PGE is a key exploration tool; in favourable circumstances PGE geochemistry and platinum nugget mineralogy can uniquely distinguish an Alaskan-type heritage from all other common PGE environments.

ECONOMIC FACTORS

TYPICAL GRADE AND TONNAGE: PGE concentrations in grab samples from lode deposits are extremely spotty such that reliable tonnages and grades are not available. The associated placer deposits are likewise extremely variable. Maximum grade of Pt from the Goodnews Mining Company records, Alaska (1957) was approximately “$37 per cubic yard” at February 1993 prices. Placers in the Tulameen district reportedly yielded some 620 kg of impure platinum between 1889 and 1936. Some of the placer deposits in the former Soviet Union have yielded exceptional platinum nuggets of up to 11.3 kg.
ECONOMIC LIMITATIONS: The chromitite-PGE association appears to be the most important in British Columbia; without exception, all of these chromitite occurrences are small, dispersed throughout a dunite host, and all have been remobilized soon after deposition within the high-temperature magmatic environment. A small open pit operation appears to be the only potentially economic method of PGE extraction. The occurrence of the PGE as small micrometre-size inclusions in refractory chromite poses problems for processing.
END USES: PGE are primarily used as high-temperature catalysts in a variety of industries, perhaps the most familiar being platinum for automobile catalytic converters. Other uses include medical and electronic (fuel cells, thermocouples), and platinum is used in jewelry.
IMPORTANCE: PGE are classed as a strategic commodity. The most important producers are South Africa and Russia.

REFERENCES

Veios com prata, níquel, cobalto e arsênio

Veios com prata, níquel, cobalto e arsênio

FIVE-ELEMENT VEINS Ag-Ni-Co-As+/-(Bi, U) by David V. Lefebure British Columbia Geological Survey

Ref: veio, níquel, cobalto, prata, arsênio

Lefebure, D.V. (1996): Five-element Veins Ag-Ni-Co-As+/-(Bi,U), in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T, Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 89-92. IDENTIFICATION SYNONYMS: Five-element (Ni-Co-As-Ag-Bi) veins, nickel-cobalt-native silver veins, Cobalt-type silver-sulpharsenide veins, Ni-Co-Bi-Ag-U (As) association, Ag- As (Ni,Co,Bi) veins, Schneeberg-Joachimsthal-type. COMMODITY (BYPRODUCTS): Ag, U, Ni, Co, Bi (barite). EXAMPLES (British Columbia - Canada/International): No B.C. examples; Beaver and Timiskaming, Cobalt camp, Silver Islet, Thunder Bay district (Ontario, Canada), Echo Bay and Eldorado (Port Radium, Northwest Territories, Canada), Black Hawk district (New Mexico, USA), Batopilas district (Mexico), Johanngeogenstadt, Freiberg and Jachymov, Erzgebirge district (Germany), Konsberg-Modum (Norway). GEOLOGICAL CHARACTERISTICS CAPSULE DESCRIPTION: Native silver occurs in carbonate veins associated with a variety of mineral assemblages that are rare in other settings, such as Ni- Co-Fe arsenides, Ni-Co-Fe-Sb sulpharsenides and bismuth minerals. In many cases only some of these minerals are present, although the best examples of this deposit type typically contain significant Ag-Ni-Co. In some deposits uraninite (pitchblende) is an important ore mineral. TECTONIC SETTINGS: Virtually all occur in areas underlain by continental crust and are generally believed to have formed late or post-tectonically. In some cases the veins appear related to basinal subsidence and continental rifting. DEPOSTIONAL ENVIRONMENT/GEOLOGICAL SETTING: Veins are believed to be emplaced at shallow depths in a continental setting along high-angle fault systems. AGE OF MINERALIZATION: Proterozoic or younger, can be much younger than hostrocks. HOST/ASSOCIATED ROCK TYPES: Found in a wide variety of hostrocks, although metasediments, metamorphosed intrusive rocks and granitic sequences are the most common. Diabase sills are an important host in the Cobalt camp and a number of the deposits in the Thunder Bay region are within a gabbro dike. DEPOSIT FORM: Simple veins and vein sets. Veins vary from centimetre to metre thicknesses, typically changing over distances of less than tens of metres. Most vein systems appear to have limited depth extent, although some extend more than 500 m. TEXTURE/STRUCTURE: Commonly open space filling with mineral assemblages and textures commonly due to multiple episodes of deposition. Sulphides are irregularly distributed as massive pods, bands, dendrites, plates and disseminations. The mineralization is more common near the interesections of veins or veins with crosscutting faults. Fragments of wallrock are common in some veins. Faults may be filled with graphite-rich gangue, mylonite or breccia. ORE MINERALOGY (Principal and subordinate): Native silver associated with Ni-Co arsenide minerals (rammelsbergite, safflorite, niccolite, cloanthite, maucherite), sulpharsenides of Co, Ni, Fe and Sb, native bismuth, bismuthinite, argentite, ruby silver, pyrite and uraninite (pitchblende). Chalcopyrite, bornite and chalcocite are common, but minor, constituents of ore. Minor to trace galena, tetrahedrite, jamesonite, cosalite, sphalerite, arsenopyrite and rare pyrrhotite. In many deposits only a partial mineral assemblage occurs containing a subset of the many elements which may occur in these veins. These veins are characterized by the absence of gold. GANGUE MINERALOGY (Principal and subordinate): Calcite and dolomite are usually associated directly with native silver mineralization; quartz, jasper, barite and fluorite are less common. The carbonate minerals are common in the cores of some veins. ALTERATION MINERALOGY: Not conspicuous or well documented. In the Cobalt camp calcite and chlorite alteration extends 2-5 cm from the vein, approximately equivalent in width to the vein. WEATHERING: No obvious gossans because of the low sulphide content; locally “cobalt bloom”. ORE CONTROLS: Veins occupy faults which often trend in only one or two directions in a particular district. Ore shoots may be localized at dilational bends within veins. Intersections of veins are an important locus for ore. Possibly five-element veins are more common in Proterozoic rocks. GENETIC MODEL: In regions of crustal extension, faults controled the ascent of hydrothermal fluids to suitable sites for deposition of metals at depths of approximately 1 to 4 km below surface. The fluids were strongly saline brines at temperatures of 150ø to 250øC, which may have been derived from late-stage differentiation of magmas, convective circulation of water from the country rocks driven by cooling intrusive phases or formation brines migrating upwards or towards the edge of sedimentary basins. Sulphide-rich strata (including Fahlbands) and carbonaceous shales in the stratigraphy are potential sources of the metals. Deposition occurs where the fluid encounters a reductant or structural trap. ASSOCIATED DEPOSIT TYPES: ‘Classical’ U veins, polymetallic veins. In the Great Bear Lake area there are associated “giant” quartz veins with virtually no other minerals. COMMENTS: Several Co-AgñNiñBi veins are found in the Rossland Camp in British Columbia. These may be five-element veins, however, they also contain the atypical elements Au and Mo. EXPLORATION GUIDES GEOCHEMICAL SIGNATURE: The rare association of anomalous values of Ag with Ni, Co, Bi, U and As in rock samples is diagnostic. GEOPHYSICAL SIGNATURE: Associated structures may be defined by ground magnetic or VLF-EM surveys. Airborne surveys may identify prospective major structures. Gamma ray scintillometers and spectrometers can be used to detect the uraninite-bearing veins in outcrop or in float trains in glacial till, frost boils, talus or other debris. OTHER EXPLORATION GUIDES: Commonly camp or regional structural controls will define a dominant orientation for veins. ECONOMIC FACTORS GRADE AND TONNAGE: Typically range from tens of thousands of tonnes to a few hundreds of thousands of tonnes with very high grades of silver (more than 1000 g/t Ag for Canadian mines, with grades up to 30 000 g/t Ag). IMPORTANCE: There has been no significant production from a native silver vein in British Columbia, however, these veins have historically been an important Canadian and world source of Ag and U with minor production of Co. More recently the narrow widths and discontinuous nature of these veins has led to the closure of virtually all mines of this type.

Preços dos terras raras sobem 10%

Preços dos terras raras sobem 10%
O Governo Chinês está atuando energicamente contra a mineração ilegal de terras raras. Esta ação fez com que várias minas foram paralisadas e muitos mineradores presos. Na China uma grande parte da produção de terras raras vem de pequenos garimpos onde as pessoas não tem qualidade no trabalho, higiene ou segurança.
Com a paralisação houve uma subida nos preços dos óxidos de terras raras de mais de 10% somente nos últimos 14 dias.

300 fragmentos do meteorito de Chelyabinsk estudados na Russia

300 fragmentos do meteorito de Chelyabinsk estudados na Russia
Os geólogos do Vernadaky Instituto de Geoquímica  informam que o meteorito tem mais 4 bilhões de anos. A composição química do meteorito é a base de ferro, níquel, magnésio e cobalto.
Os estudos continuam e serão publicados em breve.

Tapajós The Amazonian Eldorado: Mineralization

Tapajós The Amazonian Eldorado: Mineralization
by Pedro Jacobi
	Brazil,Brasil, Amazon, amazônia, amazonia, minerals,geologia, geology, geological mapping, regional reconnaissance, geophysical, geophysics, geochem, geochemistry, geoquímica, geoquímico,  geofísico, exploração mineral, ouro,gold nuggets, pepitas, Amazônia, Tapajós, tapajos, consultant, consultants, consultores, geólogo, geóloga, geologo, geologa, geologist, áreas, negociações, metais base, cobre, estanho, ouro, export, caulim, descobertas, mineral discoveries, prospects, consultants, properties to sell, mineral areas, mineral exploration, base metals, copper, tin, porphyry, porphyries, titanium, cobalt, tantalite, rutile, ilmenite, columbite kaolin, garimpo, garimpeiro, garimpeiros, pista de pouso, trincheiras, poços, trenchs, pits, drilling, diamond drill holes, Carajas,Carajás, Pará, Pedro Jacobi, Progeo, evaluation, negotiations, negotiator, negociação, negociações,alunita, alunite, pyrophyllitem pirofilita, diásporo, sericita, sericite, chlorite, clorita, pirita, pyrite, chalcopyrite, calcopirita, galena, esfalerita, sphalerite, hydrothermal alteration, pipes, kimberlites, lamproites, diatremes, volcanoes, vulcão, diatremas, kimberlitos, diamantíferos, quartz, chalcedony, amethyst, ametista, quartzo,  calcedônia,fósseis,mineral specimens, collectors, topaz, topásio, cascalho, river flat, placers, golden, bearing, jazida, jazimentos, jazidas, orebody, ore, orebodies, deposits, mines, minas, céu aberto, open pit, underground, subterrânea, explotação, exploiting, economia mineral, economics, cash flows, volcanics, vulcânicas, granite, diorite, granodiorite, dacite, rhyolite, flows, lava, intrusions, return investment, programme, program, programas, pentlandita, nickel, sulfetos, sulfides, sulphide, oxides, iron laterites, gossan, ironstone, platinum, colecionadores, collectors, advance argillic alteration, phyllic, argílica, fílica, propilitização, propilitos, propylitization, propyllitization, sericitization, faults,  mineralization, terraces, production, evaluation, control, reports, data bank, locations, occurrences old, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro Placer deposits: More than 90% of the gold in Tapajós was extracted from thousands of alluvial deposits spread over large areas. A number of alluvial gold districts have produced more than 3Moz of gold during their mining history. Garimpos like Cuiu-Cuiu, Canta-Galo, Abacaxis and Patrocínio are classical examples of these large sedimentary systems.gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro Alluvial gold deposits are everywhere in Tapajós.gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro A quick view of satellite imagery will show 200km stretches virtually covered by mineralized placer deposits. This situation allowed the establishment of hundreds of thousands of garimpeiros. In spite of the rudimentary mining and exploration methods several rich bonanzas were found attracting prospectors from all parts of Brazil. Due to the early successes most miners thought that there was no need for improvements and the "sluice-box and pump" was used in almost all deposits. gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro During the early days the approach used to mine placer deposits was simple. The garimpo owner sold little 10 x 10m blocks to the miners. He controlled all distribution of supplies and fuel. The only accepted currency was gold itself. As such most garimpos became a shopping business rather than a mining one. It did not matter if one is getting rich or poor in the mine front provided that he pays for fuel and suppliesdots gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro As a consequence the districts were flooded with people. Soon placers were exhausted and garimpeiros started to migrate from one district to another . It was the beginning of the end of garimpeiro's alluvial mining in Tapajos. gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro During the 90's, mineral explorationists were attracted by a simple formula: the larger the mineralized placer the larger the primary source will be. Nevertheless the Tapajos geology wasn't that simple and several companies lost their money guided by that "rule". gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro In general these alluvial deposits are recent. Nevertheless during geological mapping of areas like Nova Brasília and Samauma, we observed that older sedimentary units also existed. In Nova Brasília garimpeiros were mining the so-called "segundo cascalho" which means the second pebble layer. In this case they were extracting gold from an older sedimentary horizon buried under the recent Quaternary flat. This extremely rich conglomerate horizon lies 10-20m under today's surface. Age is, very likely, Tertiary. It sits unconformably on top of weathered cataclastic gneiss. A marker horizon of peat rests 1-1.5m on top of this unit. gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro In spite of this, garimpeiros were eager to dismantle up to 20m of barren clay and intercalated sand to mine this thin (0.1-2m) ore horizon.Brazil,Brasil, Amazon, amazônia, amazonia, minerals,geologia, geology, geological mapping, regional reconnaissance, geophysical, geophysics, geochem, geochemistry, geoquímica, geoquímico,  geofísico, exploração mineral, ouro,gold nuggets, pepitas, Amazônia, Tapajós, tapajos, consultant, consultants, consultores, geólogo, geóloga, geologo, geologa, geologist, áreas, negociações, metais base, cobre, estanho, ouro, export, caulim, descobertas, mineral discoveries, prospects, consultants, properties to sell, mineral areas, mineral exploration, base metals, copper, tin, porphyry, porphyries, titanium, cobalt, tantalite, rutile, ilmenite, columbite kaolin, garimpo, garimpeiro, garimpeiros, pista de pouso, trincheiras, poços, trenchs, pits, drilling, diamond drill holes, Carajas,Carajás, Pará, Pedro Jacobi, Progeo, evaluation, negotiations, negotiator, negociação, negociações,alunita, alunite, pyrophyllitem pirofilita, diásporo, sericita, sericite, chlorite, clorita, pirita, pyrite, chalcopyrite, calcopirita, galena, esfalerita, sphalerite, hydrothermal alteration, pipes, kimberlites, lamproites, diatremes, volcanoes, vulcão, diatremas, kimberlitos, diamantíferos, quartz, chalcedony, amethyst, ametista, quartzo,  calcedônia,fósseis,mineral specimens, collectors, topaz, topásio, cascalho, river flat, placers, golden, bearing, jazida, jazimentos, jazidas, orebody, ore, orebodies, deposits, mines, minas, céu aberto, open pit, underground, subterrânea, explotação, exploiting, economia mineral, economics, cash flows, volcanics, vulcânicas, granite, diorite, granodiorite, dacite, rhyolite, flows, lava, intrusions, return investment, programme, program, programas, pentlandita, nickel, sulfetos, sulfides, sulphide, oxides, iron laterites, gossan, ironstone, platinum, colecionadores, collectors, advance argillic alteration, phyllic, argílica, fílica, propilitização, propilitos, propylitization, propyllitization, sericitization, faults,  mineralization, terraces, production, evaluation, control, reports, data bank, locations, occurrences In the Samauma region another tectonic setting was observed. Gold was transported from 20-40m high terraces to the recent alluvial deposits. Erosion has rounded the topography making difficult to the observer to visualize these terraces. Nevertheless a large area in the vicinity of the Crepori River is covered by partially eroded gold bearing paleo-terraces. Paleo-placers in Tapajós are unknown to most explorationists. gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro Quite a few have huge volumes and high grades and may generate interesting economic deposits. gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro From the exploration point of view these vertical movements and the subsequent erosion that affected the up-faulted blocks will explain most of the exploration failures (see discussions).Brazil,Brasil, Amazon, amazônia, amazonia, minerals,geologia, geology, geological mapping, regional reconnaissance, geophysical, geophysics, geochem, geochemistry, geoquímica, geoquímico,  geofísico, exploração mineral, ouro,gold nuggets, pepitas, Amazônia, Tapajós, tapajos, consultant, consultants, consultores, geólogo, geóloga, geologo, geologa, geologist, áreas, negociações, metais base, cobre, estanho, ouro, export, caulim, descobertas, mineral discoveries, prospects, consultants, properties to sell, mineral areas, mineral exploration, base metals, copper, tin, porphyry, porphyries, titanium, cobalt, tantalite, rutile, ilmenite, columbite kaolin, garimpo, garimpeiro, garimpeiros, pista de pouso, trincheiras, poços, trenchs, pits, drilling, diamond drill holes, Carajas,Carajás, Pará, Pedro Jacobi, Progeo, evaluation, negotiations, negotiator, negociação, negociações,alunita, alunite, pyrophyllitem pirofilita, diásporo, sericita, sericite, chlorite, clorita, pirita, pyrite, chalcopyrite, calcopirita, galena, esfalerita, sphalerite, hydrothermal alteration, pipes, kimberlites, lamproites, diatremes, volcanoes, vulcão, diatremas, kimberlitos, diamantíferos, quartz, chalcedony, amethyst, ametista, quartzo,  calcedônia,fósseis,mineral specimens, collectors, topaz, topásio, cascalho, river flat, placers, golden, bearing, jazida, jazimentos, jazidas, orebody, ore, orebodies, deposits, mines, minas, céu aberto, open pit, underground, subterrânea, explotação, exploiting, economia mineral, economics, cash flows, volcanics, vulcânicas, granite, diorite, granodiorite, dacite, rhyolite, flows, lava, intrusions, return investment, programme, program, programas, pentlandita, nickel, sulfetos, sulfides, sulphide, oxides, iron laterites, gossan, ironstone, platinum, colecionadores, collectors, advance argillic alteration, phyllic, argílica, fílica, propilitização, propilitos, propylitization, propyllitization, sericitization, faults,  mineralization, terraces, production, evaluation, control, reports, data bank, locations, occurrences Primary deposits: Most primary gold deposits in Tapajós are associated to Proterozoic rocks. The relationship between Proterozoic granitoids and volcanics with gold imposed a barrier for many explorationists. Most of them believed that gold deposits associated to granites are small and the chance of a world class discovery in Tapajos was non existent. gold, copper, molly, mineral exploration, brazil, amazon, geology, consultant, properties, minerals, tantalite, porphyries, consultants, quartz, amethyst, diamonds, tapajos, garimpo, garimpeiro This mistake is usual amongst geologists that can't see anything but established geological models. Brazil,Brasil, Amazon, amazônia, amazonia, minerals,geologia, geology, geological mapping, regional reconnaissance, geophysical, geophysics, geochem, geochemistry, geoquímica, geoquímico,  geofísico, exploração mineral, ouro,gold nuggets, pepitas, Amazônia, Tapajós, tapajos, consultant, consultants, consultores, geólogo, geóloga, geologo, geologa, geologist, áreas, negociações, metais base, cobre, estanho, ouro, export, caulim, descobertas, mineral discoveries, prospects, consultants, properties to sell, mineral areas, mineral exploration, base metals, copper, tin, porphyry, porphyries, titanium, cobalt, tantalite, rutile, ilmenite, columbite kaolin, garimpo, garimpeiro, garimpeiros, pista de pouso, trincheiras, poços, trenchs, pits, drilling, diamond drill holes, Carajas,Carajás, Pará, Pedro Jacobi, Progeo, evaluation, negotiations, negotiator, negociação, negociações,alunita, alunite, pyrophyllitem pirofilita, diásporo, sericita, sericite, chlorite, clorita, pirita, pyrite, chalcopyrite, calcopirita, galena, esfalerita, sphalerite, hydrothermal alteration, pipes, kimberlites, lamproites, diatremes, volcanoes, vulcão, diatremas, kimberlitos, diamantíferos, quartz, chalcedony, amethyst, ametista, quartzo,  calcedônia,fósseis,mineral specimens, collectors, topaz, topásio, cascalho, river flat, placers, golden, bearing, jazida, jazimentos, jazidas, orebody, ore, orebodies, deposits, mines, minas, céu aberto, open pit, underground, subterrânea, explotação, exploiting, economia mineral, economics, cash flows, volcanics, vulcânicas, granite, diorite, granodiorite, dacite, rhyolite, flows, lava, intrusions, return investment, programme, program, programas, pentlandita, nickel, sulfetos, sulfides, sulphide, oxides, iron laterites, gossan, ironstone, platinum, colecionadores, collectors, advance argillic alteration, phyllic, argílica, fílica, propilitização, propilitos, propylitization, propyllitization, sericitization, faults,  mineralization, terraces, production, evaluation, control, reports, data bank, locations, occurrences Mineral exploration is a subjective and creative business and as such there is no room for narrow-minded people. ouro, cobre, molibdenita, pórfiros, exploração mineral, amazônia, brasil, geologia, consultor, áreas, garimpos, minerais, quartzo, tantalita, ametista, citrino, diamantes, tapajós, The most important primary mineralization in Tapajos are: 1- Quartz veins: ouro, cobre, molibdenita, pórfiros, exploração mineral, amazônia, brasil, geologia, consultor, áreas, garimpos, minerais, quartzo, tantalita, ametista, citrino, diamantes, tapajós, In almost all districts quartz-sulfide veins are abundant. In general quartz veins are narrow and discontinuous. Quartz veins are known in all kinds of terrain and ages in Tapajos. Gold is often visible and quite frequently occur associated to rich clusters. Grades may be very high. Sulfides are mostly pyrite and secondarily chalcopyrite and galena. Pirrotite, molibdenite and sphalerite are described in a few areas. Carbonates are common. Single quartz veins may have the grade but seldom the volume. 2- Chlorite (sericite)-quartz-sulfide veins: ouro, cobre, molibdenita, pórfiros, exploração mineral, amazônia, brasil, geologia, consultor, áreas, garimpos, minerais, quartzo, tantalita, ametista, citrino, diamantes, tapajós, Important high-grade mineralization is associated to large chlorite-quartz-sulfide veins. These veins are filling open spaces in competent rocks affected by brittle deformation. Hydrothermal alteration is restricted to the selvages and is never pervasive. Host rocks vary from granites and volcanics to gneisses. Main sulfides are pyrite, chalcopyrite, pirrotite and galena. Whenever Cpy is present gold grades are bound to be exceptionally high, frequently above 30g/t. Massive sulfides, in mineralized areas, are extremely rich (up to 300g/t Au). Good correlation between copper and gold is common in several districts in Tapajos. These "juice" veins have been found in quite a few areas and will generate several economic deposits in Tapajos. An example of this type of mineralization is the Ouro Roxo gold deposit. 3-Stockworks : ouro, cobre, molibdenita, pórfiros, exploração mineral, amazônia, brasil, geologia, consultor, áreas, garimpos, minerais, quartzo, tantalita, ametista, citrino, diamantes, tapajós, During our preliminary reconnaissance, in 1993, a number of gold bearing stockworks frequently associated to large alteration systems were discovered. Latter, such discoveries help to attract some of the "non believers" back to the Tapajos. In general stockworks are associated to the upper portion of granitic intrusions ( São Jorge) to volcanics intruded by granitic bodies (Pison) to porphyry type intrusions ( Batalha and V6) and to epithermal-porphyry deposits (V3). ouro, cobre, molibdenita, pórfiros, exploração mineral, amazônia, brasil, geologia, consultor, áreas, garimpos, minerais, quartzo, tantalita, ametista, citrino, diamantes, tapajós,