DIVERSITY OF FLUIDS IN THE ORIGIN OF THE CHAPADA CU-AU DEPOSIT, GOlÁS

Abstract

neoproterozdica. O minério ocorre intimamente associado a zonas de alteração hidrotennal, sendo que ambos são controlados por fraturamento, mais intense nas proximidades de contactos de corpos intrusivos e zonas de falhas regionais. O estagio inicial da mineralização consistiu de reações entre água do mar aquecida e basaltos da sequencia de Mara Rosa (fluido hidrotermal exalativo), com lixiviação de metais das rochas basalticas e deposição em zonas de alteração hidrotermal. Posteriormente, fluido hidrotermal, originado de intrusoes dioriticas pequenas lixiviou metais de rochas encaixantes, cuja deposição enriqueceu a mineralização. Finalmente, fluidos metamorficos, gerados durante a orogenese brasiliana, formaram veios de quartzo auriferos em aieas próximas a Chapada.

The Chapada Cu–Au deposit, Mara Rosa magmatic arc, Central Brazil: Constraints on the metallogenesis of a Neoproterozoic large porphyry-type deposit

“…More recently, Kuyumjian (2000Kuyumjian ( , 1995 has reformulated his model approaching the model presented by Richardson et al (1986), suggesting that the Chapada Cu-Au deposit could have been formed by a combination of processes involving magmatic epithermal hydrothermal activity, followed by metamorphic remobilization, which the author generally called the metamorphosed or modified porphyry-epithermal system.…”

Magmatic Arc and Associated Gold, Copper, Silver, and Barite Deposits in the State of Goiás, Central Brazil: Characteristics and Speculations

“…), biotitemicrocline bearing gneiss (felsic metavolcanic protolith? ), amphibolite of calc-alkaline affinity, and hydrothermal alteration products such as epidote-rich rock (epidosite), pyrite-magnetite-quartz-sericite schist, gedrite-anthophilyte schist, kyanite schist and minor staurolite-kyanite ortho-amphibolite (Kuyumjian 1991(Kuyumjian ,1995. The deposit is controlled by a N20 0 -40 0 E trending shear zone, but subsidiary N20 0 -40 0 W, N50 0 -70 0 E, N10 0 E and NS trending shear systems are also present.…”

“…The ore body consists of pyrite-chalcopyrite-magnetite disseminated in feldspathic biotite schist, but also in sericite-rich schist and silicified zone. The ore mineralogy also includes hematite, bornite, chalcocite, sphalerite, galena, pyrrhotite and molybdenite (Richardson et al 1986, Kuyumjian 1995. Gold is very fine-grained, included in chalcopyrite, and less commonly occurs as coarse-grained gold, in Figure 1-Geological sketch map of the Brasília Belt (simplified after Fuck 1994) between sulphide grains.…”

“…Palermo (1996) proposes that the amphibolites of the Mara Rosa region are dominantly arc-type calc-alkaline metabasalts. Kuyumjian (1994Kuyumjian ( , 1995 observes that throughout the Chapada (Alto Horizonte) area (situated approximately 40 km to the south of the Mara Rosa town), the Eastern Belt, which hosts the Chapada deposit, consists of a variety of metamorphic rocks. These are metagraywackes, sillimanite-staurolite-kyanite bearing schist, quartzfeldspathic biotite schist, feldspathic metasandstone, garnet-biotite schist, metachert, banded iron formation, calc-silicate rocks and exhalites, with intercalations of calc-alkaline quartz amphibolite and quartz-garnet amphibolite.…”

“…Shear zones display NS, N10 0 -20 0 W and N20 0 -40 0 Ed trends. Brasiliano deformation places the Mara Rosa volcanicsedimentary sequence in the hangingwall of the Rio dos Bois thrust fault, whose footwall consists of Paleoproterozoic Santa Terezinha volcanic-sedimentary sequence that occurs to the east (Kuyumjian 1995). This fault has a dextral oblique and reverse sense of shear (Kuyumjian et al 2000).…”