Advanced search
Start date
Betweenand
Related content
(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Stable isotopes and fluid inclusion constraints on the fluid evolution in the Bacaba and Castanha iron oxide-copper-gold deposits, Carajas Mineral Province, Brazil

Full text
Author(s):
Silva Pestilho, Andre Luiz [1] ; Soares Monteiro, Lena Virginia [2] ; Coelho de Melo, Gustavo Henrique [3] ; Moreto, Carolina PenteadoNatividade [4] ; Juliani, Caetano [2] ; Fallick, Anthony Edward [5] ; Xavier, Roberto Perez [4]
Total Authors: 7
Affiliation:
[1] Petrobras Res & Dev Ctr CENPES, Ave Horacio Macedo 950, BR-21941915 Rio De Janeiro, RJ - Brazil
[2] Univ Sao Paulo, Inst Geosci, Rua Lago 562, BR-05508080 Sao Paulo, SP - Brazil
[3] Univ Fed Ouro Preto, Dept Geol, BR-35400000 Ouro Preto, MG - Brazil
[4] Univ Estadual Campinas, Inst Geosci, Rua Carlos Gomes 250, BR-13083896 Campinas, SP - Brazil
[5] Scottish Univ Environm Res Ctr, Glasgow G75 0QU, Lanark - Scotland
Total Affiliations: 5
Document type: Journal article
Source: ORE GEOLOGY REVIEWS; v. 126, NOV 2020.
Web of Science Citations: 0
Abstract

The evolution of the Bacaba and Castanha iron oxide-copper-gold deposits, located in the Carajas Mineral Province, Brazil, is discussed based on petrography, scanning electron microscopy, stable isotopes, and fluid inclusion analyses. The Castanha deposit is mainly hosted by ca. 2.75 Ga subvolcanic and volcanic rhyodacitic rocks, and gabbros. Early sodic (albite, scapolite) alteration was followed by high-temperature calcic-iron (ac-tinolite-magnetite), potassic (biotite), and minor chlorite and sericite alteration. Calcite, REE carbonate, and epidote represent a late and proximal alteration to ore bodies. Ore breccias with Durchbewegung structure comprise chalcopyrite + pyrrhotite + pyrite +/- cobaltpentlandite +/- sphalerite +/- marcasite and are notable due to their nickel-(zinc) enrichment. The Bacaba Deposit is hosted by the ca. 3.00 Ga Bacaba Tonalite, 2.85 Ga Serra Dourada Granite, and gabbro bodies. Early (ca. 2.70 Ga) alteration at Bacaba includes sodic (albite, scapolite), iron (magnetite), and potassic-iron (K feldspar-magnetite, biotite) associations. Well-developed late chlorite, albite, sericite, calcite-hematite-(musketovite) alteration formed during a Paleoproterozoic overprinting (ca. 2.06 Ga). The Bacaba ore is composed of (I) chalcopyrite +/- magnetite +/- bornite, and (II) chalcopyrite +/- pyrite +/- hematite/musketovite, related to early potassic-iron and late alteration, respectively. The Castanha deposit was formed from magmatic fluid (delta O-18(H2O) = 9.5 +/- 0.5%o to 5.2 +/- 1.0 parts per thousand, at 500 to 400 degrees C) and sulfur (delta S-34 = 0.1-3%o) sources, with a limited contribution of externally-derived fluids during its evolution. Ore precipitation progressed under considerably low fS(2) and fO(2) conditions, at relatively high temperatures (> 370 +/- 50 degrees C). Fluid inclusion analyses indicate greater proximity of the Castanha deposit to the source of a hot overpressured magmatic fluid, suggesting its formation in a high-temperature hydrothermal center. Fluid rock interaction coupled with increasing pH might have been the critical factors in destabilizing the metal chloride complex in the Castanha deposit. The Bacaba deposit evolved from a fluid-mixing between hot (> 450 degrees C) hypersaline CaCl2-NaCl-bearing magmatic brine (> 30 mass % equivalent) and a less saline, colder, and O-18-depleted and D-enriched fluid (e.g., seawater or low-latitude meteoric water). Mixing resulted in an oxidizing environment, dilution (salinities between 35 and 4 mass % equivalent), and temperature drop (160-190 degrees C), triggering the ore precipitation. At Bacaba, the slightly higher delta S-34 values (1.3-5.4 parts per thousand) may reflect an additional contribution of externally-derived sulfur through the thermochemical reduction of oxidized sulfur species. In the Southern Copper Belt, the regional spatial distribution of the sulfur isotope compositions shows the highest delta S-34(sulfide) values close to the Paleoproterozoic Sossego Orebody and the Alvo 118 deposit. This might suggest significant involvement of externally-derived components (e.g., diluted fluids and sulfur) during late stages of a protracted hydrothermal evolution in the Carajas IOCG deposits. (AU)

FAPESP's process: 09/02747-0 - Stable isotope systematic applied to the characterization of the hydrothermal paleo-systems of the Alvo Bacaba and Alvo Castanha, Carajás Mineral Province, PA.
Grantee:Andre Luiz Silva Pestilho
Support Opportunities: Scholarships in Brazil - Master