Gênese do depósito polimetálico Sn (W, Zn, Cu, Pb) Morro Potosi, Rondônia
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Data
2019-08-23
Autores
Nogueira, Eduardo Hansen
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Universidade Estadual Paulista (Unesp)
Resumo
O depósito polimetálico Sn (W, Zn, Cu, Pb) Morro Potosi, localizado no município de Itapuã do Oeste, região centro-norte do Estado de Rondônia, foi o primeiro depósito primário de estanho descoberto na Província Estanífera de Rondônia, em 1977. Até 1987, ano de encerramento das atividades exploratória da mina, foram exploradas 8 000 t de Sn apenas em seus primeiros 55 metros de profundidade. O depósito é caracterizado como um exogreisen brechado, com aproximadamente 170 m de profundidade, formado sobre os gnaisses do embasamento (Complexo Jamari). A mineralização está associada a greisens, microgranito, topazito, veios de quartzo e vênulas e miárolos tardios. A primeira fase de mineralização é caracterizada por cassiterita disseminada em greisens constituídos por quartzo, muscovita, sericita e topázio, com fluorita, rutilo tantalífero, zircão, monazita e óxido de Bi e W como minerais acessórios. A segunda fase compreende diques e veios de microgranito com cassiterita disseminada, que cortam o gnaisse e constituem a matriz de uma brecha cujos fragmentos são formados pelo próprio gnaisse. Diques e veios de topazito com cassiterita disseminada cortam o gnaisse e o greisen e formam a matriz de brechas com fragmentos de dimensão e formatos variados. Veios e vênulas de quartzo cortam as litologias anteriores. Possuem muscovita, topázio, cassiterita, wolframita, esfalerita, calcopirita e pirita como principais acessórios, além de quantidades subordinadas de galena, arsenopirita e estanita. Vênulas e miárolos tardios ocorrem como último estágio de mineralização. São constituídos por proporções variadas de quartzo, fluorita, muscovita, calcita, zeólita, esfalerita, calcopirita, pirita, dickita, caulinita e outros argilominerais, além de proporções menores de cassiterita, galena, arsenopirita, estanita, cobaltita, rutilo, covellita, bismuto nativo, hematita, molibdenita, tetraedrita-tennantita e boulangerita. Estudo inclusões fluidas em greisen, topazito, veio de quartzo e vênulas e miárolos tardios revelaram fluidos pertencentes ao sistemas NaCl-KCl-H2O e NaCl-KCl-CO2-H2O, de salinidade moderada a baixa (1 a 12,2 eq. %NaCl em peso) e com diminuição progressiva das temperaturas de homogeneização total das fases iniciais para as fases tardias de mineralização.
The Potosi Hill polymetallic deposit (Sn, W, Zn, Cu, Pb), located in Itapuã do Oeste, in the northern region of Rondônia State, was the first primary tin deposit discovered in Rondônia Tin Province, in 1977. In 1987 8000 t Sn only in its first 55 meters deep. The deposit is characterized as a breccia exogreisen body, with approximately 170 m deep, formed on the basement gneiss rocks (Jamari Complex). Mineralization is associated with greisens, microgranite, topazite, quartz veins and late miarolitic cavities and veinlets. The first mineralization stage is characterized by disseminated cassiterite in greisens consisting of quartz, muscovite, sericite and topaz, with fluorite, tantaliferous rutile, zircon, monazite and Bi and W oxide as accessory minerals. The second phase comprises microgranite dikes and veins with disseminated cassiterite, which crosscut the gneiss and constitute the matrix of a breccia with fragments of gneiss. Topazite dikes and veins with disseminated cassiterite crosscut the gneiss and the greisen and constitute the matrix of breccias with fragments of size and varied formats. Quartz veins and veinlets crosscut the previous rocks. They have muscovite, topaz, cassiterite, wolframite, sphalerite, chalcopyrite and pyrite as main accessories, as well as subordinate amounts of galena, arsenopyrite and stannite. Late miarolitic cavities and veinlets occur as the last stage of mineralization. They consist of different proportions of quartz, fluorite, muscovite, calcite, zeolite, sphalerite, chalcopyrite, pyrite, dickite, kaolinite and other clay minerals, as well as minor proportions of cassiterite, galena, arsenopyrite, stannite, cobalt, rutile, covellite, native bismuth, hematite, molybdenite, tetrahedrite-tennantite and boulangerite. Fluid inclusion studies in greisen, topazite, quartz veins and late miarolitic cavities recognized the fluid systems NaCl-KCl-H2O and NaCl-KCl-CO2-H2O, with moderate to low salinity (1 to 12.2 wt. %NaCl) and with progressive reduction of total homogenization temperatures from the initial phases to the late mineralization phases.
The Potosi Hill polymetallic deposit (Sn, W, Zn, Cu, Pb), located in Itapuã do Oeste, in the northern region of Rondônia State, was the first primary tin deposit discovered in Rondônia Tin Province, in 1977. In 1987 8000 t Sn only in its first 55 meters deep. The deposit is characterized as a breccia exogreisen body, with approximately 170 m deep, formed on the basement gneiss rocks (Jamari Complex). Mineralization is associated with greisens, microgranite, topazite, quartz veins and late miarolitic cavities and veinlets. The first mineralization stage is characterized by disseminated cassiterite in greisens consisting of quartz, muscovite, sericite and topaz, with fluorite, tantaliferous rutile, zircon, monazite and Bi and W oxide as accessory minerals. The second phase comprises microgranite dikes and veins with disseminated cassiterite, which crosscut the gneiss and constitute the matrix of a breccia with fragments of gneiss. Topazite dikes and veins with disseminated cassiterite crosscut the gneiss and the greisen and constitute the matrix of breccias with fragments of size and varied formats. Quartz veins and veinlets crosscut the previous rocks. They have muscovite, topaz, cassiterite, wolframite, sphalerite, chalcopyrite and pyrite as main accessories, as well as subordinate amounts of galena, arsenopyrite and stannite. Late miarolitic cavities and veinlets occur as the last stage of mineralization. They consist of different proportions of quartz, fluorite, muscovite, calcite, zeolite, sphalerite, chalcopyrite, pyrite, dickite, kaolinite and other clay minerals, as well as minor proportions of cassiterite, galena, arsenopyrite, stannite, cobalt, rutile, covellite, native bismuth, hematite, molybdenite, tetrahedrite-tennantite and boulangerite. Fluid inclusion studies in greisen, topazite, quartz veins and late miarolitic cavities recognized the fluid systems NaCl-KCl-H2O and NaCl-KCl-CO2-H2O, with moderate to low salinity (1 to 12.2 wt. %NaCl) and with progressive reduction of total homogenization temperatures from the initial phases to the late mineralization phases.
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Província Estanífera de Rondônia, Depósito Morro Potosi, Greisens, Inclusões fluidas, Rondonia Tin Province, Potosi Hill deposit, Fluid inclusions