Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil.
Autor(a) principal: | |
---|---|
Data de Publicação: | 1998 |
Outros Autores: | , |
Tipo de documento: | Artigo |
Idioma: | eng |
Título da fonte: | Repositório Institucional de Geociências - RIGEO |
Texto Completo: | https://rigeo.cprm.gov.br/handle/doc/1266 |
Resumo: | The potassium feldspar variety adularia was found in the Davi and Joel primary gold prospects located in the Tapajós Mineral Province, southwestern Pará State, Brazil. In both areas adularia occupies fractures and vugs intimately associated with mineralized quartz veins hosted by hydrothermally altered Proterozoic subvolcanic mafic rocks. Adularia constitutes small (1-4 mm) red to pink crystals of pseudo-orthorhombic form. The Felsöbanya habit was identified in specimens from the Joel prospect. Microprobe analyses show that adularia has a composition near to pure KalSi3O8. X-ray diffraction data indicate that the feldspars correspond to predominantly triclinic types with structural state near that of maximum microcline. This high degree of ordering is relatively rare in adularia and may be attributed to the extensive action of late fluids over originally metastable, disordered crystals whose primitive monoclinic form is still preserved. Fluid inclusion studies in quartz crystals adjacent to adularia show that the feldspar formed under temperatures of 240° -320°C at Davi and 220° - 340°C at Joel. The trapped fluids are poor in or devoid of CO2. Fluid salinity was low, averaging 1.15 at Davi and 0.43 at Joel, attaining exceptionally values up to 11 wt.% NaCl equivalent. Considering that the presence of adularia is indicative of boiling, it is possible to estimate a maximum depth of 1.5 km for the formation of adularia and the associated quartz veins. The presence of adularia in the Davi and Joel prospects is important in the definition of the typology of primary gold of the Tapajós Province as this feldspar is a typical mineral of epithermal deposits of the adularia-sericite category. Other features also point to the epithermal nature of the mentioned occurrences. These include the non-metamorphic character of the host rocks and their hydrothermal alteration pattern; the open-space filling textures of the veins and their mineral assemblage; and the brittle nature of the deformation imprinted in both veins and wallrocks. The composition of fluids in inclusions also lies within the limits admitted for adularia-sericite epithermal deposits. The temperatures of formation of the adularia and quartz veins, in turn, belong to a high temperature rank in epithermal deposits, suggesting that the Davi and Joel prospects correpond to exposures of the deeper, higher temperature sectors of their original hydrothermal systems. Two other aspects should be emphasized concerning the definition of an epithermal typology for gold occurrences in the Tapajós region. The Proterozoic age is an unusually old one for this type of deposit, as the majority of their representatives in the world are Cenozoic; and the definition is interesting for gold exploration in connection with the potential for bulk-tonnage deposits. |
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DREHER, Ana MariaVLACH, Silvio R. F.MARTINI, Sérgio L.2014-07-17T13:44:47Z2014-07-17T13:44:47Z1998DREHER, Ana M; VLACH, Silvio R. F; MARTINI, Sérgio L. Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. Revista Brasileira de Geociências, São Paulo, v.28, n.3, p. 397-404, il. 1998.03757536https://rigeo.cprm.gov.br/handle/doc/1266The potassium feldspar variety adularia was found in the Davi and Joel primary gold prospects located in the Tapajós Mineral Province, southwestern Pará State, Brazil. In both areas adularia occupies fractures and vugs intimately associated with mineralized quartz veins hosted by hydrothermally altered Proterozoic subvolcanic mafic rocks. Adularia constitutes small (1-4 mm) red to pink crystals of pseudo-orthorhombic form. The Felsöbanya habit was identified in specimens from the Joel prospect. Microprobe analyses show that adularia has a composition near to pure KalSi3O8. X-ray diffraction data indicate that the feldspars correspond to predominantly triclinic types with structural state near that of maximum microcline. This high degree of ordering is relatively rare in adularia and may be attributed to the extensive action of late fluids over originally metastable, disordered crystals whose primitive monoclinic form is still preserved. Fluid inclusion studies in quartz crystals adjacent to adularia show that the feldspar formed under temperatures of 240° -320°C at Davi and 220° - 340°C at Joel. The trapped fluids are poor in or devoid of CO2. Fluid salinity was low, averaging 1.15 at Davi and 0.43 at Joel, attaining exceptionally values up to 11 wt.% NaCl equivalent. Considering that the presence of adularia is indicative of boiling, it is possible to estimate a maximum depth of 1.5 km for the formation of adularia and the associated quartz veins. The presence of adularia in the Davi and Joel prospects is important in the definition of the typology of primary gold of the Tapajós Province as this feldspar is a typical mineral of epithermal deposits of the adularia-sericite category. Other features also point to the epithermal nature of the mentioned occurrences. These include the non-metamorphic character of the host rocks and their hydrothermal alteration pattern; the open-space filling textures of the veins and their mineral assemblage; and the brittle nature of the deformation imprinted in both veins and wallrocks. The composition of fluids in inclusions also lies within the limits admitted for adularia-sericite epithermal deposits. The temperatures of formation of the adularia and quartz veins, in turn, belong to a high temperature rank in epithermal deposits, suggesting that the Davi and Joel prospects correpond to exposures of the deeper, higher temperature sectors of their original hydrothermal systems. Two other aspects should be emphasized concerning the definition of an epithermal typology for gold occurrences in the Tapajós region. The Proterozoic age is an unusually old one for this type of deposit, as the majority of their representatives in the world are Cenozoic; and the definition is interesting for gold exploration in connection with the potential for bulk-tonnage deposits.Sociedade Brasileira de GeologiaPROVINCIA MINERALOURODEPÓSITOSMORFOLOGIAQUIMICAGEOLOGIA REGIONALGEOLOGIA ECONÔMICABRASILAdularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil.info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/articleSão Pauloinfo:eu-repo/semantics/openAccessengreponame:Repositório Institucional de Geociências - RIGEOinstname:Companhia de Pesquisa de Recursos Minerais (CPRM)instacron:CPRMTEXTAdularia associated with epithermal gold veins in the Tapajós_AMDreher.pdf.txtAdularia associated with epithermal gold veins in the Tapajós_AMDreher.pdf.txtExtracted texttext/plain51602http://rigeo.cprm.gov.br/jspui/bitstream/doc/1266/3/Adularia%20associated%20with%20epithermal%20gold%20veins%20in%20the%20Tapaj%c3%b3s_AMDreher.pdf.txt8ded362c456ee6c3fa76ed203b3d824bMD53THUMBNAILAdularia associated with epithermal gold veins in the Tapajós_AMDreher.pdf.jpgAdularia associated with epithermal gold veins in the Tapajós_AMDreher.pdf.jpgGenerated Thumbnailimage/jpeg1553http://rigeo.cprm.gov.br/jspui/bitstream/doc/1266/4/Adularia%20associated%20with%20epithermal%20gold%20veins%20in%20the%20Tapaj%c3%b3s_AMDreher.pdf.jpge3791da436c5c7612f8209116be8d593MD54ORIGINALAdularia associated with epithermal gold veins in the Tapajós_AMDreher.pdfAdularia associated with epithermal gold veins in the Tapajós_AMDreher.pdfproducao cientificaapplication/pdf1836229http://rigeo.cprm.gov.br/jspui/bitstream/doc/1266/1/Adularia%20associated%20with%20epithermal%20gold%20veins%20in%20the%20Tapaj%c3%b3s_AMDreher.pdff253cf52dfffae4dfa465a66366a3301MD51LICENSElicense.txtlicense.txttext/plain; charset=utf-81748http://rigeo.cprm.gov.br/jspui/bitstream/doc/1266/2/license.txt8a4605be74aa9ea9d79846c1fba20a33MD52doc/12662023-02-13 11:09:00.056oai:rigeo.sgb.gov.br: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Repositório InstitucionalONGhttp://rigeo.cprm.gov.br/oai/requestrigeo@sgb.gov.bropendoar:2023-02-13T14:09Repositório Institucional de Geociências - RIGEO - Companhia de Pesquisa de Recursos Minerais (CPRM)false |
dc.title.pt_BR.fl_str_mv |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. |
title |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. |
spellingShingle |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. DREHER, Ana Maria PROVINCIA MINERAL OURO DEPÓSITOS MORFOLOGIA QUIMICA GEOLOGIA REGIONAL GEOLOGIA ECONÔMICA BRASIL |
title_short |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. |
title_full |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. |
title_fullStr |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. |
title_full_unstemmed |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. |
title_sort |
Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. |
author |
DREHER, Ana Maria |
author_facet |
DREHER, Ana Maria VLACH, Silvio R. F. MARTINI, Sérgio L. |
author_role |
author |
author2 |
VLACH, Silvio R. F. MARTINI, Sérgio L. |
author2_role |
author author |
dc.contributor.author.fl_str_mv |
DREHER, Ana Maria VLACH, Silvio R. F. MARTINI, Sérgio L. |
dc.subject.por.fl_str_mv |
PROVINCIA MINERAL OURO DEPÓSITOS MORFOLOGIA QUIMICA GEOLOGIA REGIONAL GEOLOGIA ECONÔMICA BRASIL |
topic |
PROVINCIA MINERAL OURO DEPÓSITOS MORFOLOGIA QUIMICA GEOLOGIA REGIONAL GEOLOGIA ECONÔMICA BRASIL |
description |
The potassium feldspar variety adularia was found in the Davi and Joel primary gold prospects located in the Tapajós Mineral Province, southwestern Pará State, Brazil. In both areas adularia occupies fractures and vugs intimately associated with mineralized quartz veins hosted by hydrothermally altered Proterozoic subvolcanic mafic rocks. Adularia constitutes small (1-4 mm) red to pink crystals of pseudo-orthorhombic form. The Felsöbanya habit was identified in specimens from the Joel prospect. Microprobe analyses show that adularia has a composition near to pure KalSi3O8. X-ray diffraction data indicate that the feldspars correspond to predominantly triclinic types with structural state near that of maximum microcline. This high degree of ordering is relatively rare in adularia and may be attributed to the extensive action of late fluids over originally metastable, disordered crystals whose primitive monoclinic form is still preserved. Fluid inclusion studies in quartz crystals adjacent to adularia show that the feldspar formed under temperatures of 240° -320°C at Davi and 220° - 340°C at Joel. The trapped fluids are poor in or devoid of CO2. Fluid salinity was low, averaging 1.15 at Davi and 0.43 at Joel, attaining exceptionally values up to 11 wt.% NaCl equivalent. Considering that the presence of adularia is indicative of boiling, it is possible to estimate a maximum depth of 1.5 km for the formation of adularia and the associated quartz veins. The presence of adularia in the Davi and Joel prospects is important in the definition of the typology of primary gold of the Tapajós Province as this feldspar is a typical mineral of epithermal deposits of the adularia-sericite category. Other features also point to the epithermal nature of the mentioned occurrences. These include the non-metamorphic character of the host rocks and their hydrothermal alteration pattern; the open-space filling textures of the veins and their mineral assemblage; and the brittle nature of the deformation imprinted in both veins and wallrocks. The composition of fluids in inclusions also lies within the limits admitted for adularia-sericite epithermal deposits. The temperatures of formation of the adularia and quartz veins, in turn, belong to a high temperature rank in epithermal deposits, suggesting that the Davi and Joel prospects correpond to exposures of the deeper, higher temperature sectors of their original hydrothermal systems. Two other aspects should be emphasized concerning the definition of an epithermal typology for gold occurrences in the Tapajós region. The Proterozoic age is an unusually old one for this type of deposit, as the majority of their representatives in the world are Cenozoic; and the definition is interesting for gold exploration in connection with the potential for bulk-tonnage deposits. |
publishDate |
1998 |
dc.date.issued.fl_str_mv |
1998 |
dc.date.accessioned.fl_str_mv |
2014-07-17T13:44:47Z |
dc.date.available.fl_str_mv |
2014-07-17T13:44:47Z |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/article |
format |
article |
status_str |
publishedVersion |
dc.identifier.citation.fl_str_mv |
DREHER, Ana M; VLACH, Silvio R. F; MARTINI, Sérgio L. Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. Revista Brasileira de Geociências, São Paulo, v.28, n.3, p. 397-404, il. 1998. |
dc.identifier.uri.fl_str_mv |
https://rigeo.cprm.gov.br/handle/doc/1266 |
dc.identifier.issn.none.fl_str_mv |
03757536 |
identifier_str_mv |
DREHER, Ana M; VLACH, Silvio R. F; MARTINI, Sérgio L. Adularia associated with epithermal gold veins in the Tapajós mineral province, Pará state, northern Brazil. Revista Brasileira de Geociências, São Paulo, v.28, n.3, p. 397-404, il. 1998. 03757536 |
url |
https://rigeo.cprm.gov.br/handle/doc/1266 |
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eng |
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eng |
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openAccess |
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Sociedade Brasileira de Geologia |
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Sociedade Brasileira de Geologia |
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Repositório Institucional de Geociências - RIGEO |
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