{"title":"Stalactitic rhodochrosite from the 25 de Mayo and Nueve veins, Capillitas, Catamarca, Argentina: Physical and chemical variations","authors":"María Florencia, MÁRQUEZ-ZAVALÍA, James R. Craig","doi":"10.3190/jgeosci.354","DOIUrl":null,"url":null,"abstract":"Capillitas is an epithermal vein-type deposit in Argentina known for its mineralogical diversity, with more than one hundred and twenty described minerals, including five new species, and for the presence of banded and stalactitic rhodochrosite. Stalactites occur as single or combined cylinders of different sizes, from a few cm to 1.36 m in length and diameters up to 8 cm. Their cross-sections may show diverse aspects: from simple concentric banding to more intricate textures, whereas their external surface can be smooth, with undulations or with a poker-chip-like texture. The color of the stalactites varies from white to raspberry pink, with occasional brown bands toward the edges corresponding to a variety of rhodochrosite called “capillitite”. The contents of MnO range from 27.50 to 61.71 wt. % as it may be significantly replaced by CaO, FeO, ZnO and MgO. Replacements are reflected in the various shades of pink and brown displayed by this mineral. The different substitutions in the pink specimens exert only a minor influence on the unit cell parameters, whereas, in the brown variety, their size is significantly smaller with average values for pink rhodochrosite ( n = 24): a 4.776 Å, c 15.690 Å and a cell volume of 310.3 Å 3 , whereas, “capillitite” unit-cell parameters ( n = 7) are: a = 4.739, c = 15.558 with a unit-cell volume of 302.6 Å 3 . Conditions of formation of the banded rhodochrosite of the 25 de Mayo vein, obtained from fluid inclusions data, indicate temperatures of 145 ° to 150 °C and salinities of up to 4 wt. % NaCl(eq). The formation of the stalactites is explained by the infiltration of epithermal aqueous liquid, oversa - turated with Mn and bicarbonate, into a transiently vapor-filled, isolated cavity.","PeriodicalId":15957,"journal":{"name":"Journal of Geosciences","volume":" ","pages":""},"PeriodicalIF":1.1000,"publicationDate":"2022-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Geosciences","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.3190/jgeosci.354","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
Capillitas is an epithermal vein-type deposit in Argentina known for its mineralogical diversity, with more than one hundred and twenty described minerals, including five new species, and for the presence of banded and stalactitic rhodochrosite. Stalactites occur as single or combined cylinders of different sizes, from a few cm to 1.36 m in length and diameters up to 8 cm. Their cross-sections may show diverse aspects: from simple concentric banding to more intricate textures, whereas their external surface can be smooth, with undulations or with a poker-chip-like texture. The color of the stalactites varies from white to raspberry pink, with occasional brown bands toward the edges corresponding to a variety of rhodochrosite called “capillitite”. The contents of MnO range from 27.50 to 61.71 wt. % as it may be significantly replaced by CaO, FeO, ZnO and MgO. Replacements are reflected in the various shades of pink and brown displayed by this mineral. The different substitutions in the pink specimens exert only a minor influence on the unit cell parameters, whereas, in the brown variety, their size is significantly smaller with average values for pink rhodochrosite ( n = 24): a 4.776 Å, c 15.690 Å and a cell volume of 310.3 Å 3 , whereas, “capillitite” unit-cell parameters ( n = 7) are: a = 4.739, c = 15.558 with a unit-cell volume of 302.6 Å 3 . Conditions of formation of the banded rhodochrosite of the 25 de Mayo vein, obtained from fluid inclusions data, indicate temperatures of 145 ° to 150 °C and salinities of up to 4 wt. % NaCl(eq). The formation of the stalactites is explained by the infiltration of epithermal aqueous liquid, oversa - turated with Mn and bicarbonate, into a transiently vapor-filled, isolated cavity.
期刊介绍:
The Journal of Geosciences is an international peer-reviewed journal published by the Czech Geological Society with support from the Czech Geological Survey. It accepts high-quality original research or review papers dealing with all aspects of the nature and origin of igneous and metamorphic rocks. The Journal focuses, mainly but not exclusively, on:
-Process-oriented regional studies of igneous and metamorphic complexes-
Research in structural geology and tectonics-
Igneous and metamorphic petrology-
Mineral chemistry and mineralogy-
Major- and trace-element geochemistry, isotope geochemistry-
Dating igneous activity and metamorphic events-
Experimental petrology and mineralogy-
Theoretical models of igneous and metamorphic processes-
Mineralizing processes and mineral deposits.
All the papers are written in English, even though they may be accompanied by an additional Czech abstract. Each contribution is a subject to peer review by at least two independent reviewers, typically at least one from abroad. The Journal appears 2 to 4 times a year. Formally it is divided in annual volumes, each of them including 4 issues.