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Cassiterite crystallization experiments in alkali carbonate aqueous solutions using a hydrothermal diamond-anvil cell

Liu Yongchao, Li Jiankang and Chou I-Ming
Cassiterite crystallization experiments in alkali carbonate aqueous solutions using a hydrothermal diamond-anvil cell
American Mineralogist (May 2020) 105 (5): 664-673

Abstract

Ore-forming fluids enriched in alkali carbonate are commonly observed in natural melt and fluid inclusions associated with tin mineralization, particularly in granitic pegmatite. However, the roles of alkali carbonates remain unclear. Hence, to investigate the roles of alkali carbonate, herein, cassiterite (SnO (sub 2) ) crystallization experiments in SnO (sub 2) -Li (sub 2) CO (sub 3) -H (sub 2) O and SnO (sub 2) -Na (sub 2) CO (sub 3) -H (sub 2) O systems were conducted using a hydrothermal diamond-anvil cell. The results showed that SnO (sub 2) could dissolve into the alkali carbonate aqueous solution during heating, and long prismatic cassiterite crystals grew during the subsequent cooling stage at average rates of 0.61 X 10 (super -6) to 8.22 X 10 (super -6) cm/s in length and 3.40-19.07 mu m (super 3) /s in volume. The mole fraction of cassiterite crystallized from the SnO (sub 2) -Li (sub 2) CO (sub 3) -H (sub 2) O system ranges from 0.03 to 0.41 mol%, which depends on the Li (sub 2) CO (sub 3) content dissolved in the aqueous solution. In situ Raman analysis of the alkali carbonate-rich aqueous solution in the sample chamber suggests that the dissolution of SnO (sub 2) can be attributed to the alkaline conditions produced by hydrolysis of alkali carbonate in which Sn(OH) (sub 6) (super 2-) may be a potential tin-transporting species. The cassiterite crystallization conditions obtained in our SnO (sub 2) -alkali carbonate-H (sub 2) O systems primarily fell within the 400-850 degrees C and 300-850 MPa temperature and pressure ranges, respectively; furthermore, cassiterite crystallization ended in rare metal pegmatite-forming conditions. These crystallization features of cassiterite are similar to those formed in tin-mineralized granitic pegmatites. It indicates that an alkali carbonate-rich aqueous solution or hydrous melt can work as a favorable transport medium for tin and provides the necessary conditions for cassiterite crystallization in granitic pegmatite, bearing the roles in decreasing the viscosity of hydrous melts and enhancing the solubility of SnO (sub 2) in ore-forming melts or fluids. These roles of alkali carbonate can also be extended for the mineralization of other rare metals (e.g., Li and Be) in granitic pegmatite.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 105
Serial Issue: 5
Title: Cassiterite crystallization experiments in alkali carbonate aqueous solutions using a hydrothermal diamond-anvil cell
Affiliation: Chinese Academy of Geological Sciences, Institute of Mineral Resources, Beijing, China
Pages: 664-673
Published: 202005
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 88
Accession Number: 2020-049474
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Chinese Academy of Sciences, Institute of Deep-Sea Science and Engineering, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202014
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