Arid
DOI10.1016/j.apgeochem.2012.10.030
Stable isotopic composition of soil calcite (O, C) and gypsum (S) overlying Cu deposits in the Atacama Desert, Chile: Implications for mineral exploration, salt sources, and paleoenvironmental reconstruction
Leybourne, Matthew I.1; Cameron, Eion M.2; Reich, Martin3,4; Palacios, Carlos3; Faure, Kevin5; Johannesson, Karen H.6
通讯作者Leybourne, Matthew I.
来源期刊APPLIED GEOCHEMISTRY
ISSN0883-2927
出版年2013
卷号29页码:55-72
英文摘要

Soils overlying two porphyry Cu deposits (Spence, Gaby Sur) and the Pampa del Tamarugal, Atacama Desert, Northern Chile were collected in order to investigate the extent to which saline groundwaters influence "soil’’ chemistry in regions with thick Miocene and younger sediment cover. Soil carbonate (calcite) was analyzed for C and O isotopes and pedogenic gypsum for S isotopes. Soil calcite is present in all soils at the Spence deposit, but increases volumetrically above two fracture zones that cut the Miocene gravels, including gravels that overlie the deposit. The C isotope composition of carbonate from the soils overlying fracture zones is indistinguishable from pedogenic carbonate elsewhere at the Spence deposit; all delta C-13(VPDB) values fall within a narrow range (1.40-4.23 parts per thousand), consistent with the carbonate having formed in equilibrium with atmospheric CO2. However, delta O-18(VPDB) for carbonate over both fracture zones is statistically different from carbonate elsewhere (average delta O-18(VPDB) = 0.82 parts per thousand vs. -2.23 parts per thousand, respectively), suggesting involvement of groundwater in their formation. The composition of soils at the Tamarugal anomaly has been most strongly affected by earthquake-related surface flooding and evaporation of groundwater; delta C-13(VPDB) values (-4.28 parts per thousand to -2.04 parts per thousand) are interpreted to be a mixture of dissolved inorganic C (DIC) from groundwater and atmospheric CO2. At the Spence deposit, soils only rarely contain sufficient SO4 for S isotope analysis; the SO4-bearing soils occur only above the fracture zones in the gravel. Results are uniform (3.7-4.9 parts per thousand delta S-34(CDT)), which is near the middle of the range for SO4 in groundwater (0.9-7.3 parts per thousand). Sulfur in soils at the Gaby Sur deposit (3.8-6.1% delta S-34(CDT)) is dominated by gypsum, which primarily occurs on the flanks and tops of hills, suggesting deposition from SO4-rich fogs. Sulfate in Gaby Sur deposit gypsum is possibly derived by condensation of airborne SO4 from volcanic SO2 from the nearby Andes. At the Gaby Sur deposit and Tamarugal anomaly, pedogenic stable isotopes cannot distinguish between S from porphyry or redeposited SO4 from interior salars.


The three sites studied have had different histories of salt accumulation and display variable influence of groundwater, which is interpreted to have been forced to the surface during earthquakes. The clear accumulation of salts associated with fractures at the Spence deposit, and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process. The interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism. (c) 2012 Elsevier Ltd. All rights reserved.


类型Article
语种英语
国家Canada ; Chile ; New Zealand ; USA
收录类别SCI-E
WOS记录号WOS:000314687100005
WOS关键词PORPHYRY COPPER-DEPOSIT ; NORTHERN CHILE ; CARBON-DIOXIDE ; PEDOGENIC CARBONATE ; GEOCHEMICAL ANOMALIES ; PALEOSOL CARBONATES ; OXYGEN ISOTOPES ; COASTAL RANGE ; LA-ESCONDIDA ; SULFATE
WOS类目Geochemistry & Geophysics
WOS研究方向Geochemistry & Geophysics
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/175768
作者单位1.ALS Geochem, N Vancouver, BC V7H 0A7, Canada;
2.Eion Cameron Geochem Inc, Carp, ON K0A 1L0, Canada;
3.Univ Chile, Fac Ciencias Fis & Matemat, Dept Geol, Santiago, Chile;
4.Univ Chile, Andean Geothermal Ctr Excellence CEGA, Santiago, Chile;
5.GNS Sci, Lower Hutt, New Zealand;
6.Tulane Univ, Dept Earth & Environm Sci, New Orleans, LA 70118 USA
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Leybourne, Matthew I.,Cameron, Eion M.,Reich, Martin,et al. Stable isotopic composition of soil calcite (O, C) and gypsum (S) overlying Cu deposits in the Atacama Desert, Chile: Implications for mineral exploration, salt sources, and paleoenvironmental reconstruction[J],2013,29:55-72.
APA Leybourne, Matthew I.,Cameron, Eion M.,Reich, Martin,Palacios, Carlos,Faure, Kevin,&Johannesson, Karen H..(2013).Stable isotopic composition of soil calcite (O, C) and gypsum (S) overlying Cu deposits in the Atacama Desert, Chile: Implications for mineral exploration, salt sources, and paleoenvironmental reconstruction.APPLIED GEOCHEMISTRY,29,55-72.
MLA Leybourne, Matthew I.,et al."Stable isotopic composition of soil calcite (O, C) and gypsum (S) overlying Cu deposits in the Atacama Desert, Chile: Implications for mineral exploration, salt sources, and paleoenvironmental reconstruction".APPLIED GEOCHEMISTRY 29(2013):55-72.
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