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The importance of CO 2 on freezing point measurements of fluid inclusions; evidence from active geothermal systems and implications for epithermal ore deposition

1985; Volume: 80; Issue: 5 Linguagem: Inglês

10.2113/gsecongeo.80.5.1379

1554-0774

Jeffrey W. Hedenquist, Richard W. Henley,

CO2 Sequestration and Geologic Interactions

Other| August 01, 1985 The importance of CO 2 on freezing point measurements of fluid inclusions; evidence from active geothermal systems and implications for epithermal ore deposition Jeffrey W. Hedenquist; Jeffrey W. Hedenquist DSIR Chem. Div., Taupo, New Zealand Search for other works by this author on: GSW Google Scholar Richard W. Henley Richard W. Henley Search for other works by this author on: GSW Google Scholar Author and Article Information Jeffrey W. Hedenquist DSIR Chem. Div., Taupo, New Zealand Richard W. Henley Publisher: Society of Economic Geologists First Online: 02 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 GeoRef, Copyright 2004, American Geological Institute. Reference includes data supplied by Institute of Geological and Nuclear Sciences (SIRIS), Lower Hutt, New Zealand Economic Geology (1985) 80 (5): 1379–1406. https://doi.org/10.2113/gsecongeo.80.5.1379 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Jeffrey W. Hedenquist, Richard W. Henley; The importance of CO 2 on freezing point measurements of fluid inclusions; evidence from active geothermal systems and implications for epithermal ore deposition. Economic Geology 1985;; 80 (5): 1379–1406. doi: https://doi.org/10.2113/gsecongeo.80.5.1379 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract In studies of epithermal precious and base metal ore deposits, estimates of salinity (total dissolved salts) are frequently in error when based on fluid inclusion ice melting measurements in the absence of an independent determination of the CO 2 content of the inclusion fluid. For a fluid of known composition the melting pint of ice (T m ) may be calculated from T m = -sigma K i m i where K i is the molal freezing (or melting) point depression constant and m i is the molality of a component i (i = Na (super +) , K (super +) , Cl (super -) , CO 2 etc) for fully dissociated solute species such as Cl (super -) , in the salinity range considered here K = 1.72 Kelvin/molal, and for undissociated, nonpolar species such as CO 2 , K = 1.86 Kelvin/molal. Fluid inclusion ice-melting data from New Zealand geothermal fields correlate well with values calculated using the above equation and the measured compositions of discharges from wells from which the inclusion samples were obtained. Loss of the dominant dissolved gas, CO 2 during boiling at depth results in large, systematic decreases in apparent salinity (in terms of T m ) in the Broadlands field. Misinterpretation of fluid inclusion freezing data may lead to substantial errors in the reconstruction of the physico-chemical environment of ore formation in fossil systems. For example in the absence of CO 2 analyses, inclusion fluids similar in gas content to the Broadlands geothermal fluid (NaCl 0.2 wt %, CO 2 up to 4.4 wt %) may be interpreted to have salinities of 0.85 wt percent NaCl leading to errors of 23% in the estimated depth of formation at 280 degrees C -0.5 unit in the estimated pH of the ore fluid, and on the order of 200 times in the estimated solubility of an ore component such as lead. Such errors may be transmitted into subsequent estimation of fluid flux or duration of ore formation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.