Title: Quartz Solubility in the H2O-NaCl System: A Framework for Understanding Vein Formation in Porphyry Copper Deposits
Abstract: Research Article| August 01, 2018 Quartz Solubility in the H2O-NaCl System: A Framework for Understanding Vein Formation in Porphyry Copper Deposits Thomas Monecke; Thomas Monecke 1Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, Colorado 80401 † Corresponding author: e-mail, [email protected] Search for other works by this author on: GSW Google Scholar Jochen Monecke; Jochen Monecke 2Institute of Theoretical Physics, TU Bergakademie Freiberg, Leipziger Straβe 23, 09596 Freiberg, Germany Search for other works by this author on: GSW Google Scholar T. James Reynolds; T. James Reynolds 3FLUID INC., 1401 Wewatta St. #PH3, Denver, Colorado 80202 Search for other works by this author on: GSW Google Scholar Subaru Tsuruoka; Subaru Tsuruoka 1Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, Colorado 80401 Search for other works by this author on: GSW Google Scholar Mitchell M. Bennett; Mitchell M. Bennett 1Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, Colorado 804014U.S. Geological Survey, MS 973, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Wiley B. Skewes; Wiley B. Skewes 1Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, Colorado 80401 Search for other works by this author on: GSW Google Scholar Richard M. Palin Richard M. Palin 1Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, Colorado 80401 Search for other works by this author on: GSW Google Scholar Economic Geology (2018) 113 (5): 1007–1046. https://doi.org/10.5382/econgeo.2018.4580 Article history accepted: 07 May 2018 first online: 31 Jul 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation Thomas Monecke, Jochen Monecke, T. James Reynolds, Subaru Tsuruoka, Mitchell M. Bennett, Wiley B. Skewes, Richard M. Palin; Quartz Solubility in the H2O-NaCl System: A Framework for Understanding Vein Formation in Porphyry Copper Deposits. Economic Geology 2018;; 113 (5): 1007–1046. doi: https://doi.org/10.5382/econgeo.2018.4580 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyEconomic Geology Search Advanced Search Abstract Porphyry copper deposits consist of low-grade stockwork and disseminated sulfide zones that contain characteristic vein generations formed during the evolution of the magmatic-hydrothermal systems. The present contribution proposes an interpretive framework for the formation of porphyry veins that is based on quartz solubility calculations in the H2O-NaCl system at temperatures of 100° to 1,000°C and pressures of 1 to 2,000 bar. The model predicts that high-temperature (≳500°C) quartz in A veins of deep (≳4 km) porphyry deposits forms as a result of the cooling of ascending intermediate-density fluids at lithostatic conditions. In deposits of intermediate depths (~1.5–4 km), A vein quartz is mostly formed through cooling of ascending hydrothermal fluids under closed-system conditions or quasi-isobaric cooling under open-system conditions within the two-phase field of the H2O-NaCl system. In shallow (≲1.5 km) porphyry deposits, rapid decompression can also result in quartz precipitation, forming so-called banded veins. The high-temperature quartz in A veins is associated with potassic alteration. During continued cooling of the magmatic-hydrothermal system, quartz is formed at intermediate temperatures (≳375°–500°C). This quartz overprints earlier A veins and forms B veins. The fluid inclusion inventory of this quartz generation suggests formation at fluctuating pressure conditions, marking the lithostatic to hydrostatic transition, and the change of wall-rock behavior from ductile to brittle conditions. The quartz is precipitated because of cooling and decompression of the magmatic-hydrothermal fluids under K-feldspar-stable conditions. Textural evidence from many porphyry veins suggests that hypogene sulfide minerals present in A and B veins postdate the quartz, as contacts between quartz and sulfide minerals commonly show dissolution textures. Hypogene sulfide minerals in C veins form at conditions of retrograde quartz solubility, explaining why these veins contain little to no quartz. The quartz solubility calculations suggest that C vein formation occurs at temperatures of ~375° to 450°C from low-salinity, single-phase fluids escaping from the lithostatic to the hydrostatic environment. At the upper end of this temperature range, C veins are biotite stable. However, these veins are associated with chlorite, chlorite-K-feldspar, or chlorite-sericite alteration in most deposits. Late quartz is formed during continued cooling of the hydrothermal fluids at ≲375°C within the single-phase field of the H2O-NaCl system as quartz solubility under these conditions decreases with temperature. This process is responsible for the formation of quartz in D veins and later base metal-bearing E veins, which are associated with phyllic, advanced argillic, or argillic alteration. You do not currently have access to this article.
Publication Year: 2018
Publication Date: 2018-07-31
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 85
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