Research Article| January 01, 2007 Processes controlling water and hydrocarbon composition in seeps from the Salton Sea geothermal system, California, USA Henrik Svensen; Henrik Svensen 1Physics of Geological Processes (PGP), Department of Physics, P.O. Box 1048 Blindern, University of Oslo, 0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar Dag A. Karlsen; Dag A. Karlsen 2Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar Anne Sturz; Anne Sturz 3Department of Marine Science and Environmental Studies, University of San Diego, 5998 Alcalá Park, San Diego, California 92110, USA Search for other works by this author on: GSW Google Scholar Kristian Backer-Owe; Kristian Backer-Owe 4Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar David A. Banks; David A. Banks 5School of Earth and Environment, The University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Sverre Planke Sverre Planke 6Volcanic Basin Petroleum Research, Oslo Research Park, Norway, and Physics of Geological Processes (PGP), Department of Physics, P.O. Box 1048 Blindern, University of Oslo, 0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar Author and Article Information Henrik Svensen 1Physics of Geological Processes (PGP), Department of Physics, P.O. Box 1048 Blindern, University of Oslo, 0316 Oslo, Norway Dag A. Karlsen 2Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway Anne Sturz 3Department of Marine Science and Environmental Studies, University of San Diego, 5998 Alcalá Park, San Diego, California 92110, USA Kristian Backer-Owe 4Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway David A. Banks 5School of Earth and Environment, The University of Leeds, Leeds LS2 9JT, UK Sverre Planke 6Volcanic Basin Petroleum Research, Oslo Research Park, Norway, and Physics of Geological Processes (PGP), Department of Physics, P.O. Box 1048 Blindern, University of Oslo, 0316 Oslo, Norway Publisher: Geological Society of America Received: 14 Jul 2006 Revision Received: 04 Sep 2006 Accepted: 07 Sep 2006 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2007) 35 (1): 85–88. https://doi.org/10.1130/G23101A.1 Article history Received: 14 Jul 2006 Revision Received: 04 Sep 2006 Accepted: 07 Sep 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Henrik Svensen, Dag A. Karlsen, Anne Sturz, Kristian Backer-Owe, David A. Banks, Sverre Planke; Processes controlling water and hydrocarbon composition in seeps from the Salton Sea geothermal system, California, USA. Geology 2007;; 35 (1): 85–88. doi: https://doi.org/10.1130/G23101A.1 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 SocietyGeology Search Advanced Search Abstract Water-, mud-, gas-, and petroleum-bearing seeps are part of the Salton Sea geothermal system (SSGS) in Southern California. Seeps in the Davis-Schrimpf seep field (∼14,000 m2) show considerable variations in water temperature, pH, density, and solute content. Water-rich springs have low densities (<1.4 g/cm3), Cl contents as high as 45,000 ppm, and temperatures between 15 and 34 °C. Gryphons expel denser water-mud mixtures (to 1.7 g/cm3), have low salinities (3600–5200 ppm Cl), and have temperatures between 23 and 63 °C. The main driver for the seep system is CO2 (>98 vol%). Halogen geochemistry of the waters indicates that mixing of deep and shallow waters occurs and that near-surface dissolution of halite may overprint the original fluid compositions. Carbon isotopic analyses suggest that hydrocarbon seep gases have a thermogenic origin. This hypothesis is supported by the presence of petroleum in a water-dominated spring, composed of 53% saturated compounds, 35% aromatics, and 12% polar compounds. The abundance of polyaromatic hydrocarbons and immature biomarkers suggests a hydrothermal formation of the petroleum, making the SSGS a relevant analogue to less accessible hydrothermal seep systems, e.g., the Guaymas Basin in the Gulf of California. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Research Article| September 01, 2014 Structural Control, Hydrothermal Alteration Zonation, and Fluid Chemistry of the Concealed, High-Grade 4EE Iron Orebody at the Paraburdoo 4E Deposit, Hamersley Province, Western Australia Warren S. Thorne; Warren S. Thorne † 1Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia †Corresponding author: e-mail, specularite@hotmail.com Search for other works by this author on: GSW Google Scholar Steffen G. Hagemann; Steffen G. Hagemann 1Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar David Sepe; David Sepe 1Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Hilke J. Dalstra; Hilke J. Dalstra 2Rio Tinto Exploration, 37 Belmont Avenue, Belmont, WA 6984, Australia Search for other works by this author on: GSW Google Scholar David A. Banks David A. Banks 3School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, United Kingdom Search for other works by this author on: GSW Google Scholar Economic Geology (2014) 109 (6): 1529–1562. https://doi.org/10.2113/econgeo.109.6.1529 Article history received: 10 Feb 2013 accepted: 02 Nov 2013 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Warren S. Thorne, Steffen G. Hagemann, David Sepe, Hilke J. Dalstra, David A. Banks; Structural Control, Hydrothermal Alteration Zonation, and Fluid Chemistry of the Concealed, High-Grade 4EE Iron Orebody at the Paraburdoo 4E Deposit, Hamersley Province, Western Australia. Economic Geology 2014;; 109 (6): 1529–1562. doi: https://doi.org/10.2113/econgeo.109.6.1529 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 High-grade iron ore of the 4EE orebody of the 4E deposit (>200 Mt at 63.5 wt % Fe) occurs as a southerly dipping sheet within banded iron formation (BIF) of the Paleoproterozoic Dales Gorge and Joffre members of the Brockman Iron Formation. Structural reconstruction of the 4E deposit shows that reactivation of the 18E fault and development of the NW-striking, steeply SW dipping 4E and 4EE normal faults resulted in preservation of the 4EE orebody below the 4E deposit, and 400 m below the modern topographic surface.Three hypogene alteration zones between low-grade BIF and high-grade iron ore are observed: (1) distal magnetite-quartz-dolomite-stilpnomelane-hematite ± pyrite, (2) intermediate magnetite-dolomite-hematite-chlorite-quartz-stilpnomelane, and (3) proximal hematite-dolomite-chlorite ± pyrite ± magnetite. Hydrothermal alteration is temporally and spatially constrained by NW-trending dolerite dikes that intruded the 4E and 4EE faults prior to hypogene alteration. Six vein types (V1–V6) are recognized at the 4E deposit. The veins both cut and parallel the primary BIF layers and were emplaced contemporaneously with the hydrothermal alteration zones that record the transformation of low-grade BIF to high-grade iron ore.Our integrated structural-hydrothermal alteration and fluid flow model proposes that during early stage 1a, hypogene fluid flow in the 4E orebody occurred during a period of continental extension and enhanced heat flow within sedimentary basins to the south of the Paraburdoo Range. Heated basinal brines were focused by the NW-striking, steeply SW dipping 4E and 4EE normal faults and reacted with BIF of the Dales Gorge and Joffre members. The warm to hot (160°–255°C), Ca-rich (26.6–31.9 equiv wt % CaCl2) basinal brine interacted with magnetite-chert layers, transforming them into magnetite-quartz-dolomite-stilpnomelane-hematite-pyrite BIF. The iron-rich brine (up to 2.8 wt % Fe) likely originated from evaporated seawater that had lost Mg and Na and gained Li and Ca through fluid-rock reactions with volcaniclastic rocks and carbonate successions within the Wittenoom Formation. The first incursion of deeply circulating, low-salinity (5.8–9.5 wt % NaCl equiv), heated (106°–201°C) modified meteoric water is recorded in late stage 1a minerals. This modified meteoric water had lost some of its Na through wall rock interaction with plagioclase, possibly by interaction with dolerite of the Weeli Wooli Formation that directly overlies the Joffre and Dales Gorge members.Stage 1b involved continuing reactions between the hydrothermal fluids and the magnetite-quartz-dolomite-stilpnomelane-hematite-pyrite BIF, and produced both the intermediate magnetite-dolomite-hematite-chlorite-pyrite and the proximal hematite-dolomite-magnetite-stilpnomelane alteration assemblages. Microplaty (10–80 μm), platy (100–250 μm), and anhedral hematite increasingly replace magnetite in the intermediate alteration zone, forming the proximal alteration zones that consist of microplaty, platy, anhedral hematite and magnetite. The intermediate and proximal alteration zones represent the mixing of a hot (250°–400°C), high-salinity, Ca-rich (30–40 wt % CaCl2 equiv), Sr-rich basinal brine with low-temperature and low-salinity (~5 wt % NaCl equiv) modified meteoric water that was heated (~100°–200°C) during its descent into the upper crust. Heterogeneous mixing of the two end-member fluids resulted in the trapping of primary fluid inclusion assemblages containing a wide range of trapping temperatures (up to 200°C) and salinities (up to 25 wt % NaCl equiv).Stage 1c of the hypogene hydrothermal fluid is characterized by low-temperature (<110°C), low-salinity (~5 wt % NaCl) meteoric water that interacted with the proximal hematite-dolomite-magnetite-stilpnomelane–altered BIF, leaving a porous, hematite-apatite high-grade ore. Supergene alteration affected the orebody since the Cretaceous and produced a hematite-goethite alteration assemblage, resulting in destruction of the hypogene alteration zones that are only preserved below the depth of modern weathering.Discovery of the concealed 4EE orebody of the 4E deposit demonstrates that structural geology plays a critical role in the exploration for high-grade iron orebodies. Structural reconstruction should be considered a critical exploration activity in structurally complex terranes where concealed orebodies may exist. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The deposit occurs in a mid-Miocene monzonite magmatic complex represented by three different intrusions, namely Intrusion 1 (INT#1), Intrusion 2 (INT#2, INT #2A), and Intrusion 3 (INT#3). Gold mineralization is hosted in all intrusions, but INT#1 is the best mineralized body followed by INT#2. SEM-CL imaging has identified two different veins (V1 and V2) and four distinct generations of quartz formation in the different intrusions. These are: (i) CL-light gray, mosaic-equigranular quartz (Q1), (ii) CL-gray or CL-bright quartz (Q2) that dissolved and was overgrown on Q1, (iii) CL-dark and CL-gray growth zoned quartz (Q3), and (iv) CL-dark or CL-gray micro-fracture quartz fillings (Q4). Fluid inclusion studies show that the gold-hosted early phase Q1 quartz of V1 and V2 veins in INT#1 and INT#2 was precipitated at high temperatures (between 424 and 594 °C). The coexisting and similar ranges of Th values of vapor-rich (low salinity, from 1% to 7% NaCl equiv.) and halite-bearing (high salinity: >30% NaCl) fluid inclusions in Q1 indicates that the magmatic fluid had separated into vapor and high salinity liquid along the appropriate isotherm. Fluid inclusions in Q2 quartz in INT#1 and INT#2 were trapped at lower temperatures between 303 and 380 °C and had lower salinities between 3% and 20% NaCl equiv. The zoned Q3 quartz accompanied by pyrite in V2 veins of both INT#2 and INT#3 precipitated at temperatures between 310 and 373 °C with a salinity range from 5.4% to 10% NaCl eq. The latest generation of fracture filling Q4 quartz, cuts the earlier generations with fluid inclusion Th temperature range from 257 to 333 °C and salinity range from 3% to 12.5% NaCl equiv. The low salinity and low formation temperature of Q4 may be due to the mixing of meteoric water with the hydrothermal system, or late-stage epithermal overprinting. The separation of the magmatic fluid into vapor and aqueous saline pairs in the Q1 quartz of the V1 vein of the INT#1 and INT#2 and CO2-poor fluids indicates the shallow formation of the Kışladağ porphyry gold deposit.
The Lamego orogenic gold deposit (440,742 oz gold measured reserves and 2.4 million t measured resources, with an average grade of 5.71 g/t Au and a cut-off grade of 2.15 g/t Au; AngloGold Ashanti Córrego do Sítio Mineração S/A (AGA) personal communication, 2014) is located in the 5 km-long trend that includes the world-class Cuiabá deposit. It is hosted in the Neoarchean metavolcano–sedimentary rocks of the Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil. Mineralization is associated mainly with metachert–banded iron formation (BIF) and carbonaceous phyllites in the reclined Lamego fold, in which the Cabeça de Pedra orebody represents the hinge zone. Mineralization is concentrated in silicification zones and their quartz veins, as well as in sulfide minerals, product of BIF sulfidation. Hydrothermal alteration varies according to host rock, with abundant sulfide–carbonate in BIF, and sericite–chlorite in carbonaceous phyllite. Quartz vein classification according to structural relationships and host rocks identified three vein systems. The V1 system, mainly composed of smoky quartz (Qtz I) and pyrite, is extensional, crosscuts the bedding plane S0 of BIF, and is parallel to the fold axis. The V2 system, of the same composition, is represented by veins that are parallel to the S1–2 foliation and S0. This system is also characterized by silicification zones in the BIF–carbonaceous phyllite contact that has its maximum expression in the hinge zone of folds. The V3 system has milky quartz (Qtz II) veins, which result from the recrystallization of smoky quartz, located mainly in shear zones and faults; these veins form structures en echelon and vein arrays. The most common ore minerals are pyrite, As-pyrite and arsenopyrite. Fluid inclusion-FI trapped in all quartz veins present composition in the H2O–CO2 ± CH4–NaCl system. Fluid evolution can be interpreted in two stages: i) aqueous–carbonic fluid trapped in Qtz I, of low salinity (~ 2% equiv. wt.% NaCl), and ii) carbonic–aqueous fluid, of moderate salinity (average 9 eq. wt.% NaCl) hosted in Qtz II. Both stages are characterized by decrepitation temperatures in the range of 200 to > 300 °C, and suggest a fluid of metamorphic origin. Applying an arsenopyrite geothermometer, the calculated formation temperature for the Cabeça de Pedra orebody is 300 to 375 °C. The vertical intersection of the isochors allows a minimum pressure calculation of 2.6 kbar. The composition of individual FIs of this orebody, obtained by LA-ICP-MS analyses, compared with results of FIs for the Carvoaria Velha deposit, Córrego do Sítio lineament, highlights a standard composition typical of metamorphic fluids with Na > K > Ca > Mg, which increase or decrease in concentration as a function of salinity in both deposits. Trace elements vary according to fluid–rock reactions, and are directly related to the host rock composition. The comparison of data sets of the two deposits shows that the Cabeça de Pedra FIs have a higher enrichment in Zn, while Cu, As and Sb are richer in Carvoaria Velha, suggesting influence of the host rock geochemistry. The suggested mechanisms for gold precipitation at the Cabeça de Pedra orebody, Lamego gold deposit are: i) hydrolysis of the carbonaceous matter of phyllite and BIF, affecting fO2, destabilizing sulfur complexes and enhancing gold precipitation; ii) replacement of BIF iron carbonates by sulfides; and iii) continuous pressure changes that lead to silica precipitation and free gold. Other than playing the long-recognized role of the carbonaceous phyllites as a fluid barrier, the data highlight their importance as a source of metals.
Abstract The pilot hole (VB) of the German Continental Deep Drilling Program (KTB) was drilled to a depth of 4000 m, where large amounts of free fluids were met. The KTB‐VB 4000 m fluid can be related to either Mesozoic seawater or formation water from Permo‐Carboniferous sedimentary rocks of the Weiden embayment. During the Upper Cretaceous uplift of the Bohemian Massif both fluids could have passed organic‐rich Triassic to Carboniferous formations of the Weiden embayment before invading the uplifted and fractured basement rocks of Devonian amphibolites and metagabbros, where the chemical composition of the fluids was changed by albitization, adularization, and chloritization. Results of chemical mass balances for both sources are presented. In order to concentrate the formation water from the Weiden embayment significant amphibolitization has to be assumed. During a 1‐year pumping test the chemical composition of the 4000 m fluids remained constant. The accuracy of chemical analyses is critically reviewed. An improved preconcentration method of rare earth elements and yttrium in high‐Ca‐bearing saline fluids is described.
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