Redox-controlled generation of the giant porphyry Cu–Au deposit at Pulang, southwest China

Some porphyry Cu–Au deposits with relatively reduced ore assemblages, characterized by high hydrothermal pyrrhotite contents and a lack of primary hematite and magnetite, are generally considered to be associated with reduced I-type granitoids. However, the role of magmatic oxygen fugacity ( f O 2 )...

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Veröffentlicht in:Contributions to mineralogy and petrology 2019-02, Vol.174 (2), p.1-34, Article 12
Hauptverfasser: Li, Weikai, Yang, Zhiming, Cao, Kang, Lu, Yongjun, Sun, Maoyu
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description Some porphyry Cu–Au deposits with relatively reduced ore assemblages, characterized by high hydrothermal pyrrhotite contents and a lack of primary hematite and magnetite, are generally considered to be associated with reduced I-type granitoids. However, the role of magmatic oxygen fugacity ( f O 2 ) in controlling Cu–Au mineralization in such reduced porphyry deposits is poorly understood. The giant Late Triassic (ca 216 Ma) Pulang porphyry Cu–Au deposit of southwest China shows typical reduced ore assemblages. This study reported the systematical variation of upper crustal magmatic f O 2 of Pulang deposit, based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization-related porphyries (early P1 and late P2 porphyry). Results indicate that magma of the mineralization-related porphyries experienced complex f O 2 fluctuations during its upper crustal evolution. The early primary magma had very high initial f O 2 , with ΔFMQ ≥ + 3.0 at depths of > 12 km [ΔFMQ is the deviation of log f O 2 from the fayalite–magnetite–quartz (FMQ) buffer]. The f O 2 of evolved parental magma subsequently decreased, with ΔFMQ ≤ + 1.9, due to injection of relatively reduced dioritic magmas (ΔFMQ = + 1.4 to + 2.3) from a deeper chamber (17–21 km depth) into the primary magma chamber at 10–12 km depth. Magma mixing had largely ceased at 6–10 km depth. The parental magma then ponded within the reduced Tumugou formation at a depth of ~ 3.7 km where magmatic f O 2 decreased to a moderately oxidized state (ΔFMQ = ~ + 1.6), and finally to a moderately reduced state [reflected by log(Fe 2 O 3 /FeO) ratios of  − 0.5 for P2 porphyry]. Results of this study of magmatic f O 2 indicate that porphyry magmas associated with reduced Pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the Tumugou Formation. The sharp f O 2 decrease at very shallow depth pr
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However, the role of magmatic oxygen fugacity ( f O 2 ) in controlling Cu–Au mineralization in such reduced porphyry deposits is poorly understood. The giant Late Triassic (ca 216 Ma) Pulang porphyry Cu–Au deposit of southwest China shows typical reduced ore assemblages. This study reported the systematical variation of upper crustal magmatic f O 2 of Pulang deposit, based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization-related porphyries (early P1 and late P2 porphyry). Results indicate that magma of the mineralization-related porphyries experienced complex f O 2 fluctuations during its upper crustal evolution. The early primary magma had very high initial f O 2 , with ΔFMQ ≥ + 3.0 at depths of &gt; 12 km [ΔFMQ is the deviation of log f O 2 from the fayalite–magnetite–quartz (FMQ) buffer]. The f O 2 of evolved parental magma subsequently decreased, with ΔFMQ ≤ + 1.9, due to injection of relatively reduced dioritic magmas (ΔFMQ = + 1.4 to + 2.3) from a deeper chamber (17–21 km depth) into the primary magma chamber at 10–12 km depth. Magma mixing had largely ceased at 6–10 km depth. The parental magma then ponded within the reduced Tumugou formation at a depth of ~ 3.7 km where magmatic f O 2 decreased to a moderately oxidized state (ΔFMQ = ~ + 1.6), and finally to a moderately reduced state [reflected by log(Fe 2 O 3 /FeO) ratios of &lt; − 0.5 for P1 porphyry] due to contamination of parental magma by wall-rock Tumugou Formation. This decrease of f O 2 in the parental magma resulted in separation of magmatic sulfide, and the subsequent exsolution of reduced ore fluids responsible for the generation of Pulang ore assemblages. The f O 2 of the residual parental magma increased after exsolution of the reduced fluids to ΔFMQ values of + 3.2 to + 4.2 [also reflected by high log(Fe 2 O 3 /FeO) ratios of &gt; − 0.5 for P2 porphyry]. Results of this study of magmatic f O 2 indicate that porphyry magmas associated with reduced Pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the Tumugou Formation. The sharp f O 2 decrease at very shallow depth prevented the early loss of Cu and Au because the magma remained oxidized until it was emplaced at ~ 3.7 km depth. Moderately reduced magmas may thus have a genetic association with porphyry Cu–Au mineralization.</description><identifier>ISSN: 0010-7999</identifier><identifier>EISSN: 1432-0967</identifier><identifier>DOI: 10.1007/s00410-019-1546-x</identifier><language>eng</language><publisher>Berlin/Heidelberg: Springer Berlin Heidelberg</publisher><subject>Contamination ; Copper (Metal) ; Crystallization ; Depth ; Earth and Environmental Science ; Earth Sciences ; Evolution ; Fayalite ; Fluids ; Fugacity ; Geology ; Gold ; Granite ; Haematite ; Hematite ; Iron oxides ; Lava ; Magma ; Magma chambers ; Magnetite ; Mineral Resources ; Mineralization ; Mineralogy ; Original Paper ; Oxidoreductions ; Parenting ; Petrology ; Porphyry ; Porphyry copper ; Primaries ; Pyrrhotite ; Ratios ; Reduced ores ; Sedimentary rocks ; Solid solutions ; Spinel group ; Sulfides ; Sulphides ; Triassic</subject><ispartof>Contributions to mineralogy and petrology, 2019-02, Vol.174 (2), p.1-34, Article 12</ispartof><rights>Springer-Verlag GmbH Germany, part of Springer Nature 2019</rights><rights>COPYRIGHT 2019 Springer</rights><rights>Contributions to Mineralogy and Petrology is a copyright of Springer, (2019). All Rights Reserved.</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-a444t-23379c5a4bb507da11e7f62ac013aeeea1d63e0d98b723edc5b41d9b91f659f73</citedby><cites>FETCH-LOGICAL-a444t-23379c5a4bb507da11e7f62ac013aeeea1d63e0d98b723edc5b41d9b91f659f73</cites></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktopdf>$$Uhttps://link.springer.com/content/pdf/10.1007/s00410-019-1546-x$$EPDF$$P50$$Gspringer$$H</linktopdf><linktohtml>$$Uhttps://link.springer.com/10.1007/s00410-019-1546-x$$EHTML$$P50$$Gspringer$$H</linktohtml><link.rule.ids>314,776,780,27901,27902,41464,42533,51294</link.rule.ids></links><search><creatorcontrib>Li, Weikai</creatorcontrib><creatorcontrib>Yang, Zhiming</creatorcontrib><creatorcontrib>Cao, Kang</creatorcontrib><creatorcontrib>Lu, Yongjun</creatorcontrib><creatorcontrib>Sun, Maoyu</creatorcontrib><title>Redox-controlled generation of the giant porphyry Cu–Au deposit at Pulang, southwest China</title><title>Contributions to mineralogy and petrology</title><addtitle>Contrib Mineral Petrol</addtitle><description>Some porphyry Cu–Au deposits with relatively reduced ore assemblages, characterized by high hydrothermal pyrrhotite contents and a lack of primary hematite and magnetite, are generally considered to be associated with reduced I-type granitoids. However, the role of magmatic oxygen fugacity ( f O 2 ) in controlling Cu–Au mineralization in such reduced porphyry deposits is poorly understood. The giant Late Triassic (ca 216 Ma) Pulang porphyry Cu–Au deposit of southwest China shows typical reduced ore assemblages. This study reported the systematical variation of upper crustal magmatic f O 2 of Pulang deposit, based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization-related porphyries (early P1 and late P2 porphyry). Results indicate that magma of the mineralization-related porphyries experienced complex f O 2 fluctuations during its upper crustal evolution. The early primary magma had very high initial f O 2 , with ΔFMQ ≥ + 3.0 at depths of &gt; 12 km [ΔFMQ is the deviation of log f O 2 from the fayalite–magnetite–quartz (FMQ) buffer]. The f O 2 of evolved parental magma subsequently decreased, with ΔFMQ ≤ + 1.9, due to injection of relatively reduced dioritic magmas (ΔFMQ = + 1.4 to + 2.3) from a deeper chamber (17–21 km depth) into the primary magma chamber at 10–12 km depth. Magma mixing had largely ceased at 6–10 km depth. The parental magma then ponded within the reduced Tumugou formation at a depth of ~ 3.7 km where magmatic f O 2 decreased to a moderately oxidized state (ΔFMQ = ~ + 1.6), and finally to a moderately reduced state [reflected by log(Fe 2 O 3 /FeO) ratios of &lt; − 0.5 for P1 porphyry] due to contamination of parental magma by wall-rock Tumugou Formation. This decrease of f O 2 in the parental magma resulted in separation of magmatic sulfide, and the subsequent exsolution of reduced ore fluids responsible for the generation of Pulang ore assemblages. The f O 2 of the residual parental magma increased after exsolution of the reduced fluids to ΔFMQ values of + 3.2 to + 4.2 [also reflected by high log(Fe 2 O 3 /FeO) ratios of &gt; − 0.5 for P2 porphyry]. Results of this study of magmatic f O 2 indicate that porphyry magmas associated with reduced Pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the Tumugou Formation. The sharp f O 2 decrease at very shallow depth prevented the early loss of Cu and Au because the magma remained oxidized until it was emplaced at ~ 3.7 km depth. Moderately reduced magmas may thus have a genetic association with porphyry Cu–Au mineralization.</description><subject>Contamination</subject><subject>Copper (Metal)</subject><subject>Crystallization</subject><subject>Depth</subject><subject>Earth and Environmental Science</subject><subject>Earth Sciences</subject><subject>Evolution</subject><subject>Fayalite</subject><subject>Fluids</subject><subject>Fugacity</subject><subject>Geology</subject><subject>Gold</subject><subject>Granite</subject><subject>Haematite</subject><subject>Hematite</subject><subject>Iron oxides</subject><subject>Lava</subject><subject>Magma</subject><subject>Magma chambers</subject><subject>Magnetite</subject><subject>Mineral Resources</subject><subject>Mineralization</subject><subject>Mineralogy</subject><subject>Original Paper</subject><subject>Oxidoreductions</subject><subject>Parenting</subject><subject>Petrology</subject><subject>Porphyry</subject><subject>Porphyry copper</subject><subject>Primaries</subject><subject>Pyrrhotite</subject><subject>Ratios</subject><subject>Reduced ores</subject><subject>Sedimentary rocks</subject><subject>Solid solutions</subject><subject>Spinel group</subject><subject>Sulfides</subject><subject>Sulphides</subject><subject>Triassic</subject><issn>0010-7999</issn><issn>1432-0967</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2019</creationdate><recordtype>article</recordtype><sourceid>8G5</sourceid><sourceid>BENPR</sourceid><sourceid>GUQSH</sourceid><sourceid>M2O</sourceid><recordid>eNp1kVGrFCEUxyUK2m59gN6EXvOmo6Pr47LULbhQRL0F4oxnZr3M6qQO7b71HfqGfZK8TFDBhg-i_n4ezvkj9JzRa0apepUpFYwSyjRhrZDk9ABtmOANoVqqh2hDaX1VWuvH6EnOd7Set7rdoC8fwcUT6WMoKU4TODxCgGSLjwHHAZcD4NHbUPAc03w4pzPeLz-__9gt2MEcsy_YFvxhmWwYX-Icl3L4Brng_cEH-xQ9GuyU4dnv_Qp9fvP60_4tuX1_826_uyVWCFFIw7nSfWtF17VUOcsYqEE2tqeMWwCwzEkO1OltpxoOrm87wZzuNBtkqwfFr9CL9d85xa9LLW_u4pJCLWkapriQXLK_qNFOYHwYYkm2P_rcm12r2FZuVSsrRS5Q61CmGGDw9fof_voCX5eDo-8vCmwV-hRzTjCYOfmjTWfDqLnP0qxZmpqluc_SnKrTrE6ubBgh_Wnw_9IvFg6hzw</recordid><startdate>20190201</startdate><enddate>20190201</enddate><creator>Li, Weikai</creator><creator>Yang, Zhiming</creator><creator>Cao, Kang</creator><creator>Lu, Yongjun</creator><creator>Sun, Maoyu</creator><general>Springer Berlin Heidelberg</general><general>Springer</general><general>Springer Nature B.V</general><scope>AAYXX</scope><scope>CITATION</scope><scope>3V.</scope><scope>7TN</scope><scope>7XB</scope><scope>88I</scope><scope>8FE</scope><scope>8FG</scope><scope>8FK</scope><scope>8G5</scope><scope>ABJCF</scope><scope>ABUWG</scope><scope>AEUYN</scope><scope>AFKRA</scope><scope>AZQEC</scope><scope>BENPR</scope><scope>BGLVJ</scope><scope>BHPHI</scope><scope>BKSAR</scope><scope>CCPQU</scope><scope>D1I</scope><scope>DWQXO</scope><scope>F1W</scope><scope>GNUQQ</scope><scope>GUQSH</scope><scope>H96</scope><scope>HCIFZ</scope><scope>KB.</scope><scope>L.G</scope><scope>L6V</scope><scope>M2O</scope><scope>M2P</scope><scope>M7S</scope><scope>MBDVC</scope><scope>PCBAR</scope><scope>PDBOC</scope><scope>PQEST</scope><scope>PQQKQ</scope><scope>PQUKI</scope><scope>PTHSS</scope><scope>Q9U</scope><scope>R05</scope></search><sort><creationdate>20190201</creationdate><title>Redox-controlled generation of the giant porphyry Cu–Au deposit at Pulang, southwest China</title><author>Li, Weikai ; Yang, Zhiming ; Cao, Kang ; Lu, Yongjun ; Sun, Maoyu</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-a444t-23379c5a4bb507da11e7f62ac013aeeea1d63e0d98b723edc5b41d9b91f659f73</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2019</creationdate><topic>Contamination</topic><topic>Copper (Metal)</topic><topic>Crystallization</topic><topic>Depth</topic><topic>Earth and Environmental Science</topic><topic>Earth Sciences</topic><topic>Evolution</topic><topic>Fayalite</topic><topic>Fluids</topic><topic>Fugacity</topic><topic>Geology</topic><topic>Gold</topic><topic>Granite</topic><topic>Haematite</topic><topic>Hematite</topic><topic>Iron oxides</topic><topic>Lava</topic><topic>Magma</topic><topic>Magma chambers</topic><topic>Magnetite</topic><topic>Mineral Resources</topic><topic>Mineralization</topic><topic>Mineralogy</topic><topic>Original Paper</topic><topic>Oxidoreductions</topic><topic>Parenting</topic><topic>Petrology</topic><topic>Porphyry</topic><topic>Porphyry copper</topic><topic>Primaries</topic><topic>Pyrrhotite</topic><topic>Ratios</topic><topic>Reduced ores</topic><topic>Sedimentary rocks</topic><topic>Solid solutions</topic><topic>Spinel group</topic><topic>Sulfides</topic><topic>Sulphides</topic><topic>Triassic</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Li, Weikai</creatorcontrib><creatorcontrib>Yang, Zhiming</creatorcontrib><creatorcontrib>Cao, Kang</creatorcontrib><creatorcontrib>Lu, Yongjun</creatorcontrib><creatorcontrib>Sun, Maoyu</creatorcontrib><collection>CrossRef</collection><collection>ProQuest Central (Corporate)</collection><collection>Oceanic Abstracts</collection><collection>ProQuest Central (purchase pre-March 2016)</collection><collection>Science Database (Alumni Edition)</collection><collection>ProQuest SciTech Collection</collection><collection>ProQuest Technology Collection</collection><collection>ProQuest Central (Alumni) (purchase pre-March 2016)</collection><collection>Research Library (Alumni Edition)</collection><collection>Materials Science &amp; 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However, the role of magmatic oxygen fugacity ( f O 2 ) in controlling Cu–Au mineralization in such reduced porphyry deposits is poorly understood. The giant Late Triassic (ca 216 Ma) Pulang porphyry Cu–Au deposit of southwest China shows typical reduced ore assemblages. This study reported the systematical variation of upper crustal magmatic f O 2 of Pulang deposit, based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization-related porphyries (early P1 and late P2 porphyry). Results indicate that magma of the mineralization-related porphyries experienced complex f O 2 fluctuations during its upper crustal evolution. The early primary magma had very high initial f O 2 , with ΔFMQ ≥ + 3.0 at depths of &gt; 12 km [ΔFMQ is the deviation of log f O 2 from the fayalite–magnetite–quartz (FMQ) buffer]. The f O 2 of evolved parental magma subsequently decreased, with ΔFMQ ≤ + 1.9, due to injection of relatively reduced dioritic magmas (ΔFMQ = + 1.4 to + 2.3) from a deeper chamber (17–21 km depth) into the primary magma chamber at 10–12 km depth. Magma mixing had largely ceased at 6–10 km depth. The parental magma then ponded within the reduced Tumugou formation at a depth of ~ 3.7 km where magmatic f O 2 decreased to a moderately oxidized state (ΔFMQ = ~ + 1.6), and finally to a moderately reduced state [reflected by log(Fe 2 O 3 /FeO) ratios of &lt; − 0.5 for P1 porphyry] due to contamination of parental magma by wall-rock Tumugou Formation. This decrease of f O 2 in the parental magma resulted in separation of magmatic sulfide, and the subsequent exsolution of reduced ore fluids responsible for the generation of Pulang ore assemblages. The f O 2 of the residual parental magma increased after exsolution of the reduced fluids to ΔFMQ values of + 3.2 to + 4.2 [also reflected by high log(Fe 2 O 3 /FeO) ratios of &gt; − 0.5 for P2 porphyry]. Results of this study of magmatic f O 2 indicate that porphyry magmas associated with reduced Pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the Tumugou Formation. The sharp f O 2 decrease at very shallow depth prevented the early loss of Cu and Au because the magma remained oxidized until it was emplaced at ~ 3.7 km depth. Moderately reduced magmas may thus have a genetic association with porphyry Cu–Au mineralization.</abstract><cop>Berlin/Heidelberg</cop><pub>Springer Berlin Heidelberg</pub><doi>10.1007/s00410-019-1546-x</doi><tpages>34</tpages></addata></record>
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subjects Contamination
Copper (Metal)
Crystallization
Depth
Earth and Environmental Science
Earth Sciences
Evolution
Fayalite
Fluids
Fugacity
Geology
Gold
Granite
Haematite
Hematite
Iron oxides
Lava
Magma
Magma chambers
Magnetite
Mineral Resources
Mineralization
Mineralogy
Original Paper
Oxidoreductions
Parenting
Petrology
Porphyry
Porphyry copper
Primaries
Pyrrhotite
Ratios
Reduced ores
Sedimentary rocks
Solid solutions
Spinel group
Sulfides
Sulphides
Triassic
title Redox-controlled generation of the giant porphyry Cu–Au deposit at Pulang, southwest China
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