Pub Date : 2023-03-01DOI: 10.5382/econgeo.118.2.ip01
{"title":"Interesting Papers in Other Journals","authors":"","doi":"10.5382/econgeo.118.2.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.2.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136173716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lin Yang, Qingfei Wang, D. Groves, Huajian Li, D. Zhai, Xuan Wang, Jun Deng
The Cenozoic Daping orogenic gold deposit, on the southeastern margin of the Tibetan Plateau, China, contains four lode types that contain a total of 55 t gold. Pyrite-chalcopyrite–dominated (VA) and galena-dominated polymetallic sulfide veins (VB) hosted by Neoproterozoic diorite are associated with quartz-sericite-chlorite ± epidote (± barite in VB veins) alteration. Pyrite-dominated (VC) and pyrite-pyrrhotite–dominated veins (VD) hosted by Silurian dolostone (intercalated with carbon-bearing argillaceous limestone in VD veins) are related to ankerite-siderite-quartz ± sericite alteration. All have free gold spatially and temporally associated with pyrite, chalcopyrite, galena, pyrrhotite, or quartz. Most VA and VB veins are controlled by steeply SW-dipping ductile-brittle shear zones with jigsaw wall-rock breccias in VB veins, whereas gently SW-dipping faults host VC and VD veins. There are some significant differences between different veins: (1) there were more acidic mineralization conditions for VA and VB veins relative to VC and VD veins, and more oxidized conditions for VB veins relative to other veins; (2) pyrite is rich in Co-Ni in VA and VB veins, compared to enrichment in As-Au for VC and VD veins; (3) sulfide δ34S values of 3.2 to 11.8‰ (median 8.2‰) for VA, VC, and VD veins contrast with −4.6 to +0.9‰ (median 0‰) for VB veins. The contrasting mineral parageneses, pH values, and pyrite geochemistry can be attributed to fluid-rock interaction as evidenced by replacements of amphibole by sericite in diorite and dolomite by ankerite and siderite in dolostone. The lower (~8‰) VB sulfide δ34S values and interpreted fluid oxidation relative to other veins, together with the presence of breccias and barite, can be explained by phase separation due to flash vaporization triggered by extreme hydrofracturing. The consistent NW-trending vein sets, similar median S-O isotope ratios of original ore fluids, and lack of multistage overlap of gold mineralization and alteration zones support a single-source fluid for gold mineralization at Daping. This study is diagnostic rather than just indicative in that it systematically and quantitatively portrays the mineralization diversity in an orogenic gold system formed by a single-source fluid regulated by the external fluid-rock interactions and internal hydrofracturing.
{"title":"MINERAL ASSEMBLAGES, FLUID INCLUSIONS, PYRITE TRACE ELEMENTS, AND S-O ISOTOPES OF GOLD ORES FROM THE CENOZOIC DAPING DEPOSIT, SW CHINA: IMPLICATIONS FOR THE GENESIS OF COMPLEX OROGENIC LODE GOLD SYSTEMS","authors":"Lin Yang, Qingfei Wang, D. Groves, Huajian Li, D. Zhai, Xuan Wang, Jun Deng","doi":"10.5382/econgeo.4995","DOIUrl":"https://doi.org/10.5382/econgeo.4995","url":null,"abstract":"\u0000 The Cenozoic Daping orogenic gold deposit, on the southeastern margin of the Tibetan Plateau, China, contains four lode types that contain a total of 55 t gold. Pyrite-chalcopyrite–dominated (VA) and galena-dominated polymetallic sulfide veins (VB) hosted by Neoproterozoic diorite are associated with quartz-sericite-chlorite ± epidote (± barite in VB veins) alteration. Pyrite-dominated (VC) and pyrite-pyrrhotite–dominated veins (VD) hosted by Silurian dolostone (intercalated with carbon-bearing argillaceous limestone in VD veins) are related to ankerite-siderite-quartz ± sericite alteration. All have free gold spatially and temporally associated with pyrite, chalcopyrite, galena, pyrrhotite, or quartz. Most VA and VB veins are controlled by steeply SW-dipping ductile-brittle shear zones with jigsaw wall-rock breccias in VB veins, whereas gently SW-dipping faults host VC and VD veins.\u0000 There are some significant differences between different veins: (1) there were more acidic mineralization conditions for VA and VB veins relative to VC and VD veins, and more oxidized conditions for VB veins relative to other veins; (2) pyrite is rich in Co-Ni in VA and VB veins, compared to enrichment in As-Au for VC and VD veins; (3) sulfide δ34S values of 3.2 to 11.8‰ (median 8.2‰) for VA, VC, and VD veins contrast with −4.6 to +0.9‰ (median 0‰) for VB veins. The contrasting mineral parageneses, pH values, and pyrite geochemistry can be attributed to fluid-rock interaction as evidenced by replacements of amphibole by sericite in diorite and dolomite by ankerite and siderite in dolostone. The lower (~8‰) VB sulfide δ34S values and interpreted fluid oxidation relative to other veins, together with the presence of breccias and barite, can be explained by phase separation due to flash vaporization triggered by extreme hydrofracturing. The consistent NW-trending vein sets, similar median S-O isotope ratios of original ore fluids, and lack of multistage overlap of gold mineralization and alteration zones support a single-source fluid for gold mineralization at Daping. This study is diagnostic rather than just indicative in that it systematically and quantitatively portrays the mineralization diversity in an orogenic gold system formed by a single-source fluid regulated by the external fluid-rock interactions and internal hydrofracturing.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"43 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81352022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. McClenaghan, C. Beckett-Brown, M. McCurdy, S. Casselman
Case studies around porphyry Cu deposits in the glaciated regions of the Canadian Cordillera have identified the indicator mineral signatures of these deposits in till samples and demonstrated that these are useful methods for porphyry Cu exploration. This study applies the same indicator methods to stream sediment samples around the Casino calc-alkaline porphyry Cu-Au-Mo deposit in the unglaciated terrain of west-central Yukon, Canada. It is one of the largest porphyry Cu-Au-Mo deposits in Canada and is hosted in Late Cretaceous quartz monzonite and associated breccias. Bulk (8–16 kg) coarse-grained stream sediment samples were collected in creeks around the deposit, nearby porphyry Cu occurrences and background areas. The Casino deposit has an obvious indicator mineral signature in the <2-mm heavy (>3.2-specific gravity [SG]) and mid-density (2.8- to 3.2-SG) fractions of stream sediments that is detectable at least 18 km downstream and includes gold, chalcopyrite, tourmaline, molybdenite, sphalerite, jarosite, goethite, and pyrite. In contrast, not all of these mineralogically anomalous samples have corresponding anomalous geochemical signatures in the fine fraction. The porphyry indicator minerals identified in this study are similar to those reported for glaciated terrain with the addition of molybdenite and secondary minerals. Indicator mineral methods provide physical evidence of nearby mineralization and can be chemically analyzed to provide insights about the nature of the mineralizing system. Government and exploration surveys could benefit from the addition of indicator mineral methods to routine stream sediment sampling protocols in unglaciated regions of the Yukon and elsewhere globally where porphyry Cu exploration is conducted.
{"title":"Stream Sediment Indicator Mineral Signatures of the Casino Porphyry Cu-Au-Mo Deposit, Yukon, Canada","authors":"M. McClenaghan, C. Beckett-Brown, M. McCurdy, S. Casselman","doi":"10.5382/econgeo.4970","DOIUrl":"https://doi.org/10.5382/econgeo.4970","url":null,"abstract":"\u0000 Case studies around porphyry Cu deposits in the glaciated regions of the Canadian Cordillera have identified the indicator mineral signatures of these deposits in till samples and demonstrated that these are useful methods for porphyry Cu exploration. This study applies the same indicator methods to stream sediment samples around the Casino calc-alkaline porphyry Cu-Au-Mo deposit in the unglaciated terrain of west-central Yukon, Canada. It is one of the largest porphyry Cu-Au-Mo deposits in Canada and is hosted in Late Cretaceous quartz monzonite and associated breccias. Bulk (8–16 kg) coarse-grained stream sediment samples were collected in creeks around the deposit, nearby porphyry Cu occurrences and background areas. The Casino deposit has an obvious indicator mineral signature in the <2-mm heavy (>3.2-specific gravity [SG]) and mid-density (2.8- to 3.2-SG) fractions of stream sediments that is detectable at least 18 km downstream and includes gold, chalcopyrite, tourmaline, molybdenite, sphalerite, jarosite, goethite, and pyrite. In contrast, not all of these mineralogically anomalous samples have corresponding anomalous geochemical signatures in the fine fraction. The porphyry indicator minerals identified in this study are similar to those reported for glaciated terrain with the addition of molybdenite and secondary minerals. Indicator mineral methods provide physical evidence of nearby mineralization and can be chemically analyzed to provide insights about the nature of the mineralizing system. Government and exploration surveys could benefit from the addition of indicator mineral methods to routine stream sediment sampling protocols in unglaciated regions of the Yukon and elsewhere globally where porphyry Cu exploration is conducted.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"72 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88230871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Charles D. Beard, Kathryn M. Goodenough, Anouk M. Borst, Frances Wall, Pete R. Siegfried, Eimear A. Deady, Claudia Pohl, William Hutchison, Adrian A. Finch, Benjamin F. Walter, Holly A.L. Elliott, Klaus Brauch
Abstract Development of renewable energy infrastructure requires critical raw materials, such as the rare earth elements (REEs, including scandium) and niobium, and is driving expansion and diversification in their supply chains. Although alternative sources are being explored, the majority of the world’s resources of these elements are found in alkaline-silicate rocks and carbonatites. These magmatic systems also represent major sources of fluorine and phosphorus. Exploration models for critical raw materials are comparatively less well developed than those for major and precious metals, such as iron, copper, and gold, where most of the mineral exploration industry continues to focus. The diversity of lithologic relationships and a complex nomenclature for many alkaline rock types represent further barriers to the exploration and exploitation of REE-high field strength element (HFSE) resources that will facilitate the green revolution. We used a global review of maps, cross sections, and geophysical, geochemical, and petrological observations from alkaline systems to inform our description of the alkaline-silicate REE + HFSE mineral system from continental scale (1,000s km) down to deposit scale (~1 km lateral). Continental-scale targeting criteria include a geodynamic trigger for low-degree mantle melting at high pressure and a mantle source enriched in REEs, volatile elements, and alkalies. At the province and district scales, targeting criteria relate to magmatic-system longevity and the conditions required for extensive fractional crystallization and the residual enrichment of the REEs and HFSEs. A compilation of maps and geophysical data were used to construct an interactive 3-D geologic model (25-km cube) that places mineralization within a depth and horizontal reference frame. It shows typical lithologic relationships surrounding orthomagmatic REE-Nb-Ta-Zr-Hf mineralization in layered agpaitic syenites, roof zone REE-Nb-Ta mineralization, and mineralization of REE-Nb-Zr associated with peralkaline granites and pegmatites. The resulting geologic model is presented together with recommended geophysical and geochemical approaches for exploration targeting, as well as mineral processing and environmental factors pertinent for the development of mineral resources hosted by alkaline-silicate magmatic systems.
{"title":"Alkaline-Silicate REE-HFSE Systems","authors":"Charles D. Beard, Kathryn M. Goodenough, Anouk M. Borst, Frances Wall, Pete R. Siegfried, Eimear A. Deady, Claudia Pohl, William Hutchison, Adrian A. Finch, Benjamin F. Walter, Holly A.L. Elliott, Klaus Brauch","doi":"10.5382/econgeo.4956","DOIUrl":"https://doi.org/10.5382/econgeo.4956","url":null,"abstract":"Abstract Development of renewable energy infrastructure requires critical raw materials, such as the rare earth elements (REEs, including scandium) and niobium, and is driving expansion and diversification in their supply chains. Although alternative sources are being explored, the majority of the world’s resources of these elements are found in alkaline-silicate rocks and carbonatites. These magmatic systems also represent major sources of fluorine and phosphorus. Exploration models for critical raw materials are comparatively less well developed than those for major and precious metals, such as iron, copper, and gold, where most of the mineral exploration industry continues to focus. The diversity of lithologic relationships and a complex nomenclature for many alkaline rock types represent further barriers to the exploration and exploitation of REE-high field strength element (HFSE) resources that will facilitate the green revolution. We used a global review of maps, cross sections, and geophysical, geochemical, and petrological observations from alkaline systems to inform our description of the alkaline-silicate REE + HFSE mineral system from continental scale (1,000s km) down to deposit scale (~1 km lateral). Continental-scale targeting criteria include a geodynamic trigger for low-degree mantle melting at high pressure and a mantle source enriched in REEs, volatile elements, and alkalies. At the province and district scales, targeting criteria relate to magmatic-system longevity and the conditions required for extensive fractional crystallization and the residual enrichment of the REEs and HFSEs. A compilation of maps and geophysical data were used to construct an interactive 3-D geologic model (25-km cube) that places mineralization within a depth and horizontal reference frame. It shows typical lithologic relationships surrounding orthomagmatic REE-Nb-Ta-Zr-Hf mineralization in layered agpaitic syenites, roof zone REE-Nb-Ta mineralization, and mineralization of REE-Nb-Zr associated with peralkaline granites and pegmatites. The resulting geologic model is presented together with recommended geophysical and geochemical approaches for exploration targeting, as well as mineral processing and environmental factors pertinent for the development of mineral resources hosted by alkaline-silicate magmatic systems.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"260 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135449926","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Schlicht, O. Rouxel, J. Deans, Stephen Fox, Y. Katzir, K. Kitajima, S. Kasemann, A. Meixner, W. Bach
A better characterization of subsurface processes in hydrothermal systems is key to a deeper understanding of fluid-rock interaction and ore-forming mechanisms. Vent systems in oceanic crust close to subduction zones, like at Brothers volcano and in the eastern Manus basin, are known to be especially ore rich. We measured B concentrations and isotope ratios of unaltered and altered lava that were recovered from drilling sites at Brothers volcano and Snowcap (eastern Manus basin) to test their sensitivity for changing alteration conditions with depth. In addition, for Brothers volcano, quartz-water oxygen isotope thermometry was used to constrain variations in alteration temperature with depth. All altered rocks are depleted in B compared to unaltered rocks and point to interaction with a high-temperature (>150°C) hydrothermal fluid. The δ11B values of altered rocks are variable, from slightly lower to significantly higher than those of unaltered rocks. For Brothers volcano, at the Upper Cone, we suggest a gradual evolution from a fluid- to a more rock-dominated system with increasing depth. In contrast, the downhole variations of δ11B at Snowcap as well as δ11B and δ18O variations at the NW Caldera (Site U1530) of Brothers volcano are suggested to indicate changes in water-rock ratios and, in the latter case, also temperature, with depth due to permeability contrasts between different lithology and alteration type boundaries. Furthermore, δ11B values from the NW Caldera (Site U1527) might point to a structural impact on the fluid pathway. These differences in the subseafloor fluid flow regime, which ranges from more pervasive and fluid-controlled to stronger and controlled by lithological and structural features, have significant influence on alteration conditions and may also impact metal precipitation within the sea floor.
{"title":"Boron and Oxygen Isotope Systematics of Two Hydrothermal Systems in Modern Back-Arc and Arc Crust (PACMANUS and Brothers Volcano, W-Pacific)","authors":"L. Schlicht, O. Rouxel, J. Deans, Stephen Fox, Y. Katzir, K. Kitajima, S. Kasemann, A. Meixner, W. Bach","doi":"10.5382/econgeo.4986","DOIUrl":"https://doi.org/10.5382/econgeo.4986","url":null,"abstract":"\u0000 A better characterization of subsurface processes in hydrothermal systems is key to a deeper understanding of fluid-rock interaction and ore-forming mechanisms. Vent systems in oceanic crust close to subduction zones, like at Brothers volcano and in the eastern Manus basin, are known to be especially ore rich. We measured B concentrations and isotope ratios of unaltered and altered lava that were recovered from drilling sites at Brothers volcano and Snowcap (eastern Manus basin) to test their sensitivity for changing alteration conditions with depth. In addition, for Brothers volcano, quartz-water oxygen isotope thermometry was used to constrain variations in alteration temperature with depth. All altered rocks are depleted in B compared to unaltered rocks and point to interaction with a high-temperature (>150°C) hydrothermal fluid. The δ11B values of altered rocks are variable, from slightly lower to significantly higher than those of unaltered rocks. For Brothers volcano, at the Upper Cone, we suggest a gradual evolution from a fluid- to a more rock-dominated system with increasing depth. In contrast, the downhole variations of δ11B at Snowcap as well as δ11B and δ18O variations at the NW Caldera (Site U1530) of Brothers volcano are suggested to indicate changes in water-rock ratios and, in the latter case, also temperature, with depth due to permeability contrasts between different lithology and alteration type boundaries. Furthermore, δ11B values from the NW Caldera (Site U1527) might point to a structural impact on the fluid pathway. These differences in the subseafloor fluid flow regime, which ranges from more pervasive and fluid-controlled to stronger and controlled by lithological and structural features, have significant influence on alteration conditions and may also impact metal precipitation within the sea floor.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"1 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87561757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-01DOI: 10.5382/econgeo.118.1.ip01
{"title":"INTERESTING PAPERS IN OTHER JOURNALS","authors":"","doi":"10.5382/econgeo.118.1.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.1.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"22 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88367027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Kreiner, C. Holm-Denoma, Laura S. Pianowski, Zachary Flood, D. Stevenson, G. Graham, J. Vazquez, R. Creaser
The Taurus porphyry Cu-Mo district contains four mineralized porphyry centers in the eastern interior of Alaska. All four centers were emplaced during a magmatic episode that spanned from ca. 72 to 67 Ma, with seven distinct igneous suites. Each igneous suite resulted in hydrothermal alteration and mineralization, with younger pulses overprinting older pulses. Each magmatic-hydrothermal system is not present at all four mineralized centers. Apart from the Dennison occurrence, each mineralized center records pulses of repeated intermediate-silicic magmatism and associated alteration and mineralization. Laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon crystallization ages indicate that an early quartz porphyry dike swarm ranges in age from ca. 71 to 70 Ma and is associated with potassic, sericitic, and propylitic alteration. Quartz latite intrusions were emplaced at ca. 69 Ma and exhibit early sodiccalcic alteration overprinted by potassic, sericitic, and propylitic alteration. The Taurus monzonite suite is cut by quartz latite but yielded an ca. 70 Ma emplacement age and exhibits the largest footprint of potassic and sericitic alteration. Feldspar porphyry dikes were emplaced ca. 69 Ma and have significant tourmaline-bearing potassic and sericitic alteration. This suite was followed by development of an igneous breccia with a monzonitic igneous matrix. Sodic-calcic alteration was associated with the igneous brecciation. A small stock of monzonite was emplaced at ca. 68 Ma causing locally pervasive sericite-tourmaline-pyrite alteration. The youngest suite of magmatism dated in the district is a series of granodiorite porphyry dikes with weak sodic-calcic and propylitic alteration that truncates earlier alteration assemblages. Mineralization in the district consists of chalcopyrite and molybdenite associated with sugary quartz veins with potassium feldspar and biotite alteration envelopes (A veins). Less common banded quartz-molybdenite veins (B veins) occur with potassium feldspar envelopes. Gold occurs throughout the district and is strongly correlated with copper grade. Sericitic alteration contains lower copper contents and is predominantly associated with quartz-pyrite veins with sericite envelopes (D veins). Pyrrhotite and local arsenopyrite are present in sericitic assemblages. Pyrrhotite also occurs as inclusions in pyrite within D veins. Magmas across the district exhibit oxidized characteristics, evidenced by the presence of abundant magnetite, rare titanite, and elevated Eu/Eu* and Ce/Ce* in zircon. Zircon Th/U and Yb/Gd compositions suggest a fractionation path controlled by apatite, titanite, and hornblende. Zircon rare earth element ratios and trace element data indicate two distinct batches of magma evolved from mafic parental compositions to monzonite and granodioritic compositions via fractional crystallization. In the early pulse of magma (ca. 72–69 Ma), fractional crystallization was key to ore formatio
{"title":"Geochronology and Mapping Constraints on the Time-Space Evolution of the Igneous and Hydrothermal Systems in the Taurus Cu-Mo District, Eastern Alaska","authors":"D. Kreiner, C. Holm-Denoma, Laura S. Pianowski, Zachary Flood, D. Stevenson, G. Graham, J. Vazquez, R. Creaser","doi":"10.5382/econgeo.4999","DOIUrl":"https://doi.org/10.5382/econgeo.4999","url":null,"abstract":"\u0000 The Taurus porphyry Cu-Mo district contains four mineralized porphyry centers in the eastern interior of Alaska. All four centers were emplaced during a magmatic episode that spanned from ca. 72 to 67 Ma, with seven distinct igneous suites. Each igneous suite resulted in hydrothermal alteration and mineralization, with younger pulses overprinting older pulses. Each magmatic-hydrothermal system is not present at all four mineralized centers. Apart from the Dennison occurrence, each mineralized center records pulses of repeated intermediate-silicic magmatism and associated alteration and mineralization.\u0000 Laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon crystallization ages indicate that an early quartz porphyry dike swarm ranges in age from ca. 71 to 70 Ma and is associated with potassic, sericitic, and propylitic alteration. Quartz latite intrusions were emplaced at ca. 69 Ma and exhibit early sodiccalcic alteration overprinted by potassic, sericitic, and propylitic alteration. The Taurus monzonite suite is cut by quartz latite but yielded an ca. 70 Ma emplacement age and exhibits the largest footprint of potassic and sericitic alteration. Feldspar porphyry dikes were emplaced ca. 69 Ma and have significant tourmaline-bearing potassic and sericitic alteration. This suite was followed by development of an igneous breccia with a monzonitic igneous matrix. Sodic-calcic alteration was associated with the igneous brecciation. A small stock of monzonite was emplaced at ca. 68 Ma causing locally pervasive sericite-tourmaline-pyrite alteration. The youngest suite of magmatism dated in the district is a series of granodiorite porphyry dikes with weak sodic-calcic and propylitic alteration that truncates earlier alteration assemblages.\u0000 Mineralization in the district consists of chalcopyrite and molybdenite associated with sugary quartz veins with potassium feldspar and biotite alteration envelopes (A veins). Less common banded quartz-molybdenite veins (B veins) occur with potassium feldspar envelopes. Gold occurs throughout the district and is strongly correlated with copper grade. Sericitic alteration contains lower copper contents and is predominantly associated with quartz-pyrite veins with sericite envelopes (D veins). Pyrrhotite and local arsenopyrite are present in sericitic assemblages. Pyrrhotite also occurs as inclusions in pyrite within D veins.\u0000 Magmas across the district exhibit oxidized characteristics, evidenced by the presence of abundant magnetite, rare titanite, and elevated Eu/Eu* and Ce/Ce* in zircon. Zircon Th/U and Yb/Gd compositions suggest a fractionation path controlled by apatite, titanite, and hornblende. Zircon rare earth element ratios and trace element data indicate two distinct batches of magma evolved from mafic parental compositions to monzonite and granodioritic compositions via fractional crystallization. In the early pulse of magma (ca. 72–69 Ma), fractional crystallization was key to ore formatio","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"107 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88634343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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