Skarn ores have recently been identified beneath the historically mined placer Sn deposit at Kanbauk of the Dawei region, southern Myanmar. A large-tonnage skarn ore reserve at Kanbauk is estimated to be over 100 million tonnes, with reported ore grades of 0.17% WO3, 0.26% Sn, and 15.4% CaF2, potentially making it one of the largest W-Sn skarn deposits in the Southeast Asian tin belt. The mineralized skarns lie between marbles to the east and metasediments of the Mergui Group to the west. The timing of the mineralization is unclear, and thus the genetic relationship with regional magmatic events is not known. We report laser ablation-inductively coupled plasma-mass spectrometry U-Pb ages of garnet and cassiterite from the mineralized skarns. Garnet grains from the massive prograde skarns are typically subhedral to euhedral and show both sector and oscillatory zoning. They have 15 to 23% andradite (Ad), 55 to 67% grossularite (Gr), and 16 to 30% pyralspite (Py) (Ad15-23Gr55-67Py16-30) and contain 0.08 to 306 ppm U with a lower intercept 206Pb/238U age of 56.0 ± 1.5 Ma. Cassiterite grains from retrograde veinlets are subhedral to anhedral and have U contents from 110 to 12,000 ppm with a lower intercept 206Pb/238U age of 54.2 ± 1.7 Ma. Garnet and cassiterite have ages consistent within error and can be taken to indicate the formation of the Kanbauk W-Sn(-F) skarn deposit at around 55 Ma. Together with published ages of primary Sn-W deposits in the Dawei region, our study confirms a westwardly younging trend of mineralization toward the coast and provides support for rollback of the Neo-Tethyan subducting slab since the Late Cretaceous, which is considered as the main mechanism for the regional, extensive Sn-W mineralization.
{"title":"IN SITU U-Pb DATING OF GARNET AND CASSITERITE FROM THE KANBAUK W-Sn(-F) SKARN DEPOSIT, DAWEI REGION, SOUTHERN MYANMAR: NEW INSIGHTS ON THE REGIONAL Sn-W METALLOGENY IN THE SOUTHEAST ASIAN TIN BELT","authors":"Wen Winston Zhao, Mei‐Fu Zhou, S. Dudka","doi":"10.5382/econgeo.5002","DOIUrl":"https://doi.org/10.5382/econgeo.5002","url":null,"abstract":"\u0000 Skarn ores have recently been identified beneath the historically mined placer Sn deposit at Kanbauk of the Dawei region, southern Myanmar. A large-tonnage skarn ore reserve at Kanbauk is estimated to be over 100 million tonnes, with reported ore grades of 0.17% WO3, 0.26% Sn, and 15.4% CaF2, potentially making it one of the largest W-Sn skarn deposits in the Southeast Asian tin belt. The mineralized skarns lie between marbles to the east and metasediments of the Mergui Group to the west. The timing of the mineralization is unclear, and thus the genetic relationship with regional magmatic events is not known. We report laser ablation-inductively coupled plasma-mass spectrometry U-Pb ages of garnet and cassiterite from the mineralized skarns. Garnet grains from the massive prograde skarns are typically subhedral to euhedral and show both sector and oscillatory zoning. They have 15 to 23% andradite (Ad), 55 to 67% grossularite (Gr), and 16 to 30% pyralspite (Py) (Ad15-23Gr55-67Py16-30) and contain 0.08 to 306 ppm U with a lower intercept 206Pb/238U age of 56.0 ± 1.5 Ma. Cassiterite grains from retrograde veinlets are subhedral to anhedral and have U contents from 110 to 12,000 ppm with a lower intercept 206Pb/238U age of 54.2 ± 1.7 Ma. Garnet and cassiterite have ages consistent within error and can be taken to indicate the formation of the Kanbauk W-Sn(-F) skarn deposit at around 55 Ma. Together with published ages of primary Sn-W deposits in the Dawei region, our study confirms a westwardly younging trend of mineralization toward the coast and provides support for rollback of the Neo-Tethyan subducting slab since the Late Cretaceous, which is considered as the main mechanism for the regional, extensive Sn-W mineralization.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"32 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72724585","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}
The ABM deposit, Finlayson Lake district, Yukon, Canada, is a bimodal-felsic, replacement-style volcanogenic massive sulfide (VMS) deposit (19.1 Mt @ 6.6 wt % Zn, 0.9 wt % Cu, 2.0 wt % Pb, 1.4 g/t Au, and 148 g/t Ag) hosted by Late Devonian continental back-arc–related volcanosedimentary rocks of the Kudz Ze Kayah formation. The VMS-related hydrothermal alteration associated with the deposit extends >1 km beyond the mineralization. Zones of pervasive sericite and chlorite alteration occur proximal to the massive sulfide lenses (<50 m) both in the hanging wall and the footwall, and zones of pervasive sericite and moderate sericite ± chlorite alteration extend laterally from the mineralization and into the hanging wall and footwall for hundreds to thousands of meters. Geochemical data and petrographic observations indicate that feldspar destruction and formation of white mica and chlorite were the main alteration processes. In both the hanging wall and footwall to the mineralization, base (e.g., Zn, Cu, Pb) and trace metals (e.g., Sb, Tl, Mo) form halos with elevated values up to 100 and 200 m, respectively. The paragenesis and the formation conditions of the hydrothermal alteration were determined through petrography of hydrothermal alteration assemblages and their crosscutting relationships, electron microprobe analyses of the compositions of white mica, chlorite, and carbonate, and illite-chlorite geothermometry. These data suggest that the sericite ± chlorite assemblage was the earliest and most extensive phase of the hydrothermal alteration that formed at temperatures around 215° ± 30°C. Overprinting the sericite-chlorite assemblage is the pervasive sericite assemblage that formed at temperatures around 250° ± 15°C. The pervasive chlorite assemblage formed at temperatures around 320° ± 10°C and overprints the preceding sericite-rich assemblages. Microprobe analyses of white mica and chlorite generally show that Mg-rich varieties are more common proximal to mineralization and formed earlier in the deposit paragenesis than Fe-rich varieties. Mineralogy derived from short-wave infrared data for mica and chlorite, however, shows no clear spatial trends across the deposit due to complex overprinting relationships between alteration minerals.
{"title":"Evolution of the Hydrothermal System Associated with the ABM Replacement-Style Volcanogenic Massive Sulfide Deposit, Finlayson Lake District, Yukon, Canada","authors":"N. Denisová, S. Piercey","doi":"10.5382/econgeo.5004","DOIUrl":"https://doi.org/10.5382/econgeo.5004","url":null,"abstract":"\u0000 The ABM deposit, Finlayson Lake district, Yukon, Canada, is a bimodal-felsic, replacement-style volcanogenic massive sulfide (VMS) deposit (19.1 Mt @ 6.6 wt % Zn, 0.9 wt % Cu, 2.0 wt % Pb, 1.4 g/t Au, and 148 g/t Ag) hosted by Late Devonian continental back-arc–related volcanosedimentary rocks of the Kudz Ze Kayah formation. The VMS-related hydrothermal alteration associated with the deposit extends >1 km beyond the mineralization. Zones of pervasive sericite and chlorite alteration occur proximal to the massive sulfide lenses (<50 m) both in the hanging wall and the footwall, and zones of pervasive sericite and moderate sericite ± chlorite alteration extend laterally from the mineralization and into the hanging wall and footwall for hundreds to thousands of meters. Geochemical data and petrographic observations indicate that feldspar destruction and formation of white mica and chlorite were the main alteration processes. In both the hanging wall and footwall to the mineralization, base (e.g., Zn, Cu, Pb) and trace metals (e.g., Sb, Tl, Mo) form halos with elevated values up to 100 and 200 m, respectively.\u0000 The paragenesis and the formation conditions of the hydrothermal alteration were determined through petrography of hydrothermal alteration assemblages and their crosscutting relationships, electron microprobe analyses of the compositions of white mica, chlorite, and carbonate, and illite-chlorite geothermometry. These data suggest that the sericite ± chlorite assemblage was the earliest and most extensive phase of the hydrothermal alteration that formed at temperatures around 215° ± 30°C. Overprinting the sericite-chlorite assemblage is the pervasive sericite assemblage that formed at temperatures around 250° ± 15°C. The pervasive chlorite assemblage formed at temperatures around 320° ± 10°C and overprints the preceding sericite-rich assemblages. Microprobe analyses of white mica and chlorite generally show that Mg-rich varieties are more common proximal to mineralization and formed earlier in the deposit paragenesis than Fe-rich varieties. Mineralogy derived from short-wave infrared data for mica and chlorite, however, shows no clear spatial trends across the deposit due to complex overprinting relationships between alteration minerals.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"21 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86043436","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}
J. Perelló, R. Sillitoe, Joaquín Rossello, Julián Forestier, Guido Merino, Diego Charchaflié
Filo del Sol is a composite porphyry-epithermal deposit, straddling the frontier between Argentina and Chile at latitude 28°29′ S, that has attracted a great deal of recent attention because of several drill intersections in excess of 1 km long with unusually high Cu, Au, and Ag grades. The deposit is part of the 8.5-km-long, N- to NE-trending Filo del Sol alignment of porphyry and high-sulfidation epithermal centers, which, in turn, is located in the newly defined Vicuña metallogenic belt that unites the well-known late Oligocene to middle Miocene Maricunga and El Indio belts. The deposit is hosted by Permian felsic volcanic rocks intruded by Triassic monzogranite and, nearer the surface, by shallowly dipping Late Cretaceous volcano-sedimentary rocks. These lithologic units were intruded by several generations of mafic dikes and high-level sills and, in the middle Miocene, by a parallel swarm of composite diorite porphyry dikes. An intermineral magmatic-hydrothermal breccia body is closely associated with the porphyry dikes and subsequently cut at shallow levels by a smaller, finer-grained breccia of phreatic and, possibly, phreatomagmatic origin. Early Cu-Au mineralization, mainly as chalcopyrite, is associated with K-feldspar- and biotite-bearing potassic alteration and accompanying A-type quartz-veinlet stockworks. The potassic zone was massively overprinted and extensively reconstituted by a zone of vuggy residual quartz and silicification in the core of the deposit, flanked by quartz-alunite as part of a more extensive lithocap. These alteration types host high-sulfidation Cu-Au-Ag mineralization as pyrite with early enargite and later bornite, chalcocite, covellite, and numerous Ag-bearing sulfosalts, with the highest grades typically confined to vuggy residual quartz. Largely barren, steam-heated alteration is preserved above and overprinted on the lithocap. The results of radiometric dating (six U-Pb and 22 Re-Os ages) show that porphyry intrusion and potassic alteration began at ~15 Ma and lasted for nearly 1 m.y., although most of the molybdenite samples reported ages from 14.7 to 14.4 ± 0.06 Ma. This short interval coincided with a pulse of regional compressive tectonism accommodated by high-angle, thick-skinned, reverse faulting of basement-cored blocks, and concomitant uplift and exhumation. This uplift gave rise to ~1 km of erosion during formation of the Filo del Sol deposit, thereby accounting for the extreme telescoping of high-sulfidation over porphyry mineralization. Spatial association of these middle Miocene intrusion centers with dated middle Permian and Eocene mineralization suggests deep-seated structural control of the Filo del Sol alignment. Ongoing supergene processes under low-pH conditions produced a near-surface resource dominated by chalcanthite, with minor underlying chalcocite enrichment, as well as partially oxidizing a shallow zone of high-grade Ag mineralization.
Filo del Sol是一个复合斑岩-浅成热液矿床，位于南纬28°29′S，横跨阿根廷和智利之间的边界，由于几个超过1公里长的钻孔交叉点具有异常高的Cu、Au和Ag品位，最近引起了人们的广泛关注。该矿床位于新近确定的Vicuña成矿带中，该成矿带连接着著名的晚渐新世至中新世中期Maricunga和El Indio带。该成矿带长8.5 km，由N- ne向Filo del Sol斑岩和高硫化浅成热液中心组成。矿床赋存于二叠纪长英质火山岩中，受三叠纪二长花岗岩侵入，近地表为浅浸的晚白垩世火山沉积岩。这些岩性单元被几代基性岩脉和高级岩脉侵入，在中新世中期，被平行的闪长斑岩岩脉群侵入。矿间岩浆-热液角砾岩体与斑岩岩脉密切相关，随后在浅层被较小的、细粒的潜水成因角砾岩切割，也可能是潜水成因角砾岩。早期铜金成矿以黄铜矿为主，与含钾长石和黑云母的钾蚀变有关，并伴有a型石英脉入口网。钾质带被大量叠印，并被矿床核心的空洞残余石英和硅化区广泛重建，两侧是石英明矾石，作为更广泛的岩盖的一部分。这些蚀变类型含有高硫化铜-金-银矿化，如黄铁矿、早期辉石矿和晚期斑铜矿、辉铜矿、钴岩矿和大量含银亚硫酸盐，最高品位通常局限于孔洞残余石英中。大部分贫瘠的、蒸汽加热的蚀变被保存在上面，并叠印在岩盖上。放射性测年(6个U-Pb年龄和22个Re-Os年龄)结果表明，斑岩侵入和钾蚀变始于~15 Ma，持续时间近1 Ma，而辉钼矿样品的年龄大多在14.7 ~ 14.4±0.06 Ma之间。这一短间隔与区域挤压构造运动的脉冲相吻合，该运动由基底核块体的高角度、厚皮、逆断裂以及伴随的隆升和掘出所适应。在Filo del Sol矿床形成过程中，这种隆起造成了约1公里的侵蚀，从而导致了斑岩矿化的高硫化物的极端伸缩。这些中中新世侵入中心与中二叠世和始新世成矿时间的空间关联表明，Filo del Sol走向受深层构造控制。在低ph条件下持续的表生作用形成了以辉铜矿为主的近地表资源，下伏辉铜矿少量富集，并部分氧化了浅层高品位银矿化带。
{"title":"Geology of Porphyry Cu-Au and Epithermal Cu-Au-Ag Mineralization at Filo del Sol, Argentina-Chile: Extreme Telescoping During Andean Uplift","authors":"J. Perelló, R. Sillitoe, Joaquín Rossello, Julián Forestier, Guido Merino, Diego Charchaflié","doi":"10.5382/econgeo.5029","DOIUrl":"https://doi.org/10.5382/econgeo.5029","url":null,"abstract":"\u0000 Filo del Sol is a composite porphyry-epithermal deposit, straddling the frontier between Argentina and Chile at latitude 28°29′ S, that has attracted a great deal of recent attention because of several drill intersections in excess of 1 km long with unusually high Cu, Au, and Ag grades. The deposit is part of the 8.5-km-long, N- to NE-trending Filo del Sol alignment of porphyry and high-sulfidation epithermal centers, which, in turn, is located in the newly defined Vicuña metallogenic belt that unites the well-known late Oligocene to middle Miocene Maricunga and El Indio belts. The deposit is hosted by Permian felsic volcanic rocks intruded by Triassic monzogranite and, nearer the surface, by shallowly dipping Late Cretaceous volcano-sedimentary rocks. These lithologic units were intruded by several generations of mafic dikes and high-level sills and, in the middle Miocene, by a parallel swarm of composite diorite porphyry dikes. An intermineral magmatic-hydrothermal breccia body is closely associated with the porphyry dikes and subsequently cut at shallow levels by a smaller, finer-grained breccia of phreatic and, possibly, phreatomagmatic origin. Early Cu-Au mineralization, mainly as chalcopyrite, is associated with K-feldspar- and biotite-bearing potassic alteration and accompanying A-type quartz-veinlet stockworks. The potassic zone was massively overprinted and extensively reconstituted by a zone of vuggy residual quartz and silicification in the core of the deposit, flanked by quartz-alunite as part of a more extensive lithocap. These alteration types host high-sulfidation Cu-Au-Ag mineralization as pyrite with early enargite and later bornite, chalcocite, covellite, and numerous Ag-bearing sulfosalts, with the highest grades typically confined to vuggy residual quartz. Largely barren, steam-heated alteration is preserved above and overprinted on the lithocap. The results of radiometric dating (six U-Pb and 22 Re-Os ages) show that porphyry intrusion and potassic alteration began at ~15 Ma and lasted for nearly 1 m.y., although most of the molybdenite samples reported ages from 14.7 to 14.4 ± 0.06 Ma. This short interval coincided with a pulse of regional compressive tectonism accommodated by high-angle, thick-skinned, reverse faulting of basement-cored blocks, and concomitant uplift and exhumation. This uplift gave rise to ~1 km of erosion during formation of the Filo del Sol deposit, thereby accounting for the extreme telescoping of high-sulfidation over porphyry mineralization. Spatial association of these middle Miocene intrusion centers with dated middle Permian and Eocene mineralization suggests deep-seated structural control of the Filo del Sol alignment. Ongoing supergene processes under low-pH conditions produced a near-surface resource dominated by chalcanthite, with minor underlying chalcocite enrichment, as well as partially oxidizing a shallow zone of high-grade Ag mineralization.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"170 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75997757","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}
J. Declercq, R. Bowell, C. Brough, A. Barnes, R. Griffiths
Mineral carbonation reactions consume CO2 and thus have the potential for the long-term fixation of atmospheric CO2. This paper explores the possibility of integrating industrial-scale carbon storage into mining operations. Ultramafic rocks are typically considered to be one the most promising rocks for carbon capture and storage owing to their high content of Mg-bearing silicate minerals, such as forsterite (Mg2SiO4) and serpentine (Mg3Si2O5(OH)4). Beyond the thermodynamic considerations showing that magnesite (MgCO3) and quartz (SiO2) form from forsterite and serpentine alteration, the degree to which CO2 is carbonated depends on the kinetics of the reaction. For industrial carbon capture and storage to be viable, reasonable carbonation efficiency has to be achieved. To this effect, the reaction rates have to be increased, which can be achieved either by increasing the reactive surface area, increasing the reaction temperature, or using reagents to drive the reactions. However, these approaches are usually energy demanding or not efficient enough. As part of its activities, the mining industry excavates tens or hundreds of million metric tons of rock per mine and in certain areas these mafic rock groups can represent a significant percentage of the waste material left on the surface. This could represent a locally important source of readily available material for carbon capture and storage if the conversion process is sufficiently efficient. To test and quantify the carbonation potential of mine waste, a sample of serpentine skarn waste rock obtained from an iron ore mine in Sweden was reacted for 60 weeks in a laboratory humidity-cell test (HCT) at 20°C. The results show the dissolution of olivine, the precipitation of serpentine, an increase in the neutralization potential of the sample, and the appearance of inorganic carbon during the 60 weeks of testing. At ambient temperatures the sluggish precipitation kinetics of secondary phases will favor the formation of more hydrous Mg silicate phases, such as serpentine (Mg3Si2O5(OH)4), in place of Mg-bearing carbonates. This reaction lowers considerably the efficiency of forsterite carbonation, as only 25% of the Mg released from forsterite dissolution to form carbonate minerals. This study aims to model the carbonation efficiency of Mg silicates through the use of models supported by laboratory testwork and taking the example of a mine site in northern Sweden. This study evaluates the reaction of CO2 with Mg-bearing silicate rocks and the demonstration that carbonation reactions occur with Mg silicate wastes consuming CO2. Consequently, weathering of waste rock may well represent an important sink for carbon in the environment.
{"title":"Role of Mg Gangue Minerals in Natural Analogue CO2 Sequestration","authors":"J. Declercq, R. Bowell, C. Brough, A. Barnes, R. Griffiths","doi":"10.5382/econgeo.4981","DOIUrl":"https://doi.org/10.5382/econgeo.4981","url":null,"abstract":"\u0000 Mineral carbonation reactions consume CO2 and thus have the potential for the long-term fixation of atmospheric CO2. This paper explores the possibility of integrating industrial-scale carbon storage into mining operations. Ultramafic rocks are typically considered to be one the most promising rocks for carbon capture and storage owing to their high content of Mg-bearing silicate minerals, such as forsterite (Mg2SiO4) and serpentine (Mg3Si2O5(OH)4). Beyond the thermodynamic considerations showing that magnesite (MgCO3) and quartz (SiO2) form from forsterite and serpentine alteration, the degree to which CO2 is carbonated depends on the kinetics of the reaction. For industrial carbon capture and storage to be viable, reasonable carbonation efficiency has to be achieved. To this effect, the reaction rates have to be increased, which can be achieved either by increasing the reactive surface area, increasing the reaction temperature, or using reagents to drive the reactions. However, these approaches are usually energy demanding or not efficient enough.\u0000 As part of its activities, the mining industry excavates tens or hundreds of million metric tons of rock per mine and in certain areas these mafic rock groups can represent a significant percentage of the waste material left on the surface. This could represent a locally important source of readily available material for carbon capture and storage if the conversion process is sufficiently efficient.\u0000 To test and quantify the carbonation potential of mine waste, a sample of serpentine skarn waste rock obtained from an iron ore mine in Sweden was reacted for 60 weeks in a laboratory humidity-cell test (HCT) at 20°C. The results show the dissolution of olivine, the precipitation of serpentine, an increase in the neutralization potential of the sample, and the appearance of inorganic carbon during the 60 weeks of testing. At ambient temperatures the sluggish precipitation kinetics of secondary phases will favor the formation of more hydrous Mg silicate phases, such as serpentine (Mg3Si2O5(OH)4), in place of Mg-bearing carbonates. This reaction lowers considerably the efficiency of forsterite carbonation, as only 25% of the Mg released from forsterite dissolution to form carbonate minerals. This study aims to model the carbonation efficiency of Mg silicates through the use of models supported by laboratory testwork and taking the example of a mine site in northern Sweden.\u0000 This study evaluates the reaction of CO2 with Mg-bearing silicate rocks and the demonstration that carbonation reactions occur with Mg silicate wastes consuming CO2. Consequently, weathering of waste rock may well represent an important sink for carbon in the environment.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"28 6 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88897326","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 : 2023-05-01DOI: 10.5382/econgeo.118.3.ip01
{"title":"Interesting Papers in Other Journals","authors":"","doi":"10.5382/econgeo.118.3.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.3.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"444 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136012226","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}
Brandon Sullivan, M. Locmelis, Bolorchimeg N. Tunnell, C. Seeger, M. Moroni, S. Dare, R. Mathur, Thomas Schott
The U.S. state of Missouri contains seven major and numerous lesser Fe oxide deposits within the 1.47 Ga St. Francois Mountains terrane. These deposits have been previously described as iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG) deposits and are speculated to contain significant resources of critical minerals, most notably rare earth elements and cobalt. One of the less-studied deposits in the region is the 1.455 Ga Kratz Spring deposit. The deposit consists of two steeply dipping magnetite bodies beneath 450 m of sedimentary cover. The genesis of the Kratz Spring deposit and its relationship to nearby IOA-IOCG deposits remains poorly constrained. To better understand the formation of the Kratz Spring deposit, we integrated stratigraphic, petrographic, and bulk rock studies with in situ trace element and Fe isotope chemistry of magnetite and hematite. Our data show that the Kratz Spring deposit is hydrothermal in origin but is divided into two subdeposits according to different fluid sources and formation conditions: (1) a deep but cooler hydrothermal Kratz Spring South deposit with a juvenile fluid source and (2) a shallow but hotter magmatic-hydrothermal Kratz Spring North deposit with variable fluid sources. Our genetic model suggests the two Kratz Spring deposits are local expressions of the same mineralization system; i.e., the Kratz Spring South deposit is a distal, lower-temperature offshoot of the feeder system that formed the Kratz Spring North deposit. Understanding the magmatic-hydrothermal plumbing system that formed Missouri’s IOA-IOCG deposits is important to guide critical mineral exploration efforts in the region.
{"title":"Genesis of the 1.45 Ga Kratz Spring Iron Oxide-Apatite Deposit Complex in Southeast Missouri, USA: Constraints from Oxide Mineral Chemistry","authors":"Brandon Sullivan, M. Locmelis, Bolorchimeg N. Tunnell, C. Seeger, M. Moroni, S. Dare, R. Mathur, Thomas Schott","doi":"10.5382/econgeo.5003","DOIUrl":"https://doi.org/10.5382/econgeo.5003","url":null,"abstract":"\u0000 The U.S. state of Missouri contains seven major and numerous lesser Fe oxide deposits within the 1.47 Ga St. Francois Mountains terrane. These deposits have been previously described as iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG) deposits and are speculated to contain significant resources of critical minerals, most notably rare earth elements and cobalt. One of the less-studied deposits in the region is the 1.455 Ga Kratz Spring deposit. The deposit consists of two steeply dipping magnetite bodies beneath 450 m of sedimentary cover. The genesis of the Kratz Spring deposit and its relationship to nearby IOA-IOCG deposits remains poorly constrained. To better understand the formation of the Kratz Spring deposit, we integrated stratigraphic, petrographic, and bulk rock studies with in situ trace element and Fe isotope chemistry of magnetite and hematite. Our data show that the Kratz Spring deposit is hydrothermal in origin but is divided into two subdeposits according to different fluid sources and formation conditions: (1) a deep but cooler hydrothermal Kratz Spring South deposit with a juvenile fluid source and (2) a shallow but hotter magmatic-hydrothermal Kratz Spring North deposit with variable fluid sources. Our genetic model suggests the two Kratz Spring deposits are local expressions of the same mineralization system; i.e., the Kratz Spring South deposit is a distal, lower-temperature offshoot of the feeder system that formed the Kratz Spring North deposit. Understanding the magmatic-hydrothermal plumbing system that formed Missouri’s IOA-IOCG deposits is important to guide critical mineral exploration efforts in the region.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"30 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78162021","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}
F. Tontini, G. Turner, A. Reyes, F. Speranza, M. Tivey, C. Massiot, C. D. de Ronde, S. Humphris
The 3-D subseafloor architecture of submarine hydrothermal systems is largely unknown, particularly at arc volcanoes. The alteration of volcanic rocks in these systems produces dramatic changes in their magnetic properties. Here, we present the first comprehensive study of paleomagnetic measurements from oriented samples of hydrothermally altered dacites from Brothers volcano (Kermadec arc), drilled during International Ocean Discovery Program (IODP) Expedition 376. These data have enabled insight into the progressive evolution of magnetic minerals in subseafloor volcanic rocks affected by variable types and degrees of hydrothermal alteration in response to varying fluid temperatures, chemistry, and associated mineralization; from initial chloritization typical of relatively low-temperature interaction with seawater to extremely altered rocks affected by higher-temperature, very acidic magmatic fluids. Hydrothermally altered samples show a significant reduction in natural remanent magnetization intensity (10–4 to 10–2 A/m) compared with unaltered samples (1–10 A/m), suggesting that primary titanomagnetite grains are destroyed during the hydrothermal alteration process. Except for a small region in proximity to the mineralized stockwork zone, no chemical remanent magnetization is observed in association with hydrothermal alteration, consistent with the widespread formation of diamagnetic and/or paramagnetic minerals such as pyrite, rutile, and leucoxene, which do not carry any natural remanent magnetization. Demagnetization experiments show that most of the oriented samples possess a stable characteristic remanent magnetization induced by the residual primary magnetic minerals formed at the time the rocks cooled on the sea floor. Partially chloritized dacites, however, are characterized by large magnetic susceptibilities, low Koenigsberger ratios, and very low magnetic coercivities, consistent with initial dissolution of smaller, singledomain magnetic grains, indicating that intensely hydrothermally altered rocks are better paleomagnetic indicators than initially chloritized samples at the periphery of the hydrothermal systems. The significant magnetic contrast between fresh and hydrothermally altered rocks, in addition to a thick layer (>300 m) of demagnetized rocks observed at Brothers volcano, confirms the empirical results that magnetic anomalies are important geophysical tools to determine the geometry of hydrothermal systems at submarine arc volcanoes.
海底热液系统的三维海底结构在很大程度上是未知的，特别是在弧火山。这些体系中火山岩的变化使它们的磁性发生了巨大的变化。在这里，我们首次对来自兄弟火山(Kermadec弧)的热液蚀变英安岩定向样品进行了全面的古地磁测量，这些样品是在国际海洋发现计划(IODP)第376次探险期间钻探的。这些数据使我们能够深入了解海底火山岩中磁性矿物的渐进演化，这些矿物受不同类型和程度的热液蚀变的影响，以响应不同的流体温度、化学性质和相关的矿化;从典型的相对低温与海水相互作用的初始绿岩化到受高温、酸性岩浆流体影响的极端蚀变岩石。热液蚀变样品的自然剩余磁化强度(10-4 ~ 10-2 a /m)明显低于未蚀变样品(1-10 a /m)，表明原生钛磁铁矿颗粒在热液蚀变过程中被破坏。除了矿化网带附近的一小块区域外，没有观察到与热液蚀变有关的化学残余磁化，这与黄铁矿、金红石、亮绿石等抗磁性和/或顺磁性矿物的广泛形成一致，这些矿物不携带任何自然残余磁化。退磁实验表明，大多数定向样品具有稳定的特征剩余磁化，这是由岩石在海底冷却时形成的残余原生磁性矿物引起的。而部分绿泥化英安岩的磁化率大，Koenigsberger比低，磁顽力极低，与初始溶蚀较小的单畴磁性颗粒一致，表明强烈热液蚀变岩石比初始绿泥化样品在热液体系外围具有更好的古地磁指示作用。新鲜岩石和热液蚀变岩石之间的显著磁性对比，以及在兄弟火山观测到的厚层(>300 m)退磁岩石，证实了磁异常是确定海底弧火山热液系统几何形状的重要地球物理工具的经验结果。
{"title":"Effects of Hydrothermal Alteration and Mineralization on the Paleomagnetic Properties of Rocks from IODP Expedition 376 at Brothers Volcano","authors":"F. Tontini, G. Turner, A. Reyes, F. Speranza, M. Tivey, C. Massiot, C. D. de Ronde, S. Humphris","doi":"10.5382/econgeo.5008","DOIUrl":"https://doi.org/10.5382/econgeo.5008","url":null,"abstract":"\u0000 The 3-D subseafloor architecture of submarine hydrothermal systems is largely unknown, particularly at arc volcanoes. The alteration of volcanic rocks in these systems produces dramatic changes in their magnetic properties. Here, we present the first comprehensive study of paleomagnetic measurements from oriented samples of hydrothermally altered dacites from Brothers volcano (Kermadec arc), drilled during International Ocean Discovery Program (IODP) Expedition 376. These data have enabled insight into the progressive evolution of magnetic minerals in subseafloor volcanic rocks affected by variable types and degrees of hydrothermal alteration in response to varying fluid temperatures, chemistry, and associated mineralization; from initial chloritization typical of relatively low-temperature interaction with seawater to extremely altered rocks affected by higher-temperature, very acidic magmatic fluids.\u0000 Hydrothermally altered samples show a significant reduction in natural remanent magnetization intensity (10–4 to 10–2 A/m) compared with unaltered samples (1–10 A/m), suggesting that primary titanomagnetite grains are destroyed during the hydrothermal alteration process. Except for a small region in proximity to the mineralized stockwork zone, no chemical remanent magnetization is observed in association with hydrothermal alteration, consistent with the widespread formation of diamagnetic and/or paramagnetic minerals such as pyrite, rutile, and leucoxene, which do not carry any natural remanent magnetization.\u0000 Demagnetization experiments show that most of the oriented samples possess a stable characteristic remanent magnetization induced by the residual primary magnetic minerals formed at the time the rocks cooled on the sea floor. Partially chloritized dacites, however, are characterized by large magnetic susceptibilities, low Koenigsberger ratios, and very low magnetic coercivities, consistent with initial dissolution of smaller, singledomain magnetic grains, indicating that intensely hydrothermally altered rocks are better paleomagnetic indicators than initially chloritized samples at the periphery of the hydrothermal systems.\u0000 The significant magnetic contrast between fresh and hydrothermally altered rocks, in addition to a thick layer (>300 m) of demagnetized rocks observed at Brothers volcano, confirms the empirical results that magnetic anomalies are important geophysical tools to determine the geometry of hydrothermal systems at submarine arc volcanoes.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"31 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82668145","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}
N. Vafeas, P. Slezak, D. Chew, M. Brodbeck, M. Hitzman, D. Hnatyshin
Uranium-Pb dating of unusual coarse-grained apatite crystals from hydrothermal dolostone breccia in the barite-rich Magcobar zone at the Silvermines deposit, Ireland, indicates an age of 331 ± 5.6 Ma for hydrothermal alteration. This age is in agreement with an Re-Os age on pyrite-sphalerite but differs from previous estimates that were based on palemomagnetism and sphalerite Rb-Sr geochronology at Silvermines. The new U-Pb age indicates the deposit largely formed epigenetically rather than as a synsedimentary deposit. The trace element composition of the apatite provides additional constraints on the geochemical evolution of the Silvermines hydrothermal system indicating that it was initiated with the expulsion of oxidizing fluids responsible for early hematite-silica precipitation. This was followed by the formation of hydrothermal dolostone breccias containing barite and the apatite dated here. The infiltration of metal-bearing hydrothermal fluids, likely derived from the basement, overlapped and followed the development of hydrothermal dolostone breccias, interacting with Carboniferous seawater during dolomitization and barite precipitation. Near-sea-floor biogenic activity, possibly enhanced due to escape of hydrothermal fluids, resulted in the reduction of seawater sulfate and formation of the sulfide-bearing fluids that facilitated the development of the Silvermines Zn-Pb deposit.
{"title":"U-Pb DATING OF APATITE FROM SILVERMINES DEPOSIT, IRELAND: A MODEL FOR HYDROTHERMAL ORE GENESIS","authors":"N. Vafeas, P. Slezak, D. Chew, M. Brodbeck, M. Hitzman, D. Hnatyshin","doi":"10.5382/econgeo.5016","DOIUrl":"https://doi.org/10.5382/econgeo.5016","url":null,"abstract":"\u0000 Uranium-Pb dating of unusual coarse-grained apatite crystals from hydrothermal dolostone breccia in the barite-rich Magcobar zone at the Silvermines deposit, Ireland, indicates an age of 331 ± 5.6 Ma for hydrothermal alteration. This age is in agreement with an Re-Os age on pyrite-sphalerite but differs from previous estimates that were based on palemomagnetism and sphalerite Rb-Sr geochronology at Silvermines. The new U-Pb age indicates the deposit largely formed epigenetically rather than as a synsedimentary deposit. The trace element composition of the apatite provides additional constraints on the geochemical evolution of the Silvermines hydrothermal system indicating that it was initiated with the expulsion of oxidizing fluids responsible for early hematite-silica precipitation. This was followed by the formation of hydrothermal dolostone breccias containing barite and the apatite dated here. The infiltration of metal-bearing hydrothermal fluids, likely derived from the basement, overlapped and followed the development of hydrothermal dolostone breccias, interacting with Carboniferous seawater during dolomitization and barite precipitation. Near-sea-floor biogenic activity, possibly enhanced due to escape of hydrothermal fluids, resulted in the reduction of seawater sulfate and formation of the sulfide-bearing fluids that facilitated the development of the Silvermines Zn-Pb deposit.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"22 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81334689","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}
Yingchao Liu, Yucai Song, M. Fard, Z. Hou, Wang Ma, Longlong Yue
Mehdiabad is the world’s largest Mississippi Valley-type (MVT) Zn-Pb deposit (394 million tonnes [Mt] of metal ore at 4.2% Zn, 1.6% Pb) and contains significant barite resources (>40 Mt). Such large accumulations of barite are not common in carbonate-hosted Zn-Pb deposits. Therefore, the origin of the barite and its association with the Zn-Pb mineralization is of significant interest for further investigation. Field work and petrographic studies indicate that the Zn-Pb-Ba orebodies in the Mehdiabad deposit are hosted by Lower Cretaceous carbonate units of the Taft and Abkuh Formations. Fine- to coarse-grained barite with lesser siderite formed in three stages (S1, S2, and S4), along with a quartz-sulfide stage (S3) with minor quartz, sphalerite, galena, chalcopyrite, and pyrite, and the main Zn-Pb sulfide stage (S5) with massive sphalerite and galena. The barites have δ34S values from 17.7 to 20.6‰, δ18O values from 13.2 to 16.8‰, Δ33SV-CDT values from –0.001 to 0.036‰, and initial 87Sr/86Sr ratios from 0.707327 ± 0.000008 to 0.708593 ± 0.000008 (V-CDT = Vienna-Canyon Diablo Troilite). The siderites have δ13CV-PDB values from –3.8 to –2.7‰, and δ18OV-SMOW values from 18.2 to 20.9‰ (V-PDB = Vienna-Pee Dee Belemnite, V-SMOW = Vienna-standard mean ocean water). These geochemical data, and the barite morphology, point to a diagenetic origin for all stages of barite. We suggest that S1 and S2 barite precipitated from pore fluids at the sulfate-methane transition zone in a methane-diffusion-limited environment with increasing methane content. S4 barite precipitated when the methane- and barium-bearing cold-seep fluid migrated to the shallow carbonate sediments and formed a methane-in-excess setting. For the three stages, the SO42- in barite came from the residual SO42- in pore fluids undergoing sulfate-driven anaerobic oxidation of methane, and the Ba2+ came from dissolved biogenic barite and terrigenous materials in the Taft and Sangestan Formations. Primary fluid inclusions trapped in S3 quartz have salinities of 5.6 to 8.1 wt % NaCl equiv and homogenization temperatures of 143.8° to 166.1°C. The quartz has δ18OV-SMOW values ranging from 9.8 to 22.5‰ and δ30Si values from –1.3 to –0.9‰. These data indicate hydrothermal fluid flow occurred between the diagenetic S2 and S4 events. Secondary fluid inclusions with salinities of 17.70 to 19.13 wt % NaCl equiv and homogenization temperatures of 123.0° to 134.0°C are found in the S3 quartz, too. They might represent the hydrothermal event formed by basinal brines in S5. According to the ore textures and the comparison of the sulfur isotopes between S5 Zn-Pb sulfides and the digenetic barites, the barite provided a host and a sulfur source for the later Zn-Pb mineralization. The relationship between barite and the Zn-Pb mineralization indicates that significant accumulations of sulfates may be a critical exploration target for this kind of giant deposit.
{"title":"The Characteristics and Origin of Barite in the Giant Mehdiabad Zn-Pb-Ba Deposit, Iran","authors":"Yingchao Liu, Yucai Song, M. Fard, Z. Hou, Wang Ma, Longlong Yue","doi":"10.5382/econgeo.5014","DOIUrl":"https://doi.org/10.5382/econgeo.5014","url":null,"abstract":"\u0000 Mehdiabad is the world’s largest Mississippi Valley-type (MVT) Zn-Pb deposit (394 million tonnes [Mt] of metal ore at 4.2% Zn, 1.6% Pb) and contains significant barite resources (>40 Mt). Such large accumulations of barite are not common in carbonate-hosted Zn-Pb deposits. Therefore, the origin of the barite and its association with the Zn-Pb mineralization is of significant interest for further investigation.\u0000 Field work and petrographic studies indicate that the Zn-Pb-Ba orebodies in the Mehdiabad deposit are hosted by Lower Cretaceous carbonate units of the Taft and Abkuh Formations. Fine- to coarse-grained barite with lesser siderite formed in three stages (S1, S2, and S4), along with a quartz-sulfide stage (S3) with minor quartz, sphalerite, galena, chalcopyrite, and pyrite, and the main Zn-Pb sulfide stage (S5) with massive sphalerite and galena.\u0000 The barites have δ34S values from 17.7 to 20.6‰, δ18O values from 13.2 to 16.8‰, Δ33SV-CDT values from –0.001 to 0.036‰, and initial 87Sr/86Sr ratios from 0.707327 ± 0.000008 to 0.708593 ± 0.000008 (V-CDT = Vienna-Canyon Diablo Troilite). The siderites have δ13CV-PDB values from –3.8 to –2.7‰, and δ18OV-SMOW values from 18.2 to 20.9‰ (V-PDB = Vienna-Pee Dee Belemnite, V-SMOW = Vienna-standard mean ocean water). These geochemical data, and the barite morphology, point to a diagenetic origin for all stages of barite. We suggest that S1 and S2 barite precipitated from pore fluids at the sulfate-methane transition zone in a methane-diffusion-limited environment with increasing methane content. S4 barite precipitated when the methane- and barium-bearing cold-seep fluid migrated to the shallow carbonate sediments and formed a methane-in-excess setting. For the three stages, the SO42- in barite came from the residual SO42- in pore fluids undergoing sulfate-driven anaerobic oxidation of methane, and the Ba2+ came from dissolved biogenic barite and terrigenous materials in the Taft and Sangestan Formations.\u0000 Primary fluid inclusions trapped in S3 quartz have salinities of 5.6 to 8.1 wt % NaCl equiv and homogenization temperatures of 143.8° to 166.1°C. The quartz has δ18OV-SMOW values ranging from 9.8 to 22.5‰ and δ30Si values from –1.3 to –0.9‰. These data indicate hydrothermal fluid flow occurred between the diagenetic S2 and S4 events. Secondary fluid inclusions with salinities of 17.70 to 19.13 wt % NaCl equiv and homogenization temperatures of 123.0° to 134.0°C are found in the S3 quartz, too. They might represent the hydrothermal event formed by basinal brines in S5.\u0000 According to the ore textures and the comparison of the sulfur isotopes between S5 Zn-Pb sulfides and the digenetic barites, the barite provided a host and a sulfur source for the later Zn-Pb mineralization. The relationship between barite and the Zn-Pb mineralization indicates that significant accumulations of sulfates may be a critical exploration target for this kind of giant deposit.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"10 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74444365","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}
André Cravinho, A. Jesus, Bruno Moreira, A. Mateus, B. Pracejus, J. Figueiras, M. Benoit, W. Bauer, F. Rocha
Despite the substantial amount of research on the Cretaceous Samail ophiolite in Oman, the factors controlling the size and metal endowment of the mafic-hosted, Cu-Au(-Zn-Ag) volcanogenic massive sulfide (VMS) deposits remain elusive. This work shows that the volcanostratigraphic position, hydrothermal venting style, and oxidation processes are critical factors controlling the distinct features of the Shinas and Mandoos deposits. Mandoos is a large (8 Mt, 1.8 wt % Cu, 0.18 g/ton Au) orebody preserving abundant primary vent-related features formed via mound growth and collapse within a wide hydrothermal field, overlying a poorly developed stockwork. The smaller Shinas deposit (0.8 Mt, 2.6 wt % Cu, 0.63 g/t Au) represents a higher-temperature system evolving from low fS2/fO2 conditions, locally sealed by jaspers, to a mound growth stage with widespread subseafloor brecciation/replacement with associated zone refining. Mandoos formed at the onset of the postaxial stage (Geotimes-Tholeiitic Alley transition), and Shinas is hosted within the Alley units. Volcanism in Samail was seemingly continuous, and the low ɛNd and Nb/Ta of the Shinas hanging-wall lavas record the onset of significant modifications of the mantle source during the postaxial stage. Mandoos is enriched in Te + As + Se ± Zn ± Ga ± Sb relative to Shinas, where higher Cu + Au + Tl ± Mo grades possibly reflect leaching of protoarc-like lavas. Rare earth element patterns in the ores mimicking the deposit footwall can be employed to constrain volcanostratigraphic positioning and indicate that the footwall lavas may also represent a source of metals. Formation of metal-rich ochres at the sea floor likely led to Cu + Au upgrading in the ores during seawater-induced oxidation, which was enhanced during subaerial gossan formation.
{"title":"Contrasting Features and Volcanostratigraphy of the Mafic-Hosted Mandoos and Shinas Volcanogenic Massive Sulfide Deposits, Samail Ophiolite, Oman","authors":"André Cravinho, A. Jesus, Bruno Moreira, A. Mateus, B. Pracejus, J. Figueiras, M. Benoit, W. Bauer, F. Rocha","doi":"10.5382/econgeo.5006","DOIUrl":"https://doi.org/10.5382/econgeo.5006","url":null,"abstract":"\u0000 Despite the substantial amount of research on the Cretaceous Samail ophiolite in Oman, the factors controlling the size and metal endowment of the mafic-hosted, Cu-Au(-Zn-Ag) volcanogenic massive sulfide (VMS) deposits remain elusive. This work shows that the volcanostratigraphic position, hydrothermal venting style, and oxidation processes are critical factors controlling the distinct features of the Shinas and Mandoos deposits.\u0000 Mandoos is a large (8 Mt, 1.8 wt % Cu, 0.18 g/ton Au) orebody preserving abundant primary vent-related features formed via mound growth and collapse within a wide hydrothermal field, overlying a poorly developed stockwork. The smaller Shinas deposit (0.8 Mt, 2.6 wt % Cu, 0.63 g/t Au) represents a higher-temperature system evolving from low fS2/fO2 conditions, locally sealed by jaspers, to a mound growth stage with widespread subseafloor brecciation/replacement with associated zone refining. Mandoos formed at the onset of the postaxial stage (Geotimes-Tholeiitic Alley transition), and Shinas is hosted within the Alley units. Volcanism in Samail was seemingly continuous, and the low ɛNd and Nb/Ta of the Shinas hanging-wall lavas record the onset of significant modifications of the mantle source during the postaxial stage.\u0000 Mandoos is enriched in Te + As + Se ± Zn ± Ga ± Sb relative to Shinas, where higher Cu + Au + Tl ± Mo grades possibly reflect leaching of protoarc-like lavas. Rare earth element patterns in the ores mimicking the deposit footwall can be employed to constrain volcanostratigraphic positioning and indicate that the footwall lavas may also represent a source of metals. Formation of metal-rich ochres at the sea floor likely led to Cu + Au upgrading in the ores during seawater-induced oxidation, which was enhanced during subaerial gossan formation.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"29 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82210375","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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