Abstract The genetic relationship between organic-rich source rocks and Hg deposits remains the subject of debate. This paper evaluates the role of organic-rich source rocks in cinnabar ore formation in the Terlingua mining district, Texas, which was deposited at relatively shallow depths in Cretaceous sedimentary rocks spatially related to intrusive alkali igneous rocks. The mineralization formed at ~45 bar and ~200°C. The aqueous ore-forming fluid had a pH of ~5 to 7 and was H2S saturated. Cinnabar was deposited as a result of H2S oxidation through mixing and cooling with local meteoric water. Both Hg0(org) and Hg0(aq) species were likely important in cinnabar ore formation. However, recent studies on the solubility of Hg0 in hydrocarbons show that at cinnabar saturation, Hg0 is more than an order of magnitude more soluble in hydrocarbons (Hg0(org) = 163 mg/kg) than Hg0 in water (Hg0(aq) = 10.8 mg/kg). Despite their proximity in some deposits, conditions of ore formation of the rare Hg oxychloride and sulfate minerals are not compatible with conditions under which most cinnabar ores formed, requiring fO2 conditions orders of magnitude more oxidizing, a relatively high chloride ion activity (>10–1), and alkaline conditions, with pH > 10. Mass dependent fractionation versus mass independent fractionation of Hg isotope data from Hg-bearing minerals in Terlingua support a genetic link to the source of Hg being the organic-rich marls and tuffaceous black shales of the Lower Eagle Ford Formation. This source rock is chronostratigraphically equivalent to the Lower Cretaceous oceanic anoxic event (OAE-2), which defines the Cenomanian-Turonian boundary. OAE-2 represents the culmination of a global anoxic ocean event at ~94.1 Ma, believed to be a consequence of volcanic activity associated with a large igneous province. Mercury was sequestered by the organic-rich source rocks of the Lower Eagle Ford Formation and associated coeval ash and tuffs. Tabular igneous bodies that intruded and uplifted the local stratigraphy formed the Terlingua monocline and provided a source of heat for hydrothermal activity and maturation of organic matter. The subsequent generation and migration of liquid hydrocarbons and formation brines from the Lower Eagle Ford Formation transported Hg0(org) updip toward the hinge line of the Terlingua monocline where mixing with oxygenated meteoric water and subsequent oxidation of H2S produced the cinnabar-rich ores.
{"title":"Elucidating the Role of Hydrocarbons in Cinnabar (HgS) Ore Formation: A Model for Hg Mineralization in the Terlingua Mining District, Big Bend National Park, SW Texas","authors":"L. Taras Bryndzia","doi":"10.5382/econgeo.5022","DOIUrl":"https://doi.org/10.5382/econgeo.5022","url":null,"abstract":"Abstract The genetic relationship between organic-rich source rocks and Hg deposits remains the subject of debate. This paper evaluates the role of organic-rich source rocks in cinnabar ore formation in the Terlingua mining district, Texas, which was deposited at relatively shallow depths in Cretaceous sedimentary rocks spatially related to intrusive alkali igneous rocks. The mineralization formed at ~45 bar and ~200°C. The aqueous ore-forming fluid had a pH of ~5 to 7 and was H2S saturated. Cinnabar was deposited as a result of H2S oxidation through mixing and cooling with local meteoric water. Both Hg0(org) and Hg0(aq) species were likely important in cinnabar ore formation. However, recent studies on the solubility of Hg0 in hydrocarbons show that at cinnabar saturation, Hg0 is more than an order of magnitude more soluble in hydrocarbons (Hg0(org) = 163 mg/kg) than Hg0 in water (Hg0(aq) = 10.8 mg/kg). Despite their proximity in some deposits, conditions of ore formation of the rare Hg oxychloride and sulfate minerals are not compatible with conditions under which most cinnabar ores formed, requiring fO2 conditions orders of magnitude more oxidizing, a relatively high chloride ion activity (>10–1), and alkaline conditions, with pH > 10. Mass dependent fractionation versus mass independent fractionation of Hg isotope data from Hg-bearing minerals in Terlingua support a genetic link to the source of Hg being the organic-rich marls and tuffaceous black shales of the Lower Eagle Ford Formation. This source rock is chronostratigraphically equivalent to the Lower Cretaceous oceanic anoxic event (OAE-2), which defines the Cenomanian-Turonian boundary. OAE-2 represents the culmination of a global anoxic ocean event at ~94.1 Ma, believed to be a consequence of volcanic activity associated with a large igneous province. Mercury was sequestered by the organic-rich source rocks of the Lower Eagle Ford Formation and associated coeval ash and tuffs. Tabular igneous bodies that intruded and uplifted the local stratigraphy formed the Terlingua monocline and provided a source of heat for hydrothermal activity and maturation of organic matter. The subsequent generation and migration of liquid hydrocarbons and formation brines from the Lower Eagle Ford Formation transported Hg0(org) updip toward the hinge line of the Terlingua monocline where mixing with oxygenated meteoric water and subsequent oxidation of H2S produced the cinnabar-rich ores.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"332 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135966233","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}
Abstract Carbonaceous materials are a key factor controlling mineralization processes in many world-class gold deposits. Haoyaoerhudong is the largest carbonaceous metasediment-hosted gold deposit on the north margin of the North China craton. Gold-bearing orebodies are hosted in carbonaceous slates and schists belonging to Mesoproterozoic rift-related successions. Typical hydrothermal minerals are pyrrhotite, quartz, biotite, graphite, apatite, titanite, and native gold. The ore mineralogy, combined with microthermometry and Raman spectra on fluid inclusions, has demonstrated three stages of hydrothermal activity: (I) quartz-biotite ± sulfide stage associated with gold mineralization (315°–510°C; ~4.8 wt % NaCl equiv; H2O-NaCl-CO2 ± CH4 ± N2 system); (II) quartz-sulfide stage, including quartz-sulfide stringers (IIa, 250°–334°C; ~5.4 wt % NaCl equiv; H2O-NaCl-CH4 ± CO2 ± N2 system) and fractured quartz-sulfide ores (IIb, 234°–308°C; ~4.1 wt % NaCl equiv; H2O-NaCl-N2 ± CH4 system); and (III) post-ore quartz-calcite stage (70°–219°C; ~4.8 wt % NaCl equiv; H2O-NaCl system). The molar ratios of CO2 and CH4 progressively decreased from stage I to II, consistent with the occurrence of graphite in alteration zones. Microscopic observation and Raman spectra suggest that the fine-grained graphite from altered schist (Gr-1/2) and coarse-sized graphite from gold-bearing veins (Gr-3/4) are of high crystallinity and exhibit characteristics indicating a hydrothermal origin. The δ13C values of graphite, varying from −27.1 to −26.0‰ Vienna-Pee Dee Belemnite (V-PDB), suggest that the carbon was of biogenetic origin. Apatite Sr isotopes (87Sr/86Sr: 0.708293–0.708842) and titanite Nd isotopes (εNd(t): –11.76 to –14.84) also indicate contributions from carbonaceous rocks during mineralization. Thermodynamic modeling demonstrates that graphite may have precipitated at Haoyaoerhudong due to cooling and reduction of the H2O-CO2-CH4 fluids at high temperatures. Graphite precipitation would significantly consume CO2 and effectively destabilize Au bisulfide complexes, facilitating the codeposition of pyrrhotite, graphite, and native gold at high temperatures (≥379°C). We infer that deposition of hydrothermal graphite is a crucial process for mesothermal-hypothermal mineralization in sediment-hosted orogenic gold deposits.
{"title":"Hydrothermal Graphite as a Trigger for High-Temperature Orogenic Gold Mineralization at Haoyaoerhudong, Northern China","authors":"Wenbo Li, Fanghua Zhang, Xueyuan Qiao, Tianyao Fu","doi":"10.5382/econgeo.5018","DOIUrl":"https://doi.org/10.5382/econgeo.5018","url":null,"abstract":"Abstract Carbonaceous materials are a key factor controlling mineralization processes in many world-class gold deposits. Haoyaoerhudong is the largest carbonaceous metasediment-hosted gold deposit on the north margin of the North China craton. Gold-bearing orebodies are hosted in carbonaceous slates and schists belonging to Mesoproterozoic rift-related successions. Typical hydrothermal minerals are pyrrhotite, quartz, biotite, graphite, apatite, titanite, and native gold. The ore mineralogy, combined with microthermometry and Raman spectra on fluid inclusions, has demonstrated three stages of hydrothermal activity: (I) quartz-biotite ± sulfide stage associated with gold mineralization (315°–510°C; ~4.8 wt % NaCl equiv; H2O-NaCl-CO2 ± CH4 ± N2 system); (II) quartz-sulfide stage, including quartz-sulfide stringers (IIa, 250°–334°C; ~5.4 wt % NaCl equiv; H2O-NaCl-CH4 ± CO2 ± N2 system) and fractured quartz-sulfide ores (IIb, 234°–308°C; ~4.1 wt % NaCl equiv; H2O-NaCl-N2 ± CH4 system); and (III) post-ore quartz-calcite stage (70°–219°C; ~4.8 wt % NaCl equiv; H2O-NaCl system). The molar ratios of CO2 and CH4 progressively decreased from stage I to II, consistent with the occurrence of graphite in alteration zones. Microscopic observation and Raman spectra suggest that the fine-grained graphite from altered schist (Gr-1/2) and coarse-sized graphite from gold-bearing veins (Gr-3/4) are of high crystallinity and exhibit characteristics indicating a hydrothermal origin. The δ13C values of graphite, varying from −27.1 to −26.0‰ Vienna-Pee Dee Belemnite (V-PDB), suggest that the carbon was of biogenetic origin. Apatite Sr isotopes (87Sr/86Sr: 0.708293–0.708842) and titanite Nd isotopes (εNd(t): –11.76 to –14.84) also indicate contributions from carbonaceous rocks during mineralization. Thermodynamic modeling demonstrates that graphite may have precipitated at Haoyaoerhudong due to cooling and reduction of the H2O-CO2-CH4 fluids at high temperatures. Graphite precipitation would significantly consume CO2 and effectively destabilize Au bisulfide complexes, facilitating the codeposition of pyrrhotite, graphite, and native gold at high temperatures (≥379°C). We infer that deposition of hydrothermal graphite is a crucial process for mesothermal-hypothermal mineralization in sediment-hosted orogenic gold deposits.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136011451","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}
Saeid Asadzadeh, Sabine Chabrillat, Thomas Cudahy, Bahman Rashidi, Carlos Roberto de Souza Filho
Abstract Porphyry copper deposits are associated with large alteration footprints, and alteration mapping plays a key role in the exploration of these deposits. Imaging spectroscopy is commonly deployed for exploration targeting, yet it has rarely been used to map deposit-scale alteration patterns before initiating drilling. To close this gap, the Shadan porphyry Cu-Au deposit was thoroughly studied using the HyMap hyperspectral data (visible near-infrared–short-wave infrared) at 5-m resolution corroborated by rock geochemistry, magnetometry, and laboratory spectroscopy. Shadan is a well-exposed deposit with near-perfect zonation located in the volcanic belts of eastern Iran containing >135 Mt of ore at 0.3% Cu and 0.4 g/t Au. Thirteen minerals, including white mica, Al smectite, kaolinite, ferric/ferrous minerals, biotite, actinolite, epidote, chlorite, tourmaline, and jarosite, were mapped by applying the multifeature extraction methodology. The propylitic zone was partitioned into actinolite, epidote, and chlorite subfacies. The compositions of biotite and white mica were observed to become Fe and Al rich, respectively, toward the mineralized zones. The chemistry of actinolite was observed to change from Fe to Mg rich inward, providing a new vectoring tool for porphyry copper exploration. The study provided significant information about fluid-rock interactions and the chemistry of the circulating fluids including the oxidation-reduction states and acidity. By integrating the mineral maps with other data sets using the fuzzy logic method, the promising (ore) zones were identified and used to plan the next-stage drilling. This work demonstrated that imaging spectroscopy can be effectively used to better understand porphyry systems and provide deposit-scale vectors toward the mineralized centers, facilitating drilling.
{"title":"Alteration Mineral Mapping of the Shadan Porphyry Cu-Au Deposit (Iran) Using Airborne Imaging Spectroscopic Data: Implications for Exploration Drilling","authors":"Saeid Asadzadeh, Sabine Chabrillat, Thomas Cudahy, Bahman Rashidi, Carlos Roberto de Souza Filho","doi":"10.5382/econgeo.5041","DOIUrl":"https://doi.org/10.5382/econgeo.5041","url":null,"abstract":"Abstract Porphyry copper deposits are associated with large alteration footprints, and alteration mapping plays a key role in the exploration of these deposits. Imaging spectroscopy is commonly deployed for exploration targeting, yet it has rarely been used to map deposit-scale alteration patterns before initiating drilling. To close this gap, the Shadan porphyry Cu-Au deposit was thoroughly studied using the HyMap hyperspectral data (visible near-infrared–short-wave infrared) at 5-m resolution corroborated by rock geochemistry, magnetometry, and laboratory spectroscopy. Shadan is a well-exposed deposit with near-perfect zonation located in the volcanic belts of eastern Iran containing >135 Mt of ore at 0.3% Cu and 0.4 g/t Au. Thirteen minerals, including white mica, Al smectite, kaolinite, ferric/ferrous minerals, biotite, actinolite, epidote, chlorite, tourmaline, and jarosite, were mapped by applying the multifeature extraction methodology. The propylitic zone was partitioned into actinolite, epidote, and chlorite subfacies. The compositions of biotite and white mica were observed to become Fe and Al rich, respectively, toward the mineralized zones. The chemistry of actinolite was observed to change from Fe to Mg rich inward, providing a new vectoring tool for porphyry copper exploration. The study provided significant information about fluid-rock interactions and the chemistry of the circulating fluids including the oxidation-reduction states and acidity. By integrating the mineral maps with other data sets using the fuzzy logic method, the promising (ore) zones were identified and used to plan the next-stage drilling. This work demonstrated that imaging spectroscopy can be effectively used to better understand porphyry systems and provide deposit-scale vectors toward the mineralized centers, facilitating drilling.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135487702","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}
Reed S. Lewis, David E. Stewart, Vincent H. Isakson, Niki E. Wintzer, Eric D. Stewart, Jeffrey D. Vervoort
Abstract Geologic mapping and associated U-Pb geochronologic work in the Stibnite-Edwardsburg area of central Idaho have provided regional geologic context for the gold-antimony-tungsten-mercury mineralization in this area. Roughly 6,000 m of strata that postdate the Mesoproterozoic Belt-Purcell Supergroup are preserved; overall, the strata young to the southwest and are found as roof pendants or septa within the Idaho batholith. Rocks suspected to be lower Paleozoic in age by early workers in the area contain detrital zircons as young as 500 Ma, confirming that age assignment. We recognized four mappable phases of Cretaceous intrusive rocks, ranging in age from about 95 to 85 Ma, but suspect additional dating and detailed mapping would better show the complexity of the intrusive history. Regional metamorphism ranges from greenschist to amphibolite facies and contact metamorphism is conspicuous near Cretaceous plutonic rocks. Lu-Hf garnet geochronology shows that regional metamorphism of the strata northwest of Stibnite occurred at about 113 Ma and thus prior to batholith intrusion. Contact metamorphism likely occurred some 15 to 30 m.y. later, depending on the specific pluton age. Four large-volume Eocene ash-flow deposits (and their hypothesized eruptive centers) were recognized. Important structures in the Stibnite area include a SW-directed thrust fault, now overturned, that repeats part of the section, and N- to NE-striking faults that have localized mineralization.
{"title":"Regional Geologic Framework of Mineral Deposits in the Stibnite-Edwardsburg Area, Central Idaho","authors":"Reed S. Lewis, David E. Stewart, Vincent H. Isakson, Niki E. Wintzer, Eric D. Stewart, Jeffrey D. Vervoort","doi":"10.5382/econgeo.5025","DOIUrl":"https://doi.org/10.5382/econgeo.5025","url":null,"abstract":"Abstract Geologic mapping and associated U-Pb geochronologic work in the Stibnite-Edwardsburg area of central Idaho have provided regional geologic context for the gold-antimony-tungsten-mercury mineralization in this area. Roughly 6,000 m of strata that postdate the Mesoproterozoic Belt-Purcell Supergroup are preserved; overall, the strata young to the southwest and are found as roof pendants or septa within the Idaho batholith. Rocks suspected to be lower Paleozoic in age by early workers in the area contain detrital zircons as young as 500 Ma, confirming that age assignment. We recognized four mappable phases of Cretaceous intrusive rocks, ranging in age from about 95 to 85 Ma, but suspect additional dating and detailed mapping would better show the complexity of the intrusive history. Regional metamorphism ranges from greenschist to amphibolite facies and contact metamorphism is conspicuous near Cretaceous plutonic rocks. Lu-Hf garnet geochronology shows that regional metamorphism of the strata northwest of Stibnite occurred at about 113 Ma and thus prior to batholith intrusion. Contact metamorphism likely occurred some 15 to 30 m.y. later, depending on the specific pluton age. Four large-volume Eocene ash-flow deposits (and their hypothesized eruptive centers) were recognized. Important structures in the Stibnite area include a SW-directed thrust fault, now overturned, that repeats part of the section, and N- to NE-striking faults that have localized mineralization.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134971821","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}
David Drejing-Carroll, Murray W. Hitzman, David Coller
Abstract The Nautanen North deposit in the Gällivare-Malmberget area of Norrbotten, Sweden, currently contains a resource of 21 Mt at 1.46% Cu, 0.78 g/t Au, 6 g/t Ag, and 99 g/t Mo and remains open at depth and along strike. This study, based on extensive examination of drill core, geochemical data, and petrographic analyses, represents the first comprehensive description of the structural controls, hydrothermal alteration facies and paragenetic sequence of mineral precipitation, and styles and relative timing of iron oxide and sulfide mineralization at the deposit. The deposit is localized between bounding shear zones within the Nautanen deformation zone. High grades of Cu occur within discrete zones of brecciation and veining and as mineralized shear bands. Breccias in the northern portion of the deposit developed within a vertically stacked, relay-like zone in response to late deformation. Hydrothermal alteration of the host rocks was initially dominated by Na facies alteration, which was subsequently overprinted by Na-Ca-Fe, HT (high-temperature) Ca-Fe, HT Ca-K-Fe, HT K-Fe, and LT (low-temperature) K-Fe facies alteration. Magnetite mineralization occurred in at least two phases: an early phase during Na and Na-Ca-Fe facies alteration accompanied by apatite that is interpreted to reflect a distal signature of formation of the proximal Malmberget magnetite-apatite deposit and a later phase coincident with HT Ca-Fe to K-Fe alteration, which overlapped with the onset of Cu and Fe sulfide mineralization under HT Ca-K-Fe and K-Fe and LT K-Fe conditions. The Nautanen North deposit is shown to meet key criteria to be classified as an iron oxide-copper-gold deposit.
瑞典Norrbotten Gällivare-Malmberget地区的Nautanen North矿床目前含Cu 1.46%， Au 0.78 g/t, Ag 6 g/t, Mo 99 g/t，资源量为21 Mt，在深度和走向上保持开放状态。本研究基于大量岩心、地球化学资料和岩石学分析，首次全面描述了矿床的构造控制、热液蚀变相和矿物沉淀共生序列，以及氧化铁和硫化物成矿的样式和相对时间。该矿床位于纳塔南变形带内的边界剪切带之间。高品位的铜赋存于角化和脉状的离散带和矿化剪切带中。矿床北部角砾岩发育在一个垂直堆积的继电器状带内，是对晚期变形的响应。储集岩热液蚀变初期以Na相蚀变为主，随后复盖Na-Ca-Fe、HT(高温)Ca-Fe、HT Ca-K-Fe、HT K-Fe、LT(低温)K-Fe相蚀变。磁铁矿成矿至少发生在两个阶段:早期发生在Na和Na-Ca-Fe相蚀变期间，伴有磷灰石，这反映了Malmberget磁铁矿-磷灰石矿床形成的远端特征;晚期发生在高温Ca-Fe到K-Fe蚀变期间，与高温Ca-K-Fe、K-Fe和LT K-Fe条件下的Cu和Fe硫化物成矿发生重叠。研究表明，南塔南北金矿床具有铁-铜-金矿床的特征。
{"title":"Geology of the Nautanen North Cu-Au-Ag-(Mo) Deposit, Norrbotten, Sweden","authors":"David Drejing-Carroll, Murray W. Hitzman, David Coller","doi":"10.5382/econgeo.5019","DOIUrl":"https://doi.org/10.5382/econgeo.5019","url":null,"abstract":"Abstract The Nautanen North deposit in the Gällivare-Malmberget area of Norrbotten, Sweden, currently contains a resource of 21 Mt at 1.46% Cu, 0.78 g/t Au, 6 g/t Ag, and 99 g/t Mo and remains open at depth and along strike. This study, based on extensive examination of drill core, geochemical data, and petrographic analyses, represents the first comprehensive description of the structural controls, hydrothermal alteration facies and paragenetic sequence of mineral precipitation, and styles and relative timing of iron oxide and sulfide mineralization at the deposit. The deposit is localized between bounding shear zones within the Nautanen deformation zone. High grades of Cu occur within discrete zones of brecciation and veining and as mineralized shear bands. Breccias in the northern portion of the deposit developed within a vertically stacked, relay-like zone in response to late deformation. Hydrothermal alteration of the host rocks was initially dominated by Na facies alteration, which was subsequently overprinted by Na-Ca-Fe, HT (high-temperature) Ca-Fe, HT Ca-K-Fe, HT K-Fe, and LT (low-temperature) K-Fe facies alteration. Magnetite mineralization occurred in at least two phases: an early phase during Na and Na-Ca-Fe facies alteration accompanied by apatite that is interpreted to reflect a distal signature of formation of the proximal Malmberget magnetite-apatite deposit and a later phase coincident with HT Ca-Fe to K-Fe alteration, which overlapped with the onset of Cu and Fe sulfide mineralization under HT Ca-K-Fe and K-Fe and LT K-Fe conditions. The Nautanen North deposit is shown to meet key criteria to be classified as an iron oxide-copper-gold deposit.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134971369","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}
Enzo Caraballo, Georges Beaudoin, Sarah Dare, Dominique Genna, Sven Petersen, Jorge M.R.S. Relvas, Stephen J. Piercey
Chalcopyrite from 51 volcanogenic massive sulfide (VMS) and sea-floor massive sulfide (SMS) deposits from six lithostratigraphic settings was analyzed for trace elements by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to evaluate its potential as an indicator mineral for exploration. Partial least squares discriminant analysis (PLS-DA) results reveal that chalcopyrite from different lithostratigraphic settings has different compositions reflecting host rock assemblages and fluid composition. Three random forest (RF) classifiers were developed to distinguish chalcopyrite from the six lithostratigraphic settings with a divisive approach. This method, which primarily classifies according to the major host-rock affinity and subsequently according to VMS settings, yielded an overall accuracy higher than 0.96 on test data. The model validation with literature data having the same elements required by the models yielded the highest accuracies (>0.90). In validation using published data with missing elements, the accuracy is moderate to high (0.60–1); however, the performances decrease significantly (<0.50) when the most important elements are missing. Similarly, RF regression models developed using all sets of analyzed elements to determine ccp/(ccp + sp) ratio (ccp = chalcopyrite; sp = sphalerite) in chalcopyrite within a single VMS setting reported high performances, thus showing a potential to predict the Cu/Zn ratio (Cu-rich vs. Zn-rich) of the mineralization based on chalcopyrite composition. This study demonstrates that trace element concentrations in chalcopyrite are primarily controlled by lithotectonic setting and can be used as predictors in an RF classifier to distinguish the different VMS subtypes.
{"title":"Trace Element Composition of Chalcopyrite from Volcanogenic Massive Sulfide Deposits: Variation and Implications for Provenance Recognition","authors":"Enzo Caraballo, Georges Beaudoin, Sarah Dare, Dominique Genna, Sven Petersen, Jorge M.R.S. Relvas, Stephen J. Piercey","doi":"10.5382/econgeo.5020","DOIUrl":"https://doi.org/10.5382/econgeo.5020","url":null,"abstract":"Chalcopyrite from 51 volcanogenic massive sulfide (VMS) and sea-floor massive sulfide (SMS) deposits from six lithostratigraphic settings was analyzed for trace elements by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to evaluate its potential as an indicator mineral for exploration. Partial least squares discriminant analysis (PLS-DA) results reveal that chalcopyrite from different lithostratigraphic settings has different compositions reflecting host rock assemblages and fluid composition. Three random forest (RF) classifiers were developed to distinguish chalcopyrite from the six lithostratigraphic settings with a divisive approach. This method, which primarily classifies according to the major host-rock affinity and subsequently according to VMS settings, yielded an overall accuracy higher than 0.96 on test data. The model validation with literature data having the same elements required by the models yielded the highest accuracies (>0.90). In validation using published data with missing elements, the accuracy is moderate to high (0.60–1); however, the performances decrease significantly (<0.50) when the most important elements are missing. Similarly, RF regression models developed using all sets of analyzed elements to determine ccp/(ccp + sp) ratio (ccp = chalcopyrite; sp = sphalerite) in chalcopyrite within a single VMS setting reported high performances, thus showing a potential to predict the Cu/Zn ratio (Cu-rich vs. Zn-rich) of the mineralization based on chalcopyrite composition. This study demonstrates that trace element concentrations in chalcopyrite are primarily controlled by lithotectonic setting and can be used as predictors in an RF classifier to distinguish the different VMS subtypes.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134971467","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 : 2023-09-01DOI: 10.5382/econgeo.118.6.ip01
{"title":"Interesting Papers in Other Journals","authors":"","doi":"10.5382/econgeo.118.6.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.6.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135200620","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. Harlaux, D. Kontak, Alan H. Clark, K. Kouzmanov, Christopher S. Holm-Denoma, Stefano Gialli, Oscar Laurent, R. Spikings, A. Chauvet, Andrea Dini, Miroslav Kalinaj, L. Fontboté
The San Rafael Sn (-Cu) deposit, located in the Eastern Cordillera of southeast Peru, is one of the world’s largest cassiterite-bearing vein systems (>1 Mt Sn produced since 1969). The deposit consists of a quartz-cassiterite-chlorite-sulfide lode system spatially associated with an upper Oligocene (ca. 24 Ma) S-type granitic pluton. Based on a revised paragenetic sequence for the deposit, we interpret the temporal setting of both magmatic (biotite, K-feldspar) and hydrothermal (muscovite, adularia, cassiterite) minerals analyzed by 40Ar/39Ar step-heating and U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) geochronology. The least-disturbed biotite sample from the megacrystic monzogranite yielded a 40Ar/39Ar plateau age of 24.10 ± 0.26 Ma (2σ), which constrains the time of cooling of the upper part of the pluton to below 300°C. Greisen developed on top of the granitic cupola and its immediate metamorphic aureole dated at 24.24 ± 0.24 Ma (2σ; 40Ar/39Ar muscovite average plateau age) is interpreted to be contemporaneous with the emplacement of pre-ore quartz-tourmaline veins and breccias. In situ U-Pb dating of cassiterite, including both botryoidal cassiterite (“wood tin”) and coarse-grained cassiterite in quartz-chlorite veins and breccias, constrains the timing of the main Sn ore stage to between 24.10 ± 0.37 and 23.47 ± 0.53 Ma (2σ). Botryoidal and coarse-grained cassiterite are characterized by similar trace element compositions with fluctuating metal concentrations across growth banding, suggesting significant changes of physicochemical conditions of the hydrothermal system during cassiterite precipitation, likely caused by rapid and repeated mixing between magmatic fluids and meteoric groundwaters. Polymetallic sulfide-rich veins and quartz-carbonate veins are constrained to have formed between 22.72 ± 0.11 and 22.29 ± 0.24 Ma (2σ), based on adularia 40Ar/39Ar plateau ages. The latter overlap partially reset 40Ar/39Ar age spectra for K-feldspar megacrysts in the host granite and thus reflect pervasive alteration by hydrothermal fluids. Collectively, the results show the magmatic-hydrothermal system spanned at least 2 m.y. with the main Sn ore stage representing <1 m.y. in the lifetime of the deposit. The latest polymetallic stages postdate the main Sn ore stage by ca. 1 m.y. and reflect the waning of the hydrothermal system, accompanied by additional incursion of meteoric groundwaters. This study provides further evidence that the present-day exposed level of the San Rafael granite was a passive host for the Sn mineralization and only provided the structural focusing for the mineralizing fluids derived from a deeper part of the magmatic system.
圣拉斐尔锡(铜)矿床位于秘鲁东南部的东科迪勒拉，是世界上最大的锡石矿脉系统之一(自1969年以来生产了超过100万吨的锡)。矿床由石英-锡石-绿泥石-硫化物矿脉系统组成，空间上与渐新统上(约24 Ma) s型花岗岩体有关。利用40Ar/39Ar分步加热和U-Pb激光烧蚀-电感耦合等离子体质谱(LA-ICP-MS)年代学方法，对该矿床岩浆矿物(黑云母、钾长石)和热液矿物(白云母、钾长石、锡石)的时间背景进行了解释。微晶二长花岗岩中扰动最小的黑云母样品的40Ar/39Ar平台年龄为24.10±0.26 Ma (2σ)，这限制了岩体上部冷却的时间在300℃以下。Greisen发育于花岗质冲天炉顶部，其直接变质光晕年龄为24.24±0.24 Ma (2σ;40Ar/39Ar白云母平均高原年龄)被解释为与成矿前石英-电气石脉和角砾岩侵位同时期。锡石的原位U-Pb定年(包括石英绿泥石脉和角砾岩中的粗粒锡石(“木锡”)和壶状锡石)将锡石主阶段的时间限制在24.10±0.37 ~ 23.47±0.53 Ma (2σ)之间。矿脉状锡石和粗粒锡石的微量元素组成相似，金属浓度在生长带上波动，表明锡石降水过程中热液系统的物理化学条件发生了显著变化，可能是岩浆流体与大气地下水快速反复混合所致。根据40Ar/39Ar的高原年龄，富硫化物多金属脉和石英-碳酸盐脉形成于22.72±0.11 ~ 22.29±0.24 Ma (2σ)之间。后者的重叠部分重置了成矿岩体中钾长石巨晶的40Ar/39Ar年龄谱，从而反映了热液流体的普遍蚀变。结果表明，岩浆-热液系统的跨度至少为2 m.，其中主锡矿期在矿床生命周期中占比小于1 m.。最新的多金属阶段比主要的锡矿阶段晚约1亿年，反映了热液系统的减弱，伴随着大气地下水的额外入侵。该研究进一步证明了圣拉斐尔花岗岩现今暴露水平是锡成矿的被动宿主，仅为岩浆系统深部的成矿流体提供了构造聚焦。
{"title":"Depositing >1.5 Mt of Tin Within <1 m.y. of Initial Granitic Intrusion in the San Rafael Tin (-Copper) Deposit, Southeastern Peru","authors":"M. Harlaux, D. Kontak, Alan H. Clark, K. Kouzmanov, Christopher S. Holm-Denoma, Stefano Gialli, Oscar Laurent, R. Spikings, A. Chauvet, Andrea Dini, Miroslav Kalinaj, L. Fontboté","doi":"10.5382/econgeo.5021","DOIUrl":"https://doi.org/10.5382/econgeo.5021","url":null,"abstract":"\u0000 The San Rafael Sn (-Cu) deposit, located in the Eastern Cordillera of southeast Peru, is one of the world’s largest cassiterite-bearing vein systems (>1 Mt Sn produced since 1969). The deposit consists of a quartz-cassiterite-chlorite-sulfide lode system spatially associated with an upper Oligocene (ca. 24 Ma) S-type granitic pluton. Based on a revised paragenetic sequence for the deposit, we interpret the temporal setting of both magmatic (biotite, K-feldspar) and hydrothermal (muscovite, adularia, cassiterite) minerals analyzed by 40Ar/39Ar step-heating and U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) geochronology. The least-disturbed biotite sample from the megacrystic monzogranite yielded a 40Ar/39Ar plateau age of 24.10 ± 0.26 Ma (2σ), which constrains the time of cooling of the upper part of the pluton to below 300°C. Greisen developed on top of the granitic cupola and its immediate metamorphic aureole dated at 24.24 ± 0.24 Ma (2σ; 40Ar/39Ar muscovite average plateau age) is interpreted to be contemporaneous with the emplacement of pre-ore quartz-tourmaline veins and breccias. In situ U-Pb dating of cassiterite, including both botryoidal cassiterite (“wood tin”) and coarse-grained cassiterite in quartz-chlorite veins and breccias, constrains the timing of the main Sn ore stage to between 24.10 ± 0.37 and 23.47 ± 0.53 Ma (2σ). Botryoidal and coarse-grained cassiterite are characterized by similar trace element compositions with fluctuating metal concentrations across growth banding, suggesting significant changes of physicochemical conditions of the hydrothermal system during cassiterite precipitation, likely caused by rapid and repeated mixing between magmatic fluids and meteoric groundwaters. Polymetallic sulfide-rich veins and quartz-carbonate veins are constrained to have formed between 22.72 ± 0.11 and 22.29 ± 0.24 Ma (2σ), based on adularia 40Ar/39Ar plateau ages. The latter overlap partially reset 40Ar/39Ar age spectra for K-feldspar megacrysts in the host granite and thus reflect pervasive alteration by hydrothermal fluids. Collectively, the results show the magmatic-hydrothermal system spanned at least 2 m.y. with the main Sn ore stage representing <1 m.y. in the lifetime of the deposit. The latest polymetallic stages postdate the main Sn ore stage by ca. 1 m.y. and reflect the waning of the hydrothermal system, accompanied by additional incursion of meteoric groundwaters. This study provides further evidence that the present-day exposed level of the San Rafael granite was a passive host for the Sn mineralization and only provided the structural focusing for the mineralizing fluids derived from a deeper part of the magmatic system.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"12 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86557421","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 : 2023-09-01DOI: 10.5382/econgeo.118.7.ip01
{"title":"Interesting Papers in Other Journals","authors":"","doi":"10.5382/econgeo.118.7.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.7.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135782176","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}
Shengchao Xue, Qingfei Wang, Ya-lei Wang, Wenlei Song, Jun Deng
Addition of crustal sulfur to the Jinchuan magma or oxidation of the magma associated with carbonate assimilation has been considered to be the main cause of sulfide saturation in the magma by two opposing groups of researchers. To address this controversy, we have carried out an integrated mineralogical and C-S-Sr-Nd isotope study of the Jinchuan magmatic Ni-Cu-platinum group element (PGE) sulfide ore deposit. Pure marble, olivine marble, serpentine marble, and hybrid rocks occur in the contact zone. The δ13Ccarb values of the Jinchuan sulfide-bearing ultramafic rocks containing calcite xenocryst are from –4.7 to –2.9‰, which are similar to or slightly lower than those of the marbles and associated hybrid rocks (–3.9 to 0.8‰) but significantly higher than those of the calcite-barren intrusive rocks (–9.3 to –8.0‰). This, together with the calcite xenocryst and calcium-silicate minerals in hybrid rocks and some intrusive rocks, indicates that carbonate assimilation took place during magma-carbonate interaction. Only less than several hundred ppm of the CO2 gas produced in the reaction zone could be added to the Jinchuan magma. Such a trace amount of additional CO2 was rapidly swamped by the much greater mass of FeO in the magma, resulting in little change in the FeO/Fe2O3 of the magma, and thereby negligible change of magma redox state. This is evident from similar calculated fO2 values for the calcite-bearing (~QFM+0.7) and calcite-barren (~QFM+0.6) intrusive rocks. The new results rule out the possibility that sulfide saturation in the Jinchuan magma resulted from in situ carbonate assimilation. The Sr-Nd isotope data from this study and previous studies are consistent with up to 20% bulk contamination with siliceous crustal materials at depth, followed by minor amounts of in situ carbonate assimilation by the Jinchuan magma. Our new sulfur isotope data expand the range of δ34S for the Jinchuan deposit significantly. The new range is from −7.6 to 3.0‰, with an average of −1.8‰, which is generally lower than the mantle value (0 ± 2‰). The new result supports the premise that crustal sulfur was involved in the genesis of the Jinchuan deposit. Very high, crustal-like S/Se ratios (as high as 8080) for some of the samples from the deposit provide additional support for the interpretation. The country rocks in the vicinity of the Jinchuan deposit analyzed to date have δ34S values varying from −4.0 to 11.3‰, with an average of 2.9‰, which is higher than both the mantle value and the average value of the Jinchuan deposit, suggesting that the Jinchuan magma acquired some crustal sulfur at depth, likely concurrent with the siliceous assimilation. Numerical modeling of δ34S-S/Se of sulfide ores and country rocks further illustrates that the observed variations of δ34S and S/Se ratios are related to the assimilation of S-rich rocks located at depth, followed by progressive dilution of the contaminated δ34S-S/Se signature. Based on the new results, we con
{"title":"The Roles of Various Types of Crustal Contamination in the Genesis of the Jinchuan Magmatic Ni-Cu-PGE Deposit: New Mineralogical and C-S-Sr-Nd Isotope Constraints","authors":"Shengchao Xue, Qingfei Wang, Ya-lei Wang, Wenlei Song, Jun Deng","doi":"10.5382/econgeo.5017","DOIUrl":"https://doi.org/10.5382/econgeo.5017","url":null,"abstract":"\u0000 Addition of crustal sulfur to the Jinchuan magma or oxidation of the magma associated with carbonate assimilation has been considered to be the main cause of sulfide saturation in the magma by two opposing groups of researchers. To address this controversy, we have carried out an integrated mineralogical and C-S-Sr-Nd isotope study of the Jinchuan magmatic Ni-Cu-platinum group element (PGE) sulfide ore deposit. Pure marble, olivine marble, serpentine marble, and hybrid rocks occur in the contact zone. The δ13Ccarb values of the Jinchuan sulfide-bearing ultramafic rocks containing calcite xenocryst are from –4.7 to –2.9‰, which are similar to or slightly lower than those of the marbles and associated hybrid rocks (–3.9 to 0.8‰) but significantly higher than those of the calcite-barren intrusive rocks (–9.3 to –8.0‰). This, together with the calcite xenocryst and calcium-silicate minerals in hybrid rocks and some intrusive rocks, indicates that carbonate assimilation took place during magma-carbonate interaction. Only less than several hundred ppm of the CO2 gas produced in the reaction zone could be added to the Jinchuan magma. Such a trace amount of additional CO2 was rapidly swamped by the much greater mass of FeO in the magma, resulting in little change in the FeO/Fe2O3 of the magma, and thereby negligible change of magma redox state. This is evident from similar calculated fO2 values for the calcite-bearing (~QFM+0.7) and calcite-barren (~QFM+0.6) intrusive rocks. The new results rule out the possibility that sulfide saturation in the Jinchuan magma resulted from in situ carbonate assimilation. The Sr-Nd isotope data from this study and previous studies are consistent with up to 20% bulk contamination with siliceous crustal materials at depth, followed by minor amounts of in situ carbonate assimilation by the Jinchuan magma. Our new sulfur isotope data expand the range of δ34S for the Jinchuan deposit significantly. The new range is from −7.6 to 3.0‰, with an average of −1.8‰, which is generally lower than the mantle value (0 ± 2‰). The new result supports the premise that crustal sulfur was involved in the genesis of the Jinchuan deposit. Very high, crustal-like S/Se ratios (as high as 8080) for some of the samples from the deposit provide additional support for the interpretation. The country rocks in the vicinity of the Jinchuan deposit analyzed to date have δ34S values varying from −4.0 to 11.3‰, with an average of 2.9‰, which is higher than both the mantle value and the average value of the Jinchuan deposit, suggesting that the Jinchuan magma acquired some crustal sulfur at depth, likely concurrent with the siliceous assimilation. Numerical modeling of δ34S-S/Se of sulfide ores and country rocks further illustrates that the observed variations of δ34S and S/Se ratios are related to the assimilation of S-rich rocks located at depth, followed by progressive dilution of the contaminated δ34S-S/Se signature. Based on the new results, we con","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"47 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83966383","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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