T. Davies, J. Richards, R. Creaser, L. Heaman, T. Chacko, A. Simonetti, J. Williamson, D. W. McDonald
The Three Bluffs gold deposit is located in the Committee Bay greenstone belt, which forms part of the Rae domain of the western Churchill province, Nunavut, Canada. Gold mineralization is hosted by iron formation of the Neoarchean volcanosedimentary Prince Albert Group, and is associated with silicification (quartz veining) and sulfidation of magnetite and other Fe-rich minerals. Conventional U-Pb zircon dating of a conformable dacite unit within the volcanosedimentary host-rock sequence and a crosscutting diorite intrusion confirm a ~2.7 Ga age for deposition of the supracrustal package. U-Pb monazite dates and Pb isotopic analyses of sulfides were obtained by laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS). A subset of U-Pb monazite (1813.8 ± 8.7 Ma) and Re-Os arsenopyrite (1822 ± 21 Ma) dates, combined with a Pb-Pb secondary errorchron age for pyrite and arsenopyrite (1829 ± 77 Ma), suggest that gold mineralization associated with sulfidation of the iron formation occurred at ~1815 Ma, prior to high-grade (upper amphibolite facies) tectonometamorphism in the Three Bluffs area (D 2TB /(M 2TB ). An ~1815 Ma age for deposit formation is broadly consistent with evidence from elsewhere in the western Churchill province and to the southwest in Manitoba and Saskatchewan for a late Trans-Hudson (1.9–1.8 Ga) gold mineralizing event. The majority of U-Pb monazite ages form a second population at 1780.6 ± 4.2 Ma, similar to the age of the majority of Re-Os arsenopyrite analyses (1763 ± 11 Ma). These dates are thought to reflect the timing of peak M 2TB metamorphism. 40 Ar/ 39 Ar dating of amphibole, biotite, and muscovite yielded plateau ages ranging from 1723.8 ± 9.0 Ma to 1710 ± 17 Ma, which are interpreted to record the timing of postpeak metamorphic cooling to below the respective closure temperatures for Ar diffusion in these minerals.
{"title":"Paleoproterozoic Age Relationships in the Three Bluffs Archean Iron Formation-Hosted Gold Deposit, Committee Bay Greenstone Belt, Nunavut, Canada","authors":"T. Davies, J. Richards, R. Creaser, L. Heaman, T. Chacko, A. Simonetti, J. Williamson, D. W. McDonald","doi":"10.2113/GSEMG.19.3-4.55","DOIUrl":"https://doi.org/10.2113/GSEMG.19.3-4.55","url":null,"abstract":"The Three Bluffs gold deposit is located in the Committee Bay greenstone belt, which forms part of the Rae domain of the western Churchill province, Nunavut, Canada. Gold mineralization is hosted by iron formation of the Neoarchean volcanosedimentary Prince Albert Group, and is associated with silicification (quartz veining) and sulfidation of magnetite and other Fe-rich minerals. Conventional U-Pb zircon dating of a conformable dacite unit within the volcanosedimentary host-rock sequence and a crosscutting diorite intrusion confirm a ~2.7 Ga age for deposition of the supracrustal package. U-Pb monazite dates and Pb isotopic analyses of sulfides were obtained by laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS). A subset of U-Pb monazite (1813.8 ± 8.7 Ma) and Re-Os arsenopyrite (1822 ± 21 Ma) dates, combined with a Pb-Pb secondary errorchron age for pyrite and arsenopyrite (1829 ± 77 Ma), suggest that gold mineralization associated with sulfidation of the iron formation occurred at ~1815 Ma, prior to high-grade (upper amphibolite facies) tectonometamorphism in the Three Bluffs area (D 2TB /(M 2TB ). An ~1815 Ma age for deposit formation is broadly consistent with evidence from elsewhere in the western Churchill province and to the southwest in Manitoba and Saskatchewan for a late Trans-Hudson (1.9–1.8 Ga) gold mineralizing event. The majority of U-Pb monazite ages form a second population at 1780.6 ± 4.2 Ma, similar to the age of the majority of Re-Os arsenopyrite analyses (1763 ± 11 Ma). These dates are thought to reflect the timing of peak M 2TB metamorphism. 40 Ar/ 39 Ar dating of amphibole, biotite, and muscovite yielded plateau ages ranging from 1723.8 ± 9.0 Ma to 1710 ± 17 Ma, which are interpreted to record the timing of postpeak metamorphic cooling to below the respective closure temperatures for Ar diffusion in these minerals.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122818030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-07-01DOI: 10.2113/GSEMG.19.3-4.117
J. Asfahani
The Schlumberger configuration used in geoelectrical sounding is slightly adapted here to obtain reliable data for both shallow and deep penetration depths from the same survey. In this configuration, two kinds of current electrode half-spacings are used: the first enables construction of vertical electrical resistivity sounding (VES) curves for shallow depths (<50 m), and the second for depths ≤250 m. For a given VES location, two field curves are measured and interpreted using two standard approaches. Practical characteristics of such a modified configuration are illustrated with two field applications in Syria. The first aims to characterize the structure of Quaternary and recent deposits in the Al-Ghab depression region, and the second deals with exploration for phosphatic sedimentary units in the Al-Sharquieh mine.
{"title":"Geophysical Case Study of Shallow and Deep Structures Based on Traditional and Modified Interpretation Methods: Application to Tectonic Studies and Mineral Exploration","authors":"J. Asfahani","doi":"10.2113/GSEMG.19.3-4.117","DOIUrl":"https://doi.org/10.2113/GSEMG.19.3-4.117","url":null,"abstract":"The Schlumberger configuration used in geoelectrical sounding is slightly adapted here to obtain reliable data for both shallow and deep penetration depths from the same survey. In this configuration, two kinds of current electrode half-spacings are used: the first enables construction of vertical electrical resistivity sounding (VES) curves for shallow depths (<50 m), and the second for depths ≤250 m. For a given VES location, two field curves are measured and interpreted using two standard approaches. Practical characteristics of such a modified configuration are illustrated with two field applications in Syria. The first aims to characterize the structure of Quaternary and recent deposits in the Al-Ghab depression region, and the second deals with exploration for phosphatic sedimentary units in the Al-Sharquieh mine.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"286 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131544122","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Potter, R. Taylor, P. Jones, K. Rees, I. Campbell
The Cobalt embayment is a large domain of Paleoproterozoic clastic sedimentary rocks that unconformably overlies the Archean Abitibi greenstone belt. Regionally extensive sills and dikes of Nipissing diabase, emplaced circa 2219 Ma, occur throughout the embayment and are the preferential host to gold-bearing polymetallic vein systems on the Merico-Ethel property, near the northeastern margin of the Cobalt embayment. These gold-bearing, polymetallic veins are predominantly east–west-trending, steeply dipping, discordant calcite-quartz vein systems that formed close to the time of crystallization (within ~15 m.y., based on Pb-Pb ages) of the Nipissing diabase. The ore mineralogy is complex in character, typically comprising sulfides, arsenides, native metals (gold and silver), and specular hematite, preferentially concentrated along the interface between silicate and calcite gangue. A simplified sequence of mineral deposition in the veins is: (1) “Early-stage” pyrite ± chalcopyrite hosted in quartz ± chlorite gangue; (2) “Main-stage” polymetallic (Cu + Co + As + Ag + Au + Bi ± Pb ± Ni ± U) sulfides, arsenides, and native metals hosted in calcite gangue; and (3) “Late-stage” calcite flooding ± galena. Wall-rock alteration in Nipissing diabase is restricted to narrow (<5 cm) haloes of calcite-chlorite-epidote-bearing assemblages, whereas a weak alteration halo of specular hematite, calcite, and allanite-epidote has been observed in the surrounding sedimentary rocks. In terms of their age, geology, mineralogy, paragenesis, and morphology, the gold-bearing vein systems at Merico-Ethel closely resemble the silver-sulfarsenide vein deposits of the historic Cobalt and Gowganda mining camps. These observations indicate that the Au-bearing veins are variants of the Ag-vein systems and as such, have a common genesis belt.
钴湾是一大片古元古代碎屑沉积岩域，不整合覆于太古宙阿比提比绿岩带之上。区域性广泛的尼皮辛辉绿岩岩脉脉分布在2219 Ma左右，是靠近Cobalt脉体东北缘的Merico-Ethel产矿中含金多金属脉系的首选寄主。这些含金多金属脉体主要为东西向、急倾、不和谐方解石-石英脉系，形成于尼皮辛辉绿岩结晶时期(根据Pb-Pb年龄，在~ 15m内)。矿石矿物学特征复杂，通常包括硫化物、砷化物、天然金属(金和银)和镜面赤铁矿，优先集中在硅酸盐和方解石脉石之间的界面上。脉体中矿物沉积的简化顺序为:(1)“早期”黄铁矿±石英中的黄铜矿±绿泥石脉石;(2)“主阶段”多金属(Cu + Co + As + Ag + Au + Bi±Pb±Ni±U)硫化物、砷化物和原生金属赋存于方解石脉石中;(3)“晚期”方解石泛洪±方铅矿。尼皮辛辉绿岩的围岩蚀变仅限于方解石-绿泥石-绿帘石组合的狭窄(<5厘米)蚀变晕，而在周围的沉积岩中观察到反射赤铁矿、方解石和allanite-绿帘石的弱蚀变晕。在年代、地质、矿物学、共生和形态方面，Merico-Ethel的含金矿脉系统与历史悠久的Cobalt和Gowganda采矿营地的银硫化物矿脉矿床非常相似。这些观测结果表明，含金脉系是银脉系的变种，具有共同的成因带。
{"title":"The Geological Setting, Mineralogy, and Paragenesis of Gold-Bearing Polymetallic (Cu+Co+Ag+Au+Bi±Pb±Ni±U) Veins of the Merico-Ethel Property, Elk Lake, Northeastern Ontario, Canada","authors":"E. Potter, R. Taylor, P. Jones, K. Rees, I. Campbell","doi":"10.2113/GSEMG.19.3-4.81","DOIUrl":"https://doi.org/10.2113/GSEMG.19.3-4.81","url":null,"abstract":"The Cobalt embayment is a large domain of Paleoproterozoic clastic sedimentary rocks that unconformably overlies the Archean Abitibi greenstone belt. Regionally extensive sills and dikes of Nipissing diabase, emplaced circa 2219 Ma, occur throughout the embayment and are the preferential host to gold-bearing polymetallic vein systems on the Merico-Ethel property, near the northeastern margin of the Cobalt embayment. These gold-bearing, polymetallic veins are predominantly east–west-trending, steeply dipping, discordant calcite-quartz vein systems that formed close to the time of crystallization (within ~15 m.y., based on Pb-Pb ages) of the Nipissing diabase. The ore mineralogy is complex in character, typically comprising sulfides, arsenides, native metals (gold and silver), and specular hematite, preferentially concentrated along the interface between silicate and calcite gangue. A simplified sequence of mineral deposition in the veins is: (1) “Early-stage” pyrite ± chalcopyrite hosted in quartz ± chlorite gangue; (2) “Main-stage” polymetallic (Cu + Co + As + Ag + Au + Bi ± Pb ± Ni ± U) sulfides, arsenides, and native metals hosted in calcite gangue; and (3) “Late-stage” calcite flooding ± galena. Wall-rock alteration in Nipissing diabase is restricted to narrow (<5 cm) haloes of calcite-chlorite-epidote-bearing assemblages, whereas a weak alteration halo of specular hematite, calcite, and allanite-epidote has been observed in the surrounding sedimentary rocks. In terms of their age, geology, mineralogy, paragenesis, and morphology, the gold-bearing vein systems at Merico-Ethel closely resemble the silver-sulfarsenide vein deposits of the historic Cobalt and Gowganda mining camps. These observations indicate that the Au-bearing veins are variants of the Ag-vein systems and as such, have a common genesis belt.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123898642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-07-01DOI: 10.2113/GSEMG.19.3-4.135
G. Chi, J. Lai, A. Solomon
The Buffalo gold deposit is a small deposit consisting of auriferous quartz-tourmaline veins within a granodiorite stock in the Red Lake greenstone belt. This study aims to characterize the mineralizing fluids through fluid inclusion and stable isotope analyses and to compare them with those of the world-class Campbell-Red Lake deposit. Four types of fluid inclusions were recognized, including carbonic, aqueous-carbonic, aqueous, and halite-bearing aqueous, with the carbonic type being the most abundant. Raman analyses indicate that the carbonic phase mainly consists of CO 2 , with minor amounts of N 2 and CH 4 , and rarely detectable H 2 S. The homogenization temperatures of the carbonic inclusions range from −41.7° to 30.9°C. The homogenization temperatures and salinities of the aqueous, halite-bearing aqueous, and aqueous-carbonic inclusions are 130° to 276°C and 9.7 to 23.6 wt.% NaCl equiv., 155° to 207°C and 32.9 to 42.3 wt.% NaCl equiv., and 215° to 357°C and 8.3 to 19.7 wt.% NaCl equiv., respectively. The δ 18 O VSMOW values of tourmaline range from 8.2‰ to 9.0‰, and those of quartz from 11.4‰ to 11.9‰, with estimated fluid temperatures from 323° to 399°C based on the quartz-tourmaline isotopic geothermometer. It is postulated that separate CO 2 -dominated and aqueous fluids intermittently invaded the fracture/vein system in response to fluid pressure fluctuations, with limited mixing. The CO 2 -dominated fluid, previously recognized in Campbell-Red Lake as the main mineralizing fluid, is inferred to have been derived from deeper parts of the crust. This deep CO 2 -dominated fluid reservoir might have been a common source for gold mineralization in the Red Lake greenstone belt.
{"title":"Fluid Inclusion and Stable Isotope Study of the Buffalo Gold Deposit, Red Lake Greenstone Belt, Northwestern Ontario, Canada","authors":"G. Chi, J. Lai, A. Solomon","doi":"10.2113/GSEMG.19.3-4.135","DOIUrl":"https://doi.org/10.2113/GSEMG.19.3-4.135","url":null,"abstract":"The Buffalo gold deposit is a small deposit consisting of auriferous quartz-tourmaline veins within a granodiorite stock in the Red Lake greenstone belt. This study aims to characterize the mineralizing fluids through fluid inclusion and stable isotope analyses and to compare them with those of the world-class Campbell-Red Lake deposit. Four types of fluid inclusions were recognized, including carbonic, aqueous-carbonic, aqueous, and halite-bearing aqueous, with the carbonic type being the most abundant. Raman analyses indicate that the carbonic phase mainly consists of CO 2 , with minor amounts of N 2 and CH 4 , and rarely detectable H 2 S. The homogenization temperatures of the carbonic inclusions range from −41.7° to 30.9°C. The homogenization temperatures and salinities of the aqueous, halite-bearing aqueous, and aqueous-carbonic inclusions are 130° to 276°C and 9.7 to 23.6 wt.% NaCl equiv., 155° to 207°C and 32.9 to 42.3 wt.% NaCl equiv., and 215° to 357°C and 8.3 to 19.7 wt.% NaCl equiv., respectively. The δ 18 O VSMOW values of tourmaline range from 8.2‰ to 9.0‰, and those of quartz from 11.4‰ to 11.9‰, with estimated fluid temperatures from 323° to 399°C based on the quartz-tourmaline isotopic geothermometer. It is postulated that separate CO 2 -dominated and aqueous fluids intermittently invaded the fracture/vein system in response to fluid pressure fluctuations, with limited mixing. The CO 2 -dominated fluid, previously recognized in Campbell-Red Lake as the main mineralizing fluid, is inferred to have been derived from deeper parts of the crust. This deep CO 2 -dominated fluid reservoir might have been a common source for gold mineralization in the Red Lake greenstone belt.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133454971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
O. Rabeau, M. Legault, A. Cheilletz, M. Jébrak, J. Royer, Lizhen Cheng
By compiling geological, structural, geophysical, and geochemical information into a 3D geological model, we evaluated the orogenic gold potential in the vicinity of a hidden segment of an important Archean fault zone, the Cadillac–Larder Lake fault (CLLF) in the region of Rouyn-Noranda. The segment of CLLF in the present study is partly covered by Proterozoic sedimentary rocks. Because more than 2000 t Au have been extracted along the CLLF to date, our objective is to evaluate the gold potential at depth along a poorly known segment of this fault. A 3D geological model (50 km × 9 km × 1.5 km) including the covered segment was built through the compilation and homogenization of available geological data and the construction of 23 cross sections. The geology under the Proterozoic cover was evaluated using geophysical inversions, drill holes (42 in total), and surrounding geology. All available assays were filtered and upscaled to a 250 m × 250 m × 250 m regular cell grid to determine and quantify spatial relationships between geological features and mineralized occurrences using the weights of evidence method. Structural features, such as E–W-trending faults and fault intersections, and certain lithologies with a high primary porosity such as volcanoclastic rocks of the Blake River Group and Timiskaming sedimentary rocks, proved to be very prospective, yielding favourable factors with a weight of evidence index W + > 0.24. These salient features were then assigned a combination index for ultimately evaluating the orogenic gold potential under the sedimentary cover. The zones resulting in an optimization of exploration targeting were attributed the highest probability, representing ~1% of the initial volume.
通过将地质、构造、地球物理和地球化学信息整合到三维地质模型中，对鲁恩-诺兰达地区重要太古代断裂带Cadillac-Larder湖断裂(CLLF)隐伏段附近的造山带金潜力进行了评价。本研究的CLLF段部分被元古代沉积岩覆盖。由于迄今为止沿CLLF已提取了超过2000吨的Au，我们的目标是评估沿该断层鲜为人知的部分的深度黄金潜力。通过对现有地质资料的整理、均匀化和23个断面的构建，建立了包含覆盖段的50 km × 9 km × 1.5 km的三维地质模型。利用地球物理反演、钻孔(共42个)和周围地质对元古代盖层下的地质进行了评价。所有可用的分析都经过过滤并升级为250 m × 250 m × 250 m的规则细胞网格，使用证据权重法确定和量化地质特征与矿化产状之间的空间关系。东西向断裂和断裂交汇等构造特征，以及布雷克河群火山碎屑岩、蒂米斯卡明沉积岩等原生孔隙度较高的岩性具有较好的勘探前景，证据权指数W + > 0.24。这些显著特征被赋以综合指数，最终评价了沉积盖层下的造山带金潜力。导致勘探目标优化的区域概率最高，约占初始体积的1%。
{"title":"Gold Potential of a Hidden Archean Fault Zone: The Case of the Cadillac–Larder Lake Fault","authors":"O. Rabeau, M. Legault, A. Cheilletz, M. Jébrak, J. Royer, Lizhen Cheng","doi":"10.2113/GSEMG.19.3-4.99","DOIUrl":"https://doi.org/10.2113/GSEMG.19.3-4.99","url":null,"abstract":"By compiling geological, structural, geophysical, and geochemical information into a 3D geological model, we evaluated the orogenic gold potential in the vicinity of a hidden segment of an important Archean fault zone, the Cadillac–Larder Lake fault (CLLF) in the region of Rouyn-Noranda. The segment of CLLF in the present study is partly covered by Proterozoic sedimentary rocks. Because more than 2000 t Au have been extracted along the CLLF to date, our objective is to evaluate the gold potential at depth along a poorly known segment of this fault. A 3D geological model (50 km × 9 km × 1.5 km) including the covered segment was built through the compilation and homogenization of available geological data and the construction of 23 cross sections. The geology under the Proterozoic cover was evaluated using geophysical inversions, drill holes (42 in total), and surrounding geology. All available assays were filtered and upscaled to a 250 m × 250 m × 250 m regular cell grid to determine and quantify spatial relationships between geological features and mineralized occurrences using the weights of evidence method. Structural features, such as E–W-trending faults and fault intersections, and certain lithologies with a high primary porosity such as volcanoclastic rocks of the Blake River Group and Timiskaming sedimentary rocks, proved to be very prospective, yielding favourable factors with a weight of evidence index W + > 0.24. These salient features were then assigned a combination index for ultimately evaluating the orogenic gold potential under the sedimentary cover. The zones resulting in an optimization of exploration targeting were attributed the highest probability, representing ~1% of the initial volume.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114808517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-07-01DOI: 10.2113/GSEMG.17.3-4.163
J. Scott, J. Richards, L. Heaman, R. Creaser, G. S. Salazar
Schaft Creek is a calc-alkaline porphyry Cu-Mo-(Au) deposit located in northwestern British Columbia. The deposit formed in a volcanic arc setting, likely on a back-arc rifted continental fragment. It is hosted by Late Triassic basaltic to andesitic volcanic rocks of the Stuhini Group (Stikine Terrane), and is associated with porphyritic granodiorite dikes emanating from the nearby Hickman batholith. The age of the Hickman batholith is approximately constrained here by a composite U–Pb zircon date of 222.1 ± 9.6 Ma, which is in broad agreement with a well-constrained age for mineralization at Schaft Creek of 222.0 ± 0.8 Ma (Re–Os molybdenite). The deposit is in most respects typical of calc-alkaline porphyry systems, but displays silica-poor sericite-chlorite alteration in mafic country rocks in place of classic phyllic alteration. The deposit comprises three distinct, but related, zones: the northern Paramount zone, the Main zone, and the West Breccia zone. Two phases of mineralization are observed. The first phase occurs as hydrothermal veins and breccias, and minor disseminations. It consists of bornite, chalcopyrite, molybdenite, and pyrite with potassic and sericite-chlorite alteration. The second phase is minor and consists of veins of molybdenite ± specularite, as well as Cu–Pb-Zn sulfide veins without any significant corresponding alteration. Extensive structural modification has affected the deposit both during and after its formation.
Schaft Creek是位于不列颠哥伦比亚省西北部的一个钙碱性斑岩型铜钼(金)矿床。该矿床形成于火山弧环境，可能是在弧后裂陷的大陆碎片上。它赋存于斯图希尼群(Stikine地块)的晚三叠世玄武岩-安山岩火山岩中，与附近Hickman岩基的斑岩花岗闪长岩岩脉有关。Hickman岩基的年龄约为222.1±9.6 Ma的复合U-Pb锆石，与Schaft Creek的222.0±0.8 Ma (Re-Os辉钼矿)的成矿年龄基本一致。该矿床在大多数方面都是典型的钙碱性斑岩体系，但在基性岩中表现出硅-绢云母-绿泥石蚀变，而不是典型的叶状蚀变。该矿床包括三个不同但又相互关联的带:派拉蒙北部带、主带和西角砾岩带。观察到两个矿化阶段。第一阶段以热液脉和角砾岩为主，并有少量展布。它由斑铜矿、黄铜矿、辉钼矿和黄铁矿组成，并伴有钾化和绢云母绿泥石蚀变。第二阶段规模较小，由辉钼矿±镜铁矿脉体和铜铅锌硫化物脉体组成，未见明显蚀变。广泛的构造改造对矿床形成期间和形成后都产生了影响。
{"title":"The Schaft Creek Porphyry Cu-Mo-(Au) Deposit, Northwestern British Columbia","authors":"J. Scott, J. Richards, L. Heaman, R. Creaser, G. S. Salazar","doi":"10.2113/GSEMG.17.3-4.163","DOIUrl":"https://doi.org/10.2113/GSEMG.17.3-4.163","url":null,"abstract":"Schaft Creek is a calc-alkaline porphyry Cu-Mo-(Au) deposit located in northwestern British Columbia. The deposit formed in a volcanic arc setting, likely on a back-arc rifted continental fragment. It is hosted by Late Triassic basaltic to andesitic volcanic rocks of the Stuhini Group (Stikine Terrane), and is associated with porphyritic granodiorite dikes emanating from the nearby Hickman batholith. The age of the Hickman batholith is approximately constrained here by a composite U–Pb zircon date of 222.1 ± 9.6 Ma, which is in broad agreement with a well-constrained age for mineralization at Schaft Creek of 222.0 ± 0.8 Ma (Re–Os molybdenite). The deposit is in most respects typical of calc-alkaline porphyry systems, but displays silica-poor sericite-chlorite alteration in mafic country rocks in place of classic phyllic alteration. The deposit comprises three distinct, but related, zones: the northern Paramount zone, the Main zone, and the West Breccia zone. Two phases of mineralization are observed. The first phase occurs as hydrothermal veins and breccias, and minor disseminations. It consists of bornite, chalcopyrite, molybdenite, and pyrite with potassic and sericite-chlorite alteration. The second phase is minor and consists of veins of molybdenite ± specularite, as well as Cu–Pb-Zn sulfide veins without any significant corresponding alteration. Extensive structural modification has affected the deposit both during and after its formation.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127600857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-07-01DOI: 10.2113/GSEMG.17.3-4.197
C. E. Suh, A. Cabral, E. Shemang, L. Mbinkar, G. Mboudou
Two iron deposits within the Precambrian mineral belt of Cameroon are described in detail for the first time: the Archean Metzimevin replacement iron deposit enclosed in Fe-enriched itabirite, and the Proterozoic granite-hosted, shear zone-related Mayo Binka magnetite deposit. In the Metzimevin deposit, quartz is corroded and microplaty hematite overprints martite-textured hematite. The Mayo Binka massive magnetite veins show evidence of deformation in magnetite (fracturing and microbrecciation) and in overgrowths of specular hematite (mechanical twinning and undulating extinction). The magnetite is partially replaced by hematite (martitization) and goethite. Ores from both deposits have >88% total Fe2O3 and low contents of contaminants such as SiO2, Al2O3, MgO, CaO, P2O5, and TiO2. They are also poor in Cu, Pb, Zn, V, Cr, and Ni. The Metzimevin massive hematite is characterized by an accentuated light rare earth element depletion relative to the Fe-enriched itabirite. It is suggested that the Metzimevin iron deposit is the result of hypogene leaching of gangue minerals from, and further hematitization of, an itabirite protore. Although the genesis of the Mayo Binka massive magnetite is unclear, it is spatially related to Neoproterozoic granitic rocks. The data allow some comparison of these little known, but potentially economic iron deposits, with some of the world’s better investigated deposits, and are useful to the exploration efforts for iron ore currently underway in Cameroon and the Central African subregion.
{"title":"Two Contrasting Iron Deposits in the Precambrian Mineral Belt of Cameroon, West Africa","authors":"C. E. Suh, A. Cabral, E. Shemang, L. Mbinkar, G. Mboudou","doi":"10.2113/GSEMG.17.3-4.197","DOIUrl":"https://doi.org/10.2113/GSEMG.17.3-4.197","url":null,"abstract":"Two iron deposits within the Precambrian mineral belt of Cameroon are described in detail for the first time: the Archean Metzimevin replacement iron deposit enclosed in Fe-enriched itabirite, and the Proterozoic granite-hosted, shear zone-related Mayo Binka magnetite deposit. In the Metzimevin deposit, quartz is corroded and microplaty hematite overprints martite-textured hematite. The Mayo Binka massive magnetite veins show evidence of deformation in magnetite (fracturing and microbrecciation) and in overgrowths of specular hematite (mechanical twinning and undulating extinction). The magnetite is partially replaced by hematite (martitization) and goethite. Ores from both deposits have >88% total Fe2O3 and low contents of contaminants such as SiO2, Al2O3, MgO, CaO, P2O5, and TiO2. They are also poor in Cu, Pb, Zn, V, Cr, and Ni. The Metzimevin massive hematite is characterized by an accentuated light rare earth element depletion relative to the Fe-enriched itabirite. It is suggested that the Metzimevin iron deposit is the result of hypogene leaching of gangue minerals from, and further hematitization of, an itabirite protore. Although the genesis of the Mayo Binka massive magnetite is unclear, it is spatially related to Neoproterozoic granitic rocks. The data allow some comparison of these little known, but potentially economic iron deposits, with some of the world’s better investigated deposits, and are useful to the exploration efforts for iron ore currently underway in Cameroon and the Central African subregion.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"65 Suppl 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127386185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-07-01DOI: 10.2113/GSEMG.17.3-4.131
M. Abzalov
Control of analytical data quality is usually referred to in the mining industry as Quality Assurance and Quality Control (QAQC), and involves the monitoring of sample quality and quantification of analytical accuracy and precision. QAQC procedures normally involve using sample duplicates and specially prepared standards whose grade is known. Numerous case studies indicate that reliable control of sample precision is achieved by using approximately 5% to 10% of field duplicates and 3% to 5% of pulp duplicates. These duplicate samples should be prepared and analyzed in the primary laboratory. Bias in the analytical results can be identified by inclusion of 3% to 5% of the standard in each sample batch. Several different standards are used, with values spanning the practical range of grades in the actual samples. A blank (a sample in which the concentration of metal of interest is below detection limit) should also be included. Standard samples alone cannot identify biases introduced during sample preparation, and therefore approximately 5% of the duplicate samples (coarse rejects and pulp) should be processed and assayed at another, external, reputable laboratory. This paper discusses techniques used for estimation of errors in precision and accuracy, and overviews diagnostic tools. It is shown that one of the most commonly used methods, the Thompson-Howarth technique, produces consistently lower results than other methods. These results reflect the nature of this method, which relies on the assumption of a normally distributed error, and thus produces biased results when errors have a skewed distribution. This study concurs with the suggestion of Stanley and Lawie (2007: Exploration and Mining Geology, v. 16, p. 265–274) to use the average coefficient of variation ( CV AVR (%) ) as the universal measure of relative precision error in mine geology applications: ![Graphic][1] Based on case studies, an acceptable level of sample precision is proposed for several different deposit types. [1]: /embed/inline-graphic-1.gif
分析数据质量的控制在采矿业中通常被称为质量保证和质量控制(QAQC)，涉及对样品质量的监测和分析准确性和精密度的量化。qqc程序通常涉及使用样品副本和专门准备的标准，其等级是已知的。许多案例研究表明，通过使用大约5%至10%的现场重复和3%至5%的纸浆重复，可以实现可靠的样品精度控制。这些重复样品应在主实验室制备和分析。分析结果中的偏差可以通过在每个样品批次中加入3%至5%的标准品来确定。使用了几种不同的标准，其值跨越实际样品中等级的实际范围。空白(样品中感兴趣的金属浓度低于检测限)也应包括在内。标准样品本身无法识别样品制备过程中引入的偏差，因此大约5%的重复样品(粗次品和纸浆)应在另一个外部信誉良好的实验室进行处理和分析。本文讨论了用于估计精度和准确度误差的技术，并概述了诊断工具。这表明，最常用的方法之一，汤普森-豪沃斯技术，产生的结果始终低于其他方法。这些结果反映了该方法的本质，该方法依赖于假设误差为正态分布，因此当误差呈偏态分布时，会产生偏倚的结果。本研究与Stanley和Lawie (2007: Exploration and Mining Geology, v. 16, p. 265-274)的建议一致，即使用平均变异系数(CV AVR(%))作为矿山地质应用中相对精度误差的通用度量:!根据案例研究，对几种不同的矿床类型提出了可接受的样品精度水平。[1]: / /嵌入内联- - 1. - gif图像
{"title":"Quality Control of Assay Data: A Review of Procedures for Measuring and Monitoring Precision and Accuracy","authors":"M. Abzalov","doi":"10.2113/GSEMG.17.3-4.131","DOIUrl":"https://doi.org/10.2113/GSEMG.17.3-4.131","url":null,"abstract":"Control of analytical data quality is usually referred to in the mining industry as Quality Assurance and Quality Control (QAQC), and involves the monitoring of sample quality and quantification of analytical accuracy and precision. QAQC procedures normally involve using sample duplicates and specially prepared standards whose grade is known. Numerous case studies indicate that reliable control of sample precision is achieved by using approximately 5% to 10% of field duplicates and 3% to 5% of pulp duplicates. These duplicate samples should be prepared and analyzed in the primary laboratory.\u0000\u0000Bias in the analytical results can be identified by inclusion of 3% to 5% of the standard in each sample batch. Several different standards are used, with values spanning the practical range of grades in the actual samples. A blank (a sample in which the concentration of metal of interest is below detection limit) should also be included. Standard samples alone cannot identify biases introduced during sample preparation, and therefore approximately 5% of the duplicate samples (coarse rejects and pulp) should be processed and assayed at another, external, reputable laboratory.\u0000\u0000This paper discusses techniques used for estimation of errors in precision and accuracy, and overviews diagnostic tools. It is shown that one of the most commonly used methods, the Thompson-Howarth technique, produces consistently lower results than other methods. These results reflect the nature of this method, which relies on the assumption of a normally distributed error, and thus produces biased results when errors have a skewed distribution. This study concurs with the suggestion of Stanley and Lawie (2007: Exploration and Mining Geology, v. 16, p. 265–274) to use the average coefficient of variation ( CV AVR (%) ) as the universal measure of relative precision error in mine geology applications:\u0000\u0000![Graphic][1] \u0000\u0000Based on case studies, an acceptable level of sample precision is proposed for several different deposit types.\u0000\u0000 [1]: /embed/inline-graphic-1.gif","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121391376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-07-01DOI: 10.2113/GSEMG.17.3-4.145
F. Lotfi, A. Belkabir, A. C. Brown, E. Marcoux, S. Brunet, L. Maacha
Koudiat Aicha is a small Zn-Pb-Cu deposit, enclosed in the Visean Sarhlef volcano-sedimentary series of the Moroccan Hercynian Jebilet massif. Base metal mineralization is located between a basal unit consisting of black argillite with arenite intercalations, and an upper unit composed of black argillite with locally fossiliferous calcareous units towards the top. Paraconcordant gabbro sills are present in both the upper and basal units, and the enclosing strata. Three successive phases of deformation linked to regional deformation overprint the volcano-sedimentary rocks and gabbros, as well as the sulfide mineralization. The mineral deposit includes several lenses of massive to semimassive pyrrhotite, 1 to 20 m thick, with a large halo of disseminated sulfide veinlets and sulfide nodules within a zone of intense chlorite alteration in the footwall. The ore mineralogy consists of massive to semimassive pyrrhotite with lesser amounts of sphalerite, chalcopyrite, arsenopyrite, galena, pyrite, and stannite. Lead isotope results ( 206 Pb/ 204 Pb averaging 18.27) suggest that the metals of the Koudiat Aicha deposit are derived from the volcano-sedimentary host rocks. Sulfur isotopes also indicate a volcano-sedimentary origin, with bacterial reduction of sulfate (δ 34 S CDT = −7.5‰ to −10.5‰). The conditions for sulfide metamorphic equilibration range from 250° to 330°C (sphalerite and chlorite geothermometers). The gabbroic sills could have been a local heat source for hydrothermal circulation. Based on these geological and mineralogical features, a Besshi-type model seems appropriate for the genesis of the Koudiat Aicha mineralization.
{"title":"Geology and Mineralogy of the Hercynian Koudiat Aïcha Polymetallic (Zn-Pb-Cu) Massive Sulfide Deposit, Central Jebilet, Morocco","authors":"F. Lotfi, A. Belkabir, A. C. Brown, E. Marcoux, S. Brunet, L. Maacha","doi":"10.2113/GSEMG.17.3-4.145","DOIUrl":"https://doi.org/10.2113/GSEMG.17.3-4.145","url":null,"abstract":"Koudiat Aicha is a small Zn-Pb-Cu deposit, enclosed in the Visean Sarhlef volcano-sedimentary series of the Moroccan Hercynian Jebilet massif. Base metal mineralization is located between a basal unit consisting of black argillite with arenite intercalations, and an upper unit composed of black argillite with locally fossiliferous calcareous units towards the top. Paraconcordant gabbro sills are present in both the upper and basal units, and the enclosing strata. Three successive phases of deformation linked to regional deformation overprint the volcano-sedimentary rocks and gabbros, as well as the sulfide mineralization. The mineral deposit includes several lenses of massive to semimassive pyrrhotite, 1 to 20 m thick, with a large halo of disseminated sulfide veinlets and sulfide nodules within a zone of intense chlorite alteration in the footwall. The ore mineralogy consists of massive to semimassive pyrrhotite with lesser amounts of sphalerite, chalcopyrite, arsenopyrite, galena, pyrite, and stannite. Lead isotope results ( 206 Pb/ 204 Pb averaging 18.27) suggest that the metals of the Koudiat Aicha deposit are derived from the volcano-sedimentary host rocks. Sulfur isotopes also indicate a volcano-sedimentary origin, with bacterial reduction of sulfate (δ 34 S CDT = −7.5‰ to −10.5‰). The conditions for sulfide metamorphic equilibration range from 250° to 330°C (sphalerite and chlorite geothermometers). The gabbroic sills could have been a local heat source for hydrothermal circulation. Based on these geological and mineralogical features, a Besshi-type model seems appropriate for the genesis of the Koudiat Aicha mineralization.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132202660","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2007-07-01DOI: 10.2113/GSEMG.16.3-4.145
M. Lanfranchini, R. D. Barrio, R. O. Etcheverry
The El Abuelo Ca-Fe-magnetite skarn and related hydrothermal quartz veins are located at Cerro Pepita Hill, in southwestern Chubut province of southern Argentina, 1700 km southwest of Buenos Aires. These deposits are developed in a continental magmatic arc environment linked to the Andean orogeny. Iron skarn mineralization is mainly hosted by an Upper Jurassic to Early Cretaceous sedimentary sequence interbedded with Upper Jurassic basaltic andesite, and is spatially associated with Early Cretaceous calc-alkaline dikes. Ore grades vary between 40 and 63 wt.% Fe. In addition, anomalous metal contents (>10 000 ppm Cu and up to 81 g/t Ag) are present in the hydrothermal quartz veins. At least three paragenetic mineral assemblages have been identified in the El Abuelo exoskarn: (1) amphibole > epidote ± chlorite ± quartz, formed by isochemical contact metamorphism; (2) Fe-clinopyroxene ± Ca-garnet, formed during prograde metasomatic anhydrous exoskarn formation; and (3) actinolite ± epidote ± chlorite ± quartz ± magnetite > titanite, resulting from hydrous retrograde alteration of exoskarn. Endoskarn alteration involved an early Mg-Fe-clinopyroxene ± Fe-garnet assemblage followed by retrograde actinolite replacement of pyroxene. Lower temperature hydrothermal alteration related to quartz veins was superimposed on the skarn assemblages, showing an innermost sericite ± adularia ± pyrite ± chalcopyrite assemblage and an external propylitic halo. Some metallogenic characteristics of the mineralization and the geological setting resemble those in several iron oxide copper-gold deposits elsewhere in the world.
El Abuelo钙铁磁铁矿矽卡岩及其相关热液石英脉位于阿根廷南部Chubut省西南部的Cerro Pepita Hill，位于布宜诺斯艾利斯西南1700公里处。这些矿床发育在与安第斯造山运动有关的大陆岩浆弧环境中。铁夕卡岩成矿主要赋存于与上侏罗统玄武安山岩互层的上侏罗统—早白垩世沉积序列中，在空间上与早白垩世钙碱性岩脉有关。矿石品位在40%到63%之间变化。此外，热液石英脉中存在异常金属含量(Cu > 10000 ppm, Ag高达81 g/t)。在El Abuelo外矽卡岩中发现了至少3种共生矿物组合:(1)角闪洞>绿绿石±绿泥石±石英，由等化学接触变质作用形成;(2)铁斜辉石±钙石榴石，形成于渐进式交代无水外矽卡岩形成过程;放光石±绿帘石±绿泥石±石英±磁铁矿>钛矿，为外矽卡岩含水逆行蚀变所致。内矽卡岩蚀变包括早期mg - fe -斜辉石±fe -石榴石组合，随后是辉石的逆行放射石替代。与石英脉有关的低温热液蚀变叠加在矽卡岩组合上，表现为最内层绢云母±adularia±黄铁矿±黄铜矿组合和外层丙基晕。其成矿特征和地质环境与世界上其他几个氧化铁铜金矿床相似。
{"title":"Geology and Chemistry of the El Abuelo Calcic Fe-skarn and Related Cu-(Ag)-Bearing Hydrothermal Veins, Chubut Province, Southern Argentina","authors":"M. Lanfranchini, R. D. Barrio, R. O. Etcheverry","doi":"10.2113/GSEMG.16.3-4.145","DOIUrl":"https://doi.org/10.2113/GSEMG.16.3-4.145","url":null,"abstract":"The El Abuelo Ca-Fe-magnetite skarn and related hydrothermal quartz veins are located at Cerro Pepita Hill, in southwestern Chubut province of southern Argentina, 1700 km southwest of Buenos Aires. These deposits are developed in a continental magmatic arc environment linked to the Andean orogeny. Iron skarn mineralization is mainly hosted by an Upper Jurassic to Early Cretaceous sedimentary sequence interbedded with Upper Jurassic basaltic andesite, and is spatially associated with Early Cretaceous calc-alkaline dikes. Ore grades vary between 40 and 63 wt.% Fe. In addition, anomalous metal contents (>10 000 ppm Cu and up to 81 g/t Ag) are present in the hydrothermal quartz veins.\u0000\u0000At least three paragenetic mineral assemblages have been identified in the El Abuelo exoskarn: (1) amphibole > epidote ± chlorite ± quartz, formed by isochemical contact metamorphism; (2) Fe-clinopyroxene ± Ca-garnet, formed during prograde metasomatic anhydrous exoskarn formation; and (3) actinolite ± epidote ± chlorite ± quartz ± magnetite > titanite, resulting from hydrous retrograde alteration of exoskarn. Endoskarn alteration involved an early Mg-Fe-clinopyroxene ± Fe-garnet assemblage followed by retrograde actinolite replacement of pyroxene. Lower temperature hydrothermal alteration related to quartz veins was superimposed on the skarn assemblages, showing an innermost sericite ± adularia ± pyrite ± chalcopyrite assemblage and an external propylitic halo.\u0000\u0000Some metallogenic characteristics of the mineralization and the geological setting resemble those in several iron oxide copper-gold deposits elsewhere in the world.","PeriodicalId":206160,"journal":{"name":"Exploration and Mining Geology","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125039465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：