Clarence Stream Research Articles

Devonian intrusions of southwestern New Brunswick, Canada: U-Pb geochronology, petrogenesis and genetic constraints on gold mineralization

ABSTRACT The Clarence Stream intrusion-related gold deposit is hosted within metasedimentary and metavolcanic sequences of the Ordovician Cookson and Silurian Mascarene groups that were intruded by several phases of the Late Silurian to Early Devonian Saint George Plutonic Suite. Based on geochemical and geochronological data, the intrusive rocks in the deposit are categorized into three distinct suites, including gabbroic, granitoid, and Whittier Ridge Granite (WRG). The gabbroic suite is the same as the East Branch Brook metagabbro intrusion, which exhibits a subalkaline mafic composition fractionated from a depleted mantle in a suprasubduction zone setting. The granitoid suite shows the same geochemical characteristics and age as the metaluminous to slightly peraluminous Magaguadavic Granite and its fractionated phases. The WRG suite reflects characteristics of calc-alkaline, metaluminous to peraluminous I-type granites in the area, such as Sorrel Ridge and Mount Douglas granitic plutons. In situ U-Pb zircon geochronology yielded an age of 419.5 ± 3.8 Ma for a monzodiorite from the gabbroic suite. Porphyritic granite and alkali granite from granitoid suite yielded U-Pb zircon age of 402.4 ± 1.8 Ma and 394.3 ± 3.8 Ma, respectively. Geochronologic data from the WRG suite reflect two different crystallization ages of 383.8 Ma (382.4 ± 3.1 to 385.1 ± 4) and 372.4 Ma (367.4 ± 1.3 to 377.1 ± 1.9). Several pieces of evidence demonstrate that the gold mineralizing events occurred after the emplacement of the East Branch Brook metagabbroic dykes and are linked to the various intrusive phases of the nearby syntectonic Early Devonian Magaguadavic Granite. The absence of gold and sulphide mineralization in felsic dykes related to the WRG confirms that this plutonic body formed adjacent to the gold zones after the main gold mineralizing event.

Application of portable X-ray and micro-X-ray fluorescence spectrometry to characterize alteration and mineralization within various gold deposits hosted in southern New Brunswick, Canada

New Brunswick hosts multiple types of gold deposits related to various stages of Appalachian orogenesis. Some of these structurally controlled deposits are considered intrusion-related; however, the majority have characteristics of orogenic deposits. The geochronology and genesis of the gold and antimony deposits in southern New Brunswick have been studied to varying degrees, but the relationship between mineralization and tectonism remains unresolved. This study involves the examination and comparison of auriferous quartz (-carbonate) veins associated with orogenic and intrusion-related gold mineralization of southern New Brunswick. The Belleisle Bay and Annidale groups (Annidale area) are host to mainly orogenic type gold mineralization, whereas in the Cookson and Mascarene groups (Clarence Stream area), gold mineralization is characterized as intrusion-related. For this study, the Devil Pike Brook deposit and Sheba Pit, East Scotch Settlement BP gold occurrences and the Bald Hill antimony deposit represent the Annidale area, whereas the South (Central and East subzones), George Murphy, Richard, and Jubilee zones represent gold mineralized areas in the Clarence Stream region.To facilitate the geochemical investigation of the various deposits and occurrences, an Olympus Vanta™ portable X-ray fluorescence spectrometer (pXRF) was used to rapidly analyse the composition of the different auriferous quartz (-carbonate) veins and characterize the alteration assemblages related to gold mineralization. The precision and accuracy of the pXRF data was monitored through QA/QC procedures, with the resulting corrected pXRF data undergoing principal component analysis (PCA) to fully interrogate the large data set.The PCA results highlight hydrothermal alteration and mineralization geochemical trends in the studied orogenic and intrusion-related gold deposits and occurrences. Some gold pathfinder elements reflect these different trends on the PC analysis on the studied samples. From the different PCs, various information about alteration and mineralization can be deduced. In Annidale area PC1 retrieves positive loadings of S, Cu, As, Pb, Zn, Fe, and Sb consistent with mineralization, PC2 displays positive loadings of Ca, Sr, Y, Mn and Ti, and PC3 extracts information about K, Rb, Ba, Zr, and Al consistent with alteration. In the Clarence Stream area, PC1 retrieved information about Al, K, Zr, Ba, Nb, Th and Rb consistent with alteration, PC2 displays positive loadings of As, Sb, Fe, Co, and S consistent with mineralization and PC3 extracts information about Zn, Pb, Mn, Fe, Cu, S and Si.Data obtained from the micro-X-Ray fluorescence–energy dispersive spectrometer (μ-XRF) analyses of the same sample suite concur with the alteration and mineralization characteristics identified using pXRF; these data indicate that chloritic and sericitic alteration with sulphides are associated with quartz (-carbonate) veins. The μ-XRF analysis is also helpful to further investigate sulphide and gold mineralization, as well as to locate potentially datable minerals, such as titanite, rutile, zircon, apatite, and monazite, in the gold-bearing quartz (-carbonate) veins; these data identified rutile and titanite in the Annidale samples and apatite in Clarence Stream samples that are being followed up geochronologically.

Devonian Intrusion-Related Mineralization in Southwestern New Brunswick: Mount Pleasant Sn–W–Mo–Zn–In and Clarence Stream Au–Sb Deposits

Devonian Intrusion-Related Mineralization in Southwestern New Brunswick: Mount Pleasant Sn–W–Mo–Zn–In and Clarence Stream Au–Sb Deposits

Determination of the leaching parameters for a refractory gold ore containing aurostibite and antimony minerals: Part II — AD Zone

Following a successful investigation on the Central Zone sample, a cyanidation study was conducted on an ore sample from the AD-MW Zone of Clarence Stream Property, owned by Freewest Resources Canada, to develop a leaching strategy to extract gold. At a grade of 6.48 g/t, gold is present in the forms of aurostibite, free gold and electrum. The ore contains 4.3% berthierite/gudmundite, 1.3% pyrrhotite, 0.7% pyrite, 0.07% stibnite and 0.9% arsenopyrite. Similar to the Central Zone, the extraction of gold from the AD-MW Zone can be performed at atmospheric pressure, pH 10.5 and with a low concentration of cyanide. The grind size had no effect on gold extraction between a P80 of 28 to 71 μm. The oxygen and cyanide requirement significantly increased with a finer grind. Consequently, a very close control of cyanide addition is required to minimize passivation of gold. Lead nitrate, added in the pretreatment, increased the extraction of gold by 2.3%. Leaching at pH < 10 improved gold extraction but increased the cyanide consumption by 5%. Passivation of gold occurred when the pretreatment was longer than 2 hours. A longer pretreatment reduced the cyanide consumption by 5%. Mineralogical characterization of the leach residue with no gravity pretreatment prior to leaching indicated the presence of unleached gold grains and passivated gold grains. Removal of coarse gold by gravity increased the extraction by 2.8% (leach residue at 0.74 g/t Au). Increasing the DO to 16 ppm or the lead nitrate from 500 to 1,000 g/t increased the overall gold extraction to 90.4% (leach residue at 0.62 g/t), which is the maximum gold extraction obtained. The leaching parameters were 800 ppm NaCN, DO 16 ppm and pH 10.5 for a duration of 120 hours. The associated cyanide consumption was 4.0 kg/t. Gold leaching was not sensitive to cyanide concentration. Reducing the cyanide concentration to 250 ppm resulted in a gold extraction of 89.5% with a cyanide consumption of 2.6 kg/t.

Evaluation of leaching parameters for a refractory gold ore containing aurostibite and antimony minerals: Part I – Central zone

A cyanidation study was conducted on a mild refractory gold ore sample from the Central zone of Clarence Stream Property, owned by Freewest Resources Canada, to develop a leaching strategy to extract gold. Gold, at a grade of 8.00 g/t, is present as native gold, electrum and aurostibite. The ore also contains 2.8% pyrrhotite, together with several antimony minerals (0.8% berthierite and gudmundite, 0.18% native antimony and stibnite). It also exhibits weak preg-robbing properties with 0.16% organic carbon. Aurostibite, a gold antimony compound, is particularly known to be insoluble in cyanide solution. The antimony dissolves in cyanide solution to form antimonates, which retards gold dissolution. Industrial practice of extracting gold from aurostibite generally consists of producing a flotation concentrate, which is leached in a pipe reactor at low alkalinity and high oxygen pressure with about 20 g/L cyanide. The proposed new approach is efficient and allows the extraction of gold directly from an ore at atmospheric pressure and a low cyanide concentration at pH 10.5. The effects of grinding, pre-treatment, lead nitrate, kerosene and cyanide concentrations have been investigated. The maximum gold extraction obtained on the ore was 87.9% using 800 ppm NaCN, 500 g/t lead nitrate, 30 g/t kerosene, DO (dissolved oxygen) 10 ppm and pH 10.5 in 168 h. The associated cyanide consumption was 1.3 kg/t. The additions of lead nitrate and kerosene increased gold extraction. In comparison to a P 80 of 74 μm, a P 80 of 30 μm significantly increased gold extraction. Gold in solid solution in gudmundite and arsenopyrite was believed to be responsible for the un-leached fraction until mineralogical analysis of hydroseparation concentrates of leach residues showed that most of the un-leached gold occurs as aurostibite, either as locked grains in sulphides/sulpharsenides or as grains with passivation rims of an Au–Sb–O phase. Coarse gold was also found. Gold extraction was not sensitive to cyanide concentration from 250 to 1200 ppm NaCN and high pH was detrimental. Decreasing the cyanide concentration reduced the cyanide consumption from 1.39 to 0.85 kg/t. The removal of coarse gold using a Knelson concentrator and a Mosley table prior to leaching increased the gold extraction to 90.4% (leach residue at 0.77 g/t).

Preface to Special Issue on Metallogeny and Setting of Gold Systems in Southern New Brunswick: Implications for Exploration in the Northern Appalachians

The presence of numerous gold occurrences peripheral to the Early Devonian Saint George batholith in southwestern New Brunswick (Fig. 1⇓) has been known for several decades, and in many cases has been documented in historical reports. Although it was suspected that there was a link between the granitic intrusions and the gold mineralization, sound evidence for such a genetic relationship was lacking until the recent discovery of the Clarence Stream gold deposit by a local prospector in 1999. As research at Clarence Stream progressed, it became evident that the mineralizing event was closely linked with the emplacement of a felsic intrusion, namely the I-type Magaguadavic granodiorite. This granodiorite-gold association and the extensive nature of the felsic intrusions that comprise the Saint George batholith in southwestern New Brunswick exemplified similarities to the newly recognized intrusion-related gold (IRG) systems as first introduced by Thompson et al. (1999). This specific class of gold deposits, whose genetic model was developed based on the various economic deposits in the Tintina belt in Yukon and Alaska, are typically found in provinces formerly mined for tin and tungsten, are genetically linked to reduced I-type intermediate intrusions (i.e., granodiorite), and have a strong Au-As-Sb-Bi signature (Thompson et al., 1999; Lang et al., 2000; Thompson and Newberry, 2000; Lang and Baker, 2001). To further investigate this granodiorite-gold association, it was deemed necessary to conduct a regional study of the area. This regional approach took on …

Deformation and Structural Controls on Gold Mineralization in the Clarence Stream Shear Zone, Southwestern New Brunswick, Canada

The Main zone of the Clarence Stream gold deposit is hosted by a shear zone adjacent to the Saint George batholith in southwestern New Brunswick. The mineralization history relates to progressive deformation in the shear zone and the intrusion of the Magaguadavic granodiorite. Of three phases of deformation that have affected the area (D 1 –D 3 ), D 1 is not observed in the Clarence Stream shear zone. Two suites of igneous rocks intrude the shear zone: post-D 2 , pre-D 3 gabbro; and granitic dikes, which crosscut the gabbros. Granitic dikes show a diverse range of relationships to D 3 features, from pre-syn-D 3 mylonitic fabrics in transposed and highly deformed enclaves, to nondeformed and entirely discordant dikes (post-D 3 ). A variety of veins occur within this shear zone. Zoisite-bearing and later, crosscutting epidote-bearing veins are preserved as relics in quartz-mylonites, and predate quartz veins that host gold mineralization. The epidote-bearing veins are associated with pseudotachylitic cataclasite dikes, consistent with transient brittle failure during ductile deformation. Deformation relates to right-lateral strike-slip motion across the shear zone, and subhorizontal and near-vertical stretching lineations imply transpression. A late (late- or post-D 3 ) dip-slip phase of motion is also apparent, and cooling followed a metamorphic peak early in D 2 –D 3 history. Deformation of the shear zone, and more localized transient brittle failure, provided the permeability for fluid movement and vein emplacement. This scenario is similar to the findings of other studies, in which geochemical, tracer isotopic, and age-dating (U/Pb, 40 Ar/ 39 Ar) results suggest that the adjacent Magaguadavic granodiorite provided heat and metals.

Gold Mineralization at the Anomaly A Deposit, Clarence Stream Area, Southwestern New Brunswick: Distal Deposits of a Syn-Deformational Intrusion-Related Gold System?

Gold-bearing mineralization at Anomaly A occurs in polydeformed Ordovician turbidites of the Kendall Mountain Formation of the St. Croix belt in southwestern New Brunswick, and is hosted by WSW-trending, shallow-dipping, brittle–ductile high-strain zones associated with the latest stage of the second of four regional deformation events. Gold-bearing syn-deformational stockwork, massive, and multiply brecciated quartz-sulfide veined zones form irregular pods and sheets up to several meters thick, which contain arsenopyrite, pyrrhotite, pyrite, stibnite, and a variety of rare minerals that are gold-bearing. Mineralized zones are enveloped by locally auriferous, weakly to intensely altered wall rock. Vein paragenesis includes: (1) early (pre- to syn-D 2 ) quartz-chlorite veins that are largely the product of migration of quartz by pressure solution; (2) crosscutting, multiphase, vuggy quartz-sulfide veins that contain most of the gold and are interpreted to be structurally controlled; (3) late, crosscutting, nondeformed, non-gold-bearing veins containing laumontite, chlorite, muscovite, quartz, fluorite, and base metal sulfides. Carbonate-poor alteration associated with zones of gold mineralization is lithology-specific, and appears to reflect overprinting of multiple events. Major elements removed during alteration include Si, Na, Mn, and Mg. The minor and trace elements removed include Co, Li, Sc, and possibly Sr, Ni, and Zn. Minor and trace elements added include Au, Ag, As, Sb, S, and possibly F, Cu, Pb, and Zr. On the basis of proximity, time constraints, and a similar ore mineral assemblage, gold mineralization at Anomaly A is interpreted to be a distal equivalent of the intrusion-related gold mineralization at the nearby Clarence Stream Main zone deposit.

History, Tectonic Setting, and Models for Instrusion-Related Gold Deposits in Southwestern New Brunswick, Canada: Examples from the Clarence Stream Area

Throughout the Paleozoic, a variety of gold depositional environments were created in the New Brunswick segment of the northern Appalachians because of the complexity of arc and continental plate collisions and subsequent erosion of the orogen. In southwestern New Brunswick, recent exploration and research has focused on deposits and occurrences that can be broadly classified as intrusion-related, generated by late- to post-orogenic felsic to intermediate plutonic rocks emplaced during the Early to Middle Devonian. This work has led to the establishment of models for gold mineralization and guidelines for exploration in this area, which might also be applicable elsewhere in the southern part of the province and, perhaps, throughout the northern Appalachians. The deposits in the vicinity of Clarence Stream in southwestern New Brunswick exemplify this deposit type, and highlight the emergence of a possible major gold district in the region.

Architecture of Gold Mineralization at Anomaly A of the Clarence Stream Deposits, Southern New Brunswick

The Anomaly A area of the Clarence Stream gold deposits in southwestern New Brunswick contains mineralized structures that bear geometrical relationships to regional folding events. The four mineralized zones of Anomaly A (AD, MW, 93, and Murphy) are hosted by turbiditic graywacke, quartzose wacke, siltstone, and argillite sequences of the Kendall Mountain Formation. A regional scale structural analysis reflects at least four deformational events, three of which appear to control the folded geometry of Anomaly A (D2, D3, and D4). F2 and F3 folds are coaxial and are refolded into a dome and basin geometry by F4 folds. The mineralized zones are subparallel to axial surfaces of F2 folds. Structural analysis of a mineralized zone exposed at surface indicates that gold mineralization is hosted by a quartz-vein system that comprises veins generated during both D2 and D3. Three dimensional representations of Anomaly A created using drill-core data and ®GoCAD suggest that the quartz-vein system was emplaced in fault structures during D2 as well as within brecciated dilation zones during D3. Three of the four zones that make up Anomaly A have F2 hinge surfaces that can be linked through a geometry compatible with the style of F3 and F4 folds. The apparent continuity of these three zones indicates the potential for kilometer-scale mineralized structures at Anomaly A.

Characteristics of Mineralization at the Main Zone of the Clarence Stream Gold Deposit, Southwestern New Brunswick, Canada: Evidence for an Intrusion-Related Gold System in the Northern Appalachian Orogen

Mineralization at the Main zone of the Clarence Stream gold deposit in southwestern New Brunswick occurs within a parallel series of quartz veins that occupy a NE-trending, steeply north-dip- ping, brittle-ductile shear zone related to the nearby terrane-bounding Sawyer Brook fault. This deforma- tion zone cuts volcaniclastic sedimentary and volcanic rocks of the Silurian Waweig Formation, and is intruded by mantle-derived East Branch Brook gabbroic dikes and a number of felsic dikes. Intermittent shear-zone reactivation during local magmatic activity induced heterogeneous deformation and alteration of the country rocks and dikes. The terminal phase of shearing is associated with narrow pegmatite-aplite dikes that grade laterally into granophyric granite, and into an auriferous quartz vein. Gold, aurostibite, and gold-antimony intergrowths, predominantly with vein quartz, are associated with a low ƒO2 sulfide mineral assemblage (pyrrhotite, arsenopyrite, and berthierite) that has a sulfur isotopic signature consistent with a magmatic source. Gold saturation and deposition occurred episodically between 300° and 360°C at low activity of sulfur, predominantly in response to pressure reduction during brittle failure combined with the effects of decreasing temperature and sulfidation reactions during fluid-wall-rock interaction. Geo - chronological studies demonstrate that the timing of the emplacement of the pegmatite-aplite dikes and associated auriferous veins overlap with that of the Early Devonian Magaguadavic granite. Moreover, the composition of the dikes is consistent with their derivation from this granite as late fractionates. The Main zone of the Clarence Stream deposit is therefore interpreted to be intrusion-related, with the Magaguad- avic granite being the ultimate source of the gold-bearing fluids. © 2008 Canadian Institute of Mining, Metallurgy and Petroleum. All rights reserved.

Geochemistry and petrogenesis of the East Branch Brook metagabbroic dykes in the Sawyer Brook fault zone, Clarence Stream gold prospect, southwestern New Brunswick

The East Branch Brook (EBB) metagabbroic dykes, host to a portion of the Clarence Stream gold deposit, are situated within the contact metamorphic aureole of the Middle Devonian I-type Magaguadavic Granite on the northwestern margin of the post-orogenic Saint George Bathohth. They are highly deformed, light- (type I), intermediate- (type 2) to dark-coloured (type 3) dykes containing auriferous quartz veins that occupy brittle to ductile northeast-trending shear zones in shallow marine, hornfelsed, volcaniclastic, sedimentary rocks of the Silurian Waweig and Oak Bay formations. The shear zones parallel the regional structure as a result of proximity to the faulted boundary (Sawyer Brook fault) between the Ordovician St. Croix terrane to the northwest and the Silurian to Early Devonian Mascarcne Basin to the southeast. Geochemical studies of the EBB dykes indicate that three pulses (Fe-rich. intermediate, and Mg-rich) of subalkaline to slightly alkaline continental tholeiitc magmas were generated in a transpressional environment during the Early Silurian to Early Devonian Positive εNd values indicate their derivation from a partially depleted mantle source during faulting and nft-related events&#x0D; Although the geochemical data (Fe- and Ti-depletion) indicate calc-alkaline affinity for the nearby Bocabec intrusive complex, εNd values and primitive mantle-normalized spider diagram patterns are similar to those of the EBB dykes. In contrast, the St. Stephen Intrusion appears more primitive with within-plate tholeiitic to slightly alkalie affinity&#x0D; &#x0D; RÉSUMÉ&#x0D; Les dykes metagabbroïques du ruisseau East Branch, qui abritent une partie du gite aurifière dc Clarence Stream, sont situées à l'inténeur de 1'auréolc de métamorphismc de contact du granite du Dévonian moyen de type 1 de Magaguadavic sur la limite nord-ouest du batholithe postorogénique de Saint George. Il s'agit de dykes extrémemeni déformés de teinte pàle (type 1) et intermédiaire (type 2) à foncée (type 3) renfermant des filons de quartz aurifere qui occupent des zones de eisaillement cassantes à déformables, orientées ver\ Ic nord-est. dans des roches sédimcntaires volcanoclastiques à coméenncs marines peu profondes des formations silunennes de Wawcig el d'Oak Bay. La proximilé de la limite faillée (faille du runsseau Sawyer) entre le terrane ordovicien de St. Croix, au nord-ouest et le bassin du Silurien au Dévonien inférieur de Mascarenc. au sud-est, a amené les zones du eisaillement à longer parallélement la structure régionale. Des éludes géochimiques des dykes du ruisseau East Branch révèlent que trois impulsions (composante riche en Fer. composante intermédiaire et composante riche en Mg) de magmas tholéutiques continentaux, allant de subalcalins à légèrement alcalms sont survenues dans un environnement transpressionnel pendant la période du Silurien inferieur au Dévonien infèrieur. Les vateurs positives de εNd lémoignent de leur provenance d'un manteau particllement appauri pendant la formation de failles et des phénomènes apparcntes à une distension&#x0D; &#x0D; Même les données géeochimiques (appaurassement en Fe et en Ti) revèlent unc affinité calcoalcaline du complexe intrusif proche de Bocabec. les valeurs de εNd et les configurations de diagrammes en araignée normalisées du manteau primitif sont analogues a celles des dykes du ruisseau East Branch Par contre, l'intrusion de Saint Stephen semble plus primitive avec une affinite mira-plaques allant de tholénlique à légèrcment alcaline&#x0D; &#x0D; Traduit par la rédaction