Copper Cliff Research Articles

Panel Destressing Strategies for Remnant Pillar Extraction

Large-scale panel destressing is a rockburst mitigation technique employed in deep hard rock mines during remnant pillar extraction. Panels are choke blasted in the pillar footwall to cutoff the far-field major stress in the mining area and deviate them around the pillar. In this study, the effects of panel geometry and far-field stress magnitude are investigated. Destress blast performance is assessed by measuring change to the energy release rate (ERR) of all mining steps during the extraction of a simplified remnant pillar due to destressing. It is demonstrated that the energy release rate (ERR) of critical stopes is reduced by 30% with the base panel geometry. The panel thickness is shown to have the most influence on the efficiency of destressing, followed by the stand-off distance between the panel and the pillar and the overhang length of the panel. The effect of far-field stress magnitude on the ERR is also investigated, and the destress blast performance is expressed as an equivalent major principal stress reduction. It is shown that with the base panel geometry, the destressing program offers the same ERR reduction as a 9.6 MPa reduction in the far-field stress for the most critical stopes. Finally, the Copper Cliff Mine (CCM) panel destressing program is presented as a case study. The ore at risk and ERR are calculated over the extraction and destressing sequence in the pillar with a pillar-wide numerical model.

N2 in deep subsurface fracture fluids of the Canadian Shield: Source and possible recycling processes

In addition to high concentrations of CH4 and H2, abundant dissolved N2 is found in subsurface fracture fluids in Precambrian cratons around the world. These fracture fluids have hydrogeological isolation times on order of thousands to millions and even billions of years. Assessing the sources and sinks of N2 and related (bio)geochemical processes that drive the nitrogen cycle in these long isolated systems can shed insights into the nitrogen cycle on early Earth with implications for other planets and moons. In this study, we collected dissolved gas samples from deep subsurface fracture fluids at seven sites (Kidd Creek, LaRonde, Nickel Rim, Fraser, Copper Cliff South, Thompson, and Birchtree) in the Canadian Shield. Multiple gas components (e.g., H2, O2 and Ar) were integrated with δ15NN2 values to characterize the N2 signatures. Results show that the dissolved N2 in deep subsurface fracture fluids from the Canadian Shield sites are more 15N-enriched than those from the Fennoscandian Shield and the Witwatersrand Basin in the Kaapvaal Craton. The nitrogen isotopic signatures of the Canadian Shield samples coupled with their hydrogeological framework indicate the N2 was sourced from fixed ammonium in silicate minerals in host rocks and was generated by metamorphic devolatilization. Modeling of nitrogen devolatilization from host rocks supports this interpretation, but also suggests that a second process, likely abiotic N2 reduction, is required to account for the observed 15N enrichment in the N2 samples from the Canadian Shield. A 10-year monitoring study for one of the boreholes, at 2.4 km of the Kidd Creek Observatory, shows a steady decrease in δ15NN2 values with time, which coincides with the temporal isotopic evolution of some other gas components in this borehole. Although it cannot be confirmed at this time, this isotopic shift in N2 may be potentially attributed to microbial processes (e.g., anaerobic oxidation of ammonium). Nevertheless, the large 15N enrichments for the majority of the samples in this study suggest that the nitrogen cycle in the deep saline fracture fluids in the Canadian Shield is dominated by abiotic processes. This is in contrast to the nitrogen cycles in the subsurface fracture fluids in the Fennoscandian Shield and the Witwatersrand Basin, which have been shown to be strongly affected by extant microbial ecosystems discovered in those fracture waters.

Structural controls on the localization of the mineralized Copper Cliff embayment and the Copper Cliff Offset dyke, Sudbury Igneous Complex, Canada

The Main Mass of the Sudbury Igneous Complex (SIC) is a 1.5–5 km thick, layered sheet of impact melt rocks, intensely studied because of the magmatic Ni-Cu-PGE sulfide deposits associated with the base of the Main Mass and connected dykes, known as the Sublayer and Offset dykes, respectively. The mode of emplacement of the mineralized Offset dykes that connect to the Main Mass through morphologic crater-floor irregularities (embayments) and the style of post-cratering deformation that affected the Offset dykes is not fully understood. This field-based study of the Copper Cliff Embayment (CCE) and Offset (CCO) dyke contributes to unraveling the mode of melt emplacement and the role of pre-impact faults in the deformation of the southern SIC. Field relationships indicate that the CCO dyke formed before the CCE and Sublayer were chemically fully evolved. Respective melts were injected into footwall rocks weakened by pre-impact deformation and cratering as a protracted event, with barren quartz diorite (QD) emplaced prior to mineralized, inclusion-bearing quartz diorite (IQD). Massive sulfide ore bodies appear to have formed late in the evolution of the dyke and physical separation (decoupling) of silicate magma and sulfide melt is required. NW-SE-shortening folded and faulted the strata hosting the CCO dyke and deformation was facilitated through re-activated E-W-striking, pre-impact faults. Restoring the initial geometry of the dyke and embayment, using 3D modelling and field constraints, helped to refine total slip estimates along major faults and confirmed that melts migrated gravitationally downward into the CCO dyke.

Effect of Stress Anisotropy on the Efficiency of Large-Scale Destress Blasting

Large-scale panel destressing is a rockburst control technique that is used to create a stress shadow in the ore pillar to be mined. The technique aims to reduce the pillar burst proneness by deviating the major induced principal stresses away from the concerned zone of interest. The destress panels, situated in the pillar hanging wall, are choke-blasted with high explosive energy density, and the blast-induced damage in the panel is accompanied by stress dissipation and stiffness reduction due to fragmentation in the panel. These two effects are traditionally modeled holistically with stiffness and stress reduction factors α and β, respectively, applied to the destressed zone. This paper focuses on the interpretation of Phase 3 destress blasting results at Copper Cliff Mine (CCM) where a stress increase (rather than decrease) was detected in the ore pillar crown, while a stress decrease was recorded in the ore pillar sill (as expected). It is hypothesized that high mining-induced stress anisotropy in the pillar crown caused blast-induced fractures to propagate in the orientation of the major principal stress, a condition that would hinder the destressing effect in that orientation. To verify the hypothesis, a series of panel anisotropic rock fragmentation and stress dissipation factors are iteratively tested in a 3-dimensional back analysis of the Phase 3 destress blast. The analysis takes into consideration the stope extraction schedule per the mine plan to better replicate the mining-induced stress condition in the panel and the ore pillar. The results show good agreement with stress measurements taken in situ using borehole stress cells installed in the ore pillar prior to destressing. The paper discusses the implications of preferential fracture propagation orientation and how it might affect the efficiency of destress blasting.

Mafic intrusions in the footwall of the Sudbury Igneous Complex: Origin of the Sudbury impact melt sheet and its associated ore deposits

The majority of the mafic intrusions and volcanic rocks in the footwall of the Sudbury Igneous Complex (SIC), which is believed to have formed from a melt sheet produced by the impact of a very large bolide, belong to one of two large mafic igneous suites, viz: the ∼2450 Ma East Bull Lake (EBL) suite of intrusions or the ∼2200 Ma Nipissing Diabase suite of intrusions. This has been established by U-Pb LA-ICP-MS dating of zircons from the newly recognized Frood intrusion, which hosts the Frood and Stobie ore bodies, and two of the Sudbury Gabbro intrusions, and comparison of the geochemistry of these intrusions with that of the EBL intrusive suite and the Nipissing Diabase suite. The age of the Frood intrusion (2421 ± 32 Ma) falls within error of other EBL-type intrusions whereas the ages of the Nairn (2203 ± 11 Ma) and Totten (2168 ± 11 Ma) intrusions fall within error of published ages for the Nipissing Diabase. Moreover, the primitive mantle-normalized patterns of the petrogenetic trace elements on extended spidergrams of the Nairn and Totten Sudbury Gabbros are similar to those of the Nipissing Diabase as are those of the Frood intrusion to other members of the EBL intrusive suite.The Ni-Cu-PGE sulfide deposits at Sudbury are associated with the lower contact of the SIC, where a discontinuous inclusion-rich norite contains much of the mineralization at the contact, and an inclusion-bearing quartz diorite is directly associated with the mineralization of the radial and concentric offset dykes. The Sublayer rocks and the overlying unit of melanocratic norites provide strong evidence for a relationship between the ore deposits and both inclusions and melts of mafic-ultramafic target rocks. The most common pre-impact mafic-ultramafic target rocks are intrusions of the EBL and Nipissing Diabase suites, although there are also Archean-aged mafic-ultramafic enclaves in the gneisses beneath the North Range of the SIC. The Totten orebody in the Worthington Offset and the Kelly Lake ore body in the Copper Cliff Offset are directly associated with footwall rocks comprising Sudbury Gabbro and Nipissing Gabbro, respectively, whereas the Frood-Stobie Offset and the associated Frood and Stobie ore deposits are sandwiched in a breccia belt containing large rafts of amphibole megacrystic gabbro belonging to the extensively broken-up Frood intrusion. Olivine-bearing mafic and ultramafic rocks, some of which exhibit shock metamorphic features, but others do not, are common inclusion types and occur in diverse Sublayer environments. The unshocked melanorite and olivine melanorite inclusions share common geochemical characteristicsde, indicating that they were derived from a similar source. Their geochemistry is also similar to that of the Frood Intrusion as well as the East Bull Lake intrusion; this indicates that they may have been sourced from East Bull Lake-type intrusions that were incorporated into the melt sheet at the time of melt generation.Mass balance calculations indicate that the felsic country rocks which account for 77% of the total volume of the SIC and contain 18 ppm Ni and 21 ppm Cu together with the sulfide-poor mafic country rocks which account for 23% of the SIC and contain 133 ppm Ni and 92 ppm Cu have too little Ni and Cu to account for the Ni and Cu contents of the quartz diorite, the composition of which provides an indication of that of the initial melt sheet.Calculations using the R-factor equation of Campbell and Naldrett (1979) indicate that the magmas that formed the norites and the ore deposits had 137 ppm Ni and 121 ppm Cu. Mass balance calculations have been used to determine if the country rocks have sufficient Ni and Cu in them to generate the ore deposits. The weighted median Ni content of the sulfide poor (<200 ppm Cu) mafic country rocks is 133 ppm and hence very similar to that of the ore-forming magma. However, the weighted median Cu contents of these rocks is only 90 ppm and hence too low to provide all of the Cu required by the ore-forming magma. What the mass balance calculation shows is that a contribution of Cu (and Ni) in the ore-forming magma was derived from pre-existing Ni-Cu-PGE sulphides associated with the mafic target rocks. This contribution was diluted by the lower concentrations of Ni and Cu from the Proterozoic metasedimentary rocks and the Archean granitoids and gneisses. For this reason, a contribution from magmatic sulfides in the mafic target rocks is required, and this may have been similar to the known disseminated concentrations of Cu-PGE-Ni sulfides present in mafic intrusions in the Sudbury area.

White Mica Geochemistry: Discriminating Between Barren and Mineralized Porphyry Systems

AbstractThe Grasshopper prospect, located 23 km west-southwest from Dillon, Montana, presents exposed zones of phyllic alteration assemblages comprising the early and late phyllic styles. The mineral chemistry of white micas from both phyllic alteration zones was evaluated by short-wave infrared spectroscopy, electron microprobe analysis, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The early phyllic expression consists of white to green micas characterized by longer Al-OH absorption wavelengths (2,204–2,210 nm), whereas the late phyllic phase contains white micas with shorter Al-OH absorption wavelengths (2,197–2,204 nm). Correlation with electron microprobe data found that the Tschermak substitution in the white micas is mainly controlled by Mg concentrations. Based on LA-ICP-MS data, higher Mn and Sr concentrations characterize white micas from the early phyllic alteration, whereas higher concentrations of B, Ba, Cr, Cs, Cu, Li, Rb, Sc, Sn, Ti, Tl, V, and W are present in white micas from the late phyllic style. Systematic zoning patterns of trace element concentrations in white micas from the early and late phyllic alteration styles were confirmed at Grasshopper. In general, increasing trends toward the center of the system were observed in V, Cu, Sc, Sn, W, and Zn, whereas increasing trends outward from the hydrothermal center were reported in Li and Cs. Comparison of the trace element concentrations of white micas from the early phyllic style from the barren system of Grasshopper and the mineralized system of Copper Cliff indicates significant differences in Zn, Cr, B, Tl, Sn, and Cs. Therefore, we propose a preliminary discrimination (Zn + Cr + B vs. Tl + Sn + Cs) plot that can be used to differentiate white micas from the early phyllic alteration among mineralized and weakly to unmineralized systems.

Large-scale destress blasting for seismicity control in hard rock mines: A case study

Destress blasting is a rockburst control technique where highly stressed rock is blasted to reduce the local stress and stiffness of the rock, thereby reducing its burst proneness. The technique is commonly practiced in deep hard rock mines in burst prone developments, as well as in sill or crown pillars which become burst-prone as the orebody is extracted. Large-scale destressing is a variant of destress blasting where panels are created parallel to the orebody strike with a longhole, fanning blast pattern from cross cut drifts situated in the host rock. The aim of panel destressing is to reduce the stress concentration in the ore blocks or pillars to be mined. This paper focuses on the large-scale destress blasting program conducted at Vale’s Copper Cliff Mine (CCM) in Ontario, Canada. The merits of panel destressing are examined through field measurements of mining induced stress changes in the pillar. The destressing mechanism is simulated with a rock fragmentation factor (α) and stress reduction/dissipation factor (β). A 3D model is built and validated with measured induced stress changes. It is shown that the best correlation between the numerical model and field measurements is obtained when the combination of α and β indicates that the blast causes high fragmentation (α = 0.05) and high stress release (β = 0.95) in the destress panel. It is demonstrated that the burst proneness of the ore blocks in the panel stress shadow is reduced in terms of the brittle shear ratio (BSR) and the burst potential index (BPI).

The Sinter Plant Boys: Jean Gagnon and the Personal Costs of Fighting to Compensate Sudbury Families

From 1948 to 1963, the International Nickel Company of Canada (Inco) operated a sintering plant in Copper Cliff, Ontario, to produce nickel and nickel oxide from sulphur matte. Sintering created a refined dust made of nickel sulphides and other oxides, and also produced considerable sulphur dioxide. The workers who were exposed to this dust without protective equipment—ingesting these toxic particles—later developed various forms of lung, sinus, and throat cancers. Spearheading the push to seek redress and proper remuneration for survivors and their families was Jean “Johnny” Gagnon, an 11-year veteran of the sinter plant and the Chairman of the Sinter Plant Action Committee for United Steelworkers Local 6500. Through his tireless efforts, Gagnon won compensation for many workers and their families. However, his victories came with a price: he incurred mental, physical, and personal costs while fighting to obtain compensation for his “boys.”

Cathodoluminescence and trace-element chemistry of quartz from Sudbury offset dikes: Observations, interpretations, and genetic implications

Abstract Offset dikes, radial and concentric fractures infilled with quartz diorite, are important hosts of Ni-Cu-PGE mineralization in the Sudbury area. To better understand their emplacement and evolution, the cathodoluminescence (CL) and trace-element chemistry of quartz were examined in quartz diorite from the Foy, Trill, Whistle, Hess, Parkin (North Range), and Copper Cliff (South Range) offsets. Although the potential causes of the CL response in quartz are considered, the primary focus was the qualitative textures and patterns, as these can provide valuable paragenetic information. Quartz from the North Range displays a strong blue luminescence dominated by homogenous and sharply zoned CL patterns, while that from the Copper Cliff offset displays a weak CL response. Locally recrystallized granoblastic quartz shows diffuse concentric zoning and other heterogeneous CL patterns. Trace-element EPMA-WDS analyses indicate that quartz from the Foy, Trill, and Whistle offsets is enriched in Al (30–600 ppm) and Ti (50–520 ppm) as compared to Fe (&amp;lt;25–490 ppm), while quartz from the Parkin and Hess offsets is enriched in Fe (270–700 ppm) as compared to Ti (44–211 ppm) and Al (95–250 ppm). In contrast to the North Range offsets, quartz from Copper Cliff has low Al concentrations (30–85 ppm) and very low Ti concentrations (&amp;lt;25 ppm). Application of the Ti-in-quartz geothermometer indicates that quartz from the North Range offsets crystallized above 600 °C, while that from the Copper Cliff offset crystallized below 600 °C. The CL responses and trace-element compositions of anhedral quartz from the North Range offsets are consistent with primary crystallization of quartz from magmatic quartz diorite, while those of the granoblastic quartz record dynamic recrystallization and Ostwald ripening. Copper Cliff quartz is anomalous in its CL response, trace-element content, and crystallization temperature, which may reflect overprinting during regional metamorphism of the South Range of the Sudbury Igneous Complex. Quartz CL is demonstrated to be an important tool for discerning and discriminating between paragenetic processes related to the formation of the offset dikes and has clear applications to the study of other quartz-bearing igneous rocks in the Sudbury area.

Quantitative Energy-Based Evaluation of the Intensity of Mining-Induced Seismic Activity in a Fractured Rock Mass

To elucidate the mechanism of seismic activity taking place away from extracted stopes in underground mines, this study focuses on the influence of a fracture network on the intensity of seismic activity from an energy point of view. Four seismically active regions with local geological structures and one non-active region were identified on 3880 level in the 100 and 900 Orebody areas at Copper Cliff Mine. Subsequently, cube-shaped discrete element method (DEM) models with fracture networks of the regions were generated. The stress analysis for two regions out of the four revealed that the elastic strain energy related to tensile failure quantitatively agrees well with the cumulative radiated seismic energy of the microseismic database. For the other two regions, the computed tensile failure-related strain energy was smaller than the radiated energy, leading to the postulation that the seismicity in the region was caused by violent shear rupture. The postulation was verified by quantitatively computing energy released by brittle shear failure. Then, for the seismically inactive region, the DEM analysis yielded quite small tensile failure-related strain energy. Considering these results, it was concluded that strain energy stored within rock mass with tensile failure potential can be used as an indicator for the intensity of seismicity taking place away from extracted stopes. Also, the seismic energy calculation methodology can give a reasonable estimation of seismic energy released by shear rupture taking place in geologically abnormal regions. These findings should lay a foundation for the further development of a guideline and/or simple formulation to evaluate the risk for mining-induced seismicity.

A Systematic Method for Classifying and Grouping Late Noachian and Early Hesperian Rock Targets Analyzed by the Mars Exploration Rover Opportunity at Endeavour Crater, Mars

AbstractThe Mars rover Opportunity has collected in situ compositional data with the Alpha Particle X‐ray Spectrometer at almost 500 sites. To analyze these data, hierarchical clustering analysis and an error‐weighted similarity index are applied to a subset of 57 APXS target compositions and selected Martian meteorites. Hierarchical clustering provides a rapid first approximation of compositional relationships, whereas the error‐weighted similarity index provides an in‐depth and quantifiable comparison of individual composition pairs. These analyses are combined into a statistical grouping model that provides insight into lithologic relationships and is critically informed by examination of Panoramic Camera and Microscopic Imager images. Major lithologies are (1) the Burns formation sulfate sandstones; (2) Shoemaker impact breccias (Endeavour crater ejecta/rim deposits); (3) the morphologically distinct Grasberg formation, associated with Endeavour crater rim deposits; (4) the Matijevic formation, an exposure interpreted to be Endeavour crater target rocks; and (5) erratics or other rocks that do not cluster with groups 1–4. The Grasberg formation is more similar to the Shoemaker formation than any other formation, and thus likely incorporated eroded Shoemaker material. The lowest Shoemaker member (Copper Cliff breccia) may contain material from the preimpact Matijevic formation. The Matijevic formation is the most chemically distinct formation and is most similar to the volcanic erratic rock “Marquette Island.” Clustering and similarity index values also show that regolith breccia Martian meteorites (represented by the NWA 7475/7034 paired meteorites) are similar in bulk composition to Mars surface materials at Meridiani, especially the Matijevic formation.

White Mica Geochemistry of the Copper Cliff Porphyry Cu Deposit: Insights from a Vectoring Tool Applied to Exploration

White Mica Geochemistry of the Copper Cliff Porphyry Cu Deposit: Insights from a Vectoring Tool Applied to Exploration

Formation of large-scale impact melt dikes: A case study of the Foy Offset Dike at the Sudbury impact structure, Canada

Hypervelocity impacts frequently result in the formation of dikes in the crater floor and central uplift. Impact melt-bearing dikes in large terrestrial impact basins – such as the Offset Dikes at the Sudbury impact structure – occur at a large scale, often tens of meters wide and several kilometers in length. The Offset Dikes host significant Ni–Cu–PGE deposits, which include several well-known mines, such as Totten and Copper Cliff that have been mined for nearly 100 years. The Offset Dikes typically consist of a clast- and sulfide-rich core and clast-poor margins. Their formation has been a subject of debate for decades. The most widely proposed model is the early emplacement of clast-poor impact melt shortly after the impact event, followed by the later emplacement of clast- and sulfide-rich impact melt in the center of the dike. An alternative hypothesis is that a single pulse of clast-rich impact melt flowed into the fractured target rocks and flow differentiation resulted in a clast-rich core and a clast-poor margin. In this study, we examine field and petrographic relationships of the Foy Offset Dike to better understand its emplacement. Our results show that the characteristics of the Foy Offset Dike – namely the gradational nature of the contact between the clast-rich and clast-poor phases, the alignment of clasts sub-parallel to this contact, the geochemical similarities and the presence of sulfides within both phases of the dike – are more consistent with the single injection and flow differentiation hypothesis.

Binding of Cu, Co, and Cs to fluorescent components of natural organic matter (NOM) from three contrasting sites.

Aqueous natural organic matter (NOM) contains different types of functional groups (carboxylic, phenolic, sulfidic, etc.), and hence could change the speciation of metals in environmental systems. This work is a proof-of-concept study on the interaction of three metals (Cu, Co, and Cs) with NOM using fluorescence spectroscopy. The specific aim was to determine the conditional stability constants for these three metals with NOM optical components, obtained from the quenching of fluorescence signals. Three contrasting water types were sampled in Northern Ontario: a pristine source (Cross Rd.), an urban-impacted source (Junction Creek), and an industrially impacted creek (Copper Cliff creek). In this investigation, Cu2+ was used as a benchmark, whereas Co2+ and Cs+ analyses were novel applications of this technique. Humic-like (H-like; terrestrial and microbial), fulvic-like (F-like), and protein-like (P-like) fluorescence components were found in various proportions at the three sampling sites. For these samples, the fluorescence signals of the H-, F-, and P-like components were quenched upon additions of Cu2+. The computed conditional stability constants (as log Kc) ranged from 4.46 to 6.06. In contrast, Kc values with Co2+ were measurable only for the two H-like components of the pristine sample (log Kc 3.02-4.05). Cesium (Cs+) induced quenching only for the P-like component at the industrial-impacted site (log Kc 4.82-5.03). While this study corroborates earlier reports that Cu2+-NOM interactions can be measured by fluorescence, we are showing for the first time a direct chemical interaction of Co2+ and Cs+ with specific NOM components, as reported by fluorescence quenching.

Characterization of Aseismic Fault-Slip in a Deep Hard Rock Mine Through Numerical Modelling: Case Study

Seismic moment is a predominantly utilized parameter for assessing fault-slip potential when the numerical modelling of fault-slip is carried out. However, relying on seismic moment as an indicator for fault-slip might lead to incorrect conclusions, as fault-slip can be inherently seismic or aseismic. The present study examines the behaviour of a fault in Copper Cliff Mine, Canada, with a 3D numerical model encompassing major geological structures in the area of interest. Three types of numerical analyses are conducted, namely elastic and elasto-plastic analyses in static conditions and elasto-plastic analysis in dynamic conditions. The static analyses show that the fault most likely had undergone shear failure at the pre-mining stage. It is then demonstrated that mining activities induce further shear movements along the fault plane as well as within the fault material, as the fault is composed of thick, severely fractured materials. Notwithstanding the results, no large seismic events with Mw > 0.1 were recorded within the fault from microseismic-monitoring systems between 2006 and 2014, implying that the shear movements are aseismic and static. Furthermore, microseismic database analysis using 350,000 events that took place between 2004 and 2014 indicates that the fault is not seismically active. It is found from the dynamic analysis that the maximum slip rate during fault-slip is not more than 0.3 m/s, even when the fault-slip is simulated with an instantaneous stress drop. This result substantiates the assumption that the fault is not seismically active and shear movements are dominantly aseismic. It is therefore suggested that other factors such as stress re-distribution induced by the aseismic slip be considered in order to assess damage that could be caused by the fault movements. The present study sheds light on the importance of distinguishing aseismic from seismic fault-slip for optimizing support systems in underground mines.

Tools used in mineral exploration for measuring the conductivity and the resistivity in drillholes and on drill core: observations on their range of sensitivity

A study has been undertaken to acquire conductivity data using the EM39 low-induction-number conductivity tool. Measurements were taken in three holes in the Sudbury, Ontario, area: at Victoria in the south-west part of the Sudbury structure; at Levack, in the north range; and at the Lady Violet deposit near Copper Cliff. These data were compared with pre-existing data acquired using four other tools and measurements taken on core extracted from the holes. The four tools are the DGI galvanic downhole resistivity tool, the IFG downhole conductivity tool, and the handheld KT-10 and GDD meters. The comparison shows that each tool has a finite range of sensitivity. The resistivity tool used by DGI Geoscience is sensitive to conductivities primarily in the range 0.01 to 100 mS/m; the EM39 tool is sensitive to conductivities in the range of ~30 mS/m to 3000 mS/m and the IFG tool to conductivities greater than 30 mS/m. In the sub-ranges where the ranges of two instruments overlap, one might expect a good correlation between the measurements derived from the two tools. However, this is not always the case, as the instruments can have a different volume of sensitivity: the EM39 has a coil separation of 50 cm and will see material greater than 20 cm away from the hole; whereas the IFG conductivity tool seems to have a smaller spatial scale of sensitivity due to its 10 cm coil size. The handheld instruments used to log the conductivity of the core are sensitive to more conductive material (greater than ~1 S/m). The scale of the sensors of these handheld instruments is a few cm, so they are focussing on a very local estimate. The spatial characteristics of the handheld instruments are similar to the IFG tool, so there is a reasonable linear correlation between the conductivities derived from these three different instruments. However, the slopes are not unity; for example, the GDD instrument gives values three times greater than the KT-10. When selecting tools for measuring the resistivity and conductivity, ensure that the values that you expect to measure fall within the range of sensitivity of the instrument and that the features sought are comparable in size to the volume of sensitivity.

Discontinuum Modelling Approach for Stress Analysis at a Seismic Source: Case Study

Rockbursts in underground mines can cause devastating damage to mine workings; hence, it is important to be able to assess the potential for their occurrence. The present study focuses on a large seismic event that took place at an underground base metal mine in Canada. The event took place in a dyke near the 100/900 orebodies on 3880 Level (1180 m below surface) of the Copper Cliff Mine in Sudbury, Canada. A 3D continuum stress analysis of the orebodies, i.e., 100 and 900, using an orebody-wide model encompassing the major geological structures and in situ stress heterogeneity in the mine shows low potential for rockburst at the seismic source location—a result which contradicts the fact that a large seismic event actually took place. A postulation is thus made that there had been highly stressed regions caused by geological disturbances at the source location before mining activities took place. In order to verify the postulation, a further study is undertaken with the discrete element modelling technique, whereby a cube-shaped model containing a fracture network is subjected to a stress state similar to that at the source location. A model parametrical study is conducted with respect to the distribution of the fracture (joint) network and its mechanical properties. The results reveal that when joints are densely distributed at the source location, the stress state becomes significantly burst prone. It is observed that the length, density, stiffness, and orientation of joints have a large influence on the stress state along the joints, while the friction angle, cohesion, and tensile strength do not influence the stress state. A cube-shaped model is constructed with joint sets actually mapped at the mine and a stress analysis is performed. The results demonstrate the generation of highly stressed regions due to the interaction of the joints with the applied in situ stress fields, thus leading to burst-prone conditions. The present study numerically confirms that a preexisting fracture network found within a stiff rockmass could lead to burst-prone stress state at relatively moderate mining depths.

Smelter Fumes, Local Interests, and Political Contestation in Sudbury, Ontario, during the 1910s

During the second half of the 1910s the problem of sulphur smoke in Sudbury, Ontario, pitted farmers against the mining-smelting industry that comprised the dominant sector of the local economy. Increased demand for nickel from World War I had resulted in expanded activities in the nearby Copper Cliff and O’Donnell roast yards, which in turn produced more smoke and destroyed crops. Local business leaders, represented by the Sudbury Board of Trade, sought to balance the needs of the agriculture and mining-smelting sectors and facilitate their coexistence in the region. Among the measures pursued, farmers and some Board of Trade members turned to nuisance litigation, with the objective of obtaining monetary awards and injunctions affecting the operation of the roast yards. While the amounts of the awards were disappointing for the farmers, the spectre of an injunction was sufficient to convince the provincial government to ban civil litigation in favour of an arbitration process accommodating industry. This article provides an account of the political activism over Sudbury’s smoke nuisance that failed to bring about emission controls, highlighting the contextual factors contributing to this failure.

An estimation of the variability in automated quantitative mineralogy measurements through inter-laboratory testing

Presently there are about 160 installations of automated mineralogy instruments such as QEM∗SCAN, MLA, TIMA, MINERALOGIC and INCAMineral. These instruments determine mineral quantities, and perform mineral liberation and mineral association analyses. Since the late 1990’s the scientific community of applied mineralogy and automated mineralogy has expressed the need of determining the variability in the measurements of mineral quantities and mineral liberation analyses through inter laboratory testing of suitable reference materials to improve confidence in the quantitative mineralogy measurements. A sample representing the −28+65 mesh size fraction of a sulphide flotation rougher concentrate from the Clarabelle mill in Copper Cliff, Vale (Sudbury, Ontario) was prepared for this testing. This rougher concentrate contains chalcopyrite, pyrrhotite, pentlandite, pyrite, quartz and feldspars as the dominant minerals. A 10-gram sub-sample was sent to the participating laboratories of the round robin. The sub-samples were analyzed by the participating laboratories to determine the mineral quantities, the liberation of chalcopyrite and the mineral association analysis for chalcopyrite. The findings indicate that there is a good agreement in the mineral quantities. The liberation analysis results also indicate a good agreement with the exception of two participants. These results indicate that correct mineral quantities do not necessarily imply correct mineral liberation. The testing also revealed that there was no consensus on how the mineral associations are treated and reported. We recommend that the modal analysis by liberation classes should be the preferred approach in reporting the mineral associations because it is more relevant to understand the mineral concentration operations.

Magnetic susceptibility mapping of the Sudbury area, Ontario, Canada: evaluating pollution distributions decades later

This study evaluates the use of magnetic susceptibility and magnetic parameter measurements in assessing spatial and temporal variations of pollutants that emanated from mining industries in and around Sudbury, Ontario, Canada. For this purpose, in situ magnetic susceptibility (κin situ) was measured at 106 sites on a grid of 10 km × 10 km and 5 km × 5 km. The κin situ values ranged from 2 × 10−5 to 149 × 10−5 SI, and the highest κin situ values were observed near the active (Copper Cliff) and inactive (Coniston) mining sites. The lowest κin situ values were measured at increased distances from possible pollution sources; therefore, mapping of in situ magnetic susceptibility values is a proxy to polluted areas in and around Sudbury. To evaluate potential anthropogenic and (or) lithogenic input to κin situ, low-frequency mass specific magnetic susceptibility (χlf) variations with depth were classified into four different types of profiles. For further investigation of magnetic minerals in the samples, laboratory measurements of magnetic susceptibility, frequency dependence of magnetic susceptibility, hysteresis properties, thermosusceptibility curves, anhysteretic and isothermal magnetizations, and scanning electron microscopy – energy-dispersive X-ray spectroscopy (SEM–EDS) were also conducted on the soil samples. Laboratory measurements indicated that ferrimagnetic minerals (e.g., magnetite) of variable grain size were the dominant magnetic minerals, with the exception of one site that contained an iron sulfide (greigite) phase near a mine waste site. Magnetic spherules observed in SEM micrographs are of variable sizes (6–60 μm), suggesting that suspended particulate matter (PM10) is present, and may be a health concern. At some sites, EDS analysis showed that heavy metals (Co, Al, and Ni), which threaten human health, are also present in the study area.