This map and the related geodatabase illustrate the bedrock geology of central Ellesmere Island and eastern Axel Heiberg Island. Major features of the area include high-grade Paleoproterozoic metasedimentary and granitoid rocks of the Inglefield Orogen, unconformable lower Paleozoic shelf (and some deep-water strata) of the Central Ellesmere fold belt, the foreland clastic wedge of the Ellesmerian Orogen, unconformable Upper Paleozoic and Mesozoic strata of the Sverdrup Basin, and diverse Paleogene clastic rocks derived from the Eurekan Orogen. The Silurian and Devonian interval includes the depositional record of Bache Uplift.
This map and the related geodatabase illustrate the bedrock geology of central and eastern Prince of Wales Island, Somerset Island, and northern Boothia Peninsula. Major features of the area include Archean and Paleoproterozoic granitoid and metasedimentary rocks of Boothia Uplift overlain unconformably by Paleoproterozoic and Mesoproterozoic sediments, which are, in turn, unconformably overlain by Cambrian to Devonian strata of Arctic Platform. The higher Silurian and Lower Devonian interval provides a multiphase depositional record of Boothia Uplift. Youngest events are recorded by Cretaceous kimberlite diatremes and outliers of Paleogene strata.
This map and the related geodatabase illustrate the bedrock geology of central and northeastern Victoria Island, Stefansson Island, and western Prince of Wales Island. Major features of the area include inliers of Neoarchean basement granitoid rocks; clastic rock-dominated sections associated with the late Paleoproterozoic Kilohigok Basin, and Mesoproterozoic Elu Basin; extensive Meso- and Neoproterozoic strata of Amundsen Basin, diabase sills, and extrusive basaltic rocks related to the Franklin Large Igneous Province (ca. 723 Ma) and unconformable Cambrian to Devonian strata of Arctic Platform.
This map and the related geodatabase illustrate the bedrock geology of King William Island and southern Boothia Peninsula. Major features of the area include Archean and Paleoproterozoic granitoid and metasedimentary rocks of Boothia Uplift, unconformably overlain by generally flat-lying Cambrian to Silurian strata of the Arctic Platform.
This map and the related geodatabase illustrate the bedrock geology of eastern Melville Island, Byam Martin Island, and western Bathurst Island, including smaller islands in the same area. Major features of the area include the westerly trending salt-involved Parry Islands fold belt developed in Middle and Upper Devonian foreland basin strata, and unconformable Carboniferous and younger strata. A separate phase of salt tectonics, including diapirs of northeastern Melville Island, is associated with the evolution of the Sverdrup Basin.
Mineralization in hydrothermal ore systems has proximity, association and abundance relationships with fluid pathways (e.g. faults and lithological contacts) based on the concept of deformation-induced permeability being localized along such features. To empirically calibrate the abundance relationship between these features and gold mineralization, a measure known as geological complexity has been quantified. A fractal dimension representing the degree of geological complexity is evaluated using a box-counting method on the combination of faults and lithological contacts on a series of maps over the Kurnalpi Terrane of the Archaean Yilgarn Craton. Using multi-scale geological datasets from the Kurnalpi Terrane, we show that geological complexity and its relationship to known occurrences of orogenic gold mineralization varies depending on scale and degree of interpretation of the maps analyzed. In terms of scale, stronger correlations are observed for higher resolution 'outcrop' geological and structural maps. Even when the percentage of outcrop was taken into consideration, the higher resolution maps still showed greater correlations between geological complexity and gold mineralization. Differing solid geological interpretations at the same scale significantly affect the degree of quantified geological complexity and its correlation with known gold mineralization. The study results also illustrate a negative correlation between gold mineralization and gradients in the geological complexity. This outcome is contrary to results obtained by previous workers, and indicates that geological complexity, rather than complexity gradients, is useful as an input predictor map for prospectivity analysis and exploration targeting in the Kurnalpi region and other regions containing similar orogenic gold systems. Furthermore, the results indicate that interpreted solid geology maps, while critical for manual conceptual targeting, may actually be less effective than outcrop maps as a predictive layer in automated conceptual and empirical prospectivity analysis.
Abstract Fault stepovers are features where the main trace of a fault steps from one segment to the next in either an underlapping or overlapping manner. Stepovers exert a critical influence on crustal permeability and are known to control phenomena such as the migration of hydrocarbons and the location of geothermal fields. In the Kalgoorlie‐Ora Banda greenstone district, Western Australia, we demonstrate a spatial association between stepovers and gold deposits. It is shown that although underlapping stepover geometries are typically rare in fault systems, they are anomalously associated with gold deposits. Further, the along‐strike and across‐strike dimensions of both underlapping and overlapping fault stepovers fit, to a first‐order approximation, the same self‐similar trend. Boundary element modelling of Coulomb failure stress changes is used to explain these observations in terms of damage generated by rupture events on the bounding fault segments and associated aftershock sequences. Our models indicate that a larger region of damage and permeability enhancement is created around underlapping stepovers than around overlapping stepovers. By taking into account both the enhancement and decay of permeability during the seismic cycle, it is estimated that a 5 Moz goldfield could feasibly form in 1–16 earthquake‐aftershock sequences, potentially representing durations of just 10–8000 years. The existence of supergiant gold deposits is evidence that crustal permeability attains transiently high values on the order of 10 −12 m 2 . It should be expected that transient and time‐integrated permeability values have a distinct three‐dimensional structure in continental crust due to stepover‐related channels.
This map and geodatabase illustrate the geology of the Canadian Arctic Islands including all lands north and west of Baffin Island. Major features include high-grade Archean and Paleoproterozoic metasedimentary and granitoid rocks of Ellesmere and lands to south and southwest. To the north and west is Cambrian to Devonian cover that grades to deformed rocks of the Ellesmerian Orogen on Ellesmere Island and in the central and western Arctic Islands. The Ellesmerian Orogen features Devonian molasse detached on Ordovician evaporites, outer shelf carbonates of Ellesmere Island detached in the Neoproterozoic, deep water strata including volcanics and turbidites, and Pearya terrane, accreted to ancestral North America in the Silurian. Unconformable on all this are Carboniferous to Paleogene strata of Sverdrup Basin which features a second deformation belt of Paleogene age, the Eurekan Orogen. Youngest rocks are Neogene and widely represented in the western Arctic Islands from Meighen to Banks islands.
This map and the related geodatabase illustrate the bedrock geology of part of northern Ellesmere Island including Quttinirpaaq National Park. Major features of the area include: Pearya Terrane; volcanic, deep water and shelf facies of the Clements Markham, Hazen and Central Ellesmere fold belts; rift-related Upper Paleozoic strata; post-rift Permian and Mesozoic strata of Sverdrup basin; and Paleogene strata associated with the Eurekan Orogeny and fault displacements within and bordering Nares Strait.
The most abundant iron sulphide minerals in igneous, metamorphic, and some sedimentary rocks are FeS2 (pyrite/marcasite) and Fe1-xS (pyrrhotite). The oxidation of pyrite and pyrrhotite in bedrock aggregates and mine tailings is undesirable to infrastructure and the environment because such chemical reactions are linked with concrete deterioration and acid mine drainage, respectively. The oxidation rate of pyrrhotite is up to one hundred times greater than that of pyrite; thus, pyrrhotite oxidation is of particular concern to society. Pyrrhotite-bearing concrete aggregates may lead to rapid expansion cracking and failure of critical concrete infrastructure including bridges, buildings, and houses, posing a significant safety concern. Additionally, premature disintegration of concrete requires replacement of concrete, leading to excessive aggregate resource extraction and associated increases in CO2 emissions. Considering the widespread concrete infrastructure across Canada, the distribution of pyrrhotite in bedrock used for aggregate is of fundamental importance to the short- and long-term safety of Canadians at the national, regional, and local scales. This pilot study details the initial steps taken to generate national-scale geospatial models of pyrrhotite occurrences in bedrock across Canada and illustrates the associated map products. In total, 12,577 known pyrrhotite occurrences were identified from publicly available provincial and territorial mineral occurrence datasets. The overall modelling strategy involved normalizing the number of pyrrhotite occurrences with respect to the total surface area of major bedrock types and characterizing three different classes of pyrrhotite occurrence density (< 1, 1–4, and 4–10 occurrences/1000 km2). The maps illustrate that pyrrhotite occurrence density is highest in volcanic rocks and undifferentiated sedimentary and volcanic rocks, moderate in intrusive and unknown rocks, and lowest in sedimentary and metamorphic rocks. Sedimentary rocks with no pyrrhotite occurrences span large surface areas across central-western Canada thus resulting in an overall low pyrrhotite occurrence density (< 1 occurrence/1000 km2) for this rock type, despite the fact that numerous pyrrhotite occurrences are identified in sedimentary rocks and may be abundant locally or regionally. Volcanic, undifferentiated sedimentary and volcanic, intrusive, and unknown rocks occur throughout the Canadian Shield of central and northern Canada, the Cordillera of western Canada, and the Appalachians of eastern Canada, but bedrock type and associated occurrence density are highly variable within these geological domains. Comparison of pyrrhotite occurrence density maps for Canada with pyrrhotite permissive geology maps for the United States of America illustrates that rocks with a high pyrrhotite occurrence density in Canada (volcanic rocks and undifferentiated sedimentary and volcanic rocks), are contiguous overall with areas of pyrrhotite potential in the United States. Inconsistencies across the international border reflect the differing methodologies and assumptions consisting of a statistically based approach for Canada and a qualitative approach for the United States. In the Cordillera and Appalachians, such discontinuities across the international border may reflect the underestimation of pyrrhotite occurrences in sedimentary rocks of Canada because of the impact of high surface area on the pyrrhotite occurrence density calculations. The maps presented herein are a first step in illustrating the distribution of pyrrhotite-bearing bedrock across Canada and greater North America. These national-scale map products are useful first-order references for selecting regions for follow-up studies on bedrock pyrrhotite occurrences. Regional and local geospatial analysis combined with field work for ground truthing will be important aspects of future research, especially in the vicinity of population centres where bedrock is utilized for concrete aggregate. Detailed regional and local studies of pyrrhotite occurrences in bedrock will help guide the extraction of safe concrete aggregate and contribute to the long-term sustainability of bedrock resources, safe infrastructure, and a habitable climate.
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