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<jats:p> The Editorial Calendar details upcoming (approximately one year in advance) publication plans for The Leading Edge. This includes all special sections, guest editors, and information about submitting articles to TLE. </jats:p>

<jats:p> I am old enough to have experienced a change in thinking among oil and gas (O&amp;G) executives and professionals — from a general skepticism, or even denial, to a more open mind toward climate change and carbon emissions. Perhaps arising as a late and uncomfortable reaction to scientific consensus and demands from consumers, shareholders, and the government, the energy industry nevertheless has come to acknowledge the impact it has on the environment and is taking proactive steps to counter the impact. This change in thinking also represents a business opportunity. O&amp;G and service companies have a unique competence in dealing with the large uncertainty and extreme capital intensity of energy projects. They are experienced in scaling up technologies and developing cost-effective solutions. As such, they can make a big difference in a low-carbon and renewable future. In what some might view as a paradox, O&amp;G practitioners can become the champions of the energy transition. </jats:p>

<jats:p> This special section of The Leading Edge focuses on the issue of critical minerals from the perspective of recent progress in mining exploration and anticipated future needs as the global energy economy transitions to higher use of, and reliance on, renewables. The definition of a “critical mineral” is itself context dependent. For example, minerals such as lithium, nickel, cobalt, manganese, and graphite each are essential to the development of modern, high-efficiency lithium-ion batteries, and any disruptions to these minerals — whether through supply chain issues or raw, geologic access — ultimately impacts the future of this now-pervasive, and increasingly necessary, energy storage technology. Similarly, rare earth elements (REEs) have long been central to the manufacture of permanent magnets, which themselves are key components of wind turbines and electric vehicles, the latter of which account for 14% of global passenger car sales in 2022, up from 9% in the previous year. In the United States alone, the market forecast for electric vehicles is expected to grow to roughly US$137 billion in 2028, up from $24 billion in 2020. Lastly, the more “common” but still “critical” minerals copper and aluminum are the backbone of the rapidly expanding global energy distribution systems upon which our modern society is built. </jats:p>

<jats:p> Historical exploration for economic nickel (Ni) mineralization has often targeted magmatic sulfide deposits in extensional settings. However, convergent-margin-hosted Alaskan-type complexes represent a potentially underexplored source of Ni. Case studies of the geophysical responses associated with two magmatic Ni deposits (one is typical, and one is associated with an Alaskan-type complex) are presented, and the results are compared. Data were assessed from historical and newly acquired airborne geophysical surveys that were collected over the Mayville property in southeast Manitoba and the Turnagain property in northern British Columbia. The properties were explored by Mustang Minerals Corporation and Giga Metals Corporation, respectively. Airborne electromagnetic (EM) and magnetic data were utilized to compare the two properties and the mineralized zones. The review showed that the Mayville magmatic sulfide deposit was directly detectible with EM methods, and the passive and active-source methods were complementary to one another. The EM data did not directly detect the Turnagain Alaskan-type deposit, but the magnetics data proved to be successful in defining the geologic framework. Implications for future targeting and exploration for economic Ni mineralization are considered. </jats:p>

<jats:p> The Metal Earth project integrates geophysics, geology, geochemistry, and geochronology to improve the understanding of metal endowment in Precambrian terranes. Magnetics (airborne), gravity, magnetotellurics, and reflection seismic methods are the primary geophysical tools employed. Data were collected along 13 transects in the initial phase of the project. All geophysical tools are crucial for understanding the structure of the shallow, middle, and deeper crust and identifying pathways along which the constituents of critical minerals might have migrated from a source to a deposit. The magnetic data are used predominantly to help map the geology away from the transects, and the gravity data are useful for extending the near-surface geology to depths up to 8 km. The magnetotelluric data show the upper Archean crust to about 10 km as highly resistive, except for some conductive subvertical zones that correspond to major deformation zones, many of which are known to be metalliferous. This suggests that these conductive zones could have been hydrothermal fluid pathways feeding the mineral deposits. These zones can be traced to larger horizontal conductive zones in the midcrust. The seismic reflection data are consistent with and complement this: the upper crust is primarily nonreflective; however, the midcrust shows many horizontal reflectors, usually with a consistent dip to the north. Processing crooked-line seismic data is problematic, and techniques have been developed to improve the imaging, including multifocusing, 3D processing, full-waveform inversion, and cross-dip moveout methods. Passive seismic data have also been collected. Ambient-noise surface-wave tomography can be used to infer broad zones of similar seismic velocity between major reflectors, while receiver function analysis has been used to identify deeper structures such as horizontal features at or below the Moho and a dipping structure evident to about 70 km depth. </jats:p>

<jats:p> China launched the Deep Resources Exploration and Mining (DREAM) program in 2016. Since then, the program has made significant progress in the exploration of critical minerals, such as rare earth, rare, and rare scattered metals. A “five-in-one” model, based on climate, landform, parent rocks, carrier minerals, and pH values of weathering crust, has been established for rare earth prospecting in South China. It has led to a major breakthrough in the discovery of a new type of ion-adsorption rare earth deposit in the weathered crust of low-grade metamorphic rocks in southern Jiangxi, South China. A pegmatite beryllium (Be), skarn beryllium-tungsten (Be-W), cassiterite sulfide tin-tungsten-beryllium (Sn-W-Be), independent fluorite, and lead-zinc (Pb-Zn) vein five-in-one model was developed for the prospecting of rare metals such as Be and W and polymetals in the Zhaxikang-Cuonadong ore-concentrated area of the eastern Himalayas. A series of metallogenic models has been proposed for the investigation of lithium (Li) resources, leading to important breakthroughs in the prospecting of large to superlarge Li deposits in the Jiajika (western Sichuan), Dahongliutan (southwestern Xinjiang), and Xiaoshiqiao (central Yunnan) ore fields. Meanwhile, the DREAM program has achieved significant advancements in its knowledge of the ultranormal enrichment of indium, germanium, gallium, niobium, and rare earth elements in the western Yangtze block, Southwest China. </jats:p>

<jats:p> If current predictions of anthropogenically induced climate change are accurate, and they are becoming more robust and prescient with time, the world must transition away from fossil fuels and embrace transportation, energy generation, and energy storage from renewables so that future generations are not in peril. More than 190 countries have each signed the Paris Agreement, which has as its goal a reduction of global greenhouse gas emissions to limit the global temperature increase in this century to 2°C while pursuing efforts to limit the increase even further to 1.5°C. Additionally, more than 70 countries, including the biggest polluters, have set a net-zero greenhouse gas emissions target, which covers about 76% of global emissions — a commendable and laudable goal. However, a number of fundamental challenges make achieving this goal difficult, perhaps impossible. One such challenge is the lack of a broad appreciation that there needs to be much more mining of metals and minerals, in excess of already mining more than at any other time in prior human history. For example, one estimate is that there needs to be as much copper mined over the next 20–25 years as has been mined to date. Many countries have become aware of the need for access to “critical minerals” for futureproofing, but they appear to be unaware of the fundamental issues that will hamper that access. This is a fast-moving issue. Some of the specific details raised here will become less relevant, and new ones will appear. However, the core issues raised, of the need for a more positive public perception of mining, of the need for more mining, and of the need for far more skilled talent, will not change. </jats:p>

<jats:p> Rock-physics models for carbonate reservoirs assume that the mineral elastic moduli are known variables. A review of publications reveals a range of values for calcite that are out of date and misleading. We present a robust compilation for future investigations. We subsequently discuss the application of calcite elastic moduli for rock-physics modeling and interpretation of wireline data through a case study data set from an offshore Canada carbonate reservoir. The data set exhibits an offset between the zero-porosity intercept and the calcite elastic moduli values. Our experience indicates that this phenomenon is present in many wireline data sets from carbonate reservoirs around the world. We demonstrate that the data can be reconciled to the mineral elastic moduli through the interpretation of microcracks in the formation (defined by a crack density of 0.06). Understanding the microcrack effect in relatively low-porosity formations is important for the correct calibration of pore microstructure parameters and for fluid-substitution calculations. Results in the case study data set show a relatively high sensitivity to changes in fluid saturation. The sensitivity can be reduced through the use of effective mineral elastic moduli that are derived from the data. We justify the effective mineral elastic moduli as a representation of the mineral moduli plus microcracks. The effective mineral elastic moduli are proposed as a relatively simple method to constrain the fluid substitution calculations in low-porosity formations where microcracks are present. </jats:p>

<jats:p> The most commonly used amplitude variation with offset (AVO) space is (A,B) space. When a collection of data points is displayed in this space, it is referred to as an intercept-gradient crossplot. At times, however, alternative AVO spaces have been proposed, using for example the reflectivities of Kρ and µρ or of λ and µ as coordinate axes instead of A and B. It is shown here that these and other AVO spaces are mathematically equivalent, and it is shown how to convert from one to another. Properties that are preserved in the conversion are identified, as well as some that are not. One property that is not preserved is the angle, in (A,B) space known as the χ angle, associated with a particular rock property or fluid effect. Projections in intercept-gradient crossplots are often referred to as rotations. A rotation keeps the length of a vector the same, whereas a projection changes it. The χ angle, commonly referred to as a rotation angle, is in fact a projection angle. It is the angle of a line onto which points are projected. To clarify the process, a fairly comprehensive description is included in this paper. There are an infinite number of possible AVO spaces. All are mathematically equivalent, and it is easy to convert between them. It is not a given that (A,B) space is always the best for a particular goal. Several other AVO spaces are discussed. </jats:p>

<jats:p> Geophysical Monitoring for Geologic Carbon Storage, edited by Lianjie Huang, 2022. </jats:p>