Borehole mining update: A century from 1926 to 2026 – What’s next?

Borehole mining (BHM) is a remotely operated waterjet mining method carried out through wellbores drilled and cased from the surface directly into the production interval. Mining operations are performed using a waterjet tool composed of at least two concentric tubular columns, which create two hydraulic passages: one for pumping high-pressure water down, and the other for transporting the produced slurry to the surface. At the lower end of the dual column, a bottom head is installed, equipped with a hydromonitor that generates a powerful water jet, and an eductor (jet pump). The tool is suspended from a drill rig via a swivel, enabling its rotation and advancement along the borehole. While the waterjet continuously cuts the rock and produces slurry, the eductor lifts the slurry to the surface. In a slurry collection tank or pond, the cuttings are separated and the clarified water is recycled. As ore is extracted, BHM stopes are typically formed that may remain open for an extended time before caving in. BHM benefits Direct and quick access to the ore eliminates many conventional mining activities, such as earthworks, mine construction, and the development and maintenance of extensive surface and underground infrastructures. Workforce requirements are substantially reduced, along with the need for hauling fleets, heavy machinery and specialized equipment. Most importantly, BHM requires no underground personnel, thereby eliminating the need for ventilation, climate control, dewatering, underground transportation and other high-cost support systems typical of conventional mining, while elevating operational safety to levels previously unattainable. As a result, both BHM’s capital and operating expenditures (CapEx and OpEx) are significantly reduced, permitting the development of mineral resources previously considered uneconomic, impractical, hazardous or inaccessible. BHM is a rapid mineless technology designed for computer-managed, artificial intelligence (AI)-driven operations, enabling real-time monitoring and remote control via Wi-Fi and satellite communications.Additional advantages of BHM include: A minimal surface footprint, with limited disturbance to subsoil, groundwater and air. Broad applicability across exploration, mining, oil, natural gas and groundwater stimulation, underground construction and other sectors. Selectivity, allowing the extraction of targeted intervals while leaving waste material in place. High operational speed, reducing preparation, major mining activities and reclamation time to a fraction of that required for conventional mining. Fully electrified operations, further lowering the carbon footprint. Operational flexibility in remote, desert, and subfreezing environments, as well as offshore from floating vessels, making BHM deployable virtually anytime and anywhere. To compare underground mining (UGM) and BHM performance, a key performance indicator (KPI) is presented in Table 1. The information in Table 1 corresponds to a hypothetical 1.4-Mt (1.5-million-st) orebody that can be developed using either underground mining or BHM technology. The KPI indicates that BHM is six times more cost effective than conventional underground mining. 1926 invention and modern tools Figure 1a presents an illustration from U.S. Patent No. 1,612,611, titled “Method and apparatus for recovering oil from loose oil-bearing strata” (Claytor, 1926). According to this patent, the tool comprises at least two concentric pipes forming an extension section, a swivel, and a bottom head equipped with a retractable hydromonitor and eductor. While being the first patented BHM tool, this invention anticipated the equipment deployed some 60 years later in the world’s most commercially successful BHM project (Abramov, 2020). Figures 1 and 2 illustrate the major similarities between the 1926 design and modern BHM tools. The retractable hydromonitor, invented by E. Claytor (Fig. 1a), was also realized in the same BHM project (Abramov, 2020) (Fig. 2). (a) An illustration from US Patent 1,612,611 (Claytor, 1926). (b) A modern BHM mining tool (1 = swivel, 2 = extension section, 3 = hydromonitor,4 = eductor). Over the century since 1926, materials, technologies and equipment have evolved dramatically, and Claytor’s original concept has undergone numerous variations that were designed, tested and patented. Many of these were later abandoned, while others matured and entered commercial batch production. As BHM technology advanced, numerous techniques and procedures were also developed, patented and field-implemented. Ultimately, the simplest, most robust, and most cost-effective designs survived extended real-world trials, demonstrating high performance and long-term reliability. BHM main parameters Across many regions worldwide, heavy ores such as uranium, gold, iron and manganese have been extracted using BHM. Table 2 lists key parameters, including mining depth, ore specific gravity, abrasiveness and slurry consistency, which influence pumping characteristics, technological parameters and tool design. Beyond the heavy mineral ores, BHM has been successfully applied to the recovery of a broad spectrum of weakly consolidated resources, including titanium-bearing minerals (ilmenite and rutile), zirconium, germanium, critical minerals, rare earth elements (REEs), as well as phosphorite, diamonds, coal, silica sand, amber, bauxite and other industrial and specialty commodities. Numerous institutions, companies and research organizations worldwide have advanced BHM through the development of specialized equipment, extraction technologies and operational methodologies. Over several decades, significant investments have supported research and development, pilot programs and full-scale field trials, some of which progressed to sustained pilot and commercial production. Fig. 2. Retractable BHM hydromonitor. Importantly, nearly a century of documented BHM deployment indicates a strong environmental performance record, with no confirmed major ecological incidents — such as groundwater contamination, soil degradation, deforestation, air pollution, or comparable adverse impacts — reported in the technical or regulatory literature. World critical minerals demand The U.S. Geological Survey’s (USGS) top 10 critical minerals, their usage, related minerals and U.S. import percentage are presented in Table 3. Other critical minerals include gallium, germanium, indium, tin, bauxite, phosphorus and several others. In addition to graphite, manganese and tantalum, the United States is 100 percent import-reliant for bismuth, rubidium, thallium and hafnium. Furthermore, an additional 12 critical minerals are 85 to 95 percent import-dependent, underscoring the nation’s structural vulnerability in mineral supply chains. The United States hosts dozens — if not hundreds — of documented critical mineral deposits, many containing lithium, cobalt, nickel, REEs, gallium, manganese and other critical minerals (USGS, n.d.). However, only a small fraction of these resources is currently under active production. The five principal factors constraining their development are: (1) economic viability, (2) lack of infrastructure, (3) technological limitations, (4) environmental concerns and (5) remote or inaccessible locations. All five of these constraints are addressable through BHM methodologies. Even more encouraging opportunities lie ahead. Beyond onshore resources exists yet another domain containing immense quantities of mineral wealth that remains largely untapped: the sub-seafloor environment. But before examining the technological aspects of accessing these resources using BHM, a critical distinction must be clearly established. When it comes to underwater mining, it is nearly 100 percent about the recovery of polymetallic nodules from the ocean floor. This approach faces alarming criticism from scientists, environmental organizations and coastal communities, who argue that nodule extraction inevitably disrupts benthic ecosystems and marine life. The distinction between seafloor harvesting and BHM is both essential and fundamental. BHM targets mineral resources located beneath the ocean floor, accessing them through drilled wellbores without disturbing seafloor sediments and benthic habitats. As such, offshore BHM represents a materially different technical and environmental paradigm from conventional seabed nodule collection. Moreover, there is another fundamental difference between seafloor collecting operations and BHM: the nature of the mining process itself. Whereas nodule harvesting is predominantly a continuous, two-dimensional operation conducted across the seafloor, BHM is cyclic and three-dimensional. From one wellbore to the next, a typical operational sequence includes: (1) drill rig mobilization, (2) drilling and casing, (3) mining, (4) wellbore sealing and (5) rig demobilization and repositioning to the next location — after which the cycle is repeated. What’s the difference between continental and offshore BHM? In essence, the only difference is that the drill rig is mounted on the deck of a mining vessel rather than on land; otherwise, the operation remains fundamentally the same. Figure 3 presents a schematic diagram of offshore borehole mining. A vessel — platform, ship or pontoon — is moored at the target location, and reverse circulating (RC) drilling of an access well is initiated. A drill bit pinpoint penetrates the ocean floor and continues downward for tens to hundreds of meters until the orebody is reached. A steel casing is then installed from the vessel deck to the production interval. Typically, the casing shoe is set within the upper boundary of the orebody, leaving the remainder of the borehole open (Fig. 3). A BHM tool is subsequently lowered into the casing string, positioning its bottom head below the casing shoe. Below-the-ocean-floor borehole mining. All BHM operations are conducted in essentially the same manner as onshore. The generated slurry is entrained by the downhole eductor and hydraulically conveyed to the surface through the slurry line. Upon discharge into a collecting bin, gravity settling and phase separation occur. Solid ore cuttings are recovered, while the process water is clarified and recirculated within a closed-loop system for reuse in continuous mining cycles. The recovered solids are transferred to a marine transport vessel for shipment to an onshore processing facility — a logistics approach that is both more economical and environmentally efficient than conventional land-based haulage. No tailings, slurry or spent process water are discharged into the marine environment. The system operates as a fully contained closed circuit, ensuring complete retention of process fluids and solids. Upon completion of mining in a borehole, the BHM tool is retrieved. Where required, the casing string is partially withdrawn, the borehole is permanently sealed, and the remaining casing is fully removed. These measures ensure hydraulic isolation of the penetrated strata and prevent any communication between subsurface formations and the ocean. All BHM applications and specialized techniques, including backfilling, are equally applicable in onshore and offshore environments. The same operational methods, process controls and wellbore management practices are employed, with only the platform and marine support systems adapted for offshore deployment. What holds borehole mining back? After nearly a century of successful demos, trials and practical deployments, why does BHM remain overshadowed by its worldwide adopted predecessors — surface and underground mining? Various technical, economic, and human factors contribute to its slower adoption. Method limitations. BHM is most effective in materials that can be efficiently cut, loosened and hydraulically transported by high-pressure waterjets. Very hard rock formations fall outside the method’s natural operating envelope unless assisted by preconditioning techniques such as drill and blast. Lower unit productivity. Hourly throughput per borehole is modest compared with high-capacity systems such as bucket-wheel or longwall machines. Achieving competitive production rates is solved by mining through multiple boreholes simultaneously. Limited real-time process visibility. Historically, BHM has lacked advanced telemetry and feedback systems capable of providing real-time information on waterjet orientation, cutting radius, stope geometry and extracted volumes. This operation “blindness” deters investors and some engineers. Importantly, many of these sensing and navigation technologies now exist and remain largely an integration challenge rather than a fundamental technical barrier. Terminology misconceptions. The classification of BHM alongside in situ recovery (ISR) or solution mining has created confusion. Unlike chemical leaching methods, BHM is a purely mechanical waterjet excavation process. This misconception has sometimes led to unwarranted environmental concerns and regulatory hesitation. Subsidence concerns. In certain circumstances, ore extraction may pose a risk of seafloor subsidence. To mitigate or prevent this risk, conventional and well-established underground mining practices, such as room-and-pillar layouts and backfilling, applied effectively. Although these methods typically limit recovery to 50–65 percent and 75–80 percent, respectively, they fulfill their primary purpose: preventing subsidence, thereby reducing environmental impact and protecting the seafloor. Unfamiliarity, inertia, conservatism. BHM remains outside mainstream mining practice. Limited standardization, fewer reference projects and a relatively small pool of experienced practitioners contribute to conservative attitudes among operators, regulators and financiers. As with many emerging methods, adoption is slowed more by perception and precedent than by technical feasibility. It is important to recognize that BHM is not intended to replace conventional mining. Rather, it serves as a complementary technology occupying its own distinct and valuable niche. Under certain geological, environmental and logistical conditions, BHM may represent the most efficient, or even the only viable extraction solution, such as sub-seafloor resource development. From space to sub-seafloor and back Two of the most distinguishing attributes of borehole mining are that the technology is (1) unmanned and (2) remotely operated. Operations are controlled, monitored and continuously optimized from a remote operations center using real-time data streams from downhole sensors, surface instrumentation, and integrated process control systems. This operational model closely parallels extraterrestrial mining concepts, in which autonomous mechanical systems perform complex tasks in hostile and inaccessible environments under remote human supervision — a compelling and technically accurate analogy for mining beneath the seafloor. Although offshore BHM is much “closer to home,” investment levels in the two domains differ astronomically. At the same time, because space and underwater mining share many underlying concepts and technologies, each stands to benefit substantially from the other’s advances. Nevertheless, this comparison, combined with the inherently cyclic nature of BHM and rapid advances in remote sensing, automation and data analytics, clearly points toward AI-controlled and digital twin (DT)–assisted borehole mining as the next evolutionary stage of the method. In this context, offshore borehole mining emerges as an especially strong candidate for such technological advancement. Conclusion The centennial anniversary shall not pass unnoticed into history. While BHM may still appear new and exotic, it has been in use for nearly a century. Beyond land-based applications, it has also been successfully deployed from the water surface to mine abandoned and flooded openpits, restoring them to production, hence sufficiently extending their operational life. The hurdles and roadblocks outlined above should be seen not as limitations but as challenges that can be systematically overcome. Historically, many of these obstacles persisted simply because neither the need nor the enabling technologies yet existed. The emerging AI-DT era presents a natural fit for BHM, opening unprecedented new opportunities and horizons. Today, 100 years after the Claytor invention, borehole mining is no longer merely viable or promising. It is a mature, digitally enabled and automation-ready technology — fully prepared to splash down beyond the continental coastline, reduce the U.S. vulnerability in critical minerals supply chains and redefine how mineral resources are accessed in the 21st century. (References are available from the author.)

Borehole mining update: A century from 1926 to 2026 – What’s next?

Authored by: Gregory Abramov

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