Hot dry rock (HDR) is a kind of clean energy with significant potential. Since the 1970s, the United States, Japan, France, Australia, and other countries have attempted to conduct several EGS (Enhanced Geothermal System) projects to extract thermal energy by breaking through key technologies. However, up to now, the development of HDR is still in the research, development, and demonstration stage. An HDR exploration borehole (with 236°C at a depth of 3705 m) was drilled into Triassic granite in the Gonghe Basin in northwest China in 2017. Subsequently, China Geological Survey (CGS) launched the HDR resources exploration and production demonstration project in 2019. After three years of efforts, a sequence of significant technological breakthroughs have been made, including the genetic model of deep heat sources, directional drilling and well completion in high-temperature hard rocks, large-scale reservoir stimulation, reservoir characterization, and productivity evaluation, reservoir connectivity and flow circulation, efficient thermoelectric conversion, monitoring, and geological risk assessment, etc. Then the whole-process technological system for HDR exploration and production has been preliminarily established accordingly. The first power generation test was completed in November 2021. The results of this project will provide scientific support for HDR development and utilization in the future.

The reserves of hot dry rock (HDR) geothermal resources are huge. The main method used to develop HDR geothermal resources is called an enhanced geothermal system (EGS), and this generally uses hydraulic fracturing. After nearly 50 years of research and development, more and more countries have joined the ranks engaged in the exploration and development of HDR in the world. This paper summarizes the base technologies, key technologies, and game-changing technologies used to promote the commercialization of HDR geothermal resources. According to the present situation of the exploration, development, and utilization of HDR at home and abroad, the evaluation and site selection, efficient and low-cost drilling, and geothermal utilization of HDR geothermal resources are defined as the base technologies. Key technologies include the high-resolution exploration and characterization of HDR, efficient and complex fracture network reservoir creation, effective microseismic control, fracture network connectivity, and reservoir characterization. Game-changing technologies include downhole liquid explosion fracture creation, downhole in-situ efficient heat transfer and power generation, and the use of CO₂ and other working fluids for high-efficient power generation. Most of the base technologies already have industrial applications, but future efforts must focus on reducing costs. The majority of key technologies are still in the site demonstration and validation phase and have not yet been applied on an industrial scale. However, breakthroughs in cost reduction and application effectiveness are urgently needed for these key technologies. Game-changing technologies remain at the laboratory research stage, but any breakthroughs in this area could significantly advance the efficient development of HDR geothermal resources. In addition, we conducted a comparative analysis of the respective advantages of China and the United States in some key technologies of HDR development. On this basis, we summarized the key challenges identified throughout the discussion and highlighted the most pressing research priorities. We hope these technologies can guide new breakthroughs in HDR geothermal development in China and other countries, helping to establish a batch of HDR exploitation demonstration areas. In addition, we look forward to fostering collaboration between China and the United States through technical comparisons, jointly promoting the commercial development of HDR geothermal resources.

To elucidate the solute sources, migration and enrichment mechanisms of water bodies in the endorheic lake region of the Qiangtang Plateau on the Tibetan Plateau and clarify the hydrogeochemical cycling patterns in alpine arid environments, this study focuses on two core scientific objectives: quantitative identification of the multi-source contributions of aquatic solutes, and revelation of the key processes governing the enrichment of strategic elements including lithium (Li) and boron (B). To achieve these goals, we conducted systematic hydrogeological field investigations and collected 28 multi-type water samples, covering springs, rivers, thermal springs, freshwater lakes, salt lake brines, atmospheric precipitation, and glacial meltwater. The physicochemical properties, major ions, and trace elements of all samples were comprehensively analyzed. On this basis, the hydrogeochemical characteristics, evolutionary processes, and solute origins of regional waters were systematically explored. Combined with PHREEQC numerical simulation, principal component analysis (PCA), and Pearson correlation analysis, the dominant controlling factors of water geochemistry were quantified, and a conceptual hydrogeochemical evolution model was established. The results reveal a clear hydrogeochemical evolutionary gradient across the study area: water bodies evolve from low-salinity HCO₃-Ca recharge end-members and transitional HCO₃·SO₄-Ca(Mg) type water to highly mineralized Cl-Na (SO₄·Cl-Na) salt lake brines, accompanied by synchronous enrichment of Li, B, arsenic (As), and other characteristic elements. Solute accumulation in regional waters is governed by the ternary coupling effects of evaporative concentration, rock weathering and leaching, and deep geothermal fluid input, while cation exchange and mineral dissolution–precipitation reactions further modulate ionic composition and ratios. Elements including As, Li, B, and chloride (Cl⁻) exhibit conservative migration behaviors in non-hydrothermal waters, whereas thermal springs possess unique geochemical signatures driven by deep fluid recharge. PCA results indicate that evaporative concentration serves as the primary controlling factor with a contribution rate of 55.39%; rock weathering provides the basic solute load (17.09%); and the coupled processes of deep fluid mixing and carbonate precipitation regulate elemental fractionation (14.21%). These findings systematically clarify the hydrogeochemical evolution laws and multi-source coupling mechanisms of inland lake waters in the Qiangtang Plateau. Furthermore, this study establishes a conceptual framework of “multi-source recharge–water–rock interaction–evaporative concentration”, advances the understanding of alpine hydrological cycling under climate change, and provides a solid scientific foundation for hydrological cycle research and green exploration of strategic mineral resources in endorheic salt lake regions.

To reveal the solute sources, migration and enrichment mechanisms of water bodies in the endorheic lake region of the Qiangtang Plateau, Tibetan Plateau, and to clarify the hydrogeochemical cycling patterns in alpine arid zones, this study took typical en-dorheic lake areas in the region as the research object, conducted a systematic hydro-geological survey, collected 28 groups of water samples of various types (including springs, rivers, thermal springs, freshwater lakes, salt lake brines, atmospheric precip-itation and glacial meltwater), tested their major ions, trace elements and physical properties, and comprehensively investigated the hydrogeochemical characteristics, evolution laws and solute sources of water bodies, quantified the dominant control-ling factors and established a conceptual hydrogeochemical model by combining methods such as PHREEQC modeling, principal component analysis (PCA) and Pear-son correlation analysis; the results show that water bodies in the study area exhibit a distinct evolutionary gradient, from the low-salinity HCO₃-Ca recharge end-member, through transitional HCO₃·SO₄-Ca(Mg) water, to highly mineralized Cl-Na(SO₄·Cl-Na) salt lake brine, with synchronous enrichment of Li, B, As and other elements; solute sources are controlled by a ternary coupling mechanism of evaporative concentration, rock weathering and leaching, and deep geothermal fluid input, while cation ex-change and mineral dissolution-precipitation further regulate ionic ratios; As, Li, B and Cl⁻ display conservative migration in non-hydrothermal waters, whereas thermal springs show unique geochemical signatures due to the input of deep-seated fluids; PCA reveals that evaporative concentration (contribution rate 55.39%) is the dominant controlling factor, rock weathering (17.09%) provides the basic solute load, and the coupled process of deep fluid mixing and carbonate precipitation (14.21%) regulates elemental fractionation, and this study constructs a conceptual model of "multi-source recharge–water–rock interaction–evaporative concentration", which clarifies the evo-lutionary laws of regional water bodies and provides a scientific basis for water cycle research and green exploration of strategic mineral resources in salt lakes of the en-dorheic regions on the plateau.